JP2000335888A - Counterbalance valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase free flow, and to provide a low-cost counterbalance valve by forming a valve main body compact, and simplifying the whole constitution. SOLUTION: This device receives energization force of a spring 4 by one end surface, and energization force by pilot pressure from a second port P2 by the other end surface, it has a pressure receiving surface 11d to generate force against energization force of the spring 4 when oil pressure is generated at a fourth port P4, a spool 12A slidably included in a spool hole 11a is provided, and the spool 12A and the spool hole 11a are formed to let a first and a third ports P1, P3 continuous to open the valve when energization by the pilot pressure from the second port P2 received by the other end surface exceeds total of energization force of the spring 4 and energization force by oil pressure on the side of an actuator 3 where out-of-control load is generated, and when oil pressure as energization force exceeding total of energization force of the spring and energization force by oil pressure on the side of the actuator 3 where out-of-control load is generated is generated at the fourth port P4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a counterbalance valve.

[0002]

2. Description of the Related Art A counterbalance valve measures a load pressure of a boom cylinder (an example of an actuator) generated by a dead weight of a crane or a suspended load, and a load pressure of each hydraulic motor generated by an inertial turning or inertial running of a hydraulic shovel. This device is used as back pressure to prevent the boom cylinder from shortening faster than the operator can control and prevent each hydraulic motor from running idle. This will be specifically described with reference to FIG.

The counterbalance valve is roughly divided into an external pilot type 1A shown in FIG. 3A and an internal pilot type 1B shown in FIG. 3B. These have first and second ports Q1 and Q2 in the valve body 11, and fit the first and second check valves 12 and 13 therein. The first check valve 12 allows only fluid flow from the first port Q1 to the third port Q2. The second check valve 13 is urged to the closing side by a spring 13a, receives the pilot pressure Pp via an orifice 13b, and opens when the pilot pressure Pp overcomes the urging force of the spring 13a. Allow the fluid to flow to Q1. Details are as follows.

As shown in FIG. 3, for example, the first port Q1 is connected to one port A on the secondary side of the directional control valve 2, and the second port Q2 is connected to the bottom side of the boom cylinder 3. The head side of the boom cylinder 3 is the direction switching valve 2
Is connected to the other port B on the secondary side. Direction switching valve 2
Is the neutral position (center position in the figure), the extended position (right position in the figure)
And a shortened position (left position in the figure).
The ports A and B are provided on the secondary side, and the port P for receiving oil from the hydraulic pump 5 and the drain port T to the tank 5 are provided on the primary side. The operation is as follows.

(1) When the directional control valve 2 is in the neutral position,
The oil from the hydraulic pump 5 returns to the tank 5 via the ports P and T. A load pressure based on the load W such as the weight of the crane or the suspended load is generated in the second port Q2. However, since the pilot pressure Pp is low (substantially zero or negative pressure), the spring 13
The second check valve 13 is closed by the biasing force a. Also, the first check valve 12 is closed. Therefore, the boom cylinder 3
Has stopped. (2) When the direction switching valve 2 is switched to the left position, the hydraulic pressure from the hydraulic pump 5 flows into the first port Q1 and the second port Q2. The hydraulic pressure of the first port Q1 flows into the bottom via the second port Q2, and returns the low-pressure oil on the head side to the tank 5. Thereby, the boom cylinder 3 extends. The flow rate at this time is called a free flow. (3) When the directional control valve 2 is switched to the left position, the oil on the head side (FIG. 3 (a)) flowing from the hydraulic pump 5 is boosted together with the oil on the bottom side (FIG. 3 (b)), and this is the pilot pressure. When it becomes Pp and overcomes the urging force of the spring 13a, the second check valve 13 is opened, and the oil in the second port Q2 is returned to the tank 5 through the first port Q1. Thereby, the boom cylinder 3 is shortened. That is, as soon as the directional control valve 2 is moved to the left position by the second check valve 13, the boom cylinder 3 is not reduced by the load W beyond the control amount of the directional control valve 2.

FIG. 3 shows a hydraulic circuit having a counterbalance valve, not the actual structure of the counterbalance valve. As an actual structure, the first and second check valves 1
The second and third ports are arranged in parallel between the first and second ports Q1 and Q2 (for example, a technique described in JP-A-58-118383). (For example, FIG. 1 described in JP-A-59-62782), the first check valve 12 is connected to the second check valve 1.
3 (for example, FIG. 2 described in JP-A-59-62782).

[0007]

However, the above prior art has the following problems. (1) When the first and second check valves 12 and 13 are arranged in parallel between the first and second ports Q1 and Q2, the first and second check valves 12 and 13 are arranged in parallel, so that the free flow is performed. (For example, the extension speed of the boom cylinder 3 increases). However, because of the parallel arrangement, the size of the counterbalance valve becomes large. Furthermore, the first and second ports Q1, Q
2, the holes in which the first and second check valves 12 and 13 are fitted, and the holes for introducing the pilot pressure Pp are entangled with each other, and the inside of the counterbalance valve is complicated. (2) When the first check valve 12 is fitted inside the second check valve 13, the valve body 11 is downsized, but the free flow is reduced. (3) When the second check valve 13 is fitted inside the first check valve 12, the free flow is large, but the second check valve 1
3 and the inside of the valve body 11 become complicated, and the internal resistance increases.
That is, when the second check valve 13 is fitted inside the first check valve 12, the second check valve 13 needs to be urged against the valve body 11 by a spring 13a or the like. Therefore, the installation positions of the spring 13a and the port for receiving the pilot pressure Pp are complicated. For example, the counterbalance valve described in JP-A-59-62782 also has a complicated structure in the valve body and the second check valve.

The present invention has been made in view of the above-mentioned problems of the prior art,
It is an object of the present invention to provide an inexpensive counterbalance valve by increasing the free flow by reducing the size of the valve body and simplifying the overall configuration.

[0009]

In order to achieve the above object, a counterbalance valve according to a first aspect of the present invention comprises a directional control valve, and an oil inflow side and an oil outflow side by switching the directional control valve. Is operated by switching, and receives an externally controlled load based on gravity or inertia force, and is provided between the direction switching valve and the actuator, has a spring, and applies a pilot pressure to a side facing the spring force. A counterbalance valve having an opening / closing function that opens when the biasing force due to the pilot pressure exceeds the biasing force of the spring, and a check function that allows only the oil flow to the side where an uncontrolled load of the actuator is generated. A third port connected to the side of the actuator where an uncontrolled load occurs,
A fourth port connected to the side of the actuator that does not generate an uncontrolled load and the directional control valve, a second port for receiving the hydraulic pressure of the first port as pilot pressure, and one end communicating with the first to fourth ports; A valve body having a spool hole in which the spring is incorporated, a biasing force of the spring on one end face and a biasing force of a hydraulic pressure on a side where an externally controlled load of the actuator is generated, and a second port from the second port on the other end face. Receiving the biasing force due to the pilot pressure, a biasing force is generated on the side surface which opposes the biasing force of the spring and the biasing force of the hydraulic pressure on the side where an uncontrolled load of the actuator is generated when hydraulic pressure is generated at the third port. A spool having a pressure receiving surface and slidably fitted in the spool hole, wherein the spool and the spool hole receive a biasing force due to pilot pressure from the second port received at the other end surface. When the sum of the urging force of the spring and the urging force of the hydraulic pressure on the side where an uncontrolled load of the actuator is generated is exceeded, the urging force of the spring and the urging force of the hydraulic pressure on the side where the uncontrolled load of the actuator is generated at the fourth port When the hydraulic pressure which becomes the urging force exceeding the sum of the pressures is generated, the first and third ports are connected to each other to open the valve.

According to the first aspect of the present invention, the pressure oil is supplied to the first port and the second port of the counter balance valve via the direction switching valve, and the pressure oil of the second port received at the other end face of the spool is supplied. When the urging force used as the pilot pressure exceeds the sum of the urging force of the spring and the urging force of the hydraulic pressure on the side where an uncontrolled load of the actuator occurs, the spool is connected so that the first port and the third port communicate with each other. Open the valve. For this reason, the pressure oil supplied to the first port of the counterbalance valve via the directional switching valve is supplied from the first port to the side of the actuator where an externally controlled load is generated, and the pressure oil is supplied to the actuator in a direction opposite to the direction of the externally controlled load. Activate Pressure oil is supplied via the directional control valve to the side where no uncontrolled load of the actuator is generated and to the fourth port of the counterbalance valve, and the biasing force of the spring and the non-controlled load of the actuator are generated at the fourth port. When a hydraulic pressure that exceeds the sum of the biasing force due to the hydraulic pressure is generated, the valve is opened so that the first port and the third port communicate with each other. For this reason, the pressure oil on the side where the load of the actuator is generated is discharged from the first port and the third port of the counter balance valve via the direction switching valve, and the actuator is operated in the direction of the uncontrolled load. Therefore, when the pilot pressure is applied to the side opposite to the spring force and the urging force by the pilot pressure exceeds the urging force of the spring, the opening / closing function opens, and the oil flows to the side where the uncontrolled load of the directional control valve and the actuator occurs. Since the check function of allowing only one is performed by one spool, the size of the counterbalance valve can be reduced, and the flow path area can be increased if the size of the valve body is the same. For this reason, the free flow increases, the flow path resistance is reduced, and the efficiency can be improved. Further, since only one spool is required, the configuration of the counterbalance valve is simplified, and the production cost can be greatly reduced.

[0011] A counterbalance valve according to a second aspect of the present invention comprises:
In the first invention, a piston is provided in the spool hole, and one end of the piston faces the other end of the spool with the same cross-sectional area, and the other end having a larger cross-sectional area than the other end of the spool has a pilot port from the second port. A communication hole is slidably fitted in the spool so as to receive the pressure, and a communication hole is provided in the spool, the communication hole being opened at both end surfaces of the spool, and being opened at the side surface of the spool to introduce the hydraulic pressure of the first port. A first opening between one end of the spool and an opening on the side of the spool.
An aperture is provided, and a second aperture is provided between an opening on the other end surface of the spool and an opening on a side surface of the spool.

According to the second aspect, the hydraulic pressure from the third port acts as pilot pressure on both end faces of the spool via the communication hole, the first throttle, and the second throttle. Since the moving speed of the spool is slowed by the first throttle and the second throttle, hunting can be reduced as compared with the conventional check valve shown in FIG. Further, even if the hydraulic pressure of the third port acts on the other end surface of the spool and the one end surface of the piston via the second restrictor, the urging force of the second port pressure oil received at the other end surface of the piston as pilot pressure is applied. When the sum of the urging force of the spring and the urging force of the hydraulic pressure on the side where an uncontrolled load of the actuator occurs, the spool opens so that the first port and the third port communicate with each other. Therefore, even if the hunting prevention effect of the counterbalance valve is improved,
The operation and effect of the invention of (1) are obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment, and FIG. 2 shows a second embodiment. First, each embodiment will be described briefly. As shown in FIGS.
Are connected between the directional control valve 2 and the boom cylinder 3, the valve body 11 has first and second ports P1 and P2, and a spool 12 (reference numeral 12 in the first embodiment).
A, reference numeral 12B) is fitted in the second embodiment. Details are as follows. Note that the same elements as those in FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted.

First, the configuration of the first embodiment will be described. A spool 12A is slidably fitted in the spool hole 11a of the valve body 11. The valve body 11 includes a first port P1 and a second port P2 connected to the A port of the directional control valve 2.
A third port P3 connected to a bottom chamber of the boom cylinder 3 (a side on which a load outside the control is generated);
Rod chamber (side where no load outside control occurs) and directional control valve 2
And a fourth port P4 connected to the B port. The valve body 11 on the left end side of the spool 12A has a communication hole 1 formed in the center of the spool 12A and in the radial direction.
First pressure receiving chamber 11b communicating with third port P3 via 2a
Is formed. The first pressure receiving chamber 11b is provided with a spring 4 for urging the spool 12A to the right, and the cross-sectional area of the spool 12A facing the first pressure receiving chamber 11b is formed by a diameter D1. A second pressure receiving chamber 11c communicating with the second port P2 is provided in the valve body 11 on the right end side of the spool 12A.
Is formed. Spool 1 facing second pressure receiving chamber 11c
The diameter D2 of the cross-sectional area of 2A is formed larger than D1. The outer diameters D1 of the left and right ends 12g, 12f of the spool 12A are equal to each other. The outer diameter D2 of the central portion 12h is
It is the same as the diameter D2 of the spool 12A facing the pressure receiving chamber 11c, and is larger than the outer diameter D1 of each of the left and right ends 12f and 12g.
Valve body 1 closer to the central region in the axial direction than second pressure receiving chamber 11c
In 1, a third pressure receiving chamber 11d communicating with the fourth port P4 is formed. Spool 12 facing third pressure receiving chamber 11d
The pressure receiving area of A is formed at {π (D22−D12) / 4}. The poppet portion 1 has a spool 12A in which a left outer periphery of a substantially central region protrudes and a right side of the protruding portion is a slope.
2b, and an oil passage 12c communicating with the third port P3 between the poppet portion 12b and the right outer periphery of the substantially central region and between the poppet portion 12b and the inner wall of the valve body 11. The inner wall of the valve body 11 has a diameter D at a contact portion with the poppet portion 12b.
It has a second sheet surface 12d. That is, at the neutral position (stop position) c of the direction switching valve 2, the spool 12A is urged toward the closing side by the urging force of the spring 4 and the urging force of the pressure oil in the first pressure receiving chamber 11b. Communication hole 12a and first pressure receiving chamber 11
b is communicated via a throttle 6 built in the spool 12A.

(1) When the directional control valve 2 is at the neutral position c, the oil from the hydraulic pump 5 returns to the tank 6 via the ports P and T. A load pressure based on the load W by the bottom side of the boom cylinder 3 is generated in the third port P3, and this load pressure acts on the pressure receiving area (= πD12 / 4) of the spool 12A facing the first pressure receiving chamber 11b. And the spool 12A is pushed rightward in cooperation with the urging force F of the spring 4. For this reason, the poppet portion 12b of the spool 12A is
d, the connection between the first port P1 and the third port P3 is cut off, and the boom cylinder 3 is stopped.

(2) Move the direction switching valve 2 to the left position (extended position)
When the mode is switched to a, the pressure oil from the hydraulic pump 5 flows into the first port P1 and the second port P2. The same hydraulic pressure acts on the first port P1 and the second port P2. For this reason,
The poppet portion 12b of the pressure receiving area of the second pressure receiving chamber 11c
Of the same pressure receiving area as the pressure receiving area (.pi. (D22 -D12) / 4) is balanced with the biasing force of the poppet portion 12b. Therefore, of the pressure receiving area of the second pressure receiving chamber 11c, πD
When the left urging force acting on the pressure receiving area of 12/4 exceeds the sum of the urging force of the spring and the urging force of the hydraulic pressure in the first pressure receiving chamber 11b, the spool 12A moves to the left and the spool 12A
Is separated from the sheet surface 12d. Therefore, the first port P1 and the third port P3 communicate with each other, and the pressure oil of the first port P1 supplied through the A port of the directional control valve 2 passes through the spool 12A to the third port P3.
Flows into the bottom side of the boom cylinder 3, and the low-pressure oil on the head side returns to the tank 5 via the B port of the direction switching valve 2. Therefore, the boom cylinder 3 extends.

(3) Move the direction switching valve 2 to the right position (shortened position)
When switching to b, the pressure oil from the hydraulic pump 5 flows into the rod side of the boom cylinder 3 and the fourth port P4 via the B port of the directional switching valve 2. The pressure receiving area of the spool 12A facing the third pressure receiving chamber 11d ｛π (D22−D12) /
When the urging force acting on 4 ° exceeds the sum of the urging force of the spring 4 and the urging force of the hydraulic pressure in the first pressure receiving chamber 11b, the spool 12A moves to the left and the poppet 12 of the spool 12A.
b moves away from the sheet surface 12d. In this manner, the poppet portion 12b and the seat surface 12d are opened in accordance with the operation amount of the direction switching valve 2, that is, the hydraulic pressure of the third pressure receiving chamber 11d, to allow communication between the first port P1 and the third port P3. . Therefore, the pressure oil in the bottom chamber of the boom cylinder 3 flows from the first port P1 through the third port P3 and the spool 12A to the tank 5 via the A port of the direction switching valve 2 in accordance with the operation amount of the direction switching valve 2. Return to Therefore, the boom cylinder 3 contracts. That is, the poppet unit 1 according to the operation amount of the direction switching valve 2
Since the opening amount between the valve 2b and the seat surface 12d is controlled, the boom cylinder 3 may be shortened by the load W beyond the operation amount of the direction switching valve 2 as soon as the direction switching valve 2 is set to the right position b. Disappears.

The second embodiment is as shown in FIG. The second embodiment differs from the first embodiment in FIG. 1 in that the spool 12B is particularly different. So explain the differences,
Duplicate description is omitted.

The spool 12B is the spool 1 of the first embodiment.
It is different from 2A as follows. However, the poppet part 12
The arrangement relationship between b and the sheet surface 12d is the same as that of the spool 12A of the first embodiment. That is, each outer periphery of the right end 12f, the left end 12g, and the center 12h of the spool 12B is slidably fitted inside the valve body 11. Left and right ends 12g, 12f
Are equal to each other. The outer diameter D2 of the central portion 12h is larger than the outer diameters D1 of the left and right end portions 12f and 12g (D2>
D1). The right end portion 1f is provided on the right side of the valve body 11 of the right end portion 12f.
2f, one end of an outer diameter D1 facing the second port P2
The piston 13 having the other end of the pressure receiving area D2 facing the second pressure receiving chamber 11c communicating with the piston 13 is slidably fitted inside. Thus, the right end portion 12 of the spool 12B is
A fourth pressure receiving chamber 11 e is formed between f and one end of the piston 13.

(1) The operation of the directional control valve 2 at the neutral position (stop position) c is the same as the operation of the first embodiment.
Duplicate description is omitted.

(2) Move the directional control valve 2 to the left position (extended position)
When the mode is switched to a, the pressure oil from the hydraulic pump 5 flows into the first port P1 and the second port P2. As in the first embodiment, of the pressure receiving area of the second pressure receiving chamber 11c, πD12 / 4
When the left urging force acting on the pressure receiving area of the above exceeds the sum of the urging force of the spring and the urging force of the hydraulic pressure of the first pressure receiving chamber 11b,
The spool 12A moves to the left, and the poppet portion 12b of the spool 12A moves away from the sheet surface 12d. Therefore, the first port P1 and the third port P3 communicate with each other, and the first port P1 supplied through the A port of the directional control valve 2 is connected to the first port P1.
Pressure oil flows into the bottom side of the boom cylinder 3 from the third port P3 via the spool 12A, and the low-pressure oil on the head side returns to the tank 5 through the B port of the direction switching valve 2. Therefore, the boom cylinder 3 extends. When the boom cylinder 3 starts to extend, the third port P
Although the oil pressure of 3 rises, the first throttle 6 and the second throttle 7 suppress the sudden increase in the pilot pressure in the first pressure receiving chamber 11b and the fourth pressure receiving chamber 11e. For this reason, hunting of the spool 12B is prevented, and the extension operation of the boom cylinder 3 is stabilized.

(3) Move the directional control valve 2 to the right position (shortened position)
When switching to b, the pressure oil from the hydraulic pump 5 flows into the rod side of the boom cylinder 3 and the fourth port P4 via the B port of the directional switching valve 2. As in the first embodiment, the third
Pressure receiving area of spool 12B facing pressure receiving chamber 11d ｛π
The urging force acting on (D22−D12) / 4 ° is
Exceeds the sum of the urging force of the first pressure receiving chamber 11b and the urging force of the hydraulic pressure of the first pressure receiving chamber 11b, the spool 12B moves to the left and the spool 1
The 2B poppet portion 12b is separated from the sheet surface 12d.
Thus, the operation amount of the direction switching valve 2, that is, the third pressure receiving chamber 1
Poppet part 12b and seat surface 12d according to the hydraulic pressure of 1d
To communicate between the first port P1 and the third port P3. Therefore, the pressure oil in the bottom chamber of the boom cylinder 3 is supplied to the third port P in accordance with the operation amount of the direction switching valve 2.
3. From the first port P1 via the spool 12A, return to the tank 5 via the A port of the directional control valve 2. Therefore, the boom cylinder 3 contracts. That is, since the opening amount between the poppet portion 12b and the seat surface 12d is controlled in accordance with the operation amount of the direction switching valve 2, as soon as the direction switching valve 2 is set to the right position b,
When the boom cylinder 3 has a load W greater than the operation amount of the directional control valve 2,
Will not be shortened. When the boom cylinder 3 is shortened and then stopped, the hydraulic pressure of the third port P3 rises due to the inertial force of the load W. However, similar to the case of the extension position a, the first throttle 6 and the second throttle 7 allow the hydraulic pressure to rise. The rapid rise in pilot pressure in the first pressure receiving chamber 11b and the fourth pressure receiving chamber 11e is suppressed. As a result, hunting of the spool 12B is prevented, and the shortening operation of the boom cylinder 3 is stabilized.

As described above, the present invention has the following effects. (1) An opening / closing function that opens when the urging force due to the pilot pressure exceeds the urging force of the spring by receiving the pilot pressure on the side opposing the spring force, and oil to the side where a load outside the control of the directional control valve and the actuator is generated. Since the check function allowing only the flow is performed by one spool, the size of the counterbalance valve can be reduced, and the flow path area can be increased if the size of the valve body is the same. For this reason, the free flow increases, the flow path resistance is reduced, and the efficiency can be improved. Further, since only one spool is required, the configuration of the counterbalance valve is simplified, and the production cost can be greatly reduced. (2) Since the moving speed of the spool is reduced by the first and second throttles, hunting can be reduced as compared with the conventional check valve shown in FIG. Further, even if the hydraulic pressure of the third port acts on the other end surface of the spool and the one end surface of the piston via the second restrictor, the urging force of the second port pressure oil received at the other end surface of the piston as pilot pressure is applied. When the force exceeds the sum of the urging force of the spring and the urging force of the hydraulic pressure on the side where an uncontrolled load of the actuator occurs, the spool moves to the first port and the third port.
Open the valve so that it can communicate with the port. For this reason, even if the hunting prevention effect of the counterbalance valve is improved,
Regardless of this, the operation and effect of the first invention can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional technique.

[Explanation of symbols]

1: counter balance valve, 2: directional switching valve, 3: boom cylinder (an example of an actuator), 4: spring,
11; valve element 11b; first pressure receiving chamber 11c; second
11d; 3rd pressure receiving chamber, 11e; 4th pressure receiving chamber, 12, 12A, 12B; spool, 13; piston, P1; 1st port, P2; 2nd port, P
3: 3rd port, P4: 4th port.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3F205 AA05 BA06 KA10 3H059 AA12 BB16 BB22 BB37 CA02 CA04 CB12 CD05 CD12 EE05 FF03 FF14

Claims (2)

[Claims] An oil inflow side and an oil outflow side are operated by switching the direction switching valve (2) and the direction switching valve (2).
And an actuator (3) that receives an uncontrolled load based on gravity or inertia force, and is provided between the directional control valve (2) and the actuator (3), and has a spring (4) and opposes the spring force. The opening / closing function that opens when the biasing force due to the pilot pressure exceeds the biasing force of the spring (4) due to the pilot pressure on the side, and the directional control valve (2) and the actuator (3) to the side where an uncontrolled load occurs. In a counterbalance valve having a check function that allows only oil flow, the third port (P3) connected to the side where the uncontrolled load of the actuator (3) occurs, the side where the uncontrolled load of the actuator (3) does not occur Port (P4) connected to the directional control valve (2) and the second port receiving the hydraulic pressure of the first port (P1) as pilot pressure
A valve body (11) communicating with the port (P2) and the first to fourth ports (P1 to P4) and having a spool hole (11a) in which the spring (4) is built in one end; Receiving the urging force of the spring (4) and the urging force of the hydraulic pressure on the side of the actuator (3) that generates an uncontrolled load, and receiving the urging force of the pilot pressure from the second port (P2) on the other end surface, When the hydraulic pressure is generated at the third port (P3) on the side surface, the urging force of the spring (4) and the actuator
(3) has a pressure receiving surface on which an urging force is generated in opposition to the urging force by the hydraulic pressure on the side where the uncontrolled load is generated, and the spool hole (11
a) and a spool (12) slidably fitted in the spool (12). The spool (12) and the spool hole (11a) are biased by the pilot pressure from the second port (P2) received at the other end face. Exceeds the sum of the urging force of the spring (4) and the urging force of the hydraulic pressure on the side of the actuator (3) that generates an uncontrolled load, and the urging force of the spring (4) is applied to the fourth port (P4). The first and third ports (P1 and P3) are opened when a hydraulic pressure is generated that exceeds the sum of the external force of the actuator (3) and the hydraulic pressure on the side where the uncontrolled load of the actuator (3) occurs. A counterbalance valve formed so as to open. 2. The counterbalance valve according to claim 1, wherein the piston (13) is opposed to the spool (12B) in the spool hole (11a) at one end surface with the same cross-sectional area as the other end surface of the spool (12B). The other end face having a larger cross-sectional area than the other end face of the spool (12B) is slidably fitted so as to receive the pilot pressure from the second port (P2), and the spool (12B) is inserted into the spool (12B). The spool (1) is opened at both end faces of the spool (1) to introduce the hydraulic pressure of the first port (P1).
2B), a communication hole (12a) that opens on the side surface of the spool (12B) and a first throttle (1) between the opening on one end surface of the spool (12B) and the opening on the side surface of the spool (12B) are provided in the communication hole (12a). 6) and the opening at the other end of the spool (12B) and the spool (12B).
A counterbalance valve characterized in that a second throttle (7) is provided between the opening and the side surface of (B).