JPH0510307A - Direction selector valve for preventing out-of-control operation of actuator - Google Patents

Abstract

PURPOSE:To prevent a hydraulic motor from being operated out of control and suddenly even in the case where the spool of a remote control type direction selector valve which receives a restoration instruction signal to a neutral position does not return to a regular position, by installing a selector valve which is switched in correspondence with the operating lever of a joy stick. CONSTITUTION:An oil passage 22a having a throttle 22b which connects a spring chamber 23 and a pump chamber 4 is formed on the valve piece 22 of the load check valve 21 of a remote control type direction selecting valve 20. The spring chamber 23 and a P port 6 are connected through a bypass 26. Further, a selector valve 27 which is switched in correspondence with the operation of the operating lever 15a at a joy stick 15 is in installed in the bypass 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional control valve for preventing runaway of an actuator, in particular, a hydraulic excavator equipped with a remote control type control device, other civil engineering, construction machinery, etc. The present invention relates to a directional control valve for preventing a runaway of an actuator, which can be driven without causing a swing or a runaway.

[0002]

2. Description of the Related Art Actuators such as hydraulic motors for traveling and turning of conventional hydraulic excavators, other civil engineering and construction machines, etc.
An example of a directional control valve for an actuator that operates the remote controller with a remote control type steering device is shown in FIG.

This is a variable discharge pump as a hydraulic power source for a hydraulic motor 12 as an actuator for running a construction machine (reference numeral "1" in FIG. 3 showing an embodiment of the present invention.
The pilot oil pressure (operation signal) from the pilot valve 16 operated by the operation lever (see reference numeral “15a” in FIG. 4) of the joystick 15 as a control device is used to Oil passages 16a, 16
By alternately applying to the left and right ends (FIG. 7) of the spool 3 of the remote control type directional control valve 2 via b, the spool 3 of the directional control valve 2 is moved to the left or right side. The pressure oil is moved to supply the pressure oil to the tank 8a and is discharged to the tank 8a. Also, a required pressure is applied between the pump chamber 4 and the P port 6 as the hydraulic pressure source side port of the direction switching valve 2. A load check valve 5 which is released by the above is provided.

This remote control type directional control valve 2
When a pressure exceeding the set pressure by the compression spring 5c of the load check valve 5 is generated in the hydraulic circuit of the construction machine or the like including the above, the valve body 5a of the load check valve 5 moves backward (in FIG. 7, it rises). However, the pressure oil that exceeds the set pressure is P
It is supplied to the pressure oil motor 12 via the port 6, the B port (cylinder port) 7b (or the A port 7a, the same) and the like. Reference numeral 11 is a counter balancing valve.

Since the spring chamber 5b of the load check valve 5 of the directional control valve 2 and the P port 6 are always in communication with each other, the hydraulic pressures P ₂ and P _{2 of the} spring chamber 5b are maintained. Matches P ₃ . P ₂ = P ₃

On the other hand, the pump chamber 4 and the spring chamber 5b of the direction switching valve 2 are always shut off as shown in FIG. 7 by the valve body 5a of the load check valve 5 which is elastically pressed by the compression spring 5c. the b - a compressive force Fs of the spring 5c of de check valve 5, if the area of the contact portion between the valve body 5a and the valve seat and S, the condition of _{P 1> P 3 + Fs /} S is fully When the valve spring 5a
It rises against c (FIG. 7), and the pressure oil in the pump chamber 4 is supplied to the P port 6 side through the load check valve 5.

Therefore, the joystick 1 as described above is used.
In accordance with the operation signal of the pilot valve 16 operated by the operation lever 15a of No. 5, the spool 3 of the remote control type directional control valve 2 is switched via the pilot oil passages 16a and 16b, thereby the hydraulic motor is operated. Actuator such as 12
For hydraulic excavators that drive pressure oil to and from it, other civil engineering and construction machinery, as long as each part installed in the hydraulic circuit operates normally, it is supplied from the variable discharge pump 1. The traveling hydraulic motor 12 is moved through the direction switching valve 2 by the pressure oil to operate the lever 15 of the joystick 15.
It can be driven according to the operation instruction of a.

[0008]

However, in this one, the actuator such as the traveling motor 12 is
Operation lever-1 of joystick 15 as a control device
By operating 5a, the pilot type directional control valve 2
When the operation lever 15a of the joystick 15 is returned to the neutral position after moving the scroll 3 in the required direction, the spool 3 of the directional control valve 2 temporarily moves, for example, in the case of a thermal shock. For some reason, such as generation or catching of cutting chips (iron pieces), the directional control valve 2 does not respond (backward) according to the return operation command signal by the operation lever 15a of the joystick 15, or the same return instruction. The spool 3 of the directional control valve 2 does not respond to the signal at all, and the spool 3 of the directional control valve 2 is maintained in the position before the return command signal is transmitted, that is, the state where the stick 3 is kept, and the traveling hydraulic motor 12 continues to rotate. As a result, there is a risk that the construction machine or the like will run or turn carelessly, that is, runaway.

Therefore, in an operator operating a conventional construction machine or the like equipped with the remote control type directional control valve 2 as described above, an actuator such as a hydraulic motor 12 thereof has the above-mentioned structure. It was necessary to always pay close attention to prevent inadvertent runaway such as.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides a load check valve on the valve body of a remote control type directional control valve for construction machines and the like. An oil passage with a throttle that connects the pump chamber and the spring chamber of the directional switching valve is provided in the valve body of the load check valve, and the spring chamber of the directional switching valve and the P port are equipped with a switching valve. It is connected by bypass, and the switching valve is switched so as to open the bypass by an operation signal of a control device such as the construction machine, and the load check valve is opened at a predetermined pressure. ..

(Operation) Since the present invention has the above-described structure, it is controlled by an operation signal from a control device such as a construction machine.
Change over the hydraulic control mode by switching the directional control valve.
The actuator such as a hydraulic motor is driven by operating the actuator such as a hydraulic motor, and returning the spool of the directional control valve to the neutral position by the operation signal of the control device. In addition to stopping in the same manner as in the example, when a double return command signal to the neutral position of the directional control valve is transmitted by the control device, the switching valve of the bypass is closed in response to this, and the hydraulic spring chamber and P Since the port is shut off, the flow of oil does not occur in the flow passage with the throttle, so that the pressures before and after the throttle are the same, and the load check valve is closed.
If a double return command signal is sent to the neutral position of the remote control type directional control valve by the control device, the spool of the directional control valve is moved to its neutral position for some reason. Even when an abnormality that does not recover occurs, the supply of pressure oil to the actuator such as the hydraulic motor is stopped, and the actuator is inadvertently run,
Prevent or reduce runaway such as turning.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a directional control valve for preventing runaway of an actuator according to the present invention will be described below with reference to FIGS. Note that the same names and reference numerals are used for the parts common to the conventional example shown in FIG.

(First Embodiment) FIGS. 1 to 3 are schematic explanatory views of a first embodiment of a directional control valve for preventing a runaway of an actuator according to the present invention. FIG. 1 is a runaway of the actuator. FIG. 2 is a schematic longitudinal cross-sectional view showing a magnified view of a road check valve, which is a main part of the directional control valve for prevention, FIG. 2 is a schematic longitudinal cross-sectional view showing the directional control valve longitudinally, and FIG. It is explanatory drawing of the hydraulic circuit for hydraulic motor drive by a direction switching valve.

1 to 3, 1 is a variable discharge pump as a hydraulic source, 1a is a pilot pump for generating pilot pressure, 2 is a remote control type directional control valve, 3 is a directional control valve 2. Of the hydraulic pressure source side, 6 is a P port, 7a and 7b are A ports and B
Port (cylinder port), 8 is a tank port, 8a is a tank, 11 is a counter balancing valve, 12 is a traveling hydraulic motor as an actuator, and 15 is a construction machine such as a power shovel (not shown). Is a joystick as a control device for the, and 16 is a lever for operating the joystick 15.
(Refer to the reference numeral “15a” in FIG. 4 showing the first embodiment of the present invention.) The pilot valves 16a and 16b are pilot oil passages, and the pilot oil passages 16a and 16b are the operation lever 15a of the joystick 15. A pilot signal transmitted from a pilot valve 16 that is switched by operation is sent to a remote control of a hydraulic circuit of the construction machine or the like.
2 is transmitted to both sides of the spool 3, the spool 3 is moved to the right or left in FIG. 2, and the pressure oil from the variable displacement pump 1 is passed through the same direction switching valve 20. Is supplied to the hydraulic motor 12 and the pressure oil of the hydraulic motor 12 is discharged to the tank 8a via the same direction switching valve 20.

The operation lever of the joystick 15
By switching the pilot valve 16 by operating 15a,
An operation signal transmitted to the remote control type directional control valve 20 via the pilot oil passages 16a and 16b is applied to the remote control type directional control valve 20, and the spool 3 thereof is moved to the right or left. To move the actuator such as the hydraulic motor 12 to drive the pressure oil on the pump chamber 4 side of the directional switching valve 20 to the P port 6 side via the load check valve 21. A point with a structure for releasing (however, this roll
Except that the valve body 22 of the check valve 21 is provided with an oil passage 22a with a throttle 22b which will be described later), this first embodiment is the remote control type directional control valve 2 of the conventional example shown in FIG. Is the same as.

Reference numeral 20 is a remote control type directional control valve capable of preventing runaway of the hydraulic motor 12 as an actuator, 20a is a valve main body of the directional control valve 20, and 21 is provided in the valve main body 20a. A load check valve, 22 is a valve element of the load check valve 21, 22a is an oil passage provided in the central portion of the valve element 22 in the longitudinal direction (the vertical direction in FIG. 1), and 22b is an oil passage 22a. The throttle provided and 23 are load check valves 21.
Spring chamber, 24 is a compression spring provided in the spring chamber 23, 26 is a bypass, and the bypass 26 connects the pump chamber 4 of the direction switching valve 20 and the spring chamber 23, whereby the pump of the direction switching valve 20 is pumped. Chamber 4 and P
And the oil passage 22 of the valve body 22 of the road check valve 21.
a, the spring chamber 23 and the bypass 26 are connected.

Reference numeral 27 denotes a switching valve provided in the bypass 26. The switching valve 27 is a lever for operating the joystick 15 as a control device for a construction machine such as a power shovel (not shown) (the first embodiment of the present invention is shown. Reference numeral "15a" in FIG.
The operation signal transmitted from the switching pilot valve 16 via the pilot oil passage 16c causes the bypass 26 to open or close so as to open or close the bypass 26. Specifically, this switching valve Numeral 27 is closed when the traveling hydraulic motor 12 of the construction machine is in a stopped state, that is, when the spool 3 of the directional control valve 20 is returned to the neutral position.

(Operation of the First Embodiment) First, the pressure oil having the hydraulic pressure P ₁ of the variable discharge type pump 1 is pump chamber 4, A or B port 7a of the remote control type directional control valve 20. Alternatively, through an actuator 7b or the like, an actuator for a construction machine (not shown)
Is supplied to the traveling hydraulic motor 12 as a motor, and the pressure oil of the hydraulic motor 12 is discharged to the tank 8a via the direction switching valve 20.

At this time, the pump chamber 4 and P of the direction switching valve 20
Since the bypass 26 communicates with the port 6, the valve body 2 is elastically pressed by the compression spring 24 of the load check valve 21.
2, the switching valve 27 is opened as long as the construction machine or the like is in an operating state, and in this state, the hydraulic pressure P ₁ of the pressure oil in the pump chamber 4 is P
It is higher than the hydraulic pressure P ₃ of the pressure oil on the port 6 side. P ₁ > P _{3 In} addition, this action includes the direction of the conventional example shown in FIG. 7 including that the load check valve 21 is opened by the hydraulic pressure higher than the set pressure of the spring 24 provided in the spring chamber 23. It is almost the same as the switching valve 2.

Next, a lever for operating the joystick 15
15a to operate the directional control valve 20 from the pilot valve 16
When an operation command signal for returning the spool 3 to the neutral position is transmitted, the signal is transmitted to the left and right ends of the spool 3 of the directional control valve 20 via the pilot oil passages 16a and 16b, and the spool is rotated. -Le 3 returns to the neutral position. Simultaneously with the return signal to the neutral position of the spool 3, the signal transmitted from the pilot valve 16 is transmitted to the switching valve 27 via the pilot oil passage 16c, and the switching valve 27 is brought into the state shown in FIG. The bypass 26 is cut off, and the load check valve 2
Oil pressure P ₂ of the spring chamber 23 of 1 and oil pressure P of the pump chamber ₄
Matches ₁ P ₁ = P ₂

Therefore, the force in the opening direction of the valve body 22 of the load check valve 21 in this state is a diameter of the contact portion of the valve seat of the valve body 22 of the same load check valve 21 is a, and its spring is If the diameter on the chamber 23 side is b, and b> a, as in the load check valve 21 shown in FIG. 1, (a / 2) ² π × P ₁ + {(b / 2) ² π− (A / 2) ² π} × P ₃ .

On the other hand, the force in the closing direction of the load check valve 21 in this state is (b / 2) ² π × P ₂ + F, where F is the elasticity of the compression spring 24 of the spring chamber 23.

The condition for opening the valve body 22 of the load check valve 21 is that the force in the opening direction of the valve body 22 is made larger than the force in the closing direction, (a / 2) ² π × P ₁ + [b / 2) ² π × P ₃ − (a / 2) ² π × P ₃ − (b / 2) ² π × P ₂ −F> 0 ...

When the switching valve 27 moves to the right side from the state shown in FIGS. 1 and 2 and the bypass 26 communicates, P ₂ = P _3, and in this state, P ₁ When the condition of> P ₃ + F / (a / 2) ² π is satisfied, the valve element 22 rises against the compression spring 24 (FIG. 1), the load check valve 21 is opened, and the pump The pressure oil in the chamber 4 flows out to the P port 6 side through the opened load check valve 21.

In the operating state of the traveling hydraulic motor 12, when the switching valve 27 is in the closed position shown in FIGS. 1 and 2, the bypass 26 is shut off by the switching valve 27. Since the pressure oil of the oil pressure P ₁ of the pump chamber 4 is introduced into the spring chamber 23 of the direction switching valve 20 via the oil passage 22a with the throttle 22b, the oil pressure of the spring chamber 23 is changed to P ₂
Then, P ₃ <P ₂ = P ₁ .

Therefore, in this state, the above equation becomes (P ₃ -P ₁ ) × {(b / 2) ² π- (a / 2) ² π} -F> 0 ...

On the other hand, in the drive state in which pressure oil is supplied from the pump chamber 4 to the hydraulic motor 12 side, the relationship between the oil pressure P ₁ of the pump chamber 4 and the oil pressure P ₃ of the P port 6 is P _{Since 1} > P ₃ ∴P ₃ −P ₁ <0, the above equation does not hold in this state, and
Pressure oil cannot be supplied to the hydraulic motor 12.

On the other hand, the operation lever of the joystick 15
At the same time that the drive command signal for the traveling motor 12 is transmitted from the pilot valve 16 by the 15a, the pilot oil passage 1
The switching valve 27 open position from 6c switching changing open signal is transmitted (FIG. 1), since the switching valve switching switched to the open, it becomes P ₃ = P _2, the b - de check valve 21 is normal It has the same function as the load check valve (see reference numeral "5" in FIG. 7).

In the above description, the directional control valve 20 for preventing the runaway of the actuator is applied to the hydraulic circuit including the traveling hydraulic motor 12 as the actuator of the construction machine. Although not shown, the directional control valve 20 for preventing runaway of the actuator is used for preventing runaway of a hydraulic motor as various hydraulic actuators, including a hydraulic motor for turning a swinging body of a crane vehicle (not shown). It can also be implemented as a directional valve.

(Drive Command Signal Extraction Unit) FIG. 4 shows a drive command signal extraction unit in the first embodiment of the present invention, that is,
It is a schematic explanatory view showing a relationship between a switching valve provided in a bypass of the remote control type directional switching valve and a control device such as a construction machine. It should be noted that the same names and reference numerals are used for the portions common to the first embodiment shown in FIGS.

In FIG. 4, 1a is a pilot pump,
8a is a tank, 15 is a joystick as a control device for construction machines, 15a is an operating lever of the joystick 15, 16 is a pilot valve switched by the operation of the operating lever 15a, and 16a and 16b are transmitted from the pilot valve 16. Pilot oil passages for transmitting operation command signals to the direction switching valve 20, 16d are pilot oil passages 16a, 16b
Command signal (detection signal) detected by the detection unit 30 from
To a switching valve 27, and 26 is a remote control type directional switching valve 20 (see FIGS. 1 to 3).
2 is a bypass connecting the spring chamber 23 and the P port 6, and 27 is a switching valve provided in the bypass 26.

Operation lever 15a of the joystick 15
Operation, the spool 3 of the remote control type directional control valve 20 as shown in FIGS. 1 and 2 is moved, and the traveling hydraulic motor 12 is driven in the same manner as described above. When the operation lever 15a of the joystick 15 is operated, the pilot valve 16 transmits the pilot oil passage 1
The detection unit 30 detects whether or not an operation command signal transmitted to the spool 3 of the directional control valve 20 via 6a, 16b, that is, a signal for operating the directional control valve 20 is output, and this detection is performed. A detection signal from the portion 30 is provided to a bypass valve 26 which connects the P port 6 with the spring chamber 23 of the load check valve 21 having the oil passage 22a and the throttle 22b via the pilot oil passage 16c. 27, and the switching valve 27 is automatically switched to open or closed according to the operation of the operation lever 15a of the joystick 15.

(Second Embodiment) FIG. 5 shows a second embodiment of a directional control valve for preventing runaway of an actuator according to the present invention, showing a switching valve provided in a bypass of the directional control valve and a construction machine or the like. It is a schematic explanatory view showing a relationship with a control device. Note that the same names and reference numerals are used for the parts common to the first embodiment shown in FIGS. 1 to 4.

In FIG. 5, 1a is a pilot pump,
8a is a tank, 15 is a joystick as a control device for construction equipment construction, 15a is its operating lever, and 20 is a remote control type directional control valve, the structure of which is shown in FIGS. This is the same as the directional control valve 20 of the embodiment.
Reference numeral 26 is a spring chamber 23 of the directional control valve 20 and a P port 6
By-pass connecting to and, 27 is a switching valve provided in the bypass 26, and 32 is a lever 15a for operating the joystick 15.
Is a detector for detecting the operation angle of.

(Operation of Second Embodiment) Joystick 1
The operation signal transmitted from the pilot valve 16 by operating the operation lever 15a of FIG.
In addition to sending to the remote control type directional control valve 20 via b and moving the spool 3 to drive the traveling hydraulic motor 12, in addition to the operation of the joystick 15 in the third embodiment. The operating state of the lever 15a is, for example,
The operation angle is detected by the detector 32, and the switching valve 27 of the bypass 26 is detected by the detection signal of the detector 32.
To open or close. The other functions are almost the same as those in the first embodiment. In the second embodiment, whichever of the spool 3 of the directional control valve 20 and the spool of the pilot valve (not shown) sticks can be dealt with.

(Third Embodiment) FIG. 6 shows a third embodiment of a directional control valve for preventing runaway of an actuator according to the present invention, which is provided in a bypass of a remote control directional control valve thereof. It is a schematic explanatory view showing a relationship between a valve and a control device such as a construction machine. It should be noted that the same names and reference numerals are used for the portions common to the first embodiment shown in FIGS.

In FIG. 6, 15 'is an electric joystick as a control device, and 15a' is a joystick 1.
5'operation lever, 16 'is an operation signal output unit, 16
a ′ and 16b ′ are operation signals of the operation signal output unit 16 ′,
The operation signal line that has substantially the same structure as the remote control type directional control valve 20 of the first embodiment shown in FIGS. 1 and 2 and is transmitted to the spool 3 of the electric type directional control valve 20. is there. 26
Is a bypass connecting the spring chamber 23 of the direction switching valve 20 and the P port 6, 27 is a switching valve provided in the bypass 26, and 34 is a lever 15 for operating the joystick 15 '.
A detector for electrically detecting the operation state of a ', 36 is a power source for driving the operation signal output section 16' so as to be proportional to the operation angle of the operation lever 15a '.

(Operation of Third Embodiment) By operating the operation lever 15a 'of the electric joystick 15, the operation signal output section 16' is switched to transmit the operation signal, and the operation signal line 1
1 and 2 through 6a 'and 16b', the spool 3 of the remote control type directional control valve 20 is moved by a required amount, and the traveling hydraulic motor 12 is driven. In this third embodiment, the electric joystick 15 '
The operating state of the operating lever 15a 'is detected by the electrical detector 34 as a voltage value, for example, and the detection signal (voltage value) is applied to the switching valve 27, and the switching valve 27 is switched to open or closed. Further, the bypass 26 is automatically switched to open or closed. The other functions are almost the same as those in the first embodiment. In this case, due to a failure of the operation signal output unit 16 ',
It also corresponds when the signal is output.

[0039]

(1) A load check valve is provided in the valve body of a remote control type directional control valve for construction machines and the like,
The valve body of the load check valve is provided with an oil passage with a throttle for communicating the pump chamber and the spring chamber of the directional switching valve, and the spring chamber of the directional switching valve and the P port are bypassed with a switching valve. The switching valve is switched to open the bypass and the road check valve is opened at a predetermined pressure in accordance with an operation signal of a control device such as the construction machine. As long as the control device such as the construction machine is in the operating state, the bypass connecting the pump chamber of the directional switching valve and the P port is opened by the switching valve by the operation signal of the operating device, and the pressure oil in the pump chamber is opened. Is released to the P port and has the same function as the conventional directional control valve of this kind, but if the control device is returned to the neutral position, it can be transferred to actuators such as hydraulic motors for traveling and turning. Supply of pressure oil from the pump room At the same time as being cut, the bypass switching valve is shut off in response to the return operation signal to the neutral position of the control device, and the spool of the directional switching valve does not respond to the return command signal of the control device. Even if a stick state occurs, there is no risk that the actuator will continue to run or turn carelessly and run out of control.

(2) The operating state of the control device of the remote control type directional control valve is detected by a detector or the like, and the detection signal causes the bypass directional control valve of the directional control valve to operate.
Since it is automatically switched to respond to the operating state, it can be operated without substantially changing the operating procedure of the operator of the construction machine or the like with the operating procedure of the existing device of the same type. Since normal operation can be expected without paying special attention to the operation, it is possible to continue operation for a long time without causing any particular fatigue and maintaining the desired effect.

(3) An oil passage with a throttle is provided in the valve body of the load check valve of the existing directional control valve, and its spring chamber and P port are operated by the operating device of the actuator. The present invention can be easily applied to an existing directional switching valve by a simple modification by simply connecting by a bypass with a switching valve that switches depending on the state.

[Brief description of drawings]

FIG. 1 is a schematic longitudinal explanatory view showing an enlarged load check valve portion, which is a main part of a first embodiment of a directional control valve for preventing runaway of an actuator according to the present invention.

FIG. 2 is a schematic vertical cross sectional view showing the runaway preventing directional control valve in a vertical cross section.

FIG. 3 is an explanatory view of a hydraulic circuit for driving a hydraulic motor by the runaway preventing directional control valve.

FIG. 4 is a schematic explanatory view of a connection structure of a switching valve provided in a bypass of the runaway preventing directional switching valve of the first embodiment of the present invention and a control device such as a construction machine.

FIG. 5 is a schematic explanatory view showing a relationship among a control device, a detector, a switching valve and the like of a runaway preventing directional switching valve of a second embodiment of the present invention.

FIG. 6 is a schematic explanatory view showing a relationship among a control device, a detector, a switching valve and the like of a runaway preventing directional switching valve of a third embodiment of the present invention.

FIG. 7 is a schematic longitudinal explanatory view of a conventional directional control valve of a hydraulic actuator.

[Explanation of symbols]

 1 ... Variable discharge pump 3 ... Spool 4 ... Pump chamber 6 ... P port 7a ... A port 7b ... B port 8 ... Tank port 12 ... Hydraulic pressure Motor 15 ... Joystick (control device) 15 '... Voltage joystick (control device) 15a ... Operation lever 16 ... Pilot valve 16a, 16b ... Pilot oil passage 16a', 16b '... Electric operation signal Circuit 20 ... Remote control type directional control valve 21 ... Road check valve 22 ... Valve body 22a ... Oil passage 22b ... Throttle 23 ... Spring chamber 24 ... Spring 26 ... Bypass 27 ... ... Switching valve 30 ... Detector 32 ... Detector 34 ... Detector

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area F15B 11/08 A 9026-3H

Claims (1)

Claim: What is claimed is: 1. A load check valve is provided in a valve body of a remote control type directional control valve of a construction machine, and the directional control valve is provided in a valve body of the load check valve. Is provided with an oil passage with a throttle for communicating the pump chamber and the spring chamber, the spring chamber of the directional switching valve and the P port are connected by a bypass with a switching valve, and the control device of the construction machine or the like is connected. A directional control valve for preventing runaway of an actuator, wherein the bypass valve of the switching valve is switched to open by an operation signal, and the load check valve is opened at a predetermined pressure.