JP2021139484A - Hydraulic actuator, vehicle differential lock device and hydraulic circuit of single-acting hydraulic cylinder - Google Patents

Abstract

To provide a technology for easily suppressing oil leakage to a non-pressurization chamber of a single-acting hydraulic cylinder.SOLUTION: A hydraulic actuator having a single-acting hydraulic cylinder 10 in which the inside of a cylinder case 11 is partitioned into a pressurization chamber 10A and a non-pressurization chamber 10B by a piston 12, a restoration spring 15 is arranged in the non-pressurization chamber 10B, and the piston 12 is advanced and retreated by a working fluid which is supplied to the pressurization chamber 10A through a supply conduit 23, comprises: a first check valve 25 interposed in the supply conduit 23; a bypass path 24 for connecting an upstream-side position of the supply conduit 23 rather than the first check valve 25 and a downstream-side position thereof rather than the first check valve 25, and bypassing the first check valve 25; and a second check valve 26 interposed in the bypass path 24, and inverted in a flow direction of fluid to the first check valve 25 with respect to the pressurization chamber 10A.SELECTED DRAWING: Figure 2

Description

The present invention relates to a technique using a single-acting hydraulic cylinder, and relates to a hydraulic actuator, a vehicle diff lock device, and a hydraulic circuit of the single-acting hydraulic cylinder.
Here, in the single-acting hydraulic cylinder of the present invention, the inside of the cylinder case is partitioned by a piston and has two chambers, one of which can be pressurized with hydraulic oil and operates in the other chamber. The structure is such that oil is not supplied.

In the single-acting cylinder, a piston rod is arranged in a cylinder tube (cylinder case), the inside of the cylinder tube is divided into two chambers, and a single supply port for supplying oil is provided in only one chamber. (Refer to Patent Document 1 and the like).
Further, a packing is provided on the outer peripheral surface of the piston so that the piston can slide (advance and retreat) along the inner surface of the cylinder tube in a state where the inner surface of the cylinder tube and the piston are sealed. ..

When a single-acting cylinder is used as a hydraulic actuator, it returns to the chamber (called a non-pressurized chamber) opposite to the chamber (called a pressurized chamber) on which hydraulic pressure is supplied and pressurized. Spring is placed. Then, in the hydraulic actuator, when the pressurizing chamber is pressurized with the hydraulic oil, the piston moves to the non-pressurizing chamber side against the spring force of the spring, and when the pressurization by the hydraulic oil is released, The spring force of the spring causes the piston to be returned to the pressurizing chamber side and return to the initial position.

As a device using such a hydraulic actuator composed of a single-acting cylinder, for example, there is a vehicle diff lock device provided in the axle shaft of the vehicle (Patent Document 2).
In this diff lock device, a hydraulic actuator is used as a drive unit of a shift mechanism that shifts the sleeve in the axial direction. Specifically, a shift fork is connected to the tip of the piston rod of the cylinder in a cantilever shape, and the axial position of the sleeve is shifted at the tip of the shift fork by moving the piston rod forward and backward with the operation of the hydraulic actuator. Controls the connection and release of diff locks.

Japanese Unexamined Patent Publication No. 2016-176566 Japanese Unexamined Patent Publication No. 2010-121641

In the cylinder, a gap is required between the cylinder case and the piston in order for the piston to move forward and backward (movable), and an O-ring or other piston packing is inserted in the gap to seal the gap. There is. Then, the piston packing may have increased rattling due to deterioration over time, wear, etc. due to use, and oil leakage may occur due to poor sealing due to the piston packing. Therefore, for example, a machine including a cylinder is subjected to regular maintenance at predetermined intervals.

However, even before regular maintenance and even in a situation where it is estimated that no seal failure has occurred in the piston packing, a small amount of oil leaks to the non-pressurized chamber side (per unit time) according to the operation of the machine. (A state in which the amount of leakage is small) may continue to occur. Since a small amount of oil leak to the non-pressurized chamber side does not affect the operation of the cylinder itself or is small, it takes time to notice the occurrence of the oil leak, and as a result, a large amount of oil leaks.

For example, when the above oil leak occurs in the cylinder used in the diff lock device, the leaked oil gradually accumulates in the axle case, and is noticed only when, for example, there is an oil leak from the axle case. Further, in this case, since the piston packing does not have a defective seal, it may take some time to notice that the cause is the cylinder.
When an oil leak is found due to defective packing, conventional measures such as replacement of the piston packing or replacement of the cylinder itself can be considered. However, the countermeasure against the oil leak is a work outside the regular maintenance, and there is a problem that the machine cannot be used until the failure is investigated and the repair is completed. Moreover, when it is mounted on a large machine, special equipment and tools are required.

The present invention focuses on the above points, and an object of the present invention is to provide a technique for easily suppressing oil leakage to a non-pressurized chamber in a single-acting hydraulic cylinder.

In the single-acting hydraulic cylinder, the inventor found that a small amount of oil leaked to the non-pressurized chamber side (leakage amount per unit time) with the use of the cylinder, even though the piston packing did not have a defective seal. We enthusiastically examined the reason why the condition (small) continues to occur. As a result of the examination, it was found that the cause was as follows.
That is, in the state where the pressurizing chamber is pressurized, the piston is uniformly pushed by the hydraulic pressure, so that the piston is suppressed from tilting and sealing failure does not occur. On the other hand, when the pressure is not applied, the hydraulic pressure that suppresses the tilt of the piston does not act, so that the piston may tilt slightly and rattle. During such non-pressurization, a small amount of oil may leak to the non-pressurized chamber side. Such oil leakage is likely to occur in an environment where vibration is input or in an environment in which a one-sided load (cantilever load) is applied to the piston rod.

Here, the one-sided load is a load input at a position offset in the radial direction of the piston rod with respect to the piston rod, and the bending moment acts on the piston rod by the input of this one-sided load, and the input load is large. Indeed, the bending moment becomes large.
However, even if the piston packing itself is deteriorated, a small amount of oil may leak to the non-pressurized chamber side during non-pressurization.
The present invention has been made based on the above findings.

That is, in order to solve the problem, in one aspect of the present invention, the inside of the cylinder case is divided into a first chamber and a second chamber by a piston, and a return spring is arranged in the first chamber, and a return spring is arranged. A hydraulic actuator including a single-acting hydraulic cylinder in which the piston advances and retreats by hydraulic oil supplied to the second chamber through the supply path, the first check valve inserted in the supply path, and the supply. A bypass path that connects a position on the upstream side of the first check valve and a position on the downstream side of the first check valve in the road to bypass the first check valve, and an interposition in the bypass path. The gist is that the second chamber is provided with the first check valve and the second check valve in which the flow direction of the fluid is opposite to that of the first check valve.

Another aspect of the present invention is a vehicle diff lock device including the hydraulic actuator of the above aspect and a shift fork connected to a piston rod fixed to the piston of the hydraulic actuator.

In another aspect of the present invention, the inside of the cylinder case is divided into a first chamber and a second chamber by a piston, a return spring is arranged in the first chamber, and a return spring is arranged, and the inside of the cylinder case is arranged via a supply port. It is a hydraulic circuit for a single-acting hydraulic cylinder in which the piston moves forward and backward by the hydraulic oil supplied to the second chamber, and is interposed in the supply path connecting the hydraulic pump and the supply port and in the middle of the supply path. A switching valve that is inserted to switch between communication of the hydraulic pump to the second chamber and communication to the oil tank of the second chamber, and a first check valve inserted in the supply path. , A bypass path that connects the position upstream of the first check valve and the position downstream of the first check valve in the supply path to bypass the first check valve, and the bypass path. The first check valve and the second check valve in which the flow direction of the fluid is opposite to each other are provided with respect to the second chamber. The gist is that it is located between the switching valve and the supply port.

In one aspect of the present invention, a simple configuration makes it possible to suppress oil leakage during non-pressurization.

It is a figure explaining the diff lock device which concerns on embodiment based on this invention. It is a figure explaining the drive part by the cylinder of the shift mechanism of a diff lock device. It is a figure which shows the non-pressurized state, (a) is a figure explaining a single-acting hydraulic cylinder, (b) is a figure explaining a hydraulic circuit. It is a figure which shows the state at the time of pressurization, (a) is a figure explaining a single-acting hydraulic cylinder, (b) is a figure explaining a hydraulic circuit. It is a figure which shows the state from the time of pressurization to the time of depressurization, (a) is a figure explaining a single-acting hydraulic cylinder, and (b) is a figure explaining a hydraulic circuit. It is a figure which shows the reference hydraulic circuit.

Next, an embodiment of the present invention will be described.
In the present embodiment, a case where a hydraulic actuator composed of a single-acting hydraulic cylinder is used for a vehicle diff lock device will be described as an example. The present invention can be applied to any machine using a single-acting cylinder, even if it is not a diff lock device. In particular, the present invention is particularly effective for a machine in which vibration is easily input to the cylinder and a machine in which a single load is applied to the piston rod.

As shown in FIG. 1, the diff lock device 4 is housed in the axle case 3 of the axle. In FIG. 1, reference numeral 1 is a wheel and reference numeral 2 is an axle.
A known mechanism can be adopted as the basic configuration of the diff lock device 4.

(composition)
In the present embodiment, as shown in FIG. 2, the shift fork 20 is connected to the tip of the piston rod 14 of the single-acting hydraulic cylinder 10 (also simply referred to as the hydraulic cylinder 10), and the piston rod accompanies the operation of the hydraulic actuator. By advancing and retreating the 14th, the axial position of the sleeve 21 (coupling) is shifted by the tip portion 20a of the shift fork 20, and the connection and disconnection of the differential lock can be controlled.
Here, the position of the tip portion 20a of the shift fork 20 is offset in the radial direction of the piston rod 14 with respect to the piston rod 14, that is, the shift fork 20 has a cantilever shape with respect to the load. Therefore, a one-sided load is applied to the piston rod 14.

In the single-acting hydraulic cylinder 10, as shown in FIGS. 2 and 3A, the piston 12 is arranged in the cylinder case 11, and the inside of the cylinder case 11 is pressurized by the piston 12 in the pressurizing chamber 10A (FIG. 2). The room on the right side: the second room) and the non-pressurized room 10B (the room on the left side in FIG. 2: the first room).
A piston rod 14 is integrally connected to the piston 12. The piston rod 14 extends to the non-pressurizing chamber 10B side, and the tip end portion of the piston rod 14 projects to the outside of the cylinder case 11. A shift fork 20 is connected to the tip of the piston rod 14.

Further, in the non-pressurizing chamber 10B, a return spring 15 is arranged in parallel with the piston rod 14, and the piston 12 is urged toward the pressurizing chamber 10A by the spring 15. The states of FIGS. 2 and 3A indicate a state in which the pressurizing chamber 10A is in a non-pressurized state and the piston 12 is moved to the rightmost wall surface in the cylinder case 11 by the spring force of the spring 15. There is.
A supply port 10C communicating with the pressurizing chamber 10A is formed in the cylinder case 11, and hydraulic oil can be supplied to the pressurizing chamber 10A via the supply port 10C.
One end of the supply line 23 is connected to the supply port 10C as shown in FIG. The other end of the supply pipeline 23 is connected to the electromagnetic switching valve 29 as shown in FIG. As shown in FIG. 1, the switching valve 29 of the present embodiment is composed of two positions and four ports.

Further, the switching valve 29 is connected to a pressurizing pipe line 27 having one end connected to the discharge port of the hydraulic pump 30 and a return pipe line 28 having one end connected to the oil tank 31. When the switching valve 29 is in the first position, the supply line 23 and the pressurizing line 27 are in a communicating state, and the supply line 23 and the return line 28 are in a non-communication state. It has become. When the switching valve 29 is in the second position, the supply line 23 and the pressurizing line 27 are in a non-communication state, and the supply line 23 and the return line 28 are in a communication state. It has become. The switching valve 29 is controlled to either a first position or a second position in response to a command from the control device 32. FIG. 1 illustrates a case where the switching valve 29 is in the first position.
Here, the supply line is formed by the supply line 23 and the pressurizing line 27.

In the present embodiment, the first check valve 25 is inserted into the supply line 23 between the supply port 10C and the switching valve 29. Further, between the supply port 10C and the switching valve 29, a first position in the supply line 23 on the upstream side of the first check valve 25 and a position on the downstream side of the first check valve 25 are connected to each other. A bypass path 24 that bypasses the check valve 25 of the above is provided. A second check valve 26 is inserted in the bypass path 24.
The first check valve 25 and the second check valve 26 are arranged so that the flow directions of the fluids are opposite to those of the pressurizing chamber 10A. In the example of FIG. 1, the first check valve 25 allows the flow of hydraulic oil to the pressurizing chamber 10A, and the second check valve 26 allows the flow of hydraulic oil from the pressurizing chamber 10A. It is possible. Even if the second check valve 26 allows the hydraulic oil to flow into the pressurizing chamber 10A and the first check valve 25 allows the hydraulic oil to flow from the pressurizing chamber 10A. good.
The first check valve 25 and the second check valve 26 have, for example, a check set pressure of 0.04 MPa.

It is preferable that the first check valve 25 and the second check valve 26 are arranged along the supply line 23 closer to the supply port 10C than the switching valve 29. For example, the first check valve 25 and the second check valve 26 are preferably provided at a position within 50 cm from the supply port 10C along the supply pipeline 23.
Here, it is preferable that the first check valve 25 and the second check valve 26 are arranged as close to the supply port 10C as possible, but maintenance of the first check valve 25 and the second check valve 26 and maintenance of the second check valve 26 are performed. Assuming that the first check valve 25 and the second check valve 26 are to be provided later, it is preferable to provide them outside the cylinder case 11.
Here, the first check valve 25, the second check valve 26, and the bypass path 24 may be formed in the cylinder case 11.

(Operation and others)
In the hydraulic actuator and the vehicle differential lock device 4 of the present embodiment, the switching valve 29 is in the second position in the non-pressurized state, and the pressurizing chamber 10A is in a state of communicating with the oil tank 31. As shown in FIG. 3, the piston 12 is located at the right end of the pressurizing chamber 10A by the spring force of the spring 15. FIG. 2 shows this non-pressurized state.
Next, when the switching valve 29 is switched to the first position while the pump 30 is in the driving state, the pressurizing chamber 10A communicates with the pump 30. Therefore, as a result of pressure feeding of the hydraulic oil to the pressurizing chamber 10A, as shown in FIG. 4, the piston 12 moves to the non-pressurizing chamber 10B side, and the sleeve 21 shown in FIG. 2 shifts to the left side. At this time, the hydraulic oil pumped from the pump 30 is supplied to the pressurizing chamber 10A via the first check valve 25, and the second check valve 26 is closed and does not flow on the bypass path 24 side. Here, the spring force of the first check valve 25 is set to a value smaller than the hydraulic force.

When the switching valve 29 is switched to the second position from this state, the hydraulic oil in the pressurizing chamber 10A is oiled through the supply port 10C as the piston 12 moves toward the pressurizing chamber 10A due to the spring force of the spring 15. Although it moves to the tank 31 side, as shown in FIG. 5B, the first check valve 25 side is in a closed state, and the oil tank is passed through the second check valve 26 provided in the bypass path 24. It flows to the 31 side. Here, the spring force of the second check valve 26 is set to a value smaller than the spring force of the spring 15.
When the piston 12 moves to the right end of the pressurizing chamber 10A at the second position of the switching valve 29, the state returns to the state shown in FIG. 3 and the hydraulic oil does not move from the pressurizing chamber 10A to the supply pipe line 23 side.

At this time, if the first check valve 25 and the second check valve 26 are not provided, the hydraulic oil in the supply pipe line 23 can flow to the pressurizing chamber 10A side by free fall. If the piston 12 is tilted, some hydraulic oil may move to the non-pressurized side.
On the other hand, in the present embodiment, the hydraulic oil in the non-pressure fed state (free fall) is prevented from moving to the pressurizing chamber 10A side by the first check valve 25 and the second check valve 26. Here, the spring force of the first check valve 25 is set to a value larger than the force of the hydraulic oil existing in the supply pipe line 23 and capable of free fall toward the pressurizing chamber 10A.

That is, when the piston 12 moves to the pressurizing chamber 10A side by the spring 15, the hydraulic oil in the pressurizing chamber 10A moves to the supply pipe line 23 side, but when the movement of the piston 12 stops, FIG. As described above, the first check valve 25 and the second check valve 26 do not return to the pressurizing chamber 10A side through the supply line 23.
Further, when the first check valve 25 and the second check valve 26 are closed together, the positions from the first check valve 25 and the second check valve 26 to the supply port 10C become negative pressure, and the first check valve 25 and the second check valve 26 become negative pressure. The hydraulic oil in the supply port 10C from the check valve 25 and the second check valve 26 also becomes difficult to move to the pressurizing chamber 10A side.

Here, in the present embodiment, as shown in FIG. 2, the shift fork 20 is connected to the end of the piston rod 14 in a cantilever shape, and the shift fork 20 is displaced in the radial direction from the axial direction of the piston rod 14. As a result of the load being input to the tip portion 20a, a one-sided load is input to the piston rod 14 as the piston 12 moves forward and backward (movable), and the piston 12 tends to tilt. When a load is applied to the piston rod 14 and the piston 12 is tilted, a sealing defect occurs in a part of the circumferential direction even if the piston 12 is sealed by the piston packing 13, and the pressure chamber 10A side passes through the sealing defective portion. The hydraulic oil may move to the non-pressurized chamber 10B side.

When the first check valve 25 and the second check valve 26 are not provided, the oil tank 31 side of the supply line 23 is open to the atmosphere, so that the hydraulic oil in the supply line 23 is large. The hydraulic oil may move to the non-pressurized chamber 10B side if there is a seal defective portion.
On the other hand, in the present embodiment, in the non-pressurized state, the first check valve 25 and the second check valve 26 close the middle of the supply line 23, and the inside of the supply line 23 is closed. The hydraulic oil is released to the atmosphere and prevented from moving to the pressurized side. As a result, even if the piston 12 is tilted during non-pressurization and there is a part with a defective seal in the circumferential direction, the hydraulic oil moves (oil leak) from the pressurizing chamber 10A to the non-pressurizing chamber 10B. Occurrence is prevented.

If the piston 12 has a defective seal during pressurization, a large amount of hydraulic oil leaks in a short time, so that the defect is likely to be detected at an early stage. On the other hand, a small amount of hydraulic oil leaks when not pressurized tends to take a long time to leak.
Further, in the diff lock device 4, a large load is input as a single load, the piston tends to tilt when no pressurization is applied, and the above-mentioned small amount of oil leakage is likely to occur.

(effect)
This embodiment has the following effects.
(1) In the present embodiment, the inside of the cylinder case 11 is divided into a first chamber and a second chamber by a piston 12, a return spring 15 is arranged in the first chamber, and a supply path (supply). A hydraulic actuator including a single-acting hydraulic cylinder 10 in which the piston 12 advances and retreats by hydraulic oil supplied to the second chamber through the pipeline 23), and a first check valve inserted in the supply path. A bypass path that connects the 25 and the position on the upstream side of the first check valve 25 and the position on the downstream side of the first check valve 25 in the supply path to bypass the first check valve 25. A second check valve 25, which is inserted through the bypass path 24 and has a fluid flow direction opposite to that of the first check valve 25, is provided with respect to the second chamber.

For example, in the present embodiment, the inside of the cylinder case is divided into a first chamber and a second chamber by a piston, a return spring is arranged in the first chamber, and the second chamber is provided via a supply port. This is a hydraulic circuit that drives a single-acting hydraulic cylinder in which the piston moves forward and backward by the hydraulic oil supplied to the chamber, and is a supply path (supply line 23, pressurization line) that connects the hydraulic pump 30 and the supply port 10C. 27), a switching valve that is inserted in the middle of the supply path to switch between the connection of the hydraulic pump to the second chamber and the connection of the second chamber to the oil tank, and the supply path. The first check valve inserted in the above, and the position on the upstream side of the first check valve and the position on the downstream side of the first check valve in the supply path are connected to each other. The first check valve and the second check valve in which the flow direction of the fluid is opposite to each other are provided with respect to the second chamber. The check valve and the bypass path are arranged between the switching valve and the supply port.

According to this configuration, when the hydraulic cylinder 10 is in the non-pressurized state and the movement of the piston 12 is stopped, the hydraulic oil in the supply pipe line 23 is suppressed from returning to the pressurizing chamber 10A. As a result, it is possible to prevent the hydraulic oil from leaking from the pressurizing chamber 10A to the non-pressurizing chamber 10B even if there is a defective seal portion of the piston 12 in the non-pressurized state.
Further, in the present embodiment, as shown in FIG. 1, the above effect is obtained by using simple parts (bypass path 24 and two check valves 25 and 26). Therefore, it can be retrofitted to the existing device.

Here, the bypass path 24 and the two check valves 25 and 26 may be used as one hydraulic block (the portion of the symbol X surrounded by the alternate long and short dash line in FIG. 1).
Even if a three-position switching valve as shown in FIG. 6 is used as the switching valve 29, the same effect as described above can be obtained. However, in this case, it is necessary to incorporate the switching valve 29 as shown in FIG. 6 from the beginning and set the processing of the control device 32 corresponding thereto. On the other hand, in the present embodiment, with a simpler configuration, it is possible to prevent the hydraulic oil from leaking from the pressurizing chamber 10A to the non-pressurizing chamber 10B even if there is a defective seal portion of the piston 12. ..
Here, the hydraulic oil leaking to the non-pressurized chamber 10B side overflows from the non-pressurized chamber 10B and leaks to the outside of the cylinder case 11 of the hydraulic cylinder 10.

(2) In the present embodiment, the first check valve and the second check valve are arranged along the supply path (supply line 23) closer to the supply port than the switching valve. ..
According to this configuration, the amount of hydraulic oil located between the first check valve 25 and the second check valve 26 and the supply port 10C can be reduced.
Here, when the first check valve 25 and the second check valve 26 are closed, there is a slight negative pressure between the first check valve 25 and the second check valve 26 and the supply port 10C. Although it is difficult to move to the pressurizing chamber 10A side, when vibration is input to the hydraulic cylinder 10 in the non-pressurized state, the vibration causes the supply port from the first check valve 25 and the second check valve 26. The hydraulic oil during 10C may move to the pressurizing chamber 10A side. Therefore, it is preferable that the first check valve 25 and the second check valve 26 are arranged close to the supply port 10C.
For example, the first check valve 25 and the second check valve 26 are preferably provided at a position within 50 cm along the supply path from the connection portion of the supply path to the second chamber.

(3) The present embodiment is a hydraulic actuator in which a one-sided load is applied to the piston rod 14 connected to the piston 12 as the piston 12 moves forward and backward.
In the vehicle differential lock device 4 including the hydraulic actuator and the shift fork 20 connected to the piston rod 14 fixed to the piston 12 of the hydraulic actuator, the piston 12 moves forward and backward with respect to the piston rod 14 connected to the piston 12. Along with this, it becomes a hydraulic actuator to which one load is applied.
In this configuration, a one-sided load (cantilever load) is applied to the piston rod 14. At the time of pressurization, the tilt of the piston 12 is suppressed by the hydraulic pressure, but at the time of non-pressurization, the piston 12 is likely to be tilted by one load. Therefore, the hydraulic oil in the pressurizing chamber 10A may leak to the non-pressurizing chamber 10B side during non-pressurization. On the other hand, in the present embodiment, as described above, the occurrence of oil leakage of the hydraulic oil is prevented, and the occurrence of oil leakage is less likely to occur until the periodic maintenance of the diff lock device 4.

4 diff lock device 10 Single-acting hydraulic cylinder 10A Pressurizing chamber (second chamber)
10B non-pressurized chamber (first chamber)
10C Supply port 11 Cylinder case 12 Piston 13 Piston packing 14 Piston rod 15 Spring 20 Shift fork 20a Tip 21 Sleeve 23 Supply pipeline (supply route)
24 Bypass path 25 First check valve 26 Second check valve 27 Pressurized pipeline (supply path)
28 Return line 29 Electromagnetic switching valve 30 Hydraulic pump 31 Oil tank 32 Control device

Claims (7)

The inside of the cylinder case is divided into a first chamber and a second chamber by a piston, a return spring is arranged in the first chamber, and a hydraulic oil supplied to the second chamber through a supply path is used. A hydraulic actuator including a single-acting hydraulic cylinder in which the piston moves forward and backward.
The first check valve inserted in the supply path and
A bypass path in the supply path that connects a position upstream of the first check valve and a position downstream of the first check valve to bypass the first check valve.
A second check valve inserted through the bypass path and having a fluid flow direction opposite to that of the first check valve with respect to the second chamber.
A hydraulic actuator characterized by being provided with. The first check valve and the second check valve are claimed so as to be provided at a position within 50 cm along the supply path from the supply port communicating with the second chamber. Item 1. The hydraulic actuator according to item 1. The hydraulic actuator according to claim 1 or 2, wherein a one-sided load is applied to the piston rod connected to the piston as the piston moves forward and backward. A vehicle diff lock device comprising the hydraulic actuator according to any one of claims 1 to 3 and a shift fork connected to a piston rod fixed to the piston of the hydraulic actuator. The inside of the cylinder case is divided into a first chamber and a second chamber by a piston, a return spring is arranged in the first chamber, and an operation of being supplied to the second chamber via a supply port is performed. A hydraulic circuit for a single-acting hydraulic cylinder in which the piston moves back and forth due to oil.
A supply path connecting the hydraulic pump and the above supply port,
A switching valve inserted in the middle of the supply path to switch between the communication of the hydraulic pump to the second chamber and the communication of the hydraulic pump to the oil tank of the second chamber.
The first check valve inserted in the supply path and
A bypass path in the supply path that connects a position upstream of the first check valve and a position downstream of the first check valve to bypass the first check valve.
A second check valve inserted through the bypass path and having a fluid flow direction opposite to that of the first check valve with respect to the second chamber.
With
The first check valve and the bypass path are arranged between the switching valve and the supply port.
A hydraulic circuit for a single-acting hydraulic cylinder. The single-acting type according to claim 5, wherein the first check valve and the second check valve are arranged along the supply path closer to the supply port than the switching valve. Hydraulic circuit of hydraulic cylinder. The single-acting type according to claim 5 or 6, wherein the first check valve and the second check valve are provided at a position within 50 cm from the supply port along the supply path. Hydraulic circuit of hydraulic cylinder.

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