Sintered body and method for producing sintered body

Abstract

This sintered body comprises: a base part that is formed in a columnar shape having a lateral surface section and a base end surface continuous to the lateral surface section with a first arc-shaped section or a first inclined section forming an obtuse angle therebetween; an insertion hole into which, at the center thereof, a rod of a shock absorber is to be inserted; a boss part that is provided around the insertion hole in a manner projecting in an axial direction from the base end surface; a plurality of first through holes and a plurality of second through holes that are provided on the outer circumferential side of the boss part and alternately along the circumferential direction; and a plurality of round parts which are provided in a manner projecting in the axial direction from the base end surface to form a chamber by surrounding the first through holes, and on which a valve body of a piston is seated or unseated. The round parts are provided along the outer circumference of the base end surface, and each have: an outer edge section that is continuous to the lateral surface section with a second arc-shaped section or a second inclined section forming an obtuse angle therebetween; and a pair of arm sections that extend from both ends of the outer edge section toward the boss part.

Description

Sintered body and method for producing the same

[0001] The present invention relates to a sintered body and a method for manufacturing a sintered body. This application claims priority based on Japanese Patent Application No. 2024-025202, filed on February 22, 2024, the contents of which are incorporated herein by reference.

[0002] Some shock absorbers generate a damping force by moving a piston provided on a piston rod within a cylinder (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-063557

[0004] Incidentally, some shock absorbers of this type use a sintered body to form the piston, but there is a demand for suppressing the increase in cost of such a sintered body.

[0005] An object of the present invention is to provide a sintered body and a method for producing the same that can suppress increases in costs.

[0006] In order to solve the above problems and achieve the above object, the present invention employs the following aspects. That is, one aspect of the present invention is a sintered body constituting a piston used in a shock absorber, comprising: a cylindrical base portion having a side portion and a base end surface continuous with the side portion via a first arc-shaped portion or a first inclined portion forming an obtuse angle; an insertion hole at the center through which a rod of the shock absorber is inserted; a boss portion protruding axially from the base end surface and provided around the insertion hole; a plurality of first through holes and a plurality of second through holes on the outer periphery of the boss portion and provided alternately along the circumferential direction; and a plurality of round portions protruding axially from the base end surface, forming chambers surrounding the first through holes, and on which a valve body of the piston is seated and released; wherein the round portion has: an outer edge portion provided along the outer periphery of the base end surface and continuous with the side portion via a second arc-shaped portion or a second inclined portion forming an obtuse angle; and a set of arms extending from both ends of the outer edge portion toward the boss portion.

[0007] Another aspect of the present invention is a method for manufacturing a sintered body that constitutes a piston used in a shock absorber, comprising: a compression step of compressing powder metal in a mold to form a molded product having a base and a rounded portion; a sintering step of heating the molded product and processing it into a sintered body; and a removal step of removing a portion of the sintered body, wherein the base has a cylindrical main body, a first inclined portion that extends annularly radially outward from the main body and that gradually reduces the axial size of the base, and a flat portion that extends radially outward beyond the first inclined portion, and the rounded portion on which the valve body of the piston is seated and released has an outer edge portion where a second inclined portion is adjacent to the first inclined portion, and a set of arms that extend from both ends of the outer edge portion toward the center of the base, and is provided in plurality so as to protrude in the axial direction from one end face of the main body, and in the removal step, a portion radially outward of a predetermined position of the first inclined portion is removed to form a side portion that is a circumferential surface of the base, and An end face of the base portion is formed with an arc-shaped portion that is continuous with the side surface portion or a slope that is continuous with the side surface portion and forms an obtuse angle, which is the remaining portion of the first slope portion.

[0008] According to the above aspects of the present invention, it is possible to suppress an increase in costs.

[0009] FIG. 1 is a cross-sectional view showing a shock absorber including a sintered body according to an embodiment of the present invention. The symbol CL indicates a central axis shared by the shock absorber and the sintered body. FIG. 2 is a partially enlarged side view showing a main portion of a piston rod of a shock absorber including the sintered body. Here, (a) is a view of the main portion from one direction, and (b) is a view of (a) as viewed from the arrow O. FIG. 3 is a view showing a first piston and a second piston of a shock absorber including the sintered body, and is a partially enlarged cross-sectional view showing part P in FIG. 1. FIG. 4 is a view showing a second piston of a shock absorber including the sintered body, and is a partially enlarged cross-sectional view showing part Q in FIG. 3. FIG. 5 is a plan view showing a second piston body made of the sintered body. FIG. 6 is a bottom view showing the second piston body made of the sintered body. FIG. 7 is a partially enlarged cross-sectional view showing the second piston body made of the sintered body. FIG. 8 is a partially enlarged plan view showing the second piston body made of the sintered body. FIG. 9 is a partially enlarged perspective view showing a portion of the second piston body made of the sintered body. FIG. 11 is a partially enlarged bottom view showing the second piston body made of the sintered body. FIG. 12 is a partially enlarged cross-sectional view showing a molded product of the second piston body made of the sintered body. Fig. 1 is a partially enlarged cross-sectional view showing a molded product of the second piston body which is the same sintered body; Fig. 2 is a partially enlarged cross-sectional view showing a molded product of the second piston body which is the same sintered body and a mold; Fig. 3 is a partially enlarged cross-sectional view showing a molded product and a mold; Fig. 4 is a partially enlarged cross-sectional view showing a modified example of the second piston body which is the sintered body; Fig. 5 is a partially enlarged cross-sectional view showing a modified example of the second piston body which is the same sintered body.

[0010] An embodiment of the sintered body and the manufacturing method thereof according to the present invention will be described with reference to the drawings. In each drawing, the symbol CL indicates a central axis shared by the shock absorber and the sintered body.

[0011] A shock absorber 1 including the sintered body of this embodiment is used in suspension devices for railway vehicles and automobiles such as two-wheeled and four-wheeled vehicles. Specifically, the shock absorber 1 is used in suspension devices for four-wheeled automobiles. As shown in FIG. 1 , the shock absorber 1 is a double-tube shock absorber equipped with a cylinder 4 having an inner tube 2 and an outer tube 3. The inner tube 2 is cylindrical. The outer tube 3 is cylindrical with a bottom and has a larger diameter than the inner tube 2. The outer tube 3 is disposed radially outside the inner tube 2 and coaxially with the inner tube 2. A reservoir chamber 5 is formed between the outer tube 3 and the inner tube 2.

[0012] The outer cylinder 3 has a tubular portion 8 and a bottom portion 9. The tubular portion 8 is cylindrical. The bottom portion 9 closes one axial end of the tubular portion 8. The tubular portion 8 has an opening on the side opposite the bottom portion 9. A mounting eye 10 is fixed to the bottom portion 9 on the side opposite the tubular portion 8 in the axial direction.

[0013] The shock absorber 1 includes a valve body 12 and a rod guide 13. The valve body 12 is annular and is provided on the bottom 9 side of the inner cylinder 2 and the outer cylinder 3 in the axial direction. The rod guide 13 is annular and is provided on the opposite side of the inner cylinder 2 and the outer cylinder 3 from the bottom 9 in the axial direction. The valve body 12 constitutes a base valve 15. The valve body 12 has a stepped outer periphery, and is placed on the bottom 9 with its large diameter portion positioned radially relative to the cylindrical portion 8. The rod guide 13 also has a stepped outer periphery, and its large diameter portion is positioned radially relative to the cylindrical portion 8 and fitted thereto.

[0014] One axial end of the inner cylinder 2 is fitted into a small-diameter portion of the outer periphery of the valve body 12. One axial end of the inner cylinder 2 engages with the bottom 9 of the outer cylinder 3 via the valve body 12. The other axial end of the inner cylinder 2 is fitted into a small-diameter portion of the outer periphery of the rod guide 13. The other axial end of the inner cylinder 2 engages with the cylindrical portion 8 of the outer cylinder 3 via the rod guide 13. In this state, the inner cylinder 2 is positioned radially relative to the outer cylinder 3. Here, the space between the valve body 12 and the bottom 9 is in communication with the inner cylinder 2 and the outer cylinder 3. Therefore, the space between the valve body 12 and the bottom 9, like the space between the inner cylinder 2 and the outer cylinder 3, forms a reservoir chamber 5.

[0015] The shock absorber 1 is provided with a seal member 18. The seal member 18 is provided on the opposite side of the rod guide 13 from the bottom 9. This seal member 18 is also fitted into the inner periphery of the tubular portion 8, similar to the rod guide 13. A locking portion 19 is formed on the end of the tubular portion 8 opposite the bottom 9. The locking portion 19 is formed by plastically deforming the tubular portion 8 radially inward by crimping, such as curling. The seal member 18 is sandwiched between the locking portion 19 and the rod guide 13. The seal member 18 closes the opening of the outer cylinder 3, and is specifically an oil seal.

[0016] The shock absorber 1 includes a first piston body 21. The first piston body 21 is slidably disposed within the cylinder 4. The first piston body 21 is slidably disposed within the inner tube 2 of the cylinder 4. The first piston body 21 divides the inner tube 2 into two chambers: a first chamber 22 (upstream region) and a second chamber 23. The first chamber 22 is disposed between the first piston body 21 and the rod guide 13 within the inner tube 2. The second chamber 23 is disposed between the first piston body 21 and the valve body 12 within the inner tube 2. The second chamber 23 is separated from a reservoir chamber 5 by the valve body 12. The first chamber 22 and the second chamber 23 within the cylinder 4 are filled with oil L, which is a fluid. The reservoir chamber 5 within the cylinder 4 is filled with gas G and oil L, which are fluids. Therefore, the shock absorber 1 is a hydraulic shock absorber that uses oil L, which is a fluid.

[0017] The shock absorber 1 includes a rod 31, which is a rod-shaped shaft member. One axial end portion of the rod 31 is disposed inside the cylinder 4 and is connected and fixed to the first piston body 21. The other axial end portion of the rod 31 extends outside the cylinder 4. The rod 31 is made of metal and passes through the first chamber 22. The rod 31 does not pass through the second chamber 23. Therefore, the first chamber 22 is a rod-side chamber through which the rod 31 passes. The second chamber 23 is a bottom-side chamber on the bottom 9 side of the cylinder 4.

[0018] The first piston body 21 and the rod 31 move together. During the extension stroke of the shock absorber 1, in which the rod 31 increases the amount of protrusion from the cylinder 4, the first piston body 21 moves toward the first chamber 22. During the compression stroke of the shock absorber 1, in which the rod 31 decreases the amount of protrusion from the cylinder 4, the first piston body 21 moves toward the second chamber 23.

[0019] Both the rod guide 13 and the seal member 18 are annular. The rod 31 is slidably inserted through the rod guide 13 and the seal member 18 and extends from the inside to the outside of the cylinder 4. One axial end of the rod 31 is fixed to the first piston body 21 inside the cylinder 4. The other axial end of the rod 31 extends to the outside of the cylinder 4 via the rod guide 13 and the seal member 18.

[0020] The rod guide 13 supports the rod 31 relative to the cylinder 4 so that it can move in the axial direction while restricting its movement in the radial direction. The rod guide 13 guides the axial movement of the rod 31. The outer periphery of the seal member 18 is in close contact with the outer tube 3 of the cylinder 4. The inner periphery of the seal member 18 is in sliding contact with the outer periphery of the rod 31 that moves in the axial direction. In this way, the seal member 18 prevents the oil L and gas G in the cylinder 4 from leaking to the outside.

[0021] The rod 31 has a main shaft portion 32 and an attachment shaft portion 33. The attachment shaft portion 33 has a smaller diameter than the main shaft portion 32. The main shaft portion 32 of the rod 31 is slidably fitted into the rod guide 13 and the seal member 18. The attachment shaft portion 33 of the rod 31 is disposed in the cylinder 4 and is connected to the first piston body 21 and the like. The end of the main shaft portion 32 on the attachment shaft portion 33 side widens in a direction perpendicular to the axis.

[0022] 2, the mounting shaft portion 33 has a base end side cylindrical portion 41, an intermediate shaft portion 42, a tip end side cylindrical portion 43, and a threaded shaft portion 44. The mounting shaft portion 33 is provided with the base end side cylindrical portion 41, the intermediate shaft portion 42, the tip end side cylindrical portion 43, and the threaded shaft portion 44 in this order from the main shaft portion 32 side in the axial direction.

[0023] The base-end side cylindrical portion 41 is a cylindrical portion, and is provided on the main shaft portion 32 side, i.e., the base end side, in the axial direction of the mounting shaft portion 33. The base-end side cylindrical portion 41 has an outer peripheral surface 41a on the radially outer side that is a cylindrical surface that is continuous around the entire circumferential direction of the base-end side cylindrical portion 41.

[0024] The tip-side cylindrical portion 43 is a cylindrical portion and is provided on the opposite side of the base-side cylindrical portion 41 from the main shaft portion 32 in the axial direction of the mounting shaft portion 33, i.e., on the tip side. The tip-side cylindrical portion 43 has an outer peripheral surface 43a on the radially outer side that is a cylindrical surface that is continuous around the entire circumferential direction of the tip-side cylindrical portion 43. The outer peripheral surface 43a of the tip-side cylindrical portion 43 is coaxial with the outer peripheral surface 41a of the base-side cylindrical portion 41. In this embodiment, the outer peripheral surface 43a of the tip-side cylindrical portion 43 has the same diameter as the outer peripheral surface 41a of the base-side cylindrical portion 41, but they do not have to be the same diameter.

[0025] The intermediate shaft portion 42 is provided at an axially intermediate position of the mounting shaft portion 33. The intermediate shaft portion 42 has, on its radially outer side, a pair of outer end surfaces 42a, a base-end circumferential groove 51, a pair of axial grooves 52, and a tip-end circumferential groove 53.

[0026] Each of the pair of outer end surfaces 42a has the shape of a portion of a cylindrical surface that is coaxial and has the same diameter as the outer peripheral surface 41a of the base-side cylindrical portion 41 and the outer peripheral surface 43a of the tip-side cylindrical portion 43. In other words, the pair of outer end surfaces 42a are arranged on the same cylindrical surface as the outer peripheral surface 41a of the base-side cylindrical portion 41 and the outer peripheral surface 43a of the tip-side cylindrical portion 43. The pair of outer end surfaces 42a are 180 degrees out of phase with each other in the circumferential direction of the intermediate shaft portion 42. However, while the pair of outer end surfaces 42a is formed at two locations 180 degrees out of phase with each other in this embodiment, this is not limited to this. For example, the outer end surface 42a may be provided at one location in the circumferential direction of the intermediate shaft portion, or at three or more locations. Furthermore, if multiple outer end surfaces 42a are provided, their phases may be symmetrical as in this embodiment or asymmetrical.

[0027] The base-side circumferential groove 51 is provided at the end of the intermediate shaft 42 on the base-side cylindrical portion 41 side in the axial direction. The base-side circumferential groove 51 is recessed inward in the radial direction of the base-side circumferential groove 51 and the intermediate shaft 42 from the outer circumferential surface 41 a of the base-side cylindrical portion 41 and the pair of outer end surfaces 42 a of the intermediate shaft 42. The base-side circumferential groove 51 has an annular shape that continues around the entire circumferential direction of the intermediate shaft 42.

[0028] The tip side circumferential groove 53 is provided at an end of the intermediate shaft portion 42 on the tip side cylindrical portion 43 side in the axial direction. The tip side circumferential groove 53 is recessed inward in the radial direction of the tip side cylindrical portion 43 and the intermediate shaft portion 42 from the outer circumferential surface 43 a of the tip side cylindrical portion 43 and the pair of outer end surfaces 42 a of the intermediate shaft portion 42. The tip side circumferential groove 53 has an annular shape that continues around the entire circumferential direction of the intermediate shaft portion 42.

[0029] The pair of axial grooves 52 are recessed radially inward from the pair of outer end surfaces 42a of the intermediate shaft portion 42. The pair of axial grooves 52 have the same shape, and the inner bottom surfaces of the radially inner sides of the intermediate shaft portion 42 form flat surfaces extending perpendicular to the radial direction of the intermediate shaft portion 42. The pair of axial grooves 52 extend in the axial direction of the rod 31. The pair of axial grooves 52 are provided 180 degrees out of phase with each other in the circumferential direction of the intermediate shaft portion 42 and extend parallel to each other. The outer end surfaces 42a and the axial grooves 52 are alternately arranged in the circumferential direction of the intermediate shaft portion 42. One axial end of the pair of axial grooves 52 of the intermediate shaft portion 42 opens into the base-end circumferential groove 51, and the other axial end of the pair of axial grooves 52 of the intermediate shaft portion 42 opens into the tip-end circumferential groove 53.

[0030] As shown in Figure 3, the passage in the base-end circumferential groove 51, the passage in the pair of axial grooves 52, and the passage in the tip-end circumferential groove 53 constitute an axial flow passage 54 formed in the rod 31 and extending in the axial direction of the rod 31.

[0031] The threaded shaft portion 44 is provided on the axial side of the mounting shaft portion 33 opposite to the main shaft portion 32, i.e., on the tip end side. The threaded shaft portion 44 is cylindrical, and has a male thread 57 formed on the radially outer side.

[0032] The shock absorber 1 is supported by the vehicle body, for example, with the protruding portion of the rod 31 from the cylinder 4 shown in Figure 1 positioned at the top in the vertical direction. In this case, the shock absorber 1 is connected to the wheel side with the mounting eye 10 fixed to the bottom 9 of the cylinder 4 positioned at the bottom in the vertical direction. If the shock absorber 1 is a single-tube type, it can also be configured in the opposite way, with the cylinder 4 side supported by the vehicle body and the rod 31 connected to the wheel side.

[0033] As shown in FIG. 3, the first piston body 21 is composed of a metal body member 61 supported by the rod 31, and an annular friction member 62 integrally attached to the outer circumferential surface of the body member 61 and sliding within the inner cylinder 2.

[0034] The main body member 61 is formed with a plurality of passage holes 71 (only one is shown in FIG. 3 because it is a cross-sectional view) and an annular passage groove 72 that connects the ends of these passage holes 71 opposite the first chamber 22. The main body member 61 is also formed with a plurality of passage holes 75 (only one is shown in FIG. 3 because it is a cross-sectional view) and an annular passage groove 76 that connects the ends of these passage holes 75 on the first chamber 22 side. The plurality of passage holes 71 are formed in the circumferential direction of the main body member 61 with one passage hole 75 sandwiched between each other.

[0035] The passages in the plurality of passage holes 71 and the passage in the passage groove 72 constitute a piston passage 81 that penetrates the first piston body 21 in the axial direction of the first piston body 21 and can communicate between the first chamber 22 and the second chamber 23. The passages in the plurality of passage holes 75 and the passage in the passage groove 76 constitute a piston passage 82 that penetrates the first piston body 21 in the axial direction of the first piston body 21 and can communicate between the first chamber 22 and the second chamber 23.

[0036] The piston passage 81 is provided with a valve mechanism 85, which is a valve that opens and closes the piston passage 81 to generate a damping force. The valve mechanism 85 is arranged on the second chamber 23 side, which is one axial end side of the first piston body 21, and is attached to the rod 31. By arranging the valve mechanism 85 on the second chamber 23 side, the oil L that flows out from the first chamber 22 flows toward the second chamber 23 in the piston passage 81 when the first piston body 21 moves toward the first chamber 22, i.e., during the extension stroke. The valve mechanism 85 provided for the piston passage 81 serves as an extension-side valve mechanism that suppresses the flow of oil L from the extension-side piston passage 81 to the second chamber 23 to generate a damping force.

[0037] The piston passage 82 is provided with a valve mechanism 86, which is a valve that opens and closes the piston passage 82 to generate a damping force. The valve mechanism 86 is arranged on the first chamber 22 side, which is the other axial end side of the first piston body 21, and is attached to the rod 31. By arranging the valve mechanism 86 on the first chamber 22 side, the oil L that flows out from the second chamber 23 flows toward the first chamber 22 in the piston passage 82 when the first piston body 21 moves toward the second chamber 23, i.e., during the compression stroke. The valve mechanism 86 provided for the piston passage 82 serves as a compression-side valve mechanism that suppresses the flow of oil L from the compression-side piston passage 82 to the first chamber 22 to generate a damping force.

[0038] As a result of the above, the piston passage 81 and the piston passage 82 are connected so that the oil liquid L, which is a fluid, flows between the first chamber 22 and the second chamber 23 as the first piston body 21 moves, and the oil liquid L passes through the piston passage 81 when the rod 31 and the first piston body 21 move toward the extension side, and the oil liquid L passes through the piston passage 82 when the rod 31 and the first piston body 21 move toward the contraction side.

[0039] The main body member 61 is made up of two members: a first component 91 and a second component 92. The first component 91 constitutes the portion of the main body member 61 on the second chamber 23 side in the axial direction, and the second component 92 constitutes the portion of the main body member 61 on the first chamber 22 side in the axial direction.

[0040] The first component 91 has a generally circular disk shape. A circular fixing hole 101 is formed in the radial center of the first component 91, penetrating the first component 91 in the axial direction of the first component 91. The fixing hole 101 is a portion of the first component 91 into which the mounting shaft portion 33 of the rod 31 is fitted.

[0041] A passage groove 102 extending in the radial direction of the first component 91 is formed on an end face of the first component 91 on the second component 92 side in the axial direction. The passage in the passage groove 102 forms an in-piston flow path 103 that communicates with the piston passage 81.

[0042] The above-mentioned passage groove 72 is formed at the axial end of the first component 91 on the second chamber 23 side. An annular valve seat portion 105 constituting a part of the valve mechanism 85 is formed at the axial end of the first component 91 on the second chamber 23 side, radially outward from the opening of the passage groove 72 on the second chamber 23 side. In addition, a boss portion 106 is formed at the axial end of the main body member 61 on the second chamber 23 side, radially inward from the opening of the passage groove 72 on the second chamber 23 side.

[0043] The first component 91 has an engaging protrusion 108 formed thereon, which protrudes outward along the axial direction of the first component 91 from an end face of the first component 91 on the second component 92 side in the axial direction of the first component 91. The engaging protrusion 108 is provided partially in the circumferential direction of the first component 91.

[0044] The second component 92 has a generally circular disk shape. A circular fixing hole 111 is formed in the radial center of the second component 92, penetrating the second component 92 in the axial direction of the second component 92. The fixing hole 111 is a portion of the second component 92 into which the mounting shaft portion 33 of the rod 31 is fitted.

[0045] The above-mentioned passage groove 76 is formed at the axial end of the second component 92 on the first chamber 22 side. An annular valve seat portion 115 constituting a part of the valve mechanism 86 is formed at the axial end of the second component 92 on the first chamber 22 side, radially outward from the opening of the passage groove 76 on the first chamber 22 side. In addition, a boss portion 116 is formed at the axial end of the main body member 61 on the first chamber 22 side, radially inward from the opening of the passage groove 76 on the first chamber 22 side.

[0046] The second component 92 has engagement recesses 118 formed therein that are recessed inward along the axial direction of the second component 92 from an end face of the second component 92 that faces the first component 91 in the axial direction of the second component 92. The engagement recesses 118 are provided partially in the circumferential direction of the second component 92.

[0047] The first component 91 and the second component 92 are connected by engaging the engaging protrusion 108 of the first component 91 with the engaging recess 118 of the second component 92. As a result, the first component 91 and the second component 92 are connected in a state where they are positioned in the circumferential direction so as to form the piston passages 81 and 82. In this state, the friction member 62 is placed over the radially outer sides of the first component 91 and the second component 92. As a result, the first component 91 and the second component 92 are integrated to form the main body member 61, and the first component 91, the second component 92, and the friction member 62 are integrated to form the first piston body 21.

[0048] In the first component 91, the opening of the compression-side piston passage 82 on the second chamber 23 side is disposed radially outward of the valve seat portion 105. In addition, in the second component 92, the opening of the extension-side piston passage 81 on the first chamber 22 side is disposed radially outward of the valve seat portion 115.

[0049] The first piston body 21 has a fixing hole 111 that fits into the outer peripheral surface 41a (shown in FIG. 2 ) of the base-side cylindrical portion 41 of the rod 31, and a fixing hole 101 (shown in FIG. 3 ) that fits into a pair of outer end surfaces 42a (shown in FIG. 2 ) of the intermediate shaft portion 42 of the rod 31. In other words, the rod 31 has the base-side cylindrical portion 41, which is a cylindrical portion that is inserted into the fixing hole 111 (shown in FIG. 3 ). The first piston body 21 is disposed such that the intra-piston flow path 103 overlaps the base-side circumferential groove 51 of the rod 31 in the axial direction of the rod 31. This allows the intra-piston flow path 103 to communicate with the axial flow path 54 of the rod 31 without circumferentially aligning the first piston body 21 with the rod 31.

[0050] The compression-side valve mechanism 86 includes a valve seat portion 115 of the first piston body 21. The valve mechanism 86 has, in order from the first piston body 21 side in the axial direction, one disk 121 and multiple disks 122. On the axial side of the multiple disks 122 opposite to disk 121, in order from the multiple disks 122 side, are provided one disk 123, one disk 124, and one annular member 125. The disks 121 to 124 and the annular member 125 are all circular flat plates with holes, and the outer peripheral surface 41a (shown in FIG. 2) of the base-end cylindrical portion 41 of the mounting shaft portion 33 is fitted into the inside of each of them.

[0051] 3, the disk 121 has an outer diameter that is larger than the outer diameter of the boss portion 116 of the first piston body 21 and smaller than the inner diameter of the valve seat portion 115. The disk 121 is in constant contact with the boss portion 116.

[0052] Of the multiple discs 122, the disc 122 closest to the disc 121 in the axial direction has an outer diameter equal to the outer diameter of the valve seat portion 115 of the first piston body 21. Of the multiple discs 122, the disc 122 closest to the disc 121 in the axial direction is capable of being seated on the valve seat portion 115.

[0053] The disk 123 has an outer diameter smaller than the outer diameter of the plurality of disks 122 and slightly smaller than the outer diameter of the boss portion 116 of the first piston body 21 .

[0054] The disk 124 has an outer diameter larger than that of the disk 123 .

[0055] The outer diameter of the annular member 125 is smaller than the outer diameter of the disks 124 and larger than the outer diameter of the end of the main shaft portion 32 of the rod 31 on the side of the mounting shaft portion 33 in the axial direction. The annular member 125 is thicker and more rigid than the disks 121 to 124, and abuts against the end of the main shaft portion 32 on the side of the mounting shaft portion 33 in the axial direction.

[0056] A plurality of discs 122 constitute a compression-side valve member 131 that can be seated on and removed from the valve seat portion 115. The valve member 131 is flexible, and when it leaves the valve seat portion 115, it connects the piston passage 82 to the first chamber 22. At that time, the valve member 131 suppresses the flow of oil liquid L between it and the valve seat portion 115, generating a damping force. When the valve member 131 is seated on the valve seat portion 115, it blocks communication between the piston passage 82 and the first chamber 22. The annular member 125, together with the discs 124, abuts against the valve member 131 to suppress deformation of the valve member 131 in the opening direction beyond a specified limit.

[0057] The piston passage 82 and a passage between the valve member 131 and the valve seat portion 115 that appears when the valve is open constitute a first flow path 132. The first flow path 132 is provided in the first piston body 21. The first flow path 132 is a compression-side passage through which oil L flows from the second chamber 23, which is the upstream region within the cylinder 4, to the first chamber 22, which is the downstream region, as the first piston body 21 moves toward the second chamber 23. A compression-side valve mechanism 86 that generates a damping force includes the valve member 131 and the valve seat portion 115. The valve mechanism 86 is provided in the first flow path 132. The first flow path 132 is provided in the first piston body 21 including the valve seat portion 115, and oil L passes through the first flow path 132 when the rod 31 and the first piston body 21 move toward the compression side.

[0058] Here, in the compression-side valve mechanism 86, neither the valve seat portion 115 nor the valve member 131 abutting thereon is provided with a fixed orifice that connects the first chamber 22 and the second chamber 23 even when the valve seat portion 115 and the valve member 131 are in contact with each other. Therefore, the first flow path 132 is not a passage that constantly connects the first chamber 22 and the second chamber 23.

[0059] The extension-side valve mechanism 85 includes a valve seat portion 105 of the first piston body 21. The valve mechanism 85 has, in order from the first piston body 21 side in the axial direction, a single disk 141 and multiple disks 142. On the axially opposite side of the multiple disks 142 from disk 141, in order from the multiple disks 142 side, a single disk 143 and multiple disks 144 are provided. Each of the disks 141 to 144 is a circular flat plate with holes, and a pair of outer end surfaces 42a (shown in FIG. 2) of the intermediate shaft portion 42 of the mounting shaft portion 33 are fitted into the inside of each of the disks 141 to 144.

[0060] The disk 141 has an outer diameter larger than the outer diameter of the boss portion 106 of the first piston body 21 and smaller than the inner diameter of the valve seat portion 105. The disk 141 is in constant contact with the boss portion 106.

[0061] Of the multiple discs 142, the disc 142 closest to the disc 141 in the axial direction has an outer diameter equal to the outer diameter of the valve seat portion 105 of the first piston body 21. Of the multiple discs 142, the disc 142 closest to the disc 141 in the axial direction is capable of being seated on the valve seat portion 105.

[0062] The disk 143 has an outer diameter smaller than the outer diameter of any of the plurality of disks 142 and equal to the outer diameter of the boss portion 106 of the first piston body 21 .

[0063] The plurality of disks 144 have an outer diameter larger than that of the disk 143 .

[0064] A plurality of discs 142 constitute an extension-side valve member 151 that can be seated on and removed from the valve seat portion 105. The valve member 151 is flexible, and when it is removed from the valve seat portion 105, it connects the piston passage 81 to the second chamber 23. At that time, the valve member 151 suppresses the flow of oil liquid L between the valve seat portion 105 and the valve member 151, thereby generating a damping force. When the valve member 151 is seated on the valve seat portion 105, it blocks communication between the piston passage 81 and the second chamber 23.

[0065] The piston passage 81 and a passage between the valve member 151 and the valve seat portion 105 that appears when the valve is open constitute a first flow path 152. The first flow path 152 is formed in the first piston body 21. The first flow path 152 is an extension-side flow path through which oil L flows from the first chamber 22, which is the upstream region within the cylinder 4, to the second chamber 23, which is the downstream region, as the first piston body 21 moves toward the first chamber 22. The extension-side valve mechanism 85 that generates a damping force includes the valve member 151 and the valve seat portion 105. The valve mechanism 85 is provided in this first flow path 152. The first flow path 152 is provided in the first piston body 21 including the valve seat portion 105, and oil L passes through the first flow path 152 when the rod 31 and the first piston body 21 move toward the extension side.

[0066] In the extension-side valve mechanism 85, a fixed orifice that communicates between the first chamber 22 and the second chamber 23 is not formed in either the valve seat portion 105 or the valve member 151 that abuts thereon. Therefore, the first flow path 152 is not a flow path that constantly communicates between the first chamber 22 and the second chamber 23.

[0067] The in-piston flow path 103 provided in the first piston body 21 communicates with the first chamber 22 via a part of the piston passage 81 that is closer to the first chamber 22 than the in-piston flow path 103. The in-piston flow path 103 and a part of the piston passage 81 provided in the first piston body 21 that is closer to the first chamber 22 than the in-piston flow path 103 constitute a first-chamber-side flow path 156. The in-piston flow path 103, which is at least a part of the first-chamber-side flow path 156, is provided in parallel to the first flow path 152.

[0068] The first piston body 21, the disk 121, the valve member 131, the disk 141, and the valve member 151 constitute a first piston 155 that divides the interior of the inner tube 2 of the cylinder 4 into a first chamber 22 and a second chamber 23. The first piston 155 divides the interior of the inner tube 2 of the cylinder 4 into the first chamber 22, which is an upstream region during the extension stroke, and the second chamber 23, which is a downstream region during the extension stroke. The first piston 155 has circular fixing holes 101, 111 that penetrate the first piston 155 in the axial direction, a first flow path 152 that can communicate between the first chamber 22, which is the upstream region during the extension stroke, and the second chamber 23, which is the downstream region during the extension stroke, a flexible valve member 151 that can close the first flow path 152, and a first-chamber-side flow path 156 in which at least a portion of the in-piston flow path 103 is arranged parallel to the first flow path 152.

[0069] 4, on the axial side of disk 144 opposite disk 143, there are provided, in order from the disk 144 side, one disk 160, one spring member 161, multiple disks 162, one valve member 163 (valve body), and one second piston body 166 (sintered body) having one O-ring 165 provided on its outer periphery. Also, on the axial side of second piston body 166 opposite valve member 163, there are provided, in order from the second piston body 166 side, one valve member 167 (valve body), multiple disks 168, one spring member 169, and one disk 170. Also, on the axial side of disk 170 opposite spring member 169, there are provided, in order from the disk 170 side, one disk 172, one disk 173, and one disk 174. In addition, on the axial side of disk 174 opposite disk 173, there are provided, in order from the disk 174 side, one disk 176, one disc spring 177, one case member 178, one disk 181, and one annular member 182.

[0070] The mounting shaft portion 33 of the rod 31 is fitted inside the disks 160, 162, 168, 170, 172, 173, 174, 176, 181, spring members 161, 169, valve members 163, 167, second piston body 166, disc spring 177, case member 178, and annular member 182. At this time, the disk 160, spring member 161, disk 162, valve member 163, and second piston body 166 are fitted inside the pair of outer end surfaces 42a (shown in FIG. 2 ) of the intermediate shaft portion 42 of the mounting shaft portion 33. As shown in FIG. 4 , the second piston body 166, the valve member 167, the disk 168, the spring member 169, the disk 170, the disk 172, the disk 173, the disk 174, the disk 176, the disc spring 177, the case member 178, the disk 181, and the annular member 182 each have the outer circumferential surface 43 a (shown in FIG. 2 ) of the tip-side cylindrical portion 43 of the mounting shaft portion 33 fitted into their respective interiors.

[0071] 3, the mounting shaft portion 33 of the rod 31 has a threaded shaft portion 44 disposed on a portion that protrudes beyond the annular member 182. A retainer 185 is threadedly engaged with the male threads 57 on the outer periphery of the threaded shaft portion 44. The retainer 185 abuts against the annular member 182.

[0072] The disks 160, 162, 168, 170, 172, 173, 174, 176, and 181, the spring members 161 and 169, the valve members 163 and 167, the second piston body 166, the disc spring 177, the case member 178, and the annular member 182 shown in FIG. 4 are each clamped in the axial direction at least on their radially inner sides by the main shaft portion 32 of the rod 31 shown in FIG. 3 and a retainer 185.

[0073] As shown in FIG. 4, the disks 160, 162, 168, 170, 172, 173, 176, and 181, the valve members 163 and 167, and the annular member 182 are all in the form of circular flat plates having holes.

[0074] The case member 178 is a cylindrical, bottomed, one-piece molded product. The case member 178 has a bottom portion 191, an intermediate tapered portion 192, and a cylindrical portion 193. As shown in FIG. 3 , the outer diameter of the case member 178 is smaller than the outer diameter of the first piston body 21.

[0075] As shown in FIG. 4, the bottom portion 191 is in the form of a circular flat plate with holes.

[0076] The intermediate tapered portion 192 extends from the outer peripheral edge of the bottom portion 191 toward one axial side of the bottom portion 191 while expanding in diameter. The intermediate tapered portion 192 is annular.

[0077] The tubular portion 193 extends in the axial direction of the intermediate tapered portion 192 from an edge of the intermediate tapered portion 192 opposite the bottom portion 191, in the opposite direction from the bottom portion 191. The tubular portion 193 is cylindrical. Note that the case member 178 may not be provided with the intermediate tapered portion 192, and the tubular portion 193 may be directly continuous with the bottom portion 191.

[0078] The case member 178 has a bottom 191 into which the tip-side cylindrical portion 43 of the mounting shaft portion 33 of the rod 31 is fitted at the outer peripheral surface 43a shown in FIG. 2 . As shown in FIG. 4 , a plurality of passage holes 195 are formed in the bottom 191. The plurality of passage holes 195 penetrate the bottom 191 in the axial direction of the bottom 191. The plurality of passage holes 195 are arranged at equal intervals in the circumferential direction of the bottom 191 at positions equidistant from the center of the bottom 191. The case member 178 is oriented such that the bottom 191 is located on the opposite side of the disk 144 from the cylindrical portion 193 in the axial direction. The bottom 191 of the case member 178 abuts against the disk 181. The outer diameter of the disk 181 is large enough not to block the passage holes 195 of the case member 178.

[0079] The second piston body 166, the valve members 163, 167, the discs 168, 170, 172, 173, 174, 176, the spring member 169, and the disc spring 177 are arranged radially inside the case member 178.

[0080] The disc spring 177 has flexibility and includes an inner annular portion 201 and an outer tapered portion 202.

[0081] The inner annular portion 201 is a circular flat plate with holes. A passage hole 205 is formed in the inner annular portion 201, penetrating the inner annular portion 201 in the axial direction of the inner annular portion 201. The passage hole 205 has an arc shape extending in the circumferential direction of the inner annular portion 201.

[0082] The outer tapered portion 202 has a conical cylindrical shape that expands radially outward from the outer peripheral edge of the inner annular portion 201 and to one side in the axial direction.

[0083] The inner annular portion 201 of the disc spring 177 abuts against the bottom 191 of the case member 178, and the outer tapered portion 202 moves radially outward and away from the bottom 191 in the axial direction of the bottom 191. When the inner annular portion 201 of the disc spring 177 abuts against the bottom 191 of the case member 178, the disc spring 177 connects a passage hole 205 of the inner annular portion 201 to a passage hole 195 of the case member 178.

[0084] The outer diameter of the disk 176 is smaller than the outer diameter of the inner annular portion 201 of the disc spring 177 .

[0085] The disk 174 is flexible. The outer diameter of the disk 174 is larger than the outer diameter of the disc spring 177, i.e., the outer diameter of the outer tapered portion 202. The circular outer peripheral edge of the disc spring 177 on the radially outer side of the outer tapered portion 202 is in pressure contact with the outer peripheral edge of the disk 174 over the entire circumference.

[0086] The disk 174 is formed with a communication hole 211 that passes through the disk 174 in the axial direction of the disk 174. The communication hole 211 is formed in the disk 174 at a position that will not be blocked by the disk 176.

[0087] The disk 173 is flexible. The outer diameter of the disk 173 is smaller than the outer diameter of the disk 174. The outer diameter of the disk 173 is large enough to close the communication hole 211 of the disk 174. The disk 173 abuts against the disk 174 over the entire circumference. As a result, the disk 173 closes the communication hole 211 of the disk 174. When the disk 174 elastically deforms toward the bottom 191 of the case member 178 while elastically deforming the outer tapered portion 202 of the disc spring 177, the disk 173 opens the communication hole 211 of the disk 174.

[0088] The outer diameter of the disk 172 is smaller than the outer diameter of the disk 173 and smaller than the outer diameter of the disk 176 .

[0089] The disk 170 is flexible and has an outer diameter that is larger than the outer diameter of the disk 173 and slightly smaller than the outer diameter of the disk 174.

[0090] The spring member 169 has flexibility and includes a substrate portion 221 and a plurality of spring plate portions 222.

[0091] The base plate 221 is a circular flat plate with holes. The mounting shaft 33 is fitted onto the inner periphery of the base plate 221.

[0092] The plurality of spring plate portions 222 extend radially from the outer peripheral edge of the base plate portion 221. The plurality of spring plate portions 222 are spaced farther from the base plate portion 221 in the axial direction of the base plate portion 221 as they move radially outward from the base plate portion 221.

[0093] The spring member 169 abuts against the disk 170 at the base plate portion 221. The more the spring plate portions 222 are positioned radially outward of the base plate portion 221, the further away they are from the disk 170 in the axial direction of the base plate portion 221.

[0094] The disk 168 has an outer diameter smaller than that of the base plate portion 221 of the spring member 169 and larger than that of the disk 172. The disk 168 abuts against the base plate portion 221 of the spring member 169.

[0095] The valve member 167 is flexible and has an outer diameter larger than the maximum outer diameter of the spring member 169.

[0096] The second piston body 166 is a seamless, integrally molded sintered body made of sintered metal, and has a perforated disk shape as shown in Figures 5 and 6. The second piston body 166 has an insertion hole 231 formed in its radial center, penetrating the second piston body 166 in the axial direction, as shown in Figure 4. In other words, the insertion hole 231 extends in the axial direction of the second piston body 166 and penetrates the second piston body 166 in the axial direction. The mounting shaft portion 33 of the rod 31 is inserted into the center of the insertion hole 231.

[0097] As shown in FIGS. 5 and 6 , the insertion hole 231 has a first inner peripheral wall 232 and a second inner peripheral wall 233 .

[0098] The first inner peripheral wall 232 has a cylindrical inner peripheral surface. As shown in Fig. 4, the first inner peripheral wall 232 penetrates the second piston body 166 in the axial direction.

[0099] As shown in Figures 5 and 6, the second inner circumferential wall 233 is recessed radially outward from the inner circumferential surface of the first inner circumferential wall 232. The inner circumferential surface of the second inner circumferential wall 233 is semicylindrical. As shown in Figure 4, the second inner circumferential wall 233 extends linearly along the axial direction of the second piston body 166 and penetrates the second piston body 166 in the axial direction. The insertion hole 231 has one or more second inner circumferential walls 233. Here, as shown in Figures 5 and 6, the insertion hole 231 has a plurality of second inner circumferential walls 233 spaced equally apart in the circumferential direction of the first inner circumferential wall 232.

[0100] As shown in FIG. 4 , the inside of the first inner circumferential wall 232 of the insertion hole 231 forms an insertion hole main body 234 through which the mounting shaft portion 33 of the rod 31 is inserted, and the inside of the second inner circumferential wall 233 forms an expansion portion 235 that expands radially outward from the insertion hole main body 234. The second piston body 166 has the insertion hole main body 234 and one or more expansion portions 235 extending radially from the insertion hole main body 234. Here, as shown in FIGS. 5 and 6 , the second piston body 166 has a plurality of expansion portions 235 equally spaced circumferentially around the insertion hole main body 234. As shown in FIG. 4 , the insertion hole main body 234 and the expansion portion 235 each extend from one axial end face to the other axial end face of the second piston body 166, penetrating the second piston body 166.

[0101] The mounting shaft portion 33 of the rod 31 is fitted into the first inner circumferential wall 232 of the insertion hole 231 at a pair of outer end surfaces 42a of the intermediate shaft portion 42 shown in FIG. 2 and the outer circumferential surface 43a of the tip-side cylindrical portion 43. Then, as shown in FIG. 4, the second inner circumferential wall 233 moves radially away from the mounting shaft portion 33 of the rod 31. The expansion portion 235 is formed from the surface of the second piston body 166 opposite to the surface facing the first piston 155 shown in FIG. 3 to a position communicating with the axial flow path 54. The insertion hole 231 overlaps with the tip-side circumferential groove 53 of the rod 31 in the axial direction of the rod 31. Therefore, the insertion hole 231 communicates directly or indirectly with the tip-side circumferential groove 53 of the rod 31; here, it communicates directly. An intermediate chamber 237 is formed by the second inner circumferential wall 233 of the second piston body 166 and the mounting shaft portion 33 of the rod 31. The distal end circumferential groove 53 of the rod 31 allows the intermediate chamber 237 to communicate with the axial flow path 54 without circumferentially aligning the second piston body 166 with the rod 31.

[0102] As shown in Fig. 4, the second piston body 166 has a base portion 240 formed in a cylindrical shape with holes in the axial middle portion. The base portion 240 has a cylindrical side surface portion 401 on the radially outer side along the entire circumference, a flat base end surface 402 on one axial side, and a flat base end surface 403 on the other axial side. The base end surfaces 402 and 403 extend perpendicular to the side surface portion 401.

[0103] The second piston body 166 has a boss portion 241 and a valve seat portion 242 at one axial end. The boss portion 241 and the valve seat portion 242 protrude in the axial direction from the base end surface 402 of the base portion 240. As shown in FIG. 5 , the boss portion 241 has an annular shape surrounding the insertion hole 231. In other words, the boss portion 241 is provided around the insertion hole 231. The valve seat portion 242 extends outward from the boss portion 241 in the radial direction of the boss portion 241.

[0104] As shown in Fig. 4, the second piston body 166 has a boss portion 244 and a valve seat portion 245 at the other axial end opposite the boss portion 241 and the valve seat portion 242. The boss portion 244 and the valve seat portion 245 protrude in the axial direction from the base end surface 403 of the base portion 240. As shown in Fig. 6, the boss portion 244 has an annular shape surrounding the insertion hole 231. In other words, the boss portion 244 is provided around the insertion hole 231. The valve seat portion 245 extends outward from the boss portion 244 in the radial direction of the boss portion 244.

[0105] 4, the second piston body 166 has a base 240 between the boss 241 and the valve seat 242 and the boss 244 and the valve seat 245 in the axial direction. The base 240 is a disk-shaped member with holes. The insertion hole 231 passes through the base 240, the boss 241, and the boss 244.

[0106] The boss portion 241 protrudes from the inner peripheral edge of a base end face 402 on one axial side of the base portion 240 along the axial direction of the base portion 240. The valve seat portion 242 protrudes from the base end face 402 of the base portion 240 on the same side as the boss portion 241, radially outward from the boss portion 241 along the axial direction of the base portion 240.

[0107] 5, the boss portion 241 has a flat tip end surface 411 on the protruding side, i.e., the tip end surface 411 opposite the base portion 240. The valve seat portion 242 has a flat tip end surface 412 on the protruding side, i.e., the tip end surface 412 opposite the base portion 240. The tip end surface 411 of the boss portion 241 and the tip end surface 412 of the valve seat portion 242 extend in a direction perpendicular to the axis of the second piston body 166 and are arranged on the same plane.

[0108] 4, the boss portion 244 protrudes from the inner peripheral edge of the base portion 240 on the opposite side of the boss portion 241 in the axial direction, along the axial direction of the base portion 240, toward the opposite side of the boss portion 241. The valve seat portion 245 protrudes from the base portion 240 on the same side as the boss portion 244, radially outward of the boss portion 244, along the axial direction of the base portion 240.

[0109] 6, the boss portion 244 has a flat tip end surface 421 on the protruding side, i.e., the tip end surface 421 opposite the base portion 240. The valve seat portion 245 has a flat tip end surface 422 on the protruding side, i.e., the tip end surface 422 opposite the base portion 240. The tip end surface 421 of the boss portion 244 and the tip end surface 422 of the valve seat portion 245 extend in a direction perpendicular to the axis of the second piston body 166 and are arranged on the same plane.

[0110] As shown in FIG. 5 , the boss portion 241 has an annular portion 251 and a plurality of protrusions 252 .

[0111] The annular portion 251 is annular and is provided to surround the insertion hole 231 .

[0112] The protrusions 252 extend outward in the radial direction of the annular portion 251 from the outer peripheral edge of the annular portion 251. The multiple protrusions 252 are arranged at intervals in the circumferential direction of the annular portion 251.

[0113] The boss portion 241 has radial communicating grooves 253 that penetrate the annular portion 251 in the radial direction of the annular portion 251. A plurality of radial communicating grooves 253 are formed at equal intervals in the circumferential direction of the annular portion 251. The radial communicating grooves 253 are recessed from the tip end surface 411 of the boss portion 241 on the side opposite to the base portion 240 along the axial direction of the second piston body 166.

[0114] Each of the radial communicating grooves 253 is aligned in phase with a corresponding one of the plurality of second inner circumferential walls 233 of the insertion hole 231 in the circumferential direction of the annular portion 251, and communicates with the corresponding second inner circumferential wall 233. Each of the plurality of radial communicating grooves 253 is provided between adjacent protrusions 252 in the circumferential direction of the annular portion 251.

[0115] The valve seat portion 242 is a non-circular, petal-shaped irregular seat. The valve seat portion 242 has a plurality of rounded portions 255. These rounded portions 255 are of the same shape and are arranged at equal intervals around the circumference of the second piston body 166. Note that these rounded portions 255 do not need to be of the same shape; they may have two or more different shapes or may have different shapes. They may also be arranged at unequal intervals around the circumference of the second piston body 166. With this configuration, the valve-opening pressure applied to the valve member 163 (described later) is made uneven around the circumference, which makes it possible to vary the valve-opening timing and smoothly change the damping force characteristics.

[0116] The rounded portion 255 has a pair of arms 256 and an outer edge portion 257 .

[0117] Each of the pair of arms 256 extends radially outward from the outer peripheral edge of the annular portion 251 of the boss portion 241. The pair of arms 256 are arranged at a distance from each other in the circumferential direction of the annular portion 251. Each of the pair of arms 256 has an inclined portion 431 that extends from the tip surface 412 of the valve seat portion 242 toward the outside of the round portion 255 and continues to the base end surface 402. The inclined portion 431 intersects with the tip surface 412 at an obtuse angle and also intersects with the base end surface 402 at an obtuse angle.

[0118] The outer edge portion 257 connects the radially outer ends of the pair of arm portions 256 of the annular portion 251. The outer edge portion 257 extends in the circumferential direction of the annular portion 251. The outer edge portion 257 has an arc shape centered on the central axis of the second piston body 166. As shown in FIG. 7 , the outer edge portion 257 has an inclined portion 432 (second inclined portion) that extends from the tip surface 412 of the valve seat portion 242 toward the outside of the round portion 255 and continues to the side surface portion 401. The inclined portion 432 has an arc shape when the second piston body 166 is viewed in the axial direction. The inclined portion 432 has a tapered shape that forms a straight line when the second piston body 166 is cross-sectionally taken along a plane including the central axis of the second piston body 166. The inclined portion 432 intersects with the tip surface 412 at an obtuse angle and with the side surface portion 401 at an obtuse angle A. The outer edge portion 257 of the rounded portion 255 starts from the outer peripheral edge of the base portion 240 and protrudes more from the base portion 240 toward the center of the base portion 240. The inclined portion 432 is continuous with the inclined portions 431 of each of the pair of arm portions 256.

[0119] In other words, as shown in Figure 5, multiple round portions 255 are provided, protruding axially from the base end face 402, and have an outer edge portion 257 that is provided along the outer periphery of the base end face 402 and continues to the side portion 401 via an inclined portion 432 that forms an obtuse angle A, and a pair of arms 256 that extend from both ends of the outer edge portion 257 toward the boss portion 241.

[0120] Here, a pair of protrusions 252 adjacent to each other in the circumferential direction of the boss portion 241 are arranged on the inside of the round portion 255 in the circumferential direction of the second piston body 166, and a radial communicating groove 253 is arranged between this pair of protrusions 252. Therefore, a pair of protrusions 252 and one radial communicating groove 253 are arranged on the inside of the circumferential direction of the second piston body 166 of each of the multiple round portions 255.

[0121] As shown in FIG. 8 , the base 240 has an inclined portion 435 (first inclined portion) that is continuous with the base end surface 402 and the side surface 401. Therefore, the base end surface 402 is continuous with the side surface 401 via the inclined portion 435. The inclined portion 435 has an arc shape when the second piston body 166 is viewed in the axial direction. The inclined portion 435 has a tapered shape that is linear when the second piston body 166 is cross-sectionally taken along a plane including the central axis of the second piston body 166. The inclined portion 435 intersects with the base end surface 402 at an obtuse angle and with the side surface 401 at an obtuse angle B. The diameter of the inclined portion 435 decreases as it approaches the base end surface 402 in the axial direction of the second piston body 166. The obtuse angle B that the inclined portion 435 forms with the side surface portion 401 is smaller than the obtuse angle A that the inclined portion 432 shown in FIG.

[0122] As shown in FIG. 9 , the inclined portion 435 is provided between adjacent ones of the multiple round portions 255 in the circumferential direction of the second piston body 166, and is adjacent to the inclined portion 432 in the circumferential direction of the second piston body 166. As shown in FIG. 10 , the distance L1 between the inclined portion 435 of the base portion 240 and the axial center C of the side surface portion 401 is smaller than the distance L2 between the inclined portion 432 of the outer edge portion 257 and the axial center C of the side surface portion 401. In other words, the inclined portion 435 of the base portion 240 is located closer to the axial center C of the side surface portion 401 than the inclined portion 432 of the outer edge portion 257. As shown in FIG. 5 , the inclined portion 435 is formed in the base portion 240 at a position between all combinations of adjacent round portions 255 in the circumferential direction of the second piston body 166.

[0123] A recessed chamber 258 (chamber) is formed between each of the multiple rounded portions 255 and the boss portion 241 on the inner side. The recessed chamber 258 is formed by being surrounded by a part of the boss portion 241 and the rounded portion 255. The recessed chamber 258 is recessed in the axial direction of the second piston body 166 from a tip end surface 411 on the protruding side of the boss portion 241 and a tip end surface 412 on the protruding side of the valve seat portion 242. The recessed chamber 258 is formed on the inner side of all of the rounded portions 255.

[0124] A through hole 259 (communicating hole) is formed in the circumferential center of the recessed chamber 258 of the second piston body 166. In other words, the round portion 255 surrounds the through hole 259 to form the recessed chamber 258. In other words, the through hole 259 is a hole provided in an area surrounded by the outer edge portion 257 and the pair of arm portions 256. The through hole 259 is formed in the base portion 240. The through hole 259 is disposed between the pair of protrusions 262 in the recessed chamber 258 in which the through hole 259 is formed, in the circumferential direction of the second piston body 166. As shown in FIG. 4 , the through hole 259 axially penetrates the base portion 240 and the second piston body 166. The through hole 259 is a linear hole parallel to the central axis of the second piston body 166. As shown in FIG. 5 , a through hole 259 is formed in the bottom surface of all of the recessed chambers 258.

[0125] As shown in FIG. 6 , the boss portion 244 has an annular portion 261 and a plurality of protrusions 262 .

[0126] The annular portion 261 is annular and is provided to surround the insertion hole 231 .

[0127] The protrusions 262 extend outward in the radial direction of the annular portion 261 from the outer circumferential edge of the annular portion 261. The multiple protrusions 262 are arranged at intervals in the circumferential direction of the annular portion 261.

[0128] In the boss portion 244, a plurality of communication grooves 263 that cross the annular portion 261 in the radial direction of the annular portion 261 are formed at equal intervals in the circumferential direction of the annular portion 261. The communication grooves 263 are formed by being recessed in the axial direction of the second piston body 166 from the tip end surface 421 of the boss portion 244 on the side opposite to the base portion 240.

[0129] Each of the plurality of communicating grooves 263 is aligned in phase with a corresponding one of the plurality of second inner circumferential walls 233 of the insertion hole 231 in the circumferential direction of the annular portion 261, and communicates with the corresponding second inner circumferential wall 233. Each of the plurality of communicating grooves 263 is provided between adjacent protrusions 262 in the circumferential direction of the annular portion 251.

[0130] The valve seat portion 245 is a non-circular, petal-shaped irregular seat. The valve seat portion 245 has a plurality of rounded portions 265. These rounded portions 265 are of the same shape and are arranged at equal intervals around the circumference of the second piston body 166. Note that these valve seat portions 245 do not need to be of the same shape; they may have two or more different shapes or may have mutually different shapes. They may also be arranged at unequal intervals around the circumference of the second piston body 166. With this configuration, the valve-opening pressure applied to the valve member 167 (described later) is made uneven around the circumference, which makes it possible to vary the valve-opening timing and smoothly change the damping force characteristics.

[0131] A communication groove 263 is arranged in the annular portion 261 of the boss portion 244 between two round portions 265 that are adjacent to each other in the circumferential direction of the second piston body 166. Therefore, the communication groove 263 is formed in a portion of the boss portion 244 that is arranged outside the valve seat portion 245.

[0132] The rounded portion 265 has a pair of arms 266 and an outer edge portion 267 .

[0133] Each of the pair of arm portions 266 extends radially outward from the outer peripheral edge of the annular portion 261 of the boss portion 244. The pair of arm portions 266 are arranged at a distance from each other in the circumferential direction of the annular portion 261. Each of the pair of arm portions 266 has an inclined portion 441 that extends from the tip surface 422 of the valve seat portion 245 toward the outside of the round portion 265 and continues to the base end surface 403. The inclined portion 441 intersects with the tip surface 422 at an obtuse angle and also intersects with the base end surface 403 at an obtuse angle.

[0134] The outer edge portion 267 connects the radially outer ends of the pair of arm portions 266 of the annular portion 261. The outer edge portion 267 extends in the circumferential direction of the annular portion 261. The outer edge portion 267 has an arc shape centered on the central axis of the second piston body 166. As shown in FIG. 8 , the outer edge portion 267 has an inclined portion 442 (second inclined portion) that extends from the tip surface 422 of the valve seat portion 245 toward the outside of the round portion 265 and continues to the side surface portion 401. The inclined portion 442 has an arc shape when the second piston body 166 is viewed in the axial direction. The inclined portion 442 has a tapered shape that forms a straight line when the second piston body 166 is cross-sectionally taken along a plane including the central axis of the second piston body 166. The inclined portion 442 intersects with the tip surface 422 at an obtuse angle and with the side surface portion 401 at an obtuse angle A. The outer edge portion 267 of the rounded portion 265 starts from the outer peripheral edge of the base portion 240 and protrudes more from the base portion 240 toward the center of the base portion 240. The inclined portion 442 is continuous with the inclined portions 441 of each of the pair of arm portions 266.

[0135] In other words, as shown in Figure 6, the round portions 265 are provided in multiple positions protruding axially from the base end face 403, and have an outer edge portion 267 that is provided along the outer periphery of the base end face 403 and continues to the side portion 401 via an inclined portion 442 that forms an obtuse angle A, and a pair of arm portions 266 that extend from both ends of the outer edge portion 267 toward the boss portion 244.

[0136] Here, a pair of protrusions 262 adjacent to each other in the circumferential direction of the boss portion 244 is arranged on the inner side of the round portion 265 in the circumferential direction of the second piston body 166. Therefore, a pair of protrusions 262 is arranged on the inner side of each of the multiple round portions 265 in the circumferential direction of the second piston body 166.

[0137] As shown in FIG. 7 , the base 240 has an inclined portion 445 (first inclined portion) that is continuous with the base end surface 403 and the side surface 401. Therefore, the base end surface 403 is continuous with the side surface 401 via the inclined portion 445. The inclined portion 445 has an arc shape when the second piston body 166 is viewed in the axial direction. The inclined portion 445 has a tapered shape that is linear when the second piston body 166 is cross-sectionally taken along a plane including the central axis of the second piston body 166. The inclined portion 445 intersects with the base end surface 403 at an obtuse angle and with the side surface 401 at an obtuse angle B. The diameter of the inclined portion 445 decreases as it approaches the base end surface 403 in the axial direction of the second piston body 166. The obtuse angle B that the inclined portion 445 forms with the side surface portion 401 is smaller than the obtuse angle A that the inclined portion 442 shown in Fig. 8 forms with the side surface portion 401. Furthermore, the distance between the inclined portion 445 of the base portion 240 shown in Fig. 7 and the center in the axial direction of the side surface portion 401 is smaller than the distance between the inclined portion 442 of the outer edge portion 267 shown in Fig. 8 and the center in the axial direction of the side surface portion 401. In other words, the inclined portion 445 of the base portion 240 shown in Fig. 7 is located closer to the center C in the axial direction of the side surface portion 401 than the inclined portion 442 of the outer edge portion 267 shown in Fig. 8.

[0138] 11 , the inclined portion 445 is provided at a position between adjacent ones of the multiple round portions 265 in the circumferential direction of the second piston body 166, and is adjacent to the inclined portion 442 in the circumferential direction of the second piston body 166. As shown in FIG. 6 , the inclined portion 445 is formed in the base 240 at a position between all combinations of adjacent round portions 265 in the circumferential direction of the second piston body 166.

[0139] A recessed chamber 268 (chamber) is formed between each of the rounded portions 265 and the boss portion 244. The recessed chamber 268 is formed by being surrounded by a part of the boss portion 244 and the rounded portion 265.

[0140] The recessed chambers 268 are recessed in the axial direction of the second piston body 166 from a tip end surface 421 on the protruding side of the boss portion 244 and a tip end surface 422 on the protruding side of the valve seat portion 245. The recessed chambers 268 are formed inside all of the round portions 265.

[0141] A through hole 269 (communicating hole) is formed in the circumferential center of the recessed chamber 268 of the second piston body 166. In other words, the round portion 265 surrounds the through hole 269 to form the recessed chamber 268. In other words, the through hole 269 is a hole provided in an area surrounded by the outer edge portion 267 and the pair of arm portions 266. The through hole 269 is formed in the base portion 240. The through hole 269 is disposed between the pair of protrusions 262 in the recessed chamber 268 in which the through hole 269 is formed, in the circumferential direction of the second piston body 166. As shown in FIG. 4 , the through hole 269 axially penetrates the base portion 240 and the second piston body 166. The through hole 269 is a linear hole parallel to the central axis of the second piston body 166. As shown in FIG. 6 , a through hole 269 is formed in the bottom surface of all of the recessed chambers 268. The second piston body 166 has a plurality of through holes 259 and a plurality of through holes 269, which are arranged alternately one by one around the circumference of the second piston body 166, on the outer circumferential side of the boss portion 241 shown in Figure 5 and the boss portion 244 shown in Figure 6.

[0142] Here, the arrangement pitch of the plurality of round portions 255 shown in FIG. 5 in the circumferential direction of the second piston body 166 is the same as the arrangement pitch of the plurality of round portions 265 shown in FIG. 6 in the circumferential direction of the second piston body 166. The round portions 255 and the round portions 265 are shifted in phase from each other by half the arrangement pitch in the circumferential direction of the second piston body 166. In other words, the plurality of round portions 255 on the base end face 402 on one side of the base 240 shown in FIG. 5 and the plurality of round portions 265 on the base end face 403 on the other side of the base 240 shown in FIG. 6 are arranged with a phase shift. In other words, the plurality of round portions 255 and the plurality of round portions 265 are arranged with a phase shift on both the base end face 402 and the base end face 403 of the base 240.

[0143] 5, the through hole 269 is disposed between adjacent round portions 255 in the circumferential direction of the second piston body 166. Thus, the through hole 269 is disposed outside the range of the valve seat portion 242. The through hole 269 is provided between the arm portions 256 of two adjacent round portions 255 on the base 240. Thus, the through hole 269 is provided on one axial side in a region surrounded by the outer edge portion 267 of the round portion 265 and the pair of arm portions 266 as shown in FIG. 6, and on the other axial side, it is provided between the arm portions 256 of two adjacent round portions 255 on the base 240 as shown in FIG.

[0144] 6, the through hole 259 is disposed between adjacent round portions 265 in the circumferential direction of the second piston body 166. Thus, the through hole 259 is disposed outside the range of the valve seat portion 245. The through hole 259 is provided between the arm portions 266 of two adjacent round portions 265 on the base portion 240. Thus, the through hole 259 is provided on the other axial side in a region surrounded by the outer edge portion 257 of the round portion 255 and the pair of arm portions 256 as shown in FIG. 5, and on one axial side in a region between the arm portions 266 of two adjacent round portions 265 on the base portion 240 as shown in FIG.

[0145] 4, the second piston body 166 has a seal groove 271 formed in the axial center position of the outer periphery of the base 240. The seal groove 271 is annular, and is recessed radially inward from the axial middle position of the side surface portion 401 of the base 240. An O-ring 165 is disposed in the seal groove 271.

[0146] Here, when manufacturing second piston body 166, a compaction process is performed in which powdered metal is compressed in a mold to form molded product 166A shown in Figures 12 and 13. Molded product 166A has base portion 240A, which will later become base portion 240, round portion 255A, which will later become round portion 255, and round portion 265A, which will later become round portion 265.

[0147] As shown in FIG. 13 , the base 240A includes a cylindrical main body 501 (later to become the base 240), a groove 502 formed in the base end face 402 on one axial side of the main body 501, including an inclined portion 435A (first inclined portion) that extends annularly radially outward from one axial end of the main body 501 and gradually reduces the axial size of the base 240A, and the inclined portion 435A (first inclined portion) is included, and a flat portion 503 extends radially outward beyond the groove 502 including the inclined portion 435A. The base end face 402 and the flat portion 503 are arranged on the same plane. When viewed axially of the molded product 166A, the groove 502 is arc-shaped and is formed between adjacent round portions 255A in the circumferential direction of the molded product 166A, and between the base end face 402 and the flat portion 503 in the radial direction of the molded product 166A. The bottom surface of the groove 502 is a flat surface parallel to the flat portion 503 .

[0148] As shown in FIG. 12 , the base 240A includes a groove 512 formed in the base end face 403 on the other axial side of the main body 501, which includes an inclined portion 445A (first inclined portion) extending radially outward from the other axial end of the main body 501 and gradually reducing the axial size of the base 240A. The groove 512 includes an inclined portion 445A (first inclined portion) that will later become the inclined portion 445, and a flat portion 513 that extends radially outward from the groove 512 including the inclined portion 445A. The base end face 403 and the flat portion 513 are arranged on the same plane. When viewed axially of the molded product 166A, the groove 512 is arc-shaped and is formed between adjacent round portions 265A in the circumferential direction of the molded product 166A, and between the base end face 403 and the flat portion 513 in the radial direction of the molded product 166A. The bottom surface of the groove 512 is a plane parallel to the flat portion 513.

[0149] A plurality of rounded portions 255A are provided protruding in the axial direction from base end surface 402 and flat portion 503 on one axial side of main body 501. Rounded portion 255A has an outer edge portion 257A in which inclined portion 435A shown in FIG. 13 is circumferentially adjacent to inclined portion 432A (second inclined portion) shown in FIG. 12, which will later become inclined portion 432, and a pair of arms 256 extending from both circumferential ends of molding 166A of outer edge portion 257A toward the center of base 240A. Inclined portion 432A is continuous with flat portion 503 at an obtuse angle.

[0150] 13 are provided in plurality, protruding in the axial direction from the base end surface 403 and the flat portion 513 on one axial side of the main body 501. The round portion 265A has an outer edge 267A in which an inclined portion 442A (second inclined portion) shown in FIG. 13, which will later become the inclined portion 442, is circumferentially adjacent to the inclined portion 445A shown in FIG. 12, and a pair of arms 266 extending from both circumferential ends of the molding 166A of the outer edge 257A toward the center of the base 240A. The inclined portion 442A is continuous with the flat portion 513 at an obtuse angle.

[0151] The molded product 166A formed into the above shape by the compression step is heated in the sintering step and processed into a sintered body 166A.

[0152] Then, in the removal process, a portion of the outer circumferential side of the sintered body 166A is removed. In the removal process, as indicated by the two-dot chain lines in FIGS. 12 and 13 , the portions of the sintered body 166A radially outward from predetermined positions of the inclined portions 432A and 445A shown in FIG. 12 and the portions radially outward from predetermined positions of the inclined portions 435A and 442A shown in FIG. 13 are removed, and the seal groove 271 is formed. As a result, the side surface 401, which is the circumferential surface of the base 240, is formed, and the inclined portions 442 and 445, which form a continuous obtuse angle with the side surface 401, are formed on the base end surface 403 of the base 240. At the same time, the inclined portions 432 and 435, which form a continuous obtuse angle with the side surface 401, are formed on the base end surface 402 of the base 240.

[0153] In the sintered body 166A, the base 240A has a groove 502 formed in the base end surface 402, and the portion radially outward from the groove 502 is a flat portion 503. A portion of the groove 502 that remains after the removal process and is closer to the main body 501 than the bottom of the groove 502 is an inclined portion 435 that is continuous with the side surface 401 and forms an obtuse angle B.

[0154] Furthermore, the sintered body 166A has a base 240A having a groove 512 formed in the base end surface 403, and the portion radially outward from the groove 512 is a flat portion 513. A portion of the groove 512 that remains after the removal step and is closer to the main body 501 than the bottom of the groove 512 is an inclined portion 445 that is continuous with the side surface 401 and forms an obtuse angle B.

[0155] By performing the removal process, the sintered body 166A becomes the second piston body 166.

[0156] 4 , the passage within the through-hole 259 and the recessed chamber 258 to which this through-hole 259 opens constitute a passage portion 281 provided in the second piston body 166. The second piston body 166 is provided with a plurality of passage portions 281 at equal intervals in the circumferential direction of the second piston body 166. The passage portions 281 communicate with the passage within the radial communicating groove 253 and the passage within the communicating groove 263.

[0157] The through hole 269 and the recessed chamber 268 to which this through hole 269 opens constitute a passage portion 282 provided in the second piston body 166. The second piston body 166 is provided with a plurality of passage portions 282 at equal intervals in the circumferential direction of the second piston body 166.

[0158] The outer periphery of the second piston body 166 is fitted into the cylindrical portion 193 of the case member 178 with the boss portion 241 and the valve seat portion 242 facing away from the bottom portion 191 of the case member 178. In this state, the O-ring 165 seals the gap between the cylindrical portion 193 of the case member 178 and the second piston body 166.

[0159] The case member 178, O-ring 165, and second piston body 166 form a case chamber 285 inside the case member 178. The case chamber 285 is provided between a bottom 191 of the case member 178 and the second piston body 166. The valve member 167, discs 168, 170, 172, 173, 174, 176, spring member 169, and disc spring 177 are provided within this case chamber 285. The second piston body 166 has a valve seat portion 245 disposed on the case chamber 285 side.

[0160] A first chamber communication chamber 286 that stores oil L is formed within the case chamber 285. The first chamber communication chamber 286 is surrounded by the case member 178, the disc spring 177, the disk 174, the disk 173, the disk 172, the disk 170, the spring member 169, the disk 168, the valve member 167, and the second piston body 166.

[0161] A second-chamber communication chamber 287 that stores oil L is formed within the case chamber 285. The second-chamber communication chamber 287 is surrounded by the disk 173, the disk 174, the disc spring 177, and the disk 176. The first-chamber communication chamber 286 is the portion of the case chamber 285 excluding the second-chamber communication chamber 287. The second-chamber communication chamber 287 communicates with a passage within the passage hole 205 of the disc spring 177, and the passage within the passage hole 205 communicates with passages within the multiple passage holes 195 in the bottom 191 of the case member 178.

[0162] The first chamber communication chamber 286 and the second chamber communication chamber 287 are blocked from communication by the disc spring 177 , the disc 174 that abuts against the outer periphery of the disc spring 177 , and the disc 173 that abuts against the disc 174 .

[0163] As shown in Fig. 3, the annular second piston body 166 and the bottomed cylindrical case member 178 are disposed in the second chamber 23, which is one of the first chamber 22 and the second chamber 23. In this case, the valve seat portion 242 of the second piston body 166 is disposed on the second chamber 23 side. As shown in Fig. 4, the passage within the passage hole 195 of the case member 178 is constantly in communication with the second chamber 23. Therefore, the second-chamber communication chamber 287 is in communication with the second chamber 23.

[0164] The first chamber communication chamber 286 is constantly connected to the first chamber 22 via a flow path 288 in the communication groove 263 of the second piston body 166 and the intermediate chamber 237 in the second inner circumferential wall 233, the axial flow path 54 of the rod 31, and the piston internal flow path 103 and piston passage 81 provided in the first piston body 21 shown in Figure 3.

[0165] As the disk 174 shown in FIG. 4 bends in the axial direction, the volumes of the first-chamber communication chamber 286 and the second-chamber communication chamber 287 change. The second-chamber communication chamber 287 decreases in volume to absorb the increase in the volume of the first-chamber communication chamber 286, thereby discharging the oil L to the second chamber 23. The second-chamber communication chamber 287 increases in volume to absorb the decrease in the volume of the first-chamber communication chamber 286, thereby allowing the oil L to flow in from the second chamber 23. Conversely, the first-chamber communication chamber 286 decreases in volume to absorb the increase in the volume of the second-chamber communication chamber 287, thereby discharging the oil L to the first chamber 22 side shown in FIG. 3. The first-chamber communication chamber 286 increases in volume to absorb the decrease in the volume of the second-chamber communication chamber 287, thereby allowing the oil L to flow in from the first chamber 22 side. In this way, the deformation of the disk 174 is prevented from being hindered by the oil L in the first chamber communication chamber 286 and the second chamber communication chamber 287 .

[0166] As shown in FIG. 3, the plurality of passages 282 of the second piston body 166 are provided facing the second chamber 23 and are constantly in communication with the second chamber 23 .

[0167] The valve member 167 shown in FIG. 4 is flexible. The valve member 167 has an outer diameter equal to the outer diameter of the valve seat portion 245 of the second piston body 166. The valve member 167 is constantly in contact with the boss portion 244 and is capable of reseating from and reseating on the valve seat portion 245, i.e., the multiple round portions 265. When the valve member 167 is seated on the entire valve seat portion 245, it closes all of the passage portions 282. When the valve member 167 is reseated from one of the round portions 265 of the valve seat portion 245, it opens the passage portion 282 inside the unseated round portion 265.

[0168] The spring member 169 biases the valve member 167 so that it abuts against the valve seat portion 245 of the second piston body 166. The biasing force of the spring member 169 causes the valve member 167 to seat on the valve seat portion 245 and close the passage portion 282. The valve member 167 deforms against the biasing force of the spring member 169 and disengages from the valve seat portion 245, thereby opening the passage portion 282.

[0169] When the valve member 167 leaves the valve seat 245, it communicates between the plurality of passages 282 and the first-chamber communication chamber 286. As a result, the second chamber 23 communicates with the first chamber 22 via the plurality of passages 282, the first-chamber communication chamber 286, the flow path 288 in the communication groove 263 of the second piston body 166, the intermediate chamber 237 in the second inner circumferential wall 233, the axial flow path 54 of the rod 31, and the intra-piston flow path 103 and piston passage 81 provided in the first piston body 21 shown in Figure 3. At this time, the valve member 167 shown in Figure 4 suppresses the flow of oil L between it and the valve seat 245, thereby generating a damping force.

[0170] The valve member 167 is an inflow valve that opens when oil L is allowed to flow from the second chamber 23 to the first-chamber communication chamber 286 via the plurality of passages 282. The valve member 167 is a check valve that restricts the outflow of oil L from the first-chamber communication chamber 286 to the second chamber 23 via the passages 282. Here, the passages 281 open outside the range of the valve seat 245 in the second piston body 166. Therefore, the passages 281 are always in communication with the first-chamber communication chamber 286 regardless of the valve member 167 seated on the valve seat 245.

[0171] A second flow path 291 is formed by the plurality of passage portions 282, the passage between the valve member 167 and the valve seat portion 245 that appears when the valve is open, the first-chamber communication chamber 286, the flow path 288 in the communication groove 263, the intermediate chamber 237, the axial flow path 54, the in-piston flow path 103 shown in FIG. 3 , and the piston passage 81. The second flow path 291 is opened and closed by the valve member 167 shown in FIG. 4 . When the first piston body 21 moves toward the second chamber 23, the oil L flows from the second chamber 23, which is the upstream side in the cylinder 4, to the first chamber 22, which is the downstream side. The second flow path 291 serves as a compression-side passage through which the oil L flows from the second chamber 23, which is the upstream side, to the first chamber 22, which is the downstream side, when the first piston body 21 moves toward the second chamber 23, i.e., during the compression stroke. At least a portion of the second compression flow path 291, in this case the entirety of the second compression flow path 291, is arranged in parallel with the first compression flow path 132 shown in Figure 2. The second flow path 291 includes the first chamber-side flow path 156.

[0172] As shown in Fig. 4, the passage in the passage hole 195, the passage in the passage hole 205, and the second-chamber communication chamber 287 constitute a second-chamber communication flow path 292. The second-chamber communication flow path 292 is a compression-side flow path that is always connected to the second chamber 23. The compression-side second-chamber communication flow path 292 is provided separately from the second flow path 291, which is also on the compression side. The second-chamber communication flow path 292 is provided in parallel to the second flow path 291.

[0173] The valve member 167, the second piston body 166 including the valve seat portion 245, the disc 168, and the spring member 169 constitute a valve mechanism 301. The valve mechanism 301 is provided in the second flow path 291 on the compression side. The valve mechanism 301 opens and closes this second flow path 291 to suppress the flow of oil L from this second flow path 291 to the first chamber 22, thereby generating a damping force. The valve mechanism 301 is a compression side valve mechanism.

[0174] The valve mechanism 301 includes a valve seat portion 245 serving as a valve seat and a valve member 167 serving as a flexible valve body, and serves as a check valve mechanism that allows flow in the second flow path 291 from the second chamber 23, which is the upstream region, toward the first chamber 22, which is the downstream region, during the compression stroke, while restricting flow from the first chamber 22, which is the upstream region, toward the second chamber 23, which is the downstream region, during the extension stroke. In other words, the valve mechanism 301 only allows flow in the second flow path 291 from the second chamber 23, which is the upstream region, toward the first chamber 22, which is the downstream region, during the compression stroke.

[0175] The valve mechanism 301 has a valve seat portion 245 provided on the second piston body 166. The valve mechanism 301 is disposed separately from the valve mechanism 86 that generates a damping force during the same compression stroke. The valve member 167 that constitutes the compression-side valve mechanism 301 is a compression-side sub-valve.

[0176] In the compression-side valve mechanism 301, neither the valve seat portion 245 nor the valve member 167 abutting thereon has a fixed orifice formed therein that connects the first chamber 22 and the second chamber 23 even when the valve seat portion 245 and the valve member 167 are in contact with each other. In other words, the second flow path 291 does not have a fixed orifice that constantly connects the first chamber 22 and the second chamber 23. The second flow path 291 is not a passage that constantly connects the first chamber 22 and the second chamber 23.

[0177] The second flow path 291 on the compression side, which allows communication between the first chamber 22 and the second chamber 23, is arranged in parallel with the first flow path 132, which is also a compression side passage that allows communication between the first chamber 22 and the second chamber 23. A valve mechanism 86 is provided in the first flow path 132. A valve mechanism 301 is provided in the second flow path 291. Thus, the valve mechanism 86 and the valve mechanism 301 on the compression side are arranged in parallel.

[0178] The valve member 163 is flexible. The valve member 163 has an outer diameter equal to the outer diameter of the valve seat portion 242 of the second piston body 166. The valve member 163 is constantly in contact with the boss portion 241 and is capable of reseating on the valve seat portion 242, i.e., the multiple round portions 255. When the valve member 163 is seated on the entire valve seat portion 242, it closes all of the passage portions 281. When the valve member 163 is released from one of the round portions 255 of the valve seat portion 242, it opens the passage portion 281 inside the released round portion 255.

[0179] The disk 162 has an outer diameter smaller than that of the valve member 163 and smaller than that of the boss portion 241 .

[0180] The spring member 161 has flexibility and includes a substrate portion 311 and a plurality of spring plate portions 312.

[0181] The base plate 311 is a circular flat plate with holes. The mounting shaft 33 is fitted into the inner periphery of the base plate 311. The outer diameter of the base plate 311 is slightly larger than the outer diameter of the disk 162. The base plate 311 abuts against the disk 162.

[0182] The plurality of spring plate portions 312 extend radially from the outer periphery of the base plate portion 311. The plurality of spring plate portions 312 are spaced farther from the base plate portion 311 in the axial direction of the base plate portion 311 as they move radially outward from the base plate portion 311.

[0183] The maximum outer diameter of the spring member 161 is smaller than the outer diameter of the valve member 163. The spring member 161 has multiple spring plate portions 312 oriented to extend from the base plate portion 311 toward the valve member 163 in the axial direction of the base plate portion 311. The extending tip ends of the multiple spring plate portions 312 of the spring member 161 press against the outer periphery of the valve member 163. As a result, the multiple spring plate portions 312 of the spring member 161 urge the outer periphery of the valve member 163 so that it abuts against the valve seat portion 242 of the second piston body 166. The urging force of the spring member 161 causes the valve member 163 to seat on the valve seat portion 242 and close the passage portion 281. The valve member 163 deforms against the urging force of the spring member 161 and lifts off the valve seat portion 242, opening the passage portion 281.

[0184] The valve member 163 is provided in the second chamber 23. When the valve member 163 is lifted off the valve seat 242, the first-chamber communication chamber 286 and the second chamber 23 communicate with each other via the plurality of passages 281 in the second piston body 166. At this time, the valve member 163 suppresses the flow of oil L between the valve seat 242 and the valve member 163, thereby generating a damping force. The valve member 163 is a discharge valve that opens when oil L is discharged from the first-chamber communication chamber 286 to the second chamber 23 via the plurality of passages 281. The valve member 163 is a check valve that restricts the flow of oil L from the second chamber 23 into the first-chamber communication chamber 286 via the passages 281. Here, the passages 282 open outside the range of the valve seat 242 in the second piston body 166. Therefore, the passage portion 282 is always in communication with the second chamber 23 regardless of whether the valve member 163 is seated on the valve seat portion 242 .

[0185] The radial communicating groove 253 formed in the boss portion 241 of the second piston body 166 serves as a radial flow path 317. The radial flow path 317 is provided at a position facing the axial flow path 54 in the radial direction of the second piston body 166, and is connected to the intermediate chamber 237.

[0186] As shown in FIG. 3 , the second flow path 315 is made up of the first-chamber-side flow path 156 consisting of the piston passage 81 and the intra-piston flow path 103, the axial flow path 54 of the rod 31, the intermediate chamber 237 and the flow path 288 in the second inner circumferential wall 233 of the second piston body 166, the first-chamber communication chamber 286, the passage portion 281, the radial flow paths 317 shown in FIG. 4 , and the passage between the valve member 163 and the valve seat portion 242 that appears when the valve is open.

[0187] The second flow path 315 is opened and closed by a valve member 163. When the first piston body 21 moves toward the first chamber 22 (shown in FIG. 3 ), the oil L flows from the first chamber 22 (on the upstream side) in the cylinder 4 to the second chamber 23 (on the downstream side). The second flow path 315 serves as an extension-side passage through which the oil L flows from the first chamber 22 (on the upstream side) to the second chamber 23 (on the downstream side) as the first piston body 21 moves toward the first chamber 22, i.e., during the extension stroke. The extension-side second flow path 315 is provided separately from the extension-side first flow path 152. The second flow path 315 is at least partially, in this case, partially parallel to the first flow path 152. The second flow path 315 is parallel to the first flow path 152 except for a portion of the piston passage 81 closer to the first chamber 22 than the in-piston flow path 103.

[0188] 4 connects the intermediate chamber 237 of the second flow path 315 to the passage portion 281 without passing through the flow path 288 in the communication groove 263 or the first-chamber communication chamber 286. The radial flow path 317 connects the intermediate chamber 237 to the valve seat portion 242. In other words, the radial flow path 317 connects the insertion hole 231 to the valve mechanism 321 including the valve seat portion 242.

[0189] As shown in FIG. 3 , the rod 31 is formed with an axial flow path 54 which is a flow path that communicates with the first-chamber-side flow path 156 and leads toward the second chamber 23, which is the downstream region during the extension stroke; a tip-side circumferential groove 53 which is a circumferential groove provided at the end of the axial flow path 54 on the side of the second chamber 23, which is the downstream region during the extension stroke; and a tip-side cylindrical portion 43 which is a cylindrical portion provided on the second chamber 23 side of the tip-side circumferential groove 53.

[0190] 4, the outer diameter of the disk 160 is equal to the outer diameter of the valve member 163. The disk 160 is flexible.

[0191] The valve member 163, the second piston body 166 including the valve seat portion 242, the disc 162, and the spring member 161 constitute a valve mechanism 321. The valve mechanism 321 is provided in the extension-side second flow path 315 and opens and closes the second flow path 315. The valve mechanism 321 generates a damping force by suppressing the flow of hydraulic fluid L from the second flow path 315 to the second chamber 23. The valve mechanism 321 is an extension-side second damping force generating mechanism. The valve mechanism 321 is arranged separately from the valve mechanism 85 that generates a damping force during the same extension stroke. The valve member 163 that constitutes the extension-side valve mechanism 321 is an extension-side sub-valve. The valve mechanism 321 includes radial flow paths 317. In the valve mechanism 321, during the extension stroke, the oil L flows from the first chamber-side flow path 156 shown in Fig. 3 to the second chamber 23, which is the downstream region, via the axial flow path 54 including the tip-side circumferential groove 53, the intermediate chamber 237, and the radial flow paths 317 shown in Fig. 4. In other words, in the valve mechanism 321, during the extension stroke, the oil L flows from the first chamber-side flow path 156 to the second chamber 23, which is the downstream region, via the axial flow path 54 including the tip-side circumferential groove 53, the insertion hole 231, and the radial flow paths 317.

[0192] The valve mechanism 321 includes a valve seat portion 242 serving as a valve seat and a valve member 163 serving as a flexible valve body, and serves as a check valve mechanism that allows flow from the first chamber 22, which is the upstream region, toward the second chamber 23, which is the downstream region, during the extension stroke of the second flow path 315 including the first chamber-side flow path 156, while restricting flow from the second chamber 23, which is the upstream region, toward the first chamber 22, which is the downstream region, during the compression stroke. In other words, the valve mechanism 321 only allows flow from the first chamber 22, which is the upstream region, toward the second chamber 23, which is the downstream region, during the extension stroke of the second flow path 315 including the first chamber-side flow path 156.

[0193] The second chamber communication chamber 287 and the disk 174, disk 173, disc spring 177 and disk 176 that form the second chamber communication chamber 287 constitute a second chamber volume variable mechanism 325 that can change the volume of the second chamber communication chamber 287.

[0194] The second-chamber volume variable mechanism 325 deforms and moves the disks 174 and 173 together so as to move away from the bottom 191. As a result, the second-chamber volume variable mechanism 325 changes the volume of the second-chamber communication chamber 287 to increase it. At that time, if the disk 174 remains in contact with the disc spring 177 over the entire circumference, the space between the disk 174 and the outer tapered portion 202 of the disc spring 177 is blocked. In other words, if the disk 174 remains in contact with the disc spring 177 over the entire circumference when it deforms so as to move away from the bottom 191, the second-chamber communication chamber 287 and the first-chamber communication chamber 286 are kept blocked.

[0195] Furthermore, the second chamber volume variable mechanism 325 deforms and moves the disks 174 and 173 together so that they approach the bottom 191. As a result, the second chamber volume variable mechanism 325 changes the volume of the second chamber communication chamber 287 to decrease it. At this time, the disk 174 is maintained in a state where it is entirely in contact with the disc spring 177, and the gap between the disk 174 and the outer tapered portion 202 of the disc spring 177 is closed.

[0196] The first chamber communication chamber 286, which is in communication with the first chamber 22, constitutes a part of the extension-side second flow path 315. The first chamber communication chamber 286, and the second piston body 166, valve member 167, disk 168, spring member 169, disk 170, disk 172, disk 173, disk 174, disk 176, disc spring 177, and case member 178 that form the first chamber communication chamber 286, constitute a first chamber volume variable mechanism 326 that can change the volume of the first chamber communication chamber 286.

[0197] The first chamber volume variable mechanism 326 deforms and moves the disc 174 and the disc 173 together so that they move away from the disc 170. As a result, the first chamber volume variable mechanism 326 changes the volume of the first chamber communication chamber 286 to increase it. At this time, if the disc 173 remains in full contact with the disc 174, it closes the passage inside the communication hole 211 of the disc 174. In other words, the second chamber communication chamber 287 and the first chamber communication chamber 286 are kept blocked from each other.

[0198] Furthermore, the first chamber volume variable mechanism 326 deforms and moves the disks 174 and 173 so that they approach the disk 170. As a result, the first chamber volume variable mechanism 326 changes the volume of the first chamber communication chamber 286 to decrease it. At this time, the disk 173 is maintained in overall contact with the disk 174, blocking the passage in the communication hole 211 of the disk 174.

[0199] In the extension-side valve mechanism 321, neither the valve seat portion 242 nor the valve member 163 abutting thereon has a fixed orifice that communicates between the first chamber 22 and the second chamber 23, even when the valve seat portion 242 and the valve member 163 are in contact with each other. In other words, the extension-side valve mechanism 321 does not communicate between the first chamber 22 and the second chamber 23 when the valve seat portion 242 and the valve member 163 are in contact with each other. In other words, the second flow path 315 does not have a fixed orifice that constantly communicates between the first chamber 22 and the second chamber 23. The second flow path 315 is not a passage that constantly communicates between the first chamber 22 and the second chamber 23.

[0200] The spring member 161, the disk 162, the valve member 163, the O-ring 165, the second piston body 166, the valve member 167, the disk 168, the spring member 169, the disk 170, the disk 172, the disk 173, the disk 174, the disk 176, the disc spring 177, and the case member 178 constitute the second piston 331. The second piston body 166 is a sintered body that constitutes the second piston 331 used in the shock absorber 1.

[0201] Therefore, the second piston 331 has a first inner circumferential wall 232 that penetrates the center in the axial direction and through which the rod 31 is inserted, and a second inner circumferential wall 233 that is radially spaced apart from the rod 31 with respect to the first inner circumferential wall 232, and has an insertion hole 231 that directly or indirectly communicates with the tip-side circumferential groove 53 of the rod 31. The second piston 331 also has a valve mechanism 321 that includes a valve seat portion 242 that serves as a valve seat and a valve member 163 that is a flexible valve body, and that allows flow through the first-chamber-side flow path 156 only in the direction from the first chamber 22 to the second chamber 23. The second piston 331 also has a valve mechanism 301 and a valve mechanism 321. The second piston 331 also has a case member 178 that communicates with an intermediate chamber 237 formed by the second inner circumferential wall 233 and the rod 31 and forms a first-chamber communication chamber 286 that stores oil liquid L. The second piston 331 has a valve mechanism 321 that includes an insertion hole 231 that penetrates the center in the axial direction and through which the rod 31 is inserted, a valve seat portion 242 that serves as a valve seat, and a valve member 163 that is a flexible valve body disposed in the axial flow path 54, and that allows the oil liquid L to flow only in a direction from the first chamber 22 to the second chamber 23. The second piston 331 is also provided at a position opposite the axial flow path 54 and has a radial flow path 317 that communicates with the valve mechanism 321. The second piston 331 also has one or more extension sections 235 extending radially from the insertion hole main body 234 and formed from the surface opposite to the surface facing the first piston 155 to a position communicating with the axial flow path 54, a case member 178 communicating with the extension section 235 and forming a first chamber communication chamber 286 for storing oil liquid L, and a passage section 281 connecting the first chamber communication chamber 286 and the valve mechanism 321.

[0202] 3, the second piston 331 has an outer diameter smaller than that of the first piston 155. There is a radial gap between the second piston 331 and the inner cylinder 2. The second piston 331 extends across the tip-side circumferential groove 53 and the tip-side cylindrical portion 43 of the rod 31.

[0203] As described above, the first chamber volume variable mechanism 326 shown in FIG. 4 changes the volume of the first chamber communication chamber 286 by deforming and moving the disc 174 away from the disc 170. At this time, with the valve mechanism 321 open, the pressure difference between the first chamber communication chamber 286 and the second chamber communication chamber 287 may exceed a predetermined value. Then, the first chamber volume variable mechanism 326 causes the disc 174 to elastically deform the outer tapered portion 202 of the disc spring 177 toward the bottom 191, while deforming the outer periphery toward the bottom 191. As a result, the disc 174 moves away from the disc 170 in the axial direction. Then, the disc 174 communicates between the first chamber communication chamber 286 and the second chamber communication chamber 287 via the passage in the communication hole 211.

[0204] The disks 174 and 173 constitute a relief mechanism 335. When the relief mechanism 335 is open, it causes the oil L to flow from the first-chamber communication chamber 286 to the second-chamber communication chamber 287. In other words, the relief mechanism 335 causes the oil L to flow from the first chamber 22 to the second chamber 23. The relief mechanism 335 is an extension-side relief mechanism. The relief mechanism 335 is set to open after the extension-side valve mechanism 321 opens.

[0205] The second-chamber volume variable mechanism 325 changes the volume of the second-chamber communication chamber 287 so that it increases by deforming and moving the disc 174 toward the disc 170. At this time, with the valve mechanism 301 open, the pressure difference between the first-chamber communication chamber 286 and the second-chamber communication chamber 287 may exceed a predetermined value. In this case, the second-chamber volume variable mechanism 325 increases the amount of deformation on the outer periphery of the disc 174. As a result, the disc 174 moves axially away from the outer periphery of the disc spring 177. In this case, the disc 174 communicates with the second-chamber communication chamber 287 and the first-chamber communication chamber 286 via the disc 174 and the disc spring 177.

[0206] The disk 174 and the disc spring 177 constitute a relief mechanism 336. When the relief mechanism 336 is open, it causes oil L to flow from the second-chamber communication chamber 287 to the first-chamber communication chamber 286. In other words, the relief mechanism 336 causes oil L to flow from the second chamber 23 to the first chamber 22. The relief mechanism 336 is a compression-side relief mechanism. The relief mechanism 336 is set to open after the compression-side valve mechanism 301 opens.

[0207] 1, the base valve 15 has a valve mechanism 351 on the bottom 9 side of the valve body 12 in the axial direction. The base valve 15 also has a valve mechanism 352 on the opposite side of the valve body 12 from the bottom 9 in the axial direction.

[0208] When the rod 31 moves toward the compression side and the first piston body 21 moves in a direction narrowing the second chamber 23, and the pressure in the second chamber 23 becomes higher than the pressure in the reservoir chamber 5 by a predetermined value or more, the valve mechanism 351 of the base valve 15 opens, causing the oil L in the second chamber 23 to flow into the reservoir chamber 5. At that time, the valve mechanism 351 generates a damping force.

[0209] When the rod 31 moves in the extension direction and the first piston body 21 moves toward the first chamber 22, causing the pressure in the second chamber 23 to drop below the pressure in the reservoir chamber 5, the valve mechanism 352 of the base valve 15 opens, allowing the oil L in the reservoir chamber 5 to flow into the second chamber 23. At that time, the valve mechanism 352 generates a damping force. The valve mechanism 352 may be a suction valve that allows the oil L to flow from the reservoir chamber 5 into the second chamber 23 without generating a damping force.

[0210] Next, the operation of the shock absorber 1 will be described.

[0211] Of the extension-side valve mechanism 85 and valve mechanism 321 shown in FIG. 3 , the valve member 151 of the valve mechanism 85 is more rigid than the valve member 163 of the valve mechanism 321 shown in FIG. 4 and has a higher valve opening pressure than the valve member 163. Therefore, during the extension stroke, in the extremely low-speed region where the piston speed is slower than a predetermined value, the valve mechanism 85 shown in FIG. 3 remains closed while the valve mechanism 321 opens. In other words, the valve mechanism 321 opens to generate a damping force when the piston speed is slower than that of the valve mechanism 85. Furthermore, in the normal speed region where the piston speed is equal to or greater than the predetermined value, both the valve mechanism 85 and the valve mechanism 321 open. The valve member 163 shown in FIG. 4 is an extremely low-speed valve that deforms against the biasing force of the spring member 161 to open and generate a damping force in the extremely low-speed region.

[0212] That is, during the extension stroke, the first piston body 21 shown in FIG. 3 moves toward the first chamber 22, increasing the pressure in the first chamber 22 and decreasing the pressure in the second chamber 23. Here, neither the valve mechanisms 85, 86 nor the valve mechanisms 301, 321 have a fixed orifice that constantly connects the first chamber 22 and the second chamber 23. Therefore, the oil L in the first chamber 22 flows into the first-chamber-communicating chamber 286 via the first-chamber-side flow path 156 of the first piston body 21, the axial flow path 54 of the rod 31, and the intermediate chamber 237 and flow path 288 of the second piston body 166. This increases the pressure in the first-chamber-communicating chamber 286. Therefore, before the valve mechanism 321 opens, the first-chamber volume variable mechanism 326 bends a portion radially inward of the contact position of the disc 174's coned disc spring 177 against the outer tapered portion 202 toward the bottom 191. As a result, the disk 174 increases the capacity of the first-chamber communication chamber 286. As a result, the first-chamber volume variable mechanism 326 suppresses an increase in pressure in the first-chamber communication chamber 286. At this time, the disk 173 deforms following the shape of the disk 174, maintaining the closed state of the passage in the communication hole 211. Also, at this time, the disk 174 bends and moves toward the bottom 191, causing the second-chamber volume variable mechanism 325 to reduce the volume of the second-chamber communication chamber 287.

[0213] Here, during the extension stroke when the shock absorber 1 is subjected to low-frequency input (large-amplitude vibration), the amount of oil L flowing from the first chamber 22 to the first-chamber communication chamber 286 increases. This causes the disc 174 to deform significantly. As the amount of deformation of the disc 174 increases, the reaction force due to the support rigidity of the clamped inner periphery side increases, limiting the amount of deformation. This causes the first-chamber communication chamber 286 to increase in pressure. As a result, the pressure in the second flow path 315 increases to the point where the valve mechanism 321 opens.

[0214] At this time, neither the valve mechanisms 85, 86 nor the valve mechanisms 301, 321 have a fixed orifice that constantly communicates between the first chamber 22 and the second chamber 23. As a result, the damping force rises abruptly during the extension stroke when the piston speed is less than the first predetermined value at which the valve mechanism 321 opens. Furthermore, in a region where the piston speed is higher than the first predetermined value but is in an extremely low speed region that is higher than the first predetermined value but lower than a second predetermined value, the valve mechanism 321 opens while the valve mechanism 85 remains closed.

[0215] That is, the valve member 163 deforms against the biasing force of the spring member 161 and lifts off the valve seat 242. This causes the first chamber 22 and the second chamber 23 to communicate with each other through the extension-side second flow path 315. Therefore, the oil L in the first chamber 22 flows to the second chamber 23 via the first-chamber-side flow path 156 of the first piston body 21, the axial flow path 54 of the rod 31, the intermediate chamber 237, flow path 288, and passage 281 of the second piston body 166, and the passage between the valve member 163 and the valve seat 242. At this time, the oil L in the first chamber 22 also flows to the second chamber 23 via the first-chamber-side flow path 156, the axial flow path 54, the intermediate chamber 237 and radial flow paths 317 of the second piston body 166, and the passage between the valve member 163 and the valve seat 242. As a result, even in an extremely low speed region where the piston speed is slower than the second predetermined value, a damping force with a valve characteristic (a characteristic in which the damping force is approximately proportional to the piston speed) can be obtained.

[0216] Furthermore, a relief mechanism 335 is provided that opens after the valve mechanism 321 opens during the extension stroke. Therefore, when the pressure in the first-chamber communication chamber 286 increases in a normal speed region where the piston speed is equal to or greater than a second predetermined value, the relief mechanism 335 opens while the valve mechanism 321 remains open, allowing the hydraulic fluid L in the first-chamber communication chamber 286 to flow to the second chamber 23 via the second-chamber communication chamber 287 and the second-chamber communication flow path 292. Thereafter, the valve mechanism 85 opens while the valve mechanism 321 and the relief mechanism 335 remain open. That is, when the valve member 163 deforms against the biasing force of the spring member 161 and lifts off the valve seat portion 242 as described above, the hydraulic fluid L flows from the first chamber 22 to the second chamber 23 through the extension-side second flow path 315. Thereafter, while the valve mechanism 321 remains open, the relief mechanism 335 opens, allowing the hydraulic fluid L to flow from the first chamber 22 to the second chamber 23 via the second-chamber communication chamber 287 and the second-chamber communication passage 292. At this time, the flow of the hydraulic fluid L is throttled in the first-chamber-side passage 156 provided in the second passage 315. This increases the pressure applied to the valve member 151, increasing the pressure difference, causing the valve member 151 to separate from the valve seat 105, and allowing the hydraulic fluid L to flow from the first chamber 22 to the second chamber 23 via the extension-side first passage 152. Therefore, the hydraulic fluid L in the first chamber 22 flows to the second chamber 23 via the first passage 152, which is made up of the piston passage 81 and the passage between the valve member 151 and the valve seat 105.

[0217] As a result, even in the normal speed region where the piston speed is equal to or greater than the second predetermined value, a damping force with valve characteristics (where the damping force is approximately proportional to the piston speed) can be obtained. The rate of increase in the extension damping force relative to an increase in piston speed in the normal speed region is lower than the rate of increase in the extension damping force relative to an increase in piston speed in the extremely low speed region.

[0218] As described above, during the extension stroke, when the piston speed is in the normal speed range where it is equal to or greater than the second predetermined value, the valve member 151 opens, allowing the oil L to flow at a large flow rate through the first flow path 152. This reduces the flow rate through the passage between the valve member 163 and the valve seat portion 242. Therefore, for example, it is possible to reduce the rate of increase in the damping force relative to an increase in the piston speed when the piston speed is in the normal speed range (equal to or greater than the second predetermined value). This allows for greater design flexibility.

[0219] During the extension stroke when a high-frequency input (small-amplitude vibration) occurs, in which a higher frequency than the low-frequency input described above is input to the shock absorber 1, the amount of oil L flowing from the first chamber 22 into the first-chamber communication chamber 286 is small. Therefore, the deformation of the disc 174 is small, and the first-chamber volume variable mechanism 326 can absorb the volume of oil L flowing into the first-chamber communication chamber 286 by the amount of deflection of the disc 174. This reduces the pressure rise in the first-chamber communication chamber 286. Therefore, when the extremely low-speed damping force is building up, the same state as if the disc 174 were not present can be achieved. In other words, when the extremely low-speed damping force is building up, the first-chamber communication chamber 286 is constantly connected to the second chamber 23 via the second-chamber communication flow path 292, i.e., the same state as if the valve mechanism 321 were not present.

[0220] Therefore, during the extension stroke when a high frequency is input, the rise of the extremely low-speed damping force is gradual compared to when a low frequency is input or compared to conventional damping force characteristics. In other words, during the extension stroke, when the frequency of the first piston body 21 exceeds a predetermined frequency, the first chamber volume variable mechanism 326 including the disc 174 restricts the flow rate of the hydraulic fluid L to the valve member 163 of the valve mechanism 321. Note that the change in damping force (the slope of the damping force relative to the piston speed) until the valve mechanism 321 opens can be adjusted by varying the rigidity (plate thickness, etc.) of the disc 174.

[0221] Of the compression-side valve mechanism 86 and valve mechanism 301, the valve member 131 of valve mechanism 86 has greater rigidity and a higher valve opening pressure than the valve member 167 of valve mechanism 301. Therefore, during the compression stroke, in the extremely low-speed region where the piston speed is slower than a predetermined value, the valve mechanism 86 remains closed while the valve mechanism 301 opens. In other words, the valve mechanism 301 opens to generate a damping force when the piston speed is slower than that of the valve mechanism 86. In the normal speed region where the piston speed is equal to or greater than this predetermined value, both the valve mechanism 86 and the valve mechanism 301 open. The valve member 167 is an extremely low-speed valve that opens to generate a damping force when the piston speed is in the extremely low-speed region.

[0222] That is, during the compression stroke, the first piston body 21 moves toward the second chamber 23, increasing the pressure in the second chamber 23 and decreasing the pressure in the first chamber 22. Here, neither the valve mechanisms 85, 86 nor the valve mechanisms 301, 321 have a fixed orifice that constantly connects the second chamber 23 and the first chamber 22. Therefore, the oil L in the second chamber 23 flows into the second-chamber communication chamber 287 via the second-chamber communication flow path 292. This increases the pressure in the second-chamber communication chamber 287. Therefore, in the second-chamber volume variable mechanism 325, the disc 174 bends toward the disc 170 before the valve mechanism 301 opens. This causes the disc 174 to increase the volume of the second-chamber communication chamber 287. As a result, the second-chamber volume variable mechanism 325 suppresses an increase in pressure in the second-chamber communication chamber 287. At this time, the disc 173 deforms following the shape of the disc 174, maintaining the closed state of the passage in the communication hole 211. Also, at this time, the disc 174 bends and moves toward the disc 170, causing the first chamber volume variable mechanism 326 to reduce the volume of the first chamber communication chamber 286.

[0223] Here, during the compression stroke when the shock absorber 1 is subjected to low-frequency input (large-amplitude vibration), the amount of oil L flowing from the second chamber 23 to the second-chamber communication chamber 287 increases. This causes the disc 174 to deform significantly. As the amount of deformation of the disc 174 increases, the reaction force due to the support rigidity of the clamped inner periphery increases, limiting the amount of deformation. This causes the pressure in the second-chamber communication chamber 287 to increase. As a result, the pressure in the second flow path 291 increases until the valve mechanism 301 opens.

[0224] At this time, neither the valve mechanisms 85, 86 nor the valve mechanisms 301, 321 have a fixed orifice that constantly communicates between the second chamber 23 and the first chamber 22. As a result, the damping force rises abruptly during the compression stroke when the piston speed is less than the third predetermined value at which the valve mechanism 301 opens. Furthermore, in a region where the piston speed is higher than the third predetermined value but in an extremely low speed region that is higher than the third predetermined value but lower than a fourth predetermined value, the valve mechanism 301 opens while the valve mechanism 86 remains closed.

[0225] That is, when the valve member 167 deforms against the biasing force of the spring member 169 and leaves the valve seat 245, the second chamber 23 and the first chamber 22 are connected to each other through the compression-side second flow path 291. Thus, the oil L in the second chamber 23 flows into the first chamber 22 via the passage 282 in the second piston body 166, the passage between the valve member 167 and the valve seat 245, the first-chamber communication chamber 286, the flow path 288 and the intermediate chamber 237 in the second piston body 166, the axial flow path 54 in the rod 31, the first-chamber-side flow path 156 in the first piston body 21, and the piston passage 81 in the first piston body 21. As a result, a damping force with a valve characteristic (a characteristic in which the damping force is approximately proportional to the piston speed) can be obtained even in an extremely low speed region where the piston speed is lower than the fourth predetermined value.

[0226] Furthermore, a relief mechanism 336 is provided that opens after the valve mechanism 301 opens during the compression stroke. Therefore, in the normal speed region where the piston speed is equal to or greater than a fourth predetermined value, when the pressure in the second-chamber communication chamber 287 increases, the relief mechanism 336 opens while the valve mechanism 301 remains open, allowing the oil L from the second chamber 23 and the second-chamber communication chamber 287 to flow to the first chamber 22 via the first-chamber communication chamber 286. Subsequently, the valve mechanism 86 opens while the valve mechanism 301 and the relief mechanism 336 remain open. That is, when the valve member 167 leaves the valve seat portion 245 as described above, the oil L flows from the second chamber 23 to the first chamber 22 through the second flow path 291 on the compression side. Subsequently, while the valve mechanism 301 remains open, the relief mechanism 336 opens, allowing the oil L to flow from the second chamber 23 to the first chamber 22. At this time, the flow of hydraulic fluid L is throttled in the in-piston flow path 103, which is provided in the second flow path 291 downstream of the valve member 167 and the relief mechanism 336. This increases the pressure applied to the valve member 131, increasing the pressure difference. As a result, the valve member 131 is lifted off the valve seat 115, causing hydraulic fluid L to flow from the second chamber 23 to the first chamber 22 through the first flow path 132 on the compression side. Therefore, the hydraulic fluid L in the second chamber 23 flows into the first chamber 22 via the piston passage 82 and the passage between the valve member 131 and the valve seat 115.

[0227] As a result, even in the normal speed region where the piston speed is equal to or greater than the fourth predetermined value, a damping force with valve characteristics (where the damping force is approximately proportional to the piston speed) can be obtained. The rate of increase in the compression damping force with respect to an increase in piston speed in the normal speed region is lower than the rate of increase in the compression damping force with respect to an increase in piston speed in the extremely low speed region.

[0228] As described above, during the compression stroke, when the piston speed is in the normal speed range equal to or greater than the fourth predetermined value, the valve member 131 opens, allowing the oil L to flow at a large flow rate through the first flow path 132. This reduces the flow rate through the passage between the valve member 167 and the valve seat portion 245. Therefore, for example, it is possible to reduce the rate of increase in the damping force in response to an increase in piston speed when the piston speed is in the normal speed range (equal to or greater than the fourth predetermined value). This allows for greater design flexibility.

[0229] During the compression stroke when a high-frequency input (small-amplitude vibration) occurs, in which a higher frequency than the low-frequency input described above is input to the shock absorber 1, the amount of oil L flowing from the second chamber 23 into the second-chamber communication chamber 287 is small. Therefore, the deformation of the disc 174 is small. As a result, the second-chamber volume variable mechanism 325 can absorb the volume of oil L flowing into the second-chamber communication chamber 287 by the amount of deflection of the disc 174. Therefore, the pressure increase in the second-chamber communication chamber 287 is small. Therefore, when the extremely low-speed damping force is building up, the same state as when the disc 174 is not present is achieved. In other words, when the extremely low-speed damping force is building up, the second-chamber communication chamber 287 is constantly connected to the first-chamber communication chamber 286, i.e., the same state as when the valve mechanism 301 is not present.

[0230] Therefore, during the compression stroke when a high frequency is input, the rise of the extremely low-speed damping force is gradual compared to when a low frequency is input or compared to conventional damping force characteristics. In other words, when the frequency of the first piston body 21 exceeds a predetermined frequency, the second chamber volume variable mechanism 325 including the disk 174 restricts the flow rate of oil L to the valve member 167 of the valve mechanism 301. Note that the change in damping force (the slope of the damping force relative to the piston speed) until the valve mechanism 301 opens can be adjusted by varying the rigidity (plate thickness, etc.) of the disk 174.

[0231] The aforementioned Patent Document 1 discloses a shock absorber that generates a damping force by moving a piston attached to a piston rod within a cylinder. In this shock absorber, the piston includes a valve body and a piston body that seats and unseats the valve body. In some shock absorbers of this type, the piston body has multiple rounded portions spaced apart circumferentially, and the valve body seats and unseats on these rounded portions. When such a piston body is formed from a sintered metal, burrs may occur at the boundary between the axial end face of the piston body and the radially outer side face of the piston body, between adjacent rounded portions circumferentially. When such burrs occur, they must be removed using a blade while avoiding the rounded portions, which can be a cumbersome process and can increase costs.

[0232] In the second piston body 166, which is a sintered body of the embodiment, the base 240 is formed in a cylindrical shape having a side surface 401, a base end surface 402 that is continuous with the side surface 401 via an inclined portion 435, and a base end surface 403 that is continuous with the side surface 401 via an inclined portion 445. Therefore, in the second piston body 166, the side surface 401 and the base end surface 402 of the base 240 are continuous with each other via the inclined portion 435, thereby making it possible to suppress the occurrence of burrs between the side surface 401 and the base end surface 402. Furthermore, in the second piston body 166, the side surface 401 and the base end surface 403 of the base 240 are continuous with each other via the inclined portion 445, thereby making it possible to suppress the occurrence of burrs between the side surface 401 and the base end surface 403. Furthermore, in the second piston body 166, the outer edge portion 257 provided along the outer periphery of the base end face 402 of the round portion 255 is continuous with the side surface portion 401 via an inclined portion 432 that forms an obtuse angle A, thereby suppressing the occurrence of burrs between the outer edge portion 257 and the side surface portion 401. Furthermore, in the second piston body 166, the outer edge portion 267 provided along the outer periphery of the base end face 403 of the round portion 265 is continuous with the side surface portion 401 via an inclined portion 442 that forms an obtuse angle B, thereby suppressing the occurrence of burrs between the outer edge portion 267 and the side surface portion 401. Therefore, the second piston body 166 does not require or can reduce the need for burr removal work, thereby suppressing cost increases.

[0233] The second piston body 166 has a through hole 259 provided in the region of the base 240 surrounded by the outer edge 257 and the pair of arm portions 256, and a through hole 269 provided between the arm portions 256 of two adjacent round portions 255 on the base 240, so that flow paths for both the extension stroke and the compression stroke can be formed in the second piston body 166. Furthermore, the second piston body 166 has a through hole 269 provided in the region of the base 240 surrounded by the outer edge 267 and the pair of arm portions 266, and a through hole 259 provided between the arm portions 266 of two adjacent round portions 265 on the base 240, so that flow paths for both the extension stroke and the compression stroke can be formed in the second piston body 166. Therefore, the second piston body 166 can suppress an increase in cost.

[0234] In the second piston body 166, the rounded portions 255 and 265 are arranged out of phase on both the base end face 402 on one side of the base 240 and the base end face 403 on the other side. The through holes 259 provided in the area surrounded by the outer edge 257 and the pair of arms 256 function as through holes provided between the arms 266 of two adjacent rounded portions 265 on the base 240 at the base end face 403, and the through holes 269 provided in the area surrounded by the outer edge 267 and the pair of arms 266 function as through holes provided between the arms 256 of two adjacent rounded portions 255 on the base 240 at the base end face 402. Therefore, the second piston body 166 can efficiently form flow paths for both the extension stroke and the compression stroke. Therefore, the second piston body 166 can suppress cost increases.

[0235] In the second piston body 166, the obtuse angle B that the inclined portion 435 forms with respect to the side surface portion 401 is smaller than the obtuse angle A that the inclined portion 432 forms with respect to the side surface portion 401, and the obtuse angle B that the inclined portion 445 forms with respect to the side surface portion 401 is smaller than the obtuse angle A that the inclined portion 442 forms with respect to the side surface portion 401. Therefore, the second piston body 166 has good moldability.

[0236] In the second piston body 166, the inclined portion 435 of the base 240 is located closer to the axial center C of the side surface portion 401 than the inclined portion 432 of the outer edge portion 257, and the inclined portion 445 is located closer to the axial center C of the side surface portion 401 than the inclined portion 442 of the outer edge portion 267. Therefore, the second piston body 166 has good moldability.

[0237] In the manufacturing method of the second piston body 166, flat portions 503 are provided radially outward from the inclined portions 432A of the outer edge portion 257A of the rounded portion 255A of the molded product 166A formed in the compression process and the inclined portions 435A of the base portion 240A. Furthermore, flat portions 513 are provided radially outward from the inclined portions 442A of the outer edge portion 267A of the rounded portion 265A of the molded product 166A after the compression process and the inclined portions 445A of the base portion 240A. Then, after the sintering process, portions radially outward from predetermined positions of the inclined portions 435A, 445A are removed, and portions radially outward from the predetermined positions of the inclined portions 432A, 442A are removed. Therefore, for example, the mold M having the portions for forming the inclined portion 432A and the flat portion 503 has a shape as shown in Fig. 14, and the inclined portion forming portion 432a for forming the inclined portion 432A and the flat portion forming portion 503a for forming the flat portion 503 form an obtuse angle, thereby eliminating acute angles. Although not shown, the mold M has the same shape for the portions for forming the inclined portion 435A, the portions for forming the inclined portion 442A, and the portions for forming the inclined portion 445A, and therefore can eliminate acute angles.

[0238] In contrast, if the molded product 166A does not have, for example, a flat portion 503, the tip of the inclined portion forming portion 432a that forms the inclined portion 432A of the mold M will have an acute angle, as shown in Figure 15. In a mold, acute angles inevitably result in a thinner wall, making it more susceptible to wear and other effects, which can reduce the durability of the mold, and are therefore preferably avoided. However, if acute angles are avoided and the rounded end face is formed at a right angle as in the prior example, problems with burr removal will arise, as mentioned above.

[0239] On the other hand, by expanding the piston round to the full outer diameter, a larger valve disc can be used, which increases the pressure-receiving area, which is preferable in terms of valve opening characteristics. More specifically, the larger the valve disc, the greater the distance from the clamped center (fulcrum) to the outer edge, and the farther away the position where the valve opening pressure acts (force point). Therefore, even with the same plate thickness, the required valve opening pressure is lower, and valve opening characteristics are generated even in the extremely low flow velocity region, improving valve opening characteristics.

[0240] If the valve body is enlarged without increasing the round diameter, the same pressure will act on both sides of the area outside the round, and no pressure difference will occur in this area, so the above-mentioned effect will not be achieved.

[0241] In this embodiment, by providing the inclined portions 432A and 442A, the occurrence of burrs is suppressed, while by providing the flat portions 503, 513 with a diameter larger than the desired piston diameter, acute angles are eliminated from the mold M, thereby extending the life of the mold M, and by removing the flat portions 503, 513, it is possible to use a larger valve body (valve member 163, 167) with better opening characteristics.

[0242] The manufacturing method of second piston body 166 involves forming groove 502 in base end surface 402 of molded product 166A formed in the compression step, and a portion of groove 502 closer to main body portion 501 than the bottom thereof becoming inclined portion 435 that forms a continuous obtuse angle with side surface portion 401. Also, groove 512 is formed in base end surface 403 of molded product 166A, and a portion of groove 512 closer to main body portion 501 than the bottom thereof becoming inclined portion 445 that forms a continuous obtuse angle with side surface portion 401. Thus, inclined portions 435, 445 can be easily formed.

[0243] The above embodiment can be modified as in the following variations.

[0244] <Modification> As shown in FIG. 16 , instead of the inclined portion 445 of the second piston body 166, an arc-shaped portion 445D may be formed. In this case, the base 240 is formed with an arc-shaped portion 445D that is continuous with the base end surface 403 and the side surface portion 401. Therefore, the base 240 is continuous with the side surface portion 401 via the arc-shaped portion 445D. When the second piston body 166 is cross-sectioned on a plane including the central axis of the second piston body 166, the arc-shaped portion 445D forms an arc that convex toward the outside of the second piston body 166. The base end surface 403 and the side surface portion 401 intersect in the tangential direction of the arc-shaped portion 445D. The diameter of the arc-shaped portion 445D decreases as it approaches the base end surface 403 in the axial direction of the second piston body 166. In this case, the base 240 has arc-shaped portions 445D formed at positions between all combinations of adjacent round portions 265 in the circumferential direction of the second piston body 166. In this case, the second piston body 166 also has the side surface 401 of the base 240 connected to the base end face 403 via the arc-shaped portions 445D, thereby making it possible to suppress the occurrence of burrs between the side surface 401 and the base end face 403.

[0245] As shown in FIG. 17 , an arc-shaped portion 435D may be formed instead of the inclined portion 435 of the second piston body 166. In this case, the base 240 is formed with an arc-shaped portion 435D that is continuous with the base end surface 402 and the side surface portion 401. Therefore, the base 240 is continuous with the side surface portion 401 via the arc-shaped portion 435D. When the second piston body 166 is cross-sectioned on a plane including the central axis of the second piston body 166, the arc-shaped portion 435D forms an arc that convex toward the outside of the second piston body 166. The base end surface 402 and the side surface portion 401 intersect in the tangent direction of the arc-shaped portion 435D. The diameter of the arc-shaped portion 435D increases as it approaches the side surface portion 401 in the axial direction of the second piston body 166. In this case, the base 240 has arc-shaped portions 435D formed at positions between all combinations of adjacent round portions 255 in the circumferential direction of the second piston body 166. In this case, the second piston body 166 also has the side surface 401 of the base 240 connected to the base end face 402 via the arc-shaped portions 345D, thereby making it possible to suppress the occurrence of burrs between the side surface 401 and the base end face 402.

[0246] As shown in FIG. 16 , instead of the inclined portion 432 of the second piston body 166, an arc-shaped portion 432D may be formed. In this case, the outer edge portion 257 is formed with an arc-shaped portion 432D that is continuous with the tip surface 412 and the side surface portion 401. Therefore, the outer edge portion 257 is continuous with the side surface portion 401 via the arc-shaped portion 432D. When the second piston body 166 is cross-sectioned on a plane including the central axis of the second piston body 166, the arc-shaped portion 432D forms an arc that convex toward the outside of the second piston body 166. The tip surface 412 and the side surface portion 401 intersect in the tangent directions at both ends of the arc-shaped portion 432D. The diameter of the arc-shaped portion 432D increases as it approaches the side surface portion 401 in the axial direction of the second piston body 166. In this case, too, the outer edge portion 257 of the second piston body 166 is continuous with the side portion 401 via the arc-shaped portion 342D, thereby suppressing the occurrence of burrs between the side portion 401 and the base end face 402.

[0247] As shown in FIG. 17 , instead of the inclined portion 442 of the second piston body 166, an arc-shaped portion 442D may be formed. In this case, the outer edge portion 267 is formed with an arc-shaped portion 442D that is continuous with the tip surface 412 and the side surface portion 401. Therefore, the outer edge portion 267 is continuous with the side surface portion 401 via the arc-shaped portion 442D. When the second piston body 166 is cross-sectioned on a plane including the central axis of the second piston body 166, the arc-shaped portion 442D forms an arc that convex toward the outside of the second piston body 166. The tip surface 422 and the side surface portion 401 intersect in the tangent directions at both ends of the arc-shaped portion 442D. The diameter of the arc-shaped portion 442D increases as it approaches the side surface portion 401 in the axial direction of the second piston body 166. In this case too, the second piston body 166 can suppress the occurrence of burrs between the side surface 401 and the base end face 402 by having the outer edge portion 267 continue between the side surface 401 and the arc-shaped portion 442D.

[0248] The distance between the arc-shaped portion 435D of the base 240 and the center of the axial direction of the side surface portion 401 is smaller than the distance between the arc-shaped portion 432D of the outer edge portion 257 and the center C of the axial direction of the side surface portion 401. In other words, the arc-shaped portion 435D of the base 240 is positioned closer to the center C of the axial direction of the side surface portion 401 than the arc-shaped portion 432D of the outer edge portion 257. The arc-shaped portion 445D of the base 240 is also positioned closer to the center of the axial direction of the side surface portion 401 than the arc-shaped portion 442D of the outer edge portion 267.

[0249] The radius of curvature of the arc-shaped portion 435D is set to be larger than the radius of curvature of the arc-shaped portion 432D. Similarly, the radius of curvature of the arc-shaped portion 445D is set to be larger than the radius of curvature of the arc-shaped portion 442D.

[0250] In the above, an example has been described in which the inclined portions 432, 435 or the arc-shaped portions 432D, 435D are formed on the base end face 402 side of the second piston body 166, and the inclined portions 442, 445 or the arc-shaped portions 442D, 445D are formed on the base end face 403 side of the second piston body 166, but it is also possible to provide only one of the base end face 402 side and the base end face 403 side. In other words, the inclined portions 432, 435 or the arc-shaped portions 432D, 435D are formed on the base end face 402 side of the second piston body 166, and the inclined portions 442, 445 and the arc-shaped portions 442D, 445D are not formed on the base end face 403 side. Conversely, the inclined portions 442, 445 or the arcuate portions 442D, 445D may be formed on the base end surface 403 side, and the inclined portions 432, 435 and the arcuate portions 432D, 435D may not be formed on the base end surface 402 side.

[0251] According to the above aspects of the present invention, it is possible to provide a sintered body and a method for manufacturing a sintered body that can suppress cost increases, and therefore the industrial applicability is great.

[0252] 1... shock absorber, 31... rod, 163, 167... valve member (valve body), 166... ​​second piston body (sintered body), 231... insertion hole, 240... base, 241, 244... boss portion, 255, 265... round portion, 256, 266... ​​arm portion, 257, 267... outer edge portion, 258, 268... recessed chamber (chamber), 259... through hole (communicating hole), 269... through hole (communicating hole), 401... side portion, 402, 403... base end surface, 432, 442, 432A, 442A... inclined portion (second inclined portion), 435, 445, 435A, 445A... inclined portion (first inclined portion).

Claims

1. A sintered body constituting a piston used in a shock absorber, comprising: a cylindrical base portion having a side portion and a base end surface that is continuous with the side portion via a first arc-shaped portion or a first inclined portion that forms an obtuse angle; a central insertion hole through which the rod of the shock absorber is inserted; a boss portion that protrudes axially from the base end surface and is provided around the insertion hole; a plurality of first through holes and a plurality of second through holes that are provided on the outer periphery of the boss portion and are provided alternately along the circumferential direction; and a plurality of round portions that protrude axially from the base end surface and form chambers that surround the first through holes, and on which the valve body of the piston is seated and released; wherein the round portion has: an outer edge portion that is provided along the outer periphery of the base end surface and is continuous with the side portion via a second arc-shaped portion or a second inclined portion that forms an obtuse angle; and a set of arms extending from both ends of the outer edge portion toward the boss portion.

2. The sintered body according to claim 1, wherein the base portion is continuous with the side surface portion via the first inclined portion, the outer edge portion is continuous with the side surface portion via the second inclined portion, and the obtuse angle formed by the first inclined portion with respect to the side surface portion is smaller than the obtuse angle formed by the second inclined portion with respect to the side surface portion.

3. The sintered body according to claim 1, wherein the base portion is continuous with the side surface portion via the first arc-shaped portion, the outer edge portion is continuous with the side surface portion via the second arc-shaped portion, and the first arc-shaped portion has a larger radius of curvature than the second arc-shaped portion.

4. The sintered body according to claim 1, wherein the first inclined portion or the first arc-shaped portion of the base is located closer to the center of the axial direction of the side portion than the second inclined portion or the second arc-shaped portion of the outer edge portion.

5. A method for manufacturing a sintered body constituting a piston used in a shock absorber, comprising: a compression step of compressing powdered metal in a mold to form a molded product having a base and a rounded portion; a sintering step of heating the molded product and processing it into a sintered body; and a removal step of removing a portion of the sintered body, wherein the base has a cylindrical main body, a first inclined portion that extends annularly radially outward from the main body and gradually reduces the axial size of the base, and a flat portion that extends radially outward beyond the first inclined portion, and the rounded portion on which the valve body of the piston is seated and released has an outer edge portion where a second inclined portion is adjacent to the first inclined portion, and a set of arms that extend from both ends of the outer edge portion toward the center of the base, and is provided in plurality so as to protrude in the axial direction from one end face of the main body, and in the removal step, a portion radially outward of a predetermined position of the first inclined portion is removed to form a side portion that is the circumferential surface of the base, and a sintered body manufacturing method, further comprising forming, on an end face of the base, an arc-shaped portion that is continuous with the side surface portion or an inclined portion that is continuous with the side surface portion and forms an obtuse angle with the side surface portion, which is a remaining portion of the first inclined portion.

6. A method for producing a sintered body according to claim 5, wherein the base has a groove formed in the end face, and a portion of the groove closer to the main body than the bottom of the groove is an arc-shaped portion that continues from the side face or an inclined portion that continues from the side face and forms an obtuse angle, and the area radially outward from the groove is the flat portion.

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