JPH09144801A - Hydraulic shock absorber - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To improve ride comfort and durability of a bladder of an oil tank in a hydraulic shock absorber of a vehicle height automatic adjustment type. A cylinder 3 is inserted into a case 2 to form a reservoir chamber 5. A piston 14 is fitted in the cylinder 3. The pump rod 28 is inserted into the pump tube 23 in the piston rod 15 to form the pump chamber 29, and the check valves 32, 33 are formed.
Through the lower cylinder chamber 3b and the oil tank 37. By the action of the pump chamber 29 accompanying the expansion and contraction of the piston rod 15, the oil liquid is supplied from the oil tank 37 to the lower cylinder chamber 3b, and the orifice passage 36 returns the oil liquid from the lower cylinder chamber 3b to the oil tank 37 to keep the vehicle height constant. Adjust to. Since the oil tank 37 is separately provided on the outer peripheral portion of the case 2, the capacity of the reservoir chamber 5 and the oil tank 37 can be increased and the riding comfort is improved. Since the bladder 43 (flexible film) is deformed only when the vehicle height is adjusted, the frequency of deformation is low and the durability is improved.

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 mounted on a suspension system of a vehicle such as an automobile and having an automatic height adjustment function.

[0002]

2. Description of the Related Art Generally, in vehicles such as automobiles, a hydraulic shock absorber is mounted between the sprung portion and the unsprung portion of a suspension device to damp vibrations of the suspension spring to improve riding comfort and steering stability. I am trying.

By the way, in vehicles such as vans and wagons, which have a relatively large load, the vehicle height changes due to changes in the load accompanying passengers getting on and off, loading and unloading of luggage, etc. May decrease. Therefore, there is a demand for a suspension system that can automatically maintain a constant vehicle height regardless of the size of the loaded load.

Therefore, conventionally, for example, JP-A-60-261 is used.
As described in Japanese Patent No. 713, an oil tank and a reservoir filled with high-pressure gas, pump means for supplying the oil liquid of the oil tank into the cylinder by expansion and contraction of the piston rod, and the expansion and contraction position of the piston rod are disclosed. The pump means and the returning means for returning the pressure oil in the cylinder to the oil tank are provided, and the vibration length of the suspension device during traveling is used to operate the pump means and the returning means to adjust the extension length of the piston rod to a constant value. Therefore, a so-called self-pumping type hydraulic shock absorber has been proposed which automatically maintains a constant vehicle height.

[0005]

However, in the self-pumping type hydraulic shock absorber disclosed in Japanese Patent Laid-Open No. 60-261713, the inside of the reservoir that compensates for the volume change in the cylinder due to the expansion and contraction of the piston rod is made of rubber. It is divided into a gas chamber and an oil chamber by a bladder (flexible film) made of steel, but the gas in the gas chamber is compressed and expanded each time the piston rod expands and contracts, and the bladder frequently expands and contracts accordingly. Therefore, there is a problem that the bladder is easily deteriorated.

Further, the self-pumping type hydraulic shock absorber described in the above publication has an outer cylinder provided on the outer peripheral portion of the cylinder to have a double cylinder structure, and an oil tank and a reservoir are provided between the cylinder and the outer cylinder. For this reason, the gas capacity of the oil tank and the reservoir becomes small, and when the load is large, the gas reaction force increases with a small stroke of the piston rod, and the riding comfort deteriorates. Furthermore, the structure is so-called inverted, in which the piston rod is made to project from the lower end of the cylinder, so when used as a suspension strut, the structure must be complicated and expensive. The dynamic resistance also increases.

The present invention has been made in view of the above points, and a hydraulic pressure capable of sufficiently increasing the capacity of a reservoir and an oil tank and having an automatic vehicle height adjusting function excellent in durability of a bladder. The purpose is to provide a shock absorber.

[0008]

In order to solve the above problems, the hydraulic shock absorber of the present invention comprises a case having one end closed and the other end opened, and the case inserted into the case and the case. A cylinder in which an annular reservoir chamber is formed and oil is sealed inside, a base valve provided at one end of the cylinder for communicating the inside of the cylinder with the reservoir chamber, and slidable in the cylinder A piston that is fitted into the cylinder to define two chambers in the cylinder, a hollow piston rod that has one end connected to the piston and the other end that extends to the outside of the cylinder, and one end that connects to the base valve. A pump rod, the other end of which is inserted into the piston and slidably fitted to a pump tube provided in the hollow portion of the piston rod to form a pump chamber in the pump tube; An oil tank connected to one end of a pump rod and storing an oil liquid therein, a first pump passage provided in the pump rod for communicating the oil tank with a pump chamber, and the oil tank of the first pump passage. Check valve that allows only oil liquid to flow from the pump chamber to the pump chamber, a second pump passage provided in the piston rod for communicating the pump chamber and the cylinder chamber, and the pump in the second pump passage. Provided between the pump tube and the pump rod, and a second check valve that allows only the flow of the oil liquid from the chamber to the cylinder chamber, and the piston rod has the first predetermined value in accordance with the relative positions thereof. The first passage means for directly communicating the pump chamber and the cylinder chamber when extended to the position, and the cylinder when the piston rod extends to the second predetermined position. The oil tank includes a second passage means for communicating the first chamber with the chamber, and the oil tank includes an outer peripheral wall of the case, an annular upper ring and a lower ring fitted to the outer peripheral wall, and the upper ring. And a substantially cylindrical tank wall fitted to the outer peripheral portion of the lowering, the inside of which is formed by the flexible film.
It is characterized in that it is defined by an oil chamber communicating with the pump passage and a gas chamber filled with gas.

With this construction, as the piston rod expands and contracts, the pump rod moves back and forth in the pump tube, so that the oil liquid in the oil tank passes through the first pump passage and the first check valve. Is introduced into the pump chamber, the oil liquid in the pump chamber is supplied to the cylinder chamber through the second check valve and the second pump passage, the pressure in the cylinder is increased, and the piston rod extends. When the piston rod extends to the first predetermined position, the first passage means connects the pump chamber and the cylinder chamber to stop the pressure increase in the cylinder chamber, and the piston rod moves to the second position.
When extended to a predetermined position, the second passage means connects the cylinder chamber and the first pump passage, the pressure oil in the cylinder chamber is relieved to the oil tank, the pressure in the cylinder is reduced, and the piston rod is shortened. At this time, as the oil liquid in the oil tank is supplied and discharged, the bladder is deformed and the gas in the gas chamber is compressed and expanded.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, a hydraulic shock absorber 1 has a double cylinder structure in which a cylinder 3 is inserted into a cylindrical case 2 having one end opened and the other end closed. A seal member 4 is attached to the opening of 2 and an annular reservoir chamber 5 is formed between the case 2 and the cylinder 3. A substantially bottomed tubular partition member 6 into which the cylinder 3 is inserted is fitted to the bottom of the case 2, and an oil chamber is provided between the bottom of the partition 6 and the bottom of the case 2. 7 (first
A pump passage is formed, and the side wall of the partition member 6 and the case 2 are formed.
An annular passage 8 (first pump passage) is formed between the side wall and the side wall. The oil chamber 7 and the annular passage 8 are connected by an oil passage 9. The cylinder 3 is filled with oil liquid, and the reservoir chamber 5 is filled with oil liquid and high-pressure gas.

A base valve 10 is provided between the lower end of the cylinder 3 and the bottom of the partition member 6, and the inside of the cylinder 3 and the reservoir chamber 5 communicate with each other via an oil passage 11 of the base valve 10. ing. The base valve 10 has a check valve 12 that allows the flow of the oil liquid from the reservoir chamber 5 side of the oil passage 11 to the cylinder 3 side, and an orifice 13 that bypasses the check valve 12 and allows the oil passage 11 to communicate at all times. It is provided.

An annular piston 14 is slidably fitted in the cylinder 3, and the piston 14 divides the interior of the cylinder 3 into two chambers, a cylinder upper chamber 3a and a cylinder lower chamber 3b. There is. One end of a hollow piston rod 15 is inserted into the piston 14, and a nut 16 is screwed and connected to the tip of the hollow piston rod 15. The other end of the piston rod 15 is inserted into the rod guide 17 and the seal member 4 mounted on the upper end of the cylinder 3, and extends outside the cylinder 3 and the case 2.

The piston 14 has an extension side passage 18 and a compression side passage 18 for communicating the cylinder upper chamber 3a with the cylinder lower chamber 3b.
19 are provided. Then, the normally closed disc valve 20 that bends and opens the cylinder upper chamber 3a by a predetermined pressure or more to allow the oil liquid in the extension side passage 18 to flow to generate a damping force and the cylinder lower chamber 3b side A normally-closed disc valve 21 is provided which is bent by a predetermined pressure or more and opens to allow the oil liquid to flow in the compression-side oil liquid passage 19. Also,
The piston 14 has an orifice 22 that bypasses the disk valves 20 and 21 and always communicates between the cylinder upper and lower chambers 3a and 3b.
Is provided.

Inside the piston rod 15 is a pump tube
23 is inserted, its upper end is pressed by a holding spring 24 provided at the tip of the piston rod 15, and the lower end is a nut.
It is fixed in contact with 16. An annular pump passage 25 is provided between the piston rod 15 and the pump tube 23.
A (second pump passage) is formed and communicates with the cylinder lower chamber 3b via an oil passage 16a (second pump passage) provided in the nut 16.

A retainer 26 is attached to the partition member 6 and the base valve 11 by a nut 27, and a proximal end portion of a tubular pump rod 28 is connected via the retainer 26. The connecting portion between the pump rod 28 and the retainer 26 is formed into a substantially spherical shape and is in sliding contact with each other, so that the inclination of the pump rod 28 due to the operation of the hydraulic shock absorber 1 can be allowed and the positional deviation can be absorbed. It has become. The tip end side of the pump rod 28 extends along the central axis of the cylinder 3 and is slidably fitted in the pump tube 23.
A pump chamber 29 is defined in the pump tube 23 by the tip portion of the pump rod 28. The pump chamber 29 is connected to the cylinder lower chamber 3b by the pump passage 25, and
A pump passage 30 (first pump passage) in the pump rod 28 communicates with the oil chamber 7 via an oil passage 31 (first pump passage) of the retainer 26. A check valve 32 (second check valve) that allows only oil liquid to flow from the pump chamber 29 to the pump passage 25 is provided at the upper end of the pump tube 23. In addition, at the tip of the pump rod 28, a check valve 33 (first valve) that allows only oil liquid to flow from the pump passage 30 to the pump chamber 29 is provided.
Check valve) is provided.

The outer peripheral surface of the pump rod 28 is provided with a groove 34 (first passage means) extending from its tip end portion to a predetermined position along the axial direction. The groove 34 and the pump tube 23 are provided.
An oil passage 35 communicating with the pump chamber 29 is formed. When the extension length of the piston rod 15 is equal to or greater than a predetermined standard range (equal to or more than the first predetermined position which is the lower limit of the standard range), the lower end of the groove 34 extends from the lower end of the pump tube 23 to the cylinder lower chamber 3b. When the oil passage 35 is communicated with the cylinder lower chamber 3b and becomes shorter than the standard range (shorter than the first predetermined position which is the lower limit of the standard range), the groove 34 is exposed to the pump tube.
The oil passage 35 is housed in the cylinder 23 and is cut off from the cylinder lower chamber 3b. Here, the groove 34 is formed so that the depth thereof gradually decreases toward the lower end portion thereof (so that the pump rod 28 gradually expands in diameter),
The fluid passage 35 and the cylinder lower chamber 3b are slowly connected and disconnected.

An orifice passage 36 (second passage means) communicating with the pump passage 30 is provided on the side wall of the pump rod 28. The orifice passage 36 is arranged above the lower end portion of the groove 34 (a portion from the pump chamber 29),
When the extension length of the piston rod 15 is below a predetermined standard range (below the second predetermined position which is the upper limit of the standard range), it is closed by overlapping with the pump tube 23, and when it exceeds the standard range (of the standard range). When exceeding the upper limit of the second predetermined position), the lower end of the pump tube 23 is exposed to the lower cylinder chamber 3b and communicates with the lower cylinder chamber 3b.

An annular oil tank 37 is provided on the outer peripheral portion of the case 2. The oil tank 37 is a substantially cylindrical tank in which an annular upper ring 38 and a lower ring 39 are fitted to the outer peripheral wall of the case 2, and a substantially cylindrical upper case 40 and an annular lower case 41 are provided on their outer peripheral portions. The walls are fitted together to form an annular chamber 42 between the outer peripheral surfaces of these four members and the case 2. The upper ring 38 and the lower ring 39 are welded to the case 2, the upper case 40 and the lower case 41 are welded to each other, and the lower case 41 is caulked and joined to the lower ring 39. Chamber 42 inside the oil tank 37
Is a substantially cylindrical bladder 43 made of a flexible material such as rubber.
The oil chamber 42a that is in contact with the case 2 side by the (flexible film)
And the gas chamber in contact with the upper case 40 and lower case 41 sides
It is divided into two rooms of 42b. One end of the bladder 43 is sandwiched between the upper ring 38 and the upper case 40, and the other end is sandwiched between the lower ring 39 and the lower case 41, and seals between them. . The oil chamber 42a communicates with the annular passage 8 through an oil hole 44 (first pump passage) provided in the side wall of the case 2.
The oil liquid is sealed in the oil chamber 42a, and the gas chamber 42a
High pressure gas is enclosed in b.

The partition member 6 is provided with a normally closed pressure reducing valve 45 that opens when the pressure in the reservoir chamber 5 reaches a predetermined pressure and allows the oil liquid in the reservoir chamber 5 to escape to the oil chamber 7. . A spring bearing 47 that receives one end of a suspension spring 46 is externally fitted to the upper ring 38 and the upper case 40 of the oil tank 37. In the hydraulic shock absorber 1, the tip end of the piston rod 15 is connected to the vehicle body side (not shown), and the mounting eye 48 provided at the lower end of the case 2 is connected to the wheel side to suspend the vehicle. Be attached to.

The operation of the present embodiment having the above-mentioned structure will be described below.

First, the damping force generating function of the hydraulic shock absorber 1 will be described. During the extension stroke of the piston rod 15, the movement of the piston 14 pressurizes the oil liquid on the cylinder upper chamber 3a side to flow through the orifice 22 to the cylinder lower chamber 3b side,
A damping force having an orifice characteristic (the damping force is approximately proportional to the square of the piston speed) is generated. Then, when the piston speed increases and the pressure in the cylinder upper chamber 3a reaches a predetermined pressure, the disc valve 20 opens and the oil liquid flows through the extension side passage 18 to the cylinder lower chamber 3b side. Is almost proportional to the piston speed) to suppress an excessive increase of the damping force. At this time, the piston rod 15
The gas in the reservoir chamber 5 expands as much as the gas has withdrawn from the cylinder 3, and the oil liquid in the reservoir chamber 5 flows through the oil passage 11 of the base valve 10 to open the check valve 12 and flow into the lower cylinder chamber 3b. This compensates for the increase in volume in the cylinder 3 due to the withdrawal of the piston rod 15.

Further, during the compression stroke of the piston rod 15, the movement of the piston 14 pressurizes the oil liquid on the cylinder lower chamber 3b side to flow through the orifice 22 to the cylinder upper chamber 3a side, and the damping force of the orifice characteristic is generated. Occur. Then, when the piston speed increases and the pressure in the cylinder lower chamber 3b reaches a predetermined pressure, the disc valve 21 opens and the oil liquid flows through the contraction side passage 19 to the cylinder upper chamber 2a side, and the damping force of the valve characteristic. Occurs and suppresses an excessive increase in damping force. At this time, the oil liquid corresponding to the piston rod 15 entering the cylinder 3 flows into the reservoir chamber 5 through the orifice 13 of the base valve 10 and compresses the gas in the reservoir chamber 5 to allow the piston rod 15 to enter. The decrease in the volume in the cylinder 3 due to

Next, the automatic height adjusting function of the hydraulic shock absorber 1 will be described. When the vehicle is empty (standard vehicle height), the gas chamber 42b of the oil tank 37 and the reservoir chamber 5 have the same pressure, the bladder 43 of the oil tank 37 is at the position shown in FIG. Is within a given standard range. In this state, the groove 34 of the pump rod 28 is exposed to the outside of the pump tube 23, and the pump chamber 29 is communicated directly with the cylinder lower chamber 3b by the oil passage 35, so that the pumping operation is not performed.

When the vehicle load becomes higher and the vehicle height becomes lower than the standard vehicle height, and the extension length of the piston rod 15 becomes shorter than the standard range, the groove 34 of the pump rod 28 is accommodated in the pump tube 23. Then, the oil passage 35 is shut off. In this state, the piston rod is activated by the operation of the suspension system while traveling.
When 15 expands and contracts, the pump rod 28 in the pump tube 23 retracts during the expansion stroke to reduce the pressure in the pump chamber 29, open the check valve 33, and open the pump passage 30 constituting the first pump passage and the oil. Oil chamber 42a of oil tank 37 through passage 31, oil chamber 7, oil passage 9, annular passage 8 and oil hole 44
The oil liquid therein is introduced into the pump chamber 29, and as shown in FIG. 3, the bladder 43 bends accordingly and the gas in the gas chamber 42 expands. During the compression stroke, the pump rod 28 moves forward to pressurize the oil liquid in the pump chamber 29, and the check valve 32
Is supplied to the cylinder lower chamber 3b through the pump passage 25 constituting the second pump passage and the oil passage 16a to pressurize the cylinder upper and lower chambers 3a and 3b and the reservoir chamber 5 to extend the piston rod 15. Let In this way, the vehicle height is increased by repeating the pumping operation by utilizing the vibration during traveling. When the vehicle height reaches the standard vehicle height and the extension length of the piston rod 15 falls within the standard range (reaches the first predetermined position), the groove 34 of the pump rod 28 is exposed to the outside of the pump tube 23. The pump chamber 29 is directly communicated with the lower cylinder chamber 3b by the oil passage 35 to release the pumping operation.

Further, when the vehicle load becomes smaller and the vehicle height becomes higher than the standard vehicle height, and the extension length of the piston rod 15 becomes longer than the standard range (longer than the second predetermined position), the orifice. The passage 36 is exposed to the outside of the pump tube 23 and communicates with the cylinder lower chamber 3b, and the oil liquid in the cylinder lower chamber 3b is the orifice passage 36, the pump passage 30, the oil passage 31, the oil chamber 7, the oil passage 9, and the annular shape. It is returned to the oil chamber 42a of the oil tank 37 through the passage 8 and the oil hole 44, and the cylinder upper and lower chambers 3a and 3b.
And the reservoir chamber 5 is decompressed, the piston rod 15 is shortened, and the vehicle height is lowered. At this time, the bladder 43 bends and the gas in the gas chamber 42b is compressed by the amount of increase in the oil liquid in the oil chamber 42a. Piston rod with vehicle height lowered to standard vehicle height
When the extension length of 15 is within the standard range, the orifice passage 36 of the pump rod 28 overlaps the pump tube 23 and is closed, and the returning operation of the oil liquid from the cylinder lower chamber 3b is released.

In this way, by repeating the pumping operation and the returning operation by utilizing the vibration of the suspension device during traveling, the vehicle height can be automatically adjusted to be constant regardless of the load. When the pressure in the cylinder 3 and the reservoir chamber 5 suddenly rises due to the push-up from the road surface during heavy loading, the pressure reducing valve 45 of the partition member 6 is opened to remove the oil liquid in the reservoir chamber 5. By letting it escape to the oil chamber 7, it is possible to prevent an excessive increase in pressure, reduce the load on the seal portion of the hydraulic shock absorber 1, and reduce the impact on the vehicle body.

Further, a bladder is not provided in the reservoir chamber 5 in which the internal gas expands and compresses each time the piston rod 15 expands and contracts, and the oil liquid is supplied and discharged only during vehicle height adjustment (during pumping operation). Since the oil chamber 42a and the gas chamber 42b of the tank 37 are defined by the bladder 43, the bladder 43 is not deformed by the expansion and contraction of the normal piston rod 15 which is not accompanied by vehicle height adjustment. Since it is deformed only when adjusting the vehicle height, the frequency of deformation is low and the durability can be improved.

Since the reservoir chamber 5 is provided between the cylinder 3 and the case 2 and the oil tank 37 for storing the vehicle height adjusting oil liquid is separately arranged on the outer peripheral portion of the case 2, the reservoir chamber 5
Further, the capacity of the oil tank 37 can be made sufficiently large, and the riding comfort can be kept good regardless of the loaded load. Furthermore, since the hydraulic shock absorber 1 has a so-called upright structure in which the piston rod 15 is projected from the upper portion of the cylinder 3, it can be suitably used as a suspension strut.

[0030]

As described above in detail, according to the hydraulic shock absorber of the present invention, the inside of the cylinder is pressurized by the pumping operation due to the expansion and contraction of the piston rod and the piston rod extends, so that the piston rod reaches the first predetermined position. When extended, the pumping action is released by the first passage means,
Further, when the piston rod extends to the second predetermined position, the pressure oil in the cylinder chamber is returned to the oil tank by the second passage means and the piston rod is shortened. Therefore, by extending and contracting the piston rod, the extension length of the piston rod is increased. Is automatically adjusted between the first extended position and the second predetermined position. As a result, it is possible to automatically adjust the vehicle height to a constant value regardless of the size of the loaded load by utilizing the vibration of the suspension device while the vehicle is traveling.

Further, a bladder is not provided in the reservoir chamber in which the internal gas expands and compresses each time the piston rod expands and contracts,
Since the bladder defines the oil chamber and the gas chamber of the oil tank where oil is supplied and drained only when the vehicle height is adjusted (when pumping is activated), the bladder is a normal piston rod that does not involve vehicle height adjustment. Since it is not deformed by the expansion and contraction of the vehicle and is deformed only when the vehicle height is adjusted, the frequency of deformation is low and the durability can be improved.

Further, by storing the oil liquid for adjusting the vehicle height in an oil tank separately provided from the cylinder, the capacity of the reservoir chamber and the oil tank can be made sufficiently large, and the load capacity can be increased or decreased. The ride comfort can be kept good.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention.

FIG. 2 is an enlarged view of an oil tank showing the position of the bladder in the initial state where the vehicle height is not adjusted in the apparatus of FIG.

FIG. 3 is an enlarged view of the oil tank showing the position of the bladder during the pumping operation in the apparatus of FIG.

[Explanation of symbols]

 1 hydraulic shock absorber 2 case 3 cylinder 3a cylinder upper chamber 3b cylinder lower chamber 5 reservoir chamber 10 base valve 14 piston 15 piston rod 23 pump tube 25 pump passage (second pump passage) 28 pump rod 30 pump passage (first pump passage) ) 32 Check valve (second check valve) 33 Check valve (first check valve) 34 Groove (first passage means) 36 Orifice passage (second passage means) 37 Oil tank 38 Upper ring 39 Lowering 40 Upper Case (tank wall) 41 Lower case (tank wall) 42a Oil chamber 42b Gas chamber 43 Bladder (flexible membrane)

Claims (1)

[Claims] 1. A case, one end of which is closed and the other end of which is open, and a cylinder which is inserted into the case to form an annular reservoir chamber between the case and an oil liquid sealed therein. A base valve provided at one end of the cylinder for communicating the inside of the cylinder with a reservoir chamber, a piston slidably fitted in the cylinder to define two chambers in the cylinder, and one end A hollow piston rod connected to the piston and having the other end extended to the outside of the cylinder; and a pump provided in the hollow part of the piston rod, one end of which is connected to the base valve and the other end of which is inserted into the piston. A pump rod slidably fitted to the tube to form a pump chamber within the pump tube;
An oil tank connected to one end of the pump rod and storing an oil liquid therein, a first pump passage provided in the pump rod for communicating the oil tank with the pump chamber, and the first pump passage in the first pump passage. A first check valve that allows only the flow of the oil liquid from the oil tank to the pump chamber, a second pump passage that is provided in the piston rod and that communicates the pump chamber and the cylinder chamber, and a second pump passage of the second pump passage. A second check valve that allows only the flow of the oil liquid from the pump chamber to the cylinder chamber is provided between the pump tube and the pump rod, and the piston rod is connected to the first check valve depending on their relative positions. 1 When extending to a predetermined position, the first passage means for directly communicating the pump chamber and the cylinder chamber; and when the piston rod extends to a second predetermined position, The oil tank includes a second passage means for communicating the first chamber with the first pump passage, and the oil tank includes an outer peripheral wall of the case, an annular upper ring and a lower ring fitted to the outer peripheral wall, and the upper ring. And a substantially cylindrical tank wall fitted to the outer peripheral portion of the lowering, and the inside is defined by a flexible film into an oil chamber communicating with the first pump passage and a gas chamber filled with gas. A hydraulic shock absorber characterized in that