JPH11182611A - Hydraulic shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain strength reduction of a piston rod by forming of a communicating hole and reduce a machining cost. SOLUTION: This shock absorber is equipped with an expansion side communicating hole 3b which is drilled in a piston 3 and communicates between an upper chamber A and a lower chamber B, an expansion side damping valve 3e which is provided in the expansion side communicating hole 3b and generates damping force by allowing restively only flow of hydraulic fluid from the upper chamber A to the lower chamber B in the expansion side communicating hole 3b, and a sub flow passage (g) which is formed in a piston rod 2, bypasses the expansion side damping valve 3e, and communicates between the upper chamber A and the lower chamber B. The sub flow passage (g) is formed by a cutting groove 2b which cuts out the outer peripheral surface axially from the bottom end surface of the piston rod 2, and is constituted to communicate the top end side of the cutting groove 2b with the expansion side communicating hole 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic shock absorber for a vehicle, and more particularly, to a structure of a hydraulic fluid passage in the hydraulic shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a hydraulic buffer, for example, one described in Japanese Patent Application Laid-Open No. 63-33838 is known. The hydraulic shock absorber includes a cylinder, a piston slidably provided so as to define the inside of the cylinder into an upper chamber and a lower chamber, and one end penetrating through an axial hole formed in the piston. A piston rod fixed in a state and the other end protruding outside the cylinder,
A communication hole formed in the piston and communicating between the upper chamber and the lower chamber, and provided only in the communication hole to allow the hydraulic fluid to flow only from the upper chamber to the lower chamber in the communication hole. Between the upper chamber and the lower chamber, which is formed on the piston rod and bypasses the extension-side damping force generating mechanism section, the extension-side damping force generating mechanism section generating a damping force by restrictively permitting. And a bypass passage communicating with the piston rod, wherein the bypass passage has a vertical hole formed in the axial center portion of the piston rod, and a piston rod positioned above the piston fixed position. And a horizontal hole formed in the hole.

[0003]

However, the conventional hydraulic shock absorber has the following problems since it is configured as described above. That is, in the conventional hydraulic shock absorber, a step of forming a horizontal hole in the piston rod at a position higher than the piston fixing position to form a bypass flow path, Since two steps of forming a vertical hole extending from the horizontal hole to the lower end surface of the piston rod are required, the processing cost is high, and as shown in FIG. In this case, the thickness Y of the piston rod becomes thinner, so that the strength against the lateral force generated during the stroke of the hydraulic shock absorber is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and is intended to suppress a reduction in the strength of a piston rod due to the formation of a communication hole and to reduce a machining cost. It is intended to provide a shock absorber.

[0005]

In order to achieve the above object, a hydraulic shock absorber according to the present invention slides in a state where a cylinder and an upper chamber and a lower chamber are defined in the cylinder. A piston provided freely, a piston rod fixed at one end side so as to penetrate an axial hole formed in the piston, and a piston rod projected at the other end side to the outside of the cylinder; A first communication hole that communicates between the upper chamber and the lower chamber, and is provided in the first communication hole, and restricts only the flow of the hydraulic fluid from the upper chamber to the lower chamber in the first communication hole. An extension-side damping force generating mechanism that generates a damping force by allowing the expansion chamber to pass between the upper chamber and the lower chamber by bypassing the extension-side damping force generating mechanism formed on the piston rod. A second communication hole communicating with the second communication hole; Communication holes, said formed from the lower end surface of the piston rod notch to notch the outer peripheral surface in the axial direction, the upper end side of the cutout portion is a means that is configured to communicate with said first communication hole. According to a second aspect of the present invention, in the hydraulic pressure absorber according to the first aspect, the first communication hole communicates with the inner peripheral surface of the axial hole of the piston opposed to the upper end of the notch constituting the second communication hole. Means in which an annular groove was formed was adopted. In the hydraulic buffer according to the third aspect,
3. The method according to claim 1, wherein an upper end of the notch constituting the second communication hole is located below a load input point acting on the piston rod due to a lateral force generated during a stroke of the hydraulic shock absorber. The set means was used.

[0006]

In the hydraulic shock absorber according to the first aspect of the present invention, as described above, the second communication hole is formed by the notch that cuts the outer peripheral surface in the axial direction from the lower end surface of the piston rod. Since the upper end side of the notch is configured to communicate with the first communication hole formed in the piston, a bypass passage (second communication hole) is formed by the vertical hole formed in the axial center of the piston rod. Compared with the conventional example, the reduced cross-sectional area of the piston rod is the same, but the reduction can be minimized in terms of the wall thickness, and thereby the strength of the piston rod due to the formation of the second communication hole is improved. The decrease can be suppressed. In addition, since the notch that cuts the outer peripheral surface in the axial direction from the lower end surface of the piston rod can be machined in one step, compared with the conventional example that requires two steps of a horizontal hole and a vertical hole,
Processing costs can be reduced.

According to a second aspect of the present invention, in the hydraulic shock absorber, an annular groove communicating with the first communication hole is formed on an inner peripheral surface of a shaft hole of the piston opposed to an upper end of the notch constituting the second communication hole. Is formed, in the process of assembling the piston to the piston rod, there is no need to perform a circumferential alignment operation between the notch and the first communication hole. Further, in the hydraulic shock absorber according to the third aspect, the upper end of the notch constituting the second communication hole is located at a position closer to a load input point acting on the piston rod due to a lateral force generated during a stroke of the hydraulic shock absorber. Since it is at the lower position, a decrease in the strength of the piston rod can be significantly suppressed.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment of the Invention) First, the configuration of the first embodiment of the invention will be described. FIG. 1 is a cross-sectional view showing the entirety of a frequency-sensitive hydraulic buffer according to Embodiment 1 of the present invention. In this figure, reference numeral 1 denotes a cylindrical cylinder, in which a small diameter stud portion 2a formed at the lower end of a piston rod 2 is defined by a piston 3 fastened by a nut 8 into an upper chamber A and a lower chamber B. ing. A base 4 is provided at the lower end of the cylinder 1.

An outer cylinder 5 is provided on the outer periphery of the cylinder 1, and a reservoir chamber C defined by a lower chamber B and a base 4 is formed on the outer periphery of the cylinder 1. A spring seat 6 is fixed to an upper portion of the outer cylinder 5, and a mounting eye 7 for a wheel is fixed to a lower end portion.

FIG. 2 is an enlarged view of a portion E in FIG.
A plurality of compression-side communication holes 3a are formed on the outer peripheral side of the piston 3 at predetermined circumferential intervals, and a plurality of extension-side communication holes (first communication holes) are formed on the inner peripheral side at predetermined circumferential intervals. A hole 3b is formed. On the upper surface side of the piston 3, a pressure-side damping force is generated by restricting the flow of the hydraulic fluid from the lower chamber B toward the upper chamber A via the pressure-side communication hole 3a during the pressure stroke. A valve 3c is provided,
On the other hand, the hydraulic fluid flows from the upper chamber A to the lower chamber B via the plurality of openings 3d and the communication holes 3b formed on the inner peripheral side of the compression-side damping valve 3c during the extension stroke on the lower surface side. An extension-side damping valve (extension-side damping force generation mechanism) 3e that generates a damping force by restrictively permitting is provided. Further, on the inner peripheral surface at the lower end of the shaft hole 3f in the piston 3, An annular groove 3h communicating with the extension-side communication hole 3b is formed through the radial groove 3g, while the annular groove is formed on the outer peripheral surface of the lower end small diameter stud portion 2a of the piston rod 2 to which the piston 3 is fastened and fixed. A cutting groove (notch portion) 2b having a V-shaped cross section for cutting in the axial direction from the position 3h to the lower end surface is formed (see FIG. 8), and the cutting groove 2b and the annular groove 3h are formed. , Radial groove 3g, extension side communication hole 3b and opening The 3d, both damping valve 3c,
A sub-flow path (second
A communication hole g is formed. And this piston 3
Is integrally formed into the above-mentioned form by sintering.

FIG. 3 is an enlarged view of a portion F in FIG.
As shown in this figure, a cylindrical case 11 for accommodating a mechanism for changing a damping force characteristic described later is fixed to the lower end of the nut 8. A large-diameter hole 11a communicating with the sub flow path g is formed inside the case 11, and a retainer 12, an extension-side check plate 14, and an extension-side Orifice plate 15, extension-side sheet plate 16, spool housing 17, compression-side sheet plate 18, compression-side orifice plate 19, compression-side check plate 20, collar 13,
The retainer 21, the stud 22, the washer 23a, the compression side low attenuation valve 24, the sub-valve body 25, the extension side low attenuation valve 26, the washer 23b, and the retainer 28 are mounted.
These are fixed by caulking the lower end of the case 11.

More specifically, the spool housing 17 is formed in a cylindrical shape having a spool hole 17a formed in the axial center thereof, and a large-diameter hole 11 is formed in the middle of the outer peripheral surface.
An annular projecting portion 17b to which a seal ring 29 for sealing between the inner peripheral surface and the inner peripheral surface is mounted is formed.

The retainer 12 is, as shown in FIG.
A horizontal annular portion (stopper portion) 12e having a central hole 12a is provided at the center of the plate material, and five horizontal portions (pressing portions) 12d are radially formed on the outer peripheral portion thereof through notches 12b. Are provided, and each horizontal portion 1
Leg piece (peripheral wall) bent downward from the tip of 2d
12c is formed. And the horizontal annular portion 12
e, the horizontal portion (pressing portion) 12d have been formed to project upward in a state having a step, working space t ₁ on its lower surface
Are formed.

The extension side check plate 14 is shown in FIG.
As shown in FIG. 5, a notch annular hole 14a with a part thereof left is formed in a thin flexible plate material, so that an annular outer peripheral fixing portion 14b and a central circular valve portion (check valve portion) 14c are formed. And a connecting portion 14d communicating between the two.

The extension side orifice plate 15 is shown in FIG.
As shown in the figure, a central hole 15a having a smaller diameter than the valve portion 14c of the extension side check plate 14 is formed in the central portion of the thin plate material.
An arc-shaped long hole 15b is formed along the circumferential direction at a position facing the cutout annular hole 14a of the extension side check plate 14 on the outer periphery of the central hole 15a. And the center hole 15a are connected by a narrow notch 15c.

Returning to FIG. 3, the extension side sheet plate 16
A central hole 16a having a diameter smaller than that of the central hole 15a of the extension side orifice plate 15 is formed at the center of the thick plate material. The extension side check plate 14, the extension side orifice plate 15, and the extension side sheet plate 16
The same diameter as the spool housing 17 is formed, and between the retainer 12 and the spool housing 17,
Each horizontal portion 12d of the retainer 12 and the spool housing 1
7 is provided in a state where the outer peripheral portion thereof is sandwiched and fixed between the upper end face of the upper end 7 and the upper end face. The retainer 12 has a tip end portion of the leg portion 12c inserted into an upper annular space 17c formed between the case 11 and the spool housing 17, and the extension side check plate 14 and the extension side orifice plate. 15, the extension side sheet plate 16 and the outer periphery of the spool housing 17.

[0017] That is, as shown in FIG. 7, the valve portion 14c at the opening edge the upper surface of the central hole 15a in the extension side orifice plate 15 to form a seat surface a ₁ abuts cutout portion 15c of the opening width w ( FIG. 5) and forms a constant orifice b ₁ for extension side cut opening formed by the thickness h ₁ of the expansion side orifice plate 15.

Next, returning to FIG. 1, the retainer 21, the pressure side check plate 20, and the pressure side orifice plate 1 will be described.
9, and the compression-side sheet plate 18 have the same shape as the retainer 12, the expansion-side check plate 14, the expansion-side orifice plate 15, and the expansion-side sheet plate 16, respectively. forming a use constant orifice b _2. However, in the retainer 12, a step is formed between the horizontal annular portion 12e and the horizontal portion 12d as described above, whereas in the retainer 21, the step is not provided, and Are different.

The retainer 21 has a leg 21
c is inserted into a lower annular space 17d formed between the case 11 and the spool housing 17, and the collar 13, the pressure side check plate 20, the pressure side orifice plate 19, the pressure side sheet plate 18, and the spool housing 17 are inserted. Is provided in a state of being fitted to the outer periphery of.

The stud 22 has a small-diameter portion 22c in which a through hole 22b is formed in the center of the center of the lower end of the large-diameter portion 22a. That is, on the extension side, the retainer 1
To form the working space t ₁ for ensuring the relief operation of the valve portion 14c of the extension side check plate 14 by the step between the second horizontal annular portion 12e and a horizontal section 12d, a horizontal annular portion 12e of the retainer 12 while shift restricting the valve portion 14c is performed, with the pressure side, forming the working space t ₂ for ensuring the relief operation of the valve portion 20c of the compression side check plate 20 in the center hole 13a of the collar 13, the upper surface of the stud 22 Thus, the lift of the valve portion 20c is regulated.

The washer 23a and the pressure-side low-attenuation valve 2 are sequentially provided from the top on the small diameter portion 22c of the stud 22.
4, a sub-valve body 25, an extension side low attenuation valve 26, a washer 23b, and a retainer 28 are mounted.

More specifically, a partially cutout annular groove 25a is formed on the upper surface of the sub-valve body 25, and a seat surface 25b is formed on the outer periphery thereof. The damping valve 24 is in contact. The annular groove 25a communicates with the lower chamber B through a pressure-side flow passage 25c formed in the sub-valve body 25 and a communication hole 28a formed in the retainer 28.

On the other hand, a partially cut-out annular groove 25d is formed on the lower surface of the sub-valve body 25, and further on the outer periphery thereof,
A sheet surface 25e is formed, and the sheet surface 25e includes
The extension side low attenuation valve 26 is in contact with the extension side low attenuation valve 26. And
The annular groove 25d communicates with the large-diameter hole 11a by an extension-side flow passage 25f formed in the sub-valve body 25.

The spool housing 17 has a plurality of extending ports 17e vertically communicating between the upper annular space 17c and the spool hole 17a with the annular protrusion 17b interposed therebetween, and communicates between the lower annular space 17d and the spool hole 17a. A plurality of pressure side ports 17f are formed. The upper and lower sides of the spool hole 17a have extension-side pressure receiving chambers D.
Spool 31 as a movable member is provided so as to be vertically slidable defining a _first and compression phase pressure receiving chamber D _2.

Therefore, the liquid pressure on the upper chamber A side can be transmitted to the expansion side pressure receiving chamber D ₁ via the expansion side transmission path M surrounding the expansion side cutting constant orifice b ₁ . On the other hand, the compression side pressure receiving chamber D _2, the liquid pressure in the lower chamber B side through the compression side transmission path N that similarly over the compression side cutting constant orifice b ₂ is made can be transmitted.

End lands 31a and 31b for opening and closing both ports 17e and 17f are formed on the outer peripheral surface of the spool 31 at both upper and lower ends, and between the end lands 31a and 31b at an intermediate portion. Port 17e, 17
An annular groove 31c for communicating f is formed. That is, the expansion-side variable aperture H and the compression-side variable aperture J are formed between the inner peripheral edges of the end lands 31a and 31b and the ports 17a and 17b, respectively.

Inside the case 11, the sub flow path g (the upper chamber A side) around the expansion side variable throttle H, the compression side variable throttle J, and the expansion side low damping force valve 26 or the compression side low damping valve 24. ) And the lower chamber B are connected to form a bypass flow path G. Therefore, this bypass flow path G is
The sliding of No. 1 narrows either the expansion-side variable throttle H or the compression-side variable throttle J to narrow the flow path cross-sectional area. The spool 31 is elastically held at a neutral position where both variable throttles H and J are opened by upper and lower centering springs 32 and 33.

Next, the operation of the first embodiment of the invention will be described. First, a damping force generation state based on the process of the shock absorber will be described. When the piston 3 strokes, the liquid flows between the two chambers A and B. At this time, the two damping valves 3
a, 3b, and when the liquid flows through the bypass flow path G, the two variable throttles H, J and the two low attenuation valves 24,
The distribution is restricted by passing through any one of 26,
As a result, a damping force is generated.

This damping force characteristic changes depending on the amount of liquid flowing through the bypass flow path G, that is, the position of the spool 31. That is, the liquid pressure in the upper chamber A and the lower chamber B is
Through the extension side transmission path M and the compression side transmission path N, the extension side pressure receiving chamber D
It can be transmitted to the _first and pressure side pressure receiving chamber D _2.

Therefore, the spool 31 strokes due to the liquid pressure difference between the two chambers, whereby the cross-sectional area of the variable throttles H and J formed in the middle of the bypass passage G changes, and the damping force characteristics change. That is, as shown in FIG.
When 1 is in the neutral position, all of the variable throttles H and J are fully open, and have the lowest damping force characteristic. Then, when the stroke is performed in any of the upper and lower directions, the expansion-side variable throttle H (or the compression-side variable throttle J) is closed, and the liquid flow in the bypass flow path G is completely stopped, thereby achieving the highest damping force characteristics. Become.

[0031] Incidentally, both transmission paths M, since the constant orifice b ₁ for cutting in the middle of the N, b ₂ is formed, at the time of low-frequency vibration is made the transmission of the aforementioned hydraulic pressure to the high damping force characteristic However, during high-frequency vibration, the transmission of hydraulic pressure is cut by the constant orifices b ₁ and b ₂ for cutting, whereby low damping force characteristics are maintained.

When the stroke direction of the shock absorber is changed,
Since the fluid pressure in the upper chamber A or the lower chamber B, which has been rising, decreases, the liquid generated between the chambers A, B and the pressure receiving chambers D ₁ , D _2. the pressure difference, the valve portion 14c of the check plate 14 and 20, one for opening the 20c, thereby it until receiving chamber D ₁ that has been raised, constant for cutting the fluid pressure in the D ₂ orifices b _1, b ₂ can be quickly bypassed and escaped. Therefore, it is possible to increase the stroke speed of the spool 31 and to improve the switching response of the damping force characteristic.

Next, the operation and effect of the piston rod in terms of strength during the process of the shock absorber will be described. In the frequency-sensitive hydraulic shock absorber according to the first embodiment of the present invention, as described above, the extension-side communication hole 3b is formed on the inner peripheral surface of the lower end of the shaft hole 3f of the piston 3 through the radial groove 3g. An annular groove 3h communicating with the piston rod 2 is formed, and the lower end small diameter stud portion 2a of the piston rod 2 to which the piston 3 is fastened and fixed.
As shown in FIG. 8 (an end view taken along the line IIX-IIX in FIG. 2), a cutting groove 2b is formed on the outer peripheral surface of the groove to cut axially from the position of the annular groove 3h to the lower end surface. In addition, the cutting groove 2b, the annular groove 3h, the radial groove 3g, the extension side communication hole 3b, and the opening hole 3d formed on the piston 3 side bypass the damping valves 3c and 3e, thereby forming the two chambers A. , B are formed so as to form a sub flow path g, and as shown in FIG. 13, a bypass flow path (second communication hole) is formed by a vertical hole formed in the axial center portion of the piston rod 3. In comparison with the conventional example, the piston rod 3
Although the reduced cross-sectional area becomes the same, the reduction in the thickness Y of the piston rod 3 can be minimized, thereby suppressing the reduction in the strength of the piston rod 3 due to the formation of the sub-flow path g. Will be able to do that.

In the frequency-sensitive hydraulic shock absorber according to the first embodiment of the present invention, as described above, a part of the sub flow path g is formed in the annular groove 3h and the radial groove 3h formed in the piston 3 side.
g, the extension-side communication hole 3b and the opening hole 3d allow the upper end of the cutting groove 2b formed on the piston rod 2 side to form the sub-flow path g to be aligned with the lateral portion generated during the stroke of the hydraulic shock absorber. The force can be set at a position lower than the load input point acting on the piston rod 2, whereby a decrease in the strength of the piston rod 2 can be significantly suppressed.

Next, the operation and effect when assembling the shock absorber will be described. In the frequency-sensitive hydraulic shock absorber according to Embodiment 1 of the present invention, as described above, the inner peripheral surface of the lower end of the axial hole 3f of the piston 3 facing the upper end of the cutting groove 2b constituting the sub flow passage g. Since the annular groove 3h communicating with the extension side communication hole 3b via the radial groove 3g is formed on the piston rod 2, the cutting groove 2b on the piston rod 2 side and the piston 3 side This eliminates the need for the circumferential alignment with the extension-side communication hole 3b, thereby improving the efficiency of the assembling work.

As in the prior art, the piston 3
When the lateral hole is formed in the piston rod 2 above the fastening portion of the above, when the piston rod on the upper chamber A side is provided with a rebound rubber, the rebound rubber is separately provided to prevent hole interference. Do or
Although it is necessary to take measures to prevent the rebound rubber from rising, in the first embodiment of the present invention, it is necessary to form a lateral hole in the piston rod 2 by using the extension side communication hole 3b on the piston 3 side. Therefore, such a problem does not occur, thereby enabling cost reduction.

(Embodiment 2) In the frequency-sensitive hydraulic shock absorber according to Embodiment 2 of the present invention, the annular groove and the radial groove forming a part of the sub-flow path g Since it is formed on the upper surface side and the other configuration is the same as that of the first embodiment of the present invention, the same components are denoted by the same reference numerals, and the description thereof will be omitted. I will explain only.

FIG. 9 is a sectional view showing the details of the piston 3. As shown in FIG. 9, the upper end inner peripheral surface of the shaft hole 3f of the piston 3 is extended through the radial groove 3j. While an annular groove 3k communicating with the communication hole 3b is formed,
On the outer peripheral surface of the small diameter stud portion 2a at the lower end of the piston rod 2 to which the piston 3 is fixedly fastened, a cutting groove (notch portion) 2c for cutting axially from the position of the annular groove 3k to the lower end surface. Is formed, and this cutting groove 2c
And the annular groove 3k, the radial groove 3j, and the extension side communication hole 3b.
And a sub flow path (second communication hole) that connects the two chambers A and B by bypassing the damping valves 3c and 3e by the opening 3d.
g is formed. In the frequency-sensitive hydraulic shock absorber according to the second embodiment of the present invention, since it is configured as described above,
The same operations and effects as those of the first embodiment of the present invention can be obtained.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to the embodiments of the present invention, and design changes may be made without departing from the gist of the present invention. The present invention is also included in the present invention.

For example, in the embodiment of the present invention, the cutting groove 2c formed on the outer peripheral surface of the small diameter stud portion 2a at the lower end is formed as shown in FIG.
Although it was formed in a V-shaped cross section as shown in FIG. 10, it may be formed in a planing shape as shown in FIG. 10, and formed not only on one side but also on both sides as shown in FIGS. In this case, the cutting in one step is also possible.

[0041]

As described above, in the hydraulic shock absorber according to the present invention, the hydraulic shock absorber is formed on the piston rod and bypasses the extension side damping force generating mechanism to connect the upper chamber and the lower chamber. Is formed by a notch portion that cuts off the outer peripheral surface in the axial direction from the lower end surface of the piston rod, and the upper end side of the notch portion communicates with the first communication hole. An effect is obtained that the reduction in the strength of the piston rod due to the formation of the communication hole can be suppressed and the processing cost can be reduced. Further, in the hydraulic shock absorber according to the second aspect, an annular groove communicating with the first communication hole is formed on an inner peripheral surface of the axial hole of the piston facing the upper end of the notch constituting the second communication hole. Thus, in the process of assembling the piston with the piston rod, the circumferential alignment between the notch and the first communication hole is not required, and the efficiency of the assembling operation can be improved. Further, in the hydraulic shock absorber according to the third aspect, the upper end of the notch constituting the second communication hole is
Since the hydraulic shock absorber is set to a position below the load input point acting on the piston rod due to the lateral force generated during the stroke of the hydraulic shock absorber, a decrease in the strength of the piston rod can be significantly suppressed.

[Brief description of the drawings]

FIG. 1 is an overall sectional view showing a frequency-sensitive hydraulic shock absorber according to Embodiment 1 of the present invention.

FIG. 2 is an enlarged view of a portion E in FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing a main part (a part F in FIG. 1) of the frequency-sensitive hydraulic buffer according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a retainer.

FIG. 5 is a plan view showing an extension-side check plate.

FIG. 6 is a plan view showing an extension-side orifice plate.

FIG. 7 is an enlarged view of a part P in FIG. 3;

FIG. 8 is an end view taken along line IIX-IIX in FIG. 2;

FIG. 9 is a cross-sectional view illustrating a piston portion of the frequency-sensitive hydraulic shock absorber according to Embodiment 2 of the present invention.

FIG. 10 is an end view showing another example of a cutting groove.

FIG. 11 is an end view showing another example of a cutting groove.

FIG. 12 is an end view showing another example of a cutting groove.

FIG. 13 is a sectional view of a piston rod in a conventional example.

[Explanation of symbols]

 A Upper chamber B Lower chamber g Sub flow path (second communication hole) 1 Cylinder 2 Piston rod 2b Cutting groove (notch) 3 Piston 3b Extension communication hole (first communication hole) 3e Extension damping valve (extension damping) 3f Shaft center hole 3h Annular groove 2c Cutting groove (notch) 3k Annular groove

Claims (3)

[Claims] 1. A cylinder, a piston slidably provided in a state of defining an upper chamber and a lower chamber in the cylinder, and a state in which one end of the cylinder penetrates a shaft hole formed in the piston. A piston rod fixed and having the other end protruding outside the cylinder, a first communication hole formed in the piston and communicating between the upper chamber and the lower chamber; and the first communication hole. An extension-side damping force generating mechanism for generating damping force by restricting only the flow of the hydraulic fluid from the upper chamber to the lower chamber in the first communication hole and generating a damping force; A second communication hole that is formed and communicates between the upper chamber and the lower chamber by bypassing the extension-side damping force generation mechanism, wherein the second communication hole is a lower end surface of the piston rod. Notch that cuts the outer peripheral surface in the axial direction from A hydraulic buffer, wherein the upper end of the notch communicates with the first communication hole. 2. An annular groove communicating with the first communication hole is formed on an inner peripheral surface of a shaft hole of the piston facing an upper end of the notch constituting the second communication hole. Item 6. The hydraulic pressure absorber according to Item 1. 3. An upper end of the notch constituting the second communication hole is set to a position below a load input point acting on the piston rod due to a lateral force generated during a stroke of the hydraulic shock absorber. 3. The method according to claim 1, wherein
2. The hydraulic shock absorber according to 1.