Damping force generation mechanism

Abstract

This damping force generation mechanism has: an urging force generation member that is in the form of a bottomed tube and that forms a back pressure chamber that causes a first urging force generation member, which is located on the open side, to generate urging force in a valve-closing direction; a frequency sensitive mechanism that is provided in a first passage, which is provided in the bottom part of the urging force generation member and which joins the back pressure chamber and a first chamber, and that varies the urging force, the frequency sensitive mechanism being provided so as to allow movement of a movable mechanism having a sealing part that seals the first passage with an elastic member; a second passage that is parallel to or common to the first passage, and that can communicate at one side with the back pressure chamber; and a communication mechanism that is located on said one side of the second passage and that can communicate with the other side of the second passage only when the first chamber is on the upstream side.

Description

[Technical Field]

[0001] The present invention relates to a damping force generating mechanism. This application claims priority based on Japanese Patent Application No. 2022-110419, filed on July 8, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] Among the damping force generating mechanisms provided in shock absorbers, there are those that apply back pressure to a damping force generating member in a valve closing direction (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 163868 [Patent Document 2] U.S. Patent No. 10,001,189 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to prevent the damping force generating mechanism from becoming too large.

[0005] Therefore, an object of the present invention is to provide a damping force generating mechanism that can prevent an increase in size. [Means for solving the problem]

[0006] One aspect of the present invention comprises a bottomed, cylindrical biasing force generating member that forms a back pressure chamber that generates a biasing force in a valve-closing direction on a first damping force generating member arranged on the opening side; a frequency sensitive mechanism in which a movable mechanism having a sealing portion that seals the first passage with an elastic member is movably provided in a first passage provided at the bottom of the biasing force generating member and connecting the back pressure chamber and the first chamber, thereby varying the biasing force; a second passage that is parallel to or common to the first passage and has one side that can communicate with the back pressure chamber; and a communication mechanism on one side of the second passage that can communicate with the other side of the second passage only when the first chamber is upstream. [Effects of the Invention]

[0007] According to the above-described aspect, it is possible to prevent the device from becoming large. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a shock absorber including a damping force generating mechanism of a first embodiment according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a main part including a damping force generating mechanism of the first embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing the configuration of a main part of the damping force generating mechanism of the first embodiment. [Figure 4] FIG. 2 is a cross-sectional perspective view showing the configuration of a main part of the damping force generating mechanism of the first embodiment. [Figure 5] FIG. 4 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a plan view showing a disk of the damping force generating mechanism of the second embodiment. [Figure 7] FIG. 10 is a plan view showing a disk of the damping force generating mechanism of the second embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing the configuration of a main part of a modified example of the damping force generating mechanism of the second embodiment. [Figure 9] FIG. 10 is a plan view showing a disk of a modified example of the damping force generating mechanism of the second embodiment. [Figure 10]FIG. 10 is a cross-sectional view showing the configuration of a main part including a damping force generating mechanism of a third embodiment according to the present invention. [Figure 11] FIG. 10 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a third embodiment of the present invention. [Figure 12] FIG. 11 is a cross-sectional view showing the configuration of a main part of a modified example of the damping force generating mechanism of the third embodiment. [Figure 13] FIG. 10 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a fourth embodiment of the present invention. [Figure 14] FIG. 10 is a plan view showing a pilot case of the damping force generating mechanism of the fourth embodiment. [Figure 15] FIG. 10 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a fifth embodiment of the present invention. [Figure 16] FIG. 10 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a sixth embodiment of the present invention. [Figure 17] FIG. 13 is a bottom view showing a pilot case of the damping force generating mechanism of the sixth embodiment. [Figure 18] FIG. 13 is a plan view showing a disk of the damping force generating mechanism of the sixth embodiment. [Figure 19] FIG. 13 is a plan view showing a disk of the damping force generating mechanism of the sixth embodiment. [Figure 20] FIG. 13 is a cross-sectional view showing the configuration of a main part of a damping force generating mechanism according to a seventh embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [First embodiment] A shock absorber including a damping force generation mechanism 10 of a first embodiment will be described below with reference to Figures 1 to 4. For ease of explanation, the upper side in Figures 1 to 3, 5, 8, 10 to 13, 15, 16, and 20 will be referred to as "upper," and the lower side in Figures 1 to 3, 5, 8, 10 to 13, 15, 16, and 20 will be referred to as "lower." In addition, in each figure, the central axis of the shock absorber 1 may be indicated by the symbol CL.

[0010] As shown in Figure 1, shock absorber 1 is a twin-cylinder hydraulic shock absorber. Shock absorber 1 is used in a vehicle suspension device. Shock absorber 1 has a cylinder 2 in which oil liquid L is sealed as a working fluid. Cylinder 2 has an inner cylinder 3 and an outer cylinder 4. Inner cylinder 3 is cylindrical. Outer cylinder 4 is cylindrical with a bottom. The inner diameter of outer cylinder 4 is larger than the outer diameter of inner cylinder 3. Inner cylinder 3 is disposed inside outer cylinder 4. The central axis of inner cylinder 3 and the central axis of outer cylinder 4 coincide. A reservoir chamber 6 is formed between inner cylinder 3 and outer cylinder 4.

[0011] The outer cylinder 4 has a body member 11 and a bottom member 12. The body member 11 is cylindrical. The bottom member 12 is cylindrical with a bottom. The bottom member 12 is fitted onto the lower side of the body member 11 and fixed by welding. The bottom member 12 closes the lower part of the body member 11. A mounting eye 13 is fixed to the outside of the bottom member 12, opposite the body member 11 in the axial direction.

[0012] The shock absorber 1 is equipped with a piston 18. The piston 18 is slidably fitted within the inner tube 3 of the cylinder 2. The piston 18 divides the inner tube 3 into two chambers: an upper chamber 19 and a lower chamber 20 (first chamber). In the axial direction of the cylinder 2, the upper chamber 19 is located on the opposite side of the piston 18 from the bottom member 12. In the axial direction of the cylinder 2, the lower chamber 20 is located on the bottom member 12 side of the piston 18. Oil liquid L is sealed within the upper chamber 19 and the lower chamber 20 of the inner tube 3 as a working fluid. Oil liquid L and gas G are sealed within a reservoir chamber 6 between the inner tube 3 and the outer tube 4 as a working fluid.

[0013] The shock absorber 1 is equipped with a piston rod 21. One axial end of the piston rod 21 is disposed within the inner tube 3 of the cylinder 2. One end of the piston rod 21 is connected to the piston 18. The other axial end of the piston rod 21, opposite to the one end, extends from the cylinder 2 to the outside of the cylinder 2. The piston 18 is fixed to the piston rod 21. Therefore, the piston 18 and the piston rod 21 move together. In the shock absorber 1, the stroke in which the piston rod 21 moves in a direction to increase the amount of protrusion from the cylinder 2 is the extension stroke, in which the overall length is extended. In the shock absorber 1, the stroke in which the piston rod 21 moves in a direction to decrease the amount of protrusion from the cylinder 2 is the compression stroke, in which the overall length is shortened. In the shock absorber 1, the piston 18 moves toward the upper chamber 19 during the extension stroke. In the shock absorber 1, the piston 18 moves toward the lower chamber 20 during the compression stroke.

[0014] A rod guide 22 is fitted to the upper end opening side of the inner cylinder 3, on the upper end opening side of the outer cylinder 4. A seal member 23 is fitted to the outer cylinder 4 above the rod guide 22. A disk 24 is fitted to the outer cylinder 4 above the seal member 23. Both the rod guide 22 and the seal member 23 are annular. The disk 24 is a circular flat plate with holes of a constant thickness. The disk 24 abuts against the outer peripheral portion of the seal member 23. The piston rod 21 slides along the axial direction of each of the rod guide 22 and the seal member 23. The piston rod 21 extends from inside the cylinder 2 to the outside of the cylinder 2 beyond the seal member 23.

[0015] The rod guide 22 restricts radial movement of the piston rod 21 relative to the inner cylinder 3 and outer cylinder 4 of the cylinder 2. The piston rod 21 is fitted into the rod guide 22, and the piston 18 is fitted into the inner cylinder 3. This causes the central axis of the piston rod 21 to coincide with the central axis of the cylinder 2. The rod guide 22 supports the piston rod 21 so that it can move in the axial direction of the piston rod 21. The outer periphery of the seal member 23 is in close contact with the outer periphery of the piston rod 21. The piston rod 21 moves in the axial direction of the seal member 23 relative to the seal member 23. The seal member 23 prevents the oil liquid L in the inner cylinder 3 and the high-pressure gas and oil liquid L in the reservoir chamber 6 from leaking to the outside.

[0016] The rod guide 22 has an outer periphery with a larger diameter at its upper part than at its lower part. The rod guide 22 fits into the inner periphery of the upper end of the inner cylinder 3 at its smaller diameter lower part. The rod guide 22 fits into the inner periphery of the upper part of the outer cylinder 4 at its larger diameter upper part. A base valve 25 is installed on the bottom member 12 of the outer cylinder 4. The base valve 25 is positioned radially relative to the outer cylinder 4. The base valve 25 separates the lower chamber 20 and the reservoir chamber 6. The inner periphery of the lower end of the inner cylinder 3 is fitted into the base valve 25. The upper end of the outer cylinder 4 is crimped radially inward of the outer cylinder 4. The seal member 23, together with the disk 24, is fixed to the cylinder 2 by being sandwiched between this crimped portion and the rod guide 22.

[0017] The piston rod 21 has a main shaft portion 27 and a mounting shaft portion 28. The outer diameter of the mounting shaft portion 28 is smaller than the outer diameter of the main shaft portion 27. The mounting shaft portion 28 is disposed within the cylinder 2. The piston 18 is attached to the mounting shaft portion 28. The main shaft portion 27 has a stepped shaft portion 29. The stepped shaft portion 29 is provided at the end of the main shaft portion 27 on the mounting shaft portion 28 side. The stepped shaft portion 29 extends in a direction perpendicular to the central axis of the piston rod 21.

[0018] A passage groove 30 is formed on the outer periphery of the mounting shaft portion 28 of the piston rod 21. The passage groove 30 is formed by cutting out the outer periphery of the mounting shaft portion 28 along a plane parallel to the central axis of the mounting shaft portion 28. The passage groove 30 extends in the axial direction of the mounting shaft portion 28. A plurality of passage grooves 30, specifically two passage grooves 30, are formed at intervals in the circumferential direction of the mounting shaft portion 28. A male thread 31 is formed on the outer periphery of the mounting shaft portion 28 at an end portion on the opposite side of the main shaft portion 27 from the passage groove 30 in the axial direction of the mounting shaft portion 28.

[0019] The shock absorber 1 is connected to the vehicle body with, for example, the portion of the piston rod 21 that protrudes from the cylinder 2 located at the top. In this case, the shock absorber 1 is connected to the vehicle wheel side with the mounting eye 13 provided on the cylinder 2 side located at the bottom. The shock absorber 1 may also be connected to the vehicle body with the cylinder 2 side connected to the vehicle body. In this case, the piston rod 21 of the shock absorber 1 is connected to the wheel side.

[0020] When a vehicle travels, the wheels vibrate relative to the vehicle body. This vibration causes the relative positions of the cylinder 2 and the piston rod 21 of the shock absorber 1 to change. This change is suppressed by the fluid resistance of the flow paths provided in the shock absorber 1. As will be explained below, the fluid resistance of the flow paths provided in the shock absorber 1 is designed to vary depending on the speed and amplitude of the vibration. The shock absorber 1 suppresses the vibration, thereby improving the ride comfort of the vehicle.

[0021] Furthermore, in a vehicle, in addition to vibrations generated by the wheels relative to the vehicle body, inertial forces and centrifugal forces generated in the vehicle body as the vehicle travels also act between the cylinder 2 and the piston rod 21. For example, when the direction of travel is changed by operating the steering wheel, centrifugal forces are generated in the vehicle body. Then, a force based on this centrifugal force acts between the cylinder 2 and the piston rod 21. As will be explained below, the shock absorber 1 has good characteristics against vibrations based on forces generated in the vehicle body as the vehicle travels. The shock absorber 1 provides the vehicle with high driving stability.

[0022] The damping force generating mechanism 10 includes a piston 18 and has a configuration shown in FIG. The piston 18 has a piston body 35 and a sliding member 36. The piston body 35 is made of metal and has an annular shape. The piston 18 has the piston body 35 fitted onto the mounting shaft portion 28 of the piston rod 21. The sliding member 36 is made of synthetic resin and has an annular shape. The sliding member 36 is integrally attached to the outer circumferential surface of the piston body 35. The piston 18 slides relative to the inner cylinder 3 with the sliding member 36 in contact with the inner cylinder 3.

[0023] The piston body 35 is provided with a passage hole 37, a passage groove 38, a passage hole 39, and a passage groove 40. The passage hole 37 penetrates the piston body 35 in the axial direction of the piston body 35. A plurality of passage holes 37 are formed in the piston body 35 at intervals in the circumferential direction of the piston body 35. The passage hole 39 penetrates the piston body 35 in the axial direction of the piston body 35. A plurality of passage holes 39 are formed in the piston body 35 at intervals in the circumferential direction of the piston body 35. The piston body 35 is formed with one passage hole 37 and one passage hole 39 alternately at equal pitches in the circumferential direction of the piston body 35.

[0024] The passage groove 38 is formed in the piston body 35 in an annular shape in the circumferential direction of the piston body 35. The passage groove 38 is formed at the end of the piston body 35 on the lower chamber 20 side in the axial direction. All of the passage holes 37 open to the passage groove 38 at their axial end sides in the piston body 35. The passage groove 40 is formed in the piston body 35 in an annular shape in the circumferential direction of the piston body 35. The passage groove 40 is formed at the end of the piston body 35 on the upper chamber 19 side, opposite the passage groove 38 in the axial direction. All of the passage holes 39 open to the passage groove 40 at their axial end sides opposite the passage groove 38 in the axial direction of the piston body 35. The multiple passage holes 37 open at their axial end sides opposite the passage groove 38 outward from the passage groove 40 in the radial direction of the piston body 35. The ends of the plurality of passage holes 39 opposite the passage groove 40 in the axial direction of the piston body 35 open outward from the passage groove 38 in the radial direction of the piston body 35. In the piston 18, the insides of the plurality of passage holes 37 and the passage groove 38 form piston-side passages 43. In the piston 18, the insides of the plurality of passage holes 39 and the passage groove 40 form piston-side passages 44.

[0025] The damping force generating mechanism 10 has a first valve mechanism 41 provided in the piston-side passage 43. The first valve mechanism 41 opens and closes the piston-side passage 43 to generate a damping force. The first valve mechanism 41 is arranged on the lower chamber 20 side in the axial direction of the piston 18. As a result, the piston-side passage 43 becomes a passage through which oil L flows from one upper chamber 19 to the other lower chamber 20 when the piston 18 moves in one direction, toward the upper chamber 19. In other words, the piston-side passage 43 is a passage through which oil L flows from the upper chamber 19 to the lower chamber 20 during the extension stroke. The first valve mechanism 41 generates a damping force by suppressing the flow of oil L from the piston-side passage 43 to the lower chamber 20 during the extension stroke.

[0026] The damping force generating mechanism 10 has a first valve mechanism 42 provided in the piston-side passage 44. The first valve mechanism 42 opens and closes the piston-side passage 44 to generate a damping force. The first valve mechanism 42 is disposed on the upper chamber 19 side in the axial direction of the piston 18. As a result, the piston-side passage 44 becomes a passage through which oil L flows from the lower chamber 20 toward the upper chamber 19 as the piston 18 moves toward the lower chamber 20. In other words, the piston-side passage 44 is a passage through which oil L flows from the lower chamber 20 toward the upper chamber 19 during the compression stroke. The first valve mechanism 42 generates a damping force by suppressing the flow of oil L from the piston-side passage 44 to the upper chamber 19 during the compression stroke.

[0027] The piston body 35 is a disk-shaped body with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted into the inner periphery thereof.

[0028] An inner seat portion 46 and a valve seat portion 47 are formed at the axial end of the piston body 35 on the lower chamber 20 side. The inner seat portion 46 is annular. The inner seat portion 46 is located radially inward of the opening of the passage groove 38 on the lower chamber 20 side of the piston body 35. The valve seat portion 47 is annular. The valve seat portion 47 is located radially outward of the opening of the passage groove 38 on the lower chamber 20 side of the piston body 35. The valve seat portion 47 constitutes a part of the first valve mechanism 41.

[0029] An inner seat portion 48 and a valve seat portion 49 are formed at the axial end of the piston body 35 on the upper chamber 19 side. The inner seat portion 48 is annular. The inner seat portion 48 is located radially inward of the opening of the passage groove 40 on the lower chamber 20 side of the piston body 35. The valve seat portion 49 is annular. The valve seat portion 49 is located radially outward of the opening of the passage groove 40 on the upper chamber 19 side of the piston body 35. The valve seat portion 49 constitutes a part of the first valve mechanism 42.

[0030] The damping force generating mechanism 10 has, on the inner seat portion 46 side in the axial direction of the piston 18, in order from the inner seat portion 46 side in the axial direction of the piston 18, one disc 50, one first damping valve 52 (first damping force generating member), one disc 53, one disc 54, multiple discs, specifically six discs 55, one disc 56, one opening / closing disc 57, one pilot case 58 (spring force generating member), a second damping valve 60 consisting of multiple discs, specifically six discs 59, one disc 61, and one annular member 62.

[0031] The discs 50, 53 to 56, 59, 61, the open-close disc 57, the pilot case 58, and the annular member 62 are all made of metal. The discs 50, 53 to 56, 59, 61, the open-close disc 57, and the annular member 62 are all perforated circular flat plates of a uniform thickness. The discs 50, 53 to 56, 59, 61, and the open-close disc 57 are formed by press molding. The first damping valve 52 and the pilot case 58 are all annular. The mounting shaft portion 28 of the piston rod 21 is fitted inside the discs 50, 53 to 56, 59, 61, the open-close disc 57, the first damping valve 52, the pilot case 58, and the annular member 62.

[0032] 3, the pilot case 58 is cylindrical and has a bottom. The pilot case 58 is formed seamlessly as a whole by sintering. The pilot case 58 has a bottom 65 and a cylindrical portion 66.

[0033] The bottom portion 65 is a perforated disk-like plate, and the mounting shaft portion 28 of the piston rod 21 is fitted into the inner periphery of the bottom portion 65. The tubular portion 66 is cylindrical, and extends from the outer periphery of the bottom portion 65 to one side along the axial direction of the bottom portion 65. The pilot case 58 has an opening 67 on the side of the tubular portion 66 opposite the bottom portion 65 in the axial direction. In other words, the pilot case 58 is a bottomed tubular portion having the opening 67 at one end in the axial direction.

[0034] The bottom portion 65 has a bottom body portion 71 , an inner seat portion 74 , a valve seat portion 75 , an outer seat portion 76 , an inner seat portion 77 , and an outer seat portion 78 .

[0035] The bottom main body portion 71 is a disk-shaped portion with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted into its inner peripheral side. A seal groove 68 is formed in the bottom main body portion 71 on the axial side thereof facing the cylindrical portion 66. The seal groove 68 is annular, and is formed radially inward of the cylindrical portion 66 of the bottom main body portion 71. The seal groove 68 is recessed from the cylindrical portion 66 side of the bottom main body portion 71 in the axial direction, in the opposite direction from the cylindrical portion 66 in the axial direction of the bottom portion 65.

[0036] The inner seat portion 74 is formed on the inner peripheral side of the bottom main body portion 71. The inner seat portion 74 is annular. The inner seat portion 74 protrudes from the bottom main body portion 71 on the same side as the tubular portion 66 in the axial direction of the bottom main body portion 71.

[0037] The valve seat portion 75 is formed radially outward of the inner seat portion 74 of the bottom main body portion 71. The valve seat portion 72 is annular. The valve seat portion 75 protrudes from the bottom main body portion 71 on the same side as the inner seat portion 74 in the axial direction of the bottom main body portion 71. The height of the valve seat portion 75 in the axial direction of the pilot case 58 is the same as that of the inner seat portion 74.

[0038] The outer seat portion 76 is formed radially outward of the valve seat portion 75 and inward of the seal groove 68. The outer seat portion 76 is annular. The outer seat portion 76 protrudes from the bottom body portion 71 on the same side as the inner seat portion 74 and the valve seat portion 75 in the axial direction of the bottom body portion 71. The height of the outer seat portion 76 from the bottom body portion 71 in the axial direction of the pilot case 58 is higher than that of the valve seat portion 75.

[0039] A passage groove 79 is formed at the axial tip of the outer seat portion 76, penetrating the outer seat portion 76 in the radial direction. A plurality of passage grooves 79 are formed in the outer seat portion 76 at equal intervals in the circumferential direction of the outer seat portion 76.

[0040] An inner passage hole 80 is formed in the bottom main body portion 71. The inner passage hole 80 penetrates the bottom main body portion 71 in the axial direction of the bottom main body portion 71. As shown in Fig. 4, the pilot case 58 is provided with a plurality of inner passage holes 80, specifically six inner passage holes 80, at equal intervals in the circumferential direction of the pilot case 58. As shown in Fig. 3, the plurality of inner passage holes 80 open between the inner seat portion 74 and the valve seat portion 75 in the radial direction of the bottom main body portion 71.

[0041] As shown in Fig. 2, the pilot case 58 has outer passage holes 83, 84 formed in the bottom surface of the seal groove 68. The outer passage holes 83, 84 both penetrate the bottom main body portion 71 in the axial direction of the bottom main body portion 71 at the position of the bottom surface of the seal groove 68. The outer passage hole 83 is located more inward than the outer passage hole 84 in the radial direction of the pilot case 58. The outer passage hole 83 is located at the inner end position of the bottom surface of the seal groove 68 in the radial direction of the pilot case 58. The outer passage hole 84 is located at the outer end position of the bottom surface of the seal groove 68 in the radial direction of the pilot case 58.

[0042] As shown in Fig. 4, the pilot case 58 is provided with a plurality of outer passage holes 83, specifically three locations, at equal intervals in the circumferential direction of the pilot case 58. The pilot case 58 is provided with a plurality of outer passage holes 84, specifically three locations, at equal intervals in the circumferential direction of the pilot case 58. The outer passage holes 83 and the outer passage holes 84 are alternately arranged at equal intervals in the circumferential direction of the pilot case 58. The position of the inner passage hole 80 in the circumferential direction of the pilot case 58 is aligned with either the outer passage hole 83 or the outer passage hole 84.

[0043] The inner seat portion 77 is formed on the inner circumferential side of the bottom main body portion 71. The inner seat portion 77 is annular. As shown in Figure 3, the inner seat portion 77 protrudes from the inner circumferential side of the bottom main body portion 71 to the opposite side from the inner seat portion 74 in the axial direction of the bottom main body portion 71.

[0044] The outer sheet portion 78 is formed in a radially intermediate portion of the bottom body portion 71. As shown in FIG. 4, the outer sheet portion 78 is radially outward of the inner sheet portion 77 and protrudes from the bottom body portion 71 on the same side as the inner sheet portion 77 in the axial direction of the bottom body portion 71. The outer sheet portion 78 is a non-circular, petal-shaped irregular sheet. The outer sheet portion 78 has multiple, specifically six, sheet constituent portions 91. These sheet constituent portions 91 have the same shape and are arranged at equal intervals in the circumferential direction of the pilot case 58. The inner sheet portion 77 has an annular shape centered on the central axis of the pilot case 58. The multiple sheet constituent portions 91 extend radially from the inner sheet portion 77. In the axial direction of the pilot case 58, the position of the tip end surface of the multiple sheet constituent portions 91 on the opposite side from the bottom body portion 71 is equivalent to the position of the tip end surface of the inner sheet portion 77 on the opposite side from the bottom body portion 71.

[0045] A passage recess 92 is formed inside each seat constituent portion 91. The passage recess 92 is formed by being surrounded by a part of the inner seat portion 77 and the seat constituent portion 91. The passage recess 92 is recessed along the axial direction of the pilot case 58 from the tip end surface on the protruding side of the inner seat portion 77 and the tip end surface on the protruding side of the seat constituent portion 91. The bottom surface of the passage recess 92 is formed by the bottom main body portion 71. The passage recess 92 is formed inside all of the seat constituent portions 91.

[0046] The inner passage hole 80 and the outer passage holes 83, 84 are provided at positions between adjacent seat constituent portions 91 in the circumferential direction of the pilot case 58. Therefore, the inner passage hole 80 and the outer passage holes 83, 84 are provided outside the outer seat portion 78. The inner passage hole 80 and the outer passage holes 83, 84 do not open into the passage recess 92.

[0047] A passage groove 95 is formed in the inner seat portion 77, penetrating the inner seat portion 77 in the radial direction of the inner seat portion 77. The passage groove 95 is disposed at a position inside each of the plurality of seat constituent portions 91 in the circumferential direction of the bottom body portion 71. A passage in the passage groove 95 opens into the passage recess 92. The passage in the passage groove 95 communicates with the passage in the passage groove 30 of the piston rod 21 shown in FIG. 2.

[0048] The damping force generating mechanism 10 has a partitioning member 111 (movable mechanism) in the seal groove 68. The partitioning member 111 is an O-ring that is generally annular and has a circular cross section in a plane including the central axis of the ring. The partitioning member 111 is fitted into the seal groove 68 of the pilot case 58. The partitioning member 111 is made of an elastic material with sealing properties, specifically rubber. As shown in FIG. 3 , a seal portion 112 on the inner periphery of the partitioning member 111 presses against the radially inner wall surface of the seal groove 68 to seal the gap with this wall surface. A seal portion 113 on the outer periphery of the partitioning member 111 presses against the radially outer wall surface of the seal groove 68 to seal the gap with this wall surface.

[0049] 2 has an outer diameter that is larger than the outer diameter of the inner seat portion 46 of the piston 18 and smaller than the inner diameter of the valve seat portion 47. A notch 121 is formed in the disc 50. The notch 121 extends radially outward from the inner peripheral edge portion of the disc 50 that fits onto the mounting shaft portion 28. The passage within the notch 121 is constantly in communication with the piston-side passage 43 of the piston 18 and the passage within the passage groove 30 of the piston rod 21.

[0050] The first damping valve 52 is made up of a disk 131 and a seal member 132 . The disc 131 is made of metal and has a perforated circular flat plate shape of a constant thickness. The disc 131 is formed by press molding. The outer diameter of the disc 131 is larger than the outer diameter of the valve seat portion 47 of the piston 18. The mounting shaft portion 28 of the piston rod 21 is fitted onto the inner periphery of the disc 131. The disc 131 of the first damping valve 52 abuts against the valve seat portion 47. The first damping valve 52 opens and closes the opening of the piston-side passage 43 formed in the piston 18 on the side of the lower chamber 20 by the disc 131 moving away from and abutting against the valve seat portion 47.

[0051] The seal member 132 is made of an elastic material with sealing properties, specifically rubber. The seal member 132 has an annular shape. The seal member 132 is fixed to the outer periphery of the disk 131. The seal member 132 is fitted over the entire periphery onto the inner periphery surface of the cylindrical portion 66 of the pilot case 58 on the opening 67 side. The seal member 132 is axially slidable relative to the inner periphery surface of the cylindrical portion 66. The seal member 132 constantly seals the gap between the first damping valve 52 and the cylindrical portion 66. The first damping valve 52 is arranged in the opening 67 of the pilot case 58.

[0052] The disc 53 has an outer diameter equal to the outer diameter of the inner seat 46 of the piston 18. The outer diameter of the disc 53 is smaller than the minimum inner diameter of the seal member 132.

[0053] 3, the outer diameter of the disc 54 is larger than the outer diameter of the disc 53 and smaller than the minimum inner diameter of the seal member 132. A notch 141 is formed in the disc 54 from the inner peripheral edge to a position radially outward of the disc 53. The passage in the notch 141 is constantly in communication with the passage in the passage groove 30 of the piston rod 21.

[0054] Of the multiple discs, specifically six discs 55, the two discs closest to disc 54 in the axial direction have outer diameters larger than the outer diameter of disc 54. Of the six discs 55, the middle three discs in the axial direction have outer diameters larger than the outer diameter of the two discs closest to disc 54. Of the six discs 55, the one disc closest to disc 54 in the axial direction has an outer diameter larger than the outer diameter of the middle three discs. Overall, the outer diameters of the six discs 55 increase as they move away from disc 54 in the axial direction. The disk 56 has an outer diameter equal to that of the disk 53 .

[0055] The open-close disc 57 has an outer diameter that is larger than the outer diameter of a valve seat portion 75 of the pilot case 58 and smaller than the inner diameter of an outer seat portion 76. The open-close disc 57 can abut against the inner seat portion 74 and the valve seat portion 75 of the pilot case 58. The open-close disc 57 closes the passages in the multiple inner passage holes 80 by being seated on the valve seat portion 75. The open-close disc 57 opens the passages in the multiple inner passage holes 80 by being released from the valve seat portion 75.

[0056] The open-close disc 57 has a notch 151 formed from the inner peripheral edge thereof that fits onto the mounting shaft 28 to a position that is larger in diameter than the outer diameter of the disc 56 and smaller in diameter than the outer diameter of the inner seat portion 74. The passage in the notch 151 is always in communication with the passage in the passage groove 30 of the piston rod 21.

[0057] The seal portions 112, 113 of the partition member 111 are simultaneously pressed against the radially inner and radially outer wall surfaces of the seal groove 68. As a result, the area surrounded by the pilot case 58, the first damping valve 52 and the discs 53-56, the open-close disc 57, and the partition member 111 forms a back pressure chamber 171. The back pressure chamber 171 is constantly in communication with the passage in the passage groove 30 of the piston rod 21 via the passages in the notches 141, 151.

[0058] Additionally, the partition member 111 forms a variable chamber 172 between the bottom side of the seal groove 68 and the partition member 111. As shown in FIG. 2, the variable chamber 172 is constantly in communication with the lower chamber 20 via the passages in the outer passage holes 83 and 84.

[0059] A back pressure chamber 171 is formed inside the bottomed cylindrical pilot case 58 by the first damping valve 52, the discs 53 to 56, the opening / closing disc 57, and a partition member 111. The partition member 111 is provided inside the pilot case 58 and partitions the inside of the pilot case 58 into the back pressure chamber 171 and a variable chamber 172.

[0060] The disc 131 of the first damping valve 52 can be seated on the valve seat portion 47 of the piston 18. The first damping valve 52 is provided in a piston-side passage 43 formed in the piston 18, and generates a damping force by suppressing the flow of oil L caused by the piston 18 sliding toward the extension side. The first damping valve 52, together with the valve seat portion 47 of the piston 18, constitutes the first valve mechanism 41. The first damping valve 52 opens when its disc 131 is lifted off the valve seat portion 47. When this occurs, the first damping valve 52 causes oil L from the piston-side passage 43 to flow into the lower chamber 20 through the gap between the first damping valve 52 and the valve seat portion 47. The piston-side passage 43 serves as an extension-side passage through which oil L flows within the upper chamber 19 as the piston 18 moves toward the upper chamber 19. The piston-side passage 43 serves as an extension-side passage through which oil L as a working fluid flows from one upper chamber 19 toward the other lower chamber 20 during the extension stroke. The extension-side first valve mechanism 41, which is made up of a valve seat portion 47 and a first damping valve 52, is provided in the piston-side passage 43, and the first damping valve 52 opens and closes this piston-side passage 43 to suppress the flow of hydraulic fluid L, thereby generating a damping force. The lower chamber 20 is located downstream of the first damping valve 52 in the flow direction of hydraulic fluid L during the extension stroke.

[0061] In the extension-side first valve mechanism 41, neither the valve seat portion 47 nor the first damping valve 52 abutting thereon has a fixed orifice formed therein that communicates between the upper chamber 19 and the lower chamber 20, even when these are in an abutting state. In other words, the first valve mechanism 41 does not have a fixed orifice formed therein that constantly communicates between the upper chamber 19 and the lower chamber 20. The piston-side passage 43 serves as a passage upstream of the first damping valve 52 in the flow direction of the hydraulic fluid L during the extension stroke.

[0062] The passage in the notch 121 of the disc 50, the passage in the passage groove 30 of the piston rod 21, the passage in the notch 141 of the disc 54, and the passage in the notch 151 of the opening-closing disc 57 form a back pressure chamber introduction passage 176 that branches off and extends from the piston-side passage 43. The back pressure chamber introduction passage 176 communicates the upper chamber 19 with the back pressure chamber 171 via a portion of the piston-side passage 43. During the extension stroke, the back pressure chamber introduction passage 176 introduces oil L from the upper chamber 19, which is upstream of the back pressure chamber 171, into the back pressure chamber 171 via a portion of the piston-side passage 43.

[0063] The passages in the outer passage holes 83, 84 and the passage in the seal groove 68, both of which are provided in the bottom 65 of the pilot case 58, form a first passage 173 that extends between the back pressure chamber 171 and the lower chamber 20. A partition member 111 having seal portions 112, 113 that seal the first passage 173 with an elastic member is movably provided in this first passage 173.

[0064] The back pressure chamber 171 applies internal pressure to the first damping valve 52 in the direction of the piston 18, i.e., in the valve closing direction to seat the disc 131 on the valve seat portion 47. The pilot case 58 is cylindrical with a bottom and forms the back pressure chamber 171 that generates a biasing force in the valve closing direction on the first damping valve 52 that is arranged on the opening 67 side.

[0065] The inside of the inner passage hole 80 of the pilot case 58 forms a second passage 180. The open-close disc 57 is provided between the second passage 180 and the back pressure chamber 171 in an openable and closable manner. The second passage 180 in the inner passage hole 80 is provided in parallel with the first passage 173 in the outer passage holes 83 and 84 and the seal groove 68. The second passage 180 is disposed on the inner peripheral side of the pilot case 58 relative to the first passage 173. When the open-close disc 57 abuts against the valve seat portion 75 of the pilot case 58, it blocks the flow of oil L between the back pressure chamber 171 and the second passage 180 and the lower chamber 20. When the open-close disc 57 is separated from the valve seat portion 75, it allows the flow of oil L between the back pressure chamber 171 and the second passage 180 and the lower chamber 20.

[0066] Here, when the pressure on the second passage 180 and lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171 side by a predetermined value or more, the open-close disc 57 allows the flow of oil L from the lower chamber 20 and second passage 180 to the back pressure chamber 171 via the second passage 180. When the pressure on the back pressure chamber 171 side is higher than the pressure on the second passage 180 and lower chamber 20 side, the open-close disc 57 restricts the flow of oil L from the back pressure chamber 171 to the lower chamber 20 via the second passage 180.

[0067] The open-close disc 57 and the valve seat portion 75 of the pilot case 58 constitute a communication mechanism 181. One side of the second passage 180 can communicate with the back pressure chamber 171. The communication mechanism 181 is located on the one side of the second passage 180 and can communicate with the lower chamber 20, which is the other side of the second passage 180, only when the lower chamber 20 is on the upstream side. In other words, the communication mechanism 181 cannot communicate with the lower chamber 20, which is the other side of the second passage 180, when the lower chamber 20 is on the downstream side. The communication mechanism 181 restricts the flow of oil liquid L in one direction, from the back pressure chamber 171 side to the lower chamber 20 side, between the back pressure chamber 171 and the lower chamber 20. On the other hand, the communication mechanism 181 allows the flow of oil liquid L in the other direction, from the lower chamber 20 side to the back pressure chamber 171 side. The communication mechanism 181 is a check valve, and the open / close disk 57 is its valve member.

[0068] The communication mechanism 181 restricts the flow of oil L from the upper chamber 19, a portion of the piston-side passage 43, the backpressure chamber introduction passage 176, and the backpressure chamber 171 to the second passage 180 and the lower chamber 20. The communication mechanism 181 allows the flow of oil L from the lower chamber 20 and the second passage 180 to the backpressure chamber 171, the backpressure chamber introduction passage 176, a portion of the piston-side passage 43, and the upper chamber 19.

[0069] The second damping valve 60, which is made up of multiple discs 59, has an outer diameter that increases overall in the axial direction toward the pilot case 58. The outer diameter of the multiple discs 59 closest to the pilot case 58 is slightly larger than the maximum outer diameter of the tip end face of the outer seat portion 78. The second damping valve 60, which is made up of multiple discs 59, is able to seat on and separate from the outer seat portion 78.

[0070] The passage in the passage groove 30 of the piston rod 21 and the passages in the passage groove 95 and passage recess 92 of the pilot case 58 shown in FIG. 4 form a rod-side passage 191 shown in FIG. 2. The rod-side passage 191 further branches off from a back-pressure chamber introduction passage 176 that branches off from the piston-side passage 43, and is capable of communicating between the upper chamber 19 and the lower chamber 20. The outer seat portion 78 and the second damping valve 60 are provided in the rod-side passage 191 and form a second valve mechanism 201 that opens and closes the rod-side passage 191.

[0071] The second valve mechanism 201 has its second damping valve 60 seated on the outer seat portion 78. The second damping valve 60 opens during the extension stroke to provide resistance to the flow of hydraulic fluid L from the upper chamber 19 to the lower chamber 20 via part of the piston-side passage 43, part of the backpressure chamber introduction passage 176, and the rod-side passage 191. In other words, the second valve mechanism 201 generates a damping force by suppressing the flow of hydraulic fluid L from the upper chamber 19 to the lower chamber 20. The second valve mechanism 201 is an extension-side damping force generating mechanism that is provided in the rod-side passage 191 and generates a damping force by the flow of hydraulic fluid L.

[0072] In the extension-side second valve mechanism 201, a fixed orifice that connects the rod-side passage 191 to the lower chamber 20 is not formed in either the outer seat portion 78 or the second damping valve 60 that abuts thereon, even when these are in a contacting state. In other words, a fixed orifice that always communicates with the lower chamber 20 is not formed in the rod-side passage 191.

[0073] The disc 61 has an outer diameter smaller than the minimum outer diameter of the second damping valve 60 . The outer diameter of the annular member 62 is larger than the outer diameter of the disc 61. The rigidity of the annular member 62 is higher than the rigidity of the second damping valve 60.

[0074] The compression-side first valve mechanism 42 has, on the inner seat portion 48 side in the axial direction of the piston 18, in order from the inner seat portion 48 side in the axial direction of the piston 18, one disc 221, multiple discs (specifically four discs 222), one disc 223, one disc 224, and one annular member 225. The discs 221-224 and the annular member 225 are made of metal and are circular, flat plates with holes of a uniform thickness. The discs 221-224 are formed by press molding. The mounting shaft portion 28 of the piston rod 21 is fitted inside each of the discs 221-224 and the annular member 225.

[0075] The disc 221 has an outer diameter that is larger than the outer diameter of the inner seat portion 48 of the piston 18 and smaller than the inner diameter of the valve seat portion 49 . The multiple discs 222 constitute a first damping valve 231. The first damping valve 231 as a whole has an outer diameter that increases toward the disc 221 in the axial direction. The outer diameter of the multiple discs 222 closest to the disc 221 is slightly larger than the outer diameter of the valve seat portion 49 of the piston 18.

[0076] The disk 223 has an outer diameter smaller than the smallest outer diameter of the disks 222 among the plurality of disks 222 . The disk 224 has an outer diameter larger than that of the disk 223. The outer diameter of the annular member 225 is smaller than that of the disk 224 and larger than that of the disk 223. The annular member 225 is thicker and more rigid than the disk 222. The annular member 225 abuts against the shaft step portion 29 of the piston rod 21.

[0077] A first damping valve 231 made up of multiple discs 222 constitutes a first valve mechanism 42 together with a valve seat portion 49 of the piston 18. The first damping valve 231 lifts off from the valve seat portion 49 and opens. When this occurs, the first damping valve 231 allows oil L from the piston-side passage 44 to flow into the upper chamber 19 through the valve seat portion 49. The piston-side passage 44 serves as a compression-side passage through which oil L flows in the lower chamber 20 as the piston 18 moves toward the lower chamber 20. During the compression stroke, oil L as a working fluid flows from one lower chamber 20 toward the other upper chamber 19 through the piston-side passage 44. A compression-side first valve mechanism 42 made up of the valve seat portion 49 and the first damping valve 231 is provided in the piston-side passage 44. The first valve mechanism 42 opens and closes the piston-side passage 44 with the first damping valve 231 to suppress the flow of oil L, thereby generating a damping force.

[0078] In the compression side first valve mechanism 42, neither the valve seat portion 49 nor the first damping valve 231 abutting thereon has a fixed orifice formed therein that communicates between the lower chamber 20 and the upper chamber 19, even when these are in contact with each other. In other words, in the compression side first valve mechanism 42, there is no fixed orifice formed therein that constantly communicates between the lower chamber 20 and the upper chamber 19. The disk 224 and the annular member 225 suppress deformation of the first damping valve 231 in the opening direction beyond a specified limit.

[0079] The pilot case 58 and the partition member 111 constitute a frequency sensitive mechanism 211 that varies the damping force in response to the frequency of the reciprocating motion of the piston 18 (hereinafter referred to as the piston frequency). The frequency sensitive mechanism 211 has the partition member 111 that moves and deforms in response to the frequency of the reciprocating motion of the piston 18, changing the capacity of the back pressure chamber 171 that is always in communication with the upper chamber 19 and the capacity of the variable chamber 172 that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211 has the partition member 111 that is movably provided in the first passage 173. The frequency sensitive mechanism 211 varies the biasing force applied to the first damping valve 52 by the back pressure chamber 171.

[0080] During the extension stroke, the pressure in the back pressure chamber 171 becomes higher than that in the lower chamber 20. Then, under the pressure of the back pressure chamber 171, the partition member 111 moves toward the bottom surface of the seal groove 68 while maintaining a sealed state with the seal groove 68, and comes into contact with this bottom surface and is compressed and deformed. This causes the volume of the back pressure chamber 171 to expand.

[0081] During the compression stroke, the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171 side. Then, if the differential pressure between the lower chamber 20 side and the back pressure chamber 171 side is lower than a predetermined value, the partition member 111 receives the pressure on the lower chamber 20 side and moves toward the disc 55 while maintaining a sealed state with the seal groove 68, and abuts against the disc 55, undergoing compressive deformation. This expands the volume of the variable chamber 172. Furthermore, during the compression stroke, if the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171 side by a predetermined value or more, the communicating mechanism 181 opens, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171.

[0082] The mounting shaft portion 28 is inserted into the inside of each of the piston rod 21, and the annular member 225, disc 224, disc 223, the plurality of discs 222, disc 221, piston 18, disc 50, first damping valve 52, disc 53, disc 54, the plurality of discs 55, disc 56, open-close disc 57, pilot case 58, the plurality of discs 59, disc 61, and annular member 62 are stacked in this order on the shaft step portion 29. At this time, the pilot case 58 fits the seal member 132 of the first damping valve 52 into the cylindrical portion 66. Note that, before assembling the pilot case 58 to the piston rod 21, the partition member 111 is press-fitted into the seal groove 68 in advance.

[0083] With the components from the annular member 225 to the annular member 62 arranged on the piston rod 21 in this manner, the nut 235 is screwed onto the male thread 31 of the mounting shaft portion 28 that protrudes beyond the annular member 62. As a result, the inner circumferential sides or the entirety of the components from the annular member 225 to the annular member 62 stacked as described above are sandwiched between the shaft step portion 29 of the piston rod 21 and the nut 235, and are clamped in the axial direction.

[0084] As shown in FIG. 1 , the above-mentioned base valve 25 is provided between the inner tube 3 and the bottom member 12 of the outer tube 4. This base valve 25 has a base valve member 241, a disc valve 242, a disc valve 243, and a mounting pin 244. The base valve 25 is placed on the bottom member 12 at the base valve member 241, and is fitted to the inner tube 3 at the base valve member 241. The base valve member 241 separates the lower chamber 20 from the reservoir chamber 6. The disc valve 242 is provided below the base valve member 241, i.e., on the reservoir chamber 6 side. The disc valve 243 is provided above the base valve member 241, i.e., on the lower chamber 20 side. The mounting pin 244 attaches the disc valves 242 and 243 to the base valve member 241.

[0085] The base valve member 241 has an annular shape, and a mounting pin 244 is inserted through its radial center. The base valve member 241 is formed with a plurality of passage holes 245 and a plurality of passage holes 246. The plurality of passage holes 245 allow the oil L to flow between the lower chamber 20 and the reservoir chamber 6. The plurality of passage holes 246 are arranged outward of the plurality of passage holes 245 in the radial direction of the base valve member 241. The plurality of passage holes 246 allow the oil L to flow between the lower chamber 20 and the reservoir chamber 6. The disc valve 242 on the reservoir chamber 6 side allows the oil L to flow from the lower chamber 20 to the reservoir chamber 6 via the passage hole 245. On the other hand, the disc valve 242 restricts the flow of the oil L from the reservoir chamber 6 to the lower chamber 20 via the passage hole 245. The disc valve 243 allows the oil L to flow from the reservoir chamber 6 to the lower chamber 20 via the passage hole 246. On the other hand, the disc valve 243 restricts the oil L from flowing from the lower chamber 20 to the reservoir chamber 6 via the passage hole 246.

[0086] The disc valve 242 and the base valve member 241 form a damping valve mechanism 247. The damping valve mechanism 247 opens during the compression stroke of the shock absorber 1 to allow hydraulic fluid L to flow from the lower chamber 20 to the reservoir chamber 6, generating a damping force. The disc valve 243 and the base valve member 241 form a suction valve mechanism 248. The suction valve mechanism 248 opens during the extension stroke of the shock absorber 1 to allow hydraulic fluid L to flow from the reservoir chamber 6 into the lower chamber 20. The suction valve mechanism 248 mainly functions to allow hydraulic fluid to flow from the reservoir chamber 6 to the lower chamber 20 without generating any damping force, so as to compensate for a shortage of hydraulic fluid caused by the extension of the piston rod 21 from the cylinder 2.

[0087] Next, the operation of the shock absorber 1 including the damping force generating mechanism 10 will be described.

[0088] {During the extension stroke, the piston frequency is low and the piston speed is slower than the first predetermined value v1; a low-frequency, very low-speed region x1} In this low-frequency, extremely low-speed region x1, the first valve mechanism 41 and the second valve mechanism 201 do not open. Oil L from the upper chamber 19 flows into the backpressure chamber 171 through a portion of the piston-side passage 43 and the backpressure chamber introduction passage 176. This causes the partitioning member 111 of the frequency sensitive mechanism 211 to move toward the bottom of the seal groove 68, abutting against the bottom and undergoing compressive deformation. In this low-frequency, extremely low-speed region x1, the piston frequency is low and the piston 18 performs a large stroke. Therefore, a large amount of oil L is introduced from the upper chamber 19 into the backpressure chamber 171 at the beginning of the stroke. Therefore, the partitioning member 111 of the frequency sensitive mechanism 211 moves and deforms toward the bottom of the seal groove 68 to a near-limit, and then becomes less likely to deform (high spring region). Neither the first valve mechanism 41, 42 nor the second valve mechanism 201 has a fixed orifice that constantly connects the upper chamber 19 and the lower chamber 20. As a result, in the low-frequency, extremely low speed region x1, the rate of increase in damping force relative to an increase in piston speed becomes high.

[0089] {During the extension stroke, the piston frequency is a low frequency, and the piston speed is equal to or greater than the first predetermined value v1 and slower than the second predetermined value v2; a low-frequency, low-speed region x2} In this low-frequency, low-speed region x2, the oil L from the upper chamber 19 significantly moves and deforms the partition member 111 of the frequency sensitive mechanism 211 toward the bottom of the seal groove 68, similar to the low-frequency, very-low-speed region x1. Thereafter, the oil L from the upper chamber 19 via the piston-side passage 43 and the back-pressure chamber introduction passage 176 is less likely to be introduced into the back-pressure chamber 171. In the low-frequency, low-speed region x2, the pressure in the back-pressure chamber 171 is higher than in the low-frequency, very-low-speed region x1. Therefore, in the low-frequency, low-speed region x2, the oil L from the upper chamber 19 flows from the piston-side passage 43, the back-pressure chamber introduction passage 176, and the rod-side passage 191 into the lower chamber 20, opening the second damping valve 60 of the second valve mechanism 201. As a result, in the low-frequency, low-speed region x2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, very-low-speed region x1. In this low-frequency, low-speed range x2, the partition member 111 of the frequency sensitive mechanism 211 moves and deforms to near its limit, causing high pressure in the back pressure chamber 171. As a result, the biasing force from the back pressure chamber 171 is large on the first damping valve 52 of the first valve mechanism 41, and therefore the opening of the first damping valve 52 is limited.

[0090] {During the extension stroke, the piston frequency is a low frequency, and the piston speed is a low-frequency medium-to-high-speed region x3 that is equal to or greater than a second predetermined value v2} In this low-frequency medium-high speed range x3, as in the low-frequency low-speed range x2, the oil liquid L from the upper chamber 19 opens the second damping valve 60 of the second valve mechanism 201 and flows from a part of the piston-side passage 43, a part of the backpressure chamber introduction passage 176, and the rod-side passage 191 to the lower chamber 20. In the low-frequency medium-high speed range x3, the oil liquid L flows from the rod-side passage 191 to the lower chamber 20 in this way, thereby suppressing a pressure increase in the backpressure chamber 171 due to the oil liquid L being introduced into the backpressure chamber 171 via a part of the piston-side passage 43 and the backpressure chamber introduction passage 176. On the other hand, the force in the valve opening direction applied from the piston-side passage 43 to the first valve mechanism 41 increases, so the oil liquid L from the upper chamber 19 passes through the piston-side passage 43 and flows into the lower chamber 20, opening the first damping valve 52 of the first valve mechanism 41. As a result, in the low-frequency medium-high speed range x3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency low-speed range x2.

[0091] {In the extension stroke, the piston frequency is higher than the low frequency, and the piston speed is slower than the third predetermined value v3 in a high-frequency, very low-speed region x4} In this high-frequency, extremely low speed region x4, the first valve mechanism 41 and the second valve mechanism 201 do not open. Similarly to the low-frequency, extremely low speed region x1, oil L from the upper chamber 19 flows into the back pressure chamber 171 via part of the piston-side passage 43 and the back pressure chamber introduction passage 176. This causes the partitioning member 111 of the frequency sensitive mechanism 211 to move and deform toward the bottom of the seal groove 68. In this high-frequency, extremely low speed region x4, the piston frequency is high and the stroke of the piston 18 is small. Therefore, the amount of oil L introduced from the upper chamber 19 into the back pressure chamber 171 is less than in the low-frequency, extremely low speed region x1. Therefore, the partitioning member 111 of the frequency sensitive mechanism 211 does not deform to near its limit and is easily deformed (low spring region). As a result, the oil L introduced from the upper chamber 19 into the back pressure chamber 171 can be absorbed by the movement and deformation of the partitioning member 111. Therefore, in the high frequency extremely low speed region x4, although the rate of increase in damping force relative to an increase in piston speed is high, the damping force at the same piston speed is lower than in the low frequency extremely low speed region x1, resulting in softer characteristics.

[0092] {In the extension stroke, the piston frequency is higher than the low frequency, and the piston speed is equal to or higher than the third predetermined value v3 in a high-frequency, low-medium-high-speed region x5} In this high-frequency, low-, medium-, and high-speed range x5, the oil liquid L from the upper chamber 19 moves and deforms the partition member 111 of the frequency sensitive mechanism 211 toward the bottom of the seal groove 68, just as in the high-frequency, very-low speed range x4. In the high-frequency, low-, medium-, and high-speed range x5, the amount of oil liquid L introduced into the back pressure chamber 171 is small, so the deformation of the partition member 111 suppresses the increase in pressure in the back pressure chamber 171. As a result, the biasing force from the back pressure chamber 171 to the first damping valve 52 of the first valve mechanism 41 is reduced, making it easier for the first damping valve 52 to open. Therefore, the oil liquid L from the upper chamber 19 passes through the piston-side passage 43, opens the first damping valve 52 of the first valve mechanism 41, and flows into the lower chamber 20. As a result, in the high-frequency, low-, medium-, and high-speed range x5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very-low speed range x4. In addition, in the high-frequency low-medium-high speed range x5, the damping force at the same piston speed is lower than in the low-frequency low-speed range x2 and the low-frequency medium-high speed range x3, resulting in a softer characteristic. In this high-frequency low-medium-high speed range x5, the pressure increase in the back pressure chamber 171 is suppressed, so the second valve mechanism 201 remains in a closed state.

[0093] {During the compression stroke, the piston frequency is low and the piston speed is slower than the fourth predetermined value v4; a low-frequency, very low-speed region y1} In this low-frequency, extremely low-speed range y1, the first valve mechanism 42 and the communication mechanism 181 do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172 through the first passage 173 and the passages in the outer passage holes 83 and 84. This causes the partitioning member 111 of the frequency sensitive mechanism 211 to move toward the disc 55 and deform. In this low-frequency, extremely low-speed range y1, the piston frequency is low and the piston 18 performs a large stroke, so a large amount of oil L is introduced from the lower chamber 20 into the variable chamber 172 at the beginning of the stroke. Therefore, the partitioning member 111 of the frequency sensitive mechanism 211 moves and deforms toward the disc 55 to a near-limit, making it less susceptible to deformation (high spring region). Neither the first valve mechanisms 41 and 42 nor the second valve mechanism 201 have a fixed orifice that constantly connects the lower chamber 20 and the upper chamber 19. As a result, in the low-frequency, extremely low-speed region y1, the rate of increase in damping force relative to an increase in piston speed becomes high, resulting in hard characteristics.

[0094] {A low-frequency, low-speed region y2 in which the piston frequency is low and the piston speed is equal to or greater than the fourth predetermined value v4 and slower than the fifth predetermined value v5 during the compression stroke} In this low-frequency, low-speed region y2, similar to the low-frequency, very-low-speed region y1, the oil L from the lower chamber 20 moves and deforms the partition member 111 toward the disc 55 to a near-limit, and then opens the communication mechanism 181 from the second passage 180 and flows into the upper chamber 19 via the back pressure chamber 171, the back pressure chamber introduction passage 176, and part of the piston-side passage 43. As a result, in the low-frequency, low-speed region y2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, very-low-speed region y1.

[0095] {During the compression stroke, the piston frequency is a low frequency and the piston speed is a low-frequency medium-high-speed region y3 that is equal to or greater than a fifth predetermined value v5} In this low-frequency, medium-high speed range y3, as in the low-frequency, low-speed range y2, the oil L from the lower chamber 20 flows from the second passage 180 to the upper chamber 19 via the back pressure chamber 171, the back pressure chamber introduction passage 176, and a part of the piston-side passage 43, opening the communicating mechanism 181. In the low-frequency, low-medium-high speed range y2, in addition to this, the oil L from the lower chamber 20 passes through the piston-side passage 44, opens the first damping valve 231 of the first valve mechanism 42, and flows into the upper chamber 19. As a result, in the low-frequency, medium-high speed range y3, the rate of increase in damping force in response to an increase in piston speed is lower than in the low-frequency, low-speed range y2.

[0096] {A high-frequency, very-low-speed region y4 in which the piston frequency is higher than the low frequency and the piston speed is slower than the sixth predetermined value v6 during the compression stroke.} In this high-frequency, extremely low speed range y4, the first valve mechanism 42 and the communicating mechanism 181 do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172 through the passages in the outer passage holes 83 and 84 in the first passage 173. This causes the partitioning member 111 of the frequency sensitive mechanism 211 to move and deform toward the disc 55. In this high-frequency, extremely low speed range y4, the piston frequency is high and the stroke of the piston 18 is small, so the amount of oil L introduced from the lower chamber 20 into the variable chamber 172 is less than in the low-frequency, extremely low speed range y1. Therefore, the partitioning member 111 of the frequency sensitive mechanism 211 does not deform to near its limit and is prone to movement and deformation (low spring region). As a result, the movement and deformation of the partitioning member 111 can absorb the oil L introduced from the lower chamber 20 into the variable chamber 172. Therefore, in the high frequency extremely low speed region y4, the damping force at the same piston speed has softer characteristics than in the low frequency extremely low speed region y1.

[0097] {A high-frequency low-speed region y5 in which the piston frequency is higher than the above-mentioned low frequency and the piston speed is equal to or higher than the sixth predetermined value v6 and slower than the seventh predetermined value v7 during the compression stroke.} In this high-frequency, low-speed range y5, the oil L from the lower chamber 20 flows from the first passage 173 to the upper chamber 19 via the backpressure chamber 171, the backpressure chamber introduction passage 176, and part of the piston-side passage 43, opening the communication mechanism 181. In the high-frequency, low-speed range y5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very low-speed range y4. Also, in the high-frequency, low-speed range y5, the damping force at the same piston speed is lower and softer than in the low-frequency, low-speed range y2.

[0098] {A high-frequency medium-high-speed range y6 in which the piston frequency is higher than the low frequency and the piston speed is equal to or higher than the seventh predetermined value v7 during the compression stroke} In this high-frequency medium-high-speed range y6, as in the high-frequency low-speed range y5, the oil L from the lower chamber 20 flows from the first passage 173 to the upper chamber 19 via the back pressure chamber 171, the back pressure chamber introduction passage 176, and a part of the piston-side passage 43, opening the communication mechanism 181. In the high-frequency medium-high-speed range y6, in addition, the oil L from the lower chamber 20 passes through the piston-side passage 44, opens the first damping valve 231 of the first valve mechanism 42, and flows into the upper chamber 19. As a result, in the high-frequency medium-high-speed range y6, the rate of increase in damping force with respect to an increase in piston speed is lower than in the high-frequency low-speed range y5. Furthermore, in the high-frequency medium-high-speed range y6, the damping force at the same piston speed is lower and softer than in the low-frequency medium-high-speed range y3.

[0099] In addition, the shock absorber 1 has a characteristic that also includes the damping force characteristic of the damping valve mechanism 247 during the compression stroke.

[0100] The above-mentioned Patent Documents 1 and 2 disclose a damping force generating mechanism provided in a shock absorber, which applies back pressure to a damping force generating member in a valve closing direction. The damping force generating mechanism in Patent Document 1 is also provided with a frequency sensitive mechanism. However, there is a demand for damping force generating mechanisms that are not large enough.

[0101] The damping force generation mechanism 10 of the first embodiment has a pilot case 58, a frequency sensitive mechanism 211, a second passage 180, and a communication mechanism 181. The pilot case 58 is cylindrical with a bottom and defines a back pressure chamber 171 that generates a biasing force in a valve closing direction on the first damping valve 52 arranged on the opening 67 side. The frequency sensitive mechanism 211 is provided in a first passage 173 that is provided in the bottom 65 of the pilot case 58 and connects the back pressure chamber 171 and the lower chamber 20. A partition member 111 having seal portions 112, 113 that seal the first passage 173 with an elastic member is movably provided in the first passage 173, thereby varying the biasing force on the first damping valve 52 in the valve closing direction. The second passage 180 is provided in parallel to the first passage 173, and one side can communicate with the back pressure chamber 171. The communication mechanism 181 is located on the one side of the second passage 180 and can communicate with the other side of the second passage 180 only when the lower chamber 20 is on the upstream side.

[0102] As described above, the damping force generating mechanism 10 is provided with the first passage 173, which extends between the back pressure chamber 171 and the lower chamber 20, in the bottom 65 of the pilot case 58, which forms the back pressure chamber 171. The damping force generating mechanism 10 varies the biasing force applied to the first damping valve 52 in the valve closing direction by the frequency sensitive mechanism 211, which is provided in the first passage 173 with a movably mounted partition member 111 that seals the first passage 173 with seal portions 112, 113. Therefore, even though the damping force generating mechanism 10 has the frequency sensitive mechanism 211, it is possible to prevent the mechanism from becoming too large.

[0103] During the compression stroke described above, the damping force generating mechanism 10 has the partitioning member 111 of the frequency sensitive mechanism 211 move and elastically deform in a direction that narrows the back pressure chamber 171. Therefore, when the stroke reverses from the compression stroke to the extension stroke, the partitioning member 111 needs to return from its elastically deformed state and move in a direction that widens the back pressure chamber 171. As a result, if the damping force generating mechanism 10 were not provided with the communication mechanism 181, it would take time for the hydraulic fluid L to be introduced from the upper chamber 19 into the back pressure chamber 171 via part of the piston-side passage 43 and the back pressure chamber introduction passage 176, and it would take time to increase the pressure in the back pressure chamber 171. This would cause the closed state of the first damping valve 52, which is biased in the valve-closing direction by the pressure in the back pressure chamber 171, to become unstable. As a result, the first damping valve 52 is easily opened from the piston-side passage 43, allowing the oil L to flow into the lower chamber 20, causing a delay in the rise of the damping force when the stroke reverses from the compression stroke to the extension stroke.

[0104] In response to this, the damping force generating mechanism 10 is provided with the communication mechanism 181, which opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the back pressure chamber 171 via the second passage 180, thereby enabling the pressure in the back pressure chamber 171 to be increased quickly. This stabilizes the closed state of the first damping valve 52, which is biased in the valve closing direction by the pressure in the back pressure chamber 171. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0105] Furthermore, in the damping force generating mechanism 10, the second passage 180, which is opened and closed by the communication mechanism 181, is positioned closer to the inner periphery of the bottom portion 65 than the first passage 173, so that the radial size of the damping force generating mechanism 10 can be prevented from increasing.

[0106] Furthermore, the damping force generating mechanism 10 is subject to large compressive deformation because it uses an O-ring as the partition member 111 having seal portions 112, 113 that seal the first passage 173 with an elastic member. For this reason, the provision of the communication mechanism 181 is highly effective in suppressing the delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0107] [Second embodiment] Next, the second embodiment will be described, focusing on the differences from the first embodiment, mainly with reference to Figures 5 to 9. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0108] 5, a shock absorber 1A including a damping force generation mechanism 10A of the second embodiment has a piston rod 21A that is partially different from the piston rod 21, instead of the piston rod 21. The piston rod 21A has a main shaft portion 27A that is partially different from the main shaft portion 27, instead of the main shaft portion 27. The main shaft portion 27A has a shaft step portion 29A that is different from the shaft step portion 29 in that a radial groove 251 extending radially is formed, instead of the shaft step portion 29.

[0109] The piston rod 21A has a mounting shaft portion 28A that is partially different from the mounting shaft portion 28, instead of the mounting shaft portion 28. The mounting shaft portion 28A differs from the mounting shaft portion 28 in that an axial groove 252 that communicates with the radial groove 251 and extends in the axial direction is formed instead of the passage groove 30. The radial groove 251 and the axial groove 252 form a passage groove 30A that is continuously formed from the shaft step portion 29A to the outer periphery of the mounting shaft portion 28A. A male thread 31 is formed on the outer periphery of the end of the mounting shaft portion 28A that is on the opposite side of the main shaft portion 27A in the axial direction from the passage groove 30A. In the passage groove 30A, the radial groove 251 formed in the shaft step portion 29 opens into the upper chamber 19.

[0110] The damping force generating mechanism 10A is provided in the shock absorber 1A in place of the damping force generating mechanism 10. The damping force generating mechanism 10A has a piston 18A in place of the piston 18. Like the piston 18, the piston 18A is slidably fitted into the inner tube 3 of the cylinder 2 and divides the interior of the inner tube 3 into two chambers: an upper chamber 19 and a lower chamber 20.

[0111] The piston 18A has a piston body 35A and a sliding member 36A. The piston body 35A is made of metal and is formed seamlessly as a single unit. The piston body 35A is annular and formed by sintering. The piston 18A has the piston body 35A fitted onto the mounting shaft portion 28A of the piston rod 21A. The sliding member 36A is made of synthetic resin and has annular shape. The sliding member 36A is attached integrally to the outer peripheral surface of the piston body 35A. The piston 18A slides relative to the inner cylinder 3 with the sliding member 36A in contact with the inner cylinder 3.

[0112] The piston body 35A has a body base portion 256 and a body tubular portion 257. The body base portion 256 is a perforated disk. The body tubular portion 257 is cylindrical and extends to one side from the outer periphery of the body base portion 256 along the axial direction of the body base portion 256. The piston body 35A has the mounting shaft portion 28A of the piston rod 21A fitted into the inner periphery of the body base portion 256.

[0113] In the piston body 35A, a recess 258 is formed between the axial side of the body base portion 256 and the inner peripheral side of the body cylindrical portion 257. The recess 258 is recessed from one axial end of the piston body 35A along the axial direction of the piston body 35A. Thus, the piston 18A has a recess 258 in a predetermined radially inner area that is smaller in axial dimension than other areas. In the piston body 35A, the body cylindrical portion 257 extends from the body base portion 256 toward the lower chamber 20 out of the upper chamber 19 and the lower chamber 20. The sliding member 36A is attached to the outer peripheries of both the body base portion 256 and the body cylindrical portion 257.

[0114] A body base portion 256 of the piston body 35A is provided with a passage hole 37A, a passage groove 38A, a passage hole 39A, and a passage groove 40A. The passage hole 37A penetrates the main body base portion 256 in the axial direction of the main body base portion 256. A plurality of the passage holes 37A are formed in the main body base portion 256 at intervals in the circumferential direction of the main body base portion 256.

[0115] The passage hole 39A penetrates the main body base portion 256 in the axial direction of the main body base portion 256. A plurality of the passage holes 39A are formed in the main body base portion 256 at intervals in the circumferential direction of the main body base portion 256. In the main body base portion 256, the passage holes 37A and the passage holes 39A are formed alternately at equal pitches in one location each in the circumferential direction of the main body base portion 256.

[0116] The passage groove 38A is formed in the main body base portion 256 in a circular ring shape in the circumferential direction of the main body base portion 256. The passage groove 38A is formed at one end of the main body base portion 256 on the main body cylindrical portion 257 side in the axial direction. All of the passage holes 37A have ends on the main body base portion 256 on the main body cylindrical portion 257 side in the axial direction that open into the passage groove 38A.

[0117] The passage groove 40A is formed in the main body base portion 256 in a circular ring shape in the circumferential direction of the main body base portion 256. The passage groove 40A is formed at the other end of the main body base portion 256 opposite the main body cylindrical portion 257 in the axial direction. All of the passage holes 39A have ends opposite the main body cylindrical portion 257 in the axial direction of the main body base portion 256 that open into the passage groove 40A.

[0118] The ends of the plurality of passage holes 37A opposite to the passage groove 38A in the axial direction of the body base portion 256 open outward from the passage groove 40A in the radial direction of the body base portion 256. The ends of the plurality of passage holes 39A opposite to the passage groove 40A in the axial direction of the body base portion 256 open outward from the passage groove 38A in the radial direction of the body base portion 256. In the piston 18A, the insides of the plurality of passage holes 37A and the passage groove 38A form piston-side passages 43A. In the piston 18A, the insides of the plurality of passage holes 39A and the passage groove 40A form piston-side passages 44A.

[0119] The damping force generating mechanism 10A has a piston valve mechanism 201A provided for the piston-side passage 43A of the piston 18A. The piston valve mechanism 201A opens and closes the piston-side passage 43A to generate a damping force. The piston valve mechanism 201A is provided on the lower chamber 20 side of the piston 18A in the axial direction of the piston 18A. The piston-side passage 43A serves as a passage through which oil flows from the upper chamber 19 toward the lower chamber 20 when the piston 18A moves toward the upper chamber 19. In other words, the piston-side passage 43A serves as an extension-side passage through which oil flows from the upper chamber 19 toward the lower chamber 20 during the extension stroke of the shock absorber 1A. The piston valve mechanism 201A is an extension-side damping force generating unit that generates a damping force by suppressing the flow of oil in the piston-side passage 43A.

[0120] The damping force generating mechanism 10A has a first valve mechanism 42A provided for a piston-side passage 44A of the piston 18A. The first valve mechanism 42A opens and closes the piston-side passage 44A to generate a damping force. The first valve mechanism 42A is provided on the upper chamber 19 side of the piston 18A in the axial direction of the piston 18A. The piston-side passage 44A serves as a passage through which oil flows from the lower chamber 20 toward the upper chamber 19 when the piston 18A moves toward the lower chamber 20. In other words, the piston-side passage 44A serves as a compression-side passage through which oil flows from the lower chamber 20 toward the upper chamber 19 during the compression stroke of the shock absorber 1A. The first valve mechanism 42A serves as a compression-side damping force generating unit that generates a damping force by suppressing the flow of oil in the piston-side passage 44A.

[0121] An inner seat portion 46A and a valve seat portion 47A are formed at the axial end of the body base portion 256 on the lower chamber 20 side, radially inward of the cylindrical body portion 257. The inner seat portion 46A is annular. The valve seat portion 47A is also annular. The inner seat portion 46A is located radially inward of the opening of the passage groove 38A on the lower chamber 20 side of the body base portion 256. The valve seat portion 47A is located radially outward of the opening of the passage groove 38A on the lower chamber 20 side of the body base portion 256. The valve seat portion 47A constitutes a part of the piston valve mechanism 201A.

[0122] An inner seat portion 48A and a valve seat portion 49A are formed at the axial end of the body base portion 256 facing the upper chamber 19, i.e., at the axial end of the piston body 35A facing the upper chamber 19. The inner seat portion 48A is annular. The valve seat portion 49A is also annular. The inner seat portion 48A is located radially inward of the opening of the passage groove 40A facing the upper chamber 19 on the body base portion 256. The valve seat portion 49A is located radially outward of the opening of the passage groove 40A facing the upper chamber 19 on the body base portion 256. The valve seat portion 49A constitutes part of the first valve mechanism 42A.

[0123] In the main body base portion 256, openings of all of the passage holes 39A facing the lower chamber 20 are arranged on the opposite side of the main body base portion 256 in the radial direction from the passage groove 38A of the valve seat portion 47A. In the main body base portion 256, openings of all of the passage holes 37A facing the upper chamber 19 are arranged on the opposite side of the main body base portion 256 in the radial direction from the passage groove 40A of the valve seat portion 49A.

[0124] The damping force generating mechanism 10A has a damping valve 261 consisting of multiple discs, specifically four discs 260, on the lower chamber 20 side of the main body base portion 256 in the axial direction. The damping force generating mechanism 10A has, in order from the damping valve 261 side, one disc 262, one disc 263, one disc 264, and one disc 265 on the opposite side of the damping valve 261 from the main body base portion 256 in the axial direction. The discs 260, 262 to 265 are all made of metal and formed by press molding. The discs 260, 262 to 265 are all perforated flat plates of a uniform thickness. The mounting shaft portion 28A of the piston rod 21A is fitted onto the inner periphery of each of the discs 260, 262 to 265.

[0125] The outer diameter of the damping valve 261 decreases as the distance from the main body base portion 256 in the axial direction increases. The inner seat portion 46A and the valve seat portion 47A of the piston 18A abut against the disc 260 that is closest to the main body base portion 256 of the damping valve 261. The damping valve 261 opens and closes the piston-side passage 43A provided in the piston 18A by being seated on and lifted from the valve seat portion 47A, thereby generating a damping force. The damping valve 261 constitutes an extension-side piston valve mechanism 201A. The piston valve mechanism 201A does not have a fixed orifice between the damping valve 261 and the valve seat portion 47A that constantly communicates the piston-side passage 43A with the lower chamber 20.

[0126] The disk 262 has an outer diameter smaller than the outer diameter of the disk with the smallest outer diameter among the plurality of disks 260 that make up the damping valve 261 . The disk 263 has an outer diameter larger than that of the disk 262 . The outer diameter of the disk 264 is equal to the outer diameter of the disk 263. A notch 267 is formed on the outer periphery of the disk 264. As shown in Fig. 6, the disk 264 has a plurality of notches 267, specifically eight notches 267, formed at equal intervals in the circumferential direction of the disk 264.

[0127] As shown in FIG. 5, the disk 265 has an outer diameter equal to the outer diameters of the disks 263 and 264. A passage hole 268 is formed in the disk 265 at a radially intermediate position thereof. As shown in FIG. 7, the passage hole 268 has an arc shape concentric with the disk 265. The disk 265 is provided with a plurality of passage holes 268, specifically, three passage holes 268, at equal intervals in the circumferential direction of the disk 265. As shown in FIG. 5, the inner portions of the cutouts 267 and the passage holes 268 are aligned in the radial direction of the disks 264 and 265. Therefore, the cutouts 267 and the passage holes 268 communicate with each other.

[0128] The damping force generation mechanism 10A has a first damping valve 231A consisting of multiple discs, specifically three discs 222A, on the upper chamber 19 side of the piston 18A in the axial direction. The damping force generation mechanism 10A has a single disc 223A on the opposite side of the first damping valve 231A from the piston 18A in the axial direction. The damping force generation mechanism 10A has an annular member 225A on the opposite side of the disc 223A from the first damping valve 231A in the axial direction.

[0129] The disks 222A, 223A and the annular member 225A are all made of metal. The disks 222A, 223A are both flat plates with a constant thickness and are both annular. The annular member 225A is also annular. The mounting shaft portion 28A of the piston rod 21A is fitted onto the inner periphery of each of the disks 222A, 223A and the annular member 225A.

[0130] As a whole, the outer diameter of the first damping valve 231A decreases as it moves away from the main body base portion 256 in the axial direction. The outer diameter of the disc 223A is smaller than the outer diameter of the smallest one of the multiple discs 222A. The outer diameter of the annular member 225A is larger than the outer diameter of the discs 223A and smaller than the outer diameter of the smallest one of the multiple discs 222A. The annular member 225A is thicker and more rigid than the discs 222A that constitute the first damping valve 231A. The annular member 225A abuts against the shaft step portion 29A of the piston rod 21A.

[0131] The valve seat portion 49A of the piston 18A abuts against the outer periphery of the disk 222A that is closest to the main body base portion 256 in the axial direction of the first damping valve 231A. The first damping valve 231A opens and closes a piston-side passage 44A provided in the piston 18A to generate a damping force by being seated on and lifted from the valve seat portion 49A. The first damping valve 231A closes one opening of the piston-side passage 44A, which is on the upper chamber 19 side. The first damping valve 231A constitutes the compression-side first valve mechanism 42A. The first valve mechanism 42A does not have a fixed orifice between the first damping valve 231A and the valve seat portion 49A that would normally communicate the piston-side passage 44A with the upper chamber 19. The annular member 225A comes into contact with the first damping valve 231A when the first damping valve 231A deforms in the opening direction, thereby suppressing deformation of the first damping valve 231A beyond a specified limit.

[0132] The damping force generating mechanism 10A has a pilot case 58A (biasing force generating member) on the opposite side of the disc 265 from the disc 264 in the axial direction. The pilot case 58A is made of metal and is seamlessly molded into one piece by sintering. The pilot case 58A is cylindrical with a bottom, and has a bottom portion 65A and a cylindrical portion 66A.

[0133] The bottom portion 65A is a perforated disk, and the mounting shaft portion 28A of the piston rod 21A is fitted into its inner periphery. The tubular portion 66A is cylindrical and extends to one side from the outer periphery of the bottom portion 65A along the axial direction of the bottom portion 65A. The pilot case 58A has an opening 67A on the side of the tubular portion 66A opposite to the bottom portion 65A in the axial direction.

[0134] The bottom portion 65A has a bottom body portion 71A, an inner seat portion 74A, an intermediate seat portion 304, and a valve seat portion 75A. The bottom body portion 71A is a disk-shaped portion with holes, and the mounting shaft portion 28A of the piston rod 21A is fitted onto the inner circumferential side thereof. The inner seat portion 74A, the intermediate seat portion 304, and the valve seat portion 75A are provided on the axial side of the bottom main body portion 71A toward the cylindrical portion 66A, and further inward than the cylindrical portion 66A in the radial direction of the bottom main body portion 71A. The inner seat portion 74A, the intermediate seat portion 304, and the valve seat portion 75A protrude from the bottom main body portion 71A toward the cylindrical portion 66A in the axial direction of the bottom main body portion 71A.

[0135] The inner seat portion 74A is provided on the inner circumferential side of the bottom portion 65A. The inner seat portion 74A has an annular shape.

[0136] The intermediate seat portion 304 is provided radially outward of the bottom portion 65A than the inner seat portion 74A. The intermediate seat portion 304 has an annular shape that surrounds the inner seat portion 74A. A passage groove 311 is formed in the intermediate seat portion 304, penetrating the intermediate seat portion 304 in the radial direction of the intermediate seat portion 304. A plurality of passage grooves 311 are formed in the intermediate seat portion 304 at equal intervals in the circumferential direction of the intermediate seat portion 304.

[0137] The valve seat portion 75A is provided radially outward of the bottom portion 65A than the intermediate seat portion 304. The valve seat portion 75A has an annular shape that surrounds the intermediate seat portion 304.

[0138] A seal groove 68A is formed in the bottom main body portion 71A on the axially opposite side of the cylindrical portion 66A. The seal groove 68A is annular and formed on the outer peripheral side of the bottom main body portion 71A. The bottom main body portion 71A has an outer passage hole 83A that penetrates from the radially outer portion of the bottom surface of the seal groove 68A along the axial direction of the bottom main body portion 71A. The bottom main body portion 71A has a plurality of outer passage holes 83A formed at equal intervals in the circumferential direction. The outer passage hole 83A opens radially between the cylindrical portion 66A and the valve seat portion 75A of the bottom main body portion 71A.

[0139] The bottom body portion 71A has an inner passage hole 80A that penetrates the bottom body portion 71A in the axial direction, radially inward of the seal groove 68A. The bottom body portion 71A has a plurality of inner passage holes 80A that are equally spaced around the circumference of the bottom body portion 71A. The inner passage holes 80A open between the inner seat portion 74A and the intermediate seat portion 304 in the radial direction of the bottom body portion 71A. The inner passage hole 80A is located more inward than the outer passage hole 83A in the radial direction of the pilot case 58A.

[0140] A passage groove 320 that connects the inner passage hole 80A and the opening side of the seal groove 68A is formed in the bottom main body portion 71A on the opposite side of the axial direction from the cylindrical portion 66A.

[0141] The pilot case 58A abuts against the disk 265 at the end of the bottom body portion 71A opposite the cylindrical portion 66A in the axial direction. At this time, the disk 265 covers the opening of the seal groove 68A except for its radially outer portion. At this time, the passage hole 268 of the disk 265 communicates with the radially inner portion of the opening of the seal groove 68A.

[0142] The damping force generating mechanism 10A has a partitioning member 111A (movable mechanism) in the seal groove 68A. The partitioning member 111A is annular in shape as a whole, and is an O-ring with a circular cross section in a plane including the central axis of the ring. The partitioning member 111A is made of an elastic material with sealing properties, specifically rubber. The partitioning member 111A is fitted into the seal groove 68A. A seal portion 112A on the inner periphery of the partitioning member 111A presses against the radially inner wall surface of the seal groove 68A to seal a gap between the seal groove 68A and this wall surface. A seal portion 113A on the outer periphery of the partitioning member 111A presses against the radially outer wall surface of the seal groove 68A to seal a gap between the seal groove 68A and this wall surface. The partitioning member 111A moves in the axial direction of the partitioning member 111A within the seal groove 68A. The partitioning member 111A elastically deforms in the axial direction of the partitioning member 111A within the seal groove 68A.

[0143] The damping force generating mechanism 10A has, on the inner seat portion 74A side in the axial direction of the pilot case 58A, in order from the inner seat portion 74A side in the axial direction of the pilot case 58A, one opening / closing disc 57A, one disc 321, one disc 322, one disc 323, multiple discs, specifically five discs 324, one first damping valve 52A (first damping force generating member), and one seat forming member 325.

[0144] The open-close disc 57A, discs 321 to 324, and seat forming member 325 are all made of metal. The open-close disc 57A and discs 321 to 324 are all perforated circular flat plates of a uniform thickness, and are formed by press molding. The first damping valve 52A and seat forming member 325 are all annular. The mounting shaft portion 28 of the piston rod 21 is fitted inside each of the first damping valve 52A, open-close disc 57A, discs 321 to 324, and seat forming member 325.

[0145] The open-close disc 57A has an outer diameter larger than the outer diameter of the valve seat portion 75A of the pilot case 58A. The open-close disc 57A can abut against the inner seat portion 74A, the intermediate seat portion 304, and the valve seat portion 75A of the pilot case 58A. The open-close disc 57A closes the passages in the multiple inner passage holes 80A by being seated on the valve seat portion 75A. The open-close disc 57A opens the passages in the multiple inner passage holes 80A by being released from the valve seat portion 75A. The open-close disc 57A has a notch 151A that extends radially from the inner peripheral edge portion that fits onto the mounting shaft portion 28A within the range of the inner seat portion 74A of the open-close disc 57A.

[0146] The outer diameter of the disc 321 is smaller than the outer diameter of the opening-closing disc 57A and smaller than the outer diameter of the inner seat portion 74A of the pilot case 58A. The disc 321 has an outer diameter that does not cover the outer end of the notch 151A in the radial direction of the opening-closing disc 57A.

[0147] The outer diameter of the disk 322 is larger than the outer diameter of the disk 321. The disk 322 has a notch 327 formed in the outer periphery. The outer diameter of the disk 323 is smaller than the outer diameter of the disk 322 . The outer diameter of the disk 324 is smaller than the outer diameter of the disk 323 .

[0148] The first damping valve 52A is made up of a disk 131A and a seal member 132A. The disk 131A is made of metal and has a circular, flat plate shape with holes and a uniform thickness. The disk 131A is formed by press molding. The mounting shaft portion 28A of the piston rod 21A is fitted onto the inner periphery of the disk 131A.

[0149] The seal member 132A is made of an elastic material with sealing properties, specifically rubber. The seal member 132A has an annular shape. The seal member 132A is fixed to the outer periphery of the disk 131A. The seal member 132A is fitted over the entire periphery to the inner periphery surface of the cylindrical portion 66A of the pilot case 58A on the opening 67A side. The seal member 132A is axially slidable relative to the inner periphery surface of the cylindrical portion 66A. The seal member 132A constantly seals the gap between the first damping valve 52A and the cylindrical portion 66A. The first damping valve 52A is arranged in the opening 67A of the pilot case 58A.

[0150] The seat-forming member 325 is made of metal and has an annular shape. The seat-forming member 325 is seamlessly formed as a single piece by sintering. The seat-forming member 325 has a member main body portion 331, an inner seat portion 332, and a valve seat portion 333.

[0151] The member main body 331 is a disk-shaped member with holes, and the mounting shaft 28A of the piston rod 21A is fitted into the inner periphery thereof. The inner seat portion 332 protrudes from the inner peripheral edge of the member main body 331 to one axial side of the member main body 331. The inner seat portion 332 is annular. A passage groove 335 is formed in the inner seat portion 332, penetrating the inner seat portion 332 along its radial direction. The passage groove 335 communicates with the passage groove 30A of the piston rod 21A.

[0152] The valve seat portion 333 protrudes from the outer periphery of the member main body portion 331 in the axial direction of the member main body portion 331. The valve seat portion 333 is annular and surrounds the inner seat portion 332. The valve seat portion 333 protrudes from the member main body portion 331 on the same side as the inner seat portion 332 in the axial direction of the member main body portion 331.

[0153] The seat forming member 325 is oriented in the axial direction so that the inner seat portion 332 and the valve seat portion 333 are located on the first damping valve 52A side. The nut 235 abuts against the seat forming member 325 on the axial side opposite to the first damping valve 52A.

[0154] In the first damping valve 52A, the outer diameter of the disk 131A is larger than the outer diameter of the valve seat portion 333. In the first damping valve 52A, the disk 131A abuts against the valve seat portion 333.

[0155] The passage in the passage groove 30A of the piston rod 21A, the passage in the passage groove 335 of the seat forming member 325, and the passage between the inner seat portion 332 of the seat forming member 325 and the valve seat portion 333 constitute a rod-side passage 341. The first damping valve 52A opens and closes the rod-side passage 341 by the disc 131A moving away from and abutting against the valve seat portion 333.

[0156] The first damping valve 52A is provided in the rod-side passage 341 and generates a damping force by suppressing the flow of hydraulic fluid L caused by the sliding of the piston 18A toward the extension side. The first damping valve 52A constitutes the first valve mechanism 41A together with the valve seat portion 333 of the seat forming member 325. The first damping valve 52A opens when the disc 131A thereof is lifted off the valve seat portion 333. When this occurs, the first damping valve 52A causes hydraulic fluid L to flow from the rod-side passage 341 to the lower chamber 20 via the valve seat portion 333. The rod-side passage 341 serves as an extension-side passage through which hydraulic fluid L in the upper chamber 19 flows as the piston 18A moves toward the upper chamber 19. During the extension stroke, hydraulic fluid L flows from the rod-side passage 341 to the lower chamber 20 from one upper chamber 19 toward the other lower chamber 20. The extension-side first valve mechanism 41A, which consists of the valve seat portion 333 and the first damping valve 52A, is provided in the rod-side passage 341, and the first damping valve 52A opens and closes this rod-side passage 341 to suppress the flow of oil L, thereby generating a damping force.

[0157] In the extension-side first valve mechanism 41A, neither the valve seat portion 333 nor the first damping valve 52A abutting thereon has a fixed orifice formed therein that communicates between the upper chamber 19 and the lower chamber 20, even when these are in an abutting state. In other words, the extension-side first valve mechanism 41A does not have a fixed orifice formed therein that constantly communicates between the upper chamber 19 and the lower chamber 20. The rod-side passage 341 is a passage upstream of the first damping valve 52A in the flow direction of the hydraulic fluid L during the extension stroke. The lower chamber 20 is downstream of the first damping valve 52A in the flow direction of the hydraulic fluid L during the extension stroke.

[0158] The seal portions 112A and 113A of the partition member 111A are simultaneously pressed against the radially inner and radially outer wall surfaces of the seal groove 68A. As a result, the area surrounded by the pilot case 58A, the first damping valve 52A, the opening-closing disc 57A, the discs 321-324, and the partition member 111A forms a back pressure chamber 171A. The back pressure chamber 171A is constantly in communication with the passage in the passage groove 30A of the piston rod 21A via a passage in the notch 151A of the opening-closing disc 57A.

[0159] Additionally, the partitioning member 111A forms a variable chamber 172A between the partitioning member 111A of the seal groove 68A and the disc 265. The variable chamber 172A is constantly in communication with the lower chamber 20 via a passage between the outer periphery of the disc 265 and the seal groove 68A. The variable chamber 172A is constantly in communication with the lower chamber 20 via a passage hole 268 in the disc 265 and a passage in the notch 267 in the disc 264.

[0160] A back pressure chamber 171A is formed inside the bottomed cylindrical pilot case 58A by the first damping valve 52A, the opening / closing disc 57A, the discs 321 to 324, and the partition member 111A. The partition member 111A is provided inside the pilot case 58A and partitions the inside of the pilot case 58A into the back pressure chamber 171A and a variable chamber 172A.

[0161] A passage in the notch 151A of the open-close disc 57A constitutes a back pressure chamber introduction passage 176A that branches off from the rod side passage 341 and communicates with the back pressure chamber 171A. The back pressure chamber introduction passage 176A communicates the upper chamber 19 with the back pressure chamber 171A via the rod side passage 341. During the extension stroke, the back pressure chamber introduction passage 176A introduces oil L from the upper chamber 19, which is upstream of the back pressure chamber 171A, into the back pressure chamber 171A via the rod side passage 341.

[0162] The passage within outer passage hole 83A provided in bottom portion 65A of pilot case 58A, the passage within seal groove 68A, the passage within passage hole 268 of disk 265 and notch 267 of disk 264, and the passage between the outer periphery of disk 265 and seal groove 68A constitute a first passage 173A that extends to connect back pressure chamber 171A and lower chamber 20. A partition member 111A having seal portions 112A and 113A that seal first passage 173A with an elastic member is movably provided in this first passage 173A.

[0163] The back pressure chamber 171A applies internal pressure to the first damping valve 52A in the direction of the seat forming member 325, that is, in the valve closing direction to seat the disc 131A on the valve seat portion 333. The pilot case 58A is cylindrical with a bottom and forms the back pressure chamber 171A that generates a biasing force in the valve closing direction on the first damping valve 52A that is arranged on the opening 67A side.

[0164] The inside of the multiple inner passage holes 80A and the inside of the passage groove 320 of the pilot case 58A constitutes a second passage 180A. The second passage 180A is in communication with the variable chamber 172A. The open-close disc 57A is provided between the second passage 180A and the back pressure chamber 171A in an openable / closable manner. The second passage 180A is provided in parallel with the first passage 173A. The second passage 180A is disposed on the inner circumferential side of the pilot case 58A relative to the first passage 173A. When the open-close disc 57A abuts against the valve seat portion 75A of the pilot case 58A, it blocks the flow of oil L between the back pressure chamber 171A and the second passage 180A and the lower chamber 20. When the open-close disc 57A is separated from the valve seat portion 75A, it allows the flow of oil L between the back pressure chamber 171A and the second passage 180A and the lower chamber 20.

[0165] Here, when the pressure on the second passage 180A and lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171A side by a predetermined value or more, the open-close disc 57A allows the flow of oil L from the lower chamber 20 and second passage 180A to the back pressure chamber 171A. When the pressure on the back pressure chamber 171A side is higher than the pressure on the second passage 180A and lower chamber 20 side, the open-close disc 57A restricts the flow of oil L from the back pressure chamber 171A to the lower chamber 20 via the second passage 180A.

[0166] The open-close disc 57A and the valve seat portion 75A of the pilot case 58A constitute a communication mechanism 181A. One side of the second passage 180A can communicate with the back pressure chamber 171A. The communication mechanism 181A is located on the one side of the second passage 180A and can communicate with the lower chamber 20, which is the other side of the second passage 180A, only when the lower chamber 20 is on the upstream side. In other words, the communication mechanism 181A cannot communicate with the lower chamber 20, which is the other side of the second passage 180A, when the lower chamber 20 is on the downstream side. The communication mechanism 181A, between the back pressure chamber 171A and the variable pressure chamber 172A, restricts the flow of oil L in one direction from the back pressure chamber 171A side to the variable pressure chamber 172A side via the second passage 180A. On the other hand, the communication mechanism 181A allows the oil L to flow in the other direction, from the variable chamber 172A side to the back pressure chamber 171A side via the second passage 180A. The communication mechanism 181A is a check valve, and the open-close disc 57A is its valve member.

[0167] The communication mechanism 181A regulates the flow of oil L from the upper chamber 19, a portion of the rod-side passage 341, the back pressure chamber introduction passage 176A, and the back pressure chamber 171A to the second passage 180A and the lower chamber 20. The communication mechanism 181A allows the flow of oil L from the lower chamber 20 and the second passage 180A to the back pressure chamber 171A, the back pressure chamber introduction passage 176A, a portion of the rod-side passage 341, and the upper chamber 19.

[0168] The pilot case 58A and the partitioning member 111A constitute a frequency sensitive mechanism 211A that varies the damping force in response to the piston frequency. The partitioning member 111A of the frequency sensitive mechanism 211A moves and deforms in response to the frequency of the reciprocating motion of the piston 18A, changing the volume of the back pressure chamber 171A that is always in communication with the upper chamber 19 and the volume of the variable chamber 172A that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211A has the partitioning member 111A movably provided in the first passage 173A. The frequency sensitive mechanism 211A varies the biasing force applied to the first damping valve 52A by the back pressure chamber 171A.

[0169] During the extension stroke, the pressure in the back pressure chamber 171A becomes higher than that in the lower chamber 20. Then, under the pressure of the back pressure chamber 171A, the partition member 111A moves toward the disk 265 while maintaining a sealed state with the seal groove 68A, and comes into contact with the disk 265, undergoing compressive deformation. This causes the volume of the back pressure chamber 171A to expand.

[0170] During the compression stroke, the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171A side. If the pressure difference between the lower chamber 20 side and the back pressure chamber 171A side is lower than a predetermined value, the partition member 111A receives the pressure on the lower chamber 20 side and moves toward the bottom of the seal groove 68A while maintaining a sealed state with the seal groove 68A, and abuts against this bottom surface, undergoing compressive deformation. This expands the volume of the variable chamber 172A. Furthermore, during the compression stroke, if the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171A side by a predetermined value or more, the communicating mechanism 181A opens, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171A via the second passage 180A.

[0171] Next, the operation of the shock absorber 1A including the damping force generating mechanism 10A will be described.

[0172] {Low frequency, slightly slow speed range during extension stroke x1} In the low-frequency, extremely low-speed region x1, the first valve mechanism 41A and the piston valve mechanism 201A do not open. Oil L from the upper chamber 19 flows into the back pressure chamber 171A through a portion of the rod-side passage 341 and the back pressure chamber introduction passage 176A. This causes the partitioning member 111A of the frequency sensitive mechanism 211A to move toward the disc 265 and deform. In this low-frequency, extremely low-speed region x1, a large amount of oil L is introduced from the upper chamber 19 into the back pressure chamber 171A at the beginning of the stroke. Therefore, the partitioning member 111A of the frequency sensitive mechanism 211A moves and deforms toward the disc 265 to a near-limit, after which it becomes difficult to deform. Furthermore, neither the first valve mechanisms 41A, 42A nor the piston valve mechanism 201A has a fixed orifice that constantly connects the upper chamber 19 and the lower chamber 20. As a result, in the low-frequency, extremely low speed region x1, the rate of increase in damping force relative to an increase in piston speed becomes high.

[0173] {Low frequency, low speed range of extension stroke x2} In the low-frequency, low-speed region x2, the oil L from the upper chamber 19 significantly moves and deforms the partition member 111A of the frequency sensitive mechanism 211A toward the disc 265, similar to the low-frequency, very-low-speed region x1. Thereafter, the oil L from the upper chamber 19 via the rod-side passage 341 and the back-pressure chamber introduction passage 176A is less likely to be introduced into the back-pressure chamber 171A. In the low-frequency, low-speed region x2, the pressure in the back-pressure chamber 171A is higher than in the low-frequency, very-low-speed region x1. Therefore, in the low-frequency, low-speed region x2, the oil L from the upper chamber 19 flows from the piston-side passage 43A to the lower chamber 20, opening the damping valve 261 of the piston valve mechanism 201A. As a result, in the low-frequency, low-speed region x2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, very-low-speed region x1. In this low-frequency, low-speed range x2, the partition member 111A of the frequency sensitive mechanism 211A moves and deforms to near its limit, causing the pressure in the back pressure chamber 171A to become high. As a result, the biasing force from the back pressure chamber 171A on the first damping valve 52A of the first valve mechanism 41 is large, and therefore the opening of the first damping valve 52A is limited.

[0174] {Low frequency, medium to high speed range of extension stroke x3} In the low-frequency medium-high speed range x3, similarly to the low-frequency low-speed range x2, the oil liquid L from the upper chamber 19 opens the damping valve 261 of the piston valve mechanism 201A and flows from the piston-side passage 43A to the lower chamber 20. In the low-frequency medium-high speed range x3, the oil liquid L flows from the piston-side passage 43A to the lower chamber 20 in this way, thereby suppressing a pressure increase in the back pressure chamber 171A due to the oil liquid L being introduced into the back pressure chamber 171A via part of the rod-side passage 341 and the back pressure chamber introduction passage 176A. On the other hand, since the force in the valve opening direction applied to the first valve mechanism 41A through the rod-side passage 341 increases, the oil liquid L from the upper chamber 19 passes through the rod-side passage 341 and opens the first damping valve 52A of the first valve mechanism 41A and flows into the lower chamber 20. As a result, in the low-frequency medium-high speed range x3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency low-speed range x2.

[0175] {High frequency, very low speed range x 4 during extension stroke} In the high-frequency, extremely low speed region x4, the first valve mechanism 41A and the piston valve mechanism 201A do not open. Similarly to the low-frequency, extremely low speed region x1, oil L from the upper chamber 19 flows into the back pressure chamber 171A via a portion of the rod-side passage 341 and the back pressure chamber introduction passage 176A. This causes the partitioning member 111A of the frequency sensitive mechanism 211A to move and deform toward the disc 265. In this high-frequency, extremely low speed region x4, the amount of oil L introduced from the upper chamber 19 into the back pressure chamber 171A is less than in the low-frequency, extremely low speed region x1. Therefore, the partitioning member 111A of the frequency sensitive mechanism 211A does not deform to near its limit and is prone to deformation. As a result, the oil L introduced from the upper chamber 19 into the back pressure chamber 171A can be absorbed by the movement and deformation of the partitioning member 111A. Therefore, in the high frequency extremely low speed region x4, although the rate of increase in damping force relative to an increase in piston speed is high, the damping force at the same piston speed is lower than in the low frequency extremely low speed region x1, resulting in softer characteristics.

[0176] {High frequency, low, medium and high speed ranges during extension stroke x 5} In the high-frequency, low-medium-high speed range x5, the oil liquid L from the upper chamber 19 moves and deforms the partitioning member 111A of the frequency sensitive mechanism 211A toward the disc 265, similar to the high-frequency, very-low speed range x4. In the high-frequency, low-medium-high speed range x5, the amount of oil liquid L introduced into the back pressure chamber 171A is small, so the deformation of the partitioning member 111A suppresses the increase in pressure in the back pressure chamber 171A. This reduces the biasing force from the back pressure chamber 171A to the first damping valve 52A of the first valve mechanism 41A, making it easier for the first damping valve 52A to open. Therefore, the oil liquid L from the upper chamber 19 passes through the rod-side passage 341 and flows into the lower chamber 20, opening the first damping valve 52A of the first valve mechanism 41A. As a result, in the high-frequency, low-medium-high speed range x5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very-low speed range x4. In addition, in the high-frequency low-medium-high speed range x5, the damping force at the same piston speed is lower than in the low-frequency low-speed range x2 and the low-frequency medium-high speed range x3, resulting in softer characteristics. In this high-frequency low-medium-high speed range x5, the piston valve mechanism 201A remains in a closed state.

[0177] {Low frequency, very low speed region y1 of the compression stroke} In the low-frequency, extremely low-speed range y1, the first valve mechanism 42A and the communication mechanism 181A do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172A of the first passage 173A. This causes the partitioning member 111A of the frequency sensitive mechanism 211A to move toward the bottom of the seal groove 68A and deform. In this low-frequency, extremely low-speed range y1, a large amount of oil L is introduced from the lower chamber 20 into the variable chamber 172A at the beginning of the stroke. Therefore, the partitioning member 111A of the frequency sensitive mechanism 211A moves and deforms toward the bottom of the seal groove 68A to a near-limit, making it difficult to deform. Furthermore, neither the first valve mechanisms 41A, 42A nor the piston valve mechanism 201A has a fixed orifice that constantly connects the lower chamber 20 and the upper chamber 19. As a result, in the low-frequency, extremely low-speed region y1, the rate of increase in damping force relative to an increase in piston speed becomes high, resulting in hard characteristics.

[0178] {Low frequency, low speed region of the compression stroke y2} In the low-frequency low-speed region y2, similarly to the low-frequency very-low-speed region y1, the oil liquid L from the lower chamber 20 moves and deforms the partition member 111A toward the bottom surface of the seal groove 68A to near its limit, and then flows from the second passage 180A to the upper chamber 19 via the communication mechanism 181A, the back pressure chamber introduction passage 176A, and part of the rod-side passage 341. As a result, in the low-frequency low-speed region y2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency very-low-speed region y1.

[0179] {Low frequency, medium to high speed range of the compression stroke y3} In the low-frequency, medium-high speed range y3, as in the low-frequency, low-speed range y2, the oil L from the lower chamber 20 flows from the second passage 180A to the upper chamber 19 via the communicating mechanism 181A, the back pressure chamber 171A, the back pressure chamber introduction passage 176A, and a part of the rod-side passage 341. In the low-frequency, low-medium-high speed range y2, in addition to this, the oil L from the lower chamber 20 passes through the piston-side passage 44, opens the first damping valve 231A of the first valve mechanism 42A, and flows into the upper chamber 19. As a result, in the low-frequency, medium-high speed range y3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, low-speed range y2.

[0180] {High frequency, very low speed region of the compression stroke y4} In the high-frequency, extremely low-speed range y4, the first valve mechanism 42A and the communication mechanism 181A do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172A. This causes the partitioning member 111A of the frequency sensitive mechanism 211A to move toward the bottom of the seal groove 68A and deform. In this high-frequency, extremely low-speed range y4, the piston frequency is high and the stroke of the piston 18A is small, so less oil L is introduced from the lower chamber 20 into the variable chamber 172A than in the low-frequency, extremely low-speed range y1. Therefore, the partitioning member 111A of the frequency sensitive mechanism 211A does not deform to near its limit and is prone to movement and deformation. As a result, the oil L introduced from the lower chamber 20 into the variable chamber 172A can be absorbed by the movement and deformation of the partitioning member 111A. Therefore, in the high-frequency, extremely low-speed range y4, the damping force at the same piston speed exhibits softer characteristics than in the low-frequency, extremely low-speed range y1.

[0181] {High frequency, low speed region of the compression stroke y5} In the high-frequency, low-speed region y5, the oil L from the lower chamber 20 flows from the first passage 173A to the upper chamber 19 via the back pressure chamber 171A, the back pressure chamber introduction passage 176A, and a part of the rod-side passage 341, opening the communication mechanism 181A. In the high-frequency, low-speed region y5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very low-speed region y4. Also, in the high-frequency, low-speed region y5, the damping force at the same piston speed is lower and softer than in the low-frequency, low-speed region y2.

[0182] {High frequency, medium to high speed range of the contraction stroke y6} In the high-frequency medium-high-speed range y6, as in the high-frequency low-speed range y5, the oil L from the lower chamber 20 flows from the first passage 173A to the upper chamber 19 via the back pressure chamber 171A, the back pressure chamber introduction passage 176A, and a part of the rod-side passage 341, opening the communication mechanism 181A. In the high-frequency medium-high-speed range y6, the oil L from the lower chamber 20 also flows through the piston-side passage 44A, opening the first damping valve 231A of the first valve mechanism 42A, and into the upper chamber 19. As a result, in the high-frequency medium-high-speed range y6, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency low-speed range y5. Furthermore, in the high-frequency medium-high-speed range y6, the damping force at the same piston speed is lower and softer than in the low-frequency medium-high-speed range y3.

[0183] The damping force generation mechanism 10A of the second embodiment includes a pilot case 58A, a frequency sensitive mechanism 211A, a second passage 180A, and a communication mechanism 181A. The pilot case 58A is cylindrical and has a bottom. The pilot case 58A defines a back pressure chamber 171A that generates a valve-closing biasing force on the first damping valve 52A located on the opening 67A side. The frequency sensitive mechanism 211A includes a partition member 111A that is movably provided in a first passage 173A that is provided in the bottom 65A of the pilot case 58A and connects the back pressure chamber 171A to the lower chamber 20. The partition member 111A has seal members 112A and 113A that seal the first passage 173A with an elastic member, thereby varying the biasing force on the first damping valve 52A in the valve-closing direction. The second passage 180A is provided in parallel with the first passage 173A, and one side of the second passage 180A is capable of communicating with the back pressure chamber 171A. The communication mechanism 181A is located on the one side of the second passage 180A, and can communicate with the other side of the second passage 180A only when the lower chamber 20 is on the upstream side.

[0184] As described above, the damping force generating mechanism 10A is provided with the first passage 173A, which extends between the back pressure chamber 171A and the lower chamber 20, in the bottom 65A of the pilot case 58A that defines the back pressure chamber 171A. The damping force generating mechanism 10A varies the biasing force applied to the first damping valve 52A in the valve closing direction by a frequency sensitive mechanism 211A, which is provided in the first passage 173A with a movably mounted partition member 111A that seals the first passage 173A with seal portions 112A and 113A. Therefore, even though the damping force generating mechanism 10A has the frequency sensitive mechanism 211A, it is possible to prevent the mechanism from becoming too large.

[0185] Furthermore, since the damping force generating mechanism 10A is provided with the communication mechanism 181A, the communication mechanism 181A opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the backpressure chamber 171A via the second passage 180A, thereby quickly increasing the pressure in the backpressure chamber 171A. This stabilizes the closed state of the first damping valve 52A, which is biased in the valve closing direction by the pressure in the backpressure chamber 171A. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0186] Furthermore, in the damping force generating mechanism 10A, the second passage 180A that is opened and closed by the communication mechanism 181A is disposed closer to the inner periphery of the bottom portion 65A than the first passage 173A, so that an increase in radial size can be suppressed.

[0187] Furthermore, the damping force generating mechanism 10A is subject to large compressive deformation because it uses an O-ring as the partition member 111A having seals 112A and 113A that seal the first passage 173A with an elastic member. For this reason, the provision of the communication mechanism 181A is highly effective in suppressing the delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0188] In the damping force generating mechanism 10A, as shown in FIG. 8, a sintered disc 264A may be provided instead of the discs 264, 265. The disc 264A has the same outer diameter as the disc 264. As shown in FIG. 9, the disc 264A has notches 267A formed in its outer periphery. The disc 264A has a plurality of notches 267A formed at equal intervals in its circumferential direction. Passages in the plurality of notches 267A in the disc 264A connect the variable chamber 172A and the lower chamber 20. In this case, it is also possible to ensure rigidity by using a plurality of discs 263.

[0189] [Third embodiment] Next, the third embodiment will be described, focusing on the differences from the second embodiment, mainly with reference to Figures 10 to 12. Note that parts common to the second embodiment will be designated by the same names and symbols.

[0190] 10, a shock absorber 1B including a damping force generation mechanism 10B of the third embodiment is different in part of the configuration of the damping force generation mechanism 10B from the damping force generation mechanism 10A. The damping force generation mechanism 10B differs from the damping force generation mechanism 10A in the configuration between the disc 262 and the nut 235 in the axial direction of the piston rod 21A.

[0191] The damping force generating mechanism 10B has, in order from the disc 262 side in the axial direction of the piston rod 21A, a seat forming member 351 and a first damping valve 52B (first damping force generating member).

[0192] The seat-forming member 351 is made of metal and is seamlessly molded into a single piece by sintering. The seat-forming member 351 has a body portion 352, a flange portion 353, an inner seat portion 354, an intermediate seat portion 355, and a valve seat portion 356.

[0193] The body portion 352 is cylindrical, and the mounting shaft portion 28A of the piston rod 21A is fitted onto the inner circumferential side thereof.

[0194] The flange portion 353 extends from one axial end side of the body portion 352 to the outside in the radial direction of the body portion 352. The flange portion 353 is disk-shaped.

[0195] The inner seat portion 354 protrudes along the axial direction of the body portion 352 from the inner peripheral side of the end portion of the body portion 352 on the same side as the flange portion 353 in the axial direction. The inner seat portion 354 is annular.

[0196] The intermediate seat portion 355 protrudes from near the boundary between the body portion 352 and the flange portion 353 on the same side as the inner seat portion 354 in the axial direction of the body portion 352 and the flange portion 353. The intermediate seat portion 355 is annular and surrounds the inner seat portion 354 on the radially outer side.

[0197] The valve seat portion 356 protrudes from the outer periphery of the flange portion 353 on the same side as the intermediate seat portion 355 in the axial direction of the flange portion 353. The valve seat portion 356 is annular and surrounds the intermediate seat portion 355 on the radially outer side.

[0198] The seat forming member 351 is formed with a passage groove 358 in an inner seat portion 354, an intermediate seat portion 355, and at the ends of the body portion 352 and the flange portion 353 on the inner seat portion 354 and intermediate seat portion 355 sides in the axial direction. The passage groove 358 penetrates the inner seat portion 354 and the intermediate seat portion 355 in the radial direction. The passage groove 358 communicates with the passage groove 30A of the piston rod 21A. The seat forming member 351 abuts against the disk 262 at the end of the body portion 352 opposite to the flange portion 353 in the axial direction.

[0199] The first damping valve 52B is made of metal and has the shape of a circular flat plate with holes and a constant thickness. The first damping valve 52B is formed by press molding. The mounting shaft portion 28A of the piston rod 21A is fitted into the inside of the first damping valve 52B. The outer diameter of the first damping valve 52B is equal to the outer diameter of the valve seat portion 356. The first damping valve 52B opens and closes the passage between itself and the valve seat portion 356 by being seated on and removed from the valve seat portion 356.

[0200] The damping force generating mechanism 10B has a case member 360 and a pressing member 361 on the opposite side of the first damping valve 52B from the seat forming member 351 in the axial direction. The case member 360 is made of metal and is formed seamlessly as a single piece by sintering. The case member 360 is cylindrical with a bottom, and has a bottom portion 365 and a cylindrical portion 366.

[0201] The bottom portion 365 is a disk-shaped portion with holes, and the mounting shaft portion 28A of the piston rod 21A is fitted onto the inner circumferential side thereof. The tubular portion 366 is cylindrical and extends from the outer periphery of the bottom portion 365 to one side along the axial direction of the bottom portion 365. The case member 360 has an opening 367 on the side of the tubular portion 366 opposite to the bottom portion 365 in the axial direction.

[0202] The bottom portion 365 has a bottom main body portion 371 , one side sheet portion 372 , and another side sheet portion 373 . The bottom main body portion 371 is a disk-shaped portion with holes, and the mounting shaft portion 28A of the piston rod 21A is fitted onto its inner periphery. An annular groove 375 is formed on the outer periphery of the bottom main body portion 371. A passage hole 376 is formed in the bottom main body portion 371, penetrating the bottom main body portion 371 in the axial direction. The passage hole 376 is located radially inward of the annular groove 375.

[0203] The one-side seat portion 372 protrudes from the inner circumferential side of the end portion of the bottom main body portion 371 opposite the cylindrical portion 366 in the axial direction, along the axial direction of the bottom main body portion 371, toward the opposite side from the cylindrical portion 366. The one-side seat portion 372 is annular. The one-side seat portion 372 of the case member 360 abuts against the inner circumferential side of the first damping valve 52B.

[0204] The one-side seat portion 372 has a large diameter portion 381 and a small diameter portion 382. In the axial direction of the one-side seat portion 372, the large diameter portion 381 is closer to the bottom main body portion 371 than the small diameter portion 382. The outer diameter of the large diameter portion 381 is larger than the outer diameter of the small diameter portion 382. A passage groove 383 is formed at the end of the small diameter portion 382 of the one-side seat portion 372 opposite to the large diameter portion 381 in the axial direction. The passage groove 383 penetrates the small diameter portion 382 in the radial direction of the small diameter portion 382. The passage groove 383 communicates with the passage groove 30A of the piston rod 21A.

[0205] The other-side sheet portion 373 protrudes from the inner circumferential side of the end portion of the bottom main body portion 371 on the axial side of the cylindrical portion 366, along the axial direction of the bottom main body portion 371. The other-side sheet portion 373 is annular. The passage hole 376 of the bottom main body portion 371 is provided radially outward of the one-side seat portion 372 in the radial direction of the bottom main body portion 371 and between the other-side seat portion 373 and the cylindrical portion 366 .

[0206] The pressing member 361 has a cylindrical portion 391 and an inner protruding portion 392. The cylindrical portion 391 is cylindrical. The inner protruding portion 392 extends from one end of the cylindrical portion 391 in the axial direction to the inside of the cylindrical portion 391 in the radial direction. The inner protruding portion 392 is annular.

[0207] The pressing member 361 has its cylindrical portion 391 fitted onto the outer periphery of the bottom main body portion 371 of the case member 360, with the inner protruding portion 392 positioned closer to the first damping valve 52B in the axial direction than the cylindrical portion 391. The pressing member 361 is slidable in the axial direction relative to the case member 360. The pressing member 361 abuts against the outer periphery of the first damping valve 52B at its end on the inner protruding portion 392 side in the axial direction.

[0208] The damping force generating mechanism 10B includes a spring member 401 and a seal member 402. The spring member 401 is made of a metal plate and formed by press molding. The spring member 401 has a perforated disk-shaped base plate portion 405 and spring plate portions 406 extending outward from the base plate portion 405 in the radial direction of the base plate portion 405. The spring member 401 is provided with a plurality of spring plate portions 406 at equal intervals in the circumferential direction of the base plate portion 405.

[0209] The spring member 401 is placed on the end surface of the large diameter portion 381 on the small diameter portion 382 side in the axial direction, with the base portion 405 fitting into the small diameter portion 382 of the one side seat portion 372 of the case member 360. The spring member 401 has a plurality of spring plate portions 406 that abut on the end surface of the inward protruding portion 392 of the pressing member 361 on the opposite side in the axial direction from the first damping valve 52B. In this state, the plurality of spring plate portions 406 of the spring member 401 elastically deform, and urge the first damping valve 52B towards the valve seat portion 356 via the pressing member 361, pressing the first damping valve 52B against the valve seat portion 356.

[0210] The sealing member 402 is annular and fits into the annular groove 375 of the case member 360. The sealing member 402 is made of an elastic material with sealing properties, specifically rubber. The sealing member 402 is an O-ring, and constantly seals the gap between the bottom main body portion 371 and the cylindrical portion 391 of the pressing member 361.

[0211] The damping force generating mechanism 10B has, in order from the other-side seat portion 373 side, an open-close disc 57B, a partition member 111B (movable mechanism), and a stopper member 411 on the axially opposite side of the case member 360 from the first damping valve 52B, with the mounting shaft portion 28A fitted inside each of them. A nut 235 abuts on the end face of the stopper member 411 on the axially opposite side from the partition member 111B.

[0212] As shown in FIG. 11, the partition member 111B is made up of a disk 421 and a packing 422. The disk 421 is made of metal and has a circular, flat plate shape with holes and a constant thickness. The disk 421 is formed by press molding. The mounting shaft portion 28A of the piston rod 21A is fitted onto the inner periphery of the disk 421. A passage hole 425 is formed in the radial middle portion of the disk 421. The passage hole 425 penetrates the disk 421 in the axial direction of the disk 421. A plurality of passage holes 425 are formed in the disk 421 at equal intervals in the circumferential direction of the disk 421.

[0213] The packing 422 is made of an elastic material with sealing properties, specifically rubber. The packing 422 has an annular shape. The packing 422 is fixed to the outer periphery of the disk 421. The packing 422 is fitted over the entire inner periphery of the cylindrical portion 366 of the case member 360. At this time, the packing 422 contacts the inner periphery of the cylindrical portion 366 at the seal portion 112B on its outer periphery. The packing 422 is axially slidable relative to the inner periphery of the cylindrical portion 366. The packing 422 constantly seals the gap between the partition member 111B and the cylindrical portion 366. The passage hole 425 of the disk 421 is located radially inward of the packing 422.

[0214] The open-close disc 57B is made of metal. The open-close disc 57B is a circular flat plate with holes of a certain thickness and is formed by press molding. The open-close disc 57B comes into contact with the disc 421 of the partition member 111B to close the passages in the multiple passage holes 425. The open-close disc 57B opens the passages in the multiple passage holes 425 by moving away from the disc 421 of the partition member 111B.

[0215] The stopper member 411 is made of metal and has a disk shape with holes. The mounting shaft portion 28A of the piston rod 21A is fitted onto the inner circumferential side of the stopper member 411. The stopper member 411 has a tapered portion 412 at a radially intermediate position on the partition member 111B side in the axial direction of the stopper member 411. The tapered portion 412 becomes more distant from the disk 421 of the partition member 111B in the axial direction of the stopper member 411 as it moves radially outward from the stopper member 411. The stopper member 411 has a passage hole 431 formed at a radially intermediate position of the tapered portion 412. The passage hole 431 penetrates the stopper member 411 in the axial direction of the stopper member 411. When the partition member 111B deforms toward the stopper member 411 and the disk 421 abuts against the tapered portion 412, further deformation, i.e., movement, is restricted.

[0216] The stopper member 411 is provided so as to cover the opening 367 of the cylindrical portion 366 of the case member 360. The outer diameter of the stopper member 411 is smaller than the inner diameter of the cylindrical portion 366 of the case member 360. The nut 235 abuts against the stopper member 411 on the axial side opposite to the partition member 111B.

[0217] 10, in the damping force generating mechanism 10B, a pilot case 58B (biasing force generating member) is configured by a case member 360, a pressing member 361, a spring member 401, a seal member 402, and a stopper member 411. In the pilot case 58B, the bottom main body portion 371, the other-side seat portion 373, and the cylindrical portion 366 of the case member 360, and the stopper member 411 form a bottom portion 65B. In the pilot case 58B, a portion of the pressing member 361 that extends axially away from the stopper member 411 beyond the bottom main body portion 371 of the case member 360 forms a cylindrical portion 66B. In the pilot case 58B, an opening 67B is formed on the side of the cylindrical portion 66B opposite the bottom portion 65B in the axial direction.

[0218] The pilot case 58B has a tapered portion 412 inside its bottom portion 65B. The passage inside the passage hole 431 of the pilot case 58B is provided between the tapered portion 412 and the outer bottom side of the bottom portion 65B, and is always able to communicate with the lower chamber 20.

[0219] The passage in the passage groove 30A of the piston rod 21A, the passage in the passage groove 358 of the seat forming member 351, the passage between the inner seat portion 354 and the intermediate seat portion 355 of the seat forming member 351, and the passage between the intermediate seat portion 355 and the valve seat portion 356 of the seat forming member 351 constitute the rod-side passage 341B. The first damping valve 52B opens and closes the rod side passage 341B by moving away from and into contact with the valve seat portion 356.

[0220] The first damping valve 52B is provided in the rod-side passage 341B and generates a damping force by suppressing the flow of hydraulic fluid L caused by the sliding of the piston 18A toward the extension side. The first damping valve 52B, together with a valve seat portion 356 of the seat forming member 351, constitutes the first valve mechanism 41B. The first damping valve 52B opens by lifting off from the valve seat portion 356. When this occurs, the first damping valve 52B allows hydraulic fluid L from the rod-side passage 341B to flow through the gap between the rod-side passage 341B and the valve seat portion 356 and into the lower chamber 20. The rod-side passage 341B serves as an extension-side passage through which hydraulic fluid L flows within the upper chamber 19 as the piston 18A moves toward the upper chamber 19. The rod-side passage 341B serves as an extension-side passage through which hydraulic fluid L flows from one upper chamber 19 toward the other lower chamber 20 during the extension stroke. The extension-side first valve mechanism 41B, which consists of a valve seat portion 356 and a first damping valve 52B, is provided in the rod-side passage 341B, and the first damping valve 52B opens and closes this rod-side passage 341B to suppress the flow of oil L, thereby generating a damping force.

[0221] In the extension-side first valve mechanism 41B, neither the valve seat portion 356 nor the first damping valve 52B abutting thereon has a fixed orifice formed therein that communicates between the upper chamber 19 and the lower chamber 20, even when these are in an abutting state. In other words, the extension-side first valve mechanism 41B does not have a fixed orifice formed therein that constantly communicates between the upper chamber 19 and the lower chamber 20. The rod-side passage 341B is a passage upstream of the first damping valve 52B in the flow direction of the hydraulic fluid L during the extension stroke. The lower chamber 20 is downstream of the first damping valve 52B in the flow direction of the hydraulic fluid L during the extension stroke.

[0222] The seal portion 112B of the partition member 111B is in pressure contact with the inner circumferential surface of the cylindrical portion 366 of the case member 360 over the entire circumference. As a result, the area surrounded by the first damping valve 52B, the case member 360, the pressing member 361, the seal member 402, the open-close disc 57B, and the partition member 111B forms a back pressure chamber 171B. The back pressure chamber 171B is constantly in communication with the passage in the passage groove 30A of the piston rod 21A via a passage in the passage groove 383 of the pilot case 58B.

[0223] The portion surrounded by the partition member 111B and the stopper member 411 forms the variable chamber 172B. The variable chamber 172B is constantly in communication with the lower chamber 20 via a passage in the passage hole 431 of the stopper member 411.

[0224] A back pressure chamber 171B is formed inside the bottomed cylindrical pilot case 58B by the first damping valve 52B, the opening-closing disc 57B, and a partition member 111B. The partition member 111B is provided inside the pilot case 58B and partitions the inside of the pilot case 58B into the back pressure chamber 171B and a variable chamber 172B.

[0225] The passage in the passage groove 30A of the piston rod 21A and the passage in the passage groove 383 of the pilot case 58B form a back pressure chamber introduction passage 176B that branches off from the rod side passage 341B and communicates with the back pressure chamber 171B. The back pressure chamber introduction passage 176B communicates the upper chamber 19 with the back pressure chamber 171B via the rod side passage 341B. During the extension stroke, the back pressure chamber introduction passage 176B introduces oil L from the upper chamber 19, which is upstream of the back pressure chamber 171B, into the back pressure chamber 171B.

[0226] The passage inside the passage hole 431 of the stopper member 411, the variable chamber 172B, and the passage inside the passage hole 425 of the partition member 111B constitute a first passage 173B that extends to connect the back pressure chamber 171B and the lower chamber 20. A partition member 111B having a seal portion 112B that seals the first passage 173B with an elastic member is movably provided in this first passage 173B.

[0227] The back pressure chamber 171B applies internal pressure to the first damping valve 52B in the direction of the seat forming member 351, i.e., in the valve closing direction to seat the first damping valve 52B on the valve seat portion 356. The pilot case 58B is cylindrical with a bottom and forms the back pressure chamber 171B that generates a biasing force in the valve closing direction on the first damping valve 52B that is arranged on the opening 67B side.

[0228] The open-close disc 57B is provided between the first passage 173B and the back pressure chamber 171B so as to be openable and closable. When the open-close disc 57B is in surface contact with the disc 421 of the partitioning member 111B, it blocks the flow of oil L between the back pressure chamber 171B and the first passage 173B and the lower chamber 20. When the open-close disc 57B is separated from the disc 421 of the partitioning member 111B, it allows the flow of oil L between the back pressure chamber 171B and the first passage 173B and the lower chamber 20.

[0229] Here, when the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171B side by a predetermined value or more, the open-close disc 57B allows the oil L to flow from the lower chamber 20 to the back pressure chamber 171B via the first passage 173B. When the pressure on the back pressure chamber 171B side is higher than the pressure on the lower chamber 20 side, the open-close disc 57B restricts the flow of the oil L from the back pressure chamber 171B to the lower chamber 20 via the first passage 173B.

[0230] The open-close disc 57B and the disc 421 including the passage hole 425 of the partition member 111B constitute a communication mechanism 181B. One side of the first passage 173B can communicate with the back pressure chamber 171B. The communication mechanism 181B is located on the one side of the first passage 173B, and can communicate with the lower chamber 20, which is the other side of the first passage 173B, only when the lower chamber 20 is on the upstream side. In other words, when the lower chamber 20 is on the downstream side, the communication mechanism 181B cannot communicate with the lower chamber 20, which is the other side of the first passage 173B. The communication mechanism 181B restricts the flow of oil L in one direction, from the back pressure chamber 171B side to the variable chamber 172B side, between the back pressure chamber 171B and the variable chamber 172B. On the other hand, the communication mechanism 181B allows the oil L to flow in the other direction, from the variable chamber 172B side to the back pressure chamber 171B side. The communication mechanism 181B is a check valve, and the open / close disc 57B is its valve member.

[0231] The partitioning member 111B has a disc 421 having a passage hole 425, and a packing 422. The open-close disc 57B can close the passage hole 425. The open-close disc 57B opens when the first passage 173B allows oil liquid L to flow from the lower chamber 20 to the back pressure chamber 171B. The first passage 173B is provided to connect the back pressure chamber 171B and the lower chamber 20, and the partitioning member 111B is provided in the first passage 173B. The first passage 173B in which the partitioning member 111B is provided has one side that can communicate with the back pressure chamber 171B, and also serves as a passage in which a communication mechanism 181B is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side.

[0232] The communication mechanism 181B regulates the flow of oil L from the upper chamber 19, the rod-side passage 341B, the back-pressure chamber introduction passage 176B, and the back-pressure chamber 171B to the lower chamber 20 via the first passage 173B. The communication mechanism 181B allows the flow of oil L from the lower chamber 20 to the back-pressure chamber 171B, the back-pressure chamber introduction passage 176B, the rod-side passage 341B, and the upper chamber 19 via the first passage 173B.

[0233] The pilot case 58B and the partition member 111B constitute a frequency sensitive mechanism 211B that varies the damping force in response to the piston frequency. The partition member 111B of the frequency sensitive mechanism 211B moves and deforms in response to the frequency of the reciprocating motion of the piston 18A, changing the volume of the back pressure chamber 171B that is always in communication with the upper chamber 19 and the volume of the variable chamber 172B that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211B has a partition member 111B that is movably provided in the first passage 173B. The frequency sensitive mechanism 211B varies the biasing force applied to the first damping valve 52B by the back pressure chamber 171B.

[0234] During the extension stroke, the differential pressure between the back pressure chamber 171B and the lower chamber 20 becomes higher on the back pressure chamber 171B side than on the lower chamber 20 side. Then, under pressure from the back pressure chamber 171B, the partition member 111B deforms and moves together with the open-close disc 57B toward the stopper member 411 while maintaining a sealed state with the cylindrical portion 366. This causes the volume of the back pressure chamber 171B to expand.

[0235] During the compression stroke, the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171B side. If the pressure difference between the lower chamber 20 side and the back pressure chamber 171B side is lower than a predetermined value, the partition member 111B receives the pressure on the lower chamber 20 side and moves, together with the open-close disc 57B, away from the stopper member 411 while maintaining a sealed state with the cylindrical portion 366. This causes the volume of the variable chamber 172B to expand. Furthermore, during the compression stroke, if the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171B side by a predetermined value or more, the communicating mechanism 181B opens, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171B.

[0236] Next, the operation of the shock absorber 1B including the damping force generating mechanism 10B will be described.

[0237] {Low frequency, slightly slow speed range during extension stroke x1} In the low-frequency, extremely low-speed region x1, the first valve mechanism 41B and the piston valve mechanism 201A do not open. Oil L from the upper chamber 19 flows into the back pressure chamber 171B via the rod-side passage 341B and the back pressure chamber introduction passage 176B. This causes the partitioning member 111B of the frequency sensitive mechanism 211B to deform toward the stopper member 411 together with the opening-closing disc 57B. In this low-frequency, extremely low-speed region x1, a large amount of oil L is introduced from the upper chamber 19 into the back pressure chamber 171B at the beginning of the stroke. Therefore, the partitioning member 111B of the frequency sensitive mechanism 211B, together with the opening-closing disc 57B, deforms toward the stopper member 411 to a near-limit, after which it becomes difficult to deform. Furthermore, neither the first valve mechanisms 41B, 42A nor the piston valve mechanism 201A has a fixed orifice that constantly connects the upper chamber 19 and the lower chamber 20. As a result, in the low-frequency, extremely low speed region x1, the rate of increase in damping force relative to an increase in piston speed becomes high.

[0238] {Low frequency, low speed range of extension stroke x2} In the low-frequency, low-speed region x2, the oil L from the upper chamber 19 significantly deforms the partitioning member 111B of the frequency sensitive mechanism 211B together with the opening-closing disc 57B toward the stopper member 411, similar to the low-frequency, very low-speed region x1. Thereafter, the oil L from the upper chamber 19 via the rod-side passage 341B and the back-pressure chamber introduction passage 176B is less likely to be introduced into the back-pressure chamber 171B. Therefore, in the low-frequency, low-speed region x2, the oil L from the upper chamber 19 flows from the piston-side passage 43A to the lower chamber 20, opening the damping valve 261 of the piston valve mechanism 201A. As a result, in the low-frequency, low-speed region x2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, very low-speed region x1. In this low-frequency, low-speed region x2, the partitioning member 111B of the frequency sensitive mechanism 211B has moved and deformed to near its limit, causing the pressure in the back-pressure chamber 171B to become high. The first damping valve 52B of the first valve mechanism 41 receives a large biasing force from the back pressure chamber 171B, and therefore the opening of the valve is limited.

[0239] {Low frequency, medium to high speed range of extension stroke x3} In the low-frequency medium-high speed range x3, similarly to the low-frequency low-speed range x2, the oil liquid L from the upper chamber 19 opens the damping valve 261 of the piston valve mechanism 201A and flows from the piston-side passage 43A to the lower chamber 20. In the low-frequency medium-high speed range x3, the oil liquid L flows from the piston-side passage 43A to the lower chamber 20 in this way, and therefore the increase in pressure in the back pressure chamber 171B due to the oil liquid L being introduced into the back pressure chamber 171B via part of the rod-side passage 341B and the back pressure chamber introduction passage 176B is suppressed. On the other hand, since the force in the valve opening direction applied to the first valve mechanism 41B through the rod-side passage 341B increases, the oil liquid L from the upper chamber 19 passes through the rod-side passage 341B, opens the first damping valve 52B of the first valve mechanism 41B, and flows into the lower chamber 20. As a result, in the low-frequency medium-high speed range x3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency low-speed range x2.

[0240] {High frequency, very low speed range x 4 during extension stroke} In the high-frequency, extremely low speed range x4, the first valve mechanism 41B and the piston valve mechanism 201A do not open. Similarly to the low-frequency, extremely low speed range x1, oil L from the upper chamber 19 flows into the back pressure chamber 171B via the rod-side passage 341B and the back pressure chamber introduction passage 176B. This causes the partitioning member 111B of the frequency sensitive mechanism 211B to deform toward the stopper member 411 together with the opening-closing disc 57B. In this high-frequency, extremely low speed range x4, the amount of oil L introduced from the upper chamber 19 into the back pressure chamber 171B is less than in the low-frequency, extremely low speed range x1. Therefore, the partitioning member 111B of the frequency sensitive mechanism 211B does not deform to its limit and is prone to deformation. As a result, the oil L introduced from the upper chamber 19 into the back pressure chamber 171B can be absorbed by the deformation of the partitioning member 111B and the opening-closing disc 57B. Therefore, in the high frequency extremely low speed region x4, although the rate of increase in damping force relative to an increase in piston speed is high, the damping force at the same piston speed is lower than in the low frequency extremely low speed region x1, resulting in softer characteristics.

[0241] {High frequency, low, medium and high speed ranges during extension stroke x 5} In the high-frequency, low-medium-high speed range x5, the oil L from the upper chamber 19 deforms the partitioning member 111B of the frequency sensitive mechanism 211B together with the opening-closing disc 57B toward the stopper member 411, just as in the high-frequency, very-low speed range x4. In the high-frequency, low-medium-high speed range x5, the amount of oil L introduced into the back pressure chamber 171B is small, so the deformation of the partitioning member 111B suppresses the increase in pressure in the back pressure chamber 171B. This reduces the biasing force from the back pressure chamber 171B to the first damping valve 52B of the first valve mechanism 41B, making it easier for the first damping valve 52B to open. Therefore, the oil L from the upper chamber 19 passes through the rod-side passage 341B, opens the first damping valve 52B of the first valve mechanism 41B, and flows into the lower chamber 20. As a result, in the high-frequency, low-medium-high speed range x5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very-low speed range x4. In addition, in the high-frequency low-medium-high speed range x5, the damping force at the same piston speed is lower than in the low-frequency low-speed range x2 and the low-frequency medium-high speed range x3, resulting in a softer characteristic. In this high-frequency low-medium-high speed range x5, the pressure increase in the back pressure chamber 171B is suppressed, so the piston valve mechanism 201A remains in a closed state.

[0242] {Low frequency, very low speed region y1 of the compression stroke} In the low-frequency, extremely low-speed range y1, the first valve mechanism 42A and the communication mechanism 181B do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172B of the first passage 173B. This causes the partitioning member 111B of the frequency sensitive mechanism 211B to deform, together with the opening-closing disc 57B, toward the side opposite the stopper member 411. In this low-frequency, extremely low-speed range y1, a large amount of oil L is introduced from the lower chamber 20 into the variable chamber 172B at the beginning of the stroke. Therefore, the partitioning member 111B of the frequency sensitive mechanism 211B deforms nearly to its limit toward the side opposite the stopper member 411, making it difficult to deform. Furthermore, neither the first valve mechanisms 41B, 42A nor the piston valve mechanism 201A has a fixed orifice that constantly connects the lower chamber 20 and the upper chamber 19. As a result, in the low-frequency, extremely low-speed region y1, the rate of increase in damping force relative to an increase in piston speed becomes high, resulting in hard characteristics.

[0243] {Low frequency, low speed region of the compression stroke y2} In the low-frequency low-speed region y2, similarly to the low-frequency very-low-speed region y1, the oil liquid L from the lower chamber 20 moves and deforms the partition member 111B to nearly its limit in the direction opposite the stopper member 411, and then flows from the first passage 173B to the upper chamber 19 via the back pressure chamber 171B, the back pressure chamber introduction passage 176B, and the rod-side passage 341B, opening the communication mechanism 181B. As a result, in the low-frequency low-speed region y2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency very-low-speed region y1.

[0244] {Low frequency, medium to high speed range of the compression stroke y3} In the low-frequency, medium-high speed range y3, as in the low-frequency, low-speed range y2, the oil L from the lower chamber 20 flows from the first passage 173B to the upper chamber 19 via the back pressure chamber 171B, the back pressure chamber introduction passage 176B, and the rod-side passage 341B, opening the communicating mechanism 181B. In the low-frequency, low-medium-high speed range y2, in addition to this, the oil L from the lower chamber 20 passes through the piston-side passage 44, opens the first damping valve 231A of the first valve mechanism 42A, and flows into the upper chamber 19. As a result, in the low-frequency, medium-high speed range y3, the rate of increase in damping force in response to an increase in piston speed is lower than in the low-frequency, low-speed range y2.

[0245] {High frequency, very low speed region of the compression stroke y4} In the high-frequency, extremely low-speed range y4, the first valve mechanism 42A and the communication mechanism 181B do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172B. This causes the partitioning member 111B of the frequency sensitive mechanism 211B to deform, together with the open-close disc 57B, toward the side opposite the stopper member 411. In this high-frequency, extremely low-speed range y4, the piston frequency is high and the stroke of the piston 18A is small, so less oil L is introduced from the lower chamber 20 into the variable chamber 172B than in the low-frequency, extremely low-speed range y1. Therefore, the partitioning member 111B of the frequency sensitive mechanism 211B does not deform to near its limit and is prone to movement and deformation. As a result, the movement and deformation of the partitioning member 111B can absorb the oil L introduced from the lower chamber 20 into the variable chamber 172B. Therefore, in the high-frequency, extremely low-speed range y4, the damping force at the same piston speed exhibits softer characteristics than in the low-frequency, extremely low-speed range y1.

[0246] {High frequency, low speed region of the compression stroke y5} In the high-frequency, low-speed range y5, the oil L from the lower chamber 20 flows from the first passage 173B to the upper chamber 19 via the backpressure chamber 171B, the backpressure chamber introduction passage 176B, and the rod-side passage 341B, opening the communication mechanism 181B. In the high-frequency, low-speed range y5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very low-speed range y4. Also, in the high-frequency, low-speed range y5, the damping force at the same piston speed is lower and softer than in the low-frequency, low-speed range y2.

[0247] {High frequency, medium to high speed range of the contraction stroke y6} In the high-frequency medium-high-speed range y6, as in the high-frequency low-speed range y5, the oil L from the lower chamber 20 flows from the first passage 173B to the upper chamber 19 via the back pressure chamber 171B, the back pressure chamber introduction passage 176B, and the rod-side passage 341B, opening the communication mechanism 181B. In the high-frequency medium-high-speed range y6, the oil L from the lower chamber 20 also flows through the piston-side passage 44A, opening the first damping valve 231A of the first valve mechanism 42A, and into the upper chamber 19. As a result, in the high-frequency medium-high-speed range y6, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency low-speed range y5. Furthermore, in the high-frequency medium-high-speed range y6, the damping force at the same piston speed is lower and softer than in the low-frequency medium-high-speed range y3.

[0248] The damping force generation mechanism 10B of the third embodiment includes a pilot case 58B, a frequency sensitive mechanism 211B, a first passage 173B, and a communication mechanism 181B. The pilot case 58B is cylindrical and has a bottom. The pilot case 58B defines a back pressure chamber 171B that generates a valve-closing biasing force on the first damping valve 52B located on the opening 67B side. The frequency sensitive mechanism 211B includes a partition member 111B that is movably provided in the first passage 173B, the first passage 173B being provided in the bottom 65B of the pilot case 58B and capable of communicating the back pressure chamber 171B with the lower chamber 20. The partition member 111B has a seal portion 112B that seals the first passage 173B with an elastic member, thereby varying the valve-closing biasing force on the first damping valve 52B. One side of the first passage 173B is capable of communicating with the back pressure chamber 171B. The communication mechanism 181B is located on the one side of the first passage 173B, and can communicate with the other side of the first passage 173B only when the lower chamber 20 is on the upstream side.

[0249] As described above, the damping force generation mechanism 10B is provided with a first passage 173B in the bottom 65B of the pilot case 58B that defines the back pressure chamber 171B, which is capable of communicating the back pressure chamber 171B with the lower chamber 20. The damping force generation mechanism 10B varies the biasing force applied to the first damping valve 52B in the valve closing direction by a frequency sensitive mechanism 211B that is provided in the first passage 173B and has a partition member 111B that is movably mounted in the first passage 173B and seals the first passage 173B with a seal portion 112B. Therefore, even though the damping force generation mechanism 10B has the frequency sensitive mechanism 211B, it is possible to prevent the mechanism from becoming too large.

[0250] Furthermore, since the damping force generating mechanism 10B is provided with the communication mechanism 181B, the communication mechanism 181B opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the backpressure chamber 171B via the first passage 173B, thereby quickly increasing the pressure in the backpressure chamber 171B. This stabilizes the closed state of the first damping valve 52B, which is biased in the valve closing direction by the pressure in the backpressure chamber 171B. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0251] Furthermore, in the damping force generating mechanism 10B, the first passage 173B in which the partition member 111B is provided has one side that can communicate with the back pressure chamber 171B, and also serves as a passage in which a communication mechanism 181B is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side. This makes it possible to further prevent the damping force generating mechanism 10B from becoming large.

[0252] Furthermore, the damping force generating mechanism 10B has a tapered portion 412 provided inside the bottom portion 65B of the pilot case 58B. In the damping force generating mechanism 10B, the deformation, i.e., movement, of the partitioning member 111B is restricted by the tapered portion 412 when the partitioning member 111B deforms toward the stopper member 411. This makes it possible to suppress local deformation of the partitioning member 111B and improve its durability.

[0253] Furthermore, in the damping force generating mechanism 10B, a passage is formed in the pilot case 58B within the passage hole 431 that is provided between the tapered portion 412 and the outer bottom side of the bottom portion 65B and is always in communication with the lower chamber 20. Therefore, the damping force generating mechanism 10B can prevent the pilot case 58B from becoming larger.

[0254] In addition, in the damping force generation mechanism 10B, the partition member 111B has a disc 421 having a passage hole 425, and a packing 422. The open-close disc 57B can close the passage hole 425, and opens when the first passage 173B allows oil L to flow from the lower chamber 20 to the back pressure chamber 171B. Therefore, it is possible to increase the variable volume of the back pressure chamber 171B while preventing the damping force generation mechanism 10B from becoming too large.

[0255] 12, in the damping force generation mechanism 10B, the outer diameter of the flat open-close disc 57B may be increased so that the outer periphery of the open-close disc 57B abuts against the inner periphery of the packing 422 on the side opposite to the disc 421 in the axial direction of the open-close disc 57B over the entire periphery. This allows the open-close disc 57B to bend in a tapered shape, thereby applying a preload to the open-close disc 57B. This makes it possible to prevent the oil L from leaking from the back pressure chamber 171B to the lower chamber 20 via the communication mechanism 181B, particularly during the extension stroke.

[0256] [Fourth embodiment] Next, the fourth embodiment will be described, focusing on the differences from the first embodiment, mainly with reference to Figures 13 and 14. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0257] 13, a shock absorber 1C including a damping force generation mechanism 10C of the fourth embodiment has a partial configuration different from that of the damping force generation mechanism 10. The damping force generation mechanism 10C differs from the damping force generation mechanism 10 in the configuration between the disc 53 and the second damping valve 60 in the axial direction of the piston rod 21.

[0258] The damping force generating mechanism 10C has, on the opposite side of the disc 53 from the first damping valve 52 in the axial direction of the piston rod 21, in order from the disc 53 side in the axial direction of the piston rod 21, one disc 450, one disc 451, one disc 452, one spring disc 453, one opening / closing disc 57C, and one pilot case 58C (spring force generating member).

[0259] The discs 450 to 452, the spring disc 453, the opening / closing disc 57C, and the pilot case 58C are all made of metal. The discs 450 to 452 and the opening / closing disc 57C are all perforated circular flat plates of a uniform thickness. The discs 450 to 452, the spring disc 453, and the opening / closing disc 57C are formed by press molding. The spring disc 453 is disc-shaped. The pilot case 58C is annular. The mounting shaft portion 28 of the piston rod 21 is fitted inside the discs 450 to 452, the spring disc 453, the opening / closing disc 57C, and the pilot case 58C.

[0260] The pilot case 58C is cylindrical and has a bottom. The pilot case 58C is formed seamlessly as a single piece by sintering. The pilot case 58C has a bottom portion 65C and a cylindrical portion 66C. The bottom portion 65C is a disk-shaped portion with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted onto the inner periphery thereof.

[0261] The tubular portion 66C extends from one axial end of the outer periphery of the bottom portion 65C along the axial direction of the bottom portion 65C. The tubular portion 66C is cylindrical. The pilot case 58C has an opening 67 on the opposite side of the axial direction of the cylindrical portion 66C from the bottom portion 65C.

[0262] The bottom portion 65C has a bottom main body portion 71C, an inner sheet portion 77 and an outer sheet portion 78 similar to those described above.

[0263] The bottom body portion 71C is a disk-shaped portion with holes. The cylindrical portion 66C extends along the axial direction of the bottom body portion 71C from the side opposite to the inner sheet portion 77 and the outer sheet portion 78 in the axial direction of the bottom body portion 71C. A seal groove 68C is formed in the bottom main body portion 71C at a radially intermediate position of the bottom main body portion 71C. The seal groove 68C is recessed from the end face of the bottom main body portion 71C on the axial side opposite the inner seat portion 77 and the outer seat portion 78 toward the inner seat portion 77 and the outer seat portion 78 in the axial direction of the bottom main body portion 71C.

[0264] Inner passage holes 80C, 81C shown in FIG. 14 are formed in the bottom surface of the seal groove 68C of the bottom main body portion 71C. The inner passage holes 80C, 81C penetrate the bottom main body portion 71C at the position of the seal groove 68C. The inner passage hole 80C is located more inward than the inner passage hole 81C in the radial direction of the pilot case 58C. The inner passage hole 80C is located at the inner end position of the bottom surface of the seal groove 68C in the radial direction of the pilot case 58C. The inner passage hole 81C is located at the outer end position of the bottom surface of the seal groove 68C in the radial direction of the pilot case 58C. The pilot case 58C is provided with a plurality of inner passage holes 80C, 81C, specifically, three of each. The inner passage holes 80C and the inner passage holes 81C are alternately arranged at equal intervals in the circumferential direction of the pilot case 58C.

[0265] The pilot case 58C has an outer passage hole 83C formed radially outward of the seal groove 68C of the bottom main body portion 71C. The outer passage hole 83C penetrates the bottom main body portion 71C in the axial direction. The pilot case 58C has a plurality of outer passage holes 83C (specifically, six) formed at equal intervals in the circumferential direction of the pilot case 58C. The outer passage hole 83C is aligned with either the inner passage hole 80C or the inner passage hole 81C in the circumferential direction of the pilot case 58C.

[0266] The inner passage holes 80C, 81C and the outer passage hole 83C are provided at positions between adjacent seat constituent portions 91 (see FIG. 3) in the circumferential direction of the pilot case 58C. Therefore, the inner passage holes 80C, 81C and the outer passage hole 83C are provided outside the outer seat portion 78. The inner passage holes 80C, 81C and the outer passage hole 83C do not open into the passage recess 92 (see FIG. 3).

[0267] A passage groove 468 extending radially inward from the seal groove 68C is formed on the axial side of the bottom main body portion 71C opposite the inner seat portion 77. As shown in FIG. 13 , the passage groove 468 communicates the seal groove 68C with the rod-side passage 191 of the piston rod 21.

[0268] The damping force generating mechanism 10C has a partitioning member 111C (movable mechanism) in the seal groove 68C. The partitioning member 111C is an O-ring that is generally annular and has a circular cross section in a plane including the central axis of the ring. The partitioning member 111C is made of an elastic material with sealing properties, specifically rubber. The partitioning member 111C is fitted into the seal groove 68C. A seal portion 112C on the inner periphery of the partitioning member 111C presses against the radially inner wall surface of the seal groove 68C to seal the gap with this wall surface. A seal portion 113C on the outer periphery of the partitioning member 111C presses against the radially outer wall surface of the seal groove 68C to seal the gap with this wall surface.

[0269] The outer diameter of the disk 450 is larger than the outer diameter of the disk 53 and smaller than the minimum inner diameter of the seal member 132 . The disk 451 has an outer diameter equal to that of the disk 450. A notch 471 is formed on the outer periphery of the disk 451. The disk 451 is provided with a plurality of notches 471 at equal intervals in the circumferential direction. The disk 452 has an outer diameter smaller than that of the disk 451 .

[0270] The spring disc 453 has an outer diameter larger than the outer diameter of the disc 452 . The spring disc 453 has a base portion 481 and a protrusion 482 .

[0271] Before the spring disc 453 is incorporated into the damping force generating mechanism 10C, the substrate portion 481 has a circular flat plate shape with holes and a constant thickness. The protruding portion 482 protrudes to one side along the axial direction of the substrate portion 481 from a central position on the outer periphery in the radial direction of the substrate portion 481. The protruding portion 482 has an annular shape extending in the circumferential direction of the substrate portion 481.

[0272] A passage hole 485 is formed in the substrate portion 481 at a position that is outer than the disk 452 in the radial direction of the disk 452. The passage hole 485 penetrates the substrate portion 481 in the axial direction at a position that is inner than the protruding portion 482 in the radial direction of the substrate portion 481. A plurality of passage holes 485 are provided in the substrate portion 481 at equal intervals in the circumferential direction of the substrate portion 481.

[0273] The open-close disc 57C has an outer diameter larger than the outer diameter of the protrusion 482 of the spring disc 453. The open-close disc 57C extends to a position radially outward of the outer passage hole 83C of the pilot case 58C. The open-close disc 57C abuts in surface contact with the bottom main body portion 71C of the pilot case 58C, closing the seal groove 68C and the outer passage hole 83C. The open-close disc 57C entirely covers the seal groove 68C and the outer passage hole 83C. The open-close disc 57C opens the passage in the outer passage hole 83C by lifting off from the bottom main body portion 71C.

[0274] When the spring disc 453 is incorporated into the damping force generating mechanism 10C, the protrusion 482 abuts against the opening / closing disc 57C. As a result, the spring disc 453 elastically deforms in a tapered shape such that the base plate portion 481 moves away from the opening / closing disc 57C in the axial direction as it moves radially outward.

[0275] A passage hole 491 is formed in the open-close disc 57C such that its radial position coincides with the passage hole 485 of the spring disc 453. The passage hole 491 penetrates the open-close disc 57C in the axial direction of the open-close disc 57C. The passage hole 491 extends in an arc shape in the circumferential direction of the open-close disc 57C. The passage hole 491 is constantly in communication with the passage hole 485 of the spring disc 453. The passage hole 491 is located more inward than the seal groove 68C of the pilot case 58C in the radial direction of the open-close disc 57C. The passage hole 491 is constantly in communication with the passage groove 468 of the pilot case 58C.

[0276] The seal portions 112C and 113C of the partition member 111C are simultaneously pressed against the radially inner and radially outer wall surfaces of the seal groove 68C. As a result, the area surrounded by the pilot case 58C, the first damping valve 52 and discs 53, 450-452, the spring disc 453, the open-close disc 57C, and the partition member 111C forms a back pressure chamber 171C. The back pressure chamber 171C is constantly in communication with the passage in the passage groove 30 of the piston rod 21 via the passage holes 485 and 491 and the passage in the passage groove 468.

[0277] Additionally, the partition member 111C forms a variable chamber 172C between the bottom side of the seal groove 68C and the partition member 111C. The variable chamber 172C is constantly in communication with the lower chamber 20 via the passages in the inner passage holes 80C and 81C.

[0278] A back pressure chamber 171C is formed inside the bottomed cylindrical pilot case 58C by the first damping valve 52, the discs 53, 450-452, the opening / closing disc 57C, and the partition member 111C. The partition member 111C is provided inside the pilot case 58C and partitions the inside of the pilot case 58C into the back pressure chamber 171C and a variable chamber 172C.

[0279] The passage in the notch 121 (see FIG. 2) of the disc 50 (see FIG. 2), the passage in the passage groove 30 of the piston rod 21, the passage in the passage groove 468, and the passages in the passage holes 485, 491 constitute a backpressure chamber introduction passage 176C branching off from the piston-side passage 43 (see FIG. 2). The backpressure chamber introduction passage 176C connects the upper chamber 19 (see FIG. 2) and the backpressure chamber 171C via a portion of the piston-side passage 43 (see FIG. 2). During the extension stroke, the backpressure chamber introduction passage 176C introduces oil L from the upper chamber 19 (see FIG. 2), which is upstream of the backpressure chamber 171C, to the backpressure chamber 171C via a portion of the piston-side passage 43 (see FIG. 2).

[0280] The passages in the inner passage holes 80C, 81C and the passage in the seal groove 68C, both of which are provided in the bottom portion 65C of the pilot case 58C, form a first passage 173C that extends and connects the back pressure chamber 171C and the lower chamber 20. A partition member 111C having seal portions 112C, 113C that seal the first passage 173C with an elastic member is movably provided in this first passage 173C.

[0281] The back pressure chamber 171C applies internal pressure to the first damping valve 52 in the direction of the piston 18 (see FIG. 2), that is, in the valve closing direction to seat the disc 131 on the valve seat portion 47 (see FIG. 2). The pilot case 58C is cylindrical with a bottom and forms the back pressure chamber 171C that generates a biasing force in the valve closing direction on the first damping valve 52 arranged on the opening 67 side.

[0282] The inside of the outer passage hole 83C of the pilot case 58C forms a second passage 180C. The open-close disc 57C is provided between the second passage 180C and the back pressure chamber 171C in an openable / closable manner. The second passage 180C in the outer passage hole 83C is provided in parallel with the first passage 173C. The second passage 180C is disposed on the outer peripheral side of the pilot case 58C relative to the first passage 173C. When the open-close disc 57C is in surface contact with the bottom main body portion 71C of the pilot case 58C, it blocks the flow of oil L between the back pressure chamber 171C and the second passage 180C and the lower chamber 20. When the open-close disc 57C is separated from the bottom main body portion 71C of the pilot case 58C, it allows the flow of oil L between the back pressure chamber 171C and the second passage 180C and the lower chamber 20.

[0283] Here, when the pressure on the second passage 180C and lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171C side by a predetermined value or more, the open-close disc 57C and the spring disc 453 allow the flow of oil L from the lower chamber 20 and second passage 180C to the back pressure chamber 171C. When the pressure on the back pressure chamber 171C side is higher than the pressure on the second passage 180C and lower chamber 20 side, the open-close disc 57C and the spring disc 453 restrict the flow of oil L from the back pressure chamber 171C to the lower chamber 20 via the second passage 180C.

[0284] The open-close disc 57C, the spring disc 453, and a portion of the pilot case 58C on the open-close disc 57C side in the axial direction of the bottom main body portion 71C constitute a communication mechanism 181C. One side of the second passage 180C can communicate with the back pressure chamber 171C. The communication mechanism 181C is located on the one side of the second passage 180C and can communicate with the lower chamber 20, which is the other side of the second passage 180C, only when the lower chamber 20 is located on the upstream side. In other words, the communication mechanism 181C cannot communicate with the lower chamber 20, which is the other side of the second passage 180C, when the lower chamber 20 is located on the downstream side. The communication mechanism 181C restricts the flow of oil L in one direction, from the back pressure chamber 171C side to the second passage 180C side, between the back pressure chamber 171C and the second passage 180C. On the other hand, the communication mechanism 181C allows the oil L to flow in the other direction, from the second passage 180C side to the back pressure chamber 171C side. The communication mechanism 181C is a check valve, and the open / close disc 57C is its valve member.

[0285] The communication mechanism 181C restricts the flow of oil L from the upper chamber 19 (see FIG. 2), a portion of the piston-side passage 43 (see FIG. 2), the back pressure chamber introduction passage 176C, and the back pressure chamber 171C to the second passage 180C and the lower chamber 20. The communication mechanism 181C allows the flow of oil L from the lower chamber 20 and the second passage 180C to the back pressure chamber 171C, the back pressure chamber introduction passage 176C, a portion of the piston-side passage 43 (see FIG. 2), and the upper chamber 19 (see FIG. 2).

[0286] The pilot case 58C and the partition member 111C constitute a frequency sensitive mechanism 211C that varies the damping force in response to the frequency of the reciprocating motion of the piston 18 (see FIG. 2). The frequency sensitive mechanism 211C has its partition member 111C that moves and deforms in response to the frequency of the reciprocating motion of the piston 18 (see FIG. 2), changing the volume of the back pressure chamber 171C that is always in communication with the upper chamber 19 (see FIG. 2) and the volume of the variable chamber 172C that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211C has a partition member 111C that is movably provided in the first passage 173C. The frequency sensitive mechanism 211C varies the biasing force applied to the first damping valve 52 by the back pressure chamber 171C.

[0287] During the extension stroke, the differential pressure between the back pressure chamber 171C and the lower chamber 20 becomes higher on the back pressure chamber 171C side than on the lower chamber 20 side. Then, under pressure from the back pressure chamber 171C, the partition member 111C moves toward the bottom of the seal groove 68C while maintaining a sealed state with the seal groove 68C, and abuts against this bottom surface, undergoing compressive deformation. This expands the volume of the back pressure chamber 171C.

[0288] During the compression stroke, the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171C side. If the pressure difference between the lower chamber 20 side and the back pressure chamber 171C side is lower than a predetermined value, the partition member 111C receives the pressure on the lower chamber 20 side and moves toward the open-close disc 57C while maintaining a sealed state with the seal groove 68C, and abuts against the open-close disc 57C, undergoing compressive deformation. This expands the volume of the variable chamber 172C. Furthermore, during the compression stroke, if the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171C side by a predetermined value or more, the communicating mechanism 181C opens, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171C.

[0289] Next, the operation of the shock absorber 1C including the damping force generating mechanism 10C will be described.

[0290] {Low frequency, slightly slow speed range during extension stroke x1} In the low-frequency, extremely low speed region x1, the first valve mechanism 41 and the second valve mechanism 201 do not open. Oil L from the upper chamber 19 (see FIG. 2) flows into the backpressure chamber 171C via a portion of the piston-side passage 43 (see FIG. 2) and the backpressure chamber introduction passage 176C. This causes the partitioning member 111C of the frequency-sensitive mechanism 211C to move toward the bottom of the seal groove 68C, abutting against the bottom and undergoing compressive deformation. In this low-frequency, extremely low speed region x1, the partitioning member 111C of the frequency-sensitive mechanism 211C moves and deforms toward the bottom of the seal groove 68C to a near-limit, after which it becomes difficult to deform. Furthermore, neither the first valve mechanism 41, 42 (see FIG. 2) nor the second valve mechanism 201 has a fixed orifice that constantly connects the upper chamber 19 and the lower chamber 20. As a result, in the low-frequency, extremely low speed region x1, the rate of increase in damping force relative to an increase in piston speed increases.

[0291] {Low frequency, low speed range of extension stroke x2} In the low-frequency, low-speed region x2, the oil L from the upper chamber 19 (see FIG. 2) significantly moves and deforms the partition member 111C of the frequency sensitive mechanism 211C toward the bottom of the seal groove 68C, similar to the low-frequency, very low-speed region x1. Thereafter, the oil L from the upper chamber 19 (see FIG. 2) via the piston-side passage 43 (see FIG. 2) and the back-pressure chamber introduction passage 176C is less likely to be introduced into the back-pressure chamber 171C. In the low-frequency, low-speed region x2, the pressure in the back-pressure chamber 171C is higher than in the low-frequency, very low-speed region x1. Therefore, in the low-frequency, low-speed region x2, the oil L from the upper chamber 19 (see FIG. 2) flows from the piston-side passage 43 (see FIG. 2), the back-pressure chamber introduction passage 176C, and the rod-side passage 191 to the lower chamber 20, opening the second damping valve 60 of the second valve mechanism 201. As a result, in the low-frequency low-speed region x2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency very-low-speed region x1. In this low-frequency low-speed region x2, the partition member 111C of the frequency sensitive mechanism 211C has moved and deformed to near its limit, causing the pressure in the backpressure chamber 171C to become high. As a result, the biasing force from the backpressure chamber 171C on the first damping valve 52 of the first valve mechanism 41 is large, and therefore the opening of the first damping valve 52 is limited.

[0292] {Low frequency, medium to high speed range of extension stroke x3} In the low-frequency medium-high speed range x3, similarly to the low-frequency low-speed range x2, the oil liquid L from the upper chamber 19 (see FIG. 2) opens the second damping valve 60 of the second valve mechanism 201 and flows from a part of the piston-side passage 43 (see FIG. 2), a part of the backpressure chamber introduction passage 176C, and the rod-side passage 191 to the lower chamber 20. In the low-frequency medium-high speed range x3, since the oil liquid L flows from the rod-side passage 191 to the lower chamber 20 in this way, a pressure increase in the backpressure chamber 171C due to the oil liquid L introduced into the backpressure chamber 171C via a part of the piston-side passage 43 (see FIG. 2) and the backpressure chamber introduction passage 176C is suppressed. In contrast, the force in the valve opening direction applied to the first valve mechanism 41 from the piston-side passage 43 (see FIG. 2) increases, causing the oil L from the upper chamber 19 (see FIG. 2) to pass through the piston-side passage 43 (see FIG. 2), open the first damping valve 52 of the first valve mechanism 41, and flow into the lower chamber 20. As a result, in the low-frequency medium-to-high-speed range x3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency low-speed range x2.

[0293] {High frequency, very low speed range x 4 during extension stroke} In the high-frequency, extremely low speed region x4, the first valve mechanism 41 and the second valve mechanism 201 do not open. Similarly to the low-frequency, extremely low speed region x1, oil L from the upper chamber 19 (see FIG. 2) flows into the back pressure chamber 171C via a part of the piston-side passage 43 (see FIG. 2) and the back pressure chamber introduction passage 176C. This causes the partitioning member 111C of the frequency sensitive mechanism 211C to move and deform toward the bottom side of the seal groove 68C. In this high-frequency, extremely low speed region x4, the piston frequency is high and the stroke of the piston 18 (see FIG. 2) is small. Therefore, the amount of oil L introduced from the upper chamber 19 into the back pressure chamber 171C is less than in the low-frequency, extremely low speed region x1. Therefore, the partitioning member 111C of the frequency sensitive mechanism 211C does not deform to near its limit, but is prone to deformation. As a result, the oil liquid L introduced from the upper chamber 19 (see FIG. 2) into the back pressure chamber 171C can be absorbed by the movement and deformation of the partition member 111C. Therefore, in the high frequency, extremely low speed region x4, although the rate of increase in damping force relative to an increase in piston speed is high, the damping force at the same piston speed is lower than in the low frequency, extremely low speed region x1, resulting in a softer characteristic.

[0294] {High frequency, low, medium and high speed ranges during extension stroke x 5} In the high-frequency, low-, medium-, and high-speed range x5, the oil L from the upper chamber 19 (see FIG. 2) moves and deforms the partition member 111C of the frequency sensitive mechanism 211C toward the bottom of the seal groove 68C, similar to the high-frequency, very-low speed range x4. In the high-frequency, low-, medium-, and high-speed range x5, the amount of oil L introduced into the back pressure chamber 171C is small, so the deformation of the partition member 111C suppresses the increase in pressure in the back pressure chamber 171C. This reduces the biasing force from the back pressure chamber 171C to the first damping valve 52 of the first valve mechanism 41, making it easier for the first damping valve 52 to open. Therefore, the oil L from the upper chamber 19 (see FIG. 2) flows through the piston-side passage 43 (see FIG. 2) to the lower chamber 20, opening the first damping valve 52 of the first valve mechanism 41. As a result, the rate of increase in damping force relative to an increase in piston speed is lower in the high-frequency, low-, medium-, and high-speed range x5 than in the high-frequency, very-low speed range x4. In addition, in the high-frequency low-medium-high speed range x5, the damping force at the same piston speed is lower than in the low-frequency low-speed range x2 and the low-frequency medium-high speed range x3, resulting in a softer characteristic. In this high-frequency low-medium-high speed range x5, the pressure increase in the back pressure chamber 171C is suppressed, so the second valve mechanism 201 remains in a closed state.

[0295] {Low frequency, very low speed region y1 of the compression stroke} In the low-frequency, extremely low-speed range y1, the first valve mechanism 42 (see FIG. 2) and the communication mechanism 181C do not open. Then, the oil L from the lower chamber 20 is introduced into the variable chamber 172C in the first passage 173C through the passages in the inner passage holes 80C and 81C. Then, the partitioning member 111C of the frequency sensitive mechanism 211C moves toward the opening / closing disc 57C and deforms. In this low-frequency, extremely low-speed range y1, the piston frequency is low and the piston 18 (see FIG. 2) strokes greatly, so that a large amount of oil L is introduced from the lower chamber 20 into the variable chamber 172C at the beginning of the stroke. Therefore, the partitioning member 111C of the frequency sensitive mechanism 211C moves and deforms toward the opening / closing disc 57C to a near-limit, and becomes less likely to deform. Furthermore, neither the first valve mechanism 41, 42 (see FIG. 2) nor the second valve mechanism 201 has a fixed orifice that constantly connects the lower chamber 20 and the upper chamber 19. As a result, in the low-frequency, extremely low speed range y1, the rate of increase in damping force relative to an increase in piston speed becomes high, resulting in a hard characteristic.

[0296] {Low frequency, low speed region of the compression stroke y2} In the low-frequency low-speed region y2, similar to the low-frequency very-low-speed region y1, the oil L from the lower chamber 20 moves and deforms the partition member 111C toward the open-close disc 57C to a near-limit, and then flows from the second passage 180C to the upper chamber 19 (see FIG. 2) via the communication mechanism 181C that opens the back pressure chamber 171C, the back pressure chamber introduction passage 176C, and part of the piston-side passage 43 (see FIG. 2). As a result, in the low-frequency low-speed region y2, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency very-low-speed region y1.

[0297] {Low frequency, medium to high speed range of the compression stroke y3} In the low-frequency, medium-high speed range y3, as in the low-frequency, low-speed range y2, the oil L from the lower chamber 20 flows from the second passage 180C to the upper chamber 19 (see FIG. 2) by opening the communication mechanism 181C, via the back pressure chamber 171C, the back pressure chamber introduction passage 176C, and a part of the piston-side passage 43 (see FIG. 2). In the low-frequency, low-, medium-, high-speed range y2, in addition to this, the oil L from the lower chamber 20 passes through the piston-side passage 44 (see FIG. 2), opens the first damping valve 231 (see FIG. 2) of the first valve mechanism 42 (see FIG. 2), and flows into the upper chamber 19 (see FIG. 2). As a result, in the low-frequency, medium-, high-speed range y3, the rate of increase in damping force relative to an increase in piston speed is lower than in the low-frequency, low-speed range y2.

[0298] {High frequency, very low speed region of the compression stroke y4} In the high-frequency, extremely low speed range y4, the first valve mechanism 42 and the communicating mechanism 181C do not open. Oil L from the lower chamber 20 is introduced into the variable chamber 172C through the passages in the inner passage holes 80C and 81C in the first passage 173C. This causes the partitioning member 111C of the frequency sensitive mechanism 211C to deform toward the open-close disc 57C. In this high-frequency, extremely low speed range y4, the piston frequency is high and the stroke of the piston 18 is small, so the amount of oil L introduced from the lower chamber 20 into the variable chamber 172C is less than in the low-frequency, extremely low speed range y1. Therefore, the partitioning member 111C of the frequency sensitive mechanism 211C does not deform to near its limit and is prone to movement and deformation. As a result, the oil L introduced from the lower chamber 20 into the variable chamber 172C can be absorbed by the movement and deformation of the partitioning member 111C. Therefore, in the high frequency extremely low speed region y4, the damping force at the same piston speed has softer characteristics than in the low frequency extremely low speed region y1.

[0299] {High frequency, low speed region of the compression stroke y5} In the high-frequency, low-speed range y5, the oil L from the lower chamber 20 flows from the second passage 180C to the upper chamber 19 (see FIG. 2) via the backpressure chamber 171C, the backpressure chamber introduction passage 176C, and a part of the piston-side passage 43 (see FIG. 2) by opening the communication mechanism 181C. In the high-frequency, low-speed range y5, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency, very low-speed range y4. Also, in the high-frequency, low-speed range y5, the damping force at the same piston speed is lower and softer than in the low-frequency, low-speed range y2.

[0300] {High frequency, medium to high speed range of the contraction stroke y6} In the high-frequency medium-high-speed range y6, similar to the high-frequency low-speed range y5, the oil L from the lower chamber 20 flows from the second passage 180C to the upper chamber 19 (see FIG. 2) via the backpressure chamber 171C, the backpressure chamber introduction passage 176C, and a part of the piston-side passage 43 (see FIG. 2) by opening the communication mechanism 181C. In addition, in the high-frequency medium-high-speed range y6, the oil L from the lower chamber 20 passes through the piston-side passage 44 (see FIG. 2) and opens the first damping valve 231 (see FIG. 2) of the first valve mechanism 42 (see FIG. 2) to flow into the upper chamber 19 (see FIG. 2). As a result, in the high-frequency medium-high-speed range y6, the rate of increase in damping force relative to an increase in piston speed is lower than in the high-frequency low-speed range y5. Furthermore, in the high-frequency medium-high-speed range y6, the damping force at the same piston speed is lower and softer than in the low-frequency medium-high-speed range y3.

[0301] The damping force generation mechanism 10C of the fourth embodiment includes a pilot case 58C, a frequency sensitive mechanism 211C, a second passage 180C, and a communication mechanism 181C. The pilot case 58C is cylindrical and has a bottom, and defines a back pressure chamber 171C that generates a biasing force in a valve closing direction on the first damping valve 52 disposed on the opening 67 side. The frequency sensitive mechanism 211C includes a partition member 111C that is movably provided in a first passage 173C that is provided in a bottom 65C of the pilot case 58C and connects the back pressure chamber 171C and the lower chamber 20. The partition member 111C has seal portions 112C and 113C that seal the first passage 173C with an elastic member, thereby varying the biasing force applied to the first damping valve 52 in the valve closing direction. The second passage 180C is provided in parallel with the first passage 173C, and one side of the second passage 180C can communicate with the back pressure chamber 171C. The communication mechanism 181C is located on the one side of the second passage 180C, and can communicate with the other side of the second passage 180C only when the lower chamber 20 is on the upstream side.

[0302] As described above, the damping force generation mechanism 10C is provided with the first passage 173C that extends between the back pressure chamber 171C and the lower chamber 20, in the bottom 65C of the pilot case 58C that forms the back pressure chamber 171C. The damping force generation mechanism 10C varies the biasing force applied to the first damping valve 52 in the valve closing direction by a frequency sensitive mechanism 211C that is provided in the first passage 173C and that movably mounts a partition member 111C that seals the first passage 173C with seal portions 112C, 113C. Therefore, even though the damping force generation mechanism 10C has the frequency sensitive mechanism 211C, it is possible to prevent the size of the mechanism 10C from increasing.

[0303] Furthermore, since the damping force generating mechanism 10C is provided with the communication mechanism 181C, the communication mechanism 181C opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the back pressure chamber 171C via the second passage 180C, thereby enabling the pressure in the back pressure chamber 171C to be quickly increased. This stabilizes the closed state of the first damping valve 52, which is biased in the valve closing direction by the pressure in the back pressure chamber 171C. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0304] Furthermore, in the damping force generation mechanism 10C, the second passage 180C, which is opened and closed by the communication mechanism 181C, is disposed closer to the outer periphery of the bottom portion 65C than the first passage 173C. Therefore, in the damping force generation mechanism 10C, the opening of the first passage 173C on the opening / closing disc 57C side can be entirely covered by the opening / closing disc 57C of the communication mechanism 181C. This prevents the partition member 111C provided in the first passage 173C from entering the gap between the opening / closing disc 57C and the opening of the first passage 173C. This prevents a decrease in the durability of the partition member 111C.

[0305] Furthermore, the damping force generation mechanism 10C is subject to large compressive deformation because it uses an O-ring as the partition member 111C having seals 112C, 113C that seal the first passage 173C with an elastic member. For this reason, the provision of the communication mechanism 181C is highly effective in suppressing the delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0306] [Fifth embodiment] Next, the fifth embodiment will be described, focusing on the differences from the third embodiment, mainly with reference to Fig. 15. Note that parts common to the third embodiment will be designated by the same names and symbols.

[0307] As shown in FIG. 15, a shock absorber 1D including a damping force generation mechanism 10D of the fifth embodiment differs in part in the configuration of the damping force generation mechanism 10D from the damping force generation mechanism 10B.

[0308] The damping force generation mechanism 10D does not have an open / close disc 57B. The damping force generation mechanism 10D has a pilot case 58D that is partially different from the pilot case 58B instead of the pilot case 58B. The damping force generation mechanism 10D also has a partition member 111D that is partially different from the partition member 111B instead of the partition member 111B.

[0309] Pilot case 58D has case member 360D, which is partially different from case member 360, instead of case member 360. Case member 360D has bottom portion 365D, which is partially different from bottom portion 365, instead of bottom portion 365. Bottom portion 365D has a protrusion 501 that protrudes from bottom main body portion 371 on the same side as other-side seat portion 373 in the axial direction of bottom main body portion 371. Protrusion 501 is provided between other-side seat portion 373 and cylindrical portion 366 in the radial direction of bottom main body portion 371. A plurality of protrusions 501 are provided at equal intervals in the circumferential direction of bottom main body portion 371. Pilot case 58D has bottom portion 65D, which differs from bottom portion 65B in that it has protrusion 501.

[0310] Partitioning member 111D has disk 421D that is partially different from disk 421 in place of disk 421. Furthermore, partitioning member 111D has packing 422D that is partially different from packing 422 in place of packing 422. Disk 421D differs from disk 421 in that no passage holes 425 are formed therein.

[0311] The packing 422D is made of an elastic material with sealing properties, specifically rubber. The packing 422D is annular. The packing 422D is fixed to the outer periphery of the disk 421D. The packing 422D protrudes from the disk 421D to one side in the axial direction of the disk 421D. The seal portion 112D on the outer periphery of the packing 422D expands in the radial direction of the disk 421D as it becomes farther away from the disk 421D in the axial direction of the disk 421D. The inner periphery of the packing 422D expands in the radial direction of the disk 421D as it becomes farther away from the disk 421D in the axial direction of the disk 421D.

[0312] The packing 422D is fitted over the entire inner circumferential surface of the cylindrical portion 366 of the case member 360D. At this time, the packing 422D contacts the inner circumferential surface of the cylindrical portion 366 at the seal portion 112D on its outer periphery. The packing 422D is slidable in the axial direction relative to the inner circumferential surface of the cylindrical portion 366. The packing 422D seals the gap between the partition member 111D and the cylindrical portion 366. The protrusion 501 of the pilot case 58D is positioned radially inward of the disc 421D relative to the packing 422D.

[0313] The seal portion 112D of the packing 422D of the partition member 111D is in pressure contact with the inner circumferential surface of the cylindrical portion 366 of the case member 360D over the entire circumference. As a result, the area surrounded by the first damping valve 52B (see FIG. 10), the pressing member 361 (see FIG. 10), the seal member 402 (see FIG. 10), the case member 360D, and the partition member 111D forms the back pressure chamber 171D. The back pressure chamber 171D communicates with the rod side passage 341B (see FIG. 10) via a back pressure chamber introduction passage 176B (see FIG. 10).

[0314] The portion surrounded by the partition member 111D and the stopper member 411 forms the variable chamber 172D. The variable chamber 172D is constantly in communication with the lower chamber 20 via a passage in the passage hole 431 of the stopper member 411. The variable chamber 172D is constantly in communication with the lower chamber 20 via a passage between the stopper member 411 and the cylindrical portion 366 of the case member 360D.

[0315] Pilot case 58D has a cylindrical shape with a bottom, and inside thereof, partition member 111D defines back pressure chamber 171D. Partition member 111D is provided inside pilot case 58D and partitions the inside of pilot case 58D into back pressure chamber 171D and variable chamber 172D.

[0316] A first passage 173D that extends between the back pressure chamber 171D and the lower chamber 20 is constituted by the passage between the outer periphery of the stopper member 411 and the cylindrical portion 366 of the case member 360D, the passage inside the passage hole 431 of the stopper member 411, the variable chamber 172D, and the passage between the seal portion 112D of the packing 422D and the cylindrical portion 366. A partition member 111D having a seal portion 112D that seals the first passage 173D with an elastic member is movably provided in this first passage 173D.

[0317] The back pressure chamber 171D applies internal pressure to the first damping valve 52B (see FIG. 10) in the direction of the seat forming member 351 (see FIG. 10), that is, in the valve closing direction to seat the first damping valve 52B on the valve seat portion 356 (see FIG. 10). The pilot case 58D is cylindrical with a bottom and forms the back pressure chamber 171D that generates a biasing force in the valve closing direction on the first damping valve 52B that is arranged on the opening 67B (see FIG. 10) side.

[0318] The seal portion 112D of the packing 422D of the partition member 111D is provided between the first passage 173D and the back pressure chamber 171D in an openable and closable manner. When the seal portion 112D of the packing 422D is in contact with the inner circumferential surface of the cylindrical portion 366 of the case member 360D over the entire circumference, it blocks the flow of oil L between the back pressure chamber 171D and the first passage 173D and the lower chamber 20. When the seal portion 112D of the packing 422D is separated from the inner circumferential surface of the cylindrical portion 366 of the case member 360D, it allows the flow of oil L between the back pressure chamber 171D and the first passage 173D and the lower chamber 20.

[0319] Here, when the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171D side by a predetermined value or more, the seal portion 112D of the packing 422D separates from the cylindrical portion 366 to allow the oil L to flow from the lower chamber 20 to the back pressure chamber 171D via the first passage 173D. In other words, when the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171D side by a predetermined value or more, the partition member 111D tries to move axially toward the bottom main body portion 371, but the protrusion 501 of the case member 360D abuts against the disc 421D and suppresses the movement of the disc 421D toward the bottom main body portion 371. As a result, in the partition member 111D, the packing 422D is well separated from the inner circumferential surface of the cylindrical portion 366 due to the pressure difference between the variable chamber 172D and the back pressure chamber 171D, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171D via the first passage 173D. When the pressure on the back pressure chamber 171D side is higher than the pressure on the lower chamber 20 side, the seal portion 112D of the packing 422D abuts against the cylindrical portion 366 to restrict the flow of the oil L from the back pressure chamber 171D to the lower chamber 20 via the first passage 173D.

[0320] The gasket 422D and the cylindrical portion 366 of the case member 360D constitute a communication mechanism 181D. One side of the first passage 173D can communicate with the back pressure chamber 171D. The communication mechanism 181D is located on the one side of the first passage 173D and can communicate with the lower chamber 20, which is the other side of the first passage 173D, only when the lower chamber 20 is on the upstream side. In other words, the communication mechanism 181D cannot communicate with the lower chamber 20, which is the other side of the first passage 173D, when the lower chamber 20 is on the downstream side. The communication mechanism 181D restricts the flow of oil L in one direction, from the back pressure chamber 171D side to the variable chamber 172D side, between the back pressure chamber 171D and the variable chamber 172D. On the other hand, the communication mechanism 181D allows the oil L to flow in the other direction, from the variable chamber 172D side to the back pressure chamber 171D side. The communication mechanism 181D is a check valve, and the partition member 111D is its valve member.

[0321] The first passage 173D is provided with a partitioning member 111D, connecting the back pressure chamber 171D and the lower chamber 20. The first passage 173D, on which the partitioning member 111D is provided, has one side that can communicate with the back pressure chamber 171D, and also serves as a passage in which a communication mechanism 181D is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side.

[0322] The communication mechanism 181D regulates the flow of oil L from the upper chamber 19 (see FIG. 10), the rod-side passage 341B (see FIG. 10), the back-pressure chamber introduction passage 176B (see FIG. 10), and the back-pressure chamber 171D to the lower chamber 20 via the first passage 173D. The communication mechanism 181D allows the flow of oil L from the lower chamber 20 to the back-pressure chamber 171D, the back-pressure chamber introduction passage 176B (see FIG. 10), the rod-side passage 341B (see FIG. 10), and the upper chamber 19 (see FIG. 10) via the first passage 173D.

[0323] The pilot case 58D and the partitioning member 111D constitute a frequency sensitive mechanism 211D that varies the damping force in response to the piston frequency. The partitioning member 111D of the frequency sensitive mechanism 211D moves and deforms in response to the frequency of the reciprocating motion of the piston 18A (see FIG. 10), thereby varying the volume of the back pressure chamber 171D that is always in communication with the upper chamber 19 (see FIG. 10) and the volume of the variable chamber 172D that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211D has a partitioning member 111D that is movably provided in the first passage 173D. The frequency sensitive mechanism 211D varies the biasing force applied to the first damping valve 52B (see FIG. 10) by the back pressure chamber 171D.

[0324] During the extension stroke, the differential pressure between the back pressure chamber 171D and the lower chamber 20 becomes higher on the back pressure chamber 171D side than on the lower chamber 20 side. Then, under pressure from the back pressure chamber 171D, the partition member 111D deforms and moves toward the stopper member 411 while maintaining a sealed state with the cylindrical portion 366. This causes the volume of the back pressure chamber 171D to expand.

[0325] During the compression stroke, the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171D side. Then, if the pressure difference between the lower chamber 20 side and the back pressure chamber 171D side is lower than a predetermined value, the partition member 111D receives the pressure on the lower chamber 20 side and moves while deforming toward the side opposite the stopper member 411 while maintaining a sealed state with the cylindrical portion 366. This causes the volume of the variable chamber 172D to expand. Furthermore, during the compression stroke, if the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171D side by a predetermined value or more, the communicating mechanism 181D opens, allowing the oil L to flow from the lower chamber 20 to the back pressure chamber 171D.

[0326] The operation of shock absorber 1D including damping force generating mechanism 10D is almost the same as the operation of shock absorber 1B, except that communication mechanism 181D, which is provided in place of communication mechanism 181B, opens in the low-frequency low-speed range y2, the low-frequency medium-high-speed range y3, the high-frequency low-speed range y5, and the high-frequency medium-high-speed range y6 of the compression stroke.

[0327] The damping force generating mechanism 10D of the fifth embodiment includes a pilot case 58D, a frequency sensitive mechanism 211D, a first passage 173D, and a communication mechanism 181D. The pilot case 58D is cylindrical and has a bottom. The pilot case 58D defines a back pressure chamber 171D that generates a valve-closing biasing force on a first damping valve 52B (see FIG. 10) disposed on the opening 67 (see FIG. 10) side. The frequency sensitive mechanism 211D includes a partition member 111D that is movably provided in the first passage 173D, the partition member 111D having a seal portion 112D that seals the first passage 173D with an elastic member. The partition member 111D has one side that can communicate with the back pressure chamber 171D ... The communication mechanism 181D is located on the one side of the first passage 173D, and can communicate with the other side of the first passage 173D only when the lower chamber 20 is on the upstream side.

[0328] As described above, the damping force generation mechanism 10D is provided with a first passage 173D in the bottom portion 65D of the pilot case 58D that defines the back pressure chamber 171D, which is capable of communicating the back pressure chamber 171D with the lower chamber 20. The damping force generation mechanism 10D varies the biasing force applied to the first damping valve 52B (see FIG. 10) in the valve closing direction by a frequency sensitive mechanism 211D that is provided in the first passage 173D and has a partition member 111D that seals the first passage 173D with a seal portion 112D and is movably mounted thereon. Therefore, even though the damping force generation mechanism 10D has the frequency sensitive mechanism 211D, it is possible to prevent the mechanism from becoming too large.

[0329] Furthermore, since the damping force generating mechanism 10D is provided with the communication mechanism 181D, the communication mechanism 181D opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the backpressure chamber 171D via the first passage 173D, thereby enabling the pressure in the backpressure chamber 171D to be increased quickly. This stabilizes the closed state of the first damping valve 52B (see FIG. 10), which is biased in the valve closing direction by the pressure in the backpressure chamber 171D. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0330] Furthermore, in the damping force generation mechanism 10D, the first passage 173D in which the partition member 111D is provided has one side that can communicate with the back pressure chamber 171D, and also serves as a passage in which a communication mechanism 181D is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side. This makes it possible to further prevent the damping force generation mechanism 10D from becoming large.

[0331] Furthermore, in the damping force generation mechanism 10D, when the back pressure chamber 171D has a higher pressure than the variable pressure chamber 172D, the communication mechanism 181D opens the packing 422D of the partition member 111D that blocks communication between them, and introduces oil L from the variable pressure chamber 172D to the back pressure chamber 171D when the variable pressure chamber 172D has a higher pressure than the back pressure chamber 171D. This allows the configuration of the communication mechanism 181D to be simplified.

[0332] [Sixth embodiment] Next, the sixth embodiment will be described, focusing on the differences from the first embodiment, mainly with reference to Figures 16 to 19. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0333] 16, a shock absorber 1E including a damping force generation mechanism 10E of the sixth embodiment has a partial configuration different from that of the damping force generation mechanism 10. The damping force generation mechanism 10E differs from the damping force generation mechanism 10 in the configuration between the disc 50 and the disc 61 in the axial direction of the piston rod 21.

[0334] The damping force generating mechanism 10E includes, in order from the disc 50 side in the axial direction of the piston rod 21, one first damping valve 52E (first damping force generating member), one open / close disc 57E, one disc 53, one disc 54E, a plurality of, specifically six, discs 55 similar to those in the first embodiment, one pilot case 58E (biasing force generating member), one disc 511, one disc 512, and a plurality of, specifically four, discs 59 similar to those in the first embodiment. The discs 511, 512, and 59 form a second damping valve 60E.

[0335] Disk 54E differs from disk 54 in that it does not have notches 141 formed therein. The discs 511, 512, the opening / closing disc 57E, and the pilot case 58E are all made of metal. The discs 511, 512, and the opening / closing disc 57E are all perforated circular flat plates of a uniform thickness. The discs 511, 512, and the opening / closing disc 57E are formed by press molding. The pilot case 58E is annular. The mounting shaft portion 28 of the piston rod 21 is fitted inside the discs 511, 512, the opening / closing disc 57E, and the pilot case 58E.

[0336] The pilot case 58E is cylindrical and has a bottom. The pilot case 58E is formed seamlessly as a single piece by sintering. The pilot case 58E is cylindrical and has a bottom 65E instead of the bottom 65. The bottom portion 65E is a disk shape with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted onto the inner circumferential side thereof. The pilot case 58E has an opening 67 on the side of the cylindrical portion 66 opposite to the bottom portion 65E in the axial direction.

[0337] The bottom portion 65E has a bottom body portion 71E, an inner seat portion 77E, and a valve seat portion 78E. The bottom main body portion 71E is a disk-shaped portion with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted onto the inner circumferential side thereof. The cylindrical portion 66 extends along the axial direction of the bottom main body portion 71E from one axial end side on the outer circumferential side of the bottom main body portion 71E. A seal groove 68E is formed in the bottom main body portion 71E at a radially intermediate position of the bottom main body portion 71E. The seal groove 68E is annular and is formed radially inward of the cylindrical portion 66 of the bottom main body portion 71E. The seal groove 68E is recessed from the cylindrical portion 66 side of the bottom main body portion 71E in the axial direction of the bottom main body portion 71E in the opposite direction from the cylindrical portion 66.

[0338] A passage hole 84E is formed in the bottom surface of the seal groove 68E in the bottom main body portion 71E. The passage hole 84E penetrates the bottom main body portion 71E at the position of the seal groove 68E. The passage hole 84E is located at the outer end position of the bottom surface of the seal groove 68E in the radial direction of the pilot case 58E. A plurality of passage holes 84E are provided in the pilot case 58E at equal intervals in the circumferential direction of the pilot case 58E.

[0339] A passage groove 468E extending radially inward from the seal groove 68E is formed on the axial side of the bottom main body portion 71E facing the cylindrical portion 66. The passage groove 468E connects the inside of the seal groove 68E with the passage in the passage groove 30 of the piston rod 21.

[0340] The inner seat portion 77E is formed on the inner peripheral side of the bottom main body portion 71E. The inner seat portion 77E is annular. The inner seat portion 77E protrudes from the inner peripheral portion of the bottom main body portion 71E in the axial direction of the bottom main body portion 71E toward the opposite side from the tubular portion 66. A passage groove 95E is formed in the inner seat portion 77E, penetrating the inner seat portion 77E in the radial direction. The passage in the passage groove 95E is connected to the passage in the passage groove 30 of the piston rod 21.

[0341] The valve seat portion 78E protrudes in the axial direction of the bottom main body portion 71E on the opposite side to the cylindrical portion 66. The valve seat portion 78E is annular, as shown in Fig. 17. The valve seat portion 78E is provided so as to surround the inner seat portion 77E radially outward of the bottom main body portion 71E.

[0342] As shown in FIG. 16, the damping force generating mechanism 10E has a partitioning member 111E (movable mechanism) in the seal groove 68E. The partitioning member 111E is an O-ring having an overall annular shape and a circular cross section in a plane including the central axis of the ring. The partitioning member 111E is fitted into the seal groove 68E of the pilot case 58E. The partitioning member 111E is made of an elastic material with sealing properties, specifically rubber. A seal portion 112E on the inner periphery of the partitioning member 111E presses against the radially inner wall surface of the seal groove 68E to seal the gap with this wall surface. A seal portion 113E on the outer periphery of the partitioning member 111E presses against the radially outer wall surface of the seal groove 68E to seal the gap with this wall surface.

[0343] The first damping valve 52E is made up of a disk 131E and a seal member 132. The disc 131E differs from the disc 131 in that a notch 521 is formed on the inner peripheral side of the disc 131. The notch 521 is formed radially inward of the seal member 132 of the first damping valve 52E. The passage in the notch 521 communicates with the passage in the notch 121 of the disc 50.

[0344] The open-close disc 57E extends radially outward of the first damping valve 52E beyond the notch 521 of the first damping valve 52E. The open-close disc 57E comes into surface contact with the disc 131E of the first damping valve 52E to close the passage within the notch 521. The open-close disc 57E opens the passage within the passage within the notch 521 by moving away from the disc 131E.

[0345] The disc 511 has an outer diameter larger than the outer diameter of the valve seat portion 78E. As shown in Fig. 18, the disc 511 has a notch 531 formed in its outer periphery. The notch 531 has an outer notch 532 extending radially inward from the outer peripheral edge of the disc 511, and an arc-shaped inner notch 533 extending radially inward from the inner end position of the outer notch 532 in the radial direction of the disc 511 to both sides along the circumferential direction of the disc 511. The disc 511 has a plurality of notches 531 formed at equal intervals in the circumferential direction, specifically four notches 531.

[0346] As shown in Fig. 16, the disk 512 has an outer diameter equal to that of the disk 511. As shown in Fig. 19, the disk 512 has a plurality of passage holes 535, specifically three passage holes 535, formed on its outer periphery. The passage holes 535 are arc-shaped and extend along the circumferential direction of the disk 512. In the radial direction of the disks 511 and 512, the passage holes 535 are aligned with the inner cutouts 533. In other words, the passage holes 535 and the cutouts 531 communicate with each other.

[0347] The disk 511 abuts against the valve seat portion 78E of the pilot case 58E. At this time, the outer cutout portion 532 of the disk 511 traverses the valve seat portion 78E in the radial direction. Also, at this time, the inner cutout portion 533 of the disk 511 is positioned more inward than the valve seat portion 78E in the radial direction of the valve seat portion 78E.

[0348] 16, the seal portions 112E and 113E of the partition member 111E are simultaneously pressed against the radially inner and radially outer wall surfaces of the seal groove 68E. As a result, the area surrounded by the pilot case 58E, the first damping valve 52E, the discs 53, 54E, and 55, the open-close disc 57E, and the partition member 111E forms a back pressure chamber 171E. The back pressure chamber 171E is constantly in communication with the passage in the passage groove 30 of the piston rod 21 via the passage in the passage groove 468E.

[0349] Additionally, the partition member 111E forms a variable chamber 172E between the bottom side of the seal groove 68E and the partition member 111E. The variable chamber 172E is constantly in communication with the lower chamber 20 via the passage in the passage hole 84E.

[0350] A back pressure chamber 171E is formed inside the bottomed cylindrical pilot case 58E by the first damping valve 52E, the discs 53, 54E, 55, the opening / closing disc 57E, and a partition member 111E. The partition member 111E is provided inside the pilot case 58E and partitions the inside of the pilot case 58E into the back pressure chamber 171E and a variable chamber 172E.

[0351] The first damping valve 52E constitutes a first valve mechanism 41E together with a valve seat portion 47 of the piston 18. During the extension stroke, the disc 131E of the first damping valve 52E leaves the valve seat portion 47 and opens. The first damping valve 52E then allows oil L from the piston-side passage 43 to flow into the lower chamber 20 through the valve seat portion 47. The extension-side first valve mechanism 41E, which is made up of the valve seat portion 47 and the first damping valve 52E, is provided in the piston-side passage 43, and the first damping valve 52E opens and closes this piston-side passage 43 to suppress the flow of oil L, thereby generating a damping force.

[0352] The passage in the notch 121 of the disc 50, the passage in the passage groove 30 of the piston rod 21, and the passage in the passage groove 468E of the pilot case 58E constitute a backpressure chamber introduction passage 176E branching off from the piston-side passage 43. The backpressure chamber introduction passage 176E connects the upper chamber 19 (see FIG. 2) and the backpressure chamber 171E via a portion of the piston-side passage 43 (see FIG. 2). During the extension stroke, the backpressure chamber introduction passage 176E introduces oil L from the upper chamber 19 (see FIG. 2), which is upstream of the backpressure chamber 171E, into the backpressure chamber 171E via a portion of the piston-side passage 43.

[0353] In both cases, the passage in the passage hole 84E provided in the bottom portion 65E of the pilot case 58E and the passage in the seal groove 68E constitute a first passage 173E that extends to connect the back pressure chamber 171E and the lower chamber 20. A partition member 111E having seal portions 112E, 113E that seal the first passage 173E with an elastic member is movably provided in this first passage 173E. The lower chamber 20 is located downstream of the first damping valve 52E in the flow direction of the hydraulic oil L during the extension stroke.

[0354] The back pressure chamber 171E applies internal pressure to the first damping valve 52E in the direction of the piston 18, i.e., in the valve closing direction to seat the disc 131E on the valve seat portion 47. The pilot case 58E is cylindrical with a bottom and forms the back pressure chamber 171E that generates a biasing force in the valve closing direction on the first damping valve 52E that is arranged on the opening 67 side.

[0355] The second passage 180E is composed of the passages in the notch 531 and the passage hole 535 of the second damping valve 60E, the passage between the valve seat portion 78E and the inner seat portion 77E of the pilot case 58E, the passage in the passage groove 95E of the pilot case 58E, the passage in the passage groove 30 of the piston rod 21, and the passage in the notch 521 of the first damping valve 52E. The open-close disc 57E is provided between the second passage 180E and the back pressure chamber 171E so as to be able to open and close. The second passage 180E is provided in parallel with the first passage 173E in the passage hole 84E. The second passage 180E is arranged on the inner peripheral side of the pilot case 58E relative to the first passage 173E. When the open-close disc 57E is in surface contact with the disc 131E of the first damping valve 52E, it blocks the flow of oil L between the back pressure chamber 171E and the second passage 180E and the lower chamber 20. When the open-close disc 57E is separated from the disc 131E, it allows the flow of oil L between the back pressure chamber 171E and the second passage 180E and the lower chamber 20.

[0356] Here, when the pressure on the second passage 180E and lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171E side by a predetermined value or more, the open-close disc 57E allows the flow of oil L from the lower chamber 20 and second passage 180E to the back pressure chamber 171E via the second passage 180E. In a state where the pressure on the back pressure chamber 171E side is higher than the pressure on the second passage 180E and lower chamber 20 side, the open-close disc 57E restricts the flow of oil L from the back pressure chamber 171E to the lower chamber 20 via the second passage 180E.

[0357] The open-close disc 57E and the disc 131E of the first damping valve 52E constitute a communication mechanism 181E. One side of the second passage 180E can communicate with the back pressure chamber 171E. The communication mechanism 181E is located on the one side of the second passage 180E, and can communicate with the other side of the second passage 180E, that is, the lower chamber 20, only when the lower chamber 20 is located upstream. The communication mechanism 181E is a check valve, and the open-close disc 57E is its valve member.

[0358] A second damping valve 60E, which is made up of discs 59, 511, and 512, is removably seated on a valve seat portion 78E.

[0359] The passage in the passage groove 30 of the piston rod 21, the passage in the passage groove 95E of the pilot case 58E, and the passage between the inner seat portion 77E and the valve seat portion 78E form a rod-side passage 191E branching off from the piston-side passage 43. The rod-side passage 191E is capable of communicating between the upper chamber 19 and the lower chamber 20. The valve seat portion 78E and the second damping valve 60E are provided in the rod-side passage 191E and constitute a second valve mechanism 201E that opens and closes the rod-side passage 191E.

[0360] The second valve mechanism 201E has a second damping valve 60E seated on a valve seat portion 78E. The second damping valve 60E opens during the extension stroke to provide resistance to the flow of hydraulic fluid L from the upper chamber 19 to the lower chamber 20 via part of the piston-side passage 43, part of the backpressure chamber introduction passage 176E, and the rod-side passage 191E. In other words, the second valve mechanism 201E generates a damping force by suppressing the flow of hydraulic fluid L from the upper chamber 19 to the lower chamber 20. The second valve mechanism 201E is an extension-side damping force generating mechanism that is provided in the rod-side passage 191E and generates a damping force by the flow of hydraulic fluid L.

[0361] The pilot case 58E and the partition member 111E constitute a frequency sensitive mechanism 211E that varies the damping force in response to the frequency of the reciprocating motion of the piston 18. The frequency sensitive mechanism 211E has a partition member 111E that moves and deforms in response to the frequency of the reciprocating motion of the piston 18, changing the volume of the back pressure chamber 171E that is always in communication with the upper chamber 19 and the volume of the variable chamber 172E that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211E has a partition member 111E that is movably provided in the first passage 173E. The frequency sensitive mechanism 211E varies the biasing force applied to the first damping valve 52E by the back pressure chamber 171E.

[0362] During the extension stroke, oil L is introduced into the back pressure chamber 171E from the back pressure chamber introduction passage 176E. As a result, the pressure on the back pressure chamber 171E side becomes higher than the pressure on the lower chamber 20 side. Then, under pressure from the back pressure chamber 171E, the partition member 111E moves toward the bottom surface of the seal groove 68E while maintaining a sealed state with the seal groove 68E, and abuts against this bottom surface, undergoing compressive deformation. This causes the volume of the back pressure chamber 171E to expand.

[0363] During the compression stroke, when the pressure on the lower chamber 20 side becomes higher than that on the back pressure chamber 171E side, the partition member 111E receives the pressure on the lower chamber 20 side introduced from the first passage 173E, moves toward the disk 55 while maintaining a sealed state with the seal groove 68E, and abuts against the disk 55, undergoing compressive deformation. This causes the volume of the variable chamber 172E to expand.

[0364] The damping force generating mechanism 10E of the sixth embodiment includes a pilot case 58E, a frequency sensitive mechanism 211E, a second passage 180E, and a communication mechanism 181E. The pilot case 58E is cylindrical and has a bottom. The pilot case 58E defines a back pressure chamber 171E that generates a valve-closing biasing force on a first damping valve 52E disposed on the opening 67 side. The frequency sensitive mechanism 211E includes a partition member 111E that is movably provided in a first passage 173E that is provided in a bottom 65E of the pilot case 58E and connects the back pressure chamber 171E to the lower chamber 20. The partition member 111E has seal portions 112E and 113E that seal the first passage 173E with an elastic member, thereby varying the valve-closing biasing force on the first damping valve 52E. The second passage 180E is provided in parallel with the first passage 173E, and one side of the second passage 180E is capable of communicating with the back pressure chamber 171E. The communication mechanism 181E is located on the one side of the second passage 180E, and can communicate with the other side of the second passage 180E only when the lower chamber 20 is on the upstream side.

[0365] As described above, the damping force generating mechanism 10E is provided with a first passage 173E that extends between the back pressure chamber 171E and the lower chamber 20 and is located in the bottom 65E of the pilot case 58E that defines the back pressure chamber 171E. The damping force generating mechanism 10E varies the biasing force applied to the first damping valve 52E in the valve closing direction by a frequency sensitive mechanism 211E that is provided in the first passage 173E and that movably mounts a partition member 111E that seals the first passage 173E with seal portions 112E, 113E. Therefore, even though the damping force generating mechanism 10E has the frequency sensitive mechanism 211E, it is possible to prevent the mechanism from becoming too large.

[0366] Furthermore, since the damping force generating mechanism 10E is provided with the communication mechanism 181E, the communication mechanism 181E opens when the stroke is reversed from the compression stroke to the extension stroke, and introduces hydraulic oil L from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the back pressure chamber 171E via the second passage 180E. At this time, the damping force generating mechanism 10E introduces hydraulic oil L from the lower chamber 20 to the back pressure chamber 171E via the passages in the notch 531 and the passage hole 535 of the second damping valve 60E, the passage between the valve seat portion 78E and the inner seat portion 77E of the pilot case 58E, the passage in the passage groove 95E of the pilot case 58E, the passage in the passage groove 30 of the piston rod 21, and the passage in the passage groove 468E of the pilot case 58E. This allows the pressure in the back pressure chamber 171E to be increased quickly. This stabilizes the closed state of the first damping valve 52E, which is biased in the valve closing direction by the pressure in the back pressure chamber 171E, thereby suppressing the delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0367] Furthermore, in the damping force generation mechanism 10E, the second passage 180E that is opened and closed by the communication mechanism 181E is disposed closer to the inner periphery of the bottom portion 65E than the first passage 173E, so that an increase in the radial size of the damping force generation mechanism 10E can be suppressed.

[0368] Furthermore, the damping force generating mechanism 10E is subject to large compressive deformation because it uses an O-ring as the partition member 111E having seals 112E and 113E that seal the first passage 173E with an elastic member. For this reason, the provision of the communication mechanism 181E is highly effective in suppressing the delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0369] [Seventh embodiment] Next, the seventh embodiment will be described, focusing on the differences from the first embodiment, mainly with reference to Fig. 20. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0370] As shown in Fig. 20, a shock absorber 1F including a damping force generation mechanism 10F of the seventh embodiment has a configuration that is partially different from that of the damping force generation mechanism 10. In the damping force generation mechanism 10F, a disc 54F that is partially different from the disc 54 is provided instead of the disc 54. In the damping force generation mechanism 10F, a pilot case 58F that is partially different from the pilot case 58 is provided instead of the pilot case 58. The damping force generation mechanism 10F does not have an open / close disc 57.

[0371] Disk 54F differs from disk 54 in that no notch 141 is formed.

[0372] The pilot case 58F is cylindrical with a bottom. The entire pilot case 58F is seamlessly molded as a single piece by sintering. The pilot case 58F has a bottom 65F. The bottom 65F is a disk shape with holes, and the mounting shaft portion 28 of the piston rod 21 is fitted into the inner periphery of the bottom 65F. The pilot case 58F has an opening 67 on the side of the cylindrical portion 66 opposite the bottom 65F in the axial direction.

[0373] The bottom portion 65F has a bottom main body portion 71F, and an inner sheet portion 77 and an outer sheet portion 78 similar to those described above.

[0374] The bottom body portion 71F is a disk-shaped portion with holes. The cylindrical portion 66 extends along the axial direction of the bottom body portion 71F from the side opposite to the inner sheet portion 77 and the outer sheet portion 78 in the axial direction of the bottom body portion 71F. A seal groove 68F is formed in the bottom main body portion 71F at a radially intermediate position of the bottom main body portion 71F. The seal groove 68F is annular and is formed radially inward of the cylindrical portion 66 of the bottom main body portion 71F. The seal groove 68F is recessed from the cylindrical portion 66 side in the axial direction of the bottom main body portion 71F in the opposite direction from the cylindrical portion 66 in the axial direction of the bottom main body portion 71F.

[0375] In the bottom main body portion 71F, a passage hole 83F and a passage hole 84F are formed in the bottom surface of the seal groove 68F. The passage hole 83F penetrates the bottom main body portion 71F at the position of the seal groove 68F. The passage hole 83F is located at the inner end position of the bottom surface of the seal groove 68F in the radial direction of the pilot case 58F. The passage hole 84F is located at the outer end position of the bottom surface of the seal groove 68F in the radial direction of the pilot case 58F. The pilot case 58F is provided with a plurality of passage holes 83F and a plurality of passage holes 84F. The pilot case 58F is provided with the passage holes 83F and the passage holes 84F alternately in the circumferential direction of the pilot case 58F.

[0376] A passage groove 468F extending radially inward from the seal groove 68F is formed on the axial side of the bottom body portion 71F opposite the inner seat portion 77. The passage groove 468F connects the seal groove 68F with the passage in the passage groove 30 of the piston rod 21.

[0377] The damping force generating mechanism 10F has a partitioning member 111F (movable mechanism) in the seal groove 68F. The partitioning member 111F is annular in shape as a whole and is a V-packing having a V-shaped cross section in a plane including the central axis of the ring. The partitioning member 111F is fitted into the seal groove 68F of the pilot case 58F. In this case, the opening side of the V-shape of the partitioning member 111F faces away from the bottom surface of the seal groove 68F. The partitioning member 111F is made of an elastic material with sealing properties, specifically rubber. A seal portion 112F on the inner periphery of the partitioning member 111F presses against the radially inner wall surface of the seal groove 68F to seal the gap with this wall surface. A seal portion 113F on the outer periphery of the partitioning member 111F presses against the radially outer wall surface of the seal groove 68F to seal the gap with this wall surface.

[0378] In the damping force generating mechanism 10F, the disk 55 abuts against the bottom main body portion 71F of the pilot case 58F.

[0379] The seal portions 112F and 113F of the partition member 111F are simultaneously pressed against the radially inner and radially outer wall surfaces of the seal groove 68F. As a result, the area surrounded by the pilot case 58F, the first damping valve 52, the discs 53, 54F, and 55, and the partition member 111F forms a back pressure chamber 171F. The back pressure chamber 171F is constantly in communication with the passage in the passage groove 30 of the piston rod 21 via the passage in the passage groove 468F.

[0380] Additionally, the partition member 111F forms a variable chamber 172F between the bottom side of the seal groove 68F and the partition member 111F. The variable chamber 172F is constantly in communication with the lower chamber 20 via the passages in the passage holes 83F and 84F.

[0381] A back pressure chamber 171F is formed inside the bottomed cylindrical pilot case 58F by the first damping valve 52, the discs 53, 54F, 55, and the partition member 111F. The partition member 111F is provided inside the pilot case 58F and partitions the inside of the pilot case 58F into the back pressure chamber 171F and a variable chamber 172F.

[0382] The passage in the notch 121 of the disc 50, the passage in the passage groove 30 of the piston rod 21, and the passage in the passage groove 468F of the pilot case 58F constitute a backpressure chamber introduction passage 176F branching off from the piston-side passage 43. The backpressure chamber introduction passage 176F connects the upper chamber 19 and the backpressure chamber 171F via a portion of the piston-side passage 43. During the extension stroke, the backpressure chamber introduction passage 176F introduces oil L from the upper chamber 19, which is upstream of the backpressure chamber 171F, into the backpressure chamber 171F via a portion of the piston-side passage 43.

[0383] In both cases, the passages in the passage holes 83F, 84F provided in the bottom 65F of the pilot case 58F and the passage in the seal groove 68F constitute a first passage 173F that extends to connect the back pressure chamber 171F and the lower chamber 20. A partition member 111F having seal portions 112F, 113F that seal the first passage 173F with an elastic member is movably provided in this first passage 173F.

[0384] The back pressure chamber 171F applies internal pressure to the first damping valve 52 in the direction of the piston 18, i.e., in the valve closing direction to seat the disc 131 on the valve seat portion 47. The pilot case 58F is cylindrical with a bottom and forms the back pressure chamber 171F that generates a biasing force in the valve closing direction on the first damping valve 52 arranged on the opening 67 side.

[0385] The partitioning member 111F is provided in a manner that allows it to open and close in the first passage 173F. When the seal portions 112F, 113F of the partitioning member 111F are in contact with the radially inner and radially outer wall surfaces of the seal groove 68F simultaneously, the partitioning member 111F blocks the flow of oil liquid L between the back pressure chamber 171F and the lower chamber 20 via the first passage 173F. When the seal portions 112F, 113F are separated from the radially inner and radially outer wall surfaces of the seal groove 68F, the partitioning member 111F allows the flow of oil liquid L between the back pressure chamber 171F and the lower chamber 20 via the first passage 173F.

[0386] Here, when the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171B side by a predetermined value or more, the partitioning member 111F allows the oil L to flow from the lower chamber 20 to the back pressure chamber 171F via the first passage 173F. When the pressure on the back pressure chamber 171F side is higher than the pressure on the lower chamber 20 side, the partitioning member 111F restricts the flow of the oil L from the back pressure chamber 171F to the lower chamber 20 via the first passage 173F.

[0387] The partition member 111F and the radially inner and outer wall surfaces of the seal groove 68F constitute a communication mechanism 181F. One side of the first passage 173F can communicate with the back pressure chamber 171F. The communication mechanism 181F is located on the one side of the first passage 173F and can communicate with the lower chamber 20, which is the other side of the first passage 173F, only when the lower chamber 20 is on the upstream side. In other words, when the lower chamber 20 is on the downstream side, the communication mechanism 181F cannot communicate with the lower chamber 20, which is the other side of the first passage 173F. The communication mechanism 181F restricts the flow of oil liquid L in one direction, from the back pressure chamber 171F side to the variable chamber 172F side, between the back pressure chamber 171F and the variable chamber 172F. On the other hand, the communication mechanism 181F allows the oil L to flow in the other direction, from the variable chamber 172F side to the back pressure chamber 171F side. The communication mechanism 181F is a check valve, and the partition member 111F is its valve member.

[0388] The partitioning member 111F opens when the first passage 173F allows oil liquid L to flow from the lower chamber 20 to the back pressure chamber 171F. The first passage 173F is provided to connect the back pressure chamber 171F and the lower chamber 20, and the partitioning member 111F is provided therein. The first passage 173F provided with the partitioning member 111F has one side that can communicate with the back pressure chamber 171F, and also serves as a passage in which a communication mechanism 181F is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side.

[0389] The communication mechanism 181F restricts the flow of oil L from the upper chamber 19, the piston-side passage 43, the back-pressure chamber introduction passage 176F, and the back-pressure chamber 171F to the lower chamber 20 via the first passage 173F. The communication mechanism 181F allows the flow of oil L from the lower chamber 20 to the back-pressure chamber 171F, the back-pressure chamber introduction passage 176F, the piston-side passage 43, and the upper chamber 19 via the first passage 173F.

[0390] The pilot case 58F and the partition member 111F constitute a frequency sensitive mechanism 211F that varies the damping force in response to the frequency of the reciprocating motion of the piston 18. The frequency sensitive mechanism 211F has its partition member 111F that moves and deforms in response to the frequency of the reciprocating motion of the piston 18, changing the volume of the back pressure chamber 171F that is always in communication with the upper chamber 19 and the volume of the variable chamber 172F that is always in communication with the lower chamber 20. The frequency sensitive mechanism 211F has a partition member 111F that is movably provided in the first passage 173F. The frequency sensitive mechanism 211F varies the biasing force applied to the first damping valve 52 by the back pressure chamber 171F.

[0391] The damping force generating mechanism 10F operates in substantially the same manner as the damping force generating mechanism 10, except for the following points. During the extension stroke, oil L is introduced into the back pressure chamber 171F through the back pressure chamber introduction passage 176F. At this time, the differential pressure between the back pressure chamber 171F and the lower chamber 20 is such that the pressure on the back pressure chamber 171F side is higher than the pressure on the lower chamber 20 side. Then, under pressure from the back pressure chamber 171F, the partition member 111F moves toward the bottom surface of the seal groove 68F while maintaining a sealed state with the seal groove 68F, and abuts against this bottom surface and deforms. This increases the volume of the back pressure chamber 171F.

[0392] During the compression stroke, the lower chamber 20 side becomes higher in pressure than the back pressure chamber 171F side. Then, if the differential pressure between the lower chamber 20 side and the back pressure chamber 171F side is lower than a predetermined value, oil flows from the lower chamber 20 to the variable chamber 172F through the passages in the passage holes 83F and 84F of the first passage 173F, and under this pressure, the partition member 111F moves toward the disc 55 while maintaining a sealed state with the seal groove 68F, and abuts against the disc 55, causing it to deform. This increases the volume of the variable chamber 172F. Furthermore, during the compression stroke, when the pressure on the lower chamber 20 side becomes higher than the pressure on the back pressure chamber 171F side by a predetermined value or more, the partition member 111F deforms so as to reduce the outer diameter and increase the inner diameter, the communicating mechanism 181F opens, and oil L flows from the lower chamber 20 to the back pressure chamber 171F through the passage holes 83F, 84F of the first passage 173F and the passage in the seal groove 68F.

[0393] The damping force generation mechanism 10F of the seventh embodiment includes a pilot case 58F, a frequency sensitive mechanism 211F, a first passage 173F, and a communication mechanism 181F. The pilot case 58F is cylindrical and has a bottom, and defines a back pressure chamber 171F that generates a biasing force in a valve closing direction on the first damping valve 52 disposed on the opening 67 side. The frequency sensitive mechanism 211F includes a partition member 111F that is movably provided in a first passage 173F that is provided in a bottom 65F of the pilot case 58F and connects the back pressure chamber 171F and the lower chamber 20. The partition member 111F has seal portions 112F and 113F that seal the first passage 173F with an elastic member, thereby varying the biasing force applied to the first damping valve 52 in the valve closing direction. One side of the first passage 173F can communicate with the back pressure chamber 171F. The communication mechanism 181F is located on the one side of the first passage 173F, and can communicate with the other side of the first passage 173F only when the lower chamber 20 is on the upstream side.

[0394] As described above, the damping force generating mechanism 10F is provided with the first passage 173F, which extends between the back pressure chamber 171F and the lower chamber 20, in the bottom 65F of the pilot case 58F that defines the back pressure chamber 171F. The damping force generating mechanism 10F varies the biasing force applied to the first damping valve 52 in the valve closing direction by a frequency sensitive mechanism 211F, which is provided in the first passage 173F with a movably mounted partition member 111F that seals the first passage 173F with seal portions 112F, 113F. Therefore, even though the damping force generating mechanism 10F has the frequency sensitive mechanism 211F, it is possible to prevent the size of the damping force generating mechanism 10F from increasing.

[0395] Furthermore, since the damping force generating mechanism 10F is provided with the communication mechanism 181F, the communication mechanism 181F opens when the stroke reverses from the compression stroke to the extension stroke, allowing hydraulic fluid L to be introduced from the lower chamber 20, which has a higher pressure than the upper chamber 19 during the compression stroke, into the backpressure chamber 171F via the first passage 173F, thereby quickly increasing the pressure in the backpressure chamber 171F. This stabilizes the closed state of the first damping valve 52, which is biased in the valve closing direction by the pressure in the backpressure chamber 171F. This makes it possible to suppress a delay in the rise of the damping force that occurs when the stroke reverses from the compression stroke to the extension stroke.

[0396] Furthermore, in the damping force generating mechanism 10F, the first passage 173F in which the partition member 111F is provided has one side that can communicate with the back pressure chamber 171F, and also serves as a passage in which a communication mechanism 181F is provided that can communicate with the other side only when the lower chamber 20 side is the upstream side. This makes it possible to further prevent the damping force generating mechanism 10F from becoming large.

[0397] Furthermore, in the damping force generating mechanism 10F, when the partitioning member 111F is a V-packing and the lower chamber 20 side of the first passage 173F is the upstream side, the outer circumferential side or the inner circumferential side of the partitioning member 111F, which is a V-packing, becomes a passage for flowing oil L from the lower chamber 20 to the back pressure chamber 171F. This simplifies the configuration and prevents costs from increasing.

[0398] (Appendix 1) The damping force generating mechanism in Appendix 1 is as follows: a biasing force generating member having a bottomed cylindrical shape and forming a back pressure chamber for generating a biasing force in a valve closing direction in a first damping force generating member disposed on an opening side; a frequency sensitive mechanism in which a movable mechanism having a seal portion that seals the first passage with an elastic member is movably provided in a first passage that is provided at the bottom of the biasing force generating member and connects the back pressure chamber and a first chamber, and which varies the biasing force; a second passage that is parallel to or common to the first passage and has one side that can communicate with the back pressure chamber; The second passage has a communication mechanism that is on the one side of the second passage and can communicate with the other side of the second passage only when the first chamber is on the upstream side.

[0399] (Appendix 2) The damping force generating mechanism of Appendix 2 is the damping force generating mechanism of Appendix 1, The second passage is disposed radially inward of the first passage.

[0400] (Appendix 3) The damping force generating mechanism of Appendix 3 is the damping force generating mechanism of Appendix 1, The second passage is disposed on the outer circumferential side of the first passage.

[0401] (Appendix 4) The damping force generating mechanism of Supplementary Note 4 is a damping force generating mechanism of any one of Supplementary Note 1 to Supplementary Note 3, The movable mechanism is an O-ring.

[0402] (Appendix 5) The damping force generating mechanism of Appendix 5 is the damping force generating mechanism of Appendix 1, The first passage also serves as the second passage.

[0403] (Appendix 6) The damping force generating mechanism of Appendix 6 is a damping force generating mechanism of any one of Appendix 1, Appendix 2, or Appendix 5, The biasing force generating member is provided with a tapered portion, and the movement of the movable mechanism is restricted by the tapered portion.

[0404] (Appendix 7) The damping force generating mechanism of Appendix 7 is the damping force generating mechanism of Appendix 6, A passage that is always in communication is formed between the tapered portion and the outer bottom side of the biasing force generating member.

[0405] (Appendix 8) The damping force generating mechanism of Supplementary Note 8 is a damping force generating mechanism of any one of Supplementary Note 5 to Supplementary Note 7, The movable mechanism has a disk with a hole and a packing, and is provided with a valve member capable of closing the hole, and the valve member opens when the first passage acts as the second passage.

[0406] (Appendix 9) The damping force generating mechanism of Supplementary Note 9 is a damping force generating mechanism of any one of Supplementary Note 5 to Supplementary Note 7, When the movable mechanism is a V-packing and the first passage acts as the second passage, the outer circumferential side or the inner circumferential side of the V-packing serves as the second passage. [Industrial Applicability]

[0407] According to the above-described aspects of the present invention, it is possible to provide a damping force generating mechanism that can prevent an increase in size, and thus the present invention has great industrial applicability. [Explanation of symbols]

[0408] 1, 1A to 1F... shock absorber, 2... cylinder, 10, 10A to 10F... damping force generating mechanism, 20... lower chamber (first chamber), 52, 52A, 52B, 52E... first damping valve (first damping force generating member), 57B... opening / closing disc (valve member), 58, 58A to 58F... pilot case (biasing force generating member), 65, 65A to 65F... bottom, 67, 67A, 67B... opening, 111, 111A to 111F... partition material (variable mechanism), 112, 112A to 112F, 113, 113A to 113F...sealing portion, 171, 171A to 171F...back pressure chamber, 173, 173A to 173F...first passage, 180, 180A to 180F...second passage, 181, 181A to 181F...communication mechanism, 211, 211A to 211F...frequency sensitive mechanism, 412...tapered portion, 421...disc, 422...packing, 425...passage hole (hole).

Claims

1. a biasing force generating member having a bottomed cylindrical shape and forming a back pressure chamber for generating a biasing force in a valve closing direction in a first damping force generating member disposed on an opening side; a frequency sensitive mechanism in which a movable mechanism having a seal portion that seals the first passage with an elastic member is movably provided in a first passage that is provided at a bottom of the biasing force generating member and connects the back pressure chamber and a first chamber, thereby varying the biasing force; a second passage that is parallel to or common to the first passage and has one side that can communicate with the back pressure chamber; a communication mechanism that is located on the one side of the second passage and that can communicate with the other side of the second passage only when the first chamber is located upstream; A damping force generating mechanism having the above structure.

2. The damping force generating mechanism according to claim 1 , wherein the second passage is disposed radially inward of the first passage.

3. The damping force generating mechanism according to claim 1 , wherein the second passage is disposed on an outer circumferential side of the first passage.

4. The damping force generating mechanism according to any one of claims 1 to 3, wherein the movable mechanism is an O-ring.

5. 2. The damping force generating mechanism according to claim 1, wherein the first passage also serves as the second passage.

6. 6. The damping force generating mechanism according to claim 5, wherein the biasing force generating member is provided with a tapered portion, and the movement of the movable mechanism is restricted by the tapered portion.

7. 7. The damping force generating mechanism according to claim 6, wherein a passage that is always communicable is formed between the tapered portion and the outer bottom side of the biasing force generating member.

8. 8. The damping force generation mechanism according to claim 5, wherein the movable mechanism includes a disk having a hole and a packing, and a valve member capable of closing the hole is provided, and the valve member opens when the first passage acts as the second passage.

9. The damping force generation mechanism according to any one of claims 5 to 7, wherein the movable mechanism is a V-packing, and when the first passage acts as the second passage, the outer circumferential side or the inner circumferential side of the V-packing serves as the second passage.

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