JPH0520601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fluid control device that controls the operation of a fluid actuator by pilot operating four poppet-type main valves.

[Prior art] This type of fluid control device is known, for example, from Japanese Patent Application Laid-Open No. 1989-
It is disclosed in Publication No. 11703. By the way, in each poppet type main valve (logic valve) disclosed in the above publication, pilot pressure (discharged from the pilot pump) is passed through each pilot port on one side and into each pilot chamber on one side that accommodates a spring. (defined by pressure reducing valve and relief valve)
In addition, the discharge pressure of the pilot pump is supplied to each pilot chamber on the other side through each solenoid valve that opens according to the pulse width to control the supply flow rate and each pilot port on the other side. Hydraulic oil is supplied, and the hydraulic oil is discharged from each pilot chamber on the other side through each pilot port on the other side and each solenoid valve that opens according to the pulse width to control the discharge flow rate. There is. Therefore, the degree of opening of each main valve is determined by the flow rate of the hydraulic oil supplied from the pilot pump to each pilot chamber on the other side in accordance with the pulse width.

[Problems to be Solved by the Invention] However, since the hydraulic oil supplied to each pilot chamber on the other side leaks over time, it is impossible to maintain a constant opening over a long period of time. In addition, the pressure of the hydraulic oil discharged from the pilot pump decreases due to the decrease in efficiency due to long-term use of the pilot pump, so if the pilot pump is used for a long time, the correct amount of hydraulic oil will not be supplied to each pilot chamber on the other side. The valve opening degree becomes inaccurate. Furthermore, by increasing the pilot pressure that is constantly applied to each pilot chamber on one side to improve the shutoff function when each main valve is closed, the valves will resist this high pilot pressure and flow into each pilot chamber on the other side when the valves open. The supplied hydraulic oil must flow in, resulting in a large power loss. These problems are fatal to the control valve, and it cannot be used in practice.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a poppet-type fluid control device that controls communication between a supply flow path and one load flow path. A first main valve, a poppet-type second main valve that controls communication between the supply flow path and the other load flow path, and a poppet-type third main valve that controls communication between the discharge flow path and one load flow path. and a poppet-type fourth main valve that controls communication between the discharge flow path and the other load flow path, and first to fourth pilot valves that control the operations of the first to fourth main valves, respectively. Each of the main valves has a valve body having a large-diameter hole and a small-diameter hole of the same diameter connected to both ends thereof, and a valve seat formed in one of the connected stepped portions, and A poppet valve part that forms a first oil chamber around the periphery that is movable in a forward-backward manner and always communicates with one flow path, and opens and closes the valve seat by seating on or leaving the valve seat, and one side of the poppet valve part. a connecting portion that is connected to the first oil chamber and forms a second oil chamber around the first oil chamber that extends into the one small diameter hole and is in constant communication with the other flow path and communicates with the first oil chamber through the valve seat; integrally provided with a piston portion which is connected to the one side of the poppet valve portion and is slidably inserted into the one small diameter hole to form a third oil chamber at the end of the small diameter hole; a valve body that integrally includes a small diameter portion that is slidably inserted into the other small diameter hole and forms a fourth oil chamber that is connected to the high pressure side of the flow path via a throttle at the end of the same small diameter hole; A pressure control valve comprising a spring that biases the valve body toward the third oil chamber, and each of the pilot valves proportionally controlling the pilot pressure applied to the third oil chamber in accordance with a current applied value. and when the pilot pressure is less than a set value, communication between the fourth oil chamber and the return passage is cut off, and when the pilot pressure is above the set value, the fourth oil chamber and the return passage are communicated with each other. The configuration includes a switching valve.

[Operations and Effects of the Invention] In the fluid control device according to the present invention, when the pilot pressure is set to a constant pressure equal to or higher than a set value by each pressure control valve (for example, a current-controlled relief valve or a current-controlled pressure reducing valve) of each pilot valve, Since each switching valve communicates each fourth oil chamber with the return flow path, the hydraulic pressure in each fourth oil chamber is removed, and the valve body of each main valve is pushed by the pilot pressure in each third oil chamber, and the same It is held at a position where the pressing force by the pilot pressure and the acting force of the spring (the pressure in the fourth oil chamber is approximately zero) are balanced.

By the way, since the pilot pressure in each third oil chamber is set by each pressure control valve which is proportionally controlled according to the current applied value, the hydraulic oil in each third oil chamber may leak over time. Even if the pressure of the pilot pressure source changes, it will not change at all as long as there is no change in the current applied value, and the opening degree of each main valve will remain constant for a long time even when used for a long time. The opening is held accurately.

Further, when the valve body of each main valve is pushed by the pilot pressure in each third oil chamber, each fourth oil chamber is communicated with the return passage by the operation of each switching valve, and each Since the pressure in the fourth oil chamber is approximately zero, no large power loss occurs.

[Example] An example of the present invention will be described below based on the drawings.

FIG. 1 shows a fluid control device according to the invention, which includes a supply channel P1 and one load channel P2.
a poppet-type first main valve 10 that controls communication between;
A poppet-type second main valve 20 that controls communication between the supply flow path P1 and the other load flow path P3, and a discharge flow path P4.
a poppet-type third main valve 30 that controls communication between the discharge flow path P4 and the other load flow path P3, and a poppet-type fourth main valve 40 that controls communication between the discharge flow path P4 and the other load flow path P3; Current-controlled relief valves 51, 52, 53, and 5 that function as first to fourth pilot valves that control the operation of valves 10, 20, 30, and 40, respectively;
4 and switching valves 60, 70, 80, and 90.

Each of the main valves 10, 20, 30, and 40 has the same basic configuration, and as shown in FIGS. 1 and 2 using the first main valve 10 as an example, the first member 1
1A, a second member 11B, and a third member 11C; a valve body 12 that is slidably inserted into the valve body 11 in the left-right direction; and a valve body 12 that urges the valve body 12 to the left. It is constituted by a spring 13. The valve body 11 has a stepped inner hole in which small diameter holes 11b and 11c of the same diameter are connected to each other at both left and right ends of a large diameter hole 11a, and a valve seat 11d is formed in the left continuous stepped portion. It also has an annular groove 11e with which the supply flow path P1 communicates and an annular groove 11f with which the load flow path P2 communicates.

The valve body 12 is provided in a first oil chamber R that is movable forward and backward relative to the valve seat 11d and is always in communication with the supply flow path P1.
A poppet valve part 12a is formed around the valve seat 11d and seats on or leaves the valve seat 11d to cut off communication (open/close) with the valve seat 11d, and a small diameter hole on the left side is connected to the left side of the poppet valve part 12a. A connecting portion 12b that extends into the connecting portion 11b and forms a second oil chamber R2 around the second oil chamber R2 that is constantly connected to one load flow path P2 and communicates with the first oil chamber R1 through the valve seat 11d; A piston part 12c that is slidably inserted into the left small diameter hole 11b and forms a third oil chamber R13 at the end of the small diameter hole 11b is integrally provided, and a right small diameter hole is provided on the right side of the poppet valve part 12a. It is slidably inserted into the hole 11c, and a fourth oil chamber R14 is provided at the end of the small diameter hole 11c.
and a fifth oil chamber R at the end of the large diameter hole 11a.
15 is integrally provided with a small diameter cylindrical portion 12d. Therefore, the pilot pressure introduction passage is connected to the third oil chamber R13, and the fourth oil chamber R14 is connected to the throttle 14.
is connected to the first oil chamber R11 via the fifth oil chamber R11.
15 is connected to the first oil chamber R11 via a communication path. If there is no need to interpose anything in the communication path between the fifth oil chamber R15 and the first oil chamber R11, the eighth oil chamber
As shown in the figure, it is also possible to combine the fifth oil chamber R15 and the first oil chamber R11.

Note that corresponding members of the second to fourth main valves 20, 30, and 40 are given similar symbols and their explanations are omitted. (See Fig. 1) Therefore, in each main valve 10, 20, 30, 40, the first and fifth valves act on the poppet valve portions 12a, 22a, 32a, 42a of the valve bodies 12, 22, 32, 42. Oil chamber R11~R41, R15~R4
The pressing force due to the hydraulic pressure in the second oil chambers R12 to R42 acting on the poppet valve parts 12a, 22a, 32a, 42a and the piston parts 12c, 22c, 32c, 42c is canceled out. Therefore, the valve bodies 12 to 42 are first, second,
5th oil chamber R11~R41, R12~R42, R1
5 to R45 will not be pushed or moved by fluctuations in the internal oil pressure.

Each current control relief valve 51, 52, 53, 54
are connected to a pressure reducing valve 59 via throttles 55, 56, 57, 58, and each main valve 10, 20, 3
0,40 third oil chamber R13, R23, R33, R
The pilot pressure applied to 43 is proportionally controlled according to the current applied value. Note that the pressure reducing valve 59 is connected to the supply flow path P1, and controls the pressure reduction of the oil pressure supplied from the flow path P1 to a predetermined value.

Each switching valve 60, 70, 80, 90 has the same basic configuration, and as shown in FIGS. 1 and 3 using the switching valve 60 as an example, the third oil chamber R
13, and a second switching valve 62 whose operation is controlled by the first switching valve 61. The first switching valve 61 includes a spool valve body 61a and a spring 61b, and has a third oil chamber R.
When the pilot pressure applied from 13 to the oil chamber R16 through the passage P11 is less than the set value, it is in the non-operating state as shown in the figure, and the connection between the supply passage P1 and the second switching valve 62 is cut off, and the pilot pressure is lowered. When the value is greater than or equal to the set value, it becomes activated and the supply flow path P1
is connected to the second switching valve 62. Second switching valve 62
is equipped with a piston 62a integrally having a protrusion, a poppet valve body 62b, and a spring 62c, and the oil chamber R17 is connected to the supply flow path P1 by the first switching valve 61.
When connected to the reservoir T, the passage P12 communicates with the fourth oil chamber R14 and the return passage P5 which communicates with the reservoir T. When the connection is cut off and connected to the return passage P5, it becomes inoperative as shown in the figure, cutting off communication between the passage P12 communicating with the fourth oil chamber R14 and the return passage P5.

Note that corresponding members of the switching valves 70, 80, and 90 are given similar symbols and their explanations are omitted. (See Figure 1) In this embodiment configured as described above, the current control relief valve 51 in each pilot valve,
By appropriately changing the current applied values to 52, 53, and 54, the following operations can be obtained.

(1) Third oil chambers R13, R23, R33, R43 of each main valve 10, 20, 30, 40 by setting the current applied value to the current control relief valves 51, 52, 53, 54 in each pilot valve to be less than the set value. When the pilot pressure applied to is less than the set value.

At this time, the switching valves 60, 70, 80, 90 in each pilot valve are connected to each main valve 10, 2.
Communication between the fourth oil chambers R14 to R44 of Nos. 0, 30, and 40 and the return passage P5 is cut off. For this reason,
The valve bodies 12 to 42 of each main valve 10 to 40 have a throttle 14
The poppet valve portions 12a to 42a are pressed against the pilot pressure in the third oil chambers R13 to R43 by the hydraulic pressure applied to the fourth oil chambers R14 to R44 through 44 and the action of the springs 13 to 43.
are seated on the valve seats 11d to 41d, and the first
Communication between the passages communicating with the oil chambers R11 to R41 and the passages communicating with the second oil chambers R12 to R42 is cut off. Therefore, each load flow path P2, P
3 is maintained, and the liquid actuator A connected to the load channels P2 and P3 is maintained in a stopped state even when a load is applied.

(2) Current control relief valves 51, 54 in the first and fourth (or second and third) pilot valves
(or 52, 53) to the set value or more, and the third oil sac R of the first and fourth (or second and third) main valves 10, 40 (or 20, 30)
13, when each pilot pressure applied to R43 (or R23, R33) is set at or above the set value.

At this time, each switching valve 60, 9 in the first and fourth (or second and third) pilot valves
0 (or 70, 80) opens and opens the fourth oil chambers R14, R44 (or R24, R34) of the first and fourth (or second and third) main valves 10, 40 (or 20, 30). is communicated with the return flow path P5. Therefore, the fourth of the first and fourth (or second and third) main valves 10, 40 (or 20, 30)
The oil pressure in the oil chambers R14, R44 (or R24, R34) decreases, and the valve bodies 12, 42 (or 2) of the first and fourth (or second and third) main valves decrease.
2, 32) is the pressing force due to the pilot pressure in each third oil chamber R13, R43 (or R23, R33) and the acting force of the springs 13, 43 (or 23, 33) (in detail, the same acting force and the third oil chamber 4.The resultant force of the pressing force due to the hydraulic pressure remaining in the oil chamber) is held at a position where it is balanced. Therefore, to the liquid actuator A through the supply channel P1 and one load channel P2 (or the other load channel P3),
A drive circuit is formed in which fluid flows from the fluid actuator A through the other load flow path P3 (or one load flow path P2) and the discharge flow path P4, and the fluid actuator A operates.

However, in this state, the first (or second)
By giving a difference in the current applied values to the current control relief valve 51 (or 52) of the pilot valve and the current control relief valve 54 (or 53) of the fourth (or third) pilot valve, the first (or second) Main valve 10
(or 20) and the fourth (or third) main valve 40 (or 30) are fully open and the other is in an appropriate throttle state, the operation of the fluid actuator A is controlled by meter-in or meter-out control. can do. Note that during the operation of the fluid actuator A, the current control relief valve 51 (or 5
2) and the current applied value to the current control relief valve 54 (or 53) of the fourth (or third) pilot valve, it is possible to change from meter-in control to meter-out control (or vice versa). Furthermore, when the current applied to the current control relief valve 53 (or 54) in the third (or fourth) pilot valve is set to a certain value greater than the set value while the fluid actuator A is in operation, the first
A part or all of the pressure fluid being supplied to the fluid actuator A through the (or second) main valve 10 (or 20) is transferred to the third (or fourth) main valve 30.
(or 40) and is discharged to the discharge flow path P4,
The operation of the fluid actuator A is under pressure reduction control or bleed-off control.

(3) The current applied value to the current control relief valves 51, 52 in the first and second pilot valves is set to be equal to or higher than the set value, and the third of the first and second main valves 10, 20
When each pilot pressure applied to the oil chambers R13 and R23 is set at or above the set value.

At this time, the respective switching valves 60 and 70 in the first and second pilot valves are operated to open the fourth oil chambers R14 and R2 of the first and second main valves 10 and 20.
4 is communicated with the return flow path P5. For this reason, the fourth oil chamber R14 of the first and second main valves 10, 20,
The hydraulic pressure inside R24 decreases, and the first and second
The valve bodies 12 and 22 of the main valve each have a third oil chamber R13 and R
Pressure force due to pilot pressure in 23 and spring 1
3, 23 acting force (in detail, the same acting force and the 4th acting force)
It is held at a position where the resultant force (combined with the pressing force due to the hydraulic pressure remaining in the oil chamber) is balanced. Therefore, supply flow path P1 is connected to both load flow paths P2 and P3.
A differential circuit is formed in communication with the fluid actuator A, and the fluid actuator A operates at high speed. In addition, in this state,
By giving a difference in the current applied values to the current control relief valves 51 and 52 in the first and second pilot valves, the supply flow path P1 and one of the load flow paths P
2 and P3, the operation of the fluid actuator A can be controlled in a meter-in or meter-out manner.

As is clear from the above description, in the fluid control device of this embodiment, when each pilot pressure is made a constant pressure equal to or higher than a set value by each current control relief valve 51, 52, 53, 54, each switching valve 6
0, 70, 80, 90 are each fourth oil chamber R14, R
24, R34, R44 and the return passage P5, the hydraulic pressure in each fourth oil chamber is removed, and the valve body 12, 22, 32, 42 of each main valve is connected to each third oil chamber R13, R23, R33. , is pushed by the pilot pressure in R43 to a position where the pressing force by the pilot pressure and the acting force of each spring 13, 23, 33, 43 (the pressure in the fourth oil chamber is almost zero) are balanced. Retained.

By the way, each third oil chamber R13, R23, R3
3. The pilot pressure in R43 is proportionally controlled according to the current applied value by each current control relief valve 5.
1, 52, 53, and 54, even if the hydraulic oil in each third oil chamber leaks over time, or even if the pressure of the pilot pressure source changes, the current As long as there is no change in the applied value, it will not change at all, and the opening degree of each main valve 10, 20, 30, 40 will be accurately maintained at a constant opening degree for a long time even when used for a long time.

In addition, the valve bodies 12, 22, 32, 42 of each main valve
is pushed by the pilot pressure in the third oil chamber, each switching valve 60, 70, 80, 90
As a result of the operation, each of the fourth oil chambers is communicated with the return flow path, and the pressure within each of the fourth oil chambers is approximately zero, so that no large power loss occurs.

Furthermore, in the fluid control device of this embodiment,
Current control relief valve 5 in each pilot valve
The opening/closing speed of each main valve 10, 20, 30, 40 can be controlled by controlling the operation of the main valves 1, 52, 53, and 54 with a time constant, thereby reducing the shock when starting or stopping the operation of the fluid actuator A. We can also expect the effects that can be achieved.

FIG. 4 shows a modification of the above embodiment, and in the fluid control device of the modification, the first
A load passage P2 is connected to the first oil chamber R11 of the main valve 10, and a supply passage P2 is connected to the second oil chamber R12.
1 is connected, the first oil chamber R11 and the fourth oil chamber R1
4 communicates through a throttle 14 provided in the valve body 12. In addition, the first oil chamber R2 of the second main valve 20
1, the load path P3 is connected to the second oil chamber R22, the supply flow path P1 is connected to the second oil chamber R22, and the first oil chamber R
21 and the fourth oil chamber R24 communicate with each other through a throttle 24 provided in the valve body 22. The rest of the structure is the same as that of the above embodiment. It should be noted that the operation obtained by the apparatus of this embodiment is exactly the same as that of the above-mentioned embodiment, so a description thereof will be omitted.

FIG. 5 shows another embodiment of the invention,
The fluid control device of the same embodiment is based on the device shown in FIG.
Restrictions 35 and 45 are interposed between the oil chambers R35 and R45, and pilot valves 110 and 45 are interposed between the third and fourth main valves 30 and 40 and the switching valves 80 and 90, respectively.
120 is interposed. Other configurations are the 4th
The configuration of the device is the same as that shown in the figure.

Each pilot valve 110, 120 has the same basic configuration.
As shown in FIGS. 5 and 6 by way of example, the load flow path P2 applied through the throttle 35
A relief valve 111 that operates when the oil pressure in the fifth oil chamber R35 reaches a predetermined value and causes the hydraulic oil in the fifth oil chamber R35 to flow to the return passage P5, and a switching valve 112 that operates in response to the operation of this relief valve 111. It is structured as follows. The switching valve 112 includes a valve body 112a and a spring 112b, and has a passage P in the oil chamber R38.
When the hydraulic pressure in the load passage P2 applied through the relief valve 111 is not relieved by the relief valve 111, the fourth
Passage P34 and return flow path P communicating with oil chamber R34
5 is disconnected, and when the oil pressure applied to the oil chamber R37 is relieved by the relief valve 111, the oil pressure in the load passage P2 applied to the oil chamber R39 through the passage P35 causes the valve body 112 to
a slides against the spring 112b and enters the passage P34.
is connected to the return flow path P5.

Note that corresponding members of the pilot valve 120 are given similar symbols and their explanations are omitted.

In this embodiment configured as above,
Current control relief valve 5 in each pilot valve
In addition to each operation (1), (2), and (3) obtained by the device shown in Fig. 1 by appropriately changing the current applied values to 1, 52, 53, and 54, the following (4), (5) can be obtained.

(4) If an excessive load is applied to fluid actuator A when fluid actuator A is held in a stopped state due to the operation in (1) above (or if an excessive load is applied while fluid actuator A is operating) In this case, the oil pressure in the load flow path P2 (or P3) increases and the pilot valve 110 (or 120)
When the predetermined value set by the relief valve (or 121) is reached, the oil pressure in the oil passage P33 (or P43) is returned to the return passage P5 and the switching valve 112
(or 122) is activated, and the fourth oil chamber R34 (or R4) of the third (or fourth) main valve 30 (or 40) is activated.
4) flows into the return passage P5 through the switching valve 112 (or 122). Therefore, in such a case, the valve body 32 (or 42) of the third (or fourth) main valve 30 (or 40) is in the first oil chamber R3.
1 (or R41) and the 5th oil chamber R35 (or R45) and the 3rd oil chamber R33
(or R43) and the fourth oil chamber R34 (or R44) (mainly the former differential pressure), it slides against the action of the spring 33 (or 43). Therefore, the load flow path P2 (or P3) communicates with the discharge flow path P4, pressure oil flows from the fluid actuator A to the reservoir T, and the fluid actuator A and the like are protected.

(5) Set the current applied value to the current control relief valve 51 (or 52) in the first (or second) pilot valve to be equal to or higher than the set value to the first (or second) main valve 1.
0 (or 20) third oil chamber R13 (or R2
3) When each pilot pressure applied is set at or above the set value.

At this time, the switching valve 60 (or 70) in the first (or second) pilot valve operates to open the fourth oil chamber R14 (or R24) of the first (or second) main valve 10 (or 20). It is made to communicate with the return flow path P5. Therefore, the valve body 12 (or 22) of the first (or second) main valve 10 (or 20) is opened, and the supply flow path P1 is connected to the load flow path P2 (or P
3). Therefore, the hydraulic pressure in the supply flow path P1 is transmitted to the fluid actuator A through the load flow path P2 (or P3), and further through the load flow path P3.
(or P2), and the oil pressure in the flow path increases. Thus, when the oil pressure in the load passage P3 (or P2) reaches the predetermined value set by the relief valve 121 (or 111) of the pilot valve 120 (or 110), it can be understood from the operation of (4) above. As such, the valve body 42 (or 32) of the fourth (or third) main valve 40 (or 30) is opened, and the load passage P3 (or P2) communicates with the discharge passage P4. As a result, the fluid actuator A is counterbalance controlled.

In each of the above embodiments, the main valves 10 to 40
A pilot valve consisting of current-controlled relief valves 51 to 54 and switching valves 60 to 90 was adopted as a pilot valve to control each operation of It is also possible to implement the present invention by employing the valves 51A to 54A and by employing the switching valve 60A shown in FIG. 8 in place of the switching valves 60 to 90. In addition, the current control pressure reducing valves 51A to 54
Similar to the current control relief valves 51 to 54, A has a function of proportionally controlling the pilot pressure applied to the third oil chambers R13 to R43 of each of the main valves 10 to 40 in accordance with the current applied value. Also, the switching valve 60
Similar to each of the switching valves 60 to 90, operation of A is controlled by the pilot pressure, and when the pilot pressure is less than the set value, the fourth oil chamber R14 and the return passage P5 are operated.
It has a function of cutting off communication between the fourth oil chamber R14 and the return passage P5 when the pilot pressure is equal to or higher than a set value.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing one embodiment of a fluid control device according to the present invention, FIG. 2 is a detailed enlarged sectional view of the first main valve portion of the device shown in FIG. 1, and FIG.
The figure is a detailed enlarged sectional view of the switching valve part of the first pilot valve in the device shown in FIG. 1, FIG. 4 is an overall configuration diagram showing a modification of the device shown in FIG. 1, and FIG. An overall configuration diagram showing another embodiment of the fluid control device according to the invention, FIG. 6 is a detailed enlarged sectional view of the pilot valve portion of the device shown in FIG. 5, and FIG. FIG. 8 is a partial configuration diagram showing a modification of the proportional control valve. FIG. 8 is a partial construction diagram showing a modification of the first main valve and a modification of the switching valve in the pilot valve. Explanation of symbols, 10, 20, 30, 40... Main valve, 11... Valve body, 11a... Large diameter hole, 11
b, 11c...Small diameter hole, 11d...Valve seat, 12...
...Valve body, 12a...Poppet valve part, 12b...Connecting part, 12c...Piston part, 12d...Small diameter part, 13...Spring, 14...Aperture, 51-54...
...Current control relief valve (pressure control valve), 60,7
0, 80, 90...Switching valve, P1...Supply channel,
P2...One load flow path, P3...The other load flow path, P4...Discharge flow path, P5...Return flow path, R1
1...First oil chamber, R12...Second oil chamber, R13...
...3rd oil chamber, R14...4th oil chamber.

Claims (1)

[Claims] 1. A poppet-type first main valve that controls communication between the supply flow path and one load flow path, and a poppet-type second main valve that controls communication between the supply flow path and the other load flow path. valve and
a poppet-type third main valve that controls communication between the discharge flow path and one load flow path; a poppet-type fourth main valve that controls communication between the discharge flow path and the other load flow path; The first to third valves each control the operation of the fourth main valve.
a fourth pilot valve, each of the main valves having a large-diameter hole and a small-diameter hole of the same diameter connected to both ends thereof, and a valve seat formed in one of the connected stepped portions; and a poppet valve portion that is provided so as to be movable toward and away from the valve seat and forms a first oil chamber around the valve seat that is always in communication with one of the flow paths, and that opens and closes the valve seat by seating on and leaving the valve seat. A second oil chamber is formed around the poppet valve part, the second oil chamber being connected to one side of the poppet valve part, extending into the one small diameter hole, constantly communicating with the other flow path, and communicating with the first oil chamber through the valve seat. a connecting portion and a piston portion connected to the connecting portion and slidably inserted into the one small diameter hole to form a third oil chamber at the end of the small diameter hole, and a piston portion of the poppet valve portion. A small diameter portion is integrally connected to the other side and is slidably inserted into the other small diameter hole and forms a fourth oil chamber connected to the high pressure side of the flow path via a restriction at the end of the small diameter hole. and a spring that biases the valve body towards the third oil chamber, and each of the pilot valves controls the pilot pressure applied to the third oil chamber to a current applied value. a pressure control valve that performs proportional control according to the pressure control valve; and a pressure control valve that cuts off communication between the fourth oil chamber and the return passage when the pilot pressure is less than a set value, and closes the fourth oil chamber when the pilot pressure is equal to or higher than the set value. and a switching valve that communicates with the return flow path.