JPH0541442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic shock absorber, and particularly to a hydraulic shock absorber that can also be used as a vehicle height adjustment device.

[Conventional technology]

2. Description of the Related Art Generally, vehicles are equipped with a hydraulic shock absorber to improve riding comfort and handling stability when the vehicle is running. In recent years, various proposals have been made as vehicle height adjustment devices to be installed in conjunction with such vehicles.

For example, in addition to a hydraulic shock absorber, the characteristics of a leaf spring can be changed by expanding and contracting a hydraulic cylinder installed separately.
This adjusts the vehicle height, or the spring characteristics of a suspension spring installed in a hydraulic shock absorber by expanding and contracting a hydraulic cylinder integrated with the outer diameter of the hydraulic shock absorber. There are some that change the height of the vehicle and adjust the vehicle height accordingly.

According to these, by supplying pressure oil to each hydraulic cylinder, each hydraulic cylinder can be extended and the vehicle height of the vehicle can be adjusted higher, and the pressure oil can be discharged from each hydraulic cylinder. For example, the height of the vehicle can be adjusted lower.

[Problem that the invention seeks to solve]

However, if a vehicle is equipped with a vehicle height adjustment device consisting of a hydraulic cylinder in addition to a hydraulic shock absorber, the number of parts increases, resulting in an increase in costs.

In addition, if a hydraulic cylinder is installed on the outer diameter of the hydraulic shock absorber so that it is integrated with the shock absorber, the outer diameter of the hydraulic shock absorber will become thicker, and there will be restrictions on the mounting position when installing it on a vehicle. There are some inconveniences that make it easier.

In the case of an adjustment method that lowers the vehicle height by discharging pressure oil from the hydraulic cylinder, if an oil leakage failure occurs in the pressure oil supply circuit or the hydraulic cylinder, There is also a fear that the so-called bottoming out phenomenon of the vehicle may occur, making it virtually impossible for the vehicle to run.

Therefore, the present invention makes it possible to adjust the height of a vehicle without installing a separate vehicle height adjustment device in addition to the hydraulic shock absorber installed in the vehicle, and even if there is a failure in the hydraulic circuit, etc. The purpose of the present invention is to provide a new hydraulic shock absorber that does not hinder the running of a vehicle.

[Means for solving problems]

In order to solve the above problems, the configuration of the present invention is as follows.
A piston rod is movably inserted into the cylinder via a piston part provided with a check valve, the piston part divides the cylinder into a rod-side oil chamber and a piston-side oil chamber, and a reservoir chamber is provided outside the cylinder. The reservoir chamber has a hydraulic shock absorber that communicates with the piston side oil chamber via a base valve in the cylinder, and the rod side oil chamber of the hydraulic shock absorber communicates with an external pressure oil supply source via a first passage. In the hydraulic shock absorber, the piston side oil chamber of the hydraulic shock absorber and the rod side oil chamber are formed so as to communicate through a second passage. A supply/discharge valve is provided in a first passage that communicates between the rod side oil chamber and the pressure oil supply source, and a second passage that communicates the rod side oil chamber and the piston side oil chamber. is equipped with a switching valve, the switching valve has a closed position when the supply/discharge valve is open, and an open position when the supply/discharge valve is closed, and the switching valve is opened when the supply/discharge valve is closed. At times, oil is passed through the second passage to allow expansion and contraction of the hydraulic shock absorber, and
It is characterized in that when the supply/discharge valve is opened and the switching valve is closed, pressurized oil is supplied to the rod side oil chamber to enable compression of the hydraulic shock absorber. .

〔Example〕

The present invention will be explained below based on the illustrated embodiments.

As shown in FIG. 1, the hydraulic shock absorber according to the present invention includes a hydraulic shock absorber 1, an appropriate pressure oil supply source 2,
A supply/discharge valve 4 disposed in a first passage 3 that communicates the pressure oil supply source 2 with the rod side oil chamber A of the hydraulic shock absorber 1, and a rod side oil chamber A of the hydraulic shock absorber 1. and a switching valve 6 disposed in a second passage 5 communicating with the piston-side oil chamber B.

The hydraulic shock absorber 1 has an upper end connected to the vehicle body side and a lower end connected to the axle side, and has a piston part 8 slidably inside the cylinder 7. The continuous piston rod 9 is inserted in sliding contact with a bearing portion 7a inside the upper end of the cylinder 7. Further, the cylinder 7 has a rod side oil chamber A and a piston side oil chamber B partitioned by a piston part 8, and a base valve part 10 at the lower bottom inside the cylinder 7. It will be done. The rod side oil chamber A and the piston side oil chamber B are connected to the piston portion 8.
The piston side oil chamber B is communicated with the rod side oil chamber A so as to only allow oil to flow into the rod side oil chamber A via a check valve 8a disposed in the piston side oil chamber B. The base valve section 10 also includes a pressure side valve 1 consisting of a throttle.
0a is arranged, and communication with a reservoir chamber C formed between the piston side oil chamber B and an outer shell 7b arranged outside the cylinder 7 is possible via the pressure side valve 10a. It is said that In addition,
A gas chamber D is located above the reservoir chamber C. Additionally, the base valve section 10 includes a check valve 10b.
is disposed and communicated so as to only allow oil to flow from the reservoir chamber C to the piston-side oil chamber B via the check valve 10b.

The pressure oil supply source 2 consists of a bidirectional pump,
The oil is sucked up from the tank 2a and the hydraulic shock absorber 1
It is formed so as to be able to discharge pressure oil toward the tank 2a, and to suck pressure oil from the hydraulic shock absorber 1 and discharge it to the tank 2a.
The pressure oil discharged from the pressure oil supply source 2 is supplied into the rod-side oil chamber A of the hydraulic shock absorber 1 through the passage 3. In addition,
A relief valve 2b is attached to the pressure oil supply source 2.

The passage 3 is designed to allow pressure oil from the pressure oil supply source 2 to be supplied to the rod side oil chamber A of the hydraulic shock absorber 1, but in this embodiment, , connected to the passage 5 at an intermediate point. In addition, in the passage 3, there is a throttle 3.
a and a check valve 3b. That is, in the passage 3 between the supply/discharge valve 4 disposed in the passage 3 and the pressure oil supply source 2, pressure flows from the hydraulic shock absorber 1 side toward the pressure oil supply source 2. A throttle 3a that controls the flow rate of oil and a check valve 3b that allows pressure oil to flow from the pressure oil supply source 2 to the hydraulic shock absorber 1 side are arranged in parallel.

The supply/discharge valve 4 has a communication position 4a and a cutoff position 4b, and is normally located in the cutoff position 4b, but is formed so as to be switched to the communication position 4a during operation. Note that, of course, the switching of the supply/discharge valve 4 can be performed by any means. In addition, the supply/discharge valve 4 is in the communication position 4.
a, depending on the pressure oil discharge direction of the pressure oil supply source 2, pressure oil is supplied to the rod side oil chamber A of the hydraulic shock absorber 1, or pressure oil is supplied from the rod side oil chamber A. It will be discharged.

The passage 5 has an extension valve 5a consisting of a throttle.
is arranged so that a desired extension damping force is generated when oil reciprocates in the passage 5. Note that, of course, the extension valve 5a can be any valve such as a leaf valve or a plate valve instead of the throttle in this embodiment.

The switching valve 6 has a communication position 6a and a cutoff position 6b, and is normally in the communication position 6a, but is formed so that it can be switched to the cutoff position 6b only when operated. In this embodiment, the switching valve 6 is a pilot switching valve, and a pilot passage 6c is connected to the front side of the supply/discharge valve 4 in the passage 3.

The operation of the hydraulic shock absorber according to the present invention configured as above will be explained.

First, the illustrated state is a case where this device is used as a hydraulic shock absorber as a so-called shock absorber, and a load is applied from the upper end of the piston rod 9 or the lower end of the cylinder 7 is raised. When the piston part 8 in the cylinder 7 is in the pressure stroke of descending in the cylinder 7, the oil in the piston side oil chamber B flows into the rod side oil via the check valve 8a due to the descent of the piston part 8. At the same time as flowing into the chamber A, oil corresponding to the entering volume of the piston rod 9 flows into the pressure side valve 10 of the base valve section 10.
It will flow into the reservoir chamber C via a. Then, when oil passes through the pressure side valve 10a, a desired pressure side damping force is generated.

Further, the cylinder 7 internal piston portion 8 is
During the extension stroke, when the piston part 8 moves up inside the cylinder 7, the oil in the rod-side oil chamber A flows through the passage 5 and flows into the piston-side oil chamber B, and the withdrawal volume of the piston rod 9 increases. Oil corresponding to the amount of oil flows from the reservoir chamber C into the piston-side oil chamber B via the check valve 10b of the base valve portion 10. At this time, the expansion side valve 5 in the passage 5
By the oil passing through a, a desired extension damping force is generated.

Next, when this device is used as a vehicle height adjustment device, first, the supply/discharge valve 4 is switched to the connection position 4a, and the pressure oil supply source 2 is driven. Although not shown, each operation of the supply/discharge valve 4 and the pressure oil supply source 2 is performed by an input signal from a controller.

Next, when adjusting the height of the vehicle to be lower, the oil from the tank 2a is discharged into the passage 3 as pressure oil by driving the pressure oil supply source 2 in the supply direction. The pressure oil discharged into the passage 3 flows into the supply/discharge valve 4 via the check valve 3b, and is connected to the connection position 4.
It is distributed to the hydraulic shock absorber 1 side via a.

When the pressure oil is supplied into the passage 3, the switching valve 6 is switched to the shutoff position 6b by hydraulic pressure through the pilot passage 6c. This prevents the oil in the piston-side oil chamber B in the hydraulic shock absorber 1 from flowing out through the passage 5.

In the above state, pressure oil flows into the rod-side oil chamber A of the hydraulic shock absorber 1. As a result, the piston part 8 moves downward within the cylinder 7, and the oil in the piston-side oil chamber B flows into the reservoir chamber C through the throttle, which is the pressure-side valve 10a of the base valve part 10.

Further, when returning to a higher vehicle height that has been lowered as described above, the pressure oil supply source 2, which is the bidirectional pump, is driven in the discharge direction toward the tank 2a. As a result, the oil in the rod-side oil chamber A flows out into the passage 3, and is also discharged into the tank 2a of the bidirectional pump, which is the hydraulic pressure supply source 2, via the supply/discharge valve 4 located at the communication position 4a. It will be attracted. At this time, the oil that is in the passage 3 and sucked toward the tank 2a after passing through the supply/discharge valve 4 passes through the throttle 3a that is parallel to the check valve 3b, and its flow rate is controlled. This will prevent the hydraulic shock absorber 1 from rising rapidly.

In addition, in the embodiment shown in FIG.
is an extension of the passage 3 that communicates between the pressure oil supply source 2 and the rod-side oil chamber A of the hydraulic shock absorber 1, and also connects the rod-side oil chamber A and the piston-side oil chamber of the hydraulic shock absorber 1. This passage portion 3' is an extension of the passage 5 that communicates with the piston rod 9, but the passage portion 3' may be formed to pass through the piston rod 9 as shown by the broken line in the figure.

FIG. 2 shows a concrete example of the hydraulic shock absorber 1 shown in FIG. divides the inside of the cylinder 7 into a rod-side oil chamber A and a piston-side oil chamber B, and has an oil passage 11a in the piston body 11 of the piston part 8, and has an upper end opening of the oil passage 11a. It has a check valve 8a. The check valve 8a is connected to a spring 13 whose upper end is engaged with a stopper 12 which is engaged with a stepped portion of the piston rod 9.
and a leaf valve 14 energized by the spring 13. The piston body 11 is fixed to the spigot part of the piston rod 9 by a set nut 15 screwed into the lower end threaded part of the piston rod 9.

Further, a base valve part 10 is disposed at the bottom of the lower end of the cylinder 7, and the base valve part 10 is fixed inside the lower end of the outer shell 7b disposed outside the cylinder 7. A leaf valve 18 is disposed at the upper end of a valve seat 17 placed on the upper surface of the lid member 16, and a pressing member 20 biased by a spring 19 is brought into contact with the upper surface of the leaf valve 18. The spring 19 is housed in a cap 21 fitted inside the lower end of the cylinder 7. Furthermore, a central notch 21a is formed in the cap 21, and an oil passage 20a is formed in the pressing member 20. The inflowing oil bends the inner peripheral end of the leaf valve 18 and flows into the valve seat 17, and the notch 1
It is designed to flow into the reservoir chamber C via 7a. Note that a gas chamber D is located above the reservoir chamber C.

Further, in the above embodiment, the rod side oil chamber A in the cylinder 7 is communicated with the external pressure oil supply source 2 side via the passage 3' bored in the piston rod 9, and It communicates with the inside of the piston side oil chamber B via the passage 5 and the expansion side valve 5a. The passage 3' is constituted by a pipe 23 fixed to the upper end of the piston rod 9 via a plug 22, and the passage 5 communicating with the rod side oil chamber A is connected to the reservoir of the hydraulic shock absorber 1. It is constituted by a pipe 24 disposed within a chamber C and a gas chamber D. Further, although the passage 3' in the above embodiment is formed as a passage 3' indicated by a broken line in FIG. 1, instead of this,
Of course, the passage 3 may be formed as shown by the solid line in FIG.

In the embodiment described above, the outer shell 7b
A spring receiver 25 is fixed near the upper end, and the lower end of the suspension spring 26 is locked.

FIG. 3 shows another embodiment of the hydraulic shock absorber according to the modification shown in FIG. The difference is that the valve 27 has a valve 27 that is integrated with the valve 27.

That is, the valve 27 has a supply/discharge position 27a in which the passage 3 communicating between the pressure oil supply source 2 and the rod side oil chamber A of the hydraulic shock absorber 1 is opened, and a piston side oil chamber B of the hydraulic shock absorber 1 in the supply/discharge position 27a. It is formed to have a communication position 27b that opens the passage 5 that communicates with the rod side oil chamber A.
Like the above-mentioned supply/discharge valve 4, it is operated by a signal from a controller (not shown), and when it is operated, it is switched to the communication position 27b.

It goes without saying that the operation of the hydraulic shock absorber in this embodiment is the same as that in FIG. 1 above.

FIG. 4 shows the expansion side valve 5a and valve 27 in the hydraulic shock absorber shown in FIG.
This shows an embodiment in which the valve 27 is disposed inside the piston rod 9. In this embodiment, the valve 27 is in contact with a spool 28 housed inside near the lower end of the piston rod 9, and an upper end of the shaft portion 28a of the spool 28. , a push rod 29 inserted into the shaft core through hole 9a of the piston rod 9, and the push rod 29.
The actuator 30 is connected to the actuator 30 and moves the push rod 29 up and down in the axial direction of the piston rod 9.

A rod inner housing 9b is formed inside the piston rod 9 from near the lower end to the lower end, and the spool 28 is slidably housed within the rod inner housing 9b. Then, the spool 28 is connected to the stopper 3.
The guide 33 is fixed to the upper end of the guide 33 which comes into contact with the upper end of the spring 32 whose lower end is supported by the spring 32, and is always urged upward. Note that the guide 33 has a port 33a.
is drilled. In addition, the piston rod 9
The inside of the shaft core through hole 9a is communicated with the external pressure oil supply source 2 via the passage 3, and is also communicated with the rod inner housing 9b via the port 33a of the guide 33. There is.

That is, when the spool 28 is in the state shown in the figure, oil from the upper shaft core through hole 9a does not flow into the rod inner housing 9b, but the spool 28 is lowered by the operation of the actuator 30. When spool 28
The tip of the piston rod 9 is inserted into the stopper 34 below, and the oil passage is closed at the stopper 34, while the port 9c and the shaft are radially drilled through the wall thickness of the piston rod 9. The core through hole 9a is in communication with the cylinder 7, and oil from the pressure oil supply source flows into the rod side oil chamber A in the cylinder 7.

Further, when the valve 27 consisting of the spool 28 is in the closed state shown in the figure, the rod side oil chamber A and the piston side oil chamber B in the cylinder 7 are in communication, and a rebound damping force is generated. The extension valve 5a is housed in a set nut 15 that is screwed onto the lower end of the piston rod 9 and fixes the piston body 11.

That is, a leaf valve 35 is disposed at the lower end opening of the inner rod housing 9b that opens at the lower end of the piston rod 9 so as to close the opening, and the leaf valve 35 is biased from below by a spring 36. The spring 3
6 is locked from its lower end to a stopper guide 37 screwed inside the lower end of the set nut 15. The thick part of the set nut 15 has a port 15.
A is bored to allow communication between the inside of the set nut 15 and the inside of the piston side oil chamber B.

Therefore, during the extension stroke in which the piston portion 8 moves upward within the cylinder 7 from the illustrated state, the oil in the rod side oil chamber A flows into the rod inner housing 9b through the port 9c of the piston rod 9, and The outer peripheral end of the valve 35 is bent and the oil flows into the set nut 15, that is, into the piston side oil chamber B. This generates a rebound damping force. Note that this embodiment is similar to the embodiment shown in FIG. 2 in that the compression damping force is generated by the base valve portion 10 at the lower end of the cylinder 7. Further, there is no difference from the embodiment shown in FIG. 2 in that the piston portion 8 is provided with a check valve 8a consisting of a stopper 12, a spring 13, and a leaf valve 14.

FIG. 5 shows another embodiment of the hydraulic shock absorber according to the present invention, and the difference from that shown in FIGS. 1 to 4 is that the reservoir chamber C of the hydraulic shock absorber 1 and the external A passage 3 communicating with the tank 2a of
8, a discharge valve 39 is provided in the passage 38, and a supply valve 40 and It has a check valve 41.

That is, both the discharge valve 39 in the passage 38 and the supply valve 40 in the passage 3, which communicate the reservoir chamber C and the tank 2a, are operated by a signal from a controller (not shown), and in normal times, each is operated by a signal from a controller (not shown). When the ones in the cutoff positions 39b and 40b are activated, they are in the communication positions 39a and 40b, respectively.
40a, so that the pressure oil from the pressure oil supply source 2 is supplied into the rod side oil chamber A, and the oil in the piston side oil chamber B, that is, the oil in the reservoir chamber C is discharged into the tank 2a. It is something that has become popular.

Note that the check valve 41 in the passage 3 is connected to the pilot passage 6c when oil flows between the rod side oil chamber A and the piston side oil chamber B when the switching valve 6 in the passage 5 is in the communication position 6a. Care has been taken to prevent hydraulic action.

The pressure oil supply source 2 in this embodiment is composed of a one-way pump, and is formed to have a mechanism that only discharges oil into the passage 3.

FIG. 6 shows a modification of FIG. 5, and in this embodiment, the communication between the pressure oil supply source 2 and the rod-side oil chamber A of the hydraulic shock absorber 1 is at the axial center of the piston rod 9. The switching valve 6 in FIG. 5 is replaced with another switching valve 42, the pressure supply source 2 is a bidirectional pump, and the valve 40 is replaced with a bidirectional pump. This is a discharge valve, and the check valve 41 in the passage 3 in FIG. 5 is omitted.

That is, the other switching valve 42 has a supply position 42a that allows communication between the pressure oil supply source 2 and the rod side oil chamber A of the hydraulic shock absorber 1, and a supply position 42a that allows communication between the pressure oil supply source 2 and the rod side oil chamber B of the hydraulic shock absorber 1, and A communication position 42b that allows communication with the rod side oil chamber A, and the supply/discharge valve 40 is in the supply position 40.
When the switch is switched to position a and pressure oil is supplied from the pressure oil supply source 2 into the passage 3, the hydraulic pressure acts on the switching valve 42 through the pilot passage 42c, so that the switching valve 42 is switched to the supply position 42a. It is being formed.

In this embodiment as well, the supply/discharge valve 40 and the discharge valve 39 are each opened in response to a command signal from a controller (not shown), and the hydraulic shock absorber 1 expands and contracts. Of course, the operating conditions are no different from the embodiments described above.

FIG. 7 shows a partial improvement in a state in which the hydraulic shock absorber 1 in FIG. 6 is removed, and shows an embodiment in which the supply valve 40 and the discharge valve 39 in FIG. 6 are combined into a valve 43. The hydraulic pressure supply source 2 in this embodiment is made up of a bidirectional pump.

The combination valve 43 has three ports and three positions, and is configured to be switched to each position by a command signal from a controller (not shown).

Note that this embodiment has the advantage that the number of valves can be reduced.

FIG. 8 shows an embodiment that is equivalent to that shown in FIG. 6, and the hydraulic shock absorber 1 according to this embodiment is similar to the hydraulic shock absorber 1 shown in FIGS. It also corresponds to a partial improvement of .

That is, the pressure oil from the pressure oil supply source 2 is supplied via the supply valve 40 to the passage 3 consisting of the pipe 23, that is, through the shaft core through hole 9a of the piston rod 9.
It is designed to be able to flow into the switching valve 42 inside the inner rod housing 9b near the lower end of the piston rod 9. That is, when pressure oil is supplied into the shaft core through hole 9a, the spool 28 descends,
The inside of the rod-side oil chamber A in the cylinder 7 and the pressure oil supply source 2 side are communicated through the port 9c of the piston rod 9, and a port 44 is bored in the lower end of the reservoir chamber C, and a port 44 is provided at the lower end of the reservoir chamber C. It communicates with a passage 38 communicating with the tank 2a side.

Note that a set nut 15 that fixes the piston portion 8 to the lower end of the piston rod 9 includes an extension valve 5.
The fact that a is interposed is the same as in the embodiment shown in FIG.

Furthermore, in this embodiment, when forming a circuit for supplying and discharging pressure oil outside the hydraulic shock absorber 1, it goes without saying that the circuit shown in FIG. 7 may be used instead of the circuit shown in the figure.

〔Effect of the invention〕

As described above, according to the present invention, since the switching valve is provided in the first passage and the supply/discharge valve is provided in the second passage, a hydraulic shock absorber equipped as a so-called shock absorber of a vehicle can be installed in a vehicle. It can also be used as a vehicle height adjuster to adjust the height.
When equipping a vehicle, space can be saved, which is extremely advantageous.

Further, since the hydraulic shock absorber installed as a hydraulic shock absorber can also be used as a vehicle height adjustment device, there is no needless increase in the number of parts, and there is also the advantage of being inexpensive and economically advantageous.

Further, according to the present invention, even if there is a failure and oil leakage in the pressure oil circuit for adjusting the vehicle height, there is no fear that the vehicle will be unable to drive unless the hydraulic shock absorber is damaged. There are also advantages.

To restore the vehicle height, it is sufficient to remove the pressure oil from the second passage, which has the advantage of being able to restore the vehicle quickly. In particular, when a bidirectional pump is used as the pressure oil supply source, it is even faster. There is also the advantage of being able to save time.

Furthermore, when attempting to integrate the circuit that serves as the second passage for supplying or discharging pressure oil to the hydraulic shock absorber, the piping becomes simpler, which is economically advantageous, and the equipment on the vehicle is also improved. There is also the advantage that the process can be simplified and workability can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a hydraulic shock absorber according to an embodiment of the present invention, FIG. 2 is an embodiment specifically showing the hydraulic shock absorber according to FIG. A circuit diagram according to a modified example, FIG. 4 is an embodiment specifically showing the hydraulic shock absorber according to FIG. 2, and FIG. 5 is a circuit diagram showing a hydraulic shock absorber according to another embodiment of the present invention. FIG. 6 is a circuit diagram according to a modification of FIG. 5,
FIG. 7 is a circuit diagram partially showing a modification example of FIG. 6;
FIG. 8 is an embodiment specifically showing the hydraulic shock absorber according to FIG. 6. 1... Hydraulic shock absorber, 2... Pressure oil supply source, 3, 3',
5, 38... Passage, 4... Supply/discharge valve, 6, 27, 4
2...Switching valve, 7...Cylinder, 8...Piston section, 9...Piston rod, 10...Base valve section, 39...Discharge valve, 40...Supply valve, 43
...Valve, A...Rod side oil chamber, B...Piston side oil chamber, C...Reservoir chamber, D...Gas chamber.

Claims (1)

[Claims] 1. A piston rod is movably inserted into a cylinder via a piston portion provided with a check valve,
The piston part has a rod-side oil chamber and a piston-side oil chamber divided into a cylinder, and a reservoir chamber is provided outside the cylinder. A shock absorber is provided, and the rod side oil chamber of the hydraulic shock absorber is formed so as to be able to communicate with an external pressure oil supply source via a first passage, and the rod side oil chamber of the hydraulic shock absorber is configured to communicate with an external pressure oil supply source via a first passage. In a hydraulic shock absorber formed so as to be able to communicate with the rod side oil chamber via a second passage, there is no supply of oil into the first passage which communicates the rod side oil chamber with the pressure oil supply source. A drain valve is provided, and a switching valve is also provided in the second passage communicating the rod-side oil chamber and the piston-side oil chamber, and the switching valve is configured to open when the supply/discharge valve is opened. It has a position in which it closes when the supply and discharge valve is closed, and a position in which it opens when the supply and discharge valve is closed, and when the supply and discharge valve is closed and the switching valve is opened, oil flows through the second passage and the hydraulic shock absorber can expand and contract. In addition, when the supply/discharge valve is opened and the switching valve is closed, pressurized oil is supplied to the rod side oil chamber to enable compression of the hydraulic shock absorber. Hydraulic shock absorber. 2. The hydraulic shock absorber according to claim 1, wherein the pressure oil supply source is a bidirectional pump. 3. The hydraulic shock absorber according to claim 1, wherein the switching valve is a pilot switching valve and is configured to be switched to the cutoff state when pressure oil is supplied from the pressure oil supply source. 4. The hydraulic shock absorber according to claim 1, wherein the supply/discharge valve and the switching valve are a combined valve. 5. The hydraulic shock absorber according to claim 1, wherein the reservoir is opened and closed to the tank via a discharge valve.