Piston and shock absorber

Abstract

This piston (3) comprises: a piston body (31); an annular valve seat (32) provided to one end (31a) of the piston body (31); a plurality of first ports (33) disposed on the inner circumferential side of the annular valve seat (32) of the piston body (31) in the circumferential direction; and a plurality of second ports (34) disposed on the outer circumferential side of the annular valve seat (32) of the piston body (31) between the first ports (33, 33) in the circumferential direction. The first ports (33) comprise first inner R sections (33a) provided at both ends of the inner circumference, and first outer R sections (33b) provided at both ends of the outer circumference and having a radius of curvature (R1b) larger than the radius of curvature (R1a) of the first inner R section (33a). The second ports (34) comprise second inner R sections (34a) provided at both ends of the inner circumference, and second outer R sections (34b) provided at both ends of the outer circumference in the circumferential direction and having a radius of curvature (R2b) smaller than the radius of curvature (R2a) of the second inner R sections (34a).

Description

Piston and Shock Absorber

[0001] The present invention relates to improvements to a piston and a shock absorber.

[0002] For example, the piston is slidably inserted into the cylinder of a shock absorber to divide the interior of the cylinder into an extension-side chamber and a compression-side chamber, and has a plurality of extension-side ports that allow hydraulic oil to pass through when the shock absorber extends, and a plurality of compression-side ports that allow hydraulic oil to pass through when the shock absorber contracts. Furthermore, leaf valves are stacked on the upper and lower sides of the piston, and these leaf valves open and close the outlet ends of the extension-side ports and the compression-side ports.

[0003] The shock absorber employing the piston is used, for example, being interposed in parallel with a suspension spring between the vehicle body and wheels of a vehicle. When the shock absorber expands and contracts, the leaf valves apply resistance to the flow of hydraulic oil passing through the extension-side ports and compression-side ports, creating a pressure difference between the two pressure chambers and thereby generating a damping force.

[0004] Here, each extension-side port is arranged at equal intervals on the same circumference of the piston, and each compression-side port is arranged on a more outer circumferential side of the piston than the extension-side ports, at equal intervals on the same circumference, and positioned between the extension-side ports in the circumferential direction. An annular valve seat is provided between the extension-side port and the compression-side port at the end of the piston on the compression-side chamber side.

[0005] Sintering is often employed to manufacture such pistons. Specifically, to obtain the desired piston, a mold having an arc-shaped cross-section for forming the ports is inserted in advance into a sintering mold for forming the overall shape of the piston, metal powder is placed in the sintering mold and pressed, and then the powder is sintered and solidified at a temperature lower than the melting point to obtain the desired piston.

[0006] JP2014-098465A

[0007] As mentioned above, a piston with multiple arc-shaped extension ports and multiple arc-shaped compression ports can be easily obtained by sintering using a sintering mold. However, if the cross-sectional area of ​​the extension ports and compression ports is small, not only is there resistance that the leaf valve exerts on the flow of hydraulic fluid, but if the amount of hydraulic fluid passing through the extension ports and compression ports increases, resistance is generated as the hydraulic fluid passes through the extension ports and compression ports. This results in excessive damping force when the shock absorber expands and contracts at high speed, leading to a poor ride quality.

[0008] Therefore, by increasing the cross-sectional area of ​​the extension port and the compression port located on the piston, even if the amount of hydraulic fluid passing through the extension port and compression port increases, it is possible to avoid unnecessary resistance and suppress excessive damping force when the shock absorber expands and contracts at high speed.

[0009] However, if the cross-sectional areas of both the mold for forming the expandable port and the mold for forming the compressive port, which are inserted into the sintering mold, are increased in order to increase the cross-sectional area of ​​both the expandable port and the compressive port, the gap between the molds narrows, and the fluidity of the metal powder within the sintering mold deteriorates. As a result, the density of the metal powder tends to increase in the recess that forms the annular valve seat on the inner circumference of the compressive port forming mold, which is located on the outer circumference of the sintering mold and has a larger cross-sectional area than the expandable port. Consequently, areas of high and low metal powder density alternate within the recess that forms the annular valve seat in the sintering mold.

[0010] Even if a piston is sizing after being removed from the mold following sintering in this state to form an annular valve seat, the uneven density of the metal powder results in an annular valve seat that is formed with undulations in the circumferential direction.

[0011] When the annular valve seat is undulating in this way, the leaf valves stacked on the piston cannot contact the annular valve seat with uniform force, resulting in a problem where the damping force generated by the shock absorber varies from product to product.

[0012] Therefore, the present invention aims to provide a piston that contributes to the stable output of damping force while ensuring a large cross-sectional area of ​​the port, and a shock absorber capable of generating a stable damping force.

[0013] To solve the aforementioned problems, the cylinder of the present invention comprises an annular piston body, an annular valve seat projecting axially from one end of the piston body, a plurality of first ports with a circular arc cross-section arranged circumferentially on the inner circumference side of the annular valve seat of the piston body and extending from one end to the other of the piston body, and a plurality of second ports with a circular arc cross-section arranged between the first ports in the circumferential direction of the piston body on the outer circumference side of the annular valve seat of the piston body and extending from one end to the other of the piston body. The first ports have a first inner R portion provided at the corners at both ends in the circumferential direction of the inner circumference and a first outer R portion provided at the corners at both ends in the circumferential direction of the outer circumference and having a radius of curvature larger than that of the first inner R portion. The second ports have a second inner R portion provided at the corners at both ends in the circumferential direction of the inner circumference and a second outer R portion provided at the corners at both ends in the circumferential direction of the outer circumference and having a radius of curvature smaller than that of the second inner R portion.

[0014] In a piston configured in this way, even if the cross-sectional areas of the first port and the second port are made large, the width between the first outer R portion and the second inner R portion, which are diagonally opposite each other between the first and second ports, can be widened to improve the fluidity of the metal powder in the sintering mold when manufacturing the piston by sintering. Therefore, it is possible to suppress uneven density of the metal powder that has entered into the recess for forming the annular valve seat in the sintering mold, without bias in the circumferential direction. As a result, with this piston, it is possible to suppress the formation of areas with large and small springbacks in the annular valve seat of the piston after sintering, and it is possible to suppress the circumferential warping of the annular valve seat even after sizing.

[0015] Furthermore, in order to solve the problem, the buffer of the present invention comprises a cylinder, a piston rod inserted into the cylinder and movable axially relative to the cylinder, a piston connected to the piston rod and slidably inserted into the cylinder to divide the inside of the cylinder into an extension chamber and a compression chamber, and a leaf valve that opens and closes a first port by seating on and off an annular valve seat stacked on the piston.

[0016] With a buffer configured in this way, even if the cross-sectional areas of the first port and the second port are made large, the undulation of the annular valve seat can be suppressed. This prevents excessive damping force even when the liquid flow rate is high, and the leaf valves stacked on the piston can contact the annular valve seat with uniform force, resulting in a stable damping force and suppressing variations in damping force from product to product.

[0017] Figure 1 is a longitudinal cross-sectional view of a buffer in one embodiment. Figure 2 is a plan view of a piston in one embodiment. Figure 3 is a bottom view of a piston in one embodiment. Figure 4 is a cross-sectional view of the piston at angle AA in one embodiment. Figure 5 is a view from the axial direction of a part of the sintering mold for manufacturing a piston in one embodiment.

[0018] The shock absorber D of the present invention will be described below with reference to the figures. In one embodiment, as shown in Figure 1, the shock absorber D comprises a cylinder 1, a piston rod 2 inserted into the cylinder 1 and movable in the axial direction relative to the cylinder 1, and a piston 3 connected to the piston rod 2 and slidably inserted into the cylinder 1, dividing the inside of the cylinder 1 into an extension chamber R1 and a compression chamber R2.

[0019] In this embodiment of the buffer D, a sliding partition wall 7 is provided in the lower part of the cylinder 1, sliding against the inner circumference of the cylinder 1 and separating the pressure chamber R2 from the gas chamber G in which gas is sealed. The extension chamber R1 and the pressure chamber R2 are filled with a liquid such as hydraulic oil. The liquid filling the extension chamber R1 and the pressure chamber R2 can be other than hydraulic oil, such as water or an aqueous solution. When the liquid is hydraulic oil, it is preferable to fill the gas chamber G with an inert gas such as nitrogen, but it is also possible to fill the gas chamber G with a gas other than an inert gas.

[0020] In Figure 1, the lower end of the cylinder 1 is closed by a bottom cap 4, and an annular rod guide 5 is mounted at the upper end of the cylinder 1, which slidably supports the piston rod 2. Also, at the upper end of the cylinder 1 in Figure 1, above the rod guide 5 in Figure 1, a sealing member 6 is mounted in sliding contact with the outer circumference of the piston rod 2. This sealing member 6 seals the outer circumference of the piston rod 2, preventing leakage of liquid from inside the cylinder 1.

[0021] The piston rod 2 is cylindrical in shape, with a reduced outer diameter at the tip, and includes a piston fitting portion 2a with the smallest diameter at the tip, a larger diameter portion 2b which has a larger outer diameter than the piston fitting portion 2a and is provided on the upper side of the piston fitting portion 2a in Figure 1, a stepped portion 2c provided at the boundary between the piston fitting portion 2a and the larger diameter portion 2b, and a threaded portion 2d provided on the outer circumference of the tip of the piston fitting portion 2a.

[0022] As shown in Figures 1 to 4, the piston 3 comprises a piston body 31, an annular valve seat 32 projecting axially from one end 31a of the piston body 31 facing the compression chamber R2, a plurality of first ports 33 arranged on the inner circumference side of the annular valve seat 32 of the piston body 31 and connecting from one end 31a of the piston body 31 to the other end 31b facing the extension chamber R1, a plurality of second ports 34 arranged on the outer circumference side of the annular valve seat 32 of the piston body 31 and connecting from one end 31a to the other end 31b of the piston body 31, and a cylindrical skirt portion 35 that rises from one end 31a of the piston body 31 on the outer circumference side of the second ports 34.

[0023] The piston body 31 is annular and mounted on the outer circumference of the piston fitting portion 2a of the piston rod 2. The piston body 31 also includes an annular one-end inner circumferential seat portion 31c provided on the inner circumference of one end 31a facing the compression chamber R2 and projecting downward in Figure 4, an annular other-end inner circumferential seat portion 31d provided on the inner circumference of the other end 31b facing the extension chamber R1 and projecting upward in Figure 4, and four fan-shaped other-end valve seats 31e projecting upward from the other end 31b in Figure 4.

[0024] Furthermore, at one end 31a of the piston body 31, an annular valve seat 32 is provided, with a radial gap on the outer circumference of the inner circumferential seat portion 31c on the one end side, projecting downward in the axial direction from the one end 31a in Figure 4. In addition, a cylindrical skirt portion 35 is provided, with a radial gap on the outer circumference of the annular valve seat 32, rising downward in the axial direction from the outer circumference of the one end 31a of the piston body 31 in Figure 4. The piston 3 is inserted into the cylinder 1 with a piston ring 40 mounted on the outer circumference of the piston body 31 and the skirt portion 35, which slides against the inner circumference of the cylinder 1.

[0025] Furthermore, at one end 31a of the piston body 31, an annular window 31f is formed between the inner circumferential seat portion 31c on the one end side and the annular valve seat 32, and an annular recess 31g is formed between the annular valve seat 32 and the skirt portion 35.

[0026] As shown in Figure 2, the other-end valve seat 31e comprises an arc-shaped outer circumference portion 31e1 and side portions 31e2 that extend from both ends of the outer circumference portion 31e1 toward the inner circumference along the radial direction of the piston body 31 and connect to the other-end inner circumference seat portion 31d. The other-end valve seat 31e, together with the other-end inner circumference seat portion 31d, forms an independent opening window 31h which is an independent, fan-shaped recess in plan view that leads to the outlet end of the second port 34.

[0027] In this embodiment, four first ports 33 are provided on the piston body 31. Specifically, as shown in Figure 3, the four first ports 33 have an arc-shaped cross-section in plan view and are provided on the inner circumference side of the annular valve seat 32 on the piston body 31, arranged at equal intervals in the circumferential direction on the same circumference. As shown in Figure 3, one end of each first port 33 opens into the annular window 31f, and as shown in Figure 2, the other end of each first port 33 opens on the outer circumference side of the inner circumferential seat portion 31d on the other end side, between the valve seats 31e, 31e on the other end side in the circumferential direction of the piston body 31. In this way, each first port 33 opens from one end 31a of the piston body 31 and passes through to the other end 31b, connecting the extension chamber R1 and the compression chamber R2 in the cylinder 1.

[0028] Furthermore, the first port 33 has a shape in which the four corners in the circumferential direction are rounded into a circular shape, and is provided with a pair of first inner R portions 33a at both corners in the circumferential direction on the inner circumference, and a pair of first outer R portions 33b at both corners in the circumferential direction on the outer circumference. The radius of curvature R1b of the first outer R portion 33b is larger than the radius of curvature R1a of the first inner R portion 33a.

[0029] In this embodiment, four second ports 34 are provided on the piston body 31. Specifically, as shown in Figure 3, the four second ports 34 have an arc-shaped cross-section in plan view and are arranged on the outer circumference of the annular valve seat 32 on the piston body 31 at equal intervals in the circumferential direction, and are also arranged between the first ports 33, 33 in the circumferential direction of the piston body 31. As shown in Figure 3, one end of each second port 34 opens into an annular recess 31g, and as shown in Figure 2, the other end of each second port 34 opens into corresponding independent opening windows 31h. In this way, each second port 34 opens from one end 31a of the piston body 31 and continues to the other end 31b, connecting the extension chamber R1 and the compression chamber R2 in the cylinder 1.

[0030] Furthermore, the second port 34 has a shape in which the four corners in the circumferential direction are rounded into a circular shape, and is provided with a pair of second inner R portions 34a at both corners in the circumferential direction on the inner circumference, and a pair of second outer R portions 34b at both corners in the circumferential direction on the outer circumference. The radius of curvature R2b of the second outer R portion 34b is smaller than the radius of curvature R2a of the second inner R portion 34a.

[0031] Thus, the first port 33 and the second port 34 are arranged in a staggered pattern in the circumferential direction on the inner and outer sides of the annular valve seat 32, with the first outer R portion 33b of the first port 33 and the second inner R portion 34a of the second port 34 facing each other diagonally.

[0032] To increase the cross-sectional area of ​​the first port 33, it is better to decrease the radius of curvature R1a of the first inner R portion 33a and the radius of curvature R1b of the first outer R portion 33b. Similarly, to increase the cross-sectional area of ​​the second port 34, it is better to decrease the radius of curvature R2a of the second inner R portion 34a and the radius of curvature R2b of the second outer R portion 34b. However, as the radius of curvature of each R portion 33a, 33b, 34a, and 34b decreases, the space between the first outer R portion 33b of the first port 33 and the second inner R portion 34a of the second port 34, which are diagonally opposite each other, becomes narrower. When attempting to manufacture such a piston by sintering, as shown in Figure 5, the gap W1 between the first port-forming mold 101, indicated by a dashed line, which forms the first ports arranged staggered in the circumferential direction within the sintering mold 100, and the second port-forming mold 102, also indicated by a dashed line, which forms the second ports, becomes narrower, and the fluidity of the metal powder within the sintering mold 100 deteriorates. As a result, the density of the metal powder that enters the recess 100a for forming the annular valve seat 32 in the sintering mold 100 becomes higher in the inner part of the second port-forming mold 102, and the density becomes uneven in the circumferential direction of the recess 100a.

[0033] In contrast, in the piston 3 of this embodiment, the radius of curvature R1b of the first outer R portion 33b is larger than the radius of curvature R1a of the first inner R portion 33a, and the radius of curvature R2b of the second outer R portion 34b is smaller than the radius of curvature R2a of the second inner R portion 34a. Therefore, in order to increase the cross-sectional area of ​​the first port 33 and the second port 34, the radius of curvature of each R portion 33a, 33b, 34a, and 34b can be reduced, while at the same time the gap between the first outer R portion 33b and the second inner R portion 34a, which are diagonally opposite each other, can be widened. When manufacturing the piston 3 by sintering, as shown in Figure 5, the gap W2 between the first port-forming mold 103 (shown by a solid line) that forms the first port 33, which is arranged staggered in the circumferential direction within the sintering mold 100, and the second port-forming mold 104 (shown by a solid line) that forms the second port 34, becomes wider than the aforementioned gap W1. As a result, the fluidity of the metal powder within the sintering mold 100 improves, making it easier for the metal powder to pass between the first port-forming mold 103 and the second port-forming mold 104. Therefore, the density of the metal powder that has entered the recess 100a for forming the annular valve seat 32 in the sintering mold 100 does not become uneven in the circumferential direction, thus preventing the density from becoming non-uniform.

[0034] Furthermore, the radius of curvature R1b of the first outer R portion 33b and the radius of curvature R2a of the second inner R portion 34a should be set to such an extent that the fluidity of the metal powder passing between the first port forming mold 103 and the second port forming mold 104 is not lost, and should be set appropriately according to the particle size of the metal powder used in the manufacture of the piston 3.

[0035] On the other hand, the radius of curvature R1a of the first inner R portion 33a of the first port 33 and the radius of curvature R1b of the second outer R portion 34b of the second port 34, which do not face each other diagonally, should be as small as possible from the viewpoint of increasing the cross-sectional area of ​​the first port 33 and the cross-sectional area of ​​the second port 34. However, if they become too small, the corners may become sharp and brittle, so it is best to make them as small as possible without causing insufficient strength.

[0036] Furthermore, the piston 3 of this embodiment is provided with a skirt portion 35 that rises from the outer circumference of the piston body 31. Therefore, when manufacturing the piston 3 by sintering, the metal powder can easily pass between the first port-forming mold 103 and the second port-forming mold 104 within the sintering mold 100, and the metal powder can uniformly enter the annular recess 100b for forming the skirt portion 35 in the sintering mold 100, so that the strength of the skirt portion 35 of the piston 3 obtained by sintering is stable without variation from product to product.

[0037] In a piston 3 equipped with a skirt portion 35, the fitting length, which is the axial length in which it is fitted with the cylinder 1, can be increased to facilitate the axial movement of the piston 3 relative to the cylinder 1. At the same time, the axial length of the piston body 31 can be shortened, and the axial length of the piston portion including the piston 3 and the extension leaf valve 10 and compression leaf valve 11 stacked on the piston 3 (described later) can be shortened, making it easier to secure the stroke length of the shock absorber D.

[0038] Furthermore, the annular window 31f through which the first port 33 opens includes a flat surface 31f1 between the first ports 33, 33 on the same circumference, a tapered surface 31f2 provided on the inner circumference side of the flat surface 31f1 and inclined to increase in height toward the inner circumference side, and a tapered surface 31f3 provided on the outer circumference side of the flat surface 31f1 and inclined to increase in height toward the annular valve seat 32 side on the outer circumference side. More specifically, the tapered surface 31f2 on the inner circumference side of the flat surface 31f1 is provided on the same circumference as the first inner R portion 33a of the first port 33, and the tapered surface 31f3 on the outer circumference side of the flat surface 31f1 is provided on the same circumference as the first outer R portion 33b of the first port 33. When the annular window 31f is formed in this way, the first inner R portion 33a faces only the tapered surface 31f2, and the first outer R portion 33b faces only the tapered surface 31f3. Since the first inner R portion 33a and the first outer R portion 33b do not straddle the flat portion 31f1 and the tapered surfaces 31f2 and 31f3, the first port 33 can be easily formed as designed when sizing the piston 3 obtained by sintering. Note that even if the tapered surface 31f2 is provided on the same circumference as the first inner R portion 33a, or the tapered surface 31f3 is provided on the same circumference as the first outer R portion 33b, the formation of the first port 33 during sizing is also made easier, so only one of the tapered surfaces 31f2 and 31f3 may be provided. Also, if they are not needed, the tapered surfaces 31f2 and 31f3 may not be provided.

[0039] The annular recess 31g into which the second port 34 opens has only a flat surface on the same circumference between the second ports 34, 34. However, in order to facilitate the formation of the second port 34 during sizing, the annular recess 31g may have a tapered surface on its inner circumference that is inclined on the same circumference as the second inner R portion 34a, with the inner circumference being higher, or it may have a tapered surface on its outer circumference that is inclined on the same circumference as the second outer R portion 34b, with the outer circumference being higher.

[0040] As described above, an annular extension leaf valve 10, which acts as a leaf valve that seats into and out of an annular valve seat 32, is stacked at the lower end in Figure 1, which is one end of the piston 3 facing the compression chamber R2, and an annular compression leaf valve 11, which seats into and out of the other end valve seat 31e, is stacked at the upper end in Figure 1, which is the other end of the piston 3 facing the extension chamber R1.

[0041] With the extension leaf valve 10 and compression leaf valve 11 stacked on the piston 3, these components are assembled to the outer circumference of the piston fitting portion 2a at the tip of the piston rod 2. Then, when the piston nut 8 is screwed onto the threaded portion 2d, the piston 3, extension leaf valve 10, and compression leaf valve 11 are held in place by the piston nut 8 and the stepped portion 2c, and fixed to the piston rod 2.

[0042] The extension leaf valve 10 is fixed to the inner circumferential seat portion 31c at one end by being tightened by the piston nut 8 on its inner circumference, and its outer circumference is allowed to flex. When the extension leaf valve 10 is seated on the annular valve seat 32, it closes the lower end in Figure 1, which is the outlet end of the first port 33, thereby blocking the first port 33. When the outer circumference is flexed and separated from the annular valve seat 32, it opens and opens the first port 33. The outer diameter of the extension leaf valve 10 is larger than the outer diameter of the annular valve seat 32, but is sufficiently smaller than the inner diameter of the skirt portion 35. Therefore, the extension leaf valve 10 does not close the annular recess 31g into which the second port 34 opens, and the second port 34 and the compression chamber R2 are always in communication.

[0043] On the other hand, the compression leaf valve 11 is fixed to the inner circumferential seat portion 31d on the other end by being tightened by the piston nut 8 on its inner circumferential side, and is allowed to bend on its outer circumferential side. When the compression leaf valve 11 is seated on the valve seat 31e on the other end, it closes the upper end in Figure 1, which is the outlet end of the second port 34, thereby blocking the second port 34. When the outer circumferential side is bent and separated from the valve seat 31e on the other end, it opens and opens the second port 34.

[0044] Furthermore, while the compression-side leaf valve 11 closes the second port 34 when seated on the other-end-side valve seat 31e, it is spaced apart from the other end 31b of the piston body 31 by the height of the other-end-side valve seat 31e, and does not block the inlet end of the first port 33 that is open between the other-end-side valve seats 31e, 31e on the outer circumferential side of the other-end-side inner circumferential seat portion 31d. Therefore, the first port 33 is always in communication with the extension-side chamber R1.

[0045] When the piston 3 moves upward in FIG. 1 inside the cylinder 1 and the shock absorber D performs an extension operation, the compression-side leaf valve 11 is pressed toward the piston 3 by the pressure of the extension-side chamber R1, which is compressed and its pressure rises, so that the second port 34 is closed. The extension-side leaf valve 10, which receives the pressure of the extension-side chamber R1 via the first port 33, bends at its outer circumferential side to separate from the annular valve seat 32, thereby opening the first port 33. Since the extension-side leaf valve 10 provides resistance to the flow of liquid moving from the extension-side chamber R1 to the compression-side chamber R2 passing through the first port 33, the shock absorber D exhibits an extension-side damping force that impedes the extension operation.

[0046] The volume of the piston rod 2 that exits from inside the cylinder 1 accompanying the extension operation of the shock absorber D is compensated by the sliding partition 7 moving upward in FIG. 1 inside the cylinder 1 to expand the air chamber G.

[0047] On the other hand, when the piston 3 moves downward in FIG. 1 inside the cylinder 1 and the shock absorber D performs a compression operation, the extension-side leaf valve 10 is pressed toward the piston 3 by the pressure of the compression-side chamber R2, which is compressed and its pressure rises, so that the first port 33 is closed. The compression-side leaf valve 11, which receives the pressure of the compression-side chamber R2 via the second port 34, bends to separate from the other-end-side valve seat 31e, thereby opening the second port 34. Since the compression-side leaf valve 11 provides resistance to the flow of liquid moving from the compression-side chamber R2 to the extension-side chamber R1 passing through the second port 34, the shock absorber D exhibits a compression-side damping force that impedes the compression operation.

[0048] The volume of the piston rod 2 that enters into the cylinder 1 accompanying the compression operation of the shock absorber D is compensated by the sliding partition 7 moving downward in FIG. 1 inside the cylinder 1 to reduce the size of the air chamber G.

[0049] As described above, the piston 3 of this embodiment comprises an annular piston body 31, an annular valve seat 32 projecting axially from one end 31a of the piston body 31, a plurality of first ports 33 arranged circumferentially on the inner circumference side of the annular valve seat 32 of the piston body 31 and having an arc-shaped cross-section that extends from one end 31a to the other end 31b of the piston body 31, and arranged between the first ports 33, 33 in the circumferential direction of the piston body 31 on the outer circumference side of the annular valve seat 32 of the piston body 31 and having an arc-shaped cross-section that extends from one end 31a to the other end 31b of the piston body 31 The device comprises multiple second ports 34, and the first port 33 has a first inner R portion 33a provided at the corners at both ends in the circumferential direction on the inner circumference and a first outer R portion 33b provided at the corners at both ends in the circumferential direction on the outer circumference and having a radius of curvature R1b that is larger than the radius of curvature R1a of the first inner R portion 33a. The second port 34 has a second inner R portion 34a provided at the corners at both ends in the circumferential direction on the inner circumference and a second outer R portion 34b provided at the corners at both ends in the circumferential direction on the outer circumference and having a radius of curvature R2b that is smaller than the radius of curvature R2a of the second inner R portion 34a.

[0050] In the piston 3 configured in this way, even if the cross-sectional areas of the first port 33 and the second port 34 are made large, the width between the first outer R portion 33b and the second inner R portion 34a, which are diagonally opposite each other between the first port 33 and the second port 34, can be widened to improve the fluidity of the metal powder in the sintering mold 100 when manufacturing the piston 3 by sintering. Therefore, it is possible to suppress uneven density of the metal powder that has entered into the recess 100a for forming the annular valve seat 32 in the sintering mold 100, without bias in the circumferential direction. As a result, with the piston 3 of this embodiment, it is possible to suppress the formation of areas with large and small springback in the annular valve seat 32 of the piston 3 after sintering, and it is possible to suppress the circumferential warping of the annular valve seat 32 even after sizing.

[0051] As described above, with the piston 3 of this embodiment, even if the cross-sectional areas of the first port 33 and the second port 34 are made large, the undulation of the annular valve seat 32 can be suppressed. This prevents excessive damping force even when the liquid flow rate is high, and the extension leaf valve 10 stacked on the piston 3 can contact the annular valve seat 32 with a uniform force, resulting in stable damping force and suppressing variations in damping force from product to product. In summary, the piston 3 contributes to the stable damping force while ensuring large cross-sectional areas of the first port 33 and the second port 34.

[0052] Furthermore, the piston 3 of this embodiment is provided with a cylindrical skirt portion 35 that rises from one end 31a of the piston body 31, on the outer circumference side of the second port 34. With the piston 3 configured in this way, when the piston 3 is manufactured by sintering, the metal powder can easily pass between the first port forming mold 103 and the second port forming mold 104 within the sintering mold 100, and as shown in Figure 5, the metal powder can uniformly enter the annular recess 100b for forming the skirt portion 35 in the sintering mold 100, and the strength of the skirt portion 35 of the piston 3 obtained by sintering is stable without variation from product to product.

[0053] Furthermore, the piston 3 of this embodiment includes a flat surface portion 31f1 provided on the same circumference as the first port 33 and in at least a portion of the area between the first ports 33, 33, a tapered surface 31f2 provided on the same circumference as the first inner R portion 33a, and a tapered surface 31f3 provided on the same circumference as the first outer R portion 33b. With a piston 3 configured in this way, the first port 33 can be easily formed as designed when sizing is performed. As mentioned above, even if the tapered surface 31f2 is provided on the same circumference as the first inner R portion 33a, or the tapered surface 31f3 is provided on the same circumference as the first outer R portion 33b, the formation of the first port 33 is made easier during sizing, so only one of the tapered surfaces 31f2 and 31f3 may be provided. Furthermore, if the flat portion 31f1 and the tapered surfaces 31f2, 31f3 are provided at least one location between the first ports 33, 33, rather than all four locations, it will have the effect of facilitating the formation of the first port 33. In addition, for the annular recess 31g through which the second port 34 opens, a tapered surface may be provided on the same circumference as the second inner R portion 34a, or on the same circumference as the second outer R portion 34b, in addition to the flat portion. In this case, the formation of the second port 34 during sizing will be facilitated. Even when a tapered surface is provided in the annular recess 31g, if it is provided at least one location between the second ports 34, 34, rather than all four locations, it will have the effect of facilitating the formation of the second port 34.

[0054] Furthermore, the shock absorber D of this embodiment includes a cylinder 1, a piston rod 2 inserted into the cylinder 1 and movable axially relative to the cylinder 1, a piston 3 connected to the piston rod 2 and slidably inserted into the cylinder 1 to divide the inside of the cylinder 1 into an extension chamber R1 and a compression chamber R2, and an extension leaf valve (leaf valve) 10 stacked on the piston 3 and seating away from an annular valve seat 32 to open and close the first port 33.

[0055] With the buffer D configured in this way, even if the cross-sectional areas of the first port 33 and the second port 34 are made large, the undulation of the annular valve seat 32 can be suppressed. This prevents excessive damping force even when the liquid flow rate is high, and the extension leaf valve 10 stacked on the piston 3 can contact the annular valve seat 32 with a uniform force, resulting in a stable damping force and suppressing variations in damping force from product to product.

[0056] In this embodiment, the buffer D is a so-called single-cylinder type buffer in which a sliding partition wall 7 is housed inside the cylinder 1 to form an air chamber G inside the cylinder 1. However, although not shown in the figures, it may also be configured as a so-called double-cylinder type buffer in which a base valve is provided at the lower end of the cylinder 1 to provide a reservoir outside the cylinder that compensates for the volume of movement of the piston rod 2 inside the cylinder 1. Furthermore, although the piston 3 in this embodiment is equipped with a skirt portion 35, it may also be a piston without a skirt portion 35 on the outer circumference of the piston body 31, and the number of first ports 33 and second ports 34 can be appropriately changed as long as there are multiple ports.

[0057] Although preferred embodiments of the present invention have been described in detail above, modifications, alterations, and changes are permitted as long as they do not deviate from the scope of the claims.

[0058] 1...Cylinder, 2...Piston rod, 3...Piston, 10...Extension leaf valve (leaf valve), 31...Piston body, 31a...One end of piston body, 31b...Other end of piston body, 31f1...Flat surface, 31f2, 31f3...Tapered surface, 32...Annular valve seat, 33...First port, 33a...First inner R section, 33b...First outer R section, 34...Second port, 34a...Second inner R section, 34b...Second outer R section, 35...Skirt section, D...Buffer, R1...Extension chamber, R2...Compression chamber

Claims

1. A piston comprising: an annular piston body; an annular valve seat projecting axially from one end of the piston body; a plurality of first ports with a circular arc cross-section, arranged circumferentially on the inner circumference side of the annular valve seat of the piston body and extending from one end to the other of the piston body; and a plurality of second ports with a circular arc cross-section, arranged between the first ports in the circumferential direction of the piston body on the outer circumference side of the annular valve seat of the piston body and extending from one end to the other of the piston body, wherein each first port has a first inner R portion provided at the corners at both ends in the circumferential direction of the inner circumference and a first outer R portion provided at the corners at both ends in the circumferential direction of the outer circumference and having a radius of curvature larger than that of the first inner R portion; and each second port has a second inner R portion provided at the corners at both ends in the circumferential direction of the inner circumference and a second outer R portion provided at the corners at both ends in the circumferential direction of the outer circumference and having a radius of curvature smaller than that of the second inner R portion.

2. The piston according to claim 1, comprising a cylindrical skirt portion that rises from one end of the piston body and from the outer circumference of the second port.

3. A piston according to claim 1, comprising: a flat planar portion provided on the same circumference as the first port and in at least a portion between the first ports or on the same circumference as the second port and in at least a portion between the second ports; and a tapered surface provided on the same circumference as any of the first inner R portion, the first outer R portion, the second inner R portion, or the second outer R portion.

4. A shock absorber comprising: a cylinder; a piston rod inserted into the cylinder and movable axially relative to the cylinder; a piston according to claim 1, connected to the piston rod and slidably inserted into the cylinder to divide the inside of the cylinder into an extension chamber and a compression chamber; and a leaf valve that opens and closes the first port by seating toward and away from the annular valve seat stacked on the piston.

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