JP2010007817A - Hydraulic shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic shock absorber capable of suppressing sudden change of attenuating force in a high speed region of a piston speed, and capable of suitably suppressing increase of the attenuating force in the high speed region. <P>SOLUTION: The hydraulic shock absorber is provided with a piston 5 slidably fitted in a cylinder 2 and partitioning the inside of the cylinder 2 into chambers 3 and 4, a piston rod 6 having a base end fixed to the piston 5 and having a distal end protruding to the outside of the cylinder 2, a main flow passage 7 provided in the piston 5 and communicating the insides of the chambers 3 and 4, attenuating valves 8 and 9 imparting flow resistance to working fluid in the main flow passage 7 during sliding of the piston 5, a sub flow passage 10 provided separately from the main flow passage 7 and communicating the insides of the chambers 3 and 4, and a valve element 11a for opening or closing the sub flow passage 10 by expanding/contracting in operation of the expanding side or the contracting side. An elastic resin material is used for the valve element 11a, and thereby, sudden change of the attenuating force in the high speed region of the piston speed can be suppressed, and increase of the attenuating force in the high speed region can be suitably suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fluid pressure shock absorber employed in, for example, a suspension device for an automobile vehicle.

A suspension device for a vehicle such as an automobile employs a fluid pressure shock absorber, for example, a hydraulic shock absorber whose working fluid is working oil.
In general, the hydraulic shock absorber is provided with a damping valve that imparts a flow resistance to the hydraulic fluid flowing through the oil flow path in the piston when the piston is divided into two chambers and is operated on the expansion side and the contraction side. . The opening of the damping valve increases due to an increase in the pressure difference between the two chambers in the cylinder in accordance with the piston speed, and the opening for the pressure difference depends on the strain-stress characteristics of the damping valve, that is, the elastic modulus. To do. Accordingly, since the strain-stress characteristic is usually linear, that is, proportional to the first order, the damping force characteristic in the conventional hydraulic shock absorber is increased in piston speed. The rate of change of the damping force associated with increases in proportion to the first order.
Therefore, in recent years, in order to mitigate the input of vibration from the road surface to the vehicle body in order to meet market needs, in particular, the ability to actively suppress the damping force in the high speed region of the piston speed on the contraction side, that is, Products with high-cut performance have been developed.

For example, there is Patent Document 1 as a conventional technique of a hydraulic shock absorber having a performance of actively suppressing a damping force in a high speed region of a piston speed. In Patent Document 1, a bypass passage that communicates the cylinder upper chamber and the cylinder lower chamber in the piston is provided separately from the main passage, and a check valve is provided in the bypass passage. The check valve has a valve hole having a valve seat at one end and a flow hole, is slidably accommodated in the valve hole, and opens and closes the flow hole by being separated from and contacting the valve seat in the valve hole. A check plate and a spring for biasing the check plate in the valve seat direction are provided. The damping force is adjusted by the check valve and a damping valve that blocks the main passage.
JP 2005-127374 A

  In a fluid pressure shock absorber, it is desired to suppress a sudden change in damping force in a high speed region of the piston speed.

  An object of the present invention is to provide a fluid pressure buffer that can suppress a sudden change in damping force in a high speed region of the piston speed and can appropriately suppress an increase in damping force in a high speed region. .

  As means for solving the above-mentioned problems, the invention of the fluid pressure shock absorber according to claim 1 of the present invention includes a cylinder in which a working fluid is sealed, a cylinder slidably fitted in the cylinder, A main stream that connects the two chambers, the piston that defines the inside of the cylinder in two chambers, the piston rod that is fixed to the piston, the tip of which protrudes outside the cylinder, and the piston. A path, a damping valve that is disposed facing the main flow path, and applies flow resistance to the working fluid that flows through the main flow path when the piston is operated on the expansion side and the contraction side, and is provided separately from the main flow path, A sub-flow path communicating between the two chambers, and a valve body that is disposed in the sub-flow path and expands and contracts when either the expansion side or the contraction side is operated to open / close the sub-flow path. A fluid pressure buffer comprising the valve body It is characterized in that the resin material having elasticity in whole or in part is employed.

  According to the fluid pressure shock absorber of the present invention, it is possible to suppress an abrupt change in the damping force in the high speed region of the piston speed and appropriately suppress an increase in the damping force in the high speed region.

The embodiments described below naturally have the objects and effects of the invention described above, and the features of the invention, but are not limited thereto. Other problems, operations, and effects to be solved will be described in detail in the following description of embodiments.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIGS.
The fluid pressure shock absorber according to the embodiment of the present invention is provided as a hydraulic shock absorber 1 in which working oil is employed as a working fluid.
As shown in FIGS. 1 and 2, a hydraulic shock absorber 1 according to an embodiment of the present invention is provided with a cylinder 2 in which hydraulic oil is sealed, and is slidably provided in the cylinder 2. A piston 5 forming a cylinder upper chamber 3 and a cylinder lower chamber 4, a base end portion fixed to the piston 5, a piston rod 6 projecting out of the cylinder 2, and a piston 5 provided in the piston 5, A main flow path 7 for communicating the upper chamber 3 and the cylinder lower chamber 4 and the main flow path 7 are arranged so as to face the main flow path 7 and impart flow resistance to the hydraulic oil flowing through the main flow path 7 when the piston 5 operates on the expansion side and the contraction side. A sub-passage 10 that is provided in the piston rod 6 separately from the contraction-side damping valve 8 and the expansion-side damping valve 9 and the main passage 7 and communicates between the cylinder upper chamber 3 and the cylinder lower chamber 4; 10 is placed on the expansion side or the contraction side According to the first or second embodiment, when either one of the operations is performed, the expansion and contraction side damping valves 8 and 9 expand and contract in substantially the same direction as the opening and closing directions to open / close the sub-flow path 10. And a valve body 11a or 11b.

Furthermore, the hydraulic shock absorber 1 according to the present embodiment will be described in detail with reference to FIGS.
As shown in FIG. 1, the hydraulic shock absorber 1 employs a so-called twin tube structure in which a cylindrical outer tube 15 is disposed on the outer peripheral side of the cylinder 2. The cylinder 2 is disposed coaxially with the cylinder 2 at an interval on the outer peripheral side. The outer tube 15 and the cylinder 2 are fixed via a body portion (not shown) provided at the lower end portion. An annular reservoir chamber 16 is formed between the inner peripheral surface of the outer tube 15 and the outer peripheral surface of the cylinder 2. The reservoir chamber 16 is communicated with the cylinder 2 via a base valve (not shown) provided in the body portion, partially filled with hydraulic oil, and the remaining portion is filled with gas. Yes. The gas in the reservoir chamber 16 compensates for the volume change of the piston rod 6 in the cylinder 2 as the piston rod 6 enters and exits the cylinder 2, and keeps the entire volume in the cylinder 2 constant. It is.

As shown in FIG. 2, the piston rod 6 includes a piston rod main body 18 having a tip protruding outside the cylinder 2, and a piston bolt screwed to the base end of the piston rod main body 18 to which the piston 5 is fixed. 19.
The proximal end side of the piston rod main body 18 is formed in a hollow shape at a predetermined height, and a small diameter hole portion 20 and a large diameter hole portion 21 are formed. In the peripheral wall portion that forms the large-diameter hole portion 21 of the piston rod body 18, one or a plurality of through-holes 22 along the radial direction are formed at intervals in the circumferential direction. Further, a female threaded portion 24 to which the piston bolt 19 is screwed is formed on the lower inner peripheral surface of the large diameter hole portion 21.

The piston bolt 19 is formed in a hollow shape having a shaft hole 35. In the peripheral wall portion at the upper end of the piston bolt 19, one or more through holes 23 extending in the radial direction are formed at intervals in the circumferential direction. As shown in FIG. 3, the through-hole 23 is formed in an inverted triangle shape with the apex facing downward. Further, as shown in FIG. 2, a male screw portion that is screwed into a female screw portion 24 provided in the large-diameter hole portion 21 of the piston rod body 18 at a position below the through hole 23 on the upper outer peripheral surface of the piston bolt 19. 25 is formed. An annular flange portion 26 projects outwardly from the male screw portion 25 of the piston bolt 19. A male screw portion 27 to which a fixing nut 33 of the piston 5 is screwed is formed on the outer peripheral surface of the lower end of the piston bolt 19.
When the male thread portion 25 of the piston bolt 19 is screwed to the female thread portion 24 of the piston rod body 18, the lower end of the piston rod body 18 comes into contact with the upper surface of the annular flange portion 25 of the piston bolt 19, and the piston rod The through hole 22 on the main body 18 side and the through hole 23 on the piston bolt 19 side are arranged at substantially the same position in the axial direction.

As shown in FIG. 2, the piston 5 is formed in a cylindrical shape that divides the inside of the cylinder 2 into a cylinder upper chamber 3 and a cylinder lower chamber 4, and is slidable in the vertical direction within the cylinder 2. It is fixed to the piston bolt 19 which comprises.
A plurality of through-holes 30 are formed in the piston 5 in the circumferential direction as the main flow path 7 of the hydraulic fluid that allows the cylinder upper chamber 3 and the cylinder lower chamber 4 in the cylinder 2 to communicate with each other. On the upper and lower surfaces of the piston 5, a contraction-side damping valve 8 and an extension-side damping valve 9 are arranged so as to face the respective through holes 30. In addition, the through hole 30 on the right side in the drawing constitutes an extension side oil passage 30a, and the through hole 30 on the left side in the drawing constitutes a contraction side oil passage 30b.

The compression side damping valve 8, the piston 5, and the extension side damping valve 9 are sandwiched between the upper and lower support plates 31 and 32 in this order below the annular flange portion 26 of the piston bolt 19 constituting the piston rod 6. The fixing nut 33 is screwed onto the male screw portion 27 on the outer peripheral surface of the lower end of the piston bolt 19.
As a result, the piston 5 is slidably provided in the cylinder 2, and the cylinder upper chamber 3 and the cylinder lower chamber 4 are formed in the cylinder 2 by the piston 5, and the piston 5 is operated on the expansion side and the contraction side. Occasionally, the contraction-side damping valve 8 and the extension-side damping valve 9 impart flow resistance to the working oil flowing through the contraction-side and extension-side oil passages 30b and 30a in the piston 5. The shaft hole 35 of the piston bolt 19 constituting the piston rod 6, the through hole 22 on the piston rod body 18 side, and the through hole 23 on the piston bolt 19 side are provided in the cylinder 2 separately from the main flow path 7. A sub-flow path 10 that communicates between the cylinder upper chamber 3 and the cylinder lower chamber 4 is configured.

Next, the valve body 11a which concerns on 1st Embodiment is demonstrated based on FIG.2 and FIG.4.
The valve body 11a according to the first embodiment is entirely formed of a resin material having elasticity, and includes a head portion 36 and an expansion / contraction portion 37. The valve body 11a employs a needle valve in which the tip of the head part 36 is formed in a conical shape.
The head portion 36 is formed in the order of a small diameter shaft portion 38 and a large diameter shaft portion 39 from the tip side, and the tip of the small diameter shaft portion 38 is formed in a conical shape.
The expansion / contraction portion 37 is hollow, and a plurality of outer annular groove portions 40 are formed in the outer peripheral wall at intervals in the axial direction, and an inner annular groove portion 41 is also formed on the inner peripheral wall of the adjacent outer annular groove portion 40. A plurality are formed in the axial direction so as to be disposed therebetween. The elastic force (spring force) of the expansion / contraction part 37 is set larger than the elastic force of the compression side damping valve 8.

The valve body 11a is arranged in the sub-flow channel 10 so as to open / close the sub-flow channel 10. That is, the expansion / contraction portion 37 of the valve body 11 a is disposed in the small diameter hole portion 20 of the piston rod body 18, and the small diameter shaft portion 38 of the head portion 36 is located at the upper portion in the shaft hole 35 of the piston bolt 19. The piston bolt 19 is disposed at a position where the through hole 23 provided at the upper end of the piston bolt 19 is closed. As a result, the expansion / contraction part 37 of the valve body 11a expands / contracts due to the hydraulic pressure in the cylinder lower chamber 4 so that the through hole 23 of the piston bolt 19 can be opened and closed, and the sub-flow channel 10 can be opened / closed.
In addition, the resin material adopted for the valve body 11a is one in which mechanical properties such as tensile strength, Young's modulus and hardness are located in a region between the synthetic rubber and the engineering plastic. It has a mechanical property of a strength of 30 MPa or less and a Young's modulus of 5 to 900 MPa.

In the valve body 11a according to the first embodiment, the head part 36 and the expansion / contraction part 37 are integrally formed of an elastic resin material. However, as shown in FIG. For example, the head portion 36 may be made of metal, and the stretchable portion 37 may be formed of a resin material having elasticity, and these may be combined.
Further, the valve body 11a is provided with a valve body hole 11a ′ in the extendable portion 37. The valve body hole 11 a ′ communicates with a communication hole 50 provided in the piston rod body 18 and communicating with the large diameter hole portion 21 and the through hole 22. The valve body hole 11a ′ and the communication hole 50 allow the hydraulic oil in the space formed by the valve body 11a and the small diameter hole part 20 to flow through the large diameter hole part 21 when the valve body 11a contracts in the small diameter hole part 20. It escapes to the cylinder upper chamber 3 through the through hole 22.

Next, an operation of the hydraulic shock absorber 1 in which the valve body 11a according to the first embodiment is adopted, that is, a damping force characteristic of the hydraulic shock absorber 1 will be described.
The solid line in FIG. 6 shows the damping force characteristic during the contraction side stroke in the hydraulic shock absorber 1, while the dotted line in FIG. 6 shows the damping force characteristic (basic damping characteristic) during the contraction side stroke in the conventional hydraulic shock absorber. Force characteristics).
When the hydraulic shock absorber 1 is mounted on a vehicle such as an automobile, the cylinder 2 is normally fixed to the wheel and the tip of the piston rod 6 is fixed to the vehicle body. And if the vibration from a road surface is input, the piston rod 6 of this hydraulic shock absorber 1 will expand-contract. That is, particularly during the contraction stroke of the piston rod 6, the hydraulic oil in the cylinder lower chamber 4 flows from the contraction side oil flow path 30 b of the piston 5 to the contraction side damping valve 8 as the piston 5 in the cylinder 2 slides. The cylinder flows into the cylinder upper chamber 3 against the urging force, and a damping force is generated by the urging force of the compression side damping valve 8. In this state, that is, in the low speed range before the piston speed exceeds the point P (see FIG. 6), as shown in FIG. 2, the valve body 11a has a cylinder lower chamber 4 from which the expansion / contraction part 37 is contracted. Therefore, the sub-flow path 10 that communicates between the cylinder upper chamber 3 and the cylinder lower chamber 4 remains blocked.

Further, when sudden vibration from the road surface is input to the hydraulic shock absorber 1 and the piston speed exceeds the point P (see FIG. 6) in the contraction side stroke of the piston rod 6, as shown in FIG. The damping valve 8 is fully opened and the contraction-side oil flow path 30b (main flow path 7) is fully opened. In addition, a high hydraulic pressure in the cylinder lower chamber 4 is applied to the valve body 11a and the expansion / contraction part 37 is contracted. Thus, the auxiliary flow path 10 is also opened.
As a result, the generated damping force at that time is suppressed with respect to the basic damping force characteristic due to the opening area of the main flow path 7 due to the increase in the opening area of the sub flow path 10.
As shown in FIG. 6, the damping force characteristic of the hydraulic shock absorber 1 is such that the expansion / contraction part 37 of the valve body 11a does not contract in the range up to the point P (low speed range) as shown in FIG. Is a basic damping force in which the rate of change of the damping force corresponding to the increase in piston speed is approximately linear in proportion to the strain-stress characteristic (elastic modulus) of the compression side damping valve 8 while being cut off. Although it changes in the characteristics, when the piston speed exceeds the point P (high speed range), the expansion / contraction part 37 of the valve body 11a is contracted, and the sub-flow path 10 is opened in addition to the main flow path 7, and the piston speed is increased. It changes with the 1st damping force characteristic in which the change rate of the damping force corresponding to the increase becomes smaller than the basic damping force characteristic.

  Further, since the valve body 11a according to the first embodiment employs a needle valve, the opening passage area between the cylinder upper chamber 3 and the cylinder lower chamber 4 is abrupt when the expansion / contraction part 37 of the valve body 11a contracts. Therefore, a sudden change in the damping force in the high speed region of the piston speed is suppressed.

As described above, according to the hydraulic shock absorber 1 employing the valve body 11a according to the first embodiment, the conventional problems shown in the following (a) to (c) are solved.
(A) Although it is necessary to set the elastic force (spring force) of the spring higher than the elastic force of the damping valve, this causes a problem in the spring accommodation space. That is, it is difficult to arrange a spring having high elasticity in the valve hole.
(B) In the form in which the valve opening pressure is controlled using a spring, the change in the opening flow path area before and after the valve opening becomes abrupt. The problem of disturbing sex occurs.
(C) In the form in which the valve opening pressure is controlled using a spring, the valve opening pressure cannot be set freely, and it is difficult to finely suppress the damping force in the high speed region of the piston speed.
That is, according to the present invention, when a sudden vibration is input from the road surface and the piston speed reaches a high speed region during the contraction stroke of the piston rod 6, the main flow path 7 (contraction side oil flow path 30b) in the piston 5 is reached. In addition to the full opening of the valve body 11a, the expansion / contraction part 37 of the valve body 11a is contracted, so that the sub-flow path 10 is also opened. Will be.
This makes it difficult for rapid vibration to be input to the vehicle body as it is, and prevents a decrease in riding comfort. Moreover, since the resin material which has elasticity is employ | adopted for the valve body 11a the whole or one part (expandable part 37), the arrangement | positioning in a space-saving was attained.
Further, since the valve body 11a according to the first embodiment employs a needle valve, the opening passage area is not increased rapidly when the valve is opened, so that the damping force in the high speed region of the piston speed is abrupt. Change is suppressed.

  In addition, the quantity, groove width, and groove depth of the outer annular groove 40 and the inner annular groove 41 formed in the expansion / contraction part 37 of the valve body 11a according to the first embodiment are determined by the elastic force set in the expansion / contraction part 37. It is determined accordingly.

Next, the valve body 11b according to the second embodiment will be described with reference to FIG.
In addition, when explaining the valve body 11b which concerns on 2nd Embodiment, only the point which is different from the valve body 11a which concerns on 1st Embodiment is demonstrated.
In the valve body 11b according to the second embodiment, a second expansion / contraction portion 37a is added to a predetermined range of the small-diameter shaft portion 38 of the head portion 36 in addition to the valve body 11a according to the first embodiment shown in FIGS. Has been configured. The shape of the second stretchable portion 37a is the same as that of the stretchable portion 37, is formed in a hollow shape, and a plurality of outer annular groove portions 40 are formed at intervals in the axial direction on its outer peripheral wall, and also on its inner peripheral wall, A plurality of inner annular groove portions 41 are formed in the axial direction so as to be disposed between adjacent outer annular groove portions 40. In addition, the elastic force of the expansion-contraction part 37, the 2nd expansion-contraction part 37a, and the compression side damping valve 8 is set as the compression side damping valve 8 <the second expansion / contraction part 37a <the expansion / contraction part 37.

In the hydraulic shock absorber 1 in which the valve body 11b according to the second embodiment is employed, the valve body 11b corresponds to the high speed range from the middle speed range of the piston speed in the contraction side stroke of the piston rod 6. The secondary flow path 10 is opened by shrinking stepwise in the order of the second stretchable portion 37 a to the stretchable portion 37.
That is, as shown in FIG. 9, the damping force characteristic of the hydraulic shock absorber 1 employing the valve body 11b according to the second embodiment is such that the valve speed is within the range up to the point P1 (low speed range). The second expansion / contraction part 37a and the expansion / contraction part 37 of the body 11b are not contracted, and the secondary flow path 10 is kept blocked, and the piston speed of the piston 11 corresponds to the strain-stress characteristic (elastic modulus) of the compression side damping valve 8. Although the rate of change of damping force corresponding to the increase changes with a basic damping force characteristic that is proportional in a first order, the piston body 11b of the valve body 11b is in the range from the P1 point to the P2 point (medium speed range). The first damping is such that only the expansion / contraction part 37a is contracted and the sub-channel 10 is opened in a range that does not reach full opening, and the rate of change of damping force corresponding to the increase in piston speed becomes smaller than the basic damping characteristic. It changes with force characteristics. Further, when the piston speed exceeds the point P2 (high speed range), the second expansion / contraction part 37a and the expansion / contraction part 37 of the valve body 11b are in a state where the sub-flow channel 10 is fully opened in a contracted state. Thus, the change rate of the damping force corresponding to the increase of the piston speed changes with the second damping force characteristic that is smaller than the first damping force characteristic.
As a result, it is possible to finely control the degree of suppression of the damping force over a wide range from the medium speed range to the high speed range of the piston speed.

  In addition, in the valve body 11b according to the second embodiment, the second expansion / contraction part 37a and the expansion / contraction part 37 having different elastic forces are formed in two places, but three or more expansion / contraction parts may be formed.

Further, the hydraulic shock absorber 1 according to the embodiment of the present invention is configured to suppress the damping force with respect to the basic damping force characteristic particularly in a high speed region of the piston speed during the contraction stroke of the piston rod 6. However, it is also possible to suppress the damping force with respect to the basic damping force characteristic in the high speed region of the piston speed during the extension stroke of the piston rod 6.
That is, in this embodiment, as shown in FIG. 10, the lower end opening of the shaft hole 35 of the piston bolt 19 is closed, the through hole 40 along the radial direction is provided at the lower end of the peripheral wall portion, and the first end is provided at the lower end of the shaft hole 35. The valve body 11a according to the embodiment is accommodated from the expansion / contraction part 37, and the sub-flow channel 10 is opened / closed by opening / closing the through hole 40 by the expansion / contraction of the expansion / contraction part 37 of the valve body 11a by the hydraulic pressure of the cylinder upper chamber 3. Structure.

When a sudden vibration from the road surface is input and the piston speed reaches a high speed region during the extension stroke of the piston rod 6, in addition to the full opening of the main flow path 7 (extension side oil flow path 30a) in the piston 5. Thus, high hydraulic pressure in the cylinder upper chamber 3 is applied to the valve body 11a through the through hole 22, and the expansion / contraction part 37 is contracted to open the auxiliary flow path 10.
As a result, the generated damping force at that time is suppressed with respect to the basic damping force characteristic due to the opening area of the main flow path 7 due to the increase in the opening area of the sub flow path 10.

FIG. 1 is a cross-sectional view showing a hydraulic shock absorber according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of FIG. FIG. 3 is a front view of a through hole of a piston bolt employed in the hydraulic shock absorber. FIG. 4 is a cross-sectional view of the valve body according to the first embodiment employed in the hydraulic shock absorber. FIG. 5 is a cross-sectional view of a state in which the valve body according to the first embodiment employed in the hydraulic shock absorber is contracted and the auxiliary flow path is opened. FIG. 6 is a diagram illustrating a damping force characteristic when the valve body according to the first embodiment is employed in the hydraulic shock absorber. FIG. 7 is a cross-sectional view showing another example of the valve body according to the first embodiment. FIG. 8 is a cross-sectional view of a valve body according to a second embodiment employed in the hydraulic shock absorber. FIG. 9 is a diagram illustrating a damping force characteristic when the valve body according to the second embodiment is employed in the hydraulic shock absorber. FIG. 10 is a cross-sectional view showing another example of the hydraulic shock absorber of FIG. FIG. 11 is a diagram illustrating a damping force characteristic of a conventional hydraulic shock absorber.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Hydraulic buffer (fluid pressure buffer), 2 cylinder, 3 cylinder upper chamber, 4 cylinder lower chamber, 5 piston, 6 piston rod, 7 main flow path, 8 contraction side damping valve, 9 expansion side damping valve, 10 side flow Road, 11a, 11b Valve element, 36 head part, 37 telescopic part, 37a second telescopic part

Claims (5)

A cylinder filled with a working fluid;
A piston slidably fitted in the cylinder and defining the inside of the cylinder in two chambers;
A piston rod having a base end fixed to the piston and a tip protruding outside the cylinder;
A main flow path provided in the piston and communicating between the two chambers;
A damping valve disposed facing the main flow path and imparting a flow resistance to the working fluid flowing through the main flow path when the piston is extended and contracted;
A sub-flow path provided separately from the main flow path and communicating the two chambers;
A fluid pressure shock absorber provided with a valve body that is disposed in the sub-flow path and expands and contracts when either the expansion side or the contraction side is operated to open / close the sub-flow path,
The valve body is made of a resin material having elasticity in whole or in part, and a fluid pressure shock absorber.   The fluid pressure shock absorber according to claim 1, wherein the valve body includes a head portion and an expansion / contraction portion.   The fluid pressure shock absorber according to claim 2, wherein a resin material having elasticity is employed for the expansion / contraction part.   The fluid pressure shock absorber according to claim 2 or 3, wherein a plurality of the stretchable parts are formed, and the elastic force is different in each stretchable part.   The fluid pressure shock absorber according to any one of claims 2 to 4, wherein the valve body is a needle valve in which the head portion is formed in a conical shape.

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