Buffer

Abstract

To provide a buffer that reduces sudden change of damping force, facilitates tuning of transient characteristics and can ensure a stroke length of a free piston.SOLUTION: A buffer D1 comprises: a cylinder 1; a piston 2 that divides the inside of the cylinder 1 into an extension side chamber R1 and a compression side chamber R2; a damping passage P that connects the extension side chamber R1 and the compression side chamber R2; a pressure chamber R3; a free piston 4 that divides the inside of the pressure chamber R3 into an extension side pressure chamber 5 and a compression side pressure chamber 6; a spring element 7 that suppresses the displacement of the free piston 4; an extension side passage 8 that connects the extension side chamber R1 and the extension side pressure chamber 5; a compression side passage 9 that connects the compression side chamber R2 and the compression side pressure chamber 6; an extension side check valve 10 provided in the extension side passage 8; and a compression side check valve 11 provided in the compression side passage 9. When the free piston 4 moves to a stroke end, it causes the extension side pressure chamber 5 or the compression side pressure chamber 6 to function as a hydraulic lock chamber.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an improvement in a shock absorber. [Background technology]

[0002] Shock absorbers installed between the body and axle of a vehicle generally exert a damping force with constant damping force characteristics to suppress body vibration. However, in recent years, in order to further improve the ride comfort of vehicles, shock absorbers that vary the damping force in response to the frequency or amplitude of the input vibration have been developed.

[0003] A shock absorber that changes the damping force in response to the frequency includes, for example, a cylinder, a piston slidably inserted into the cylinder and dividing the inside of the cylinder into an extension-side chamber on the piston rod side and a compression-side chamber on the piston side, a main valve provided on the piston and communicating the extension-side chamber with the compression-side chamber to generate a damping force, and a frequency sensitive unit. The frequency sensitive unit includes a passage that bypasses the main valve and apparently communicates the extension-side chamber with the compression-side chamber, a pressure chamber provided in the middle of the passage, a free piston slidably inserted into the pressure chamber and dividing the pressure chamber into an extension-side pressure chamber and a compression-side pressure chamber, and a coil spring that biases the free piston (see, for example, Patent Document 1).

[0004] In the frequency sensing part, the pressure chamber is divided into an extension side pressure chamber and a compression side pressure chamber by the free piston. When the free piston moves, the volume ratio of the extension side pressure chamber and the compression side pressure chamber changes. As a result, the hydraulic oil appears to bypass the main valve and travels between the extension side chamber and the compression side chamber, changing the flow rate of the hydraulic oil passing through the main valve.

[0005] A shock absorber equipped with such a frequency sensitive part generates a high damping force in response to low frequency vibration input, and on the other hand, exhibits a damping force reduction effect and generates a low damping force in response to high frequency vibration input, thereby improving the ride comfort in the vehicle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-204628 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in this type of shock absorber, when the free piston displaces to the stroke end and collides with the housing that forms the pressure chamber, the free piston suddenly stops and the liquid passes only through the main valve, causing the damping force to increase suddenly.

[0008] Therefore, in conventional shock absorbers, a cushion rubber is provided to suppress the displacement of the free piston near the stroke end in order to mitigate the sudden change in the damping force. By providing the cushion rubber in this manner, when the free piston reaches the vicinity of the stroke end, the cushion rubber comes into contact with the free piston to generate a resilient force, thereby suppressing the free piston from moving further toward the stroke end and suppressing the free piston from stopping suddenly. Therefore, even in conventional shock absorbers equipped with a cushion rubber, the sudden change in the damping force can be mitigated to some extent, but with the cushion rubber, the time from when the free piston comes into contact with the cushion rubber to when it stops is short, and it is difficult to tune the characteristics (transient characteristics) of the transition period in which the damping force is reduced to transition from a state in which a low damping force is generated to a state in which a high damping force is generated by the main valve.

[0009] Furthermore, in order to slow down the free piston with the cushion rubber and mitigate sudden changes in damping force, it is necessary to accommodate a certain amount of cushion rubber in the pressure chamber, which shortens the stroke length of the free piston within the pressure chamber.

[0010] Therefore, an object of the present invention is to provide a shock absorber that can ease sudden changes in damping force, while easily tuning the transient characteristics when the damping force changes and ensuring the stroke length of the free piston. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides a piston rod that is slidably inserted into the cylinder and has one end connected to the piston, a damping passage that communicates with the extension-side chamber and the compression-side chamber, a pressure chamber, a free piston that is movably inserted into the pressure chamber and divides the pressure chamber into an extension-side pressure chamber and a compression-side pressure chamber, a spring element that generates a biasing force that suppresses displacement of the free piston from a neutral position with respect to the pressure chamber, an extension-side passage that communicates with the extension-side pressure chamber, and a damping passage that communicates with the compression-side chamber and the compression-side pressure chamber. the compression side pressure chamber; an extension side check valve which allows liquid to flow only from the extension side chamber to the extension side pressure chamber; and a compression side check valve which allows liquid to flow only from the compression side chamber to the compression side pressure chamber. When the free piston moves to the stroke end in the direction compressing the extension side pressure chamber, it reduces the degree of communication between the extension side passage and the extension side pressure chamber, causing the extension side pressure chamber to function as a hydraulic lock chamber, and when the free piston moves to the stroke end in the direction compressing the compression side pressure chamber, it reduces the degree of communication between the compression side passage and the compression side pressure chamber, causing the compression side pressure chamber to function as a hydraulic lock chamber.

[0012] According to the shock absorber configured in this manner, the movement of the free piston to the stroke end causes the expansion-side pressure chamber itself or the compression-side pressure chamber itself to function as a hydraulic lock chamber, so that a sudden change in the damping force can be mitigated, and the stroke length of the free piston can be secured without providing a cushion in the pressure chamber. In addition, since the shock absorber does not require a cushion, the volumes of the expansion-side pressure chamber and the compression-side pressure chamber can be secured large, and the liquid in the expansion-side pressure chamber and the compression-side pressure chamber can be used during hydraulic lock. Therefore, in the shock absorber, a sufficient flow rate of liquid can be flowed into the expansion-side chamber or the compression-side chamber while gradually restricting the degree of communication between the expansion-side pressure chamber and the expansion-side passage or the degree of communication between the compression-side pressure chamber and the compression-side passage until the hydraulic lock function is exerted, and tuning of the transient characteristics that transition from a state in which a low damping force is generated to a state in which a high damping force is generated can also be facilitated.

[0013] The shock absorber further includes a housing that accommodates a free piston therein to form a pressure chamber, the housing having a cylindrical portion, a first lid portion that closes one end of an opening of the cylindrical portion, a second lid portion that closes the other end of the opening of the cylindrical portion, a first convex portion that protrudes inward from the first lid portion, a second convex portion that protrudes inward from the second lid portion, an expansion-side suction passage that opens from an outer periphery of the first convex portion and communicates with the expansion-side chamber, and a compression-side suction passage that opens from an outer periphery of the second convex portion and communicates with the compression-side chamber, the expansion-side passage opening at a tip of the first convex portion and communicating with the expansion-side pressure chamber, the compression-side passage opening at a tip of the second convex portion and communicating with the compression-side pressure chamber, The check valve is provided in the extension side suction passage, the compression side check valve is provided in the compression side suction passage, the free piston is accommodated in the cylindrical portion and divides the inside of the housing into an extension side pressure chamber and a compression side pressure chamber, and has a cylindrical first case provided on the extension side pressure chamber side and allowing insertion of a first convex portion, and a cylindrical second case provided on the compression side pressure chamber side and allowing insertion of a second convex portion, and a flow path area between the first case and the first convex portion is reduced in accordance with a degree of penetration of the first convex portion into the first case, and a flow path area between the second case and the second convex portion is reduced in accordance with a degree of penetration of the second convex portion into the second case.

[0014] With a shock absorber configured in this manner, the timing and transient characteristics of the transition from low damping force to high damping force can be easily tuned by setting the inner circumferential shape of the first case, the outer circumferential shape of the first convex portion, and the axial length of the first case and the first convex portion, and by setting the inner circumferential shape of the second case, the outer circumferential shape of the second convex portion, and the axial length of the second case and the second convex portion.

[0015] Furthermore, the expansion-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the outer periphery of the first convex portion to open and close the open end of the expansion-side suction passage, and the compression-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the outer periphery of the second convex portion to open and close the open end of the compression-side suction passage. According to the shock absorber configured in this manner, even if the expansion-side check valve and the compression-side check valve are provided in the housing, they do not interfere with the movement of the free piston, and the stroke length of the free piston can be secured while avoiding an increase in the size of the housing.

[0016] The shock absorber may further include a housing that accommodates a free piston therein to form a pressure chamber, the housing having a cylindrical portion, a first lid portion that closes one end of an opening of the cylindrical portion, a second lid portion that closes the other end of the opening of the cylindrical portion, a first convex portion that protrudes inward from the first lid portion, an extension-side suction passage that opens from an outer periphery of the first convex portion and leads to the extension-side chamber, and a compression-side suction passage that opens from an outer periphery of the cylindrical portion and leads to the compression-side chamber, the extension-side passage opens at a tip of the first convex portion and leads to the extension-side pressure chamber, the compression-side passage penetrates the cylindrical portion and leads to the compression-side pressure chamber, the extension-side check valve is provided in the extension-side suction passage, and the compression-side check valve is provided in the compression-side suction passage, the free piston is accommodated in the cylindrical portion to divide the inside of the housing into an extension-side pressure chamber and a compression-side pressure chamber, and the housing may have a cylindrical case that is provided on the extension-side pressure chamber side to allow insertion of the first convex portion, and a shutter that is provided on the compression-side pressure chamber side to face the opening of the compression-side passage.

[0017] With the shock absorber configured in this manner, not only can the timing and transient characteristics of the transition from low damping force to high damping force be easily tuned by setting the shape of the case, the first convex portion, the shutter, etc., but also, only the first convex portion located in the extension side pressure chamber protrudes into the housing, and by providing the compression side passage in the cylindrical portion, the compression side pressure chamber can be made to function as a hydraulic lock chamber without having to provide a convex portion that reduces the volume of the pressure chamber.This makes it easier to ensure the volume within the pressure chamber, shortens the overall length of the housing, and makes it easier to ensure the stroke length of the shock absorber even if a pressure chamber is provided.

[0018] The extension-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the outer periphery of the first protrusion to open and close the open end of the extension-side suction passage, and the compression-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the inner periphery of the cylindrical portion to open and close the open end of the compression-side suction passage. According to the shock absorber configured in this manner, even if the extension-side check valve and the compression-side check valve are provided in the housing, they do not interfere with the movement of the free piston, and the stroke length of the free piston can be secured while avoiding an increase in the size of the housing.

[0019] Furthermore, the shock absorber includes a housing that accommodates a free piston therein to form a pressure chamber, the housing having a cylindrical portion, a first lid portion that closes one end of an opening of the cylindrical portion, a second lid portion that closes the other end of the opening of the cylindrical portion, a first convex portion that protrudes inward from the first lid portion, an extension-side suction passage that opens from an outer periphery of the cylindrical portion and leads to the extension-side chamber, and a compression-side suction passage that opens from an outer periphery of the first convex portion and leads to the compression-side chamber, the extension-side passage penetrates the cylindrical portion and leads to the extension-side pressure chamber, the compression-side passage opens at a tip of the first convex portion and leads to the compression-side pressure chamber, the extension-side check valve is provided in the extension-side suction passage, and the compression-side check valve is provided in the compression-side suction passage, the free piston is accommodated in the cylindrical portion to divide the inside of the housing into an extension-side pressure chamber and a compression-side pressure chamber, and the housing may have a shutter that is provided on the extension-side pressure chamber side and can face the opening of the extension-side passage, and a cylindrical case that is provided on the compression-side pressure chamber side to allow insertion of the first convex portion.

[0020] With the shock absorber configured in this manner, not only can the timing and transient characteristics of the transition from low damping force to high damping force be easily tuned by setting the shape of the case, the first convex portion, the shutter, etc., but also, only the first convex portion located in the compression side pressure chamber protrudes into the housing, and by providing the extension side passage in the cylindrical portion, the extension side pressure chamber can be made to function as a hydraulic lock chamber without having to provide a convex portion that reduces the volume of the pressure chamber.This makes it easier to ensure the volume in the pressure chamber, shortens the overall length of the housing, and makes it easier to ensure the stroke length of the shock absorber even if a pressure chamber is provided.

[0021] The expansion-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the inner circumference of the cylindrical portion to open and close the open end of the expansion-side suction passage, and the compression-side check valve may have an annular valve element that is elastic and fitted in an annular groove provided on the outer circumference of the first convex portion to open and close the open end of the compression-side suction passage. According to the shock absorber configured in this manner, even if the expansion-side check valve and the compression-side check valve are provided in the housing, they do not interfere with the movement of the free piston, and the stroke length of the free piston can be secured while avoiding an increase in the size of the housing. Effect of the Invention

[0022] Therefore, according to the shock absorber of the present invention, it is possible to easily tune the transient characteristics when the damping force changes while mitigating sudden changes in the damping force, and to ensure the stroke length of the free piston. [Brief description of the drawings]

[0023] [Figure 1] 1 is a vertical cross-sectional view of a shock absorber according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged vertical cross-sectional view of a pressure chamber portion of the shock absorber according to the embodiment of the present invention. [Diagram 3] FIG. 4 is an enlarged vertical cross-sectional view of a pressure chamber portion of a shock absorber according to a first modified example of one embodiment of the present invention. [Figure 4] FIG. 13 is an enlarged vertical sectional view of a pressure chamber portion of a shock absorber according to a second modified example of one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described below with reference to the drawings. As shown in Fig. 1, a shock absorber D1 according to an embodiment of the present invention includes a cylinder 1, a piston 2 slidably inserted into the cylinder 1 and dividing the inside of the cylinder 1 into an expansion-side chamber R1 and a compression-side chamber R2, a piston rod 3 movably inserted into the cylinder 1 and one end of which is connected to the piston 2, a damping passage P communicating the expansion-side chamber R1 and the compression-side chamber R2, a pressure chamber R3, and a piston rod movably inserted into the pressure chamber R3 and dividing the pressure chamber R3 into an expansion-side pressure chamber 5 and a compression-side pressure chamber 6. The shock absorber D1 includes a free piston 4, a spring element 7 that generates a biasing force to suppress the displacement of the free piston 4 from a neutral position relative to the pressure chamber R3, an expansion-side passage 8 that communicates the expansion-side chamber R1 with the expansion-side pressure chamber 5, a compression-side passage 9 that communicates the compression-side chamber R2 with the compression-side pressure chamber 6, an expansion-side check valve 10 that allows only the flow of liquid from the expansion-side chamber R1 to the expansion-side pressure chamber 5, and a compression-side check valve 11 that allows only the flow of liquid from the compression-side chamber R2 to the compression-side pressure chamber 6. The shock absorber D1 is interposed between the vehicle body and the axle of the vehicle to generate a damping force and suppress vibration of the vehicle body. The expansion-side chamber R1 refers to a chamber that is compressed when the vehicle body and the axle are separated and the shock absorber D1 is expanded, and the compression-side chamber R2 refers to a chamber that is compressed when the vehicle body and the axle are approached and the shock absorber D1 is contracted.

[0025] Each part of the shock absorber D1 will be described in detail below. The upper end of the cylinder 1 is closed by fitting an annular rod guide 12 into which the piston rod 3 is inserted, and the lower end of the cylinder 1 is closed by a bottom cap 13. A piston 2 connected to the piston rod 3 is slidably inserted into the cylinder 1, and the cylinder 1 is divided into an expansion side chamber R1 and a compression side chamber R2. A sliding partition wall 14 is slidably inserted into the cylinder 1 below the piston 2, and a gas chamber G is divided below the compression side chamber R2 in the cylinder 1. The expansion side chamber R1, the compression side chamber R2, and the pressure chamber R3 above the sliding partition wall 14 in the cylinder 1 are filled with a liquid such as hydraulic oil, and the gas chamber G is filled with a gas. The liquid filled into the expansion side chamber R1, the compression side chamber R2, and the pressure chamber R3 can be liquid such as water or an aqueous solution other than hydraulic oil.

[0026] A seal member 15 for sealing the outer periphery of the piston rod 3 is provided above the rod guide 12 in FIG. 1, so that the inside of the cylinder 1 is liquid-tight. In the illustrated example, the shock absorber D1 is set to be a so-called single rod type. Therefore, the volume of the piston rod 3 moving in and out of the cylinder 1 with the expansion and contraction of the shock absorber D1 is compensated for by the sliding partition wall 14 moving in the vertical direction in FIG. 1 as the volume of the gas in the gas chamber G expands or contracts. Thus, the shock absorber D1 is set to be a single cylinder type, but instead of providing the sliding partition wall 14 and the gas chamber G, a reservoir may be provided on the outer periphery or outside of the cylinder 1 to compensate for the volume of the piston rod 3 by the reservoir. Also, the shock absorber D1 may be set to be a double rod type instead of a single rod type.

[0027] 1, the piston rod 3 has a small diameter portion 3a formed at its lower end, and a threaded portion 3b formed at the tip side of the small diameter portion 3a. Also, a step portion 3c is provided by reducing the diameter of the lower end of the piston rod 3. The piston 2 is formed in an annular shape, and the small diameter portion 3a of the piston rod 3 is inserted into its inner periphery.

[0028] The piston rod 3 is formed with a vertical hole 3d that opens from the tip of the small diameter portion 3a, and a horizontal hole 3e that opens from a side portion above the small diameter portion 3a and communicates with the vertical hole 3d.

[0029] The piston 2 is provided with an expansion-side port 2a and a compression-side port 2b that communicate between the expansion-side chamber R1 and the compression-side chamber R2. An expansion-side main valve 16 made of a laminated leaf valve that opens and closes the outlet end of the expansion-side port 2a, which is the lower end in FIG. 1, is laminated on the lower side of the piston 2 in FIG. 1, and a compression-side main valve 17 made of a laminated leaf valve that opens and closes the outlet end of the compression-side port 2b, which is the upper end in FIG. 1, is laminated on the upper side of the piston 2 in FIG. 1.

[0030] The expansion side main valve 16 and the compression side main valve 17 are both formed in an annular shape, and their inner circumferences are fixed to the small diameter portion 3a of the piston rod 3, allowing deflection on the outer circumference side. The number and thickness of the leaf valves constituting the expansion side main valve 16 and the compression side main valve 17 can be arbitrarily changed according to the desired damping characteristics. The expansion side main valve 16 and the compression side main valve 17 may be valves other than leaf valves.

[0031] When the pressure in the expansion-side chamber R1 becomes higher than the pressure in the contraction-side chamber R2 during the expansion operation of the shock absorber D1, and the pressure difference between the two chambers reaches a valve opening pressure or more, the expansion-side main valve 16 bends its outer periphery to open the expansion-side port 2a, thereby providing resistance to the flow of liquid moving from the expansion-side chamber R1 to the contraction-side chamber R2. When the expansion-side main valve 16 closes the expansion-side port 2a during the contraction operation of the shock absorber D1, thereby setting the expansion-side port 2a as a one-way passage. When the pressure in the contraction-side chamber R2 becomes higher than the pressure in the expansion-side chamber R1 during the contraction operation of the shock absorber D1, the contraction-side main valve 17 bends its outer periphery to open the contraction-side port 2b, thereby providing resistance to the flow of liquid moving from the contraction-side chamber R2 to the expansion-side chamber R1. When the expansion-side main valve 17 closes the contraction-side port 2b during the expansion operation of the shock absorber D1, thereby setting the contraction-side port 2b as a one-way passage.

[0032] Therefore, in the shock absorber D1 of this example, the damping passage P is composed of the expansion-side port 2a, the expansion-side main valve 16, the compression-side port 2b, and the compression-side main valve 17. Even when the expansion-side main valve 16 closes the expansion-side port 2a, the expansion-side chamber R1 and the compression-side chamber R2 are communicated with each other through an orifice formed by a notch (not shown) provided on the outer periphery of the expansion-side main valve 16. As described above, the orifice is formed by providing a notch on the outer periphery of the expansion-side main valve 16, or by providing a recess in a valve seat provided on the piston 2 on which the expansion-side main valve 16 is seated and released. The compression-side main valve 17 may also be provided with an orifice formed by a notch or the like, similar to the expansion-side main valve 16. When the piston speed of the shock absorber D1 is the same, the expansion-side main valve 16 provides a larger resistance to the flow of liquid than the compression-side main valve 17.

[0033] Next, on the extension-side chamber side, which is above the piston 2 in FIG. 1 and above the compression-side main valve 17 in FIG. 1, an annular valve stopper 18 that restricts the compression-side main valve 17 from bending further when the compression-side main valve 17 bends by a predetermined amount is superimposed and attached to the outer periphery of the small diameter portion 3a of the piston rod 3.

[0034] 1, the extension-side main valve 16 is stacked below the piston 2, and the extension-side main valve 16 is attached to the outer periphery of the small diameter part 3a of the piston rod 3 together with the piston 2. A piston nut 21 is screwed onto the threaded part 3b of the piston rod 3 from below the extension-side main valve 16 in FIG. 1. The piston nut 21 clamps the valve stopper 18, the compression side main valve 17, the piston 2, and the extension-side main valve 16 attached to the outer periphery of the piston rod 3 between the step part 3c of the piston rod 3 and the piston nut 21, and fixes them to the piston rod 3.

[0035] The piston nut 21 fixes the piston 2, the extension-side main valve 16, and the compression-side main valve 17 to the piston rod 3 and constitutes a housing H1 that forms a pressure chamber R3 therein in cooperation with the piston rod 3. The housing H1 formed by the piston nut 21 accommodates the free piston 4, and the extension-side coil spring 7a and the compression-side coil spring 7b as the spring element 7 that positions the free piston 4 at a neutral position within the housing H1.

[0036] As shown in Figures 1 and 2, the piston nut 21 is cylindrical and has a nut portion 21a having a flange portion 21c on its outer periphery and is screwed to the screw portion 3b of the piston rod 3, and a bottomed cylindrical portion 21d having a bottom 21e and attached to the outer periphery of the flange portion 21c. The piston nut 21 is attached to the tip of the piston rod 3 to form a pressure chamber R3.

[0037] 2 of the cylindrical portion 21d of the piston nut 21 is closed by screwing the nut portion 21a to the screw portion 3b of the piston rod 3, and a first lid portion C1 of the housing H1 is formed by the nut portion 21a and the lower end in FIG. 2 which is the tip of the piston rod 3. Furthermore, a lower end of the cylindrical portion 21d is closed by the bottom portion 21e, and a second lid portion C2 of the housing H1 is formed by the bottom portion 21e.

[0038] The piston nut 21 constituting a part of the housing H1 will be described in detail below. The nut part 21a is provided with a cylindrical nut body 21b having a screw groove on the inner circumference, and a flange part 21c which is the outer circumference of the nut body 21b and protrudes radially from an axial middle part toward the outer circumference side, and is screwed to the screw part 3b of the piston rod 3 and fixed to the small diameter part 3a of the piston rod 3. Furthermore, the outer circumference diameter of the part protruding toward the pressure chamber R3 side from the flange part 21c of the nut body 21b below in FIG. 2 becomes smaller as it goes downward in FIG. 2, and the nut body 21b has a tapered surface 21b1 on the outer circumference.

[0039] The nut portion 21a configured as described above is inserted into the cylindrical portion 21d, and the open end of the upper end of the cylindrical portion 21d is crimped from the outer periphery side to grip the outer periphery of the flange portion 21c with the cylindrical portion 21d, thereby integrating the nut portion 21a and the cylindrical portion 21d. In addition, an annular groove 21b2 is provided along the circumferential direction on the outer periphery of the nut body 21b in the nut portion 21a, below the flange portion 21c and above the tapered surface 21b1, and a hole 21b3 is provided that opens into the annular groove 21b2 and penetrates the nut body 21b. When the nut body 21b is screwed to the tip of the piston rod 3, a first protrusion p1 protruding inwardly of the housing H1 is formed by a portion of the nut body 21b below the flange portion 21c in FIG. 2 and a portion of the piston rod 3 screwed to the nut body 21b. The inside of the housing H1 is connected to the expansion-side chamber R1 by a vertical hole 3d opening from the tip of the piston rod 3 and a horizontal hole 3e opening from the side of the piston rod 3, and the vertical hole 3d and the horizontal hole 3e form an expansion-side passage 8.

[0040] Furthermore, the piston rod 3 is provided with a hole 3f that opens from the outer periphery of the screw portion 3b and communicates with the vertical hole 3d and with the hole 21b3 in the nut portion 21a, and the holes 3f and 21b3 form an extension-side suction passage 22.

[0041] In addition, an annular extension-side check valve 10 is mounted in the annular groove 21b2 in the nut body 21b. The extension-side check valve 10 is elastically mounted on the outer periphery of the first protruding portion p1 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the extension-side suction passage 22. When the extension-side check valve 10 receives pressure from the extension-side suction passage 22 side and expands in diameter, it moves away from the opening of the extension-side suction passage 22 to communicate the inside of the housing H1 with the extension-side chamber R1 through the extension-side suction passage 22, and when the pressure in the housing H1 is higher than the pressure in the extension-side chamber R1, it comes into close contact with the opening of the extension-side suction passage 22 to block the extension-side suction passage 22. Note that the extension-side check valve 10 may be a C-ring made of rubber, synthetic resin, or metal, in addition to an O-ring, as long as it has elasticity and can open and close the extension-side suction passage 22.

[0042] The bottom 21e of the cylindrical portion 21d has a protrusion 21e1 at its center that protrudes inward into the housing H1. The outer diameter of the protrusion 21e1 decreases toward the top in FIG. 2, and the protrusion 21e1 has a tapered surface 21e2 on its outer periphery. The protrusion 21e1 forms a second protrusion p2 that protrudes inward from the bottom 21e as the second lid portion C2.

[0043] The protrusion 21e1 is provided with a compression side passage 9 that opens from the upper end of the protrusion 21e1 in FIG. 2 and penetrates the protrusion 21e1 in the axial direction. Thus, the inside of the housing H1 is connected to the compression side chamber R2 via the compression side passage 9. The protrusion 21e1 is further provided with an annular groove 21e3 provided on the outer periphery of the base, and a compression side suction passage 23 that opens from the annular groove 21e3 and communicates with the compression side chamber R2 via the compression side passage 9. An annular compression side check valve 11 is attached to the annular groove 21e3 of the protrusion 21e1.

[0044] The compression side check valve 11 is elastically attached to the outer periphery of the second protrusion p2 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the compression side suction passage 23. When the compression side check valve 11 receives pressure from the compression side suction passage 23 side and expands in diameter, it moves away from the opening of the compression side suction passage 23 to communicate the inside of the housing H1 with the compression side chamber R2 via the compression side suction passage 23, and when the pressure in the housing H1 is higher than the pressure in the compression side chamber R2, it comes into close contact with the opening of the compression side suction passage 23 to block the compression side suction passage 23. The compression side suction passage 23 may be provided in the cylindrical portion 21d, and in that case, the compression side check valve 11 may be provided to open and close the opening of the compression side suction passage 23 relative to the cylindrical portion 21d.

[0045] As shown in FIG. 2, the free piston 4 is in sliding contact with the inner periphery of the cylindrical portion 21d of the piston nut 21 that forms the housing H1 and can move in the vertical direction in FIG. 2 relative to the piston nut 21. The free piston 4 divides the pressure chamber R3 into an expansion-side pressure chamber 5 that is connected to the expansion-side chamber R1 by an expansion-side passage 8 and a compression-side pressure chamber 6 that is connected to the compression-side chamber R2 by a compression-side passage 9.

[0046] Specifically, the free piston 4 includes a partition portion 4a whose outer periphery is in sliding contact with the inner periphery of the cylindrical portion 21d, a cylindrical first case 4b rising from the end portion of the partition portion 4a on the upper side in FIG. 2 which corresponds to the expansion-side pressure chamber side, and a cylindrical second case 4c rising from the end portion of the partition portion 4a on the lower side in FIG. 2 which corresponds to the compression-side pressure chamber side.

[0047] The partition 4a includes a disk-shaped partition main body 4a1, an annular opposing portion 4a2 that is connected to the upper portion of the outer periphery of the partition main body 4a1 and faces the inner periphery of the cylindrical portion 21d with a small gap therebetween, an annular groove 4a3 provided on the outer periphery of the opposing portion 4a2, and a seal ring 4a4 that is housed in the annular groove 4a3 and slides against the inner periphery of the cylindrical portion 21d. Since the partition 4a includes the seal ring 4a4, the gap between the partition 4a and the cylindrical portion 21d is sealed, and the expansion-side pressure chamber 5 and the contraction-side pressure chamber 6 defined in the housing H1 are prevented from communicating with each other through the gap between the free piston 4 and the cylindrical portion 21d.

[0048] The first case 4b is cylindrical, integrally connected to the outer periphery of the upper end of the partition body 4a1 in FIG. 2 and the inner periphery of the opposing portion 4a2 in FIG. 2, and protrudes upward in FIG. 2. The first case 4b allows the first protrusion p1 to be inserted, and has a tapered surface on the inner periphery that expands in diameter toward the tip side. Therefore, when the free piston 4 moves upward in FIG. 2 in the direction of compressing the expansion-side pressure chamber 5, the first protrusion p1 can enter the back side of the first case 4b, and the free piston 4 can move upward until the inner periphery of the first case 4b abuts against the tapered surface 21b1 on the outer periphery of the first protrusion p1. In this way, when the free piston 4 moves in the direction of compressing the expansion-side pressure chamber 5, the area of ​​the annular gap between the first case 4b and the first protrusion p1 gradually decreases, and when the first case 4b and the first protrusion p1 abut, the expansion-side passage 8 that opens at the tip of the first protrusion p1 can be blocked. In this way, the flow passage area between the first case 4b and the first protrusion p1 decreases according to the degree to which the first protrusion p1 enters the first case 4b.

[0049] Since the inner periphery of the first case 4b is a tapered surface and the outer periphery of the first convex portion p1 that can enter the first case 4b is a tapered surface 21b1, it is possible to reduce the degree of change in the annular gap between the first case 4b and the first convex portion p1 relative to the amount of displacement of the free piston 4 when the free piston 4 moves in a direction to compress the expansion-side pressure chamber 5. Depending on the degree of change in the annular gap between the first case 4b and the first convex portion p1 relative to the amount of displacement of the free piston 4, a tapered surface may be provided only on one of the inner periphery of the first case 4b and the outer periphery of the first convex portion p1.

[0050] The second case 4c is cylindrical and protrudes downward from the lower end of the partition body 4a1 in FIG. 2. The second case 4c allows the second protrusion p2 to be inserted, and has a tapered surface on the inner circumference that expands toward the tip side. Therefore, when the free piston 4 moves downward in FIG. 2 in the direction compressing the compression side pressure chamber 6, the second protrusion p2 can enter the back side of the second case 4c, and the free piston 4 can move downward until the inner circumference of the second case 4c abuts against the tapered surface 21e2 on the outer circumference of the second protrusion p2. In this way, when the free piston 4 moves in the direction compressing the compression side pressure chamber 6, the passage area of ​​the annular gap between the second case 4c and the second protrusion p2 gradually decreases, and when the second case 4c and the second protrusion p2 abut against each other, the compression side passage 9 that opens at the tip of the second protrusion p2 can be blocked. In this way, the flow passage area between the second case 4c and the second protrusion p2 decreases according to the degree to which the second protrusion p2 enters the second case 4c.

[0051] Since the inner periphery of the second case 4c is a tapered surface and the outer periphery of the second convex portion p2 that can enter the second case 4c is a tapered surface 21e2, it is possible to reduce the degree of change in the annular gap between the second case 4c and the second convex portion p2 relative to the amount of displacement of the free piston 4 when the free piston 4 moves in a direction to compress the compression-side pressure chamber 6. Depending on the degree of change in the annular gap between the second case 4c and the second convex portion p2 relative to the amount of displacement of the free piston 4, a tapered surface may be provided only on one of the inner periphery of the second case 4c and the outer periphery of the second convex portion p2.

[0052] The free piston 4 is sandwiched between an extension-side coil spring 7a, which is interposed between the partition wall 4a and the flange portion 21c of the piston nut 21 and housed in the extension-side pressure chamber 5, and a compression-side coil spring 7b, which is interposed between the partition wall 4a and the outer periphery side of the protrusion 21e1 of the bottom portion 21e of the piston nut 21 and housed in the compression-side pressure chamber 6. The extension-side coil spring 7a and the compression-side coil spring 7b sandwich the free piston 4 in a compressed state, and the free piston 4 sandwiched between the extension-side coil spring 7a and the compression-side coil spring 7b is positioned at a neutral position in the pressure chamber R3. In this embodiment, the neutral position is set at a position corresponding to the stroke center of the free piston 4 in the pressure chamber R3, and the free piston 4 can stroke the same distance upward and downward in FIG. 2 from the neutral position in the pressure chamber R3. In other words, since the neutral position coincides with the stroke center of the free piston 4, the upward stroke distance of the free piston 4 from the neutral position until its movement is restricted by the abutment between the first case 4b and the first convex portion p1 is equal to the downward stroke distance of the free piston 4 from the neutral position until its movement is restricted by the abutment between the second case 4c and the second convex portion p2.

[0053] In this embodiment, the extension-side coil spring 7a and the compression-side coil spring 7b are coil springs having the same natural length and spring constant, and when the free piston 4 is placed in the neutral position, the opposing portion 4a2 of the partition wall portion 4a is placed in the center of the axial direction in the pressure chamber R3. In the shock absorber D1 of this embodiment, the first protrusion p1 is composed of the nut body 21b of the piston nut 21 and the tip portion of the small diameter portion 3a of the piston rod 3 screwed to the inner periphery of the nut body 21b, and has a longer axial length than the second protrusion p2. Therefore, when the free piston 4 is placed in the neutral position, the partition wall body 4a1, which faces the first protrusion p1 and the second protrusion p2 in the axial direction, is biased toward the second protrusion p2 side in FIG. 2 with respect to the opposing portion 4a2, and does not interfere with the first protrusion p1 and the second protrusion p2 even if the free piston 4 moves in the pressure chamber R3. Even if the first protrusion p1 forms a fixed portion by screw connection to the piston rod 3 of the housing H1 and is larger than the second protrusion p2, the stroke length of the free piston 4 can be secured because the partition portion 4a is composed of a partition main body 4a1 and an opposing portion 4a2 that is integrated with the partition main body 4a1 and is biased in the axial direction, thereby ensuring the stroke length of the free piston 4.

[0054] Next, the extension-side coil spring 7a abuts against the upper end of the opposing portion 4a2 of the partition portion 4a of the free piston 4 in FIG. 2, and the first case 4b is inserted into the inner circumference on the lower end side. Since no eccentricity occurs with respect to the free piston 4 when the extension-side coil spring 7a extends or contracts, a stable biasing force can be applied to the free piston 4.

[0055] In addition, the compression side coil spring 7b abuts against the lower end of the opposing portion 4a2 of the partition portion 4a of the free piston 4 in Figure 2, and the lower portion of the partition main body 4a1 is inserted into the inner circumference on the lower end side, so that no eccentricity occurs with respect to the free piston 4 when it expands and contracts, and a stable biasing force can be applied to the free piston 4.

[0056] Note that the spring element 7 only needs to be able to position the free piston 4 in the neutral position and to exert a biasing force in a direction in which the free piston 4 returns to the neutral position when displaced from the neutral position, and therefore may be formed of one spring connected to both the housing H1 and the free piston 4. Furthermore, the spring constituting the spring element 7 may be an elastic body such as a wave washer, a leaf spring, a disc spring, rubber, etc., other than a coil spring.

[0057] The shock absorber D1 is configured as described above, and the operation of the shock absorber D1 will be described below. When the shock absorber D1 performs an extension operation in which the piston 2 moves upward in FIG. 1 relative to the cylinder 1, the piston 2 compresses the expansion-side chamber R1 and expands the contraction-side chamber R2. Then, the pressure in the expansion-side chamber R1 increases and at the same time the pressure in the contraction-side chamber R2 decreases, causing a pressure difference between the two chambers. The liquid in the expansion-side chamber R1 pushes open the expansion-side main valve 16 and moves to the contraction-side chamber R2 through the expansion-side port 2a. In addition, since the pressure in the expansion-side chamber R1 becomes higher than the pressure in the contraction-side chamber R2, the pressure in the expansion-side pressure chamber 5 communicated with the expansion-side chamber R1 becomes higher than the pressure in the contraction-side pressure chamber 6 communicated with the contraction-side chamber R2. Then, the free piston 4 moves from the neutral position in the pressure chamber R3 in a direction compressing the contraction-side pressure chamber 6 according to the pressure difference between the pressure in the expansion-side pressure chamber 5 and the pressure in the contraction-side pressure chamber 6. Therefore, the liquid in the expansion-side chamber R1 moves to the compression-side chamber R2 not only through the expansion-side port 2a but also through an apparent passage consisting of the expansion-side passage 8, the expansion-side pressure chamber 5, the compression-side pressure chamber 6, and the compression-side passage 9.

[0058] On the other hand, when the shock absorber D1 contracts in such a manner that the piston 2 moves downward in FIG. 1 relative to the cylinder 1, the piston 2 compresses the compression side chamber R2 and expands the expansion side chamber R1. Then, the pressure in the compression side chamber R2 increases and the pressure in the expansion side chamber R1 decreases, causing a pressure difference between the two chambers, and the liquid in the compression side chamber R2 pushes open the compression side main valve 17 and moves to the expansion side chamber R1 through the compression side port 2b. Also, since the pressure in the compression side chamber R2 becomes higher than the pressure in the expansion side chamber R1, the pressure in the compression side pressure chamber 6 connected to the compression side chamber R2 becomes higher than the pressure in the expansion side pressure chamber 5 connected to the expansion side chamber R1. Then, the free piston 4 moves from the neutral position in the pressure chamber R3 in a direction compressing the expansion side pressure chamber 5 according to the pressure difference between the pressure in the compression side pressure chamber 6 and the pressure in the expansion side pressure chamber 5. Therefore, the liquid in the compression side chamber R2 moves to the expansion side chamber R1 not only through the compression side port 2b but also through an apparent passage consisting of the expansion side passage 8, the expansion side pressure chamber 5, the compression side pressure chamber 6 and the compression side passage 9.

[0059] Here, when the piston speed when the shock absorber D1 expands and contracts is the same, the amplitude when the shock absorber D1 vibrates at a low frequency is larger than the amplitude when the shock absorber D1 vibrates at a high frequency. In this way, when the frequency of the vibration input to the shock absorber D1 is low, the amplitude is large, so the flow rate of the liquid that flows between the expansion-side chamber R1 and the contraction-side chamber R2 in one period of expansion and contraction is large. The displacement of the free piston 4 also increases in proportion to this flow rate, but since the free piston 4 is biased by the spring element 7, when the displacement of the free piston 4 increases, the biasing force from the spring element 7 that the free piston 4 receives also increases. Accordingly, a pressure difference occurs between the pressure of the expansion-side pressure chamber 5 and the pressure of the contraction-side pressure chamber 6, and the pressure difference between the expansion-side chamber R1 and the expansion-side pressure chamber 5 and the pressure difference between the contraction-side chamber R2 and the contraction-side pressure chamber 6 becomes small, and the flow rate passing through the apparent flow path decreases. Since the flow rate passing through this apparent path is small, the flow rate passing through the expansion-side main valve 16 or the contraction-side main valve 17 is large, so the damping force generated by the shock absorber D1 is maintained high.

[0060] Conversely, when high-frequency vibration is input to the shock absorber D1, the amplitude is smaller than that when low-frequency vibration is input, so the flow rate of the liquid passing between the expansion-side chamber R1 and the contraction-side chamber R2 in one period of expansion and contraction is small, and the displacement of the free piston 4 is also small. Then, the biasing force from the spring element 7 that the free piston 4 receives is also small. Accordingly, the pressure in the expansion-side pressure chamber 5 and the pressure in the contraction-side pressure chamber 6 become almost equal, and the differential pressure between the expansion-side chamber R1 and the expansion-side pressure chamber 5 and the differential pressure between the contraction-side chamber R2 and the contraction-side pressure chamber 6 become larger than that when low-frequency vibration is input, and the flow rate passing through the apparent passage is increased compared to that when low-frequency vibration is input. The flow rate passing through the expansion-side main valve 16 or the contraction-side main valve 17 decreases by the amount corresponding to the increase in the flow rate passing through the apparent passage, and the damping force generated by the shock absorber D1 becomes lower than that when low-frequency vibration is input.

[0061] Therefore, the shock absorber D1 can obtain a damping force reduction effect that reduces the damping force depending on the input vibration frequency, and exerts a high damping force when the input vibration frequency is low, and exerts a low damping force when the input vibration frequency is high. Therefore, the shock absorber D1 generates a high damping force for the input of vibration in a low sprung resonance frequency band, stabilizes the posture of the vehicle, and prevents the passenger from feeling uneasy when the vehicle turns. Furthermore, the shock absorber D1 always generates a low damping force when vibration in a high unsprung resonance frequency band is input, and insulates the transmission of vibration on the axle side to the vehicle body side, thereby improving the ride comfort in the vehicle. The frequency at which the damping force decreases can be tuned by setting the resistance that the extension side passage 8 and the compression side passage 9 provide to the flow of liquid and the spring constant of the spring element 7.

[0062] In addition, when the resistance to the flow of liquid provided by the expansion-side passage 8 and the compression-side passage 9 is minimized, the liquid can freely move between the expansion-side chamber R1 and the expansion-side pressure chamber 5, and between the compression-side chamber R2 and the compression-side pressure chamber 6. Then, in a range where the amplitude of vibration of the shock absorber D1 is small and the free piston 4 does not reach the stroke end in the pressure chamber R3, the free piston 4 can freely move in the pressure chamber R3 and can move between the expansion-side chamber R1 and the compression-side chamber R2 via the apparent passages, bypassing the expansion-side main valve 16 and the compression-side main valve 17, thereby reducing the damping force generated by the shock absorber D1. On the other hand, when the vibration amplitude of the shock absorber D1 is large and the free piston 4 reaches the stroke end in the pressure chamber R3, the movement of the free piston 4 in the same direction is restricted unless the expansion / contraction direction of the shock absorber D1 is switched, so that the expansion-side chamber R1 and the compression-side chamber R2 cannot move back and forth through the apparent passage, and the shock absorber D1 generates a high damping force by the expansion-side main valve 16 and the compression-side main valve 17. In this way, when the resistance to the flow of the liquid provided by the expansion-side passage 8 and the compression-side passage 9 is minimized, the shock absorber D1 changes the damping force in response to the amplitude of the input vibration, not the frequency of the input vibration, and generates a low damping force for the input of a small amplitude vibration to insulate the transmission of the vibration on the axle side to the vehicle body side, and generates a high damping force for the input of a large amplitude vibration to suppress the vibration of the vehicle body, thereby improving the ride comfort of the vehicle.

[0063] Next, the hydraulic lock function of the shock absorber D1 will be described. When the stroke amount of the shock absorber D1 toward the extension side is large, the free piston 4 moves a large amount from the neutral position in the direction compressing the compression-side pressure chamber 6. When the free piston 4 moves from the neutral position in the direction compressing the compression-side pressure chamber 6, the second protrusion p2 penetrates deeply into the second case 4c, and the area of ​​the annular gap between the second case 4c and the second protrusion p2 gradually decreases as the movement amount of the free piston 4 increases, gradually decreasing the degree of communication between the compression-side passage 9 and the compression-side pressure chamber 6.

[0064] Therefore, as the free piston 4 moves from the neutral position in the direction compressing the compression side pressure chamber 6, it becomes gradually more difficult for the liquid in the compression side pressure chamber 6 to move to the compression side chamber R2 through the compression side passage 9, and when the free piston 4 reaches the stroke end, the second case 4c and the second protrusion p2 come into contact with each other to close the compression side pressure chamber 6. In addition, during the extension operation of the shock absorber D1, the pressure in the compression side pressure chamber 6 becomes higher than the pressure in the compression side chamber R2, so the compression side check valve 11 attached to the outer periphery of the second protrusion p2 blocks the compression side suction passage 23.

[0065] Therefore, when the free piston 4 moves from the neutral position in the direction compressing the compression side pressure chamber 6 to the vicinity of the stroke end, the liquid in the compression side pressure chamber 6 becomes less likely to move to the compression side chamber R2 as the movement of the free piston 4 progresses, and the pressure of the compression side pressure chamber 6 increases, suppressing the movement of the free piston 4 in the direction compressing the compression side pressure chamber 6. In this way, in the shock absorber D1 of this embodiment, when the free piston 4 moves from the neutral position in the direction compressing the compression side pressure chamber 6 to the vicinity of the stroke end, the degree of communication between the compression side pressure chamber 6 and the compression side passage 9 is reduced to increase the pressure of the compression side pressure chamber 6, and the compression side pressure chamber 6 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 4 in the direction compressing the compression side pressure chamber 6. Note that, during the extension operation of the shock absorber D1, the force exerted by the hydraulic lock function to suppress the displacement of the free piston 4 changes depending on the speed of the free piston 4 and the degree of communication between the compression side pressure chamber 6 and the compression side passage 9.

[0066] In addition, after the free piston 4 increases the pressure in the compression-side pressure chamber 6 to perform the hydraulic lock function, when the direction of extension and contraction of the shock absorber D1 changes from the extension operation to the contraction operation, the free piston 4 tries to move upward in FIG. 2 in the direction of compressing the expansion-side pressure chamber 5. At that time, liquid is supplied from the compression-side chamber R2 through the compression-side passage 9 to the space between the second case 4c and the second protrusion p2 of the free piston 4. Furthermore, the compression-side check valve 11 receives the pressure of the compression-side chamber R2 and expands in diameter to open, thereby opening the compression-side suction passage 23, so that liquid is quickly supplied from the compression-side chamber R2 through the compression-side suction passage 23 to the inside of the compression-side pressure chamber 6, whose communication with the compression-side passage 9 is restricted. In this way, even if the free piston 4 is displaced to the vicinity of the stroke end to reduce the degree of communication between the compression side passage 9 and the compression side pressure chamber 6, when the shock absorber D1 changes from extension to contraction, liquid is supplied from the compression side chamber R2 to the space between the second case 4c and the second convex portion p2 and to the compression side pressure chamber 6, respectively, and no excessive pressure drop is caused. Therefore, the free piston 4 can smoothly move in the direction of compressing the expansion side pressure chamber 5 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D1 is not impaired.

[0067] As described above, when the free piston 4 is displaced in the housing H1 in the direction compressing the compression side pressure chamber 6 to the vicinity of the stroke end during the extension operation of the shock absorber D1, the hydraulic lock function is exerted to suppress the movement of the free piston 4 toward the compression side stroke end, and the moving speed of the free piston 4 is gradually reduced to stop the free piston 4 at the stroke end. When the free piston 4 stops, liquid cannot pass through the apparent passage, and the entire flow rate of liquid from the expansion side chamber R1 to the compression side chamber R2 passes through the expansion side main valve 16, so the damping force generated by the shock absorber D1 becomes high. Therefore, if the shock absorber D1 generates a low damping force before the stop of the free piston 4, the damping force generated by the stop of the free piston 4 becomes high, but since the free piston 4 gradually reduces its speed due to the hydraulic lock, the flow rate of liquid passing through the apparent flow path decreases, and the flow rate of liquid passing through the expansion side main valve 16 increases accordingly, and the damping force generated by the shock absorber D1 gradually increases continuously, so that the sudden change in the damping force is mitigated.

[0068] Furthermore, when the stroke amount of the shock absorber D1 toward the contraction side is large, the free piston 4 moves a large amount from the neutral position in the direction compressing the expansion-side pressure chamber 5. When the free piston 4 moves from the neutral position in the direction compressing the expansion-side pressure chamber 5, the first protrusion p1 penetrates deeply into the first case 4b, and the area of ​​the annular gap between the first case 4b and the first protrusion p1 gradually decreases as the movement amount of the free piston 4 increases, gradually decreasing the degree of communication between the expansion-side passage 8 and the expansion-side pressure chamber 5.

[0069] Therefore, as the free piston 4 moves from the neutral position in the direction compressing the expansion-side pressure chamber 5, the liquid in the expansion-side pressure chamber 5 gradually becomes less able to move to the expansion-side chamber R1 through the expansion-side passage 8, and when the free piston 4 reaches the stroke end, the first case 4b comes into contact with the first protrusion p1 to close the expansion-side pressure chamber 5. In addition, during the contraction operation of the shock absorber D1, the pressure in the expansion-side pressure chamber 5 becomes higher than the pressure in the expansion-side chamber R1, so the expansion-side check valve 10 attached to the outer periphery of the first protrusion p1 blocks the expansion-side suction passage 22.

[0070] Therefore, when the free piston 4 moves from the neutral position in the direction compressing the expansion-side pressure chamber 5 to the vicinity of the stroke end, the liquid in the expansion-side pressure chamber 5 becomes less likely to move to the expansion-side chamber R1 as the movement of the free piston 4 progresses, and the pressure in the expansion-side pressure chamber 5 increases, suppressing the movement of the free piston 4 in the direction compressing the expansion-side pressure chamber 5. In this way, in the shock absorber D1 of this embodiment, when the free piston 4 moves from the neutral position in the direction compressing the expansion-side pressure chamber 5 to the vicinity of the stroke end, the degree of communication between the expansion-side pressure chamber 5 and the expansion-side passage 8 is reduced to increase the pressure in the expansion-side pressure chamber 5, and the expansion-side pressure chamber 5 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 4 in the direction compressing the expansion-side pressure chamber 5. Note that, during the contraction operation of the shock absorber D1, the force exerted by the hydraulic lock function to suppress the displacement of the free piston 4 changes depending on the speed of the free piston 4 and the degree of communication between the expansion-side pressure chamber 5 and the expansion-side passage 8.

[0071] In addition, after the free piston 4 increases the pressure in the expansion-side pressure chamber 5 to perform the hydraulic lock function, when the direction of extension and contraction of the shock absorber D1 changes from contraction to expansion, the free piston 4 tries to move downward in FIG. 2 in the direction of compressing the compression-side pressure chamber 6. At that time, liquid is supplied from the expansion-side chamber R1 through the expansion-side passage 8 to the space between the first case 4b and the first protruding portion p1 of the free piston 4. Furthermore, the expansion-side check valve 10 receives the pressure of the expansion-side chamber R1 and expands in diameter to open, thereby opening the expansion-side suction passage 22, so that liquid is quickly supplied from the expansion-side chamber R1 through the expansion-side suction passage 22 to the inside of the expansion-side pressure chamber 5, whose communication with the expansion-side passage 8 is restricted. In this way, even if the free piston 4 is displaced to the vicinity of the stroke end to reduce the degree of communication between the expansion-side passage 8 and the expansion-side pressure chamber 5, when the shock absorber D1 changes from contraction to extension, liquid is supplied from the expansion-side chamber R1 to the space between the first case 4b and the first convex portion p1 and to the expansion-side pressure chamber 5, respectively, and no excessive pressure drop is caused. Therefore, the free piston 4 can smoothly move in the direction of compressing the compression-side pressure chamber 6 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D1 is not impaired.

[0072] As described above, when the free piston 4 is displaced in the housing H1 in the direction compressing the expansion-side pressure chamber 5 to the vicinity of the stroke end during the contraction operation of the shock absorber D1, the hydraulic lock function is exerted to suppress the movement of the free piston 4 toward the extension-side stroke end, and the moving speed of the free piston 4 is gradually reduced to stop the free piston 4 at the stroke end. When the free piston 4 stops, liquid cannot pass through the apparent passage, and the entire flow rate of liquid from the compression-side chamber R2 to the expansion-side chamber R1 passes through the compression-side main valve 17, so the damping force generated by the shock absorber D1 becomes high. Therefore, if the shock absorber D1 generates a low damping force before the stop of the free piston 4, the damping force generated by the stop of the free piston 4 becomes high, but since the free piston 4 gradually reduces its speed due to the hydraulic lock, the flow rate of liquid passing through the apparent flow path decreases, and the flow rate of liquid passing through the compression-side main valve 17 increases accordingly, and the damping force generated by the shock absorber D1 gradually increases continuously, so that the sudden change in the damping force is mitigated.

[0073] As described above, the shock absorber D1 according to one embodiment includes the cylinder 1, the piston 2 slidably inserted into the cylinder 1 and dividing the inside of the cylinder 1 into an expansion-side chamber R1 and a compression-side chamber R2, the piston rod 3 movably inserted into the cylinder 1 and one end of which is connected to the piston 2, a damping passage P communicating between the expansion-side chamber R1 and the compression-side chamber R2, a pressure chamber R3, a free piston 4 movably inserted into the pressure chamber R3 and dividing the inside of the pressure chamber R3 into an expansion-side pressure chamber 5 and a compression-side pressure chamber 6, a spring element 7 that generates a biasing force that suppresses displacement of the free piston 4 from a neutral position with respect to the pressure chamber R3, and an expansion-side passage 8 communicating between the expansion-side chamber R1 and the expansion-side pressure chamber 5. The free piston 4 is provided with a compression side passage 9 communicating the compression side chamber R2 and the compression side pressure chamber 6, an extension side check valve 10 which allows only the flow of liquid from the extension side chamber R1 to the extension side pressure chamber 5, and a compression side check valve 11 which allows only the flow of liquid from the compression side chamber R2 to the compression side pressure chamber 6. When the free piston 4 moves to a stroke end in a direction compressing the extension side pressure chamber 5, the degree of communication between the extension side passage 8 and the extension side pressure chamber 5 is reduced, causing the expansion side pressure chamber 5 to function as a hydraulic lock chamber, and when the free piston 4 moves to a stroke end in a direction compressing the compression side pressure chamber 6, the degree of communication between the compression side passage 9 and the compression side pressure chamber 6 is reduced, causing the compression side pressure chamber 6 to function as a hydraulic lock chamber.

[0074] According to the shock absorber D1 configured as above, the movement of the free piston 4 to the stroke end causes the expansion-side pressure chamber 5 itself or the compression-side pressure chamber 6 itself to function as a hydraulic lock chamber, so that a sudden change in the damping force can be mitigated, and the stroke length of the free piston 4 can be secured without providing a cushion in the pressure chamber R3. In addition, since the shock absorber D1 does not require a cushion, the volumes in the expansion-side pressure chamber 5 and the compression-side pressure chamber 6 can be secured large, and the liquid in the expansion-side pressure chamber 5 and the compression-side pressure chamber 6 can be used during hydraulic lock. Therefore, in the shock absorber D1, a sufficient flow rate of liquid can be flowed into the expansion-side chamber R1 or the compression-side chamber R2 while gradually restricting the degree of communication between the expansion-side pressure chamber 5 and the expansion-side passage 8 or the degree of communication between the compression-side pressure chamber 6 and the compression-side passage 9 until the hydraulic lock function is exerted, and it is also easy to tune the transient characteristics in which the damping force is reduced to transition from a state in which a low damping force is generated to a state in which a high damping force is generated by the expansion-side main valve 16 or the compression-side main valve 17. If the volume of the hydraulic lock chamber is small, the flow rate of liquid discharged from the hydraulic lock chamber from the time when the free piston 4 begins to receive resistance from the hydraulic lock chamber until it is stopped by hydraulic lock will be small, so the time from when resistance begins to be applied to the free piston 4 until it is stopped by hydraulic lock and the displacement of the free piston 4 will be short, making tuning of the transient characteristics difficult. However, as described above, since the extension side pressure chamber 5 itself or the compression side pressure chamber 6 itself functions as the hydraulic lock chamber, a flow rate sufficient for tuning the transient characteristics can be ensured.

[0075] Therefore, according to the shock absorber D1 of the embodiment, it is possible to easily tune the transient characteristics when the damping force changes while mitigating a sudden change in the damping force, and to ensure the stroke length of the free piston.

[0076] Moreover, the shock absorber D1 of one embodiment includes a housing H1 that accommodates a free piston 4 therein to form a pressure chamber R3. The housing H1 includes a cylindrical portion 21d, a first lid portion C1 that closes one end of an opening of the cylindrical portion 21d, a second lid portion C2 that closes the other end of the opening of the cylindrical portion 21d, a first convex portion p1 that protrudes inward from the first lid portion C1, a second convex portion p2 that protrudes inward from the second lid portion C2, an expansion-side suction passage 22 that opens from an outer periphery of the first convex portion p1 and communicates with the expansion-side chamber R1, and a compression-side suction passage 23 that opens from an outer periphery of the second convex portion p2 and communicates with the compression-side chamber R2. The expansion-side passage 8 opens at a tip of the first convex portion p1 and communicates with the expansion-side pressure chamber 5. The compression-side passage 9 opens at a tip of the second convex portion p2 and communicates with the compression-side pressure chamber R2. 6, the expansion-side check valve 10 is provided in the expansion-side suction passage 22, and the compression-side check valve 11 is provided in the compression-side suction passage 23. The free piston 4 is accommodated in the cylindrical portion 21d to divide the inside of the housing H1 into an expansion-side pressure chamber 5 and a compression-side pressure chamber 6, and has a cylindrical first case 4b provided on the expansion-side pressure chamber 5 side to allow insertion of the first convex portion p1 and a cylindrical second case 4c provided on the compression-side pressure chamber 6 side to allow insertion of the second convex portion p2. The flow path area between the first case 4b and the first convex portion p1 is reduced in accordance with the degree of penetration of the first convex portion p1 into the first case 4b, and the flow path area between the second case 4c and the second convex portion p2 is reduced in accordance with the degree of penetration of the second convex portion p2 into the second case 4c.

[0077] In the shock absorber D1 configured in this manner, the flow path area between the expansion-side pressure chamber 5 and the expansion-side passage 8 is reduced depending on the degree of penetration of the first convex portion p1 into the first case 4b, and the flow path area between the compression-side pressure chamber 6 and the compression-side passage 9 is reduced depending on the degree of penetration of the second convex portion p2 into the second case 4c. Therefore, a sufficient flow rate of liquid can be flowed into the expansion-side chamber R1 or the compression-side chamber R2 while gradually restricting the degree of communication between the expansion-side pressure chamber 5 and the expansion-side passage 8 or the degree of communication between the compression-side pressure chamber 6 and the compression-side passage 9. In addition, the timing and transient characteristics of the transition from a low damping force to a high damping force can be easily tuned by setting the inner peripheral shape of the first case 4b, the outer peripheral shape of the first convex portion p1, and the axial length of the first case 4b and the first convex portion p1, the inner peripheral shape of the second case 4c, the outer peripheral shape of the second convex portion p2, and the axial length of the second case 4c and the second convex portion p2.

[0078] Furthermore, in one embodiment of the shock absorber D1, the expansion side check valve 10 has an annular O-ring (valve body) that is elastic and is fitted into an annular groove 21b2 provided on the outer periphery of the first convex portion p1 to open and close the opening end of the expansion side suction passage 22, and the compression side check valve 11 has an annular O-ring (valve body) that is elastic and is fitted into annular groove 21e3 provided on the outer periphery of the second convex portion p2 to open and close the opening end of the compression side suction passage 23. Thus, in one embodiment of the shock absorber D1, the extension side check valve 10 is an elastic annular valve body mounted in the annular groove 21b2 on the outer periphery of the first convex portion p1, and the compression side check valve 11 is an elastic annular valve body mounted in the annular groove 21e3 provided on the outer periphery of the second convex portion p2. Therefore, even if the extension side check valve 10 and the compression side check valve 11 are provided in the housing H1, they do not interfere with the movement of the free piston 4, and the stroke length of the free piston 4 can be secured while avoiding an increase in the size of the housing H1.

[0079] In the above-mentioned shock absorber D1, the housing H1 is provided on the compression side chamber R2 side of the piston 2, but it is also possible to adopt a structure in which the housing H1 is provided on the extension side chamber R1 side of the piston 2 of the piston rod 3 and the free piston 4 and the spring element 7 are housed within the housing H1.

[0080] Next, a shock absorber D2 in a first modified example of the embodiment will be described. In the shock absorber D1 in the embodiment, the housing H1 is formed by the piston 2, the expansion-side main valve 16, and the piston nut 21 that fixes the compression-side main valve 17 to the piston rod 3, and is installed in the compression-side chamber R2, but in the shock absorber D2 in the first modified example, as shown in Fig. 3, the piston rod 3 is used as the housing H2 and is installed in the expansion-side chamber R1. Below, the parts in which the configuration of the shock absorber D2 differs from the configuration of the shock absorber D1 will be described in detail, and the detailed description of the parts in which the configuration of the shock absorber D2 and the shock absorber D1 are the same will be omitted because they will be explained repeatedly.

[0081] The shock absorber D2 has a pressure chamber R3 in the piston rod 3, and therefore the structure of the piston rod 3 is different from that of the shock absorber D1. As shown in Fig. 3, the piston rod 3 in the shock absorber D2 includes a piston rod body 31, a piston holder 32 to which the piston 2, the extension-side main valve 16, and the compression-side main valve 17 are attached, and a housing portion 33 that connects the piston rod body 31 and the piston holder 32 and in which the pressure chamber R3 is formed. A free piston 40 and an extension-side coil spring 47a and a compression-side coil spring 47b serving as a spring element 47 for positioning the free piston 40 at a neutral position in the housing H2 are accommodated in a housing H2 provided in the piston rod 3, and the housing portion 33 is partitioned into an extension-side pressure chamber 41 and a compression-side pressure chamber 42.

[0082] Although not shown in Fig. 3, the piston rod main body 31 protrudes outward from the cylinder 1 through the inner periphery of a rod guide provided at the upper end of the cylinder 1, and has a threaded portion 31a on the outer periphery of the lower end. As shown in Fig. 3, the piston holder 32 has a piston retaining shaft 32a, a disk portion 32b provided at the upper end of the piston retaining shaft 32a in Fig. 3, a cylindrical socket 32c rising from the outer periphery of the disk portion 32b, a protrusion 32d rising from the upper end of the disk portion 32b in Fig. 3, and a vertical hole 32e that opens from the tip of the piston retaining shaft 32a, which is the lower end in Fig. 3, and leads to the upper end of the protrusion 32d in Fig. 3.

[0083] The piston retaining shaft 32a has a threaded portion 32a1 on the outer periphery of the tip, which is the lower end in Fig. 3. The valve stopper 18, the compression side main valve 17, the piston 2, and the extension side main valve 16 are assembled in this order to the outer periphery of the piston retaining shaft 32a. The valve stopper 18, the compression side main valve 17, the piston 2, and the extension side main valve 16 are fixed to the piston retaining shaft 32a by the piston nut 30, which is screwed to the threaded portion 32a1, and the disk portion 32b.

[0084] The disk portion 32b has a flange 32b1 on its outer periphery and functions as the first cover portion C3 of the housing H2. The socket 32c rises from the outer periphery of the disk portion 32b on the side opposite to the piston retaining shaft. A screw groove 32f is provided from the middle of the socket 32c in FIG. 3 to the outer periphery of the disk portion 32b and the flange 32b1.

[0085] The projection 32d rises from the axial center of the disk portion 32b toward the side opposite the piston retaining shaft, and includes an annular groove 32d1 provided in the middle portion of the outer periphery in the axial direction, and a hole 32d2 that opens from the bottom of the annular groove 32d1 and communicates with the vertical hole 32e. In addition, a groove 32d3 is provided along the vertical direction in Fig. 3 on the outer periphery of the projection 32d on the side opposite the piston retaining shaft from the annular groove 32d1. The projection 32d forms a first protrusion p3 that protrudes from the disk portion 32b as the first lid portion C3 toward the inside of the pressure chamber R3.

[0086] In addition, the vertical hole 32e provided in the piston holder 32 functions as a compression side passage 34 that connects the compression side pressure chamber 42 to the compression side chamber R2, and the hole 32d2 provided in the protrusion 32d is connected to the compression side chamber R2 through the vertical hole 32e, and together with the vertical hole 32e, forms a compression side suction passage 35 that connects the compression side chamber R2 and the compression side pressure chamber 42.

[0087] Further, an annular compression side check valve 36 is attached to the annular groove 32d1 of the projection 32d. The compression side check valve 36 is elastically attached to the outer periphery of the first protruding portion p3 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the compression side suction passage 35. When the compression side check valve 36 receives pressure from the compression side suction passage 35 side and expands in diameter, it moves away from the opening of the compression side suction passage 35 to communicate the inside of the housing H2 with the compression side chamber R2 via the compression side suction passage 35, and when the pressure in the housing H2 is higher than the pressure in the compression side chamber R2, it comes into close contact with the opening of the compression side suction passage 35 to block the compression side suction passage 35. Note that the compression side check valve 36 may be an O-ring or a C-ring made of rubber, synthetic resin, or metal, as long as it has elasticity and can open and close the compression side suction passage 35.

[0088] As shown in FIG. 3, the housing portion 33 is provided with a nut portion 33a that is cylindrical and has a flange portion 33c on its outer periphery and is screw-connected to the screw portion 31a of the piston rod body 31, and a tube portion 33d that is screw-connected to a screw groove 32f provided on the outer periphery of the disk portion 32b and the socket 32c in the piston holder 32.

[0089] The upper end of the housing portion 33 in Figure 3 is closed by screwing the nut portion 33a to the screw portion 31a of the piston rod body 31, and the second lid portion C4 of the housing H2 is formed by the nut portion 33a and the lower end in Figure 3, which is the tip of the piston rod body 31.

[0090] The nut portion 33a includes a tubular nut body 33b having a screw groove on its inner circumference, and a flange portion 33c protruding radially from the outer circumference of the lower end of the nut body 33b in FIG. 3, and is screwed to the screw portion 31a of the piston rod body 31 to be connected to the piston rod body 31. As shown in FIG. 3, the tubular portion 33d of the housing portion 33 has a thick wall thickness and a small inner diameter at the upper end side, and includes an annular groove 33d1 provided along the circumferential direction in the portion with the small inner diameter, an extension-side suction passage 37 that opens from the bottom of the annular groove 33d1 and penetrates the wall thickness, and an extension-side passage 38 that penetrates the wall thickness below the annular groove 33d1 in FIG. 3. In addition, a step portion 33d2 is formed on the inner circumference by making the inner diameter of the upper side of the tubular portion 33d small.

[0091] A screw thread 33d3 is provided on the inner periphery of the lower end of the cylindrical portion 33d of the housing portion 33, and the screw thread 33d3 is screwed into the screw groove 32f of the piston holder 32 to connect the housing portion 33 to the piston holder 32. When the piston rod body 31 and the housing portion 33 are screwed together in this manner and the housing portion 33 is screwed together with the piston holder 32, the piston rod 3 is formed and a pressure chamber R3 is formed in the housing portion 33. In this manner, the housing H2 is formed by connecting the piston rod body 31, the piston holder 32 and the housing portion 33.

[0092] An annular extension-side check valve 39 is mounted in the annular groove 33d1 provided on the inner circumference of the cylindrical portion 33d. The extension-side check valve 39 is elastically mounted in the annular groove 33d1 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the extension-side suction passage 37. When the extension-side check valve 39 receives pressure from the extension-side suction passage 37 side and contracts in diameter, it moves away from the opening of the extension-side suction passage 37 to communicate the inside of the housing H2 with the extension-side chamber R1 via the extension-side suction passage 37, and when the pressure in the housing H2 is higher than the pressure in the extension-side chamber R1, it comes into close contact with the opening of the extension-side suction passage 37 to block the extension-side suction passage 37. Note that the extension-side check valve 39 may be a C-ring made of rubber, synthetic resin, or metal, in addition to an O-ring, as long as it has elasticity and can open and close the extension-side suction passage 37.

[0093] As shown in FIG. 3, the free piston 40 is in sliding contact with the inner periphery of the cylindrical portion 33d of the housing portion 33 of the piston rod 3 that forms the housing H2, and can move in the vertical direction in FIG. 3 relative to the housing portion 33. The free piston 40 divides the pressure chamber R3 into an expansion-side pressure chamber 41 that is connected to the expansion-side chamber R1 by the expansion-side passage 38, and a compression-side pressure chamber 42 that is connected to the compression-side chamber R2 by the compression-side passage 34.

[0094] Specifically, the free piston 40 includes a partition portion 40a whose outer periphery is in sliding contact with the inner periphery of the cylindrical portion 33d, a cylindrical shutter 40b rising from the upper end of the partition portion 40a in FIG. 3 which is the extension side pressure chamber side, and a cylindrical case 40c rising from the lower end of the partition portion 40a in FIG. 3 which is the compression side pressure chamber side.

[0095] The partition 40a includes a disk-shaped partition body 40a1, an annular groove 40a2 provided on the outer periphery of the partition body 40a1, and a seal ring 40a3 housed in the annular groove 40a2 and in sliding contact with the inner periphery of the cylindrical portion 33d. Since the partition 40a includes the seal ring 40a3, the gap between the partition 40a and the cylindrical portion 33d is sealed, and the expansion-side pressure chamber 41 and the compression-side pressure chamber 42 defined in the housing H2 are prevented from communicating with each other through the gap between the free piston 40 and the cylindrical portion 33d.

[0096] The case 40c is cylindrical and protrudes downward from the lower end of the partition body 40a1 in FIG. 3, allowing the first protrusion p3 to be inserted inward. Therefore, when the free piston 40 moves downward in FIG. 3 in the direction compressing the compression side pressure chamber 42, the first protrusion p3 can enter the case 40c, and the free piston 40 can move downward until the lower end of the partition part 40a in FIG. 3 abuts against the first protrusion p3. In this way, when the free piston 40 moves in the direction compressing the compression side pressure chamber 42 and the first protrusion p3 is inserted into the case 40c, the flow passage area between the compression side pressure chamber 42 and the compression side passage 34 is almost limited to the cross-sectional area of ​​the groove 32d3 on the outer periphery of the protrusion 32d. 3, the inner diameter of the case 40c at the lower end becomes larger toward the lower end, so that even if the partition body 40a1 of the free piston 40 is displaced until it abuts against the upper end of the projection 32d, the case 40c does not interfere with the compression-side check valve 36 attached to the outer periphery of the first protrusion p3, and does not affect the operation of the compression-side check valve 36. In addition, although the groove 32d3 is provided on the outer periphery of the projection 32d in this embodiment, a groove may be provided on the inner periphery of the case 40c. Furthermore, a notch 32d4 communicating with the vertical hole 32e may be provided at the upper end of the projection 32d so that the compression-side pressure chamber 42 and the compression-side passage 34 can be communicated with each other to allow the free piston 40 to move upward quickly even if the partition body 40a1 of the free piston 40 is displaced until it abuts against the upper end of the projection 32d.

[0097] The shutter 40b is cylindrical and rises from the outer periphery of the upper end of the partition body 40a1 in FIG. 3, and can be inserted into the inner periphery of the small-diameter part of the cylinder part 33d. A groove 40b1 is provided on the outer periphery of the shutter 40b along the vertical direction in FIG. 3, which is the axial direction. Therefore, when the free piston 40 moves upward in FIG. 3, which is the direction in which the expansion-side pressure chamber 41 is compressed, the shutter 40b reaches the small-diameter part of the cylinder part 33d and faces the opening of the expansion-side passage 38, gradually blocking the opening, and when it completely faces the opening, the flow passage area between the expansion-side pressure chamber 41 and the expansion-side passage 38 is almost limited to the cross-sectional area of ​​the groove 40b1 on the outer periphery of the shutter 40b. 3, the outer diameter of the upper end of the shutter 40b is reduced toward the upper end, and even if the partition wall main body 40a1 of the free piston 40 is displaced until it abuts against the step portion 33d2 provided on the inner circumference of the cylindrical portion 33d, the shutter 40b does not interfere with the extension-side check valve 39 attached to the inner circumference of the cylindrical portion 33d, and does not affect the operation of the extension-side check valve 39. In addition, in this embodiment, the groove 40b1 is provided on the outer circumference of the shutter 40b, but the groove may be provided on the inner circumference of the cylindrical portion 33d, which is a portion with a smaller inner diameter above the step portion 33d2. In this way, since the groove 40b1 is provided on the outer circumference of the shutter 40b of the free piston 40, even if the case 40c closes the opening of the extension-side passage 38, the space between the partition wall main body 40a1 and the step portion 33d2 of the cylindrical portion 33d is communicated with the groove 40b1 to the extension-side pressure chamber 41, so that the free piston 40 can move quickly when moving downward.

[0098] The free piston 40 is sandwiched between an extension-side coil spring 47a, which is interposed between the inner circumferential side of the shutter 40b of the partition wall portion 40a and the flange portion 33c of the nut portion 33a and housed in the extension-side pressure chamber 41, and a compression-side coil spring 47b, which is interposed between the outer circumferential side of the case 40c of the partition wall portion 40a and the outer circumferential side of the protrusion 32d of the disk portion 32b of the piston holder 32 and housed in the compression-side pressure chamber 42. The extension-side coil spring 47a and the compression-side coil spring 47b sandwich the free piston 40 in a compressed state, and the free piston 40 sandwiched between the extension-side coil spring 47a and the compression-side coil spring 47b is positioned at a neutral position in the pressure chamber R3. In this embodiment, the neutral position is set at a position corresponding to the stroke center of the free piston 40 in the pressure chamber R3, but the neutral position does not necessarily have to coincide with the stroke center of the free piston 40.

[0099] In addition, the extension-side coil spring 47a is inserted into the inner periphery of the shutter 40b of the free piston 40, and no eccentricity occurs with respect to the free piston 40 when it expands or contracts, so that a stable biasing force can be applied to the free piston 40. The compression-side coil spring 47b is fitted into the outer periphery of the case 40c of the free piston 40, and no eccentricity occurs with respect to the free piston 40 when it expands or contracts, so that a stable biasing force can be applied to the free piston 40.

[0100] Note that the spring element 47 only needs to position the free piston 40 in the neutral position and exert a biasing force in a direction in which the free piston 40 returns to the neutral position when displaced from the neutral position, and therefore may be formed of one spring connected to both the housing H2 and the free piston 40. Furthermore, the spring constituting the spring element 47 may be an elastic body such as a wave washer, a leaf spring, a disc spring, rubber, etc., other than a coil spring.

[0101] The shock absorber D2 is configured as described above, and can operate in the same manner as the shock absorber D1 while the free piston 40 does not reach the stroke end, generating a high damping force for the input of low-frequency vibration and a low damping force for the input of high-frequency vibration. Thus, like the shock absorber D1, the shock absorber D2 generates a high damping force for the input of vibration in a low sprung resonance frequency band, stabilizing the posture of the vehicle and preventing the passenger from feeling uneasy when the vehicle turns, and generates a low damping force whenever vibration in a high unsprung resonance frequency band is input, insulating the transmission of vibration on the axle side to the vehicle body side, and improving the ride comfort of the vehicle. The frequency at which the damping force in the shock absorber D2 decreases can be tuned by setting the resistance that the expansion-side passage 38 and the compression-side passage 34 provide to the flow of liquid and the spring constant of the spring element 47. In addition, when the resistance to the liquid flow provided by the expansion-side passage 38 and the compression-side passage 34 is minimized, the shock absorber D2 also operates in the same manner as the shock absorber D1, and changes the damping force in response to the amplitude of the input vibration, not the frequency of the input vibration. In response to the input of a small amplitude vibration, a low damping force is generated to insulate the transmission of the vibration on the axle side to the vehicle body, and in response to the input of a large amplitude vibration, a high damping force is generated to suppress the vibration of the vehicle body, thereby improving the ride comfort of the vehicle.

[0102] Next, the hydraulic lock function of the shock absorber D2 will be described. When the stroke amount of the shock absorber D2 toward the extension side is large, the free piston 40 moves from the neutral position toward the direction of compressing the compression side pressure chamber 42 to a large amount. When the free piston 40 moves from the neutral position toward the direction of compressing the compression side pressure chamber 42, the first protrusion p3 enters the case 40c from outside the case 40c. When the first protrusion p3 is outside the case 40c, there is a sufficiently large gap between the protrusion 32d and the case 40c, and the flow path is not restricted, so that the liquid can move between the compression side pressure chamber 42 and the compression side passage 34 without much resistance. However, when the first protrusion p3 enters the case 40c, the flow path area between the first protrusion p3 and the case 40c is reduced to the cross-sectional area of ​​the groove 32d3. Therefore, it becomes difficult for the liquid in the compression side pressure chamber 42 to move to the compression side chamber R2 through the compression side passage 34, and the pressure in the compression side pressure chamber 42 increases, suppressing the movement of the free piston 40 in the direction compressing the compression side pressure chamber 42. In addition, during the extension operation of the shock absorber D2, the pressure in the compression side pressure chamber 42 becomes higher than the pressure in the compression side chamber R2, so that the compression side check valve 36 attached to the outer periphery of the first protrusion p3 blocks the compression side suction passage 35.

[0103] In this way, when the free piston 40 moves from the neutral position in the direction compressing the compression-side pressure chamber 42 to the vicinity of the stroke end, the first convex portion p3 enters the case 40c, the pressure in the compression-side pressure chamber 42 increases, and the movement of the free piston 40 in the direction compressing the compression-side pressure chamber 42 is suppressed. Therefore, in the shock absorber D2 of this embodiment, when the free piston 40 moves from the neutral position in the direction compressing the compression-side pressure chamber 42 to the vicinity of the stroke end, the degree of communication between the compression-side pressure chamber 42 and the compression-side passage 34 is reduced to increase the pressure in the compression-side pressure chamber 42, and the compression-side pressure chamber 42 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 40 in the direction compressing the compression-side pressure chamber 42.

[0104] In addition, after the free piston 40 increases the pressure in the compression-side pressure chamber 42 to exert the hydraulic lock function, when the direction of extension and contraction of the shock absorber D2 changes from the extension operation to the contraction operation, the free piston 40 tries to move upward in FIG. 3 in the direction of compressing the expansion-side pressure chamber 41. At that time, liquid is supplied from the compression-side chamber R2 through the compression-side passage 34 to the space between the case 40c and the first protruding portion p3 of the free piston 40. Furthermore, the compression-side check valve 36 receives the pressure of the compression-side chamber R2 and expands in diameter to open, thereby opening the compression-side suction passage 35, so that liquid is quickly supplied from the compression-side chamber R2 through the compression-side suction passage 35 to the inside of the compression-side pressure chamber 42, in which communication with the compression-side passage 34 is restricted. In this way, even if the free piston 40 is displaced to the vicinity of the stroke end to reduce the degree of communication between the compression-side passage 34 and the compression-side pressure chamber 42, when the shock absorber D2 changes from extension to contraction, liquid is supplied from the compression-side chamber R2 to the space between the case 40c and the first convex portion p3 and to the compression-side pressure chamber 42, respectively, and no excessive pressure drop is caused. Therefore, the free piston 40 can smoothly move in the direction of compressing the expansion-side pressure chamber 41 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D2 is not impaired.

[0105] As described above, when the free piston 40 is displaced in the housing H2 in the direction compressing the compression-side pressure chamber 42 to the vicinity of the stroke end during the extension operation of the shock absorber D2, the hydraulic lock function is exerted to suppress the movement of the free piston 40 toward the compression-side stroke end, gradually reducing the moving speed of the free piston 40 and stopping the free piston 40 at the stroke end. When the free piston 40 stops, the entire flow rate of the liquid moving from the expansion-side chamber R1 to the compression-side chamber R2 passes through the expansion-side main valve 16, so that the damping force generated by the shock absorber D2 becomes high. Therefore, if the shock absorber D2 generates a low damping force before the stop of the free piston 40, the damping force generated by the stop of the free piston 40 becomes high, but the speed of the free piston 40 is gradually reduced by the hydraulic lock, so that the sudden change in the damping force is mitigated.

[0106] In addition, when the stroke amount toward the contraction side of the shock absorber D2 is large, the free piston 40 moves from the neutral position toward the direction compressing the expansion-side pressure chamber 41. When the free piston 40 moves from the neutral position toward the direction compressing the expansion-side pressure chamber 41, the shutter 40b faces the opening of the expansion-side passage 38 provided in the cylindrical portion 33d of the housing portion 33, and the opening is gradually blocked as the movement amount of the free piston 40 increases, and the degree of communication between the expansion-side passage 38 and the expansion-side pressure chamber 41 gradually decreases. Then, when the shutter 40b of the free piston 40 completely faces the opening of the expansion-side passage 38, the flow path area between the shutter 40b and the cylindrical portion 33d is limited to the cross-sectional area of ​​the groove 40c1.

[0107] Therefore, as the free piston 40 moves from the neutral position in the direction compressing the expansion-side pressure chamber 41, the liquid in the expansion-side pressure chamber 41 gradually becomes less able to move to the expansion-side chamber R1 through the expansion-side passage 38, and the liquid in the expansion-side pressure chamber 41 becomes less able to move to the expansion-side chamber R1, so that the pressure in the expansion-side pressure chamber 41 increases and the movement of the free piston 40 in the direction compressing the expansion-side pressure chamber 41 is suppressed. In addition, when the shock absorber D2 is contracting, the pressure in the expansion-side pressure chamber 41 becomes higher than the pressure in the expansion-side chamber R1, so the expansion-side check valve 39 closes the expansion-side suction passage 37.

[0108] Therefore, when the free piston 40 moves from the neutral position in the direction compressing the expansion-side pressure chamber 41 to the vicinity of the stroke end, the liquid in the expansion-side pressure chamber 41 becomes less likely to move to the expansion-side chamber R1 as the movement of the free piston 40 progresses, and the pressure in the expansion-side pressure chamber 41 increases, suppressing the movement of the free piston 40 in the direction compressing the expansion-side pressure chamber 41. In this way, in the shock absorber D2 of this embodiment, when the free piston 40 moves from the neutral position in the direction compressing the expansion-side pressure chamber 41 to the vicinity of the stroke end, the degree of communication between the expansion-side pressure chamber 41 and the expansion-side passage 38 is reduced, the pressure in the expansion-side pressure chamber 41 is increased, and the expansion-side pressure chamber 41 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 40 in the direction compressing the expansion-side pressure chamber 41.

[0109] In addition, after the free piston 40 increases the pressure in the expansion-side pressure chamber 41 to perform the hydraulic lock function, when the direction of extension and contraction of the shock absorber D2 changes from contraction to expansion, the free piston 40 tries to move downward in FIG. 3 in the direction of compressing the compression-side pressure chamber 42. At that time, the expansion-side check valve 39 receives the pressure of the expansion-side chamber R1 and contracts to open, opening the expansion-side suction passage 37, so that liquid is quickly supplied from the expansion-side chamber R1 through the expansion-side suction passage 37 into the expansion-side pressure chamber 41, whose communication with the expansion-side passage 38 is restricted. In addition, liquid is supplied from the expansion-side pressure chamber 41 through the groove 40c1 to the space between the outer circumferential side of the shutter 40b of the partition wall portion 40a of the free piston 40 and the step portion 33d2 of the cylindrical portion 33d. In this way, even if the free piston 40 is displaced to the vicinity of the stroke end to reduce the degree of communication between the expansion-side passage 38 and the expansion-side pressure chamber 41, when the shock absorber D2 changes from contraction to extension, liquid is supplied from the expansion-side chamber R1 to the expansion-side pressure chamber 41, which does not result in an excessive pressure drop. Therefore, the free piston 40 can smoothly move in the direction of compressing the compression-side pressure chamber 42 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D2 is not impaired.

[0110] As described above, when the free piston 40 is displaced in the housing H2 in the direction compressing the expansion-side pressure chamber 41 to the vicinity of the stroke end during the contraction operation of the shock absorber D2, the hydraulic lock function is exerted to suppress the movement of the free piston 40 toward the expansion-side stroke end, and the moving speed of the free piston 40 is gradually reduced to stop the free piston 40 at the stroke end. When the free piston 40 stops, the liquid cannot pass through the apparent passage, and the entire flow rate of the liquid from the compression-side chamber R2 to the expansion-side chamber R1 passes through the compression-side main valve 17, so that the damping force generated by the shock absorber D2 becomes high. Therefore, if the shock absorber D2 generates a low damping force before the stop of the free piston 40, the damping force generated by the stop of the free piston 40 becomes high, but the free piston 40 gradually reduces its speed due to the hydraulic lock, so that the sudden change in the damping force is mitigated.

[0111] As described above, the shock absorber D2 in the first modified example of the embodiment includes a housing H2 that accommodates the free piston 40 therein to form a pressure chamber R3. The housing H2 includes a cylindrical portion 33d, a first lid portion C3 that closes one end of an opening of the cylindrical portion 33d, a second lid portion C4 that closes the other end of the opening of the cylindrical portion 33d, a first convex portion p3 that protrudes inward from the first lid portion C3, an expansion-side suction passage 37 that opens from the outer periphery of the cylindrical portion 33d and communicates with the expansion-side chamber R1, and a compression-side suction passage 35 that opens from the outer periphery of the first convex portion p3 and communicates with the compression-side chamber R2. The expansion-side passage 38 passes through the cylindrical portion 33d. The housing H2 is connected to an expansion-side pressure chamber 41 through the expansion-side passage 37, the compression-side passage 34 opens at the tip of the first convex portion p3 and communicates with a compression-side pressure chamber 42, the expansion-side check valve 39 is provided in the expansion-side suction passage 37, and the compression-side check valve 36 is provided in the compression-side suction passage 35. The free piston 40 is accommodated in the cylindrical portion 33d and divides the inside of the housing H2 into an expansion-side pressure chamber 41 and a compression-side pressure chamber 42. The free piston 40 has a shutter 40b provided on the expansion-side pressure chamber 41 side and capable of facing the opening of the expansion-side passage 38, and a cylindrical case 40c provided on the compression-side pressure chamber 42 side and allowing the insertion of the first convex portion p3.

[0112] In the shock absorber D2 in the first modified example of the embodiment, the movement of the free piston 40 to the stroke end causes the expansion-side pressure chamber 41 itself or the compression-side pressure chamber 42 itself to function as a hydraulic lock chamber, so that a sudden change in the damping force can be mitigated, and a cushion does not need to be provided in the pressure chamber R3, and the stroke length of the free piston 40 can be secured. In addition, since the shock absorber D2 does not need to provide a cushion, the volumes in the expansion-side pressure chamber 41 and the compression-side pressure chamber 42 can be secured large, and the liquid in the expansion-side pressure chamber 41 and the compression-side pressure chamber 42 can be used during hydraulic lock. Therefore, in the shock absorber D2, a sufficient flow rate of liquid can be flowed from the expansion-side pressure chamber 41 or the compression-side pressure chamber 42 to the expansion-side chamber R1 or the compression-side chamber R2 until the hydraulic lock function is exerted, and it is also easy to tune the transient characteristics that transition from a state in which a low damping force is generated by reducing the damping force to a state in which a high damping force is generated by the expansion-side main valve 16 or the compression-side main valve 17. Therefore, according to the shock absorber D2 of the first modified example of one embodiment, like the shock absorber D1, it is possible to mitigate sudden changes in the damping force while easily tuning the transient characteristics when the damping force changes and ensuring the stroke length of the free piston.

[0113] In the shock absorber D2, the passage area between the compression-side pressure chamber 42 and the compression-side passage 34 is reduced by the intrusion of the first protrusion p1 into the case 40c, and the passage area between the expansion-side pressure chamber 41 and the expansion-side passage 38 is reduced by facing the shutter 40b to the expansion-side passage 38. Therefore, a sufficient flow rate of liquid can be flowed into the expansion-side chamber R1 or the compression-side chamber R2 while gradually restricting the degree of communication between the expansion-side pressure chamber 41 and the expansion-side passage 38 or the degree of communication between the compression-side pressure chamber 42 and the compression-side passage 34.

[0114] Furthermore, the timing of transition from low damping force to high damping force and the transient characteristics can be easily tuned by setting the area of ​​the opening of the groove 40b1 of the shutter 40b and the extension-side passage 38, the number of grooves 40b1, the inner peripheral shape of the case 40c and the outer peripheral shape of the first protrusion p3, the cross-sectional area of ​​the groove 32d3 of the protrusion 32d, and the number of grooves 32d3. Also, if the cross-sectional area of ​​the groove 40b1 is set to be smaller from the tip side to the base end side of the shutter 40b, the flow path area between the cylindrical portion 33d and the shutter 40b can be reduced as the free piston 40 moves in the direction of compressing the extension-side pressure chamber 41 after starting to block the opening of the extension-side passage 38, and the transient characteristics can also be tuned by the shape of the groove 40b1. Similarly, by setting the cross-sectional area of ​​groove 32d3 to become smaller toward the base end from the tip end of protrusion 32d, the flow path area between protrusion 32d and case 40c can be made to decrease the more the free piston 40 moves in the direction of compressing the compression side pressure chamber 42 after it begins to block the opening of the compression side passage 34, and the transient characteristics can also be tuned by the shape of groove 32d3.

[0115] In addition, in the shock absorber D2 in the first modified example of one embodiment, only the first convex portion p3 arranged in the compression-side pressure chamber 42 protrudes into the housing H2. By providing the extension-side passage 38 in the cylindrical portion 33d, the extension-side pressure chamber 41 can function as a hydraulic lock chamber without providing a convex portion that reduces the volume of the pressure chamber R3 in the extension-side pressure chamber 41. This makes it easier to ensure the volume in the pressure chamber R3, thereby shortening the overall length of the housing H2 and making it easier to ensure the stroke length of the shock absorber D2 even when the pressure chamber R3 is provided.

[0116] Furthermore, in the shock absorber D2 in the first modified example of one embodiment, the expansion side check valve 39 has an annular O-ring (valve body) that is elastic and is fitted into an annular groove 33d1 provided on the inner circumference of the tubular portion 33d to open and close the opening end of the expansion side suction passage 37, and the compression side check valve 36 has an annular valve body (O-ring) that is elastic and is fitted into annular groove 32d1 provided on the outer circumference of the first convex portion p3 to open and close the opening end of the compression side suction passage 35. Thus, in the shock absorber D2 in the first modified example of one embodiment, the extension side check valve 39 is an elastic annular valve body mounted in the annular groove 33d1 on the inner circumference of the tubular portion 33d that forms the housing H2, and the compression side check valve 36 is an elastic annular valve body mounted in the annular groove 32d1 on the outer circumference of the first convex portion p3. Therefore, even if the extension side check valve 39 and the compression side check valve 36 are provided in the housing H2, they do not interfere with the movement of the free piston 40, and the stroke length of the free piston 40 can be secured while avoiding an increase in the size of the housing H2.

[0117] Also, as in the shock absorber D3 of the second modified example of the embodiment shown in Fig. 4, a housing H3 may be applied instead of the housing H1 of the shock absorber D1. The housing H3 has a configuration substantially similar to that of the housing H2 in the shock absorber D2, and the configuration of the free piston 40 is turned upside down and installed in the expansion-side chamber R1. Below, the differences in the configuration of the shock absorber D3 from the configurations of the shock absorbers D1 and D2 will be described in detail, and detailed descriptions of the same configurations as those of the shock absorbers D1 and D2 will be omitted to avoid duplication.

[0118] 4, in the shock absorber D3, the piston 2, the extension-side main valve 16, and the compression-side main valve 17, which are assembled to the outer periphery of the small diameter portion 3a of the piston rod 3, are fixed to the piston rod 3 by a piston nut 51 forming a housing H3 instead of the piston nut 21 of the shock absorber D1. A free piston 60, and an extension-side coil spring 67a and a compression-side coil spring 67b serving as a spring element 67 for positioning the free piston 60 at a neutral position within the housing H3 are accommodated within the housing H3, and the inside of the housing H3 is partitioned into an extension-side pressure chamber 61 and a compression-side pressure chamber 62.

[0119] As shown in Figure 4, the piston nut 51 is cylindrical and has a nut portion 51a having a flange portion 51c on its outer periphery and screwed to the screw portion 3b of the piston rod 3, and a bottomed cylindrical portion 51d having a bottom 51e and attached to the outer periphery of the flange portion 51c. The piston nut 51 is attached to the tip of the piston rod 3 to form a pressure chamber R3.

[0120] 4 of the cylindrical portion 51d of the piston nut 51 is closed by screwing the nut portion 51a to the screw portion 3b of the piston rod 3, and a first lid portion C5 of the housing H3 is formed by the nut portion 51a and the lower end in FIG. 4 which is the tip of the piston rod 3. Further, a lower end of the cylindrical portion 51d is closed by a bottom portion 51e, and a second lid portion C6 of the housing H3 is formed by the bottom portion 51e.

[0121] The piston nut 51 constituting a part of the housing H3 will be described in detail below. The nut part 51a includes a cylindrical nut body 51b having a screw groove on the inner circumference, and a flange part 51c that protrudes radially from an axially intermediate part on the outer circumference of the nut body 51b toward the outer circumference side, and is screwed to the screw part 3b of the piston rod 3 and fixed to the small diameter part 3a of the piston rod 3. The nut body 51b also includes an annular groove 51b1 provided along the circumferential direction on the outer circumference of the base end, a hole 51b2 that opens from the bottom of the annular groove 51b1 and extends radially, and a groove 51b3 formed on the outer circumference from the tip to the annular groove 51b1.

[0122] The nut portion 51a configured as described above is inserted into the cylindrical portion 51d, and the upper open end of the cylindrical portion 51d is crimped from the outer periphery to grip the outer periphery of the flange portion 51c with the cylindrical portion 51d, thereby integrating the nut portion 51a and the cylindrical portion 51d. When the nut body 51b is screwed to the tip of the piston rod 3, a first protrusion p4 protruding inwardly of the housing H3 is formed by a portion of the nut body 51b below the flange portion 51c in FIG. 4 and a portion of the piston rod 3 screwed to the nut body 51b.

[0123] The inside of the housing H3 is connected to the extension-side chamber R1 by a vertical hole 3d opening from the tip of the piston rod 3 and a horizontal hole 3e opening from the side of the piston rod 3, and the vertical hole 3d and the horizontal hole 3e form an extension-side passage 8. Furthermore, the piston rod 3 is provided with a hole 3f that opens from the outer periphery of the threaded portion 3b and communicates with the vertical hole 3d and also communicates with the hole 51b2 in the nut portion 51a, and the holes 3f and 51b2 form an extension-side suction passage 52.

[0124] In addition, an annular extension-side check valve 53 is mounted in the annular groove 51b1 in the nut body 51b. The extension-side check valve 53 is elastically mounted on the outer periphery of the first protruding portion p4 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the extension-side suction passage 52. When the extension-side check valve 53 receives pressure from the extension-side suction passage 52 side and expands in diameter, it moves away from the opening of the extension-side suction passage 52 to communicate the inside of the housing H3 with the extension-side chamber R1 through the extension-side suction passage 52, and when the pressure in the housing H3 is higher than the pressure in the extension-side chamber R1, it comes into close contact with the opening of the extension-side suction passage 52 to block the extension-side suction passage 52. Note that the extension-side check valve 53 may be a C-ring made of rubber, synthetic resin, or metal, in addition to an O-ring, as long as it has elasticity and can open and close the extension-side suction passage 52.

[0125] As shown in Fig. 4, the cylindrical portion 51d has a thick wall thickness and a small inner diameter at the lower end side, and the small inner diameter portion is provided with an annular groove 51d1 provided along the circumferential direction, a compression side suction passage 54 that opens from the bottom of the annular groove 51d1 and passes through the wall thickness of the cylindrical portion 51d, and a compression side passage 55 that passes through the wall thickness of the cylindrical portion 51d above the annular groove 51d1 in Fig. 4. In addition, by making the inner diameter of the lower side of the cylindrical portion 51d smaller, a step portion 51d2 is formed on the inner circumference.

[0126] An annular compression side check valve 56 is mounted in the annular groove 51d1 provided on the inner circumference of the cylindrical portion 51d. The compression side check valve 56 is elastically mounted in the annular groove 51d1 as described above, and is an O-ring serving as an annular valve body that opens and closes the open end of the compression side suction passage 54. When the compression side check valve 56 receives pressure from the compression side suction passage 54 side and contracts in diameter, it moves away from the opening of the compression side suction passage 54 to communicate the inside of the housing H3 with the compression side chamber R2 via the compression side suction passage 54, and when the pressure in the housing H3 is higher than the pressure in the compression side chamber R2, it comes into close contact with the opening of the compression side suction passage 54 to block the compression side suction passage 54. Note that the compression side check valve 56 may be a C-ring made of rubber, synthetic resin, or metal, in addition to an O-ring, as long as it has elasticity and can open and close the compression side suction passage 54.

[0127] As shown in FIG. 4, the free piston 60 is in sliding contact with the inner periphery of the cylindrical portion 51d of the piston nut 51 that forms the housing H3 and can move in the vertical direction in FIG. 4 relative to the housing H3, and divides the pressure chamber R3 into an expansion-side pressure chamber 61 that is connected to the expansion-side chamber R1 by the expansion-side passage 8 and a compression-side pressure chamber 62 that is connected to the compression-side chamber R2 by the compression-side passage 55.

[0128] Specifically, the free piston 60 includes a partition portion 60a whose outer periphery is in sliding contact with the inner periphery of the cylindrical portion 51d, a cylindrical case 60b rising from the upper end of the partition portion 60a in FIG. 4 which is the extension side pressure chamber side, and a cylindrical shutter 60c rising from the lower end of the partition portion 60a in FIG. 4 which is the compression side pressure chamber side.

[0129] The partition 60a includes a disk-shaped partition main body 60a1, an annular groove 60a2 provided on the outer periphery of the partition main body 60a1, and a seal ring 60a3 housed in the annular groove 60a2 and in sliding contact with the inner periphery of the cylindrical portion 51d. Since the partition 60a includes the seal ring 60a3, the gap between the partition 60a and the cylindrical portion 51d is sealed, and the expansion-side pressure chamber 61 and the compression-side pressure chamber 62 defined in the housing H3 are prevented from communicating with each other through the gap between the free piston 60 and the cylindrical portion 51d.

[0130] The case 60b is cylindrical and protrudes upward from the upper end of the partition body 60a1 in FIG. 2, allowing the insertion of the first protrusion p4. Therefore, when the free piston 60 moves upward in FIG. 2 in the direction compressing the expansion-side pressure chamber 61, the first protrusion p4 can enter the case 60b, and the free piston 60 can move upward until the upper end of the partition part 60a in FIG. 4 abuts against the first protrusion p4. In this way, when the free piston 60 moves in the direction compressing the expansion-side pressure chamber 61 and the first protrusion p4 is inserted into the case 60b, the flow passage area between the expansion-side pressure chamber 61 and the expansion-side passage 8 is almost limited to the cross-sectional area of ​​the groove 51d3 on the outer periphery of the nut body 51b. In addition, the inner diameter of the upper end of the case 60b in FIG. 4 is expanded toward the lower end, so that even if the partition wall body 60a1 of the free piston 60 is displaced until it abuts against the lower end of the nut body 51b, the case 60b does not interfere with the extension-side check valve 53 attached to the outer periphery of the first protrusion p4, and does not affect the operation of the extension-side check valve 53. In addition, although the groove 51d3 is provided on the outer periphery of the nut body 51b in this embodiment, a groove may be provided on the inner periphery of the case 60b. Furthermore, a notch communicating with the vertical hole 3d may be provided at the lower end of the nut body 51b and the lower end of the piston rod 3 so that the extension-side pressure chamber 61 and the extension-side passage 8 can be communicated with each other to allow the free piston 60 to move upward quickly even if the partition wall body 60a1 of the free piston 60 is displaced until it abuts against the upper end of the nut body 51b.

[0131] The shutter 60c is cylindrical and rises from the outer periphery of the lower end of the partition body 60a1 in FIG. 4, and can be inserted into the inner periphery of the small-diameter part of the cylinder part 51d. A groove 60c1 is provided on the outer periphery of the shutter 60c along the vertical direction in FIG. 4, which is the axial direction. Therefore, when the free piston 60 moves downward in FIG. 4, which is the direction in which the compression-side pressure chamber 62 is compressed, the shutter 60c reaches the small-diameter part of the cylinder part 51d and faces the opening of the compression-side passage 55, gradually blocking the opening, and when it completely faces the opening, the flow passage area between the compression-side pressure chamber 62 and the compression-side passage 55 is almost limited to the cross-sectional area of ​​the groove 60c1 on the outer periphery of the shutter 60c.

[0132] 4, the outer diameter of the lower end of the shutter 60c is reduced toward the lower end, and even if the shutter 60c is displaced to face the inner periphery of the compression-side check valve 56 attached to the inner periphery of the cylindrical portion 51d, the shutter 60c does not interfere with the compression-side check valve 56 and does not affect the operation of the compression-side check valve 56. In addition, in this embodiment, the groove 60c1 is provided on the outer periphery of the shutter 60c, but the groove may be provided on the inner periphery of the cylindrical portion 51d, which is a portion with a smaller inner diameter below the step portion 51d2. In this way, since the groove 60c1 is provided on the outer periphery of the shutter 60c of the free piston 60, even if the shutter 60c blocks the opening of the compression-side passage 55, the space between the partition body 60a1 and the step portion 51d2 of the cylindrical portion 51d is communicated with the groove 60c1 to the compression-side pressure chamber 62, so that the free piston 60 can move quickly when moving downward.

[0133] The free piston 60 is sandwiched between an extension-side coil spring 67a, which is interposed between the outer circumferential side of the case 60b of the partition wall portion 60a and the flange portion 51c of the nut portion 51a and housed in the extension-side pressure chamber 61, and a compression-side coil spring 67b, which is interposed between the inner circumferential side of the shutter 60c of the partition wall portion 60a and the bottom portion 51e of the piston nut 51 and housed in the compression-side pressure chamber 62. The extension-side coil spring 67a and the compression-side coil spring 67b sandwich the free piston 60 in a compressed state, and the free piston 60 sandwiched between the extension-side coil spring 67a and the compression-side coil spring 67b is positioned at a neutral position in the pressure chamber R3. In this embodiment, the neutral position is set at a position corresponding to the stroke center of the free piston 60 in the pressure chamber R3, but the neutral position does not necessarily have to coincide with the stroke center of the free piston 60.

[0134] In addition, the extension-side coil spring 67a is fitted to the outer periphery of the case 60b of the free piston 60, and no eccentricity occurs with respect to the free piston 60 when it expands or contracts, so that a stable biasing force can be applied to the free piston 60. The compression-side coil spring 67b is inserted into the inner periphery of the shutter 60c of the free piston 60, and no eccentricity occurs with respect to the free piston 60 when it expands or contracts, so that a stable biasing force can be applied to the free piston 60.

[0135] Note that the spring element 67 only needs to position the free piston 60 at the neutral position and exert a biasing force in a direction in which the free piston 60 returns to the neutral position when displaced from the neutral position, and therefore may be formed by one spring connected to both the housing H3 and the free piston 60. Furthermore, the spring constituting the spring element 67 may be an elastic body such as a wave washer, a leaf spring, a disc spring, rubber, etc., other than a coil spring.

[0136] The shock absorber D3 is configured as described above, and can operate in the same manner as the shock absorber D1 while the free piston 60 does not reach the stroke end, generating a high damping force for the input of low-frequency vibration and a low damping force for the input of high-frequency vibration. Thus, like the shock absorber D1, the shock absorber D3 generates a high damping force for the input of vibration in a low sprung resonance frequency band, stabilizing the posture of the vehicle and preventing the passenger from feeling uneasy when the vehicle turns, and generates a low damping force whenever vibration in a high unsprung resonance frequency band is input, insulating the transmission of vibration on the axle side to the vehicle body side, and improving the ride comfort of the vehicle. The frequency at which the damping force in the shock absorber D3 decreases can be tuned by setting the resistance that the expansion-side passage 8 and the compression-side passage 55 provide to the flow of liquid and the spring constant of the spring element 67. In addition, when the resistance to the flow of the liquid provided by the expansion-side passage 8 and the compression-side passage 55 is minimized, the shock absorber D3 also operates in the same manner as the shock absorber D1, and changes the damping force in response to the amplitude of the vibration rather than the frequency of the input vibration. In response to the input of a small amplitude vibration, a low damping force is generated to insulate the transmission of the vibration on the axle side to the vehicle body side, and in response to the input of a large amplitude vibration, a high damping force is generated to suppress the vibration of the vehicle body, thereby improving the ride comfort of the vehicle.

[0137] Next, the hydraulic lock function of the shock absorber D3 will be described. When the stroke amount of the shock absorber D3 toward the extension side is large, the movement amount of the free piston 60 from the neutral position in the direction compressing the compression side pressure chamber 62 becomes large. When the free piston 60 moves from the neutral position in the direction compressing the compression side pressure chamber 62, the shutter 60c faces the opening of the compression side passage 55 provided in the cylindrical portion 51d of the piston nut 51, and as the movement amount of the free piston 60 increases, the opening is gradually blocked, and the degree of communication between the compression side passage 55 and the compression side pressure chamber 62 gradually decreases. Then, when the shutter 60c of the free piston 60 completely faces the opening of the compression side passage 55, the flow path area between the shutter 60c and the cylindrical portion 51d is limited to the cross-sectional area of ​​the groove 60c1.

[0138] Therefore, as the free piston 60 increases in the amount of movement from the neutral position in the direction compressing the compression side pressure chamber 62, the liquid in the compression side pressure chamber 62 gradually becomes more difficult to move to the compression side chamber R2 through the compression side passage 55, and the liquid in the compression side pressure chamber 62 becomes more difficult to move to the compression side chamber R2, the pressure in the compression side pressure chamber 62 increases, and the movement of the free piston 60 in the direction compressing the compression side pressure chamber 62 is suppressed. Also, during the contraction operation of the shock absorber D3, the pressure in the compression side pressure chamber 62 becomes higher than the pressure in the compression side chamber R2, so the compression side check valve 56 blocks the compression side suction passage 54.

[0139] Therefore, when the free piston 60 moves from the neutral position in the direction compressing the compression-side pressure chamber 42 to the vicinity of the stroke end, the liquid in the compression-side pressure chamber 62 becomes less likely to move to the compression-side chamber R2 as the movement of the free piston 60 progresses, and the pressure of the compression-side pressure chamber 62 increases, suppressing the movement of the free piston 60 in the direction compressing the compression-side pressure chamber 62. In this way, in the shock absorber D3 of this embodiment, when the free piston 60 moves from the neutral position in the direction compressing the compression-side pressure chamber 62 to the vicinity of the stroke end, the degree of communication between the compression-side pressure chamber 62 and the compression-side passage 55 is reduced to increase the pressure of the compression-side pressure chamber 62, and the compression-side pressure chamber 62 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 60 in the direction compressing the compression-side pressure chamber 62.

[0140] In addition, after the free piston 60 increases the pressure in the compression-side pressure chamber 62 to perform the hydraulic lock function, when the direction of expansion and contraction of the shock absorber D3 changes from the extension operation to the contraction operation, the free piston 60 tries to move upward in FIG. 4 in the direction of compressing the expansion-side pressure chamber 61. At that time, the compression-side check valve 56 receives the pressure of the compression-side chamber R2 and contracts to open, opening the compression-side suction passage 54, so that liquid is quickly supplied from the compression-side chamber R2 through the compression-side suction passage 54 into the compression-side pressure chamber 62, whose communication with the compression-side passage 55 is restricted. In addition, liquid is supplied from the compression-side pressure chamber 62 through the groove 60c1 to the space between the outer circumferential side of the shutter 60c of the partition wall portion 60a of the free piston 60 and the step portion 51d2 of the cylindrical portion 51d. In this way, even if the free piston 60 is displaced to the vicinity of the stroke end to reduce the degree of communication between the compression side passage 55 and the compression side pressure chamber 62, when the shock absorber D3 changes from extension to contraction, liquid is supplied from the compression side chamber R2 to the compression side pressure chamber 62, which does not result in an excessive pressure drop. Therefore, the free piston 60 can smoothly move in the direction of compressing the expansion side pressure chamber 61 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D3 is not impaired.

[0141] As described above, when the free piston 60 is displaced in the housing H3 in the direction compressing the compression-side pressure chamber 62 to the vicinity of the stroke end during the extension operation of the shock absorber D3, the hydraulic lock function is exerted to suppress the movement of the free piston 60 toward the compression-side stroke end, gradually reducing the moving speed of the free piston 60 and stopping the free piston 60 at the stroke end. When the free piston 60 stops, the entire flow rate of the liquid moving from the expansion-side chamber R1 to the compression-side chamber R2 passes through the expansion-side main valve 16, so that the damping force generated by the shock absorber D3 becomes high. Therefore, if the shock absorber D3 generates a low damping force before the stop of the free piston 60, the damping force generated by the stop of the free piston 60 becomes high, but the free piston 60 gradually reduces its speed due to the hydraulic lock, so that the sudden change in the damping force is mitigated.

[0142] In addition, when the stroke amount of the shock absorber D3 toward the contraction side is large, the free piston 60 moves from the neutral position toward the direction of compressing the expansion-side pressure chamber 61 to a large amount. When the free piston 60 moves from the neutral position toward the direction of compressing the expansion-side pressure chamber 61, the first protrusion p4 enters the case 60b from outside the case 60b. When the first protrusion p4 is outside the case 60b, there is a sufficiently large gap between the nut body 51b and the case 60b, and the flow path is not restricted, so that the liquid can move between the expansion-side pressure chamber 61 and the expansion-side passage 8 without much resistance. However, when the first protrusion p4 enters the case 60b, the flow path area between the first protrusion p4 and the case 60b is reduced to the cross-sectional area of ​​the groove 51d3. Therefore, the liquid in the expansion-side pressure chamber 61 is less likely to move to the expansion-side chamber R1 through the expansion-side passage 8, and the pressure in the expansion-side pressure chamber 61 increases, suppressing the movement of the free piston 60 in the direction of compressing the expansion-side pressure chamber 61. In addition, during the contraction operation of the shock absorber D3, the pressure in the expansion-side pressure chamber 61 becomes higher than the pressure in the expansion-side chamber R1, so that the expansion-side check valve 53 attached to the outer periphery of the first protrusion p4 blocks the expansion-side suction passage 52.

[0143] In this way, when the free piston 60 moves from the neutral position in the direction compressing the expansion-side pressure chamber 61 to the vicinity of the stroke end, the first convex portion p4 enters the case 60b, the pressure in the expansion-side pressure chamber 61 increases, and the movement of the free piston 60 in the direction compressing the expansion-side pressure chamber 61 is suppressed. Therefore, in the shock absorber D3 of this embodiment, when the free piston 60 moves from the neutral position in the direction compressing the expansion-side pressure chamber 61 to the vicinity of the stroke end, the degree of communication between the expansion-side pressure chamber 61 and the expansion-side passage 8 is reduced, the pressure in the expansion-side pressure chamber 61 increases, and the expansion-side pressure chamber 61 itself functions as a hydraulic lock chamber, thereby exerting a hydraulic lock function that suppresses further movement of the free piston 60 in the direction compressing the expansion-side pressure chamber 61.

[0144] In addition, after the free piston 60 increases the pressure in the expansion-side pressure chamber 61 to perform the hydraulic lock function, when the direction of extension and contraction of the shock absorber D3 changes from contraction to expansion, the free piston 60 tries to move downward in FIG. 4 in the direction of compressing the compression-side pressure chamber 62. At that time, liquid is supplied from the expansion-side chamber R1 through the expansion-side passage 8 to the space between the case 60b and the first protruding portion p4 of the free piston 60. Furthermore, the expansion-side check valve 53 receives the pressure of the expansion-side chamber R1 and expands in diameter to open, thereby opening the expansion-side suction passage 52, so that liquid is quickly supplied from the expansion-side chamber R1 through the expansion-side suction passage 52 to the inside of the expansion-side pressure chamber 61, whose communication with the expansion-side passage 8 is restricted. In this way, even if the free piston 60 is displaced to the vicinity of the stroke end to reduce the degree of communication between the expansion-side passage 8 and the expansion-side pressure chamber 61, when the shock absorber D3 changes from contraction to extension, liquid is supplied from the expansion-side chamber R1 to the space between the case 60b and the first convex portion p4 and to the expansion-side pressure chamber 61, respectively, and no excessive pressure drop is caused. Therefore, the free piston 60 can smoothly move in the direction of compressing the compression-side pressure chamber 62 and can quickly return to the neutral position, and the frequency sensitivity characteristic or amplitude sensitivity characteristic of the shock absorber D3 is not impaired.

[0145] As described above, when the free piston 60 is displaced in the housing H3 in the direction compressing the expansion-side pressure chamber 61 to the vicinity of the stroke end during the contraction operation of the shock absorber D3, the hydraulic lock function is exerted to suppress the movement of the free piston 60 toward the expansion-side stroke end, gradually reducing the moving speed of the free piston 60 and stopping the free piston 60 at the stroke end. When the free piston 60 stops, the entire flow rate of the liquid moving from the compression-side chamber R2 to the expansion-side chamber R1 passes through the compression-side main valve 17, so that the damping force generated by the shock absorber D3 becomes high. Therefore, if the shock absorber D3 generates a low damping force before the stop of the free piston 60, the damping force generated by the stop of the free piston 60 becomes high, but the free piston 60 gradually reduces its speed due to the hydraulic lock, so that the sudden change in the damping force is mitigated.

[0146] As described above, the shock absorber D3 in the second modified example of the embodiment includes a housing H3 that accommodates the free piston 60 therein to form a pressure chamber R3. The housing H3 has a cylindrical portion 51d, a first lid portion C5 that closes one end of an opening of the cylindrical portion 51d, a second lid portion C6 that closes the other end of the opening of the cylindrical portion 51d, a first convex portion p4 that protrudes inward from the first lid portion C5, an expansion-side suction passage 52 that opens from the outer periphery of the first convex portion p4 and communicates with the expansion-side chamber R1, and a compression-side suction passage 54 that opens from the outer periphery of the cylindrical portion 51d and communicates with the compression-side chamber R2. The free piston 60 has an opening at its tip and communicates with the expansion-side pressure chamber 61, the compression-side passage 55 penetrates the cylindrical portion 51d and communicates with the compression-side pressure chamber 62, the expansion-side check valve 53 is provided in the expansion-side suction passage 52, and the compression-side check valve 56 is provided in the compression-side suction passage 54. The free piston 60 is accommodated in the cylindrical portion 51d and divides the inside of the housing H3 into an expansion-side pressure chamber 61 and a compression-side pressure chamber 62, and has a cylindrical case 60b provided on the expansion-side pressure chamber 61 side to allow the insertion of the first protrusion p4, and a shutter 60c provided on the compression-side pressure chamber 62 side to face the opening of the compression-side passage 55.

[0147] In the shock absorber D3 in the second modification of the embodiment, the movement of the free piston 60 to the stroke end causes the expansion-side pressure chamber 61 itself or the compression-side pressure chamber 62 itself to function as a hydraulic lock chamber, so that a sudden change in the damping force can be mitigated, and a cushion does not need to be provided in the pressure chamber R3, and the stroke length of the free piston 60 can be secured. In addition, since the shock absorber D3 does not need to provide a cushion, the volumes in the expansion-side pressure chamber 61 and the compression-side pressure chamber 62 can be secured to be large, and the liquid in the expansion-side pressure chamber 61 and the compression-side pressure chamber 62 can be used during hydraulic lock. Therefore, in the shock absorber D3, a sufficient flow rate of liquid can be flowed from the expansion-side pressure chamber 61 or the compression-side pressure chamber 62 to the expansion-side chamber R1 or the compression-side chamber R2 until the hydraulic lock function is exerted, and it is also easy to tune the transient characteristics that transition from a state in which a low damping force is generated by reducing the damping force to a state in which a high damping force is generated by the expansion-side main valve 16 or the compression-side main valve 17. Therefore, according to the shock absorber D3 of the second modified example of one embodiment, like the shock absorber D1, it is possible to mitigate sudden changes in the damping force, while easily tuning the transient characteristics when the damping force changes and ensuring the stroke length of the free piston.

[0148] In addition, in the shock absorber D3, the passage area between the expansion-side pressure chamber 61 and the expansion-side passage 8 is reduced by the intrusion of the first convex portion p4 into the case 60b, and the passage area between the shutter 60c and the compression-side passage 55 of the cylindrical portion 51d is reduced. Therefore, a sufficient flow rate of liquid can be caused to flow into the expansion-side chamber R1 or the compression-side chamber R2 while gradually restricting the degree of communication between the expansion-side pressure chamber 61 and the expansion-side passage 8 or the degree of communication between the compression-side pressure chamber 62 and the compression-side passage 55.

[0149] Furthermore, the timing and transient characteristics of the transition from low damping force to high damping force can be easily tuned by setting the inner peripheral shape of the case 60b and the outer peripheral shape of the first convex portion p4, the cross-sectional area of ​​the groove 51b3 of the nut body 51b, the number of grooves 51d3, the groove 60c1 of the shutter 60c and the opening area of ​​the extension-side passage 8, and the number of grooves 60c1. In this way, according to the shock absorber D3, the transient characteristics can be easily tuned by setting the shapes of the case 60b, the first convex portion p4, and the shutter 60c, etc.

[0150] In addition, if the cross-sectional area of ​​the groove 60c1 is set to be smaller from the tip side toward the base end side of the shutter 60c, the flow path area between the cylindrical portion 51d and the shutter 60c can be reduced as the free piston 60 moves in the direction compressing the compression side pressure chamber 62 after it starts to block the opening of the compression side passage 55, and the transient characteristics can be tuned by the shape of the groove 60c1. Similarly, if the cross-sectional area of ​​the groove 51b3 is set to be smaller from the tip side toward the base end side of the nut body 51b, the flow path area between the nut body 51b and the case 60b can be reduced as the free piston 60 moves in the direction compressing the expansion side pressure chamber 61 after it starts to block the opening of the expansion side passage 8, and the transient characteristics can be tuned by the shape of the groove 51b3.

[0151] Furthermore, in the shock absorber D3 in the second modified example of one embodiment, only the first convex portion p4 arranged in the expansion-side pressure chamber 61 protrudes into the housing H3, and by providing the compression-side passage 55 in the cylindrical portion 51d, the compression-side pressure chamber 62 can function as a hydraulic lock chamber without providing a convex portion in the compression-side pressure chamber 62 that reduces the volume of the pressure chamber R3. This makes it easier to ensure the volume in the pressure chamber R3, thereby shortening the overall length of the housing H3, and makes it easier to ensure the stroke length of the shock absorber D3 even when the pressure chamber R3 is provided.

[0152] Furthermore, in the shock absorber D3 in the second modified example of one embodiment, the expansion side check valve 53 has an annular O-ring (valve body) that is elastic and is fitted into an annular groove 51b1 provided on the outer periphery of the first convex portion p4 to open and close the opening end of the expansion side suction passage 52, and the compression side check valve 56 has an annular O-ring (valve body) that is elastic and is fitted into an annular groove 51d1 provided on the inner periphery of the tubular portion 51d to open and close the opening end of the compression side suction passage 54. Thus, in the shock absorber D3 in the second modified example of one embodiment, the compression side check valve 56 is an elastic annular valve body mounted in the annular groove 51d1 on the inner circumference of the tubular portion 51d that forms the housing H3, and the extension side check valve 53 is an elastic annular O-ring (valve body) mounted in the annular groove 51b1 on the outer circumference of the first convex portion p4. Therefore, even if the extension side check valve 53 and the compression side check valve 56 are provided in the housing H3, they do not interfere with the movement of the free piston 60, and the stroke length of the free piston 60 can be secured while avoiding an increase in the size of the housing H3.

[0153] Although the preferred embodiment of the present invention has been described in detail above, modifications, variations and changes can be made without departing from the scope of the appended claims. [Explanation of symbols]

[0154] 1···cylinder, 2···piston, 3···piston rod, 4, 40, 60··free piston, 4b···first case, 4c···second case, 5, 41, 61···rebound pressure chamber, 6, 42, 62···compression pressure chamber, 7, 47, 67···spring element, 8, 38···rebound passage, 9, 34, 55···compression passage, 10, 39, 53···rebound check valve, 11, 36, 56···compression check valve, 21b2, 21e3, 32d1, 33d1, 51b1, 51d1 Annular groove, 21d, 33d, 51d, cylindrical portion, 22, 37, 52, extension side suction passage, 23, 35, 54, pressure side suction passage, 40b, 60c, shutter, 40c, 60b, case, C1, C3, C5, first cover portion, C2, C4, C6, second cover portion, D1, D2, D3, shock absorber, H1, H2, H3, housing, P, damping passage, p1, p3, p4, first convex portion, p2, second convex portion, R1, extension side chamber, R2, pressure side chamber, R3, pressure chamber,

Claims

1. A cylinder; a piston slidably inserted into the cylinder and dividing the inside of the cylinder into an expansion-side chamber and a compression-side chamber; a piston rod that is movably inserted into the cylinder and has one end connected to the piston; a damping passage communicating the expansion-side chamber and the compression-side chamber; A pressure chamber; a free piston that is movably inserted into the pressure chamber and divides the pressure chamber into an extension-side pressure chamber and a compression-side pressure chamber; a spring element that generates a biasing force that suppresses displacement of the free piston from a neutral position with respect to the pressure chamber; an expansion-side passage communicating the expansion-side chamber and the expansion-side pressure chamber; a compression side passage communicating the compression side chamber and the compression side pressure chamber; an expansion-side check valve that allows only a flow of liquid from the expansion-side chamber to the expansion-side pressure chamber; a compression-side check valve that allows only the flow of liquid from the compression-side chamber to the compression-side pressure chamber, The free piston is When the expansion-side pressure chamber is moved to a stroke end in a direction in which the expansion-side pressure chamber is compressed, the degree of communication between the expansion-side passage and the expansion-side pressure chamber is reduced, causing the expansion-side pressure chamber to function as a hydraulic lock chamber, When the pressure chamber is moved to a stroke end in a direction in which the pressure chamber is compressed, the degree of communication between the pressure chamber and the pressure chamber is reduced, causing the pressure chamber to function as a hydraulic lock chamber. A shock absorber comprising:

2. a housing that accommodates the free piston therein and forms the pressure chamber; The housing includes: A cylindrical portion and A first cover portion that closes one of the openings of the cylindrical portion; A second cover portion that closes the other of the openings of the cylindrical portion; a first protrusion protruding inward from the first lid portion; a second protrusion protruding inward from the second lid portion; an expansion-side suction passage that opens from an outer periphery of the first protrusion and communicates with the expansion-side chamber; a compression-side suction passage that opens from an outer periphery of the second protrusion and communicates with the compression-side chamber, the expansion-side passage opens at a tip end of the first protrusion and communicates with the expansion-side pressure chamber, the compression-side passage opens at a tip end of the second protrusion and communicates with the compression-side pressure chamber, The extension-side check valve is provided in the extension-side suction passage, The compression side check valve is provided in the compression side suction passage, The free piston is The pressure chamber is accommodated in the cylindrical portion to divide the inside of the housing into the expansion-side pressure chamber and the compression-side pressure chamber, a cylindrical first case provided on the expansion-side pressure chamber side and allowing the first protrusion to be inserted; a cylindrical second case provided on the compression side pressure chamber side and allowing the second protrusion to be inserted, reducing a flow path area between the first case and the first protrusion in accordance with a degree of penetration of the first protrusion into the first case; A flow passage area between the second case and the second protrusion is reduced according to a degree of penetration of the second protrusion into the second case.

2. The shock absorber according to claim 1.

3. the expansion-side check valve has an annular valve body that has elasticity and is fitted in an annular groove provided on an outer periphery of the first protrusion to open and close an opening end of the expansion-side suction passage, The compression-side check valve has an annular valve body that is elastically mounted in an annular groove provided on an outer periphery of the second protrusion and opens and closes an open end of the compression-side suction passage.

3. The shock absorber according to claim 2.

4. a housing that accommodates the free piston therein and forms the pressure chamber; The housing includes: A cylindrical portion and A first cover portion that closes one of the openings of the cylindrical portion; A second cover portion that closes the other of the openings of the cylindrical portion; a first protrusion protruding inward from the first lid portion; an expansion-side suction passage that opens from an outer periphery of the first protrusion and communicates with the expansion-side chamber; a compression-side suction passage that opens from an outer periphery of the cylindrical portion and communicates with the compression-side chamber, the expansion-side passage opens at a tip end of the first protrusion and communicates with the expansion-side pressure chamber, The compression-side passage passes through the cylindrical portion and communicates with the compression-side pressure chamber, The extension-side check valve is provided in the extension-side suction passage, The compression side check valve is provided in the compression side suction passage, The free piston is The pressure chamber is accommodated in the cylindrical portion to divide the inside of the housing into the expansion-side pressure chamber and the compression-side pressure chamber, a cylindrical case provided on the expansion-side pressure chamber side and allowing the first protrusion to be inserted; a shutter provided on the pressure-side pressure chamber side and capable of facing an opening of the pressure-side passage; 2. The shock absorber according to claim 1.

5. the expansion-side check valve has an annular valve body that has elasticity and is fitted in an annular groove provided on an outer periphery of the first protrusion to open and close an opening end of the expansion-side suction passage, The compression-side check valve has an annular valve body that is elastically mounted in an annular groove provided on the inner periphery of the cylindrical portion and opens and closes the open end of the compression-side suction passage.

5. The shock absorber according to claim 4.

6. a housing that accommodates the free piston therein and forms the pressure chamber; The housing includes: A cylindrical portion and A first cover portion that closes one of the openings of the cylindrical portion; A second cover portion that closes the other of the openings of the cylindrical portion; a first protrusion protruding inward from the first lid portion; an expansion-side suction passage that opens from an outer periphery of the cylindrical portion and communicates with the expansion-side chamber; a compression-side suction passage that opens from an outer periphery of the first protrusion and communicates with the compression-side chamber, The expansion-side passage passes through the cylindrical portion and communicates with the expansion-side pressure chamber, the compression-side passage opens at a tip end of the first protrusion and communicates with the compression-side pressure chamber, The extension-side check valve is provided in the extension-side suction passage, The compression side check valve is provided in the compression side suction passage, The free piston is The pressure chamber is accommodated in the cylindrical portion to divide the inside of the housing into the expansion-side pressure chamber and the compression-side pressure chamber, a shutter provided on the expansion-side pressure chamber side and capable of facing an opening of the expansion-side passage; a cylindrical case provided on the compression side pressure chamber side and allowing the first protrusion to be inserted therein; 2. The shock absorber according to claim 1.

7. the expansion-side check valve has an annular valve body that has elasticity and is fitted in an annular groove provided on an inner circumference of the cylindrical portion to open and close an opening end of the expansion-side suction passage, The compression-side check valve has an annular valve body that is elastically mounted in an annular groove provided on an outer periphery of the first protrusion and opens and closes an open end of the compression-side suction passage.

7. The shock absorber according to claim 6.

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