Shock-absorbing device

Abstract

This shock-absorbing device has: a first valve provided in a first flow path; a first pressure-reducing flow path into which a fluid flows from a first chamber and that reduces pressure of the fluid with a first intensity; a second pressure-reducing flow path provided in parallel with the first flow path and having a cross-sectional area smaller than that of the first pressure-reducing flow path; a third pressure-reducing flow path provided in parallel with the second pressure-reducing flow path, and having a cross-sectional area smaller than that of the first pressure-reducing flow path and larger than that of the second pressure-reducing flow path; a pressure chamber located on the downstream side of the second pressure-reducing flow path and capable of applying pressure in a valve-closing direction exerted by the fluid to the first valve; a volume-changing mechanism provided in the pressure chamber, deforming in accordance with an internal pressure of the pressure chamber, and changing the volume of the pressure chamber by means of the internal pressure; and a second valve provided in parallel with the third pressure-reducing flow path, and capable of causing the fluid that has flowed in to flow to a downstream second chamber.

Description

shock absorber

[0001] This application claims priority from Japanese Patent Application No. 2023-165934, filed on September 27, 2023, the contents of which are incorporated herein by reference.

[0002] Some shock absorbers have a variable damping force that is sensitive to frequency (see, for example, Patent Document 1 listed below).

[0003] Japanese Patent Application Publication No. 2021-55850

[0004] In shock absorbers, it is required that the change in damping characteristics be gradual.

[0005] Therefore, an object of the present invention is to provide a shock absorber that can make the change in damping characteristics gentler.

[0006] One aspect of the shock absorber according to the present invention is configured to include a cylinder, a dividing member dividing the interior of the cylinder into a first chamber and a second chamber, a first flow path communicating from the first chamber to the second chamber, a first valve provided in the first flow path, a first pressure reduction flow path into which fluid flows from the first chamber and which reduces the pressure of the fluid by a first strength, a second pressure reduction flow path provided in parallel to the first flow path and having a smaller cross-sectional area than the first pressure reduction flow path, a third pressure reduction flow path provided in parallel to the second pressure reduction flow path and having a smaller cross-sectional area than the first pressure reduction flow path and a larger cross-sectional area than the second pressure reduction flow path, a pressure chamber downstream of the second pressure reduction flow path and capable of applying pressure from the fluid to the first valve in a valve closing direction, a volume change mechanism provided in the pressure chamber and deforming in response to the internal pressure of the pressure chamber to change the volume of the pressure chamber, and a second valve provided in parallel to the third pressure reduction flow path and capable of circulating the flowing fluid to the second chamber located downstream.

[0007] Another aspect of the shock absorber according to the present invention is configured to include a cylindrical cylinder with a bottom, a piston that divides the interior of the cylinder into a first chamber and a second chamber, a rod to which the piston is fixed, and a valve structure having a first flow path that communicates with the second chamber on the downstream side, with the first chamber being the upstream side, a first valve that is provided in the first flow path and has a first valve seat and a first valve body that seats and lifts off the first valve seat, a pressure chamber that can apply pressure of a fluid in a valve-closing direction to the first valve body, a second flow path that is at least partially parallel to the first flow path and that communicates with the second chamber on the downstream side, with the first chamber being the upstream side, a second valve that is provided in the second flow path and has a second valve seat and a second valve body that seats and lifts off the second valve seat, and a communicating passage that communicates from the inside of the second valve seat on the upstream side to the pressure chamber on the downstream side.

[0008] According to the above-described aspects, it is possible to provide a shock absorber that can make the change in damping characteristics gentler.

[0009] 8 is a diagram showing a shock absorber according to a first embodiment of the present invention, and is a cross-sectional view taken along a line including the center axis line CL. FIG. 11 is a diagram showing a valve structure of the shock absorber, and is a partially enlarged cross-sectional view of part A in FIG. 1. FIG. 12 is a bottom view showing a pilot case of the shock absorber. FIG. 13 is a diagram showing a modified valve structure of the shock absorber, and is a partially enlarged cross-sectional view of a part corresponding to part B in FIG. 2. FIG. 14 is a hydraulic circuit diagram showing the valve structure of the shock absorber. FIG. 15 is a hydraulic circuit diagram showing a valve opening control mechanism of the shock absorber. FIG. 16 is a characteristic diagram showing the characteristics of damping force versus piston speed of the valve structure of the shock absorber. FIG. 17 is a diagram showing a valve structure of a shock absorber according to a second embodiment of the present invention, and is a partially enlarged cross-sectional view of a part corresponding to part A in FIG. 1. FIG. 18 is a diagram showing an extremely low speed damping force generating section of the shock absorber, and is a partially enlarged cross-sectional view of part C in FIG. 8. FIG. 19 is a hydraulic circuit diagram showing the valve structure of the shock absorber. FIG. 19 is a diagram showing a valve structure of a shock absorber according to a third embodiment of the present invention, and is a partially enlarged cross-sectional view of a part corresponding to part A in FIG. 1. FIG. 19 is a diagram showing a valve opening control mechanism of the shock absorber, and is a partially enlarged cross-sectional view of part D in FIG. 11.

[0010] [First Embodiment] A first embodiment of the present invention will be described with reference to Figures 1 to 7. For ease of explanation, the upper side of the paper in Figures 1, 2, 4, 8, 9, 11, and 12 will be referred to as "top," and the lower side of the paper in Figures 1, 2, 4, 8, 9, 11, and 12 will be referred to as "bottom." In addition, the central axis CL of the shock absorber 1 may be indicated in each figure.

[0011] As shown in Figure 1, the shock absorber 1 of the first embodiment is a so-called twin-cylinder hydraulic shock absorber, and includes a cylindrical cylinder 2 with a bottom that is filled with oil L. The cylinder 2 includes a cylindrical inner cylinder 3, a cylindrical outer cylinder 4 with a bottom that is larger in diameter than the inner cylinder 3 and is arranged concentrically with the inner cylinder 3 so as to cover the inner cylinder 3, and a cover 5 that is arranged to cover the upper opening side of the outer cylinder 4. A reservoir chamber 6 is formed between the inner cylinder 3 and the outer cylinder 4. As described above, the shock absorber 1 of the first embodiment is a twin-cylinder type, but the scope of the present invention is not limited to this and can be applied to other types such as a single-cylinder type and a triple-cylinder type.

[0012] The outer cylinder 4 is made up of a cylindrical body member 11 and a bottom member 12 that closes the lower part of the body member 11. The bottom member 12 is fitted onto the lower side of the body member 11 and welded to the body member 11 around its entire circumference. In this way, the bottom member 12 is fixed to the lower side of the body member 11. A mounting eye 13 is fixed to the outer side of the bottom member 12, opposite the body member 11.

[0013] The cover 5 has a cylindrical portion 15 and an inner flange portion 16 extending radially inward from the upper end side of the cylindrical portion 15. The cover 5 is placed on the body member 11 so that the upper end opening of the body member 11 is covered with the inner flange portion 16 and the outer circumferential surface of the body member 11 is covered with the cylindrical portion 15. In this state, a portion of the cylindrical portion 15 is crimped radially inward to be fixed to the body member 11.

[0014] The shock absorber 1 includes a piston 18 (dividing member). The piston 18 is slidably fitted within the inner tube 3 of the cylinder 2. The piston 18 divides the interior of the inner tube 3 of the cylinder 2 into a first chamber 19 and a second chamber 20. An oil liquid L is sealed within the first chamber 19 and the second chamber 20 within the inner tube 3, and the oil liquid L and gas G are sealed within the reservoir chamber 6 between the inner tube 3 and the outer tube 4. There is no particular limitation on the fluid used.

[0015] The shock absorber 1 includes a rod 21. One end of the rod 21 is disposed within the inner tube 3 of the cylinder 2 and fixed to the piston 18, and the other end extends outside the cylinder 2. The piston 18 and the rod 21 move together. During the extension stroke, in which the rod 21 increases its protrusion from the cylinder 2, the piston 18 moves toward the first chamber 19. During the compression stroke, in which the rod 21 decreases its protrusion from the cylinder 2, the piston 18 moves toward the second chamber 20.

[0016] Rod guides 22 are fitted to the upper end openings of the inner cylinder 3 and the outer cylinder 4, and a seal member 23 is attached to the outer cylinder 4 above the rod guide 22, closer to the exterior of the cylinder 2. A friction member 24 is provided between the rod guide 22 and the seal member 23. The rod guide 22, the seal member 23, and the friction member 24 are all annular, and the rod 21 is slidably inserted through the rod guide 22, the friction member 24, and the seal member 23, and extends from the interior of the cylinder 2 to the exterior.

[0017] The rod guide 22 supports the rod 21 so that it can move axially while restricting its radial movement, and guides the movement of the rod 21. The seal member 23 has its outer periphery in close contact with the outer tube 4 and its inner periphery in sliding contact with the outer periphery of the rod 21 moving in the axial direction, preventing leakage of the oil L in the inner tube 3 and the gas G and oil L in the reservoir chamber 6 in the outer tube 4 to the outside. The friction member 24 has its inner periphery in sliding contact with the outer periphery of the rod 21, generating frictional resistance in the rod 21.

[0018] The rod guide 22 has a stepped outer periphery with a larger diameter at the top than at the bottom, with the smaller-diameter lower part fitting into the inner periphery of the upper end of the inner cylinder 3 and the larger-diameter upper part fitting into the inner periphery of the upper part of the outer cylinder 4. A base valve 25 that separates the second chamber 20 and the reservoir chamber 6 is installed on the bottom member 12 of the outer cylinder 4, and the inner periphery of the lower end of the inner cylinder 3 is fitted into this base valve 25. A portion (not shown) of the upper end of the outer cylinder 4 is crimped radially inward, and this crimped portion and the rod guide 22 hold the seal member 23 in place.

[0019] Rod 21 has a main shaft portion 27 and an attachment shaft portion 28 having an outer diameter smaller than that of main shaft portion 27. Attachment shaft portion 28 is disposed inside cylinder 2, and piston 18 and the like are attached to it. The end face of main shaft portion 27 on the attachment shaft portion 28 side in the axial direction of rod 21 widens in the direction perpendicular to the axis.

[0020] As shown in FIG. 2, a passage groove 29, a passage groove 30, and a passage groove 31 are formed on the outer periphery of the mounting shaft portion 28 at an axially intermediate position.

[0021] The passage groove 29 is formed around the entire circumference of the mounting shaft portion 28 and has an annular shape.

[0022] The passage groove 30 is annular and formed around the entire circumference of the mounting shaft portion 28. The passage groove 30 is provided on the opposite side of the mounting shaft portion 28 from the main shaft portion 27 relative to the passage groove 29 in the axial direction of the mounting shaft portion 28.

[0023] The passage groove 31 extends along the axial direction of the mounting shaft portion 28, and connects the passage groove 29 and the passage groove 30. The passage in the passage groove 31 connects the passage in the passage groove 29 and the passage in the passage groove 30.

[0024] The passage grooves 29 to 31 may be formed by making the inside of the rod 21B hollow.

[0025] A male thread 32 is formed on the outer periphery of the mounting shaft portion 28 at the tip end thereof 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 .

[0026] In the shock absorber 1, for example, the portion of the rod 21 protruding from the cylinder 2 shown in FIG. 1 is positioned at the top and supported by the vehicle body, and the mounting eye 13 on the cylinder 2 side is positioned at the bottom and connected to the wheel. Alternatively, the cylinder 2 may be supported by the vehicle body and the rod 21 may be connected to the wheel. When the wheel vibrates during travel, the relative positions of the cylinder 2 and the rod 21 change with the vibration. However, this change is suppressed by the fluid resistance of the flow passages formed in at least one of the piston 18 and the rod 21. As described in detail below, the fluid resistance of the flow passages formed in at least one of the piston 18 and the rod 21 is designed to vary depending on the speed and amplitude of the vibration. By suppressing the vibration, ride comfort is improved. In addition to vibrations generated by the wheels, inertial and centrifugal forces generated on the vehicle body as the vehicle travels also act between the cylinder 2 and the rod 21. For example, centrifugal force is generated on the vehicle body when the steering wheel is turned, and a force based on this centrifugal force acts between the cylinder 2 and the rod 21. As will be described below, the shock absorber 1 has good characteristics against vibrations caused by forces generated in the vehicle body as the vehicle travels, and high stability can be obtained when the vehicle is traveling.

[0027] As shown in FIG. 2, the piston 18 is composed of a metal piston body 33 supported by the rod 21, and an annular sliding member 34 that is integrally attached to the outer circumferential surface of the piston body 33 and slides within the inner cylinder 3.

[0028] The piston body 33 is formed with a plurality of passage holes 35 (only one is shown in FIG. 2 because it is a cross-section) and an annular passage groove 36 that connects the ends of these passage holes 35 opposite the first chamber 19. The piston body 33 is also formed with a plurality of passage holes 37 (only one is shown in FIG. 2 because it is a cross-section) and an annular passage groove 38 that connects the ends of these passage holes 37 on the first chamber 19 side. The plurality of passage holes 35 are formed in the circumferential direction of the piston body 33 with one passage hole 37 sandwiched between each adjacent pair.

[0029] The passages in the plurality of passage holes 35 and the passage in the passage groove 36 constitute a piston passage 39 that penetrates the piston 18 in the axial direction of the piston 18 and can communicate between the first chamber 19 and the second chamber 20. The passages in the plurality of passage holes 37 and the passage in the passage groove 38 constitute a piston passage 40 that penetrates the piston 18 in the axial direction of the piston 18 and can communicate between the first chamber 19 and the second chamber 20.

[0030] The piston passage 39 is provided with a valve mechanism 41 (first valve) that opens and closes the piston passage 39 to generate a damping force. The valve mechanism 41 is arranged on the second chamber 20 side, which is one end side of the piston 18 in the axial direction, and is attached to the rod 21. By arranging the valve mechanism 41 on the second chamber 20 side, the oil L that flows out of the first chamber 19 flows toward the second chamber 20 in the piston passage 39 when the piston 18 moves toward the first chamber 19, i.e., during the extension stroke. The valve mechanism 41 provided for the piston passage 39 serves as an extension-side valve mechanism that suppresses the flow of oil L from the extension-side piston passage 39 to the second chamber 20 to generate a damping force.

[0031] The piston passage 40 is provided with a valve mechanism 42, which is a valve that opens and closes the piston passage 40 to generate a damping force. The valve mechanism 42 is arranged on the first chamber 19 side, which is the other axial end side of the piston 18, and is attached to the rod 21. By arranging the valve mechanism 42 on the first chamber 19 side, the oil L that flows out from the second chamber 20 flows toward the first chamber 19 in the piston passage 40 when the piston 18 moves toward the second chamber 20, i.e., during the compression stroke. The valve mechanism 42 provided for the piston passage 40 is a compression-side valve mechanism that suppresses the flow of oil L from the compression-side piston passage 40 to the first chamber 19 to generate a damping force.

[0032] As a result of the above, the piston passage 39 and the piston passage 40 are connected so that the oil liquid L, which is a fluid, flows between the first chamber 19 and the second chamber 20 as the piston 18 moves. The oil liquid L passes through the piston passage 39 when the rod 21 and the piston 18 move toward the extension side, and the oil liquid L passes through the piston passage 40 when the rod 21 and the piston 18 move toward the contraction side.

[0033] The piston body 33 is composed of two members: a first component member 601 and a second component member 602. The first component member 601 constitutes the portion of the piston body 33 on the second chamber 20 side in the axial direction, and the second component member 602 constitutes the portion of the piston body 33 on the first chamber 19 side in the axial direction.

[0034] The first component member 601 has a generally circular disk shape, and an insertion hole 604 is formed in its radial center, penetrating the first component member 601 in the axial direction and allowing the insertion of the mounting shaft portion 28 of the rod 21. The insertion hole 604 has a small diameter hole portion 605 on one axial side into which the mounting shaft portion 28 of the rod 21 is fitted, and a large diameter hole portion 606 on the other axial side, the small diameter hole portion 605 having an inner diameter larger than that of the small diameter hole portion 605.

[0035] In the axial direction of the first component 601, the large diameter hole 606 is located closer to the second component 602 than the small diameter hole 605. A passage groove 607 extending in the radial direction of the first component 601 is formed in the end face of the first component 601 on the second component 602 side in the axial direction. The passage in the passage groove 607 connects the piston passage 39 with the passage in the large diameter hole 606. The passage in the passage groove 607 serves as an orifice 608 (first pressure reduction passage) that reduces pressure by narrowing the flow path between the piston passage 39 and the passage in the large diameter hole 606.

[0036] The above-mentioned passage groove 36 is formed at an axial end of the first component 601 on the second chamber 20 side. An annular valve seat portion 47 (first valve seat) constituting part of the valve mechanism 41 is formed at an axial end of the first component 601 on the second chamber 20 side, radially outward from an opening of the passage groove 36 on the second chamber 20 side. Furthermore, an inner seat portion 48 is formed at an axial end of the piston body 33 on the second chamber 20 side, radially inward from an opening of the passage groove 36 on the second chamber 20 side. The insertion hole 604 has a large diameter hole portion 606 located on the opposite side of the small diameter hole portion 605 from the valve seat portion 47 and the inner seat portion 48 in the axial direction of the first component 601.

[0037] The second component member 602 has a generally circular disk shape, and a fitting hole 611 is formed in the radial center thereof, penetrating the axial direction, for fitting the mounting shaft portion 28 of the rod 21 therein.

[0038] The above-mentioned passage groove 38 is formed at the axial end of the second component member 602 on the first chamber 19 side. An annular valve seat portion 49 that constitutes part of the valve mechanism 42 is formed at the axial end of the second component member 602 on the first chamber 19 side, radially outward from the opening of the passage groove 38 on the first chamber 19 side. Furthermore, an inner seat portion 50 is formed at the axial end of the piston body 33 on the first chamber 19 side, radially inward from the opening of the passage groove 38 on the first chamber 19 side.

[0039] The first component 601 and the second component 602 are connected in a state where they are positioned circumferentially so as to form the piston passages 39 and 40. In this state, the sliding member 34 is placed over the radially outer sides of the first component 601 and the second component 602. As a result, the first component 601 and the second component 602 are integrated together to form the piston main body 33, and the first component 601, the second component 602, and the sliding member 34 are integrated together to form the piston 18.

[0040] In the first component 601, the portion of the valve seat 47 on the radial side opposite the insertion hole 604 forms a step that is lower in the axial direction than the valve seat 47, and the opening of the compression-side piston passage 40 on the second chamber 20 side is located in this step. In addition, in the second component 602, the portion of the valve seat 49 on the radial side opposite the fitting hole 611 forms a step that is lower in the axial direction than the valve seat 49, and the opening of the extension-side piston passage 39 on the first chamber 19 side is located in this step.

[0041] In the piston 18, the mounting shaft portion 28 of the rod 21 is fitted into the small diameter hole portion 605 of the insertion hole 604 and the fitting hole 611. In the axial direction of the rod 21, the large diameter hole portion 606 of the piston 18 is positioned to overlap the passage groove 29 of the rod 21.

[0042] On the valve seat portion 47 and inner seat portion 48 sides of the piston 18, in order from the piston 18 side in the axial direction, there are provided one disk 51, one valve disk 52, one pilot valve 53, one pilot case 56 (partition member), multiple valve disks 57, one disk 58, one valve disk 59, multiple valve disks 60, one disk 61, one disk 62, and an annular member 63, with the mounting shaft portion 28 of the rod 21 fitted inside each of them. The disks 51, 58, 61, 62, the valve disks 52, 57, 59, 60, and the annular member 63 are all perforated circular flat plates of a constant thickness, into which the mounting shaft portion 28 of the rod 21 can be fitted. The pilot valve 53 and the pilot case 56 are all annular, into which the mounting shaft portion 28 of the rod 21 can be fitted inside.

[0043] The pilot case 56 is a cylindrical shape with a bottom, and a rod insertion hole 70 that passes through the pilot case 56 in the axial direction of the pilot case 56 is formed in its radial center. The pilot case 56 has a bottom 71 that is a perforated disk, a cylindrical outer cylindrical portion 72 (tubular portion) that protrudes to one side from the outer peripheral edge of the bottom 71 along the axial direction of the bottom 71, and a cylindrical inner cylindrical portion 73 that protrudes to the same side as the outer cylindrical portion 72 from the inner peripheral edge of the bottom 71 along the axial direction of the bottom 71.

[0044] The pilot case 56 also has an inner seat portion 74 that protrudes from the inner peripheral edge of the bottom 71 along the axial direction of the bottom 71 to the side opposite the inner cylindrical portion 73, an intermediate valve seat portion 75 that protrudes from outside the inner seat portion 74 in the radial direction of the bottom 71 to the same side as the inner seat portion 74 along the axial direction of the bottom 71, and an outer valve seat portion 76 (second valve seat) that protrudes from outside the intermediate valve seat portion 75 in the radial direction of the bottom 71 to the same side as the inner seat portion 74 along the axial direction of the bottom 71.

[0045] The pilot case 56 has the mounting shaft portion 28 of the rod 21 fitted into the rod insertion hole 70. At this time, the pilot case 56 is oriented in such a way that the outer cylindrical portion 72 and the inner cylindrical portion 73 extend from the bottom portion 71 toward the piston 18 in the axial direction of the rod 21. In addition, at this time, the pilot case 56 is provided with an inner seat portion 74, an intermediate valve seat portion 75, and an outer valve seat portion 76 on the surface of the bottom portion 71 facing the second chamber 20 in the axial direction of the rod 21.

[0046] The bottom portion 71 is formed with a seat portion 80 and a recess 82 on the axial side of the bottom portion 71, closer to the outer cylindrical portion 72 and the inner cylindrical portion 73. The seat portion 80 and the recess 82 are formed at a position between the outer cylindrical portion 72 and the inner cylindrical portion 73 in the radial direction of the bottom portion 71.

[0047] The seat portion 80 is annular, and the seat surface is on the side of the outer cylindrical portion 72 and the inner cylindrical portion 73 in the axial direction of the bottom portion 71. This seat surface is flat and extends perpendicular to the central axis of the bottom portion 71.

[0048] The recess 82 is annular and is provided at a radially intermediate position of the seat portion 80. The recess 82 is recessed from the seat surface of the seat portion 80 in the axial direction of the bottom portion 71. The recess 82 has a shape in which the width in the radial direction of the bottom portion 71 becomes narrower as the depth increases. Although the recess 82 is provided in an annular shape in FIG. 2 , it does not have to be annular. In other words, it is sufficient that the recess 82 is provided on at least a portion of the seat portion 80.

[0049] An outer through-hole 87 is formed in the bottom 71, penetrating along the axial direction of the bottom 71. The outer through-hole 87 is inclined with respect to the central axis of the bottom 71 so that the farther away from the recess 82 in the axial direction of the bottom 71 the outer through-hole 87 is located radially outward of the bottom 71. As shown in Fig. 3, a plurality of outer through-holes 87 are formed in the bottom 71 at equal intervals in the circumferential direction of the bottom 71. It is sufficient that at least one outer through-hole 87 is provided in the bottom 71.

[0050] As shown in Fig. 2, the bottom portion 71 is formed with an inner through-hole 88 that penetrates the bottom portion 71 in the axial direction. As shown in Fig. 3, the bottom portion 71 is formed with a plurality of inner through-holes 88 that are equally spaced apart in the circumferential direction of the bottom portion 71. It is sufficient that at least one inner through-hole 88 is provided in the bottom portion 71. The outer through-hole 87 is provided outward of the inner through-hole 88 in the radial direction of the pilot case 56, i.e., in the radial direction of the bottom portion 71.

[0051] The inner seat portion 74 is annular in shape. A passage groove 90 is formed in the inner seat portion 74, penetrating the inner seat portion 74 in the radial direction of the inner seat portion 74. A plurality of passage grooves 90 are formed in the inner seat portion 74 at equal intervals in the circumferential direction of the inner seat portion 74.

[0052] 2, the intermediate valve seat portion 75 protrudes from the bottom portion 71 in the axial direction of the bottom portion 71 on the same side as the inner seat portion 74. The height of the intermediate valve seat portion 75 protruding from the bottom portion 71 in the axial direction of the bottom portion 71 is slightly greater than the height of the inner seat portion 74 protruding from the bottom portion 71.

[0053] 3, the intermediate valve seat portion 75 has a plurality of valve seat constituent portions 91 spaced equally apart in the circumferential direction of the pilot case 56. The plurality of valve seat constituent portions 91 have the same shape and all extend radially outward from the inner seat portion 74. In this embodiment, the intermediate valve seat portions 75 are provided in a plurality of sector shapes along the circumferential direction of the bottom portion 71, but the shape is not limited to this and may be, for example, an annular shape.

[0054] The valve seat constituent portion 91 has a passage groove 94 that penetrates the radial direction of the bottom portion 71 of the valve seat constituent portion 91 at a portion that is radially outer than the bottom portion 71 .

[0055] As shown in Fig. 2, the outer valve seat portion 76 protrudes from the bottom portion 71 in the axial direction of the bottom portion 71 on the same side as the intermediate valve seat portion 75. The height of the outer valve seat portion 76 protruding from the bottom portion 71 in the axial direction of the bottom portion 71 is greater than the height of the intermediate valve seat portion 75 protruding from the bottom portion 71. As shown in Fig. 3, the outer valve seat portion 76 is annular.

[0056] An inner passage recess 95 is formed between each of the multiple valve seat forming portions 91 of the intermediate valve seat portion 75 and the inner seat portion 74. In other words, the inner passage recess 95 is formed by being surrounded by each of the multiple valve seat forming portions 91 of the intermediate valve seat portion 75 and the inner seat portion 74. The multiple inner passage recesses 95 are arranged at equal intervals in the circumferential direction of the pilot case 56. As shown in FIG. 2 , each of the multiple inner passage recesses 95 is recessed along the axial direction of the pilot case 56 from the tip end surface on the protruding side of the inner seat portion 74 and the tip end surface on the protruding side of the intermediate valve seat portion 75. The bottom surface of the inner passage recess 95 is formed by the bottom portion 71.

[0057] 3, a passage groove 94 formed in the valve seat constituent portion 91 opens into an inner passage recess 95. The inner through-hole 88 is formed in the bottom surface of the inner passage recess 95 and opens into the inner passage recess 95.

[0058] An outer passage recess 96 is formed between the outer valve seat portion 76 and the inner seat portion 74 and intermediate valve seat portion 75. The outer passage recess 96 is continuous around the entire circumference of the pilot case 56. As shown in FIG. 2 , the outer passage recess 96 is recessed in the axial direction of the pilot case 56 from the protruding-side tip surface of the inner seat portion 74, the protruding-side tip surface of the intermediate valve seat portion 75, and the protruding-side tip surface of the outer valve seat portion 76. The bottom surface of the outer passage recess 96 is formed by the bottom portion 71.

[0059] The passage groove 90 formed in the inner seat portion 74 opens into the outer passage recess 96 .

[0060] The outer through-hole 87 has an end portion on the outer valve seat portion 76 side in the axial direction of the bottom portion 71 that opens outward from the outer valve seat portion 76 in the radial direction of the pilot case 56. The outer through-hole 87 opens into the second chamber 20. The outer through-hole 87 does not open into the inner passage recess 95 or the outer passage recess 96. The inner through-hole 88 opens into the inner passage recess 95 but does not open into the outer passage recess 96.

[0061] The rod insertion hole 70 has a hole main body portion 101 provided on the central axis of the pilot case 56, and axial grooves 102 recessed from the hole main body portion 101 outward in the radial direction of the pilot case 56. As shown in Fig. 3, the pilot case 56 has a plurality of axial grooves 102 formed at equal intervals in the circumferential direction of the hole main body portion 101. In the circumferential direction of the pilot case 56, the plurality of axial grooves 102 are aligned with the corresponding passage grooves 90.

[0062] 2, the mounting shaft portion 28 of the rod 21 is fitted into the hole main body portion 101 of the rod insertion hole 70. In the axial direction of the rod 21, the axial groove 102 is aligned with the passage groove 30 of the rod 21.

[0063] The passage in the axial groove 102 of the pilot case 56 communicates with the passage in the passage grooves 29 to 31 of the rod 21 and with the passage in the passage groove 90 of the pilot case 56. A portion of the mounting shaft portion 28 of the rod 21 is disposed within the pilot case 56. The passage in the large diameter hole portion 606 of the piston 18, the passages in the passage grooves 29 to 31 of the rod 21, and the passage in the axial groove 102 of the pilot case 56 form a rod-side chamber 105 provided on the rod 21 side. The rod-side chamber 105 communicates with the piston passage 39 via an orifice 608 in the passage groove 607 of the piston 18. The rod-side chamber 105 communicates with the passage in the outer passage recess 96 via the passage in the passage groove 90 of the pilot case 56.

[0064] A free valve 111 (membrane member) is disposed within the pilot case 56, axially facing the bottom 71. The free valve 111 is a flexible, plate-like member. The outer diameter of the free valve 111 is larger than the outer diameter of the recess 82 in the radial direction of the bottom 71. The inner diameter of the free valve 111 is smaller than the inner diameter of the recess 82 in the radial direction of the bottom 71. The inner cylindrical portion 73 of the pilot case 56 and the mounting shaft portion 28 of the rod 21 penetrate radially inward through the free valve 111.

[0065] As described above, the bottom 71 of the pilot case 56 has a recess 82 covered by the free valve 111 and a seat portion 80 that abuts against the free valve 111, and has an outer through-hole 87 that penetrates the bottom 71 at the position of the recess 82. The pilot case 56 has an inner through-hole 88 in the seat portion 80 that penetrates the bottom 71 and is located radially inward of the outer through-hole 87.

[0066] The outer through-hole 87 formed in the recess 82 of the bottom 71 has an end on the recess 82 side that is radially overlapping and axially opposed to the free valve 111. The free valve 111 closes the outer through-hole 87 by coming into surface contact with the seat portion 80, and opens the outer through-hole 87 by moving away from the seat portion 80. The free valve 111 is also elastically deformable so as to enter the recess 82, and even in this case, the free valve 111 abuts against the peripheral boundary between the recess 82 and the seat portion 80 or the entire surface of the recess 82, maintaining the closed state of the outer through-hole 87.

[0067] The disk 51 has an outer diameter that is smaller than the inner diameter of the valve seat portion 47 of the piston 18 and slightly larger than the outer diameter of the inner seat portion 48 .

[0068] The valve disc 52 has an outer diameter slightly larger than the outer diameter of the valve seat portion 47 of the piston 18. The valve disc 52 abuts against the valve seat portion 47, and opens and closes the opening of the piston passage 39 by moving away from and abutting against the valve seat portion 47.

[0069] The pilot valve 53 is made up of a metal valve disc 141 and an elastic fastening member 142 that is fastened to the valve disc 141. For example, the fastening member 142 may be made of rubber and fastened to the valve disc 141 by vulcanization adhesion.

[0070] The valve disc 141 is a circular flat plate with a certain thickness and has holes, into which the mounting shaft portion 28 of the rod 21 can be fitted. The outer diameter of the valve disc 141 is slightly larger than the outer diameter of the valve disc 52. The pilot valve 53 abuts against the valve disc 52 and the inner cylindrical portion 73 of the pilot case 56 at the valve disc 141.

[0071] The fixing member 142 is fixed to the outer circumferential side of the valve disc 141, opposite the piston 18 in the axial direction. The fixing member 142 has a seal portion 145 and a support portion 146. Both the seal portion 145 and the support portion 146 are fixed to the outer circumferential side of the valve disc 141, opposite the piston 18 in the axial direction. Alternatively, as shown in FIG. 4 , the valve disc 141 may be provided with only the seal portion 145A, and may be configured with a shim 149A and a support spring 149B instead of the support portion 146. The seal portion 145A performs the same function as the seal portion 145, and the support spring 149B performs the same function as the support portion 146. In this configuration, the pilot case 56A has an inner cylindrical portion 73A that is set lower than the inner cylindrical portion 73, and multiple shims 149A are used to secure the support spring 149B.

[0072] The seal portion 145 has an annular shape and is fixed to the outer peripheral edge portion of the valve disc 141. The seal portion 145 extends from the valve disc 141 in the axial direction of the valve disc 141 to the side opposite the piston 18.

[0073] The support portion 146 has an annular shape and is formed contiguous with the seal portion 145, inside the seal portion 145 in the radial direction of the valve disc 141. Like the seal portion 145, the support portion 146 extends from the valve disc 141 in the axial direction of the valve disc 141 to the side opposite the piston 18.

[0074] The support portion 146 has at least one passage groove 148 formed therein, penetrating the support portion 146 in the radial direction thereof. This passage groove 148 may be a hole formed in the support portion 146, or a notch that cuts from the tip of the support portion 146 (the portion that comes into contact with the free valve 111, described below) toward the seal portion 145. The support portion 146 has a base end that is located closer to the valve disc 141 than the passage groove 148 and is connected to the valve disc 141, and is connected to the base end of the seal portion 145 that is connected to the valve disc 141. The seal portion 145 and the support portion 146 of the fixing member 142 are made of the same material and are formed seamlessly as a single unit.

[0075] As described above, the seal portion 145 is integrally connected to the valve disc 141. The support portion 146 is made of the same material as the seal portion 145 and, like the seal portion 145, is integrally connected to the valve disc 141. The support portion 146 is connected to the inner portion of the seal portion 145 in the radial direction of the valve disc 141. The support portion 146 also extends from the inner side of the seal portion 145 in the radial direction of the valve disc 141.

[0076] The seal portion 145 is slidably and liquid-tightly fitted over the entire inner circumferential surface of the outer cylindrical portion 72 of the pilot case 56, and constantly seals the gap between the pilot valve 53 and the outer cylindrical portion 72. In other words, the pilot valve 53 has the seal portion 145 slidably and liquid-tightly fitted to the outer cylindrical portion 72 of the pilot case 56. At this time, the valve disc 141 covers the opening of the outer cylindrical portion 72 on the opposite side of the bottom portion 71 in the axial direction of the pilot case 56.

[0077] The tip side of the support portion 146 abuts against the free valve 111. The support portion 146 presses the free valve 111 against the seat portion 80. One end of the support portion 146 is connected to the valve disc 141, and the other end abuts against the free valve 111, directly applying a biasing force to the valve disc 141 and the free valve 111 in the direction separating them.

[0078] The support portion 146 abuts against the free valve 111 opposite a portion of the free valve 111 that seats on the seat portion 80. In other words, the portion of the support portion 146 that comes into contact with the free valve 111 overlaps the radial position of the free valve 111 with the portion of the free valve 111 that seats on the seat portion 80. Specifically, the portion of the support portion 146 that comes into contact with the free valve 111 overlaps the radial position of the free valve 111 with the portion of the free valve 111 that seats on a portion of the free valve 111 that is more inward than the recessed portion 82 of the seat portion 80 in the radial direction of the bottom portion 71.

[0079] With the free valve 111 closing the outer through-hole 87, the space between the pilot valve 53, the pilot case 56, and the free valve 111 forms a pressure chamber 151, and the space between the recess 82 of the pilot case 56 and the free valve 111 forms a variable chamber 152. Thus, these two pressure chambers 151 and variable chamber 152 are defined by the free valve 111 within the pilot case 56. The pressure chamber 151 and variable chamber 152 are formed by the pilot case 56, which is a cylindrical pilot case having a bottom 71 and an outer cylindrical portion 72.

[0080] The free valve 111 blocks the flow of oil L between the pressure chamber 151 and the variable chamber 152 in the following states: when both its outer and inner peripheral sides are in contact with the seat portion 80 over the entire circumference; when both its outer and inner peripheral sides are in contact with the boundary edges of the recess 82 between the seat portion 80 and the recess 82 over the entire circumference; and when the free valve 111 is in contact with the recess 82 over the entire circumference. Furthermore, when the free valve 111 is separated from the seat portion 80 of the bottom 71, the free valve 111 allows the flow of oil L between the pressure chamber 151 and the variable chamber 152. The variable chamber 152 communicates with the second chamber 20 via a passage in the outer through-hole 87.

[0081] The support portion 146 of the fixing member 142 of the pilot valve 53 biases the free valve 111 so that it abuts against the seat portion 80. When the differential pressure between the pressure chamber 151 and the variable chamber 152 (the variable chamber 152 is higher) reaches a predetermined level, the free valve 111 moves against the biasing force of the support portion 146 and separates from the seat portion 80. At this time, the free valve 111 separates from the seat surface radially outward of the recessed portion 82, which is not biased by the support portion 146, and may not separate from the seat surface radially inward of the recessed portion 82, depending on the differential pressure. The support portion 146 of the pilot valve 53, the free valve 111, and the seat portion 80 and recess 82 of the bottom portion 71 of the pilot case 56 constitute a check valve 155 that restricts the flow of oil liquid L from the pressure chamber 151 side to the variable chamber 152 side, i.e., the second chamber 20 side, while allowing the flow of oil liquid L from the variable chamber 152 side, i.e., the second chamber 20 side, to the pressure chamber 151 side.

[0082] The free valve 111, which is the valve element of the check valve 155, is not clamped in its entirety in the axial direction and is not fixed to any component. In other words, the free valve 111 can come into contact with and move away from the support portion 146 of the pilot valve 53 and the bottom portion 71 of the pilot case 56, against which it abuts. The free valve 111 is a floating-type free valve that can move in its entirety in the axial direction. The free valve 111 is biased by only the support portion 146 of the pilot valve 53, other than by hydraulic pressure, to move toward and away from the seat portion 80.

[0083] In addition, the biasing force of the support portion 146 of the pilot valve 53 may be set so that the free valve 111 always blocks the flow of oil liquid L between the pressure chamber 151 and the variable chamber 152 regardless of the pressure state of the pressure chamber 151 and the variable chamber 152.

[0084] Because the recess 82 is formed in the bottom 71, the free valve 111 can bend due to the pressure of the hydraulic oil L in the pilot case 56. When the pressure in the pressure chamber 151 becomes higher than the pressure in the variable chamber 152, the free valve 111 bends to enter the recess 82 as described above, expanding the volume of the pressure chamber 151 and deforming to reduce the volume of the variable chamber 152 while continuing to block communication between the pressure chamber 151 and the variable chamber 152. Furthermore, from this state, when the pressure difference between the pressure in the pressure chamber 151 and the pressure in the variable chamber 152 becomes smaller, the free valve 111 decreases its entry into the recess 82, increasing the volume of the variable chamber 152 and deforming (restoring) to reduce the volume of the pressure chamber 151 while continuing to block communication between the pressure chamber 151 and the variable chamber 152.

[0085] The bottom 71 of the pilot case 56 has an outer through-hole 87 that can communicate with the pressure chamber 151 on a surface of the bottom 71 that faces the second chamber 20 and is radially outer than the outer valve seat portion 76. The pilot case 56 is provided with a free valve 111 that closes the outer through-hole 87 from the inside of the pressure chamber 151 and can change the volume of the pressure chamber 151 using the pressure within the pressure chamber 151.

[0086] As described above, the valve disc 52 can be seated on the valve seat portion 47 of the piston 18. The valve disc 141 of the pilot valve 53 abuts against the valve disc 52. The valve disc 141 of the pilot valve 53 and the valve disc 52 together constitute a valve member 161 (first valve) that seats and separates from the valve seat portion 47.

[0087] A valve member 161 consisting of the valve disc 52 and the valve disc 141, together with the valve seat portion 47 of the piston 18, constitutes the valve mechanism 41. There is no orifice between the valve member 161 and the valve seat portion 47 of the piston 18.

[0088] When the valve disc 52 of the valve member 161 is lifted off the valve seat portion 47 and opens, the oil liquid L in the first chamber 19 flows into the second chamber 20 via the piston passage 39 and the passage between the valve member 161 and the valve seat portion 47. The piston passage 39 and the passage between the valve member 161 and the valve seat portion 47 form a flow path 162 (first flow path). In other words, the piston passage 39 and the space between the separated valve member 161 and the valve seat portion 47 form the flow path 162 through which the oil liquid L flows as a fluid flowing out of the first chamber 19, which is one of the first chamber 19 and the second chamber 20. The flow path 162 is a flow path that communicates from the first chamber 19 to the second chamber 20, and is a flow path that runs from the first chamber 19 toward the valve mechanism 41 and passes through the valve mechanism 41.

[0089] This flow path 162 serves as an extension-side flow path through which oil L flows as a fluid from the first chamber 19 to the second chamber 20 when the piston 18 moves toward the first chamber 19, i.e., during the extension stroke. The extension-side valve mechanism 41, which is made up of the valve seat 47 and the valve member 161, is a valve provided in the flow path 162, and the valve member 161 acts in a direction to reduce the cross-sectional area of ​​this flow path 162, thereby suppressing the flow of oil L and generating a damping force.

[0090] The multiple valve discs 57 have the same outer diameter, which allows them to seat on the intermediate valve seat portion 75 of the pilot case 56. The multiple valve discs 57 form a valve member 171 that can seat on and remove from the intermediate valve seat portion 75. The valve member 171 abuts against the intermediate valve seat portion 75 to close the passage within the inner passage recess 95 between the inner seat portion 74 and the intermediate valve seat portion 75. When the valve member 171 moves away from the intermediate valve seat portion 75, it opens the passage within the inner passage recess 95, connecting it to the passage within the outer passage recess 96 between the intermediate valve seat portion 75 and the outer valve seat portion 76.

[0091] The intermediate valve seat 75 of the pilot case 56 and the valve member 171 constitute a valve mechanism 172 (third valve). The passage in the passage groove 94 of the intermediate valve seat 75 serves as an orifice 173 (second pressure-reducing passage) that connects the passage in the inner passage recess 95 to the outer passage recess 96, even when the valve member 171 is in contact with the intermediate valve seat 75. In other words, the orifice 173 constantly connects the passage in the inner passage recess 95 to the passage in the outer passage recess 96. The orifice 173 is provided in the valve mechanism 172, but functions as a throttle that reduces pressure by narrowing the passage between the passage in the inner passage recess 95 and the passage in the outer passage recess 96 only when the valve mechanism 172 is closed, and does not function as a throttle when the valve mechanism 172 is open. Therefore, the orifice 173 is parallel to the valve mechanism 172 in terms of the hydraulic circuit, as shown in FIG. 5 . The orifice 173 has a flow passage cross-sectional area S2 that is smaller than the flow passage cross-sectional area S1 of the orifice 608.

[0092] During the compression stroke, the check valve 155 opens, allowing hydraulic fluid L from the second chamber 20 to be introduced into the pressure chamber 151, and when the pressure in the pressure chamber 151 exceeds a predetermined value, the valve member 171 is lifted off the intermediate valve seat portion 75. Then, the valve mechanism 172 causes hydraulic fluid L from the second chamber 20 to flow into the first chamber 19 via the passage in the outer through-hole 87, the pressure chamber 151, the passage in the inner through-hole 88, the passage in the inner passage recess 95, the passage in the outer passage recess 96, the passage in the passage groove 90, the rod side chamber 105, the orifice 608, and the piston passage 39.

[0093] The disk 58 has an outer diameter that is smaller than the outer diameter of the valve member 171 and approximately equal to the outer diameter of the inner seat portion 74 of the pilot case 56 .

[0094] The valve disc 59 has an outer diameter slightly larger than the outer diameter of the outer valve seat portion 76 of the pilot case 56. The valve disc 59 abuts against the outer valve seat portion 76 and opens and closes the passage in the outer passage recess 96 by moving away from and abutting against the outer valve seat portion 76. When the valve disc 59 moves away from the outer valve seat portion 76, the passage in the outer passage recess 96 communicates with the second chamber 20. A notch 175 is formed on the outer peripheral side of the valve disc 59, and the notch 175 traverses the outer valve seat portion 76 in the radial direction.

[0095] The multiple valve discs 60 have the same outer diameter, which is equal to the outer diameter of the valve disc 59. The valve disc 59 and the multiple valve discs 60 constitute a valve member 176 (second valve body) that is removably seated on the outer valve seat portion 76. The valve member 176 abuts against the outer valve seat portion 76 to close the passage in the outer passage recess 96 between the inner seat portion 74 and the intermediate valve seat portion 75 and the outer valve seat portion 76. The valve member 171 moves away from the outer valve seat portion 76 to connect the passage in the outer passage recess 96 to the second chamber 20.

[0096] The outer valve seat portion 76 of the pilot case 56 and the valve member 176 constitute a valve mechanism 178 (second valve). When the inside of the notch 175 of the valve disc 59 of the valve member 176 abuts against the outer valve seat portion 76, the valve member 176 forms an orifice 177 (third pressure reduction flow path) that connects the passage in the outer passage recess 96 to the second chamber 20. In other words, the orifice 177 constantly connects the passage in the outer passage recess 96 to the second chamber 20. Although the orifice 177 is provided in the valve mechanism 178, it functions as a throttle that reduces the pressure by narrowing the flow path between the passage in the outer passage recess 96 and the second chamber 20 only when the valve mechanism 178 is closed, and does not function as a throttle when the valve mechanism 178 is open. Therefore, the orifice 177 is parallel to the valve mechanism 178 in terms of the hydraulic circuit, as shown in FIG. 5 . The orifice 177 has a flow path cross-sectional area S3 that is smaller than the flow path cross-sectional area S1 of the orifice 608 and larger than the flow path cross-sectional area S2 of the orifice 173. In other words, the flow path cross-sectional area S1 of the orifice 608 > the flow path cross-sectional area S3 of the orifice 177 > the flow path cross-sectional area S2 of the orifice 173.

[0097] Between the first chamber 19 and the second chamber 20, the oil liquid L flows through the piston passage 39 shown in FIG. 2 , the orifice 608, the rod side chamber 105, the passage in the passage groove 90, the passage in the outer passage recess 96, and the orifice 177 or the passage between the open valve member 176 and the outer valve seat portion 76.

[0098] The piston passage 39, the orifice 608, the rod side chamber 105, the passage in the passage groove 90, the passage in the outer passage recess 96, and the orifice 177 or the passage between the open valve member 176 and the outer valve seat portion 76 form a passage 181 (second passage) that is partially parallel to the passage 162 and through which the oil L flows from the first chamber 19 to the second chamber 20. In other words, the passage 181 is a passage that runs from the first chamber 19 to the valve mechanism 178 and passes through the orifice 177 or the open valve mechanism 178.

[0099] Here, the entire flow path 181 leading from the first chamber 19 to the valve mechanism 178 may be parallel to the flow path 162. That is, it is sufficient that at least a portion of the flow path 181 is parallel to the flow path 162. The flow path 181 has a rod-side chamber 105 that includes passages in the passage grooves 29 to 31 provided on the surface of the rod 21. Therefore, a portion of the flow path 181 is provided on the surface of the rod 21.

[0100] In the flow path 181, an orifice 608 is provided on the upstream side when the oil liquid L flows from the first chamber 19 to the second chamber 20, and an orifice 177 is provided on the downstream side. If the orifice 177 were not provided in the flow path 181, the orifice 608 would be the narrowest part with the smallest flow path cross-sectional area, and the flow path 181 has an orifice 177 whose flow path cross-sectional area is smaller than that of the orifice 608 and which always allows the oil liquid L to pass through.

[0101] The orifice 608 provided in the piston 18 allows the oil liquid L to flow in from the first chamber 19 and reduces the pressure of the oil liquid L passing through it with a first strength. The orifice 608 is provided in parallel to the flow path 162.

[0102] The orifice 173 provided in the valve mechanism 172 receives the oil liquid L from the first chamber 19 and reduces the pressure of the oil liquid L passing through it at a second strength that is stronger than the first strength. The orifice 173 is provided in parallel to the flow path 162. The orifice 173 branches off from a passage in the outer passage recess 96 of the flow path 181. The flow path cross-sectional area S2 of the orifice 173 is smaller than the flow path cross-sectional area S1 of the orifice 608. The orifice 173 communicates with the pressure chamber 151 between the pilot valve 53, the pilot case 56, and the free valve 111 via a passage in the inner passage recess 95 and a passage in the inner through-hole 88. Therefore, the first chamber 19 communicates with the pressure chamber 151 via the piston passage 39, the orifice 608, the rod side chamber 105, the passage in the passage groove 90, the passage in the outer passage recess 96, the orifice 173, the passage in the inner passage recess 95, and the passage in the inner through-hole 88. The orifice 173, the passage in the inner passage recess 95, and the passage in the inner through-hole 88 form a communication passage 182 that branches off from the flow path 181 and communicates with the pressure chamber 151.

[0103] The free valve 111 is provided in the pressure chamber 151 to which hydraulic fluid L is introduced from the first chamber 19 via the flow path 181 and the communication path 182, and is deformed in response to the internal pressure of the pressure chamber 151. The free valve 111 and the recess 82 of the pilot case 56, which allows the deformation of the free valve 111, constitute a frequency sensitive mechanism 185 (an example of a volume change mechanism in the claims) 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) by changing the volume of the pressure chamber 151. In other words, the frequency sensitive mechanism 185 is provided in the pressure chamber 151, and is deformed in response to the internal pressure of the pressure chamber 151, thereby changing the volume of the pressure chamber 151.

[0104] The pressure chamber 151 applies internal pressure to the valve member 161 in the direction of the piston 18, i.e., in the valve closing direction to seat the valve disc 52 of the valve member 161 on the valve seat portion 47. The opening of the valve member 161 is adjusted by the pressure of this pressure chamber 151. In other words, the opening of the valve mechanism 41 including the valve member 161 is adjusted by the pressure of the pressure chamber 151. The pressure chamber 151 is located downstream of the orifice 173 through which the hydraulic liquid L flows from the first chamber 19 to the second chamber 20, and is capable of applying pressure to the valve member 161 in the valve closing direction by the hydraulic liquid L.

[0105] The orifice 177 receives the oil L from the first chamber 19 and reduces the pressure of the oil L passing through it. The orifice 177 is provided in parallel to the flow path 162. The orifice 177 is provided in parallel to the orifice 173. The orifice 177 has a flow path cross-sectional area S3 that is smaller than the flow path cross-sectional area S1 of the orifice 608 and larger than the flow path cross-sectional area S2 of the orifice 173.

[0106] 5, the valve mechanism 178 is provided in parallel with the orifice 177 in terms of the hydraulic circuit, downstream of the orifice 608 through which the oil L flows from the first chamber 19 into the valve mechanism 178. The valve mechanism 178 is capable of circulating the oil L to the second chamber 20, which is downstream from the oil L flowing into the valve mechanism 178 from the first chamber 19.

[0107] The valve mechanism 41 is provided in parallel to the orifice 608. The orifice 173 is provided downstream of the orifice 608 and in series with the orifice 608.

[0108] The pilot case 56, the pilot valve 53, and the free valve 111 constitute a valve opening control mechanism 186 that has a pressure chamber 151 and applies back pressure to a valve member 161 including a valve disc 141 of the pilot valve 53 to control the opening of the valve.

[0109] The disk 61 has an outer diameter that is smaller than the outer diameter of the valve member 176 and approximately the same as the outer diameter of the inner seat portion 74 of the pilot case 56 .

[0110] The disk 62 has an outer diameter larger than the outer diameter of the disk 58 .

[0111] The outer diameter of the annular member 63 is larger than the outer diameter of the disc 62 but smaller than the outer diameter of the valve member 176. The annular member 63 has higher rigidity than the valve member 176. The disc 62 and the annular member 63 come into contact with the valve member 176 when the valve member 176 deforms in the opening direction, thereby preventing the valve member 176 from deforming in the opening direction beyond a specified limit.

[0112] The check valve 155, which is composed of the support portion 146 of the pilot valve 53, the free valve 111, and the bottom portion 71 of the pilot case 56, is provided between the pressure chamber 151 and the passages in the variable chamber 152 and the outer through-hole 87, and restricts the flow of oil liquid L from the pressure chamber 151 to the second chamber 20 via the variable chamber 152 and the passages in the outer through-hole 87, while allowing the flow of oil liquid L from the second chamber 20 to the pressure chamber 151 via the passages in the outer through-hole 87 and the variable chamber 152.

[0113] The valve member 171 leaves the intermediate valve seat portion 75 when the pressure in the pressure chamber 151 reaches a predetermined pressure. As described above, the valve member 171, together with the intermediate valve seat portion 75, constitutes the valve mechanism 172 that opens and generates a damping force when the pressure in the pressure chamber 151 reaches a predetermined pressure. The valve mechanism 172 is provided in a portion of the flow path 181 that is parallel to the flow path 162. The valve mechanism 172 is provided outside the pilot case 56, and the valve member 171 is disposed opposite the bottom 71. An inner through-hole 88 is provided in the bottom 71 of the pilot case 56, facing the valve member 171 of the valve mechanism 172.

[0114] As described above, the valve member 176 constitutes the valve mechanism 178 together with the outer valve seat portion 76. The valve mechanism 178 is provided in a portion of the flow path 181 that is parallel to the flow path 162. The valve mechanism 178 is provided outside the pilot case 56, and the valve member 176 is disposed opposite the bottom portion 71. An outer through-hole 87 is provided in the bottom portion 71 of the pilot case 56, radially outward of the valve mechanism 178. When the valve member 176 is released from the outer valve seat portion 76 and opens, it allows the oil L in the first chamber 19 to flow through the flow path 181 to the second chamber 20. When the valve member 176 is seated on the outer valve seat portion 76 and closed, it blocks communication between the flow path 181 and the second chamber 20. The pilot case 56 has an intermediate valve seat portion 75 of a valve mechanism 172 provided between an outer valve seat portion 76 and a valve member 176 and having an orifice 173 that restricts communication of the hydraulic liquid L at least more than the orifice 177 .

[0115] Compression-side valve mechanism 42 has, in order from the piston 18 side in the axial direction, one disk 201, one disk 202, multiple disks 203, multiple disks 204, one disk 205, one disk 206, and one annular member 207. Disks 201 to 206 and annular member 207 are all made of metal, and each is in the form of a perforated circular flat plate of a constant thickness, into which mounting shaft portion 28 of rod 21 can be fitted.

[0116] The discs 203, 204 constitute a valve member 212 that can be seated on and removed from the valve seat portion 49. When the valve member 212 is released from the valve seat portion 49, it connects the piston passage 40 to the first chamber 19 and suppresses the flow of oil liquid L between them, thereby generating a damping force. The piston passage 40 and the space between the valve member 212 and the valve seat portion 49 constitute a flow path 210. The inside of the cutout portion 211 of the disc 202 forms an orifice 213 that connects the first chamber 19 and the second chamber 20 via the flow path 210 even when the disc 202 is in contact with the valve seat portion 49. In other words, the piston passage 40, the orifice 213, and the space between the valve member 212 and the valve seat portion 49 that are spaced apart form the flow path 210 through which oil liquid L flows as a fluid flowing out from the second chamber 20, which is one of the first chamber 19 and the second chamber 20.

[0117] This flow path 210 serves as a compression-side flow path through which oil L flows as a fluid from the second chamber 20 to the first chamber 19 when the piston 18 moves toward the second chamber 20, i.e., during the compression stroke. A compression-side valve mechanism 42, consisting of a valve seat portion 49 and a valve member 212, is provided in the flow path 210, and the valve member 212 opens and closes this flow path 210 to suppress the flow of oil L, thereby generating a damping force. In other words, the valve member 212 is provided in the flow path 210 and suppresses the flow of oil L caused by the sliding of the piston 18 toward the compression side, thereby generating a damping force. The disc 206 and the annular member 207 suppress deformation of the valve member 212 in the opening direction beyond a specified limit.

[0118] A valve opening control mechanism 186 consisting of the pilot case 56, the pilot valve 53, and the free valve 111 includes a check valve 155 and a frequency sensitive mechanism 185. The valve opening control mechanism 186 has a free valve 111 that deforms in response to the frequency of the reciprocating motion of the piston 18, thereby varying the volume of the pressure chamber 151 that is always in communication with the first chamber 19 and the volume of the variable chamber 152 that is always in communication with the second chamber 20.

[0119] The rod 21 has the mounting shaft portions 28 fitted inside thereof, and the annular member 207, disc 206, disc 205, multiple discs 204, multiple discs 203, disc 202, disc 201, piston 18, disc 51, valve disc 52, pilot valve 53, pilot case 56, multiple valve discs 57, disc 58, valve disc 59, multiple valve discs 60, disc 61, disc 62, and annular member 63 stacked in this order on the end of the main shaft portion 27 on the mounting shaft portion 28 side. At this time, the pilot case 56 fits the seal portion 145 of the pilot valve 53 into the outer cylindrical portion 72. At this time, the free valve 111 is disposed between the bottom 71 of the pilot case 56 and the support portion 146 of the pilot valve 53.

[0120] With the parts arranged in this manner, the retainer 221 is coupled to the male thread 32 of the mounting shaft portion 28 that protrudes beyond the annular member 63. As a result, the inner circumferential sides or the entirety of the parts stacked as described above, from the annular member 207 to the annular member 63, are sandwiched between the end of the main shaft portion 27 of the rod 21 on the mounting shaft portion 28 side and the retainer 221, and are clamped in the axial direction. At this time, the valve disc 141 of the pilot valve 53, on the side opposite to the piston 18, abuts against the inner cylindrical portion 73 of the pilot case 56. At this time, the free valve 111 is not clamped in the axial direction, but is sandwiched between the support portion 146 of the pilot valve 53 and the pilot case 56.

[0121] The piston 18, the discs 51, 58, 61, 62, 201, 202, 203, 204, 205, 206, the valve discs 52, 57, 59, 60, the pilot valve 53, the pilot case 56, the annular members 63, 207, the free valve 111, and the portions of the rod 21 to which these are attached constitute a valve structure 225. Thus, the shock absorber 1 has the valve structure 225.

[0122] The valve structure 225 has a flow path 162 that communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side. The valve structure 225 has a valve mechanism 41 that is provided in the flow path 162 and includes a valve seat 47 and a valve member 161 that seats and disengages from the valve seat 47. The valve structure 225 has a pressure chamber 151 that can apply pressure from oil liquid L in a valve-closing direction to the valve member 161. The valve structure 225 has a flow path 181 that is at least partially parallel to the flow path 162 and communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side. The valve structure 225 has a valve mechanism 178 that is provided in the flow path 181 and includes an outer valve seat 76 and a valve member 176 that seats and disengages from the outer valve seat 76. The valve structure 225 has a communication path 182 that communicates from the inside of the outer valve seat 76 on the upstream side to the pressure chamber 151 on the downstream side.

[0123] A hydraulic circuit diagram of the valve structure 225 is shown in FIG. 5. As shown in FIG. 5, the valve structure 225 is provided with a flow path 162 connecting the first chamber 19 and the second chamber 20. A valve mechanism 41 is provided in the flow path 162. The valve structure 225 also is provided with a flow path 181 connecting the first chamber 19 and the second chamber 20. The flow path 181 is provided with, in this order from the first chamber 19 side, an orifice 608, a valve mechanism 178, and an orifice 177. The valve mechanism 178 and the orifice 177 are provided in parallel. The valve structure 225 also has a valve mechanism 172 and an orifice 173 in parallel, branching from between the orifice 608 of the flow path 181 and the valve mechanism 178 and orifice 177. The valve mechanism 172 and the orifice 173 are connected to the pressure chamber 151 (shown in FIG. 6) of the valve opening control mechanism 186 via a communication path 182. The pressure in the pressure chamber 151 acts on the valve member 161 of the valve mechanism 41 shown in FIG. 5. As shown in FIG. 6, the pressure chamber 151 is separated from the variable chamber 152 by a free valve 111, constituting a frequency sensitive mechanism 185. The variable chamber 152 is connected to the second chamber 20 shown in FIG. 5. The valve opening control mechanism 186 is provided with a check valve 155 between the second chamber 20 and the pressure chamber 151 shown in FIG. 6. Note that in FIG. 6, for the sake of convenience in illustrating the hydraulic circuit, the valve body of the check valve 155 is provided separately from the free valve 111 of the frequency sensitive mechanism 185, but the free valve 111 also serves as the valve body of the check valve 155. Of course, the valve body of the check valve 155 may be provided separately from the free valve 111 of the frequency sensitive mechanism 185, as shown in FIG. 6. As shown in FIG. 5, the valve structure 225 is provided with a flow path 210 connecting the second chamber 20 and the first chamber 19. The flow path 210 is provided with a valve mechanism 42 and an orifice 213 in parallel.

[0124] 5 , the shock absorber 1 has a flow path 162 that communicates from the first chamber 19 to the second chamber 20, a valve mechanism 41 that is a valve provided in the flow path 162, and an orifice 608 that receives the oil L from the first chamber 19 and reduces the pressure of the oil L by a first strength. The shock absorber 1 also has an orifice 173 that is provided in parallel to the flow path 162 and has a smaller cross-sectional area than the orifice 608, and an orifice 177 that is provided downstream of the orifice 608 in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 608 but a larger cross-sectional area than the orifice 173. 6, which is located downstream of the orifice 173 and is capable of applying pressure to the valve mechanism 41 in the valve closing direction by oil liquid L, and a frequency sensitive mechanism 185 which is provided in the pressure chamber 151 and deforms in response to the internal pressure of the pressure chamber 151, changing the volume of the pressure chamber 151. Furthermore, as shown in FIG. 5, the shock absorber 1 has a valve mechanism 178 which is located downstream of the orifice 608 and is provided in parallel to the orifice 177 and which is capable of circulating the oil liquid L which has flowed in to the second chamber 20 which is downstream.

[0125] Furthermore, in the shock absorber 1 , the valve mechanism 41 is provided in parallel to the orifice 608 , and the orifice 173 is provided downstream of the orifice 608 and in series with the orifice 608 .

[0126] 1 , the above-mentioned base valve 25 is provided between the bottom member 12 of the outer cylinder 4 and the inner cylinder 3. This base valve 25 has a base member 231 that separates the second chamber 20 from the reservoir chamber 6, a disk valve 232 provided on the lower side of this base member 231, i.e., on the reservoir chamber 6 side, a disk valve 233 provided on the upper side of the base member 231, i.e., on the second chamber 20 side, and a mounting pin 234 that attaches the disk valve 232 and the disk valve 233 to the base member 231.

[0127] The disc valve 232, together with the base member 231, constitutes a compression-side damping valve mechanism 237 that opens during the compression stroke of the shock absorber 1 to allow hydraulic fluid L to flow from the second chamber 20 to the reservoir chamber 6 and generate a damping force. The disc valve 233, together with the base member 231, constitutes a suction valve mechanism 238 that opens during the extension stroke of the shock absorber 1 to allow hydraulic fluid L to flow from the reservoir chamber 6 into the second chamber 20. The suction valve mechanism 238 mainly functions to allow hydraulic fluid to flow from the reservoir chamber 6 to the second chamber 20 without generating any damping force, so as to make up for a shortage of hydraulic fluid caused by the extension of the rod 21 from the cylinder 2.

[0128] Next, the operation of the valve structure 225 will be described with reference to the characteristic curve of the damping force versus piston speed shown in Fig. 7. In Fig. 7, the characteristic curve of the valve structure 225 is shown by solid lines Y1, Y2, and Y3.

[0129] During the extension stroke in which the rod 21 moves to the extension side, when the moving speed of the piston 18 (hereinafter referred to as the piston speed) is in the extremely low speed region X1 which is slower than a first predetermined speed and when a low frequency is input in which the piston frequency is lower than a predetermined frequency, the oil L from the first chamber 19 flows into the pressure chamber 151 via a flow path 181 which has the piston passage 39, the orifice 608, the rod side chamber 105, a passage in the passage groove 90, and a passage in the outer passage recess 96, and via a communication passage 182 which has the orifice 173, the passage in the inner passage recess 95, and a passage in the inner through-hole 88.

[0130] During the extension stroke of the low-frequency input in the extremely low speed range X1, the amplitude of the piston 18 is large. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation, and preventing hydraulic fluid L from flowing from the first chamber 19 to the pressure chamber 151. At this time, the variable chamber 152 discharges hydraulic fluid L to the second chamber 20 through the passage in the outer through-hole 87. During the extension stroke of the low-frequency input in the extremely low speed range X1, when the free valve 111 abuts against the recess 82 and restricts further deformation, the volume of the pressure chamber 151 does not increase, causing the pressure in the pressure chamber 151 to rise, restricting the opening of the valve member 161 of the valve mechanism 41. In other words, the valve member 161 of the valve mechanism 41 does not open.

[0131] Therefore, during the extension stroke when a low frequency is input in the extremely low speed region X1, the oil L from the first chamber 19 flows through a flow path 181 that includes the piston passage 39, the orifice 608, the rod side chamber 105, a passage in the passage groove 90, a passage in the outer passage recess 96, and the orifice 177, and then flows from the orifice 177 at the end of the flow path 181 to the second chamber 20. At this time, the oil L from the first chamber 19 is throttled by the orifice 608, and then further throttled by the orifice 177, which has a smaller flow path cross-sectional area than the orifice 608, before flowing into the second chamber 20. The oil L from the first chamber 19 also flows into the second chamber 20 through the flow path 210 that includes the orifice 213. Therefore, as shown by the solid line Y1 in FIG. 7 , when a low frequency is input in the extremely low speed region X1, a damping force with an orifice characteristic (the damping force is approximately proportional to the square of the piston speed) is generated. Therefore, in the extension stroke when a low frequency is input in the extremely low speed region X1, the damping force characteristic with respect to the piston speed is such that the rate of increase of the damping force becomes relatively high as the piston speed increases.

[0132] During the extension stroke, when the piston speed is in the very low speed region X1 which is slower than the first predetermined speed and the piston frequency is a high frequency input which is equal to or greater than a predetermined frequency, the oil liquid L from the first chamber 19 flows into the pressure chamber 151 through the flow path 181 which includes the orifice 608 and the communicating passage 182 which branches off from the middle of the flow path 181 and includes the orifice 173, just as when a low frequency is input in the very low speed region X1.

[0133] During the extension stroke when high frequency is input in such a very low speed range X1, the amplitude of the piston 18 is small. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, when oil L from the first chamber 19 is introduced into the pressure chamber 151 from the flow path 181 through the communication passage 182, the free valve 111, which had previously been in a flat plate shape and abutting against the seat portion 80, elastically deforms to enter the recess 82 while blocking communication between the pressure chamber 151 and the variable chamber 152, thereby expanding the volume of the pressure chamber 151 and discharging oil L from the variable chamber 152 to the second chamber 20 through the passage in the outer through-hole 87.

[0134] While the free valve 111 is deformed in this manner, oil liquid L is introduced from the first chamber 19 into the pressure chamber 151, but because the amount of oil liquid L introduced from the first chamber 19 into the pressure chamber 151 is small, the deformation of the free valve 111 is small and the free valve 111 does not come into contact with the recess 82 and is not restricted in deformation as occurs with low-frequency input. In this manner, the bending of the free valve 111 suppresses the pressure rise in the pressure chamber 151, making it easier for the valve member 161 to open.

[0135] Therefore, during the extension stroke when a high frequency input occurs in the extremely low speed range X1, oil L from the first chamber 19 flows through the flow path 181 including the orifice 608 and the orifice 177 at the end thereof into the second chamber 20. In addition, oil L also flows from the flow path 162 into the second chamber 20 while opening the valve mechanism 41, i.e., while lifting the valve member 161 off the valve seat 47. Therefore, as shown by the solid line Y2 in FIG. 7 , during the extension stroke when a high frequency input occurs in the extremely low speed range X1, a damping force with a valve characteristic (damping force approximately proportional to piston speed) is generated. During the extension stroke when a high frequency input occurs in the extremely low speed range X1, the damping force is lower than during the extension stroke when a low frequency input occurs in the extremely low speed range X1, as shown by the solid line Y1 in FIG. 7 . In other words, during the extension stroke when a high frequency input occurs in the extremely low speed range X1, the damping force characteristic is softer than during the extension stroke when a low frequency input occurs in the extremely low speed range X1. Furthermore, during the extension stroke when high frequency input is made in the very low speed region X1, the damping force characteristics relative to piston speed are such that the rate of increase in damping force relative to an increase in piston speed is lower than during the extension stroke when low frequency input is made in the very low speed region X1.

[0136] During the extension stroke, when the piston speed is equal to or greater than a first predetermined speed and is in a low-speed region X2 that is faster than a second predetermined speed that is faster than the first predetermined speed, and when a low-frequency input is made in which the piston frequency is lower than a predetermined frequency, oil liquid L from the first chamber 19 flows from the flow path 181 including the orifice 608 to the pressure chamber 151 via the connecting passage 182 including the orifice 173, just as when a low-frequency input is made in the very low-speed region X1.

[0137] During the extension stroke of such a low-frequency input in the low-speed range X2, the amplitude of the piston 18 is large, similar to the low-frequency input in the very-low-speed range X1. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation and preventing an increase in the volume of the pressure chamber 151. During the extension stroke of this low-frequency input in the low-speed range X2, the volume of the pressure chamber 151 does not increase, so the pressure in the pressure chamber 151 increases, inhibiting the opening of the valve member 161 of the valve mechanism 41. That is, even during the extension stroke of the low-frequency input in the low-speed range X2, the valve member 161 of the valve mechanism 41 does not open.

[0138] During the extension stroke when a low-frequency input is made in the low-speed range X2, the flow rate of hydraulic oil L flowing from the first chamber 19 to the flow path 181 is greater than during the extension stroke when a low-frequency input is made in the extremely low-speed range X1. Therefore, hydraulic oil L flows from the first chamber 19 to the second chamber 20 in the flow path 181 while opening the valve mechanism 178, i.e., while causing the valve member 176 to separate from the outer valve seat 76. This generates a damping force with valve characteristics. For this reason, as shown by the solid line Y1 in Figure 7, during the extension stroke when a low-frequency input is made in the low-speed range X2, the increase rate of the damping force relative to an increase in piston speed is lower than during the extension stroke when a low-frequency input is made in the extremely low-speed range X1.

[0139] During the extension stroke, when the piston speed is equal to or greater than the first predetermined speed and is in the low-speed region X2 slower than the second predetermined speed, and when a high-frequency input is applied with a piston frequency equal to or greater than a predetermined frequency, the oil liquid L from the first chamber 19 flows into the pressure chamber 151 through the flow path 181 including the orifice 608 and the connecting passage 182 including the orifice 173, just as when a high-frequency input is applied in the very low-speed region X1.

[0140] During the extension stroke when high-frequency input is made in the low-speed range X2, the amplitude of the piston 18 is small, just as during high-frequency input in the very low-speed range X1. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, the bending of the free valve 111 can suppress the pressure increase in the pressure chamber 151, making it easier for the valve member 161 to open.

[0141] Therefore, during the extension stroke when a high frequency is input in the low speed range X2, the hydraulic oil L from the first chamber 19 flows into the second chamber 20 in the flow path 181 while opening the valve mechanism 178, i.e., while lifting the valve member 176 off the outer valve seat 76. At the same time, the hydraulic oil L from the first chamber 19 flows into the second chamber 20 in the flow path 162 while opening the valve mechanism 41, i.e., while lifting the valve member 161 off the valve seat 47. For this reason, as shown by the solid line Y2 in Figure 7 , during the extension stroke when a high frequency is input in the low speed range X2, the damping force is lower than when a low frequency is input in the low speed range X2. Furthermore, during the extension stroke when a high frequency is input in the low speed range X2, the damping force characteristic relative to piston speed is such that the rate of increase in damping force relative to an increase in piston speed is lower than when a low frequency is input in the low speed range X2. Here, in the extension stroke when a high frequency is input in the low speed region X2, the characteristic of the damping force relative to the piston speed is such that the rate of increase of the damping force relative to the increase in piston speed is the same as in the extension stroke when a high frequency is input in the very low speed region X1.

[0142] During the extension stroke, when the piston speed is in the medium-high speed range X3 that is equal to or greater than a second predetermined speed and a low frequency input is applied where the piston frequency is lower than the predetermined frequency, oil L from the first chamber 19 flows into the pressure chamber 151 through the flow path 181 that includes the orifice 608 and the connecting passage 182 that includes the orifice 173, just as during the extension stroke when a low frequency input is applied in the low speed range X2.

[0143] During the extension stroke of a low-frequency input in the medium-to-high speed range X3, the amplitude of the piston 18 is large, similar to the low-frequency input in the low-speed range X2. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation and preventing an increase in the volume of the pressure chamber 151. During the extension stroke of a low-frequency input in the medium-to-high speed range X3, the volume of the pressure chamber 151 does not increase, so the pressure in the pressure chamber 151 increases. However, the relationship of the forces (hydraulic pressure) acting on the valve member 161 is such that the opening force applied from the piston passage 39, which directly communicates with the first chamber 19, is greater than the closing force applied from the pressure chamber 151. Therefore, during the low-frequency input in the medium-to-high speed range X3, the valve mechanism 41 opens. That is, the valve member 161 opens by separating from the valve seat portion 47 of the piston 18. As a result, in addition to the flow to the second chamber 20 through the flow path 181 when the valve mechanism 178 is opened, a larger amount of oil L flows into the second chamber 20 through the flow path 162, which includes the passage between the valve member 161 and the valve seat portion 47, further suppressing the increase in damping force. For this reason, as shown by the solid line Y1 in Fig. 7, in the extension stroke for a low-frequency input in the medium to high speed range X3, the characteristic of the damping force relative to the piston speed is such that the rate of increase in damping force relative to an increase in piston speed is lower than in the extension stroke for a low-frequency input in the low speed range X2.

[0144] During the extension stroke, when the piston speed is in the medium-high speed range X3 above a second predetermined speed and the piston frequency is a high frequency input above a predetermined frequency, the oil liquid L from the first chamber 19 flows through the flow path 181 including the orifice 608, as in the case of a high frequency input in the low speed range X2, and flows into the pressure chamber 151 via the connecting passage 182 including the orifice 173.

[0145] During the extension stroke when high frequency input is made in the medium to high speed range X3, the amplitude of the piston 18 is small, as is the case during the extension stroke when high frequency input is made in the low speed range X2. Therefore, the amount of oil liquid L flowing into the pressure chamber 151 is small, and deformation of the free valve 111 is small. Therefore, by bending the free valve 111, it is possible to suppress a pressure increase in the pressure chamber 151, and the valve member 161 becomes easier to open.

[0146] Therefore, during the extension stroke when a high frequency is input in the medium-to-high speed range X3, the oil L from the first chamber 19 flows into the second chamber 20 through the flow path 181, opening the valve mechanism 178, i.e., separating the valve member 176 from the outer valve seat 76. At the same time, the oil L from the first chamber 19 flows into the second chamber 20 through the flow path 162, opening the valve mechanism 41, i.e., separating the valve member 161 from the valve seat 47. For this reason, as shown by the solid line Y2 in FIG. 7 , during the extension stroke when a high frequency is input in the medium-to-high speed range X3, the damping force is lower than during the low frequency input in the medium-to-high speed range X3. Here, during the extension stroke when a high frequency is input in the medium-to-high speed range X3, the damping force characteristic with respect to piston speed is such that the rate of increase in damping force with increasing piston speed is the same as during the extension stroke when a high frequency is input in the low speed range X2.

[0147] During the compression stroke in which the rod 21 moves toward the compression side, in the extremely low speed region X4 in which the piston speed is slower than the fourth predetermined speed, the hydraulic fluid L from the second chamber 20 flows into the first chamber 19 via the compression-side piston passage 40 and the orifice 213 of the valve member 212 of the valve mechanism 42. At the same time, the hydraulic fluid L from the second chamber 20 flows into the flow path 181 from the orifice 177 and into the first chamber 19 via the flow path 181 including the orifice 608. At the same time, the hydraulic fluid L from the second chamber 20 passes through the passage in the outer through-hole 87 and the variable chamber 152, opens the check valve 155, and flows from the pressure chamber 151 and the communicating passage 182 through the orifice 173 to the first chamber 19 via the flow path 181 including the orifice 608. Therefore, during the compression stroke in the extremely low speed region X4, a damping force with orifice characteristics is generated. Therefore, as shown by the solid line Y3 in FIG. 7, in the compression stroke in the extremely low speed region X4, the damping force characteristic with respect to the piston speed is such that the rate of increase in the damping force is relatively high as the piston speed increases.

[0148] During the compression stroke in the low-speed region X5, where the piston speed is equal to or greater than the fourth predetermined speed and slower than a fifth predetermined speed, hydraulic fluid L flows from the second chamber 20 through the passage in the outer through-hole 87 and the variable chamber 152, and flows through the pressure chamber 151 and the communicating passage 182 while opening the check valve 155. Then, hydraulic fluid L flows into the first chamber 19 through the flow path 181 including the orifice 608, while opening the valve mechanism 172 at the end of the communicating passage 182, i.e., while lifting the valve member 171 off the intermediate valve seat 75. Therefore, during the compression stroke in the low-speed region X5, a damping force with a valve characteristic is generated. Therefore, as shown by the solid line Y3 in FIG. 7 , during the compression stroke in the low-speed region X5, the rate of increase in the damping force relative to an increase in piston speed is lower than during the compression stroke in the very-low-speed region X4.

[0149] During the compression stroke in the medium to high speed range X6 where the piston speed is equal to or higher than the fifth predetermined speed, the oil L flows from the second chamber 20 into the first chamber 19 via the flow path 181 including the orifice 608, opening the valve mechanism 172, just as during the compression stroke in the low speed range X5. During the compression stroke in the medium to high speed range X6, the oil L is also introduced from the second chamber 20 into the compression-side piston passage 40, opening the valve mechanism 42, i.e., causing the valve member 212 to separate from the valve seat 49, and flows into the first chamber 19. For this reason, as shown by the solid line Y3 in Fig. 7 , during the compression stroke in the medium to high speed range X6, the increase rate of the damping force relative to the increase in piston speed is lower than during the compression stroke in the low speed range X5.

[0150] The above-mentioned Patent Document 1 discloses a shock absorber in which the damping force is variable in response to frequency. In the shock absorber, it is required that the change in the damping characteristics be gradual.

[0151] The shock absorber 1 of the first embodiment has a flow path 162 that communicates from the first chamber 19 to the second chamber 20 in the cylinder 2, and a valve mechanism 41 that is provided in the flow path 162. The shock absorber 1 also has an orifice 608 that receives the oil L from the first chamber 19 and reduces the pressure of the oil L at a first strength, an orifice 173 that is provided in parallel to the flow path 162 and has a smaller cross-sectional area than the orifice 608, and an orifice 177 that is provided in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 608 but a larger cross-sectional area than the orifice 173. The shock absorber 1 also has a pressure chamber 151 that is downstream of the orifice 173 and can apply pressure from the oil L in a valve-closing direction to the valve mechanism 41, and a frequency sensitive mechanism 185 that is provided in the pressure chamber 151 and deforms in response to the internal pressure of the pressure chamber 151 to change the volume of the pressure chamber 151. The shock absorber 1 also has a valve mechanism 178 that is provided in parallel with the orifice 177 and allows the oil L that has flowed in to flow into the second chamber 20 downstream.

[0152] The shock absorber 1 has the valve mechanism 41, the valve mechanism 178, and the orifice 177, which allows for gradual changes in the damping characteristics. The shock absorber 1 also has the orifice 608 and the orifice 173, which allows for detailed adjustment of the damping force characteristics, making it possible to further smooth the changes in the damping characteristics. That is, in the shock absorber disclosed in Patent Document 1, as shown by the dashed lines Z1 and Z2 in Fig. 7, there was a large change in the damping force characteristics, particularly at the time of low-frequency input, as shown by the dashed line Z1, but the shock absorber 1 can smoothly change the damping force characteristics, as shown by the solid line Y1 in Fig. 7.

[0153] In the shock absorber 1, the valve mechanism 41 is provided in parallel to the orifice 608, and the orifice 173 is provided downstream of the orifice 608 and in series with the orifice 608. Therefore, the shock absorber 1 can adjust the damping force characteristics in more detail, and can make the change in the damping characteristics more gradual.

[0154] In the shock absorber 1, the valve structure 225 has a flow path 162 that communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side, a valve seat 47, and a valve member 161 that is provided in the flow path 162 and seats and lifts off the valve seat 47. The valve structure 225 also has a pressure chamber 151 that can apply pressure from oil liquid L in a valve-closing direction to the valve member 161, and a flow path 181 that is at least partially parallel to the flow path 162 and communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side. The valve structure 225 also has a valve mechanism 178 that is provided in the flow path 181 and includes an outer valve seat 76 and a valve member 176 that seats and lifts off the outer valve seat 76, and a communication path 182 that communicates from the inside of the outer valve seat 76 on the upstream side to the pressure chamber 151 on the downstream side. This makes it possible for the shock absorber 1 to achieve a gradual change in damping characteristics.

[0155] In the shock absorber 1, a portion of the flow path 181 is provided on the surface of or inside the rod 21, the pressure chamber 151 is formed by a bottomed, cylindrical pilot case 56 having a bottom 71 and an outer cylindrical portion 72, and the outer valve seat portion 76 is provided on the surface of the bottom 71 facing the second chamber 20. Therefore, the shock absorber 1 can be made compact.

[0156] In the shock absorber 1, the valve mechanism 178 further includes an orifice 177 that has a smaller cross-sectional area than the orifice 608, which is the narrowest part of the flow path 181, and that always allows communication of the oil liquid L. Therefore, the shock absorber 1 can make the change in damping characteristics even more gradual.

[0157] The shock absorber 1 further includes a valve mechanism 172 in which the pilot case 56 is provided between the outer valve seat portion 76 and the valve member 176, and which restricts the communication of the oil liquid L more than at least the orifice 177. Therefore, the shock absorber 1 can make the change in damping characteristics even more gradual.

[0158] In the shock absorber 1, the bottom 71 of the pilot case 56 has an outer through-hole 87 that can communicate with the pressure chamber 151 on a surface of the bottom 71 that faces the second chamber 20 and is radially outer than the outer valve seat portion 76. In the shock absorber 1, the pilot case 56 is provided with a free valve 111 that closes the outer through-hole 87 from the inside of the pressure chamber 151 and can change the volume of the pressure chamber 151 by the pressure of the oil liquid L in the pressure chamber 151. This allows the shock absorber 1 to be made compact.

[0159] Second Embodiment Next, a second embodiment will be described, focusing on differences from the first embodiment, mainly with reference to Figures 8 to 10. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0160] As shown in FIG. 8, a shock absorber 1A of the second embodiment has a valve structure 225A that is partially different from the valve structure 225 of the first embodiment instead of the valve structure 225.

[0161] Valve structure 225A has a valve mechanism 178A that is partially different from valve mechanism 178 in place of valve mechanism 178. Valve mechanism 178A has a valve member 176A that is partially different from valve member 176 in place of valve member 176. Valve member 176A has a valve disc 59A that is partially different from valve disc 59 in place of valve disc 59. Valve disc 59A has an orifice 177A that has a smaller flow path cross-sectional area than orifice 177 of valve disc 59. Valve mechanism 178A may also have an orifice-less structure that does not have orifice 177A.

[0162] The valve structure 225A has a rod 21A that is partially different from the rod 21, instead of the rod 21. The rod 21A has a mounting shaft 28A that is partially different from the mounting shaft 28, instead of the mounting shaft 28. The mounting shaft 28A has a passage groove 251 and a passage groove 252 formed on the outer periphery thereof, in addition to the passage grooves 29 to 31 of the first embodiment.

[0163] The passage groove 251 is annular and is formed around the entire circumference of the mounting shaft portion 28A. The passage groove 251 is provided on the opposite side of the mounting shaft portion 28A from the main shaft portion 27 in the axial direction of the mounting shaft portion 28A relative to the passage groove 30.

[0164] The passage groove 252 extends along the axial direction of the mounting shaft portion 28A and connects the passage groove 30 and the passage groove 251. The passage in the passage groove 252 connects the passage in the passage groove 30 and the passage in the passage groove 251.

[0165] The passage grooves 29 to 31, 251, and 252 may be formed by making the inside of the rod 21B hollow.

[0166] The valve structure 225A has an extremely low speed damping force generating portion 261. As shown in Fig. 9 , a disk 262 is provided on the axially opposite side of the valve member 176A of the valve mechanism 178A from the pilot case 56, with the mounting shaft portion 28A of the rod 21A fitted radially inward. On the axially opposite side of the disk 262 from the valve member 176A, the extremely low speed damping force generating portion 261 is provided on the axially opposite side of the disk 262 from the valve member 176A, with the mounting shaft portion 28A of the rod 21A fitted radially inward. Disks 61, 62 and an annular member 63 similar to those of the first embodiment are provided on the axially opposite side of the extremely low speed damping force generating portion 261 from the disk 262.

[0167] The extremely low speed damping force generating section 261 has, in the axial direction of the rod 21, in order from the disk 262 side, a disk 271, a spring member 272, a disk 273, a valve disk 274, a valve seat member 276 with an O-ring 275 provided on the outer periphery, a valve disk 277, a disk 278, a spring member 279, and a cap member 280.

[0168] The cap member 280 is a one-piece molded product in the shape of a cylinder with a bottom. The cap member 280 has a bottom portion 301 and a tubular portion 302. The bottom portion 301 is in the shape of a perforated disk. The cap member 280 has the mounting shaft portion 28A of the rod 21A fitted into the radially inner side of the bottom portion 301. The tubular portion 302 is cylindrical. The tubular portion 302 extends from the outer peripheral edge of the bottom portion 301 to one axial side of the bottom portion 301. In the cap member 280, the tubular portion 302 extends from the bottom portion 301 toward the pilot case 56. The bottom portion 301 of the cap member 280 abuts against the disk 61.

[0169] The spring member 279 has a base plate portion 311 and multiple spring plate portions 312. The base plate portion 311 is a perforated disk. The mounting shaft portion 28A is fitted to the radially inner side of the base plate portion 311. The multiple spring plate portions 312 are provided on the outer periphery of the base plate portion 311. The multiple spring plate portions 312 are arranged at intervals in the circumferential direction of the base plate portion 311. The multiple spring plate portions 312 extend radially outward from the base plate portion 311. The spring plate portions 312 are inclined relative to the base plate portion 311 so that the extending tip ends are spaced apart from the base plate portion 311 in the axial direction of the base plate portion 311. The base plate portion 311 of the spring member 279 abuts against the bottom portion 301 of the cap member 280. The spring member 279 is provided on the bottom portion 301 such that the spring plate portion 312 is spaced apart from the bottom portion 301 in the axial direction of the base portion 311 .

[0170] The disk 278 is a circular plate with holes and is in contact with the base portion 311 of the spring member 279.

[0171] The valve disc 277 is a single circular disc with holes. The valve disc 277 abuts against the disc 278 and a plurality of spring plate portions 312 of the spring member 279. The valve disc 277 abuts against the valve seat member 276.

[0172] The valve seat member 276 is a perforated disk. A through-hole 321 is formed in the valve seat member 276, penetrating it in the axial direction. The through-hole 321 is formed in the radial center of the valve seat member 276. The through-hole 321 has a hole main body portion 322 and an axial groove 323. The axial groove 323 is recessed from the hole main body portion 322 outward in the radial direction of the valve seat member 276. The axial groove 323 extends in the axial direction of the valve seat member 276. The axial groove 323 is located on one side of the axial center of the valve seat member 276. A plurality of axial grooves 323 are formed in the valve seat member 276, spaced equally apart in the circumferential direction of the valve seat member 276. The mounting shaft portion 28A of the rod 21A is fitted into the hole main body portion 322 of the valve seat member 276. The passage in the axial groove 323 of the valve seat member 276 communicates with the passage in the passage groove 251 of the rod 21A.

[0173] The valve seat member 276 has an inner seat portion 331, a valve seat portion 332, an inner seat portion 333, a valve seat portion 334, and a main body portion 335. The inner seat portion 331 and the valve seat portion 332 are both formed at the end of the valve seat member 276 in the axial direction on the side where the axial groove 323 is formed. The inner seat portion 331 is disposed so as to surround the hole main body portion 322 and the axial groove 323. The inner seat portion 331 is annular. The valve seat portion 332 extends outward from the inner seat portion 331 in the radial direction of the inner seat portion 331.

[0174] The inner seat portion 333 and the valve seat portion 334 are both formed at the end of the valve seat member 276 opposite the end where the axial groove 323 is formed in the axial direction. The inner seat portion 333 is disposed so as to surround the hole main body portion 322. The inner seat portion 333 has an annular shape. The valve seat portion 334 extends outward from the inner seat portion 333 in the radial direction of the inner seat portion 333.

[0175] The main body portion 335 is a portion of the valve seat member 276 between the inner seat portion 331 and the valve seat portion 332 and the inner seat portion 333 and the valve seat portion 334 in the axial direction. The main body portion 335 is in the shape of a perforated disk.

[0176] The inner seat portion 331 protrudes axially from the inner peripheral edge of the main body portion 335 on the side where the axial groove 323 is formed. The inner seat portion 331 is annular and centered on the central axis of the main body portion 335. The valve seat portion 332 protrudes radially outward from the inner seat portion 331 and axially from the main body portion 335 on the same side as the inner seat portion 331. The inner seat portion 331 has a flat tip end surface on the side opposite the main body portion 335. The valve seat portion 332 also has a flat tip end surface on the side opposite the main body portion 335. The tip end surfaces of the inner seat portion 331 and the valve seat portion 332 extend in a direction perpendicular to the axis of the main body portion 335. The tip end surfaces of the inner seat portion 331 and the valve seat portion 332 are arranged on the same plane.

[0177] The inner seat portion 333 protrudes from the inner peripheral edge of the main body portion 335 opposite the side where the axial groove 323 is formed, along the axial direction of the main body portion 335, toward the opposite side from the inner seat portion 331. The inner seat portion 333 has an annular shape centered on the central axis of the main body portion 335. The valve seat portion 334 protrudes from the main body portion 335 along the axial direction of the main body portion 335, on the radially outer side of the inner seat portion 333, toward the same side as the inner seat portion 331. The inner seat portion 333 has a flat leading end surface on the opposite side from the main body portion 335. The valve seat portion 334 also has a flat leading end surface on the opposite side from the main body portion 335. The leading end surfaces of the inner seat portion 333 and the valve seat portion 334 extend in a direction perpendicular to the axis of the main body portion 335. The leading end surfaces of the inner seat portion 333 and the valve seat portion 334 are arranged on the same plane.

[0178] The valve seat portion 332 has a plurality of valve seat constituent portions 341. These valve seat constituent portions 341 have the same shape. These valve seat constituent portions 341 are arranged at equal intervals in the circumferential direction of the main body portion 335. These valve seat constituent portions 341 extend radially outward from the inner seat portion 331 in the radial direction of the inner seat portion 331.

[0179] A passage recess 342 is formed inside each valve seat constituent portion 341. The passage recess 342 is formed by being surrounded by the valve seat constituent portion 341 and a part of the inner seat portion 331. The passage recess 342 is recessed in the axial direction of the main body portion 335 from the tip surface on the protruding side of the valve seat constituent portion 341. The bottom surface of the passage recess 342 is formed in the main body portion 335. The passage recess 342 is formed inside all of the valve seat constituent portions 341. A passage hole 343 is formed inside the passage recess 342, penetrating the main body portion 335 in the axial direction. The passage hole 343 is parallel to the central axis of the main body portion 335. The passage hole 343 is formed in the bottom surface of all of the passage recesses 342.

[0180] The valve seat portion 334 has a plurality of valve seat constituent portions 351. These valve seat constituent portions 351 have the same shape. These valve seat constituent portions 351 are arranged at equal intervals in the circumferential direction of the main body portion 335. These valve seat constituent portions 351 extend radially outward from the inner seat portion 333 in the radial direction of the inner seat portion 333. The valve seat constituent portions 351 have the same shape as the valve seat constituent portions 341.

[0181] A passage recess 352 is formed inside each valve seat constituent portion 351. The passage recess 352 is formed by being surrounded by the valve seat constituent portion 351 and a part of the inner seat portion 333. The passage recess 352 is recessed in the axial direction of the main body portion 335 from the tip surface on the protruding side of the valve seat constituent portion 351. The bottom surface of the passage recess 352 is formed in the main body portion 335. The passage recess 352 is formed inside all of the valve seat constituent portions 351. A passage hole 353 is formed inside the passage recess 352, penetrating the main body portion 335 in the axial direction. The passage hole 353 is parallel to the central axis of the main body portion 335. The passage hole 353 is formed in the bottom surface of all of the passage recesses 352.

[0182] Here, the arrangement pitch of the multiple valve seat constituent portions 341 in the circumferential direction of the main body portion 335 is the same as the arrangement pitch of the multiple valve seat constituent portions 351 in the circumferential direction of the main body portion 335. The valve seat constituent portions 341 and 351 are arranged with a half-pitch offset from each other in the circumferential direction of the main body portion 335. The passage hole 343 is arranged between the valve seat constituent portions 351 that are adjacent in the circumferential direction of the main body portion 335. Therefore, the passage hole 343 is arranged outside the range of the valve seat portion 334. The passage hole 353 is arranged between the valve seat constituent portions 341 and 341 that are adjacent in the circumferential direction of the main body portion 335. Therefore, the passage hole 353 is arranged outside the range of the valve seat portion 332.

[0183] A passage groove 355 is formed in the inner seat portion 331 of the valve seat member 276, penetrating the inner seat portion 331 in the radial direction. The passage groove 355 opens between adjacent valve seat constituent portions 341 in the circumferential direction of the main body portion 335. The passage groove 355 opens into the axial groove 323. A plurality of passage grooves 355 (only one is shown in FIG. 9 because it is a cross-section) are provided at equal intervals in the circumferential direction of the valve seat member 276.

[0184] The passage in the passage recess 352 and the passage in the passage hole 353 form a member passage 361. A plurality of member passages 361 are provided at intervals in the circumferential direction of the main body 335. The passage in the passage recess 342 and the passage in the passage hole 343 form a member passage 362. A plurality of member passages 362 are provided at intervals in the circumferential direction of the main body 335. The passage in the passage groove 355 forms an orifice 356 (third pressure reduction flow path) that narrows the flow path.

[0185] A seal groove 365 is formed in the valve seat member 276 at the axial center of the outer periphery of the main body portion 335. The seal groove 365 is recessed radially inward from the outer periphery of the main body portion 335. The seal groove 365 is annular. An O-ring 275 is disposed in this seal groove 365. The valve seat member 276 is fitted at its outer periphery into the cylindrical portion 302 of the cap member 280, with the inner seat portion 331 and the valve seat portion 332 facing the bottom portion 301 of the cap member 280. In this state, the O-ring 275 seals the gap between the cylindrical portion 302 of the cap member 280 and the valve seat member 276.

[0186] The bottom 301 side portion of the cap member 280, the O-ring 275, and the valve seat member 276 form a cap chamber 381. The cap chamber 381 is constantly in communication with the member passage 361 and the orifice 356. A valve disc 277 is provided within the cap chamber 381.

[0187] The valve disc 277 is removably seated on the valve seat portion 332. The valve disc 277 opens and closes the component passage 362 by reseating from and seating on the valve seat portion 332. When the valve disc 277 is seated on the valve seat portion 332, it closes the component passage 362. When the valve disc 277 is released from the valve seat portion 332, it opens the component passage 362. The spring member 279 presses the valve disc 277 against the valve seat portion 332 with its spring force. When the valve disc 277 is closed, it separates the component passage 362 from the cap chamber 381. When the valve disc 277 is open, it connects the component passage 362 to the cap chamber 381. Therefore, when the valve disc 277 is open, it connects the second chamber 20, the component passage 362, the cap chamber 381, the component passage 361, and the orifice 256.

[0188] The valve disc 274 is a single, perforated, circular disc. The valve disc 274 is capable of being seated on and removed from the valve seat portion 334. The valve disc 274 opens and closes the member passage 361 by being seated on and removed from the valve seat portion 334. When the valve disc 274 is seated on the valve seat portion 334, it closes the member passage 361. When the valve disc 274 is released from the valve seat portion 334, it opens the member passage 361. The valve disc 274 can be a common part having the same shape as the valve disc 277.

[0189] The disk 273 is a circular disk with holes. The disk 273 abuts against the valve disk 274. The disk 273 can be a common part having the same shape as the disk 278.

[0190] The spring member 272 has a base plate 371 and multiple spring plate portions 372. The base plate 371 is a perforated disk. The mounting shaft 28A is fitted to the radially inner side of the base plate 371. The multiple spring plate portions 372 are provided on the outer periphery of the base plate 371. The multiple spring plate portions 372 are arranged at intervals in the circumferential direction of the base plate 371. The multiple spring plate portions 372 extend radially outward from the base plate 371. The spring plate portions 372 are inclined relative to the base plate 371 so that the extending tip ends are spaced apart from the base plate 371 in the axial direction of the base plate 371. The spring member 272 abuts against the disk 273 at the base plate 371 and is attached to the mounting shaft 28A so that the spring plate portions 372 extend from the base plate 371 toward the valve disk 274 in the axial direction of the base plate 371. The spring member 272 has a plurality of spring plate portions 372 that come into contact with the valve disc 274. The spring member 272 presses the valve disc 274 against the valve seat portion 334 of the valve seat member 276 with its spring force. The spring member 272 can be a common part having the same shape as the spring member 279.

[0191] In the shock absorber 1A, the passage within the large diameter hole portion 606 of the piston 18, the passages within the passage grooves 29-31, 251, and 252 of the rod 21, the passage within the axial groove 102 of the pilot case 56, and the passage within the axial groove 323 of the valve seat member 276 constitute a rod-side chamber 105A provided on the rod 21A side. The rod-side chamber 105A communicates with the piston passage 39 via the orifice 608 of the piston 18. The rod-side chamber 105A communicates with the passage within the outer passage recess 96 via the passage within the passage groove 90 of the pilot case 56. The rod-side chamber 105A communicates with the orifice 356 of the valve seat member 276.

[0192] In the extremely low speed damping force generating unit 261, the valve seat portion 332, the valve disc 277, and the spring member 279 constitute a valve mechanism 385. The member passage 362, a passage formed between the valve disc 277 and the valve seat portion 332 when the valve is open, and the cap chamber 381 constitute a flow path 386 that communicates with the rod-side chamber 105A via the orifice 356. The valve mechanism 385 is provided in the flow path 386. When the piston 18 moves toward the second chamber 20, the valve mechanism 385 opens, allowing oil L to flow from the second chamber 20 into the flow path 386. The flow path 386 then flows into the first chamber 19 via the orifice 356, the rod-side chamber 105A, the orifice 608 of the piston 18, and the piston passage 39. The valve mechanism 385 provided in the flow path 386 generates a damping force by controlling the flow of oil L in the flow path 386.

[0193] Flow path 386 is provided in parallel with flow path 210. The valve member 212 of valve mechanism 42 provided in flow path 210 has higher rigidity than the valve disc 277 of valve mechanism 385 provided in flow path 386. Therefore, the valve member 212 of valve mechanism 42 has a higher valve opening pressure than the valve disc 277. As a result, valve mechanism 385 opens before the valve member 212 of valve mechanism 42 opens, generating a damping force.

[0194] In the extremely low speed damping force generating unit 261, the valve seat portion 334, the valve disc 274, and the spring member 272 constitute a valve mechanism 391. The cap chamber 381, the member passage 361, and a passage created between the valve disc 274 and the valve seat portion 334 when the valve is open constitute a flow path 401. The valve mechanism 391 is provided in the flow path 401. When the piston 18 moves toward the first chamber 19, the valve mechanism 391 opens the flow path 401, allowing the oil L flowing from the first chamber 19 via the piston passage 39, the orifice 608 of the piston 18, the rod side chamber 105A, and the orifice 356 to flow into the second chamber 20. The valve mechanism 391 provided in the flow path 401 generates a damping force by controlling the flow of oil in the flow path 401. The orifice 356 has a flow passage cross-sectional area smaller than that of the orifice 608 and larger than that of the orifice 173 .

[0195] Flow path 401 is provided in parallel with flow path 162 and flow path 181. The valve member 161 of valve mechanism 41 provided in flow path 162 has higher rigidity than the valve disc 274 of valve mechanism 391 provided in flow path 401. The valve member 176A of valve mechanism 178A provided in flow path 181 has higher rigidity than the valve disc 274 of valve mechanism 391 provided in flow path 401. Therefore, both valve member 161 and valve member 176A have a higher valve opening pressure than the valve disc 274. As a result, valve mechanism 391 opens before the valve member 161 of valve mechanism 41 opens and before the valve member 176A of valve mechanism 178A opens, generating a damping force.

[0196] Here, the valve structure 225A may have an orifice-less structure in which the valve mechanism 42 does not have the orifice 213. In other words, the disk 202 may not have the notch 211 formed therein.

[0197] A hydraulic circuit diagram of the valve structure 225A is as shown in Fig. 10. As shown in Fig. 10, in the valve structure 225A, an orifice 356 is provided branching off from a portion of the flow path 181 between the orifice 608 and the valve mechanism 178 and orifice 177, and an extremely low speed damping force generating unit 261 having a valve mechanism 385 and a valve mechanism 391 is provided between the orifice 356 and the second chamber 20.

[0198] 10 , the shock absorber 1A has a flow path 162 that communicates from the first chamber 19 to the second chamber 20, a valve mechanism 41 that is a valve provided in the flow path 162, and an orifice 608 that receives the oil L from the first chamber 19 and reduces the pressure of the oil L by a first strength. The shock absorber 1A also has an orifice 173 that is provided in parallel to the flow path 162 and has a smaller cross-sectional area than the orifice 608, and an orifice 356 that is provided downstream of the orifice 608 in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 608 but a larger cross-sectional area than the orifice 173. The shock absorber 1A also has a pressure chamber 151 (see FIG. 6) located downstream of the orifice 173 and capable of applying pressure to the valve mechanism 41 in the valve closing direction by oil liquid L, and a frequency sensitive mechanism 185 that is provided in the pressure chamber 151 and deforms in response to the internal pressure of the pressure chamber 151, changing the volume of the pressure chamber 151. The shock absorber 1A also has a valve 178A located downstream of the orifice 608 and arranged in parallel to the orifice 356, which allows the inflowing oil liquid L to flow to the downstream second chamber 20.

[0199] In addition, in the shock absorber 1A, the valve mechanism 41 is provided in parallel to the orifice 608, and the orifice 173 is provided downstream of the orifice 608 and in series with the orifice 608.

[0200] In the valve structure 225A, in a first extremely low speed region on the low speed side of the extremely low speed region X1 during the extension stroke in which the rod 21 moves in the extension side, the oil L in the first chamber 19 flows through the flow path 181 and from the orifice 177A at the end thereof to the second chamber 20. The oil L from the first chamber 19 also flows into the second chamber 20 through the flow path 210 including the orifice 213. Therefore, the valve structure 225A generates a damping force with orifice characteristics in the first extremely low speed region on the low speed side of the extremely low speed region X1.

[0201] In the valve structure 225A, in a second extremely low speed region that is faster than the first extremely low speed region of the extremely low speed region X1 during the extension stroke in which the rod 21 moves to the extension side, the oil L in the first chamber 19 passes from the flow path 181 through the orifice 356 and flows into the second chamber 20 in the flow path 401 while opening the valve mechanism 391. Therefore, the valve structure 225A generates a damping force with valve characteristics in the second extremely low speed region that is on the higher side of the extremely low speed region X1.

[0202] In this way, the valve structure 225A generates a damping force with valve characteristics even in the extremely low speed region X1 of the extension stroke in which the rod 21 moves toward the extension side.

[0203] In the valve structure 225A, in a third extremely low speed region on the low speed side of the extremely low speed region X4 during the compression stroke in which the rod 21 moves toward the compression side, the oil L in the second chamber 20 flows into the first chamber 19 via the piston passage 40 including the orifice 213. The oil L in the second chamber 20 also flows from the orifice 177A into the first chamber 19 via the flow path 181. Therefore, the valve structure 225A generates a damping force with orifice characteristics in the third extremely low speed region on the low speed side of the extremely low speed region X4.

[0204] In the valve structure 225A, in a fourth extremely low speed region that is faster than the third extremely low speed region of the extremely low speed region X4 during the compression stroke in which the rod 21 moves toward the compression side, the oil L in the second chamber 20 passes through the orifice 356 in the flow path 386 while opening the valve mechanism 385, and flows into the first chamber 19 via the flow path 181. Therefore, the valve structure 225A generates a damping force with valve characteristics in the fourth extremely low speed region that is on the higher side of the extremely low speed region X4.

[0205] In this way, the valve structure 225A generates a damping force with valve characteristics even in the extremely low speed range X4 of the compression stroke in which the rod 21 moves toward the compression side.

[0206] The shock absorber 1A of the second embodiment has a flow path 162 that communicates from the first chamber 19 to the second chamber 20 in the cylinder 2, and a valve mechanism 41 that is provided in the flow path 162. The shock absorber 1A also has an orifice 608 that receives the oil liquid L from the first chamber 19 and reduces the pressure of the oil liquid L at a first strength, an orifice 173 that is provided in parallel to the flow path 162 and has a smaller cross-sectional area than the orifice 608, and an orifice 356 that is provided in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 608 but a larger cross-sectional area than the orifice 173. The shock absorber 1A also has a pressure chamber 151 that is downstream of the orifice 173 and can apply pressure from the oil liquid L to the valve mechanism 41 in a valve-closing direction, and a frequency sensitive mechanism 185 that is provided in the pressure chamber 151 and deforms in response to the internal pressure of the pressure chamber 151 to change the volume of the pressure chamber 151. The shock absorber 1A also has a valve mechanism 178A that is provided in parallel with the orifice 356 and that allows the oil L that has flowed in to flow into the second chamber 20 downstream.

[0207] The shock absorber 1A can make the change in the damping characteristics gentler because it has the valve mechanism 41, the valve mechanism 178A, and the orifice 356. The shock absorber 1A further has the orifice 608 and the orifice 173, which allows for detailed adjustment of the damping force characteristics and makes it possible to make the change in the damping characteristics even gentler.

[0208] The shock absorber 1A has the extremely low speed damping force generating section 261, and therefore can generate a damping force with valve characteristics in the extremely low speed range X1 of the extension stroke and the extremely low speed range X4 of the compression stroke.

[0209] The shock absorber 1A has the same configuration as the shock absorber 1 of the first embodiment except that it has the very low speed damping force generating section 261, and therefore can achieve the same effects as the shock absorber 1 of the first embodiment.

[0210] In shock absorber 1A, by eliminating orifice 177A and orifice 213, in other words by making valve mechanism 178A and valve mechanism 42 an orifice-less structure, it is possible to generate a damping force with valve characteristics even in the first very-low speed region on the low-speed side of very-low speed region X1 and in the third very-low speed region on the low-speed side of very-low speed region X4.

[0211] [Third Embodiment] Next, a third embodiment will be described, focusing on differences from the first embodiment, mainly with reference to Figures 11 to 14. Note that parts common to the first embodiment will be designated by the same names and symbols.

[0212] 11 , the shock absorber 1B of the third embodiment has a valve structure 225B that is partially different from the valve structure 225 of the first embodiment, instead of the valve structure 225. The valve structure 225B has a rod 21B that is partially different from the rod 21 of the first embodiment, instead of the rod 21. The rod 21B has a passage hole 451 formed therein. The rod 21B has a main shaft portion 27B that differs from the main shaft portion 27 in that a portion of the passage hole 451 is formed therein, and a mounting shaft portion 28B that differs from the mounting shaft portion 28 in that the remaining portion of the passage hole 451 is formed therein.

[0213] The passage hole 451 has a radial hole portion 452 , an axial hole portion 453 , and a radial hole portion 454 .

[0214] The radial hole 452 penetrates the main shaft portion 27B in the radial direction of the main shaft portion 27B. The radial hole 452 is formed in a portion of the main shaft portion 27B on the mounting shaft portion 28B side in the axial direction. The radial hole 452 opens to the first chamber 19.

[0215] Axial hole portion 453 extends along the axial direction of rod 21B from the center of radial hole portion 452 in the radial direction of main shaft portion 27B. Axial hole portion 453 extends from radial hole portion 452 to the end face of mounting shaft portion 28B on the axial side opposite to main shaft portion 27B.

[0216] The radial hole 454 extends in the radial direction of the mounting shaft portion 28B. The radial hole 454 is formed in a portion of the mounting shaft portion 28B in the axial direction between the main shaft portion 27B and the male thread 32. The radial hole 454 intersects with the axial hole 453.

[0217] The mounting shaft portion 28B is formed with an annular passage groove 455 that is recessed radially inward from the outer peripheral surface of the mounting shaft portion 28B. The passage groove 455 is formed in a portion of the mounting shaft portion 28B in the axial direction between the main shaft portion 27B and the male thread 32. A radial hole portion 454 opens into the bottom surface of the passage groove 455.

[0218] The mounting shaft portion 28B has an axial groove 456 formed therein, recessed radially inward from the outer peripheral surface of the mounting shaft portion 28B. The axial groove 456 extends in the axial direction of the mounting shaft portion 28B. The axial groove 456 extends from the passage groove 455 along the axial direction of the mounting shaft portion 28B toward the male thread 32, to a position just short of the male thread 32. The mounting shaft portion 28B has a plurality of axial grooves 456 formed therein at intervals in the circumferential direction of the mounting shaft portion 28B.

[0219] The valve structure 225B has a blocking member 461 that is fitted into an end of the axial hole 453 on the opposite side in the axial direction from the radial hole 452. The blocking member 461 is fitted into and fixed to a portion of the axial hole 453 that is on the opposite side in the axial direction from the radial hole 452 relative to the radial hole 454. The blocking member 461 blocks a portion of the axial hole 453 that is on the opposite side in the axial direction from the radial hole 452 relative to the radial hole 454.

[0220] The valve structure 225B has a piston 18B that is partially different from the piston 18 of the first embodiment, instead of the piston 18. The piston 18B has a piston body 33B that is partially different from the piston body 33, instead of the piston body 33. The piston body 33B is integrally molded. The piston body 33B has an insertion hole 465 that penetrates the piston body 33B in the axial direction, formed in the radial center. The insertion hole 465 has an inner diameter that is equal to the inner diameter of the fitting hole 611 of the piston body 33 over substantially the entire axial length of the piston body 33B.

[0221] In the valve structure 225B, the configuration between the piston 18B and the retainer 221 is different from the configuration between the piston 18B and the retainer 221 of the valve structure 225 of the first embodiment.

[0222] The valve structure 225B has, on the valve seat portion 47 and inner seat portion 48 side of the piston 18B, in order from the piston 18B side in the axial direction, one disc 51, one valve disc 52, multiple valve discs 473, multiple valve discs 474, and multiple discs 475. The valve discs 473, 474, and discs 475 are all made of metal, and each is in the form of a perforated circular flat plate of a constant thickness into which the mounting shaft portion 28B of the rod 21B can be fitted.

[0223] The valve disc 473 is a common part similar to the valve disc 52. The valve disc 474 has an outer diameter smaller than that of the valve disc 473. The disc 475 has an outer diameter smaller than that of the valve disc 474.

[0224] The valve discs 52, 473, and 474 constitute a valve member 161B that is removably seated on the valve seat portion 47. The valve member 161B, together with the valve seat portion 47 of the piston 18B, constitutes an extension-side valve mechanism 41B (fourth valve).

[0225] The valve member 161B, like the valve member 161 of the first embodiment, abuts against the valve seat portion 47 of the valve disc 52 and opens and closes the opening of the piston passage 39 by moving away from and abutting against the valve seat portion 47.

[0226] When the valve member 161B is released from the valve seat portion 47 and opens, it causes the oil liquid L in the first chamber 19 to flow into the second chamber 20 via the piston passage 39 and the passage between the valve member 161B and the valve seat portion 47. In other words, when the valve member 161B is released from the valve seat portion 47 and opens, it comprises valve discs 52, 473, 474 which cause the oil liquid L in the first chamber 19 to flow into the second chamber 20 via the flow passage 162. When the valve member 161B is seated on the valve seat portion 47, it closes the opening of the flow passage 162 on the second chamber 20 side.

[0227] The valve structure 225B is provided, on the opposite side of the disc 475 from the piston 18B in the axial direction, with, in order from the disc 475 side, a valve member 176 consisting of multiple valve discs 60 and one valve disc 59, one disc 58, a valve member 171 consisting of multiple valve discs 57, one pilot case 56, and one pilot valve 53, all of which are similar to the valve structure 225 of the first embodiment.

[0228] In the valve structure 225B, the orientations and relative positions of the valve member 176, disc 58, valve member 171, pilot case 56, and pilot valve 53 in the axial direction of the rod 21B are opposite to those of the valve member 176, disc 58, valve member 171, pilot case 56, and pilot valve 53 in the axial direction of the rod 21B in the valve structure 225 of the first embodiment. As shown in Fig. 12, the axial groove 102 of the pilot case 56 overlaps with the passage groove 455 of the rod 21B in the axial direction of the rod 21B. The passage in the axial groove 102 communicates with the passage in the passage groove 455 of the rod 21B.

[0229] A free valve 111 similar to the valve structure 225 of the first embodiment is arranged in the pilot case 56 so as to face the outer cylindrical portion 72 side of the bottom portion 71 in the axial direction.

[0230] The valve structure 225B includes a seat member 495, a disk 496, and an annular member 63 similar to that of the first embodiment, which are provided on the opposite side of the pilot case 56 in the axial direction of the pilot valve 53, with the mounting shaft portion 28B of the rod 21B fitted inside each of them. The seat member 495 may be made of metal, but any material may be used. The seat member 495 is a circular plate with holes, into which the mounting shaft portion 28B of the rod 21B can be fitted. The disk 496 is a circular plate with holes, into which the mounting shaft portion 28B of the rod 21B can be fitted inside.

[0231] The seat member 495 has a through-hole 511 formed in its radial center, which passes through the seat member 495 in the axial direction of the seat member 495. The seat member 495 has a bottom portion 512, an inner seat portion 513, and a valve seat portion 514 (first valve seat).

[0232] The bottom portion 512 is a circular plate with holes. The inner seat portion 513 is annular and protrudes from the inner periphery of the bottom portion 512 to one side in the axial direction of the bottom portion 512.

[0233] The valve seat portion 514 has an annular shape and is located radially outward of the inner seat portion 513. The valve seat portion 514 protrudes from the bottom portion 512 along the axial direction of the bottom portion 512 to the same side as the inner seat portion 513.

[0234] A passage recess 515 is formed between the inner seat portion 513 and the valve seat portion 514. The passage recess 515 is surrounded by the inner seat portion 513 and the valve seat portion 514. The passage recess 515 is continuous around the entire circumference of the seat member 495. The passage recess 515 is recessed in the axial direction of the seat member 495 from the tip surface on the protruding side of the inner seat portion 513 and the tip surface on the protruding side of the valve seat portion 514. The bottom surface of the passage recess 515 is formed by the bottom portion 512.

[0235] A passage groove 516 is formed in the inner seat portion 513 and in a portion of the bottom portion 512 on the inner seat portion 513 side in the axial direction, penetrating the inner seat portion 513 in the radial direction of the inner seat portion 513. The passage groove 516 overlaps the passage recess 515 in the radial direction of the bottom portion 512 and opens into the passage recess 515. A plurality of passage grooves 516 are formed in the seat member 495 at intervals in the circumferential direction of the seat member 495. It is sufficient that at least one passage groove 516 is provided in the seat member 495.

[0236] The through hole 511 has a large diameter hole portion 521 and a small diameter hole portion 522. The large diameter hole portion 521 has a larger diameter than the small diameter hole portion 522. The small diameter hole portion 522 is formed in the bottom portion 512. The large diameter hole portion 521 is formed in the inner seat portion 513 and in a portion of the bottom portion 512 on the inner seat portion 513 side in the axial direction. In the seat member 495, the large diameter hole portion 521 is formed to a position deeper than the bottom surface of the passage groove 516. The mounting shaft portion 28B of the rod 21B is fitted into the small diameter hole portion 522 of the through hole 511 of the seat member 495. In the axial direction of the rod 21B, the large diameter hole portion 521 is positioned overlapping the axial groove 456 of the rod 21B. As a result, the passage in the large diameter hole portion 521 of the seat member 495 is connected to the passage in the axial groove 456 of the rod 21B.

[0237] The passage within the passage hole 451 of the rod 21B, the passage within the passage groove 455, the passage within the axial groove 456, the passage within the axial groove 102 of the pilot case 56, and the passage within the large diameter hole portion 521 of the seat member 495 constitute the rod side chamber 105B.

[0238] The pilot valve 53 has a valve disc 141 (first valve element) with an outer diameter slightly larger than the outer diameter of a valve seat portion 514 of the seat member 495. The valve disc 141 abuts against the valve seat portion 514, and opens and closes the passage in the passage recess 515 by moving away from and abutting against the valve seat portion 514.

[0239] The valve disc 141 constitutes a valve mechanism 532 (first valve) together with a valve seat portion 514 of the seat member 495. When the valve disc 141 is released from the valve seat portion 514 and opens, the oil L in the first chamber 19 shown in FIG. 11 flows into the second chamber 20 via the passage in the passage hole 451 of the rod 21B, the passage in the passage groove 455, the passage in the axial groove 456, the passage in the large diameter hole portion 521 of the seat member 495 shown in FIG. 12, the passage in the passage groove 516 of the seat member 495, the passage in the passage recess 515 of the seat member 495, and the passage between the valve disc 141 and the valve seat portion 514.

[0240] The passage in the passage hole 451 of the rod 21B, the passage in the passage groove 455, the passage in the axial groove 456, the passage in the large diameter hole portion 521 of the seat member 495, the passage in the passage groove 516, the passage in the passage recess 515, and the passage between the valve disc 141 and the valve seat portion 514 constitute a flow path 535 (first flow path) that communicates the first chamber 19 and the second chamber 20 shown in FIG. 11 . The flow path 535 is a flow path through which oil liquid L flows as a fluid flowing out from the first chamber 19, which is one of the first chamber 19 and the second chamber 20. The rod-side chamber 105B is part of the flow path 535. The passage in the passage groove 516 formed in the inner seat portion 513 of the seat member 495 constitutes an orifice 536 (first pressure reduction flow path) that reduces the pressure by throttling the flow path 535.

[0241] The flow path 535 serves as an extension-side flow path through which oil L flows as a fluid from the first chamber 19 to the second chamber 20 when the piston 18B moves toward the first chamber 19, i.e., during the extension stroke. An extension-side valve mechanism 532, consisting of the valve seat portion 514 and the valve disc 141, is provided in the flow path 535, and the valve disc 141 opens and closes the flow path 535 to suppress the flow of oil L, thereby generating a damping force. In other words, the valve disc 141 is provided in the flow path 535 to suppress the flow of oil L caused by the sliding of the piston 18B toward the extension side, thereby generating a damping force. In yet another way, the valve disc 141 allows oil from the first chamber 19, which is one of the first chamber 19 and the second chamber 20, to flow to the second chamber 20, which is the other chamber.

[0242] The rod side chamber 151B including the passage in the passage hole 451 of the rod 21B, the passage in the passage groove 90 of the pilot case 56 and the passage in the outer passage recess 96, and the orifice 177 or the passage between the open valve member 176 and the outer valve seat portion 76 form a passage 181B (second passage) that is partially parallel to the passage 535 and through which the oil liquid L flows from the first chamber 19 to the second chamber 20. In other words, the passage 181B is a passage that runs from the first chamber 19 toward the valve mechanism 178 and passes through the orifice 177 or the open valve mechanism 178.

[0243] The valve structure 225B of the third embodiment has a flow path 535 that communicates with the second chamber 20, which is located downstream of the first chamber 19. The valve structure 225B has a valve mechanism 532 that is provided in the flow path 535 and includes a valve seat 514 and a valve disc 141 that seats and disengages from the valve seat 514. The valve structure 225B has a pressure chamber 151 that can apply pressure from oil liquid L in a valve-closing direction to the valve disc 141. The valve structure 225B has a flow path 181B that is at least partially parallel to the flow path 535 and communicates with the second chamber 20, which is located downstream of the first chamber 19. The valve structure 225B has a valve mechanism 178 that is provided in the flow path 181B and includes an outer valve seat 76 and a valve member 176 that seats and disengages from the outer valve seat 76. The valve structure 225B has a communication passage 182 that communicates from the inside of the outer valve seat portion 76 on the upstream side to the pressure chamber 151 on the downstream side.

[0244] A hydraulic circuit diagram of the valve structure 225B is shown in FIG. 13 . As shown in FIG. 13 , the valve structure 225B is provided with a flow path 535 connecting the first chamber 19 and the second chamber 20. The flow path 535 is provided with an orifice 536 on the first chamber 19 side and a valve mechanism 532 on the second chamber 20 side. The valve structure 225B also is provided with a flow path 181B connecting the first chamber 19 and the second chamber 20. The flow path 181B is provided with a valve mechanism 178 and an orifice 177. The valve mechanism 178 and the orifice 177 are provided in parallel. The valve structure 225B also has a valve mechanism 172 and an orifice 173 branched from the flow path 181B and provided in parallel. The valve mechanism 172 and the orifice 173 are connected to the pressure chamber 151 (see FIG. 6 ) of the valve opening control mechanism 186 via a communication path 182. The pressure in pressure chamber 151 acts on valve disc 141. Flow path 162B and flow path 210 are provided connecting second chamber 20 and first chamber 19. Flow path 162B is provided with valve mechanism 41B. Flow path 210 is provided with valve mechanism 42 and orifice 213 in parallel.

[0245] 13 , the valve structure 225B of the shock absorber 1B has a flow path 535 that communicates from the first chamber 19 to the second chamber 20, a valve mechanism 532 that is a valve provided in the flow path 535, and an orifice 536 that receives the oil liquid L from the first chamber 19 and reduces the pressure of the oil liquid L by a first strength. The valve structure 225B also has an orifice 173 that is provided in parallel to the flow path 535 and has a smaller cross-sectional area than the orifice 536, and an orifice 177 that is provided in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 536 but a larger cross-sectional area than the orifice 173. Furthermore, the valve structure 225B has a pressure chamber 151 (see FIG. 6) located downstream of the orifice 173 and capable of applying pressure to the valve mechanism 532 in a valve-closing direction by oil liquid L, and a valve-opening control mechanism 186 including a frequency-sensitive mechanism 185 (see FIG. 6) provided in the pressure chamber 151 and deforming in response to the internal pressure of the pressure chamber 151 to change the volume of the pressure chamber 151. Furthermore, the valve structure 225B has a valve mechanism 178 provided in parallel to the orifice 177 and capable of circulating the inflowing oil liquid L to the downstream second chamber 20.

[0246] In addition, in the valve structure 225 B, the valve mechanism 532 is provided downstream of and in series with the orifice 536 , and the orifice 173 is provided in parallel with the orifice 536 .

[0247] The valve structure 225B is provided in parallel with the orifice 536 and includes a flow path 162B that communicates from the first chamber 19 to the second chamber 20, and a valve mechanism 41B that is a valve provided in the flow path 162B.

[0248] The valve structure 225B also includes a valve mechanism 41B that restricts the oil L flowing from the first chamber 19 to the second chamber 20 by the piston 18B.

[0249] Next, the operation of the valve structure 225B will be described with reference to the characteristic line diagram of the damping force versus piston speed shown in Fig. 14. In Fig. 14, the characteristic line diagram of the valve structure 225B is shown by solid lines Y11, Y12, and Y13.

[0250] During the extension stroke in which the rod 21 moves toward the extension side, when the piston speed is in the extremely low speed region X11 slower than the eleventh predetermined speed and a low frequency input is applied in which the piston frequency is lower than the predetermined frequency, the oil liquid L from the first chamber 19 flows into the pressure chamber 151 through the passage in the passage hole 451 of the rod 21B, the rod side chamber 151B, the passage in the passage groove 90 of the pilot case 56, the passage in the outer passage recess 96, and the communicating passage 182 including the orifice 173.

[0251] During the extension stroke of the low-frequency input in the extremely low speed range X11, the amplitude of the piston 18 is large. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation, and preventing hydraulic fluid L from flowing from the first chamber 19 to the pressure chamber 151. At this time, the variable chamber 152 discharges hydraulic fluid L to the second chamber 20 through the passage in the outer through-hole 87. During the extension stroke of the low-frequency input in the extremely low speed range X11, when the free valve 111 abuts against the recess 82 and restricts further deformation, the volume of the pressure chamber 151 does not increase. This increases the pressure in the pressure chamber 151, restricting the opening of the valve disc 141 of the valve mechanism 532. In other words, the valve mechanism 532 does not open the valve disc 141.

[0252] Therefore, during the extension stroke when a low frequency is input in the extremely low speed range X11, the hydraulic oil L from the first chamber 19 flows through the rod side chamber 151B including the passage in the passage hole 451 of the rod 21B, the passage in the passage groove 90 of the pilot case 56, the passage in the outer passage recess 96, and the orifice 177, i.e., through the flow path 181B, and then from the orifice 177 at the end of the flow path 181B to the second chamber 20. The hydraulic oil L from the first chamber 19 also flows to the second chamber 20 through the flow path 210 including the orifice 213. Therefore, during the extension stroke when a low frequency is input in the extremely low speed range X11, a damping force with orifice characteristics is generated, as shown by the solid line Y11 in FIG. 14 . Therefore, during the extension stroke when a low frequency is input in the extremely low speed range X11, the damping force characteristic with respect to piston speed is such that the rate of increase in the damping force is relatively high as the piston speed increases.

[0253] During the extension stroke, when the piston speed is in the very low speed region X11 which is slower than the 11th predetermined speed and the piston frequency is a high frequency input which is equal to or higher than a predetermined frequency, the oil liquid L from the first chamber 19 flows into the pressure chamber 151 through the flow path 181B and the connecting passage 182 which branches off from the middle of the flow path 181B and includes the orifice 173, just as when a low frequency is input in the very low speed region X11.

[0254] During the extension stroke when high frequency is input in this very low speed range X11, the amplitude of the piston 18 is small. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, when oil L from the first chamber 19 is introduced into the pressure chamber 151 from the flow path 181B via the communication passage 182, the free valve 111, which had previously been in a flat plate shape and abutting against the seat portion 80, elastically deforms to enter the recess 82 while blocking communication between the pressure chamber 151 and the variable chamber 152, thereby expanding the volume of the pressure chamber 151 and discharging oil L from the variable chamber 152 to the second chamber 20 via the passage in the outer through-hole 87.

[0255] While the free valve 111 is deformed in this way, the oil liquid L is introduced from the first chamber 19 into the pressure chamber 151, but because the amount of oil liquid L introduced from the first chamber 19 into the pressure chamber 151 is small, the deformation of the free valve 111 is small and the free valve 111 does not come into contact with the recess 82 and is not restricted in deformation as in the case of low-frequency input. In this way, the bending of the free valve 111 suppresses the pressure rise in the pressure chamber 151, making it easier for the valve disc 141 to open.

[0256] Therefore, during the extension stroke when a high frequency is input in the extremely low speed range X11, the oil L from the first chamber 19 flows through the flow path 181B and the orifice 177 at its end into the second chamber 20. In addition, the oil L also flows from the flow path 535 into the second chamber 20 while opening the valve mechanism 532, i.e., while lifting the valve disc 141 off the valve seat 514. Therefore, as shown by the solid line Y12 in FIG. 14 , during the extension stroke when a high frequency is input in the extremely low speed range X11, a damping force with valve characteristics is generated. Therefore, during the extension stroke when a high frequency is input in the extremely low speed range X11, the damping force is lower than during the extension stroke when a low frequency is input in the extremely low speed range X11. Furthermore, during the extension stroke when a high frequency is input in the extremely low speed range X11, the damping force characteristic with respect to piston speed is such that the rate of increase in the damping force relative to the increase in piston speed is lower than during the extension stroke when a low frequency is input in the extremely low speed range X11.

[0257] During the extension stroke, when the piston speed is equal to or greater than an 11th predetermined speed and in a low-speed region X12 that is slower than a 12th predetermined speed that is faster than the 11th predetermined speed, and when a low-frequency input is made in which the piston frequency is lower than a predetermined frequency, oil L from the first chamber 19 flows from the flow path 181B to the pressure chamber 151 through a connecting passage 182 including an orifice 173, just as when a low-frequency input is made in the very low-speed region X11.

[0258] During the extension stroke of this low-frequency input in the low-speed range X12, the amplitude of the piston 18 is large, similar to the low-frequency input in the very-low-speed range X11. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation and preventing an increase in the volume of the pressure chamber 151. During the extension stroke of this low-frequency input in the low-speed range X12, the volume of the pressure chamber 151 does not increase, so the pressure in the pressure chamber 151 increases, inhibiting the opening of the valve disc 141 of the valve mechanism 532. That is, even during the extension stroke of the low-frequency input in the low-speed range X12, the valve disc 141 of the valve mechanism 532 does not open.

[0259] During the extension stroke when a low-frequency input is made in the low-speed range X12, the flow rate of hydraulic oil L flowing from the first chamber 19 to the flow path 181B is greater than during the extension stroke when a low-frequency input is made in the extremely low-speed range X11. Therefore, hydraulic oil L flows from the first chamber 19 to the second chamber 20 in the flow path 181B while opening the valve mechanism 178, i.e., while causing the valve member 176 to separate from the outer valve seat 76. As a result, a damping force with valve characteristics is generated, as shown by the solid line Y11 in Fig. 14. Therefore, during the extension stroke when a low-frequency input is made in the low-speed range X12, the rate of increase of the damping force relative to an increase in piston speed is lower than during the extension stroke when a low-frequency input is made in the extremely low-speed range X11.

[0260] During the extension stroke, when the piston speed is equal to or higher than an 11th predetermined speed and in a low-speed region X12 that is faster than a 12th predetermined speed that is faster than the 11th predetermined speed, and when a high-frequency input is applied at a piston frequency equal to or higher than a predetermined frequency, the oil liquid L from the first chamber 19 flows into the pressure chamber 151 via the flow path 181B and the connecting passage 182 that includes the orifice 173, just as in the case of a high-frequency input in the extremely low-speed region X11.

[0261] During the extension stroke when high frequency input is performed in the low speed range X12, the amplitude of the piston 18 is small, just as during high frequency input in the very low speed range X11. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, the bending of the free valve 111 can suppress the pressure increase in the pressure chamber 151, making it easier for the valve disc 141 to open.

[0262] Therefore, during the extension stroke when a high frequency input is received in the low speed range X12, the hydraulic oil L from the first chamber 19 flows into the second chamber 20 in the flow path 181B while opening the valve mechanism 178, i.e., while lifting the valve member 176 off the outer valve seat 76. At the same time, the hydraulic oil L from the first chamber 19 flows into the second chamber 20 in the flow path 535 while opening the valve mechanism 532, i.e., while lifting the valve disc 141 off the valve seat 514. Therefore, during the extension stroke when a high frequency input is received in the low speed range X12, the damping force is lower than that during the low frequency input in the low speed range X12, as shown by the solid line Y12 in Figure 14. Furthermore, during the extension stroke when a high frequency input is received in the low speed range X12, the damping force characteristic relative to the piston speed is such that the rate of increase in the damping force relative to an increase in piston speed is lower than that during the low frequency input in the very low speed range X11. Here, in the extension stroke when a high frequency is input in the low speed region X12, the characteristic of the damping force relative to the piston speed is such that the rate of increase of the damping force relative to the increase in piston speed is the same as in the extension stroke when a high frequency is input in the very low speed region X11.

[0263] During the extension stroke, when the piston speed is equal to or higher than the 12th predetermined speed and in the medium speed range X13 that is faster than the 12th predetermined speed and slower than the 13th predetermined speed, and when the piston frequency is low frequency input that is lower than the predetermined frequency, oil L from the first chamber 19 flows through the flow path 181B and into the pressure chamber 151 via the connecting passage 182 that includes the orifice 173, just as during the extension stroke during low frequency input in the low speed range X12.

[0264] During the extension stroke of this low-frequency input in the medium speed range X13, the amplitude of the piston 18 is large, similar to the low-frequency input in the low speed range X12. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation and preventing an increase in the volume of the pressure chamber 151. During the extension stroke of this low-frequency input in the medium speed range X13, the volume of the pressure chamber 151 does not increase, so the pressure in the pressure chamber 151 increases. However, the relationship of the forces (hydraulic pressure) acting on the valve disc 141 is such that the opening force applied from the flow path 535 is greater than the closing force applied from the pressure chamber 151. Therefore, during this low-frequency input in the medium speed range X13, as the piston speed increases, the valve disc 141 of the valve mechanism 532 opens farther away from the valve seat 514 than described above. As a result, in addition to the flow to the second chamber 20 through flow path 181B when valve mechanism 178 is opened, a larger amount of oil L flows into the second chamber 20 through flow path 535, which includes the passage between the valve disc 141 and the valve seat portion 514, further suppressing the increase in damping force. For this reason, as shown by the solid line Y11 in Fig. 14, the characteristic of the damping force relative to the piston speed is such that the rate of increase in damping force relative to an increase in piston speed is lower than that of the extension stroke when a low frequency is input in the low speed range X12.

[0265] During the extension stroke, when the piston speed is in the medium speed range X13 that is equal to or greater than the 12th predetermined speed but slower than the 13th predetermined speed, and when a high frequency input is applied with a piston frequency equal to or greater than a predetermined frequency, the oil liquid L from the first chamber 19 flows through the flow path 181B, as in the case of a high frequency input in the low speed range X12, and flows into the pressure chamber 151 via the connecting passage 182 that includes the orifice 173.

[0266] During the extension stroke when high frequency is input in the medium speed range X13, the amplitude of the piston 18 is small, similar to the extension stroke when high frequency is input in the low speed range X12. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, the bending of the free valve 111 can suppress the pressure increase in the pressure chamber 151, making it easier for the valve disc 141 to open.

[0267] Therefore, during the extension stroke when a high frequency is input in the medium speed range X13, the oil L from the first chamber 19 flows into the second chamber 20 in the flow path 181B while opening the valve mechanism 178, i.e., while separating the valve member 176 from the outer valve seat portion 76. At the same time, the oil L from the first chamber 19 flows into the second chamber 20 from the flow path 535 while opening the valve mechanism 532, i.e., while separating the valve disc 141 from the valve seat portion 514. Here, during the extension stroke when a high frequency is input in the medium speed range X13, the orifice 536 is provided upstream of the valve mechanism 532, and therefore the flow rate of the oil L flowing through the valve mechanism 532 is limited by the orifice 536. Therefore, during the extension stroke when a high frequency input is made in the medium speed range X13, as shown by the solid line Y12 in Figure 14, the characteristic of the damping force relative to the piston speed is such that the rate of increase of the damping force relative to an increase in piston speed is higher than that during the extension stroke when a high frequency input is made in the low speed range X12.

[0268] During the extension stroke, when the piston speed is in the high-speed region X14 that is equal to or greater than the 13th predetermined speed and the piston frequency is a low-frequency input that is lower than the predetermined frequency, the oil L from the first chamber 19 flows through the flow path 181B and into the pressure chamber 151 via the connecting passage 182 that includes the orifice 173, just as during the extension stroke when a low-frequency input is made in the medium-speed region X13.

[0269] During the extension stroke of this low-frequency input in the high-speed range X14, the amplitude of the piston 18 is large, similar to the low-frequency input in the medium-speed range X13. Therefore, a large amount of hydraulic fluid L flows into the pressure chamber 151, resulting in significant deformation of the free valve 111. Therefore, at the beginning of the extension stroke, the deformed free valve 111 immediately abuts against the recess 82, restricting further deformation and preventing an increase in the volume of the pressure chamber 151. During the extension stroke of this low-frequency input in the high-speed range X14, the volume of the pressure chamber 151 does not increase, so the pressure in the pressure chamber 151 increases. However, the relationship of the forces (hydraulic pressure) acting on the valve disc 141 is such that the opening force applied from the flow path 535 is greater than the closing force applied from the pressure chamber 151. Therefore, during this low-frequency input in the high-speed range X14, as the piston speed increases, the valve member 161 of the valve mechanism 532 opens farther away from the valve seat 514 than described above. In addition, when low-frequency input occurs in this high-speed range X14, valve mechanism 41B opens, in other words, valve member 161B opens and moves away from valve seat 47. As a result, in addition to the flow to second chamber 20 through flow path 181B when valve mechanism 178 is opened and the flow to second chamber 20 through flow path 535 including the passage between valve member 161 and valve seat 514, oil L flows through flow path 162 between valve member 161B and valve seat 47. For this reason, the characteristic of damping force relative to piston speed, as shown by solid line Y11 in Fig. 14, becomes the same as the extension stroke when low-frequency input occurs in medium speed range X13.

[0270] During the extension stroke, when the piston speed is in a high-speed region X14 that is equal to or greater than a thirteenth predetermined speed and when a high-frequency input is applied to the piston at a frequency equal to or greater than a predetermined frequency, the oil liquid L from the first chamber 19 flows through the flow path 181B, as in the case of a high-frequency input in the medium-speed region X13, and flows into the pressure chamber 151 via the connecting passage 182 that includes the orifice 173.

[0271] During the extension stroke when high frequency is input in the high speed range X14, the amplitude of the piston 18 is small, similar to the extension stroke when high frequency is input in the medium speed range X13. Therefore, the amount of oil L flowing into the pressure chamber 151 is small, and the deformation of the free valve 111 is small. Therefore, the bending of the free valve 111 can suppress the pressure rise in the pressure chamber 151, making it easier for the valve disc 141 to open.

[0272] Therefore, during the extension stroke when a high frequency wave is input in the high speed range X14, the oil L from the first chamber 19 flows into the second chamber 20 in the flow path 181B while opening the valve mechanism 178, i.e., while separating the valve member 176 from the outer valve seat 76. At the same time, the oil L from the first chamber 19 flows into the second chamber 20 from the flow path 535 while opening the valve mechanism 532, i.e., while separating the valve member 161B from the valve seat 514. In addition, during the high frequency wave input in the high speed range X14, the oil L from the first chamber 19 flows into the second chamber 20 from the flow path 162 while opening the valve mechanism 41B, i.e., while separating the valve member 161B from the valve seat 47. For this reason, as shown by the solid line Y12 in Figure 14, during the extension stroke when a high frequency is input in the high speed range X14, the characteristic of the damping force relative to the piston speed is such that the rate of increase of the damping force relative to an increase in piston speed is lower than during the extension stroke when a high frequency is input in the medium speed range X13.

[0273] During the compression stroke in which the rod 21 moves toward the compression side, in the extremely low speed region X15 where the piston speed is slower than the 15th predetermined speed, the hydraulic fluid L from the second chamber 20 flows into the first chamber 19 via the compression-side piston passage 40 and the orifice 213 of the valve member 212 of the valve mechanism 42. At the same time, the hydraulic fluid L from the second chamber 20 flows into the flow path 181B from the orifice 177 and into the first chamber 19 via the flow path 181B. At the same time, the hydraulic fluid L from the second chamber 20 passes through the passage in the outer through-hole 87 and the variable chamber 152, opens the check valve 155, and flows from the pressure chamber 151 and the communicating passage 182 through the orifice 173 to the first chamber 19 via the flow path 181B. Therefore, during the compression stroke in the extremely low speed region X15, a damping force with orifice characteristics is generated. Therefore, in the compression stroke in the extremely low speed region X15, the damping force characteristic with respect to the piston speed is such that the rate of increase of the damping force becomes relatively high as the piston speed increases.

[0274] During the compression stroke in the low speed region X16, where the piston speed is equal to or higher than the 15th predetermined speed but slower than the 16th predetermined speed, hydraulic fluid L flows from the second chamber 20 through the passage in the outer through-hole 87 and the variable chamber 152, and flows through the pressure chamber 151 and the communicating passage 182 while opening the check valve 155. Then, hydraulic fluid L flows into the first chamber 19 via the flow path 181B, while opening the valve mechanism 172 at the end of the communicating passage 182, i.e., while lifting the valve member 171 off the intermediate valve seat 75. Therefore, during the compression stroke in the low speed region X16, a damping force with a valve characteristic is generated, as shown by the solid line Y13 in FIG. 14 . Therefore, during the compression stroke in the low speed region X16, the rate of increase in the damping force relative to an increase in piston speed is lower than during the compression stroke in the very-low speed region X15.

[0275] During the compression stroke in the medium to high speed range X17 where the piston speed is equal to or higher than the 16th predetermined speed, the oil L flows from the second chamber 20 to the first chamber 19 via the flow path 181B while opening the valve mechanism 172, just as during the compression stroke in the low speed range X16. During the compression stroke in the medium to high speed range X17, the oil L is also introduced from the second chamber 20 into the compression-side piston passage 40, opening the valve mechanism 42, i.e., causing the valve member 212 to separate from the valve seat 49, and flows into the first chamber 19. For this reason, as shown by the solid line Y13 in Fig. 14, during the compression stroke in the medium to high speed range X17, the characteristic of the damping force relative to the piston speed is such that the rate of increase in the damping force relative to an increase in piston speed is lower than during the compression stroke in the low speed range X16.

[0276] The shock absorber 1B of the third embodiment has a flow path 535 that communicates from the first chamber 19 to the second chamber 20 in the cylinder 2, and a valve mechanism 532 that is provided in the flow path 535. The shock absorber 1B also has an orifice 536 that receives the oil liquid L from the first chamber 19 and reduces the pressure of the oil liquid L at a first strength, an orifice 173 that is provided in parallel to the flow path 535 and has a smaller cross-sectional area than the orifice 536, and an orifice 177 that is provided in parallel to the orifice 173 and has a smaller cross-sectional area than the orifice 536 but a larger cross-sectional area than the orifice 173. The shock absorber 1B also has a pressure chamber 151 that is downstream of the orifice 173 and can apply pressure from the oil liquid L to the valve mechanism 532 in a valve-closing direction, and a frequency sensitive mechanism 185 that is provided in the pressure chamber 151 and deforms in response to the internal pressure of the pressure chamber 151 to change the volume of the pressure chamber 151. The shock absorber 1B also has a valve mechanism 178 that is provided in parallel with the orifice 177 and allows the oil L that has flowed in to flow into the second chamber 20 downstream.

[0277] Shock absorber 1B can make the change in damping characteristics gentler because it has valve mechanism 532, valve mechanism 178, and orifice 177. Shock absorber 1B also has orifice 536 and orifice 173, which allows for more detailed adjustment of the damping force characteristics and makes it possible to make the change in damping characteristics even gentler.

[0278] In the shock absorber 1B, a valve structure 225B has a flow path 535 that communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side, a valve seat 514 that is provided in the flow path 535, and a valve disc 141 that is seated and released on the valve seat 514. The valve structure 225B also has a pressure chamber 151 that can apply pressure from oil liquid L in a valve-closing direction to the valve disc 141, and a flow path 181B that is at least partially parallel to the flow path 535 and communicates with the second chamber 20 on the downstream side, with the first chamber 19 on the upstream side. The valve structure 225B also has a valve mechanism 178 that is provided in the flow path 181B and includes an outer valve seat 76 and a valve member 176 that is seated and released on the outer valve seat 76, and a communication path 182 that communicates from the inside of the outer valve seat 76 on the upstream side to the pressure chamber 151 on the downstream side. Therefore, the shock absorber 1B can make the change in damping characteristics gentler.

[0279] In shock absorber 1B, valve mechanism 532 of valve structure 225B is provided downstream of orifice 536 and in series with orifice 536, and orifice 173 is provided in parallel with orifice 536. Therefore, shock absorber 1B can adjust the damping force characteristics in more detail, and can make the change in damping characteristics more gradual.

[0280] Furthermore, the valve structure 225B of the shock absorber 1B is provided in parallel to the orifice 536 and includes a flow path 162B that communicates from the first chamber 19 to the second chamber 20, and a valve mechanism 41B that is a valve provided in the flow path 162B. Therefore, the shock absorber 1B can adjust the damping force characteristics in more detail, and can make the change in the damping characteristics more gradual.

[0281] 11, the valve structure 225B of the shock absorber 1B has a valve mechanism 41B that restricts the oil liquid L flowing from the first chamber 19 to the second chamber 20 by the piston 18B. Therefore, the shock absorber 1B can adjust the damping force characteristics in more detail, and can make the change in the damping characteristics more gradual.

[0282] The entire structure provided on the rods 21, 21A, 21B of the shock absorbers 1, 1A, 1B may be provided on the rods 21, 21A, 21B with the extension side and the contraction side reversed.

[0283] The above-mentioned configuration may also be provided inside a damping valve case (cylinder) that is provided outside the shock absorber either integrally or separately.

[0284] According to the above-described aspects of the present invention, it is possible to provide a shock absorber that can make the change in damping characteristics gradual, and thus the industrial applicability is great.

[0285] 1, 1A, 1B... Shock absorber, 2... Cylinder, 18, 18B... Piston (divided member), 19... First chamber, 20... Second chamber, 21, 21A, 21B... Rod, 41, 532... Valve mechanism (first valve), 41B... Valve mechanism (fourth valve), 47... Valve seat portion (first valve seat), 56... Pilot case (partition member), 71... Bottom, 72... Outer cylindrical portion (cylinder portion), 76... Outer valve seat portion (second valve seat), 87... Through hole, 111... Free valve (membrane member), 141... Valve disc (first valve body), 151... Pressure chamber, 16 1...valve member (first valve body), 162, 535...flow path (first flow path), 172...valve mechanism (third valve), 173...orifice (second pressure reduction flow path), 177, 356...orifice (third pressure reduction flow path), 176...valve member (second valve body), 178...valve mechanism (second valve), 181, 181B...flow path (second flow path), 182...communicating passage, 185...frequency sensitive mechanism (volume change mechanism), 225, 225A, 225B...valve structure, 608...orifice (first pressure reduction flow path, narrowest part), 536...orifice (first pressure reduction flow path).

Claims

a first pressure reduction flow path into which a fluid flows from the first chamber and which reduces the pressure of the fluid by a first strength; a second pressure reduction flow path provided in parallel to the first flow path and having a smaller cross-sectional area than the first pressure reduction flow path; a third pressure reduction flow path provided in parallel to the second pressure reduction flow path and having a smaller cross-sectional area than the first pressure reduction flow path and a larger cross-sectional area than the second pressure reduction flow path; a pressure chamber downstream of the second pressure reduction flow path and capable of applying pressure from the fluid to the first valve in a valve closing direction; a volume change mechanism provided in the pressure chamber and deformed in response to an internal pressure of the pressure chamber, changing a volume of the pressure chamber in response to the internal pressure; and a second valve provided in parallel to the third pressure reduction flow path and capable of circulating the flowing fluid to the second chamber downstream.

2. A shock absorber as described in claim 1, wherein the first valve is provided in parallel to the first pressure reduction passage, and the second pressure reduction passage is provided downstream of the first pressure reduction passage and in series with the first pressure reduction passage.

3. A shock absorber as described in claim 1, wherein the first valve is provided downstream of and in series with the first pressure reduction passage, and the second pressure reduction passage is provided in parallel with the first pressure reduction passage.

4. The shock absorber according to claim 3, further comprising: a second flow path provided in parallel to the first pressure reduction flow path and communicating from the first chamber to the second chamber; and a third valve provided in the second flow path.

5. A shock absorber comprising: a cylindrical cylinder with a bottom; a piston dividing the interior of the cylinder into a first chamber and a second chamber; a rod to which the piston is fixed; and a valve structure having: a first flow path communicating with the second chamber on the downstream side of the first chamber, the upstream side; a first valve provided in the first flow path, the first valve having a first valve seat and a first valve body seated and lifted on the first valve seat; a pressure chamber capable of applying pressure from a fluid in a valve closing direction to the first valve body; a second flow path at least partially parallel to the first flow path, the second flow path communicating with the second chamber on the downstream side of the first chamber, the upstream side; a second valve provided in the second flow path, the second valve having a second valve seat and a second valve body seated and lifted on the second valve seat; and a communicating passage communicating from the inside of the second valve seat on the upstream side to the pressure chamber on the downstream side.

6. A shock absorber as described in claim 5, wherein the second flow path is provided on a surface or inside of the rod, the pressure chamber is formed by a bottomed, cylindrical partition member having a bottom and a cylindrical portion, and the second valve seat is provided on a surface of the bottom facing the second chamber.

7. The shock absorber according to claim 6, wherein said second valve further has an orifice having a cross-sectional area smaller than the narrowest part of said second flow path and allowing communication of said fluid at all times.

8. The shock absorber according to claim 7, wherein the partition member further includes a third valve provided between the second valve seat and the second valve body and restricting the communication of the fluid at least more than the orifice.

9. A shock absorber as described in claim 6, wherein the bottom of the partition member has a through hole that can communicate with the pressure chamber on a surface of the bottom facing the second chamber radially outward from the second valve seat, and the partition member is provided with a membrane member that blocks the through hole from inside the pressure chamber and can change the volume of the pressure chamber by the pressure.

10. The shock absorber according to claim 5 or 6, wherein the piston has a fourth valve for restricting the fluid flowing from the first chamber to the second chamber.

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