JP2011033053A - Hydraulic shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To force a pressurization spring to reduce a force influencing a free piston in the latter half of a compression stroke of a hydraulic shock absorber and to reduce an excessive resistance to a compression stroke of a piston rod entering the inside of a cylinder tube when pressurizing an oil chamber in the cylinder tube with the free piston energized by the pressurization spring. <P>SOLUTION: A hydraulic shock absorber containing a pressurization spring 66 for energizing a free piston 61 toward a sub piston 52 side, is provided with an energization means 74 which movably keeps a relief piston 71 opposed to a free piston 61 above an opening of a communication passage 64 for communicating the inside of a cylinder tube 16 to a reservoir 30 and energizes the relief piston 71 toward the free piston 61 side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydraulic shock absorber.

  As described in Patent Document 1, as a hydraulic shock absorber, an axle side tube is slidably inserted into a vehicle body side tube, and a cylinder tube of a damper connected to the vehicle body side tube inside the vehicle body side tube is connected to the axle side tube. A main piston provided on a piston rod connected to the axle side tube is slidably inserted inside the cylinder tube, and the inside of the cylinder tube is partitioned into a piston side oil chamber and a rod side oil chamber by this main piston. An expansion-side damping valve is provided in the flow path connecting the piston-side oil chamber and the rod-side oil chamber, and a sub-piston facing the main piston is provided above the main piston inside the cylinder tube. A sub-tank chamber is defined above the piston-side oil chamber, and the piston-side oil chamber and sub-tank of the sub-piston are separated. A compression-side damping valve is provided in the flow path that enables the communication of the chamber, and a free piston that is opposed to the sub-piston is movably provided above the sub-piston inside the cylinder tube, and the sub-tank inside the cylinder tube is provided by this free piston. A volume compensation chamber is defined above the chamber, and when the free piston moves to a predetermined position, a communication path is provided to connect the sub tank chamber between the free piston and the sub piston to a reservoir outside the cylinder tube. Some have a pressure spring that urges toward the sub-piston side.

  In this hydraulic shock absorber, every time the piston rod strokes, the excess oil that adheres to the piston rod from the reservoir oil chamber and moves into the cylinder tube moves the free piston to a predetermined position. The oil can be returned from the sub tank chamber to the reservoir outside the cylinder tube via the communication path of the cylinder tube.

  The hydraulic shock absorber has a pressure spring that biases the free piston toward the sub piston. The free piston pressurizes the sub tank chamber, and this pressurizing action is propagated into the cylinder tube via the sub piston pressure side damping valve, and the damping force characteristics of the pressure side damping valve in the compression stroke when the piston rod enters the cylinder tube. It is intended to stabilize.

Patent 2870678

  In the hydraulic shock absorber described in Patent Document 1, the hydraulic shock absorber required to absorb the impact force that the vehicle receives from the road surface in the compression stroke in which the axle tube enters the vehicle body side tube and the piston rod enters the cylinder tube. The reaction force is applied to the spring force of the suspension spring that is interposed between the vehicle body side tube and the axle side tube and compressed, and to the gas chamber of the reservoir provided outside the damper inside the vehicle body side tube and the axle side tube. It is generated by the spring force of the gas that is closed and pressurized. Therefore, in the compression stroke of the hydraulic shock absorber, it is necessary to ensure a certain gas spring force by the gas chamber of the reservoir.

  However, the above-described gas spring force secured by the gas chamber of the reservoir during the compression stroke of the hydraulic shock absorber extends from the reservoir to the sub tank chamber via the communication path of the cylinder tube, and thus free together with the spring force of the above-described pressure spring. The piston is energized to pressurize the oil chamber inside the cylinder tube, and the resistance against the compression stroke of the piston rod entering the inside of the cylinder tube. In particular, in the latter half of the compression stroke, the gas spring force secured by the gas chamber of the reservoir and the spring force of the pressurizing spring exert excessive resistance against the entrance of the piston rod, impairing shock absorption performance and impairing riding comfort. There is a fear.

  An object of the present invention is to reduce the spring force exerted on the free piston by the pressurizing spring in the second half of the compression stroke of the hydraulic shock absorber when pressurizing the oil chamber in the cylinder tube by the free piston biased by the pressurizing spring. This is to reduce excessive resistance to the compression stroke of the piston rod entering the inside of the tube.

  In the first aspect of the present invention, the axle side tube is slidably inserted into the vehicle body side tube, and the cylinder tube of the damper connected to the vehicle body side tube inside the vehicle body side tube is connected to the axle side inside the axle side tube. A main piston provided on a piston rod connected to the tube is slidably inserted, and the inside of the cylinder tube is partitioned into a piston side oil chamber and a rod side oil chamber by this main piston, and the piston side oil chamber and rod of the main piston are divided. The expansion side damping valve is provided in the flow path connecting the side oil chambers, and the sub-piston facing the main piston is provided above the main piston inside the cylinder tube, and the piston-side oil chamber inside the cylinder tube is provided by this sub-piston. A subtank chamber is defined above the pipe to enable communication between the piston side oil chamber of the subpiston and the subtank chamber. A pressure-side damping valve is provided in the cylinder tube, and a free piston facing the sub-piston is movably provided above the sub-piston inside the cylinder tube, and the volume compensation chamber is defined above the sub-tank chamber inside the cylinder tube by this free piston. When the free piston moves to a predetermined position, a communication passage is provided to connect the sub tank chamber between the free piston and the sub piston to the reservoir outside the cylinder tube, with the free piston facing the sub piston. In the hydraulic shock absorber having a pressurizing spring, a relief piston facing the free piston is movably provided inside the cylinder tube above the opening of the communication path, and the relief piston is placed on the free piston side. It has an urging means to urge toward .

  According to a second aspect of the invention, in the first aspect of the invention, the urging means is made of an elastic body.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the relief piston further defines a relief chamber above the volume compensation chamber inside the cylinder tube.

(Claim 1)
(a) In a hydraulic shock absorber that pressurizes an oil chamber in a cylinder tube by a free piston urged by a pressure spring, the cylinder tube is opposed to the free piston above the opening of the communication passage communicating with the reservoir. The relief piston is provided so as to be movable, and has a biasing means for biasing the relief piston toward the free piston. Accordingly, in the compression stroke of the hydraulic shock absorber, when the free piston moves upward by an amount corresponding to the piston rod entering the cylinder tube, the gas pressure (gas spring force) extending from the reservoir gas chamber to the sub tank chamber via the communication path is increased. The pressure is increased by the contraction of the vehicle body side tube and the axle side tube, and this gas pressure compresses the urging means that urges the relief piston and moves the relief piston upward. The amount of compression deflection of the pressure spring interposed therebetween, in other words, the spring force exerted on the free piston by the pressure spring is reduced by the amount of upward movement of the relief piston. Since the gas pressure (gas spring force) from the gas chamber of the reservoir to the sub tank chamber via the communication path is higher in the second half than in the first half of the compression stroke, the degree of reduction of the spring force exerted on the free piston by the pressurizing spring is Larger in the second half than in the first half of the compression stroke. As a result, the pressure spring backed up by the relief piston biased by the biasing means pressurizes the sub tank chamber to a necessary and sufficient level in the first half of the compression stroke to stabilize the damping force characteristic of the compression side damping valve. In the latter half of the compression stroke, the pressurizing spring reduces the degree of pressurization of the sub tank chamber to reduce the resistance to the piston rod that enters the cylinder tube, ensuring shock absorbing performance and improving ride comfort.

(Claim 2)
(b) The urging means for the relief piston can be constituted by an elastic body such as a metal coil spring or rubber.

(Claim 3)
(c) The relief piston partitions the relief chamber above the volume compensation chamber inside the cylinder tube. Therefore, the spring force of the gas sealed in the sealed relief chamber can be used as an urging means for the relief piston.

FIG. 1 is an overall cross-sectional view showing the most extended state of the hydraulic shock absorber. FIG. 2 is a lower cross-sectional view of FIG. FIG. 3 is a top sectional view of FIG. FIG. 4 is an upper cross-sectional view showing the most compressed state of the hydraulic shock absorber.

  As shown in FIGS. 1 to 3, the front fork 10 (hydraulic shock absorber) has an axle side tube (inner tube) 12 slidably inserted into a vehicle body side tube (outer tube) 11. A suspension spring 13 is interposed therebetween, and the single cylinder damper 14 is inverted and is internally provided.

The vehicle body side tube 11 is supported on the vehicle body side, and the axle side tube 12 is coupled to the axle.
The upper end portion of the cylinder tube 16 (upper cylinder tube 16A) of the damper 14 is screwed to the upper end portion of the vehicle body side tube 11 via an O-ring, and the upper open end of the cylinder tube 16 is closed by a fork bolt 15. The fork bolt 15 is airtightly inserted into the inner periphery of the upper cylinder tube 16A via an O-ring and screwed.

  An oil lock collar 17 is fitted in a liquid-tight manner on the inner periphery of the lower end portion of the axle tube 12 via an O-ring. The oil lock collar 17 is fixed in a liquid-tight manner to the axle bracket 19 with an O-ring by a bottom bolt 18. It is. Further, a base end portion of a piston rod (hollow rod) 20 of the damper 14 is screwed to the bottom bolt 18 and locked by a lock nut 18A, and a tip end portion of the piston rod 20 is inserted into the cylinder tube 16. . The piston rod 20 is supported by a bush 21A of a rod guide 21 screwed into an opening on the lower end side of the cylinder tube 16 (lower cylinder tube 16B), penetrates the seal member 21B, and is inserted into the cylinder tube 16. Yes. The seal member 21 </ b> B has a unidirectional sealing function that seals an oil chamber 43 </ b> B (described later) of the cylinder tube 16 and prevents oil in the oil chamber 43 </ b> B from escaping out of the cylinder tube 16. An oil lock collar 22 is provided on the outer periphery of the rod guide 21. A rebound spring 23 is supported on the inner end face of the rod guide 21. The cylinder tubes 16A and 16B are connected and locked by a pipe nut 16C.

  The suspension spring 13 includes a spring receiver 24 mounted on the outer peripheral surface of the base end portion of the oil lock collar 17, and a perforated spring collar 25 (multiple spring collars) that are externally attached to the cylinder tube 16 (lower cylinder tube 16B) and locked in the axial direction. It is interposed between the spring receiver 26 fixed to the tip of the communication hole 25A). Also, an oil chamber 31 and a gas chamber 32 constituting a reservoir 30 are provided inside the vehicle body side tube 11 and the axle side tube 12 and outside the damper 14, and the oil chamber 31 and the gas chamber 32 form a free interface. The gas that is in contact with each other and confined in the gas chamber 32 constitutes a gas spring. The reaction force of the front fork 10 necessary to absorb the impact force that the vehicle receives from the road surface is generated by the spring force of the suspension spring 13 and the gas spring force based on the gas chamber 32, and the compression stroke of the front fork 10. Then, it is necessary to ensure a certain gas spring force by the gas chamber 32 of the reservoir 30.

  The damper 14 has a main valve device (extension side damping valve device) 40 and a sub valve device (pressure side damping valve device) 50. The damper 14 suppresses the expansion and contraction vibration of the vehicle body side tube 11 and the axle side tube 12 due to the absorption of the impact force by the suspension spring 13 and the gas spring of the gas chamber 32 by the damping force generated by the main valve device 40 and the sub valve device 50. To do.

(Main valve device 40)
The main valve device 40 has a piston holder 41 attached to the tip of the piston rod 20 and a main piston 42 attached to the piston holder 41. The main piston 42 partitions the inside of the cylinder tube 16 into a piston-side oil chamber 43A in which the piston rod 20 is not accommodated and a rod-side oil chamber 43B in which the piston rod 20 is accommodated, and slides in the cylinder tube 16. . The main piston 42 is provided with an extension side damping valve 44A and is provided with an extension side flow path 44 capable of connecting the piston side oil chamber 43A and the rod side oil chamber 43B, and a pressure side damping valve (check valve) 45A. The pressure side flow path 45 which enables communication between the oil chamber 43A and the rod side oil chamber 43B is provided.

  Further, the main valve device 40 passes the damping force adjusting rod 47 coupled to the adjuster 46 from the outside of the bottom bolt 18 through the hollow portion of the piston rod 20, and the damping force that advances and retreats in the axial direction by rotating the adjuster 46. The flow passage area of the bypass passage 48 between the piston-side oil chamber 43A and the rod-side oil chamber 43B provided in the piston holder 41 can be adjusted by the needle 47A at the tip of the adjustment rod 47.

(Sub-valve device 50)
The sub-valve device 50 has a guide pipe 51 (support shaft) screwed to the fork bolt 15 screwed to the upper end of the upper cylinder tube 16A, and a piston holder 51A screwed to the tip of the guide pipe 51. The sub-piston 52 is held on the piston holder 51A by a nut 51B or the like. The sub-piston 52 is disposed relative to the main piston 42 inside the cylinder tube 16, is in fluid-tight contact with the inner peripheral portion of the upper cylinder tube 16A, and defines a sub-tank chamber 53 above the piston-side oil chamber 43A. The sub-piston 52 is provided with a pressure-side damping valve 54A to allow the piston-side oil chamber 43A and the sub-tank chamber 53 to communicate with each other, and the extension-side damping valve 55A is provided with a piston-side oil chamber 43A and the sub-tank chamber 53. Is provided with an extension-side flow channel 55 (not shown). The piston holder 51 </ b> A includes a bypass path 56 that bypasses the pressure side flow path 54 and the extension side flow path 55 to allow the piston side oil chamber 43 </ b> A and the sub tank chamber 53 to communicate with each other.

  The damping force adjustment rod 58 screwed into the fork bolt 15 includes an adjuster 59 and is inserted into the guide pipe 51 and is flown through the bypass flow path 56 by a needle 58A at the tip which is advanced and retracted in the axial direction by the rotation operation of the adjuster 59. The road area can be adjusted. The fork bolt 15 has an adjuster 59 and its holder 59A embedded in the center of the end face of the head.

  Further, the sub valve device 50 is provided inside the upper cylinder tube 16 </ b> A so that the free piston 61 is movable in an annular space between the upper cylinder tube 16 </ b> A and the guide pipe 51. A piston ring 61A is loaded in the outer peripheral annular groove of the free piston 61, and the free piston 61 slides liquid-tightly on the inner periphery of the upper cylinder tube 16A via the piston ring 61A. An oil seal 62 is loaded in the inner peripheral recess of the free piston 61, and the free piston 61 slides liquid-tightly on the outer periphery of the guide pipe 51 via the oil seal 62. The free piston 61 defines a sub tank chamber 53 communicating with the piston side oil chamber 43 </ b> A on the side of the sub piston 52, and a volume compensation chamber 63 above the sub tank chamber 53. The volume compensation chamber 63 communicates with the gas chamber 32 through a communication hole 64 (communication passage) provided in the enlarged diameter portion of the middle portion in the axial direction of the upper cylinder tube 16A. Each time the piston rod 20 of the front fork 10 strokes, the sub-valve device 50 brings the oil in the oil chamber 31 attached to the outer peripheral surface of the piston rod 20 from the seal member 21B of the rod guide portion 21 into the cylinder tube 16. . As a result, the hydraulic oil in the oil chambers 43A, 43B, 53 inside the cylinder tube 16 gradually increases, and the free piston 61 moves upward as shown in FIG. When the piston ring 61A on the outer periphery of the free piston 61 reaches the above-mentioned enlarged diameter portion (communication hole 64) on the inner periphery of the upper cylinder tube 16A, surplus oil in the cylinder tube 16 is transferred from the sub tank chamber 53 to the volume compensation chamber 63. , And a blow function for discharging to the oil chamber 31 outside the cylinder tube 16 via the communication hole 64 and the gas chamber 32.

  Further, the sub valve device 50 includes a pressure spring 66 that biases the free piston 61 toward the sub piston 52 in the volume compensation chamber 63 inside the upper cylinder tube 16A. The pressure spring 66 is interposed between a free piston 61 that is pressurized and supported by the oil chamber pressure of the cylinder tube 16 and a relief piston 71 described later. The pressure spring 66 is a compression coil spring. In the compression stroke in which the piston rod 20 enters the cylinder tube 16, the pressure spring 66 is compressed as a result of the upward movement of the piston rod 20 oil moving up the free piston 61. As a result, the oil chamber in the cylinder tube 16 is pressurized, and this pressurizing action is propagated to the oil chamber in the cylinder tube 16 via the compression side damping valve 54A of the sub-piston 52, thereby stabilizing the damping force characteristic of the compression side damping valve 54A. In addition, the cavitation of the oil chamber in the cylinder tube 16 at the time of extension is prevented.

Accordingly, the front fork 10 performs a damping action as follows.
(When compressed)
When the front fork 10 is compressed, in the sub valve device 50, a pressure side damping force is generated by the oil flowing through the needle 58A of the sub piston 52 or the pressure side damping valve 54A, and in the main valve device 40, the oil flowing through the pressure side damping valve 45A of the main piston 42. Thus, a compression-side damping force set according to need is generated.

(When stretched)
When the front fork 10 is extended, in the main valve device 40, the extension side damping force is generated by the oil flowing through the needle 47A of the main piston 42 or the extension side damping valve 44A, and the sub valve device 50 generates almost no damping force.

The damping force on the compression side and the extension side suppresses the stretching vibration of the front fork 10.
When the front fork 10 is most compressed, the oil lock collar 22 at the lower end of the lower cylinder tube 16B of the cylinder tube 16 is fitted to the oil lock collar 17 provided at the lower end of the axle side tube 12, The oil compressed between them causes an oil lock action and prevents the damper 14 from bottoming.

  Further, when the front fork 10 is fully extended, the lower end surface of the piston holder 41 provided on the piston rod 20 abuts on the rebound spring 23 supported by the rod guide 21 provided on the opening of the cylinder tube 16. , Stretching buffering.

  However, in the compression stroke of the front fork 10, the above-described gas spring force secured by the gas chamber 32 of the reservoir 30 extends from the reservoir 30 to the sub tank chamber 53 via the communication hole 64 of the cylinder tube 16. The free piston 61 is urged together with the spring force of 66 to pressurize the oil chamber inside the cylinder tube 16, and it becomes resistance against the compression stroke of the piston rod 20 entering the inside of the cylinder tube 16. In particular, in the latter half of the compression stroke, the gas spring force secured by the gas chamber 32 of the reservoir 30 and the spring force of the pressurizing spring 66 exert an excessive resistance against the ingress of the piston rod 20, resulting in shock absorption performance. There is a risk of damage to the ride.

  Therefore, in the sub valve device 50 of the front fork 10, when the oil chamber in the cylinder tube 16 is pressurized by the free piston 61 urged by the pressure spring 66, the pressure spring 66 is used in the compression stroke of the front fork 10. In order to reduce the spring force exerted on the free piston 61 in the latter half and reduce the excessive resistance to the compression stroke of the piston rod 20 entering the cylinder tube 16, the following configuration is provided.

  That is, the sub-valve device 50 is provided with a relief piston 71 opposed to the free piston 61 inside the upper cylinder tube 16A and above the opening of the communication hole 64, and this relief piston 71 is communicated with the inside of the upper cylinder tube 16A. It can be moved in the upper region from the opening of the hole 64. The lower outer circumferential annular groove of the relief piston 71 is loaded with a guide bush 71A, and the upper outer circumferential annular groove is loaded with an O-ring (seal ring) 71B. The free piston 71 is moved upward via the guide bush 71A and O-ring 71B. The inner circumference of the cylinder tube 16A slides liquid-tightly. An oil seal 72 is loaded in the inner peripheral recess of the relief piston 71, and the relief piston 71 slides liquid-tightly on the outer periphery of the guide pipe 51 via the oil seal 72. The relief piston 71 defines a relief chamber 73 above the volume compensation chamber 63 inside the upper cylinder tube 16 </ b> A and below the fork bolt 15.

  Further, the sub valve device 50 includes a biasing means 74 that biases the relief piston 71 toward the free piston 61. The urging means 74 is interposed between the relief piston 71 supported by the spring force of the pressure spring 66 and the fork bolt 15 by being precompressed. The biasing means 74 comprises a compression coil spring. The sub-valve device 50 seals the above-described relief chamber 73 against the external space of the fork bolt 15 and the reservoir 30, and the gas spring formed by the gas confined in the relief chamber 73 is also the urging means 74 described above. It is functioning as. The biasing means 74 may be composed of only the compression spring, or may be composed of only the gas spring of the relief chamber 73.

  The sub-valve device 50 is provided with the exhaust plugs 81 and 82 screwed to the fork bolt 15. The exhaust plug 81 makes it possible to discharge air that has entered the gas chamber 32 from the sliding portion of the vehicle body side tube 11 and the axle side tube 12 by the expansion and contraction of the front fork 10. The exhaust plug 82 allows the air that has entered the relief chamber 73 from the sliding portion of the upper cylinder tube 16 </ b> A and the relief piston 71 by the expansion and contraction of the front fork 10 to be discharged.

According to the present embodiment, the following operational effects can be obtained.
(a) In the front fork 10 that pressurizes the oil chamber in the cylinder tube 16 by the free piston 61 urged by the pressure spring 66, the inside of the cylinder tube 16 is located above the opening of the communication hole 64 that communicates with the reservoir 30. The relief piston 71 facing the free piston 61 is movably provided, and has a biasing means 74 that biases the relief piston 71 toward the free piston 61 side. Therefore, when the free piston 61 moves upward in the compression stroke of the front fork 10 by the amount of the piston rod 20 entering the cylinder tube 16, the gas extending from the gas chamber 32 of the reservoir 30 to the sub tank chamber 53 through the communication hole 64. The pressure (gas spring force) is increased by the amount of contraction of the vehicle body side tube 11 and the axle side tube 12, and this gas pressure compresses the urging means 74 that urges the relief piston 71 so that the relief piston 71 moves upward. As a result, the amount of compression deflection of the pressurizing spring 66 interposed between the relief piston 71 and the free piston 61, in other words, the spring force exerted on the free piston 61 by the pressurizing spring 66 is the same as that of the relief piston. This is reduced by the amount of upward movement. Since the gas pressure (gas spring force) from the gas chamber 32 of the reservoir 30 to the sub tank chamber 53 via the communication hole 64 is higher in the second half than in the first half of the compression stroke, the pressure spring 66 exerts on the free piston 61. The degree of force reduction is greater in the second half than in the first half of the compression stroke. As a result, the pressure spring 66 backed up by the relief piston 71 urged by the urging means 74 pressurizes the sub tank chamber 53 to a necessary and sufficient level in the first half of the compression stroke, and the damping force characteristic of the compression side damping valve 54A. To stabilize. The pressurizing spring 66 reduces the degree of pressurization of the sub-tank chamber 53 in the latter half of the compression stroke to reduce the resistance to the piston rod 20 entering the cylinder tube 16 to ensure shock absorbing performance and improve riding comfort.

  (b) The biasing means 74 for the relief piston 71 can be constituted by an elastic body such as a metal coil spring or rubber.

  (c) The relief piston 71 partitions the relief chamber above the volume compensation chamber 63 inside the cylinder tube 16. Therefore, the spring force of the gas sealed in the sealed relief chamber can be used as the biasing means 74 for the relief piston 71.

  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 even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention.

  The present invention relates to a hydraulic shock absorber that pressurizes an oil chamber in a cylinder tube by a free piston urged by a pressure spring, and is disposed above the opening of a communication passage that communicates the inside of the cylinder tube with a reservoir. An urging means for urging the relief piston toward the free piston is provided. Thereby, the spring force exerted on the free piston by the pressure spring in the second half of the compression stroke of the hydraulic shock absorber can be reduced, and the excessive resistance to the compression stroke of the piston rod entering the cylinder tube can be reduced.

10 Front fork (hydraulic shock absorber)
11 Car body side tube 12 Axle side tube 14 Damper 16 Cylinder tube 20 Piston rod 30 Reservoir 32 Gas chamber 42 Main piston 43A Piston side oil chamber 43B Rod side oil chamber 44 Extension side flow path 44A Extension side damping valve 52 Sub piston 53 Sub tank chamber 54 pressure side flow path 54A pressure side damping valve 61 free piston 63 volume compensation chamber 64 communication hole (communication path)
66 Pressurizing spring 71 Free piston 73 Relief chamber 74 Energizing means

Claims (3)

Insert the axle side tube slidably into the body side tube,
A main piston provided on a piston rod connected to the axle side tube inside the axle side tube is slidably inserted into a cylinder tube of a damper connected to the body side tube inside the body side tube. The inside of the cylinder tube is partitioned into a piston-side oil chamber and a rod-side oil chamber, and an extension-side damping valve is provided in the flow path connecting the piston-side oil chamber and the rod-side oil chamber of the main piston,
A sub-piston facing the main piston is provided above the main piston inside the cylinder tube, and the sub-piston chamber is defined above the piston-side oil chamber inside the cylinder tube by the sub-piston. A pressure-side damping valve is provided in the flow path that enables communication between the sub tank chamber and
A free piston facing the sub-piston is movably provided above the sub-piston inside the cylinder tube, and the volume compensation chamber is defined above the sub-tank chamber inside the cylinder tube by the free piston,
When the free piston moves to a predetermined position, a communication passage is provided that communicates the sub tank chamber between the free piston and the sub piston to a reservoir outside the cylinder tube,
In the hydraulic shock absorber having a pressure spring that biases the free piston toward the sub-piston side,
A relief piston facing the free piston is movably provided inside the cylinder tube above the opening of the communication passage, and has a biasing means for biasing the relief piston toward the free piston. Features a hydraulic shock absorber.   2. The hydraulic shock absorber according to claim 1, wherein the biasing means is made of an elastic body.   The hydraulic shock absorber according to claim 1 or 2, wherein the relief piston partitions the relief chamber above the volume compensation chamber inside the cylinder tube.

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