JP2002070913A - Hydraulic shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an increasing trend in damping force in a high-speed range of a hydraulic shock absorber from decreasing owing to an increase in oil temperature and a reduction in oil viscosity. SOLUTION: The hydraulic shock absorber 10 is so constructed that annular clearances 82 and 83 are defined between the outer circumference of a piston 33 and the inner circumference of a piston ring 37, and that at least either of an expansion-side communicating passage 85 and a pressure-side communicating passage 86 is defined in the piston 33 to connect at least either of an expansion-side passage 40 and a pressure-side passage 39 to the annular clearance 82, 83.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a hydraulic shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a hydraulic shock absorber, two oil chambers defined on both sides of a piston in a cylinder are made conductive through an orifice or a damping valve provided in the piston.
Some piston rods exert a damping force based on their flow path resistance acting on oil passing through an orifice or damping valve as the piston rod moves. This damping force is proportional to, for example, the square (orifice) or the 2/3 power (damping valve) of the moving speed of the piston rod.

[0003]

SUMMARY OF THE INVENTION In a hydraulic shock absorber,
When the moving speed of the piston rod becomes high, the resistance loss when the oil passes through the orifice or the damping valve becomes heat and raises the oil temperature, and thus lowers the viscosity of the oil, it is based on the orifice or the damping valve. This reduces the tendency of the damping force to increase.

In Japanese Patent Application Laid-Open No. 10-274273, the friction generated by expanding the friction material provided on the outer periphery of the piston with the oil supplied by the oil supply device and pressing the friction material against the inner surface of the cylinder. A device that adjusts the damping characteristic of a hydraulic shock absorber by a force is disclosed. However, in this conventional technique, the frictional force generated by the friction material does not depend on the moving speed of the piston rod, so the increasing tendency of the damping force in a high-speed region is reduced by an increase in oil temperature and a decrease in oil viscosity. There is no effect of avoiding doing so.

An object of the present invention is to prevent the tendency of the damping force of a hydraulic shock absorber in a high speed range to decrease due to an increase in oil temperature and a decrease in oil viscosity.

[0006]

According to a first aspect of the present invention, a piston rod is movably inserted in an axial direction into a cylinder filled with hydraulic oil, and a piston is provided at an insertion end of the piston rod into the cylinder. In a hydraulic shock absorber in which two oil chambers are partitioned on both sides of a piston, a piston ring which is in sliding contact with the inner circumference of the cylinder is fitted on the outer periphery of the piston, and an orifice communicating with the two oil chambers is formed in the piston. An annular gap is provided between the outer circumference of the piston ring and the inner circumference of the piston ring, and a communication path for connecting at least one of the two oil chambers to the annular gap is provided in the piston.

According to a second aspect of the present invention, in the first aspect of the present invention, the communication passage further divides each of the two oil chambers into an annular gap formed on an outer periphery of the piston through an orifice of the piston. It is intended to be in communication.

According to a third aspect of the present invention, in the first or second aspect, two seal members are provided in the axial direction between the piston and the piston ring, and the annular gap is provided between the two seal members. And the communication path is opened in the annular gap.

According to a fourth aspect of the present invention, a piston rod is inserted movably in an axial direction into a cylinder filled with hydraulic oil,
A piston is provided at the insertion portion of the piston rod into the cylinder, two oil chambers are defined on both sides of the piston in the cylinder, and a piston ring which is in sliding contact with the inner circumference of the cylinder is fitted on the outer periphery of the piston, and the two oil chambers are formed. A piston in a hydraulic shock absorber in which an extension side flow path and a compression side flow path communicating with each other are formed in a piston, an extension side attenuation valve is provided at an open end of the extension side flow path, and a compression side attenuation valve is provided at an open end of the compression side flow path An annular gap is provided between the outer circumference of the piston ring and the inner circumference of the piston ring, and at least one of an extension side communication path and a compression side communication path that communicates at least one of the expansion side flow path and the compression side flow path with the annular gap. One is provided on the piston.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, three seals are provided in the axial direction between the piston and the piston ring, and two seals adjacent to each other on one axial side are provided. The annular gap is formed between the two sealing materials on the other side and between the two sealing materials adjacent to each other on the other side, and the extension side communication path is formed in the one annular shape between the two sealing materials adjacent on the one side. An opening is formed in the gap, and the pressure-side communication passage is opened in the other annular gap between the two sealing materials adjacent to each other on the other side.

According to a sixth aspect of the present invention, a piston rod is inserted movably in an axial direction into a cylinder filled with hydraulic oil,
A piston is provided at the insertion end of the piston rod into the cylinder, two oil chambers are defined on both sides of the piston in the cylinder, and a piston ring that is in sliding contact with the inner circumference of the cylinder is fitted on the outer periphery of the piston, and the two oil chambers are fitted. In the hydraulic shock absorber, the extension side flow path and the compression side flow path that respectively communicate with each other are formed in the piston, the extension side attenuation valve is provided at the open end of the extension side flow path, and the compression side attenuation valve is provided at the open end of the compression side flow path. An annular gap is provided between the outer circumference of the piston and the inner circumference of the piston ring, and a communication path is provided in the piston to connect the extension-side flow path and the pressure-side flow path to each other via the annular gap.

[0012]

According to the first aspect of the present invention, the following operations are provided. When the piston rod expands and contracts, the orifice generates a damping force proportional to the square of the moving speed of the piston rod, and a speed-dependent pressure difference is generated between both ends (two oil chambers) of the orifice. Therefore, when the piston rod repeats expansion and contraction, at least one of the expansion side and the pressure side of the oil chamber, which has been on the high pressure side, has a speed-dependent high pressure extending from the communication passage to the annular gap, which moves the piston ring in the radially expanding direction. Pushing apart creates a speed-dependent frictional force (frictional characteristic) between the piston ring and the cylinder. This increases the frictional force generated between the piston ring and the cylinder in the high-speed range, and reduces the tendency of the orifice-based damping force to decrease due to an increase in oil temperature and a decrease in oil viscosity. Make up and avoid by increasing

According to the second aspect of the present invention, the following operations are provided. By using an orifice provided in a piston in a part of a communication passage connecting each of two oil chambers to an annular gap, providing a communication passage by drilling from the outer periphery of the piston toward the orifice. And processing becomes easy.

According to the third aspect of the present invention, the following operations are provided. By providing two seal members between the piston and the piston ring, the sealing performance of the annular gap can be improved.

According to the fourth aspect of the invention, the following operation is provided. When the piston rod expands and contracts, the damping valves on the extension side and the compression side generate a damping force proportional to the 2/3 power of the moving speed of the piston rod, and both ends of the damping valve (two oil chambers).
Produces a speed-dependent pressure difference. Therefore, when the piston rod repeats expansion and contraction, at least one of the expansion side and the compression side of the oil chamber, which has become the high pressure side, has a speed-dependent high pressure extending from the communication path between the expansion side and the compression side to the annular gap, and this is the piston ring. Is pushed open in the diameter-expanding direction to generate a speed-dependent frictional force (frictional characteristic) between the piston ring and the cylinder. As a result, in a high-speed range, the piston ring increases the frictional force generated between the cylinder and the cylinder, and the increasing tendency of the damping force based on the extension-side and compression-side damping valves is reduced by increasing the oil temperature and decreasing the viscosity of the oil. This is compensated and avoided by the increase in the frictional force.

According to the fifth aspect of the invention, the following effects are obtained. By providing three sealing members in the axial direction between the piston and the piston ring, the sealing performance of the two annular gaps can be improved, and independent friction characteristics can be obtained on the extension side and the compression side.

According to the sixth aspect of the invention, the following operations are provided. When the piston rod expands and contracts, the extension and compression side damping valves generate a damping force in proportion to the square of the moving speed of the piston rod, and a speed-dependent pressure is applied between both ends (two oil chambers) of the damping valve. Make a difference. Therefore, when the piston rod repeats expansion and contraction, the speed-dependent high pressure on both the extension side and the compression side of the oil chamber, which has been on the high pressure side, extends from those communication passages to a common annular gap, which expands the piston ring. It is pushed radially open to generate a speed-dependent frictional force (frictional characteristic) between the piston ring and the cylinder. As a result, in a high-speed range, the piston ring increases the frictional force generated between the cylinder and the cylinder, and the increasing tendency of the damping force based on the extension-side and compression-side damping valves is reduced by increasing the oil temperature and decreasing the viscosity of the oil. This is compensated and avoided by the increase in the frictional force.

[0018]

FIG. 1 is a sectional view showing a hydraulic shock absorber of a first embodiment, FIG. 2 is a sectional view showing a damping force generator of FIG. 1, and FIG. 3 is a damping force generator of a second embodiment. FIG. 4 is a sectional view showing a damping force generator according to a third embodiment.

(First Embodiment) (FIGS. 1 and 2) As shown in FIG. 1, a hydraulic shock absorber 10 has a hollow piston rod 12 inserted into a cylinder 11 and is suspended between the cylinder 11 and an outer portion of the piston rod 12. The spring 13 is interposed.

The cylinder 11 has a vehicle body side mounting portion 14,
The piston rod 12 includes a wheel-side mounting portion 15. A spring support adjusting ring 16 and a spring support 17 are screwed around the outer periphery of the cylinder 11, and the spring support 1 is mounted on the piston rod 12.
8 is fixed, a suspension spring 13 is interposed between the spring support 17 and the spring support 18, and the spring support adjustment ring 1
The set length of the suspension spring 13 can be adjusted by the screwing of the spring support 6 and the spring receiver 17. The elastic force of the suspension spring 13 absorbs the impact force that the vehicle receives from the road surface.

The cylinder 11 has a rod guide 21 through which the piston rod 12 passes. The rod guide 21
The piston rod 12 is mounted on the cylinder 11 via an O-ring 22 in a liquid-tight manner, and the piston rod 12 is slidable in a liquid-tight manner on an inner diameter portion provided with an oil seal 23, a bush 24, and a dust seal 25. The cylinder 11 is provided with a compression side bumper 26 outside the rod guide 21, and at the time of maximum compression, the compression side bumper 26 abuts against a bumper stopper 27 provided in the piston rod 12 so that the maximum compression stroke can be regulated. Further, the cylinder 11 includes an extension-side bump rubber 28 inside the rod guide 21.

The hydraulic shock absorber 10 has a piston valve device (extension-side damping force generator) 30 and a base valve device (compression-side damping force generator) 60. Hydraulic shock absorber 1
0 is the piston valve device 30 and the base valve device 60
The expansion and contraction vibration of the cylinder 11 and the piston rod 12 due to the absorption of the impact force by the suspension spring 13 is suppressed by the damping force generated.

(Piston Valve Apparatus 30) (FIGS. 1 and 2) The piston valve apparatus 30 includes a rebound stopper / valve stopper 31, a pressure-side damping valve 32, a piston 33 at the end of the piston rod 12 inserted into the cylinder 11.
The extension side damping valve 34 and the valve stopper 35 are mounted, and these are fixed by the nut 36.

The piston 33 comes into sliding contact with the inside of the cylinder 11 in a liquid-tight manner via a piston ring 37 provided on the outer peripheral portion, and the inside of the cylinder 11 has a piston side oil chamber 38A in which the piston rod 12 is not accommodated, and a piston rod 12 Is partitioned into a rod-side oil chamber 38B in which is stored. The piston 33 includes a compression-side damping valve 32 at an open end, and a compression-side flow path 39 that enables communication between a piston-side oil chamber 38A and a rod-side oil chamber 38B. An expansion-side flow path 40 that allows the oil chamber 38A to communicate with the rod-side oil chamber 38B is provided.

In the piston valve device 30, a damping force adjusting rod 42 operated by a slider device 41 is passed through a hollow portion of the piston rod 12 so as to be able to advance and retreat. The opening area of the bypass passage 44 between the piston-side oil chamber 38A and the rod-side oil chamber 38B provided in the piston 12 is adjustable.

The slider device 41 includes the piston rod 12
Adjust holder 45 press-fitted and fixed to the wheel-side mounting portion 15 from a direction orthogonal to the axial direction of the piston rod 12.
An adjuster 46 pivotally attached to the adjust holder 45, and a ball 48 urged by a set spring in a direction perpendicular to the axis of the adjuster 46 to be engageable with the engaging concave portion on the adjust holder 45 side; And a slider 49 screwed to the screw portion of the adjuster 46. The adjuster 46 has an operation end side provided with an operation groove 46 </ b> A supported by the adjust holder 45, and the opposite end to the wheel side mounting portion 1.
5, is rotated by a tool engaged with the operation groove 46A, and the ball 48 is sequentially engaged with each of the engagement recesses arranged (equally arranged) at a plurality of positions in the circumferential direction of the adjustment holder 45, The adjusters 46 can be set to be switched to the rotation operation stop positions with a sense of moderation. On the other hand,
The slider 49 is screwed to the threaded portion of the adjuster 46, and the guide bolt 5 provided on the wheel-side mounting portion 15 is provided.
The leading end guide portion 0 is engaged with a guide groove provided in the axial direction of the slider 49. As a result, the slider device 41 moves the slider 49 by rotating the adjuster 46.
Can be advanced and retracted in a direction orthogonal to the axial direction of the adjustment rod 42.

The adjustment rod 42 is inserted into the hollow portion of the piston rod 12 in a liquid-tight manner via an O-ring 51, and adjusts the opening area of the bypass passage 44 by the needle valve 43 at the tip. At this time, the adjusting rod 42 holds the ball 52 rotatably held at the base end thereof by the thrust force based on the oil pressure of the piston side oil chamber 38A of the cylinder 11 by the tapered surface of the slider 49 described above. Pressed against.

That is, in the piston valve device 30, the tapered surface of the slider 49 is brought into contact with the ball 52 at the base end of the adjustment rod 42, and the slider 49 is rotated based on a rotation operation applied to the adjuster 46 of the slider device 41. The adjustment rod 42 is advanced and retracted in the axial direction by the advance and retreat, and the opening area of the bypass flow path 44 is adjusted by moving the needle valve 43 at the tip of the adjustment rod 42.

Therefore, when the hydraulic shock absorber 10 is compressed, the oil in the piston-side oil chamber 38A passes through the pressure-side flow path 39, opens the pressure-side damping valve 32, and is guided to the rod-side oil chamber 38B.

When the hydraulic shock absorber 10 is extended, when the relative speed between the cylinder 11 and the piston rod 12 is low, the oil in the rod-side oil chamber 38B passes through the bypass flow path 44 having the needle valve 43 and the piston-side oil. It flows into the chamber 38, and the expansion side damping force is generated by the throttle resistance of the needle valve 43 during this time.

When the relative speed between the cylinder 11 and the piston rod 12 is medium or high when the hydraulic shock absorber 10 is extended, the oil in the rod-side oil chamber 38B passes through the extension-side flow path 40 and operates the extension-side damping valve 34. Deflected and deformed piston oil chamber 38A
To produce a damping force on the extension side.

(Base Valve Apparatus 60) (FIG. 1) The base valve apparatus 60 includes a reservoir 61
And the inside sealed by the cap 62 of the reservoir 61 is a diaphragm type (a free piston type is also possible).
Are partitioned into an oil chamber and a gas chamber by the partition member (not shown). The cap 62 is provided with a gas filling valve (not shown) for filling the gas chamber with a pressurized gas.

In the base valve device 60, a valve housing 71 is provided in a communication area between the piston-side oil chamber 38A of the cylinder 11 and the oil chamber of the reservoir 61, and the plug housing 72 is screwed to the cylinder 11 by a plug bolt 72. The valve housing 71 is fixed. Valve housing 71
, A piston 73 is fixed, and the piston 73 is provided with a flow path 74. A bypass forming bolt 75 is fixed to the center of the piston 73, and a compression side valve 76 that opens the flow path 74 when compressed around the center of the bypass forming bolt 75, and an expansion side valve that conducts when the flow path 74 extends. (Check valve) (not shown) is provided.

In the base valve device 60, an adjustment lever 77 is fitted to the plug bolt 72 in a liquid-tight manner, and an adjustment rod 78 is rotatably mounted on the adjustment lever 77. The needle valve 79 engages with and can move relatively in the axial direction.
The needle valve 79 moves forward and backward with respect to the bypass passage 75A of the bypass forming bolt 75, and the bypass passage 75A
Can be adjusted.

Therefore, when the hydraulic shock absorber 10 is compressed, oil corresponding to the volume of the piston rod 12 that has entered the cylinder 11 flows from the piston side oil chamber 38A into the bypass passage 75A of the bypass forming bolt 75 or the flow of the piston 73. The oil is discharged to the oil chamber of the reservoir 61 through the passage 74. At this time, when the relative speed between the cylinder 11 and the piston rod 12 is low, the compression side damping force is obtained by the throttle resistance of the needle valve 88 provided in the bypass flow path 75A.
When the relative speed between the cylinder 11 and the piston rod 12 is medium to high, the flow path 74
The oil passing through the reservoir 6 causes the pressure side valve 76 to bend and deform, and the reservoir 6
1 to generate a compression-side damping force.

When the hydraulic shock absorber 10 is extended, the cylinder 1
The oil corresponding to the withdrawal volume of the piston rod 12 withdrawing from 1 is returned from the oil chamber of the reservoir 61 to the piston-side oil chamber 38A through the extension valve and the flow path 74.

However, in the hydraulic shock absorber 10, the tendency of the damping force of the compression damping valve 32 and the expansion damping valve 34 to increase in the high-speed range is reduced by the increase in the oil temperature and the decrease in the viscosity of the oil. To avoid this, the piston valve device 30 is provided with the following configuration.

That is, the piston ring 37 made of an elastic material is mounted in an annular groove 81 provided on the outer periphery of the piston 33, and annular gaps 82 and 83 are provided between the outer periphery of the piston 33 and the inner periphery of the piston ring 37. . At this time, piston 3
Three O-rings 84A to 84C (sealing materials) engaged with ring grooves provided in the piston 33 are provided at three axial positions between the piston ring 3 and the piston ring 37, respectively. O-ring 84A and O-ring 84B adjacent to each other
An annular gap 82 is formed between the O-rings 84B and 84C, and an annular gap 83 is formed between the adjacent O-rings 84B and 84C on the other side. The piston 33 is provided with an expansion-side communication path 85 that connects the expansion-side flow path 40 to the annular gap 82 and a compression-side communication path 86 that connects the compression-side flow path 39 to the annular gap 83.

Therefore, according to the present embodiment, the following operations are provided. When the piston rod 12 expands and contracts, the damping valves 32 and 34 on the extension side and the compression side generate a damping force proportional to the 2/3 power of the moving speed of the piston rod 12, and the damping valve 3
A speed-dependent pressure difference is created between the two ends (two oil chambers 38A, 38B) of the two and 34. Therefore, the piston rod 12
When repeatedly expands and contracts, the oil chamber 38A on the high pressure side,
The speed-dependent high pressure of each of the extension side and the compression side of 38B extends from the communication paths 85 and 86 on the extension side and the compression side to the annular gaps 82 and 83, which pushes the piston ring 37 open in the radially expanding direction, and A speed-dependent friction force (friction characteristic) is generated between the cylinders 11. This increases the frictional force generated between the piston ring 37 and the cylinder 11 in the high-speed range, and increases the damping valves 32, 3 on the extension side and the compression side.
The increase in the damping force based on No. 4 due to the increase in the oil temperature and the decrease in the viscosity of the oil is compensated for by the increase in the frictional force and is avoided.

By providing three O-rings 84A to 84C in the axial direction between the piston 33 and the piston ring 37, the sealing performance of the two annular gaps 82 and 83 is improved, and independent friction is provided on the extension side and the compression side. Properties can be obtained.

In the hydraulic shock absorber 10, only the extension-side communication passage 85 is provided if the speed-dependent friction characteristic is to be obtained only on the extension side, and if the friction characteristic is to be obtained only on the compression side, the compression-side Only the communication path 86 is provided.

Second Embodiment (FIG. 3) The second embodiment differs from the first embodiment in the configuration of the piston valve device 30. That is, the piston ring 37 is attached from an elastic body to the annular groove 91 provided on the outer periphery of the piston 33, and an annular gap 92 is provided between the outer periphery of the piston 33 and the inner periphery of the piston ring 37. At this time, at two axial positions between the piston 33 and the piston ring 37,
Two O-rings 93A, 93B (seal material) engaged with a ring groove provided in the piston 33 were provided, and an annular gap 92 was formed between the two O-rings 93A, 93B. And the extension side channel 40 and the pressure side channel 3
9 communicate with each other to the annular gap 92;
95 is provided on the piston 33, and as a result, the
And the pressure side flow path 39 are communicated with each other through communication paths 94 and 95 and an annular gap 92.

Therefore, according to the present embodiment, the following operations are provided. When the piston rod 12 expands and contracts, the extension side and compression side damping valves 32 and 34 generate a damping force in proportion to the square of the moving speed of the piston rod 12, and the damping valve 32,
A speed-dependent pressure difference is created between the two ends (the two oil chambers 38A, 38B) of 34. Therefore, when the piston rod 12 repeats expansion and contraction, the oil chambers 38A and 38
The speed-dependent high pressures on both the extension side and the compression side of B extend from their communication passages 94, 95 into a common annular gap 92, which pushes the piston ring 37 open in the radially expanding direction, and the piston ring 37 and the cylinder 11 Generates a speed-dependent frictional force (frictional characteristics) during As a result, in the high-speed range, the piston ring 37 increases the frictional force generated between the piston 11 and the cylinder 11, and the increasing tendency of the damping force based on the extension-side and compression-side damping valves 32, 34 increases the oil temperature and the oil viscosity. The reduction due to the decrease in the frictional force is compensated for by the increase in the frictional force and is avoided.

By providing two O-rings 93A and 93B between the piston 33 and the piston ring 37,
The sealing performance of the annular gap can be improved.

(Third Embodiment) (FIG. 4) The third embodiment is different from the first embodiment in that an orifice 101 communicating the two oil chambers 38A and 38B is formed in the piston 33, and the outer periphery of the piston 33 is formed. And piston ring 3
An annular gap 102 is provided between the piston 33 and the inner periphery of the piston 7, and a communication passage 103 that connects each of the two oil chambers 38A and 38B to the annular gap 102 is provided.

At this time, the communication passage 103 is connected to the two oil chambers 3
Each of 8A and 38B communicates with the annular gap 102 via the orifice 101 of the piston 33. Further, two O-rings 104A and 104B (sealing material) engaged with a ring groove provided in the piston 33 are provided at two axial positions between the piston 33 and the piston ring 37, respectively. O-ring 104A,
An annular gap 102 is formed between the communication passages 104B.
3 was opened in this annular gap 102.

Therefore, according to the present embodiment, the following operations are provided. When the piston rod 12 expands and contracts, the orifice 1
01 generates a damping force proportional to the square of the moving speed of the piston rod 12, and generates a speed-dependent pressure difference between both ends of the orifice 101 (the two oil chambers 38A and 38B).
Therefore, when the piston rod 12 repeats expansion and contraction,
Each of the speed-dependent high pressures on the extension side and the compression side of the oil chambers 38A and 38B on the high pressure side extends from the communication passage 103 to the annular gap 102, and pushes the piston ring in the radially expanding direction, thereby opening the piston ring and the cylinder. 11 a speed-dependent frictional force (frictional characteristic) is generated. This increases the frictional force generated between the piston ring and the cylinder 11 in the high-speed range, and reduces the tendency of the damping force based on the orifice 101 to decrease due to an increase in oil temperature and a decrease in oil viscosity. Make up and avoid by increasing the frictional force.

By using an orifice 101 provided in a piston in a part of a communication passage 103 which connects each of the two oil chambers 38A and 38B to an annular gap 102, the orifice 101 is drilled from the outer periphery of the piston toward the orifice 101. By providing this, the communication path 103 can be provided, which facilitates processing.

2 between the piston 33 and the piston ring
By providing two O-rings 104A, 104B,
The sealing performance of the annular gap 102 can be improved.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and the design may be changed without departing from the scope of the present invention. The present invention is also included in the present invention.

[0051]

As described above, according to the present invention, it is possible to prevent the tendency of the damping force of the hydraulic shock absorber in the high speed range to decrease due to an increase in the oil temperature and a decrease in the viscosity of the oil.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a hydraulic shock absorber according to a first embodiment.

FIG. 2 is a sectional view showing the damping force generator of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a damping force generator according to a second embodiment.

FIG. 4 is a cross-sectional view illustrating a damping force generator according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 10 hydraulic shock absorber 11 cylinder 12 piston rod 33 piston 37 piston ring 38A, 38B oil chamber 82, 83 annular gap 84A to 84CO O-ring (seal material) 85 extension side communication passage 86 compression side communication passage 92 annular gap 93A, 93B O-ring (seal material) 94, 95 Communication passage 101 Orifice 102 Annular gap 104A, 104B O-ring (seal material) 103 Communication passage

Claims (6)

[Claims] 1. A piston rod is movably inserted in an axial direction into a cylinder filled with hydraulic oil, and a piston is provided at an end of the piston rod inserted into the cylinder. Two oil chambers are defined on both sides of the piston in the cylinder. In the hydraulic shock absorber in which an orifice communicating with the two oil chambers is formed in the piston by fitting a piston ring which is in sliding contact with the inner circumference of the cylinder on the outer circumference of the piston, the gap between the outer circumference of the piston and the inner circumference of the piston ring A hydraulic passage, wherein a communication passage connecting at least one of the two oil chambers to the annular clearance is provided in the piston. 2. The communication passage connects each of two oil chambers,
The hydraulic shock absorber according to claim 1, wherein the hydraulic shock absorber communicates with an annular gap formed on an outer periphery of the piston via an orifice of the piston. 3. An annular gap is provided between the piston and the piston ring in the axial direction, the annular gap is formed between the two seals, and the communication path opens into the annular gap. The hydraulic shock absorber according to claim 1 or 2, wherein 4. A piston rod is inserted movably in the axial direction into a cylinder filled with hydraulic oil, and a piston is provided at a portion where the piston rod is inserted into the cylinder. Two oil chambers are defined on both sides of the piston in the cylinder. Then, a piston ring that is in sliding contact with the inner periphery of the cylinder is fitted on the outer periphery of the piston, and an expansion-side flow path and a pressure-side flow path that respectively communicate the two oil chambers are formed in the piston. In the hydraulic shock absorber in which the expansion-side damping valve is provided with a compression-side damping valve at the open end of the compression-side flow path, an annular gap is provided between the outer circumference of the piston and the inner circumference of the piston ring, and the expansion-side flow path and the compression-side flow A hydraulic shock absorber characterized in that at least one of an extension-side communication passage and a compression-side communication passage that communicates at least one of the passages with the annular gap is provided in the piston. 5. Three sealing members are provided in the axial direction between the piston and the piston ring, between two adjacent sealing members on one axial side and two adjacent sealing members on the other side. Between the two sealing materials adjacent to each other on the one side, and the compression-side communication path is formed on the other side. 5. The hydraulic shock absorber according to claim 4, wherein the hydraulic shock absorber opens in the other annular gap between two adjacent seal members. 6. A piston rod is inserted movably in an axial direction into a cylinder filled with hydraulic oil, and a piston is provided at an insertion end of the piston rod into the cylinder. Two oil chambers are provided on both sides of the piston in the cylinder. A piston ring is fitted on the outer periphery of the piston and slides on the inner periphery of the cylinder, and an expansion-side flow path and a pressure-side flow path that respectively communicate the two oil chambers are formed in the piston. In the hydraulic shock absorber in which the expansion side damping valve is provided at the opening end of the compression side flow path, an annular gap is provided between the outer circumference of the piston and the inner circumference of the piston ring, and the expansion side flow path and the compression side are provided. A hydraulic shock absorber characterized in that a communication path for communicating a flow path with each other through the annular gap is provided in the piston.