JPH04248001A - Pressure oil supply device - Google Patents

Abstract

PURPOSE:To reduce energy loss by lowering the set pressure of an unload valve. CONSTITUTION:Pressure oil discharged from a hydraulic pump 1 is supplied to a hydraulic actuator 4 through a closed-center directional control valve 3. An unload valve 10 is provided in a discharge passage 2 for the hydraulic pump 1 and a cylinder device 20 is provided there to push the unload valve 10 to a shutoff position. An extension room 21 in the cylinder device 20 is connected to the first and second discharge-side circuit 26, 27 for a pilot valve 5 via a shuttle valve 28. Pilot pressure is thus supplied to the extension room 21 in the cylinder device 20 when the directional control valve 3 is at the first or second pressure oil supply position by the operation of the pilot valve 5, allowing the unload valve 10 to be held at the shutoff position with the cylinder device 20.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure oil supply device for supplying oil discharged from a hydraulic pump to a hydraulic actuator.

0002

2. Description of the Related Art As shown in FIG. 1, a directional control valve 3 is provided in a discharge path 2 of a hydraulic pump 1, a hydraulic actuator 4 is connected to the outlet side of the directional control valve 3, and a pilot valve 5 is used to pump an auxiliary hydraulic pump. The discharge pressure oil of 6 is sent to the first and second pressure receiving parts 7,
8 to move the directional control valve 3 from the neutral position A to the first and second positions.
A hydraulic supply device is known that supplies oil discharged from a hydraulic pump 1 to a hydraulic actuator 4 by switching to pressure oil supply positions B and C. In such a hydraulic supply system, in the case of a closed center type that shuts off the inlet port 9 when the directional control valve 3 is in the neutral position A, the oil discharged from the hydraulic pump 1 comes to a dead end when the directional control valve 3 is in the neutral position A. As a result, the discharge pressure becomes high, so an unload valve 10 is provided in the discharge passage 2. This unload valve 10 is held at the cutoff position D by the pressure of the first pressure receiving part 11 and the spring 12, and
The first pressure receiving part 11 is supplied with the outlet side pressure of the directional control valve 3 in the load pressure circuit 14, and the discharge pressure acts on the second pressure receiving part 13, and the hydraulic pump 1 is set to a pressure difference between the pressure of the first pressure receiving part 11 and the pressure of the second pressure receiving part 13, that is, a pressure corresponding to the spring force of the spring 12.

0003

[Problem to be Solved by the Invention] In such a pressure oil supply device, when the directional control valve 3 is in the neutral position A, the load pressure circuit 1
4 communicates with the tank 15, the pressure in the first pressure receiving part 11 of the unload valve 10 becomes zero, and the discharge pressure of the hydraulic pump 1 becomes the pressure corresponding to the spring force of the spring 12, that is, the unload valve 1
When the pressure exceeds the set pressure of 0, the discharge pressure flows out from the unload valve 10 to the tank 15, and the discharge pressure is maintained at a pressure corresponding to the spring force of the spring 12, and this pressure becomes a pressure loss.

For this reason, energy loss can be reduced by lowering the set pressure of the unload valve 10 and the discharge pressure of the hydraulic pump 1, but if the set pressure of the unload valve 10 is lowered, the following will occur. There is a problem. Directional control valve 3
Or, when operated to the second pressure oil supply position B or C, the holding pressure and discharge pressure of the hydraulic actuator 4 are supplied from the internal passage 16 through the load pressure circuit 14 to the first pressure receiving part 11 of the unloading valve 10 for unloading. Since the valve 10 is set to the cutoff position D and the unloaded oil is supplied to the hydraulic actuator 4,
When the holding pressure of the hydraulic actuator 4 is low and the initial discharge pressure of the hydraulic pump 1 is low, the rise of the pressure in the first pressure receiving part 11 described above is delayed and the unload valve 10 moves to the communication position E.
The time required for switching from to cutoff position D is also delayed, resulting in poor overall responsiveness.

When the directional control valve 3 is switched to the first or second pressure oil supply position B or C, the load 17 on the hydraulic actuator 4
If it falls under its own weight, the holding pressure becomes negative pressure (vacuum pressure),
At this time, if the amount of oil in the hydraulic pump 1 is insufficient, the load pressure circuit 14
is a low pressure between negative pressure and tank pressure. On the other hand, the amount of oil in the hydraulic pump 1 is controlled by the hydraulic actuator 4 via the directional control valve 3.
However, during this process, when the inlet side pressure of the directional control valve 3 becomes equal to or higher than the set pressure of the unload valve 10, the unload valve 10 becomes the communication position E, and a part of the oil amount of the hydraulic pump 1 is transferred to the tank. 15, therefore, if the set pressure of the unload valve 10 is lowered, the amount of oil supplied to the hydraulic actuator 4 will be reduced, and recovery of the vacuum will be delayed.

As described above, in the conventional pressure oil supply system, various problems occur when the set pressure of the unload valve 10 is lowered, so the set pressure has to be increased, resulting in a large energy loss. There is. Therefore, an object of the present invention is to provide a pressure oil supply device that can solve the above-mentioned problems.

[0007]

[Means for Solving the Problem] The unload valve is pushed to the cutoff position by the switching pilot pressure of the directional control valve.

[0008]

[Operation] When the directional control valve is set to the first or second pressure oil supply position, pilot pressure is supplied to the unload valve, and the unload valve can be held at the cutoff position.

[0009]

[Example] As shown in Fig. 2, unload valve 1
A slow return valve 25 consisting of a throttle 23 and a check valve 24 is provided in a circuit 22 connected to the extension chamber 21, and the circuit 22 is connected to the first valve of the pilot valve 5. Second output circuit 26, 27
via a shuttle valve 28. Therefore, when the pilot valve 5 is operated to supply pressure oil to the first or second output circuit 26, 27 and the directional control valve 3 is switched to the first or second pressure oil supply position B, C, the pressure Oil is supplied to the extension chamber 21 of the cylinder device 20, and the unload valve 10 is directly brought to the shutoff position D without depending on the pressure difference. Therefore, even if the set pressure of the unload valve 10 is low, when the directional control valve 3 is switched to the first or second pressure oil supply position B or C, the unload valve 10 immediately becomes the cutoff position, causing various problems. Never.

FIG. 3 shows a second embodiment, in which the circuit 22 is connected to the load pressure circuit 14 by an internal passage 29 of the directional valve 3. In this way, the first pressure receiving part 11 of the unload valve 10 can be connected to the tank when the directional control valve 3 is in the neutral position A, so the throttle 23 and check valve 24 of the circuit 22 are not necessary.

FIG. 4 shows a third embodiment, in which the circuit 22 is connected to the discharge side of the auxiliary hydraulic pump 5. In this way, the shuttle valve 28 becomes unnecessary.

0012

Effects of the Invention: When the directional control valve 3 is switched to the first or second pressure oil supply position, the switching pilot pressure oil switches the unload valve 10 to the cutoff position, so the set pressure of the unload valve 10 can be lowered. However, when supplying pressure oil to the hydraulic actuator 4, the unloading valve 10 is reliably brought to the cutoff position without any time delay, thereby eliminating various problems and reducing energy loss.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram showing a conventional pressure oil supply device.

FIG. 2 is a hydraulic circuit diagram showing a first embodiment of the pressure oil supply device of the present invention.

FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the pressure oil supply device of the present invention.

FIG. 4 is a hydraulic circuit diagram showing a third embodiment of the pressure oil supply device of the present invention.

[Explanation of symbols]

1 hydraulic pump, 2 discharge path, 3 directional control valve,
4 Hydraulic actuator, 10 Unload valve, 1
1 first pressure receiving section, 12 second pressure receiving section, 14 load pressure circuit.

Claims (1)

[Claims] 1. A closed center type directional control valve 3 is provided in a discharge passage 2 of a hydraulic pump 1, and a hydraulic actuator 4 is connected to the outlet side of the directional control valve 3.
In a pressure oil supply device provided with an unload valve 10 at
1 is a load pressure circuit 1 that detects the outlet side pressure of the directional control valve 3.
4 and presses the unload valve 10 to the communication position.The second pressure receiving part 13 is connected to the inlet side of the directional control valve 3, and the unload valve 10 is set to the cutoff position by the switching pilot pressure of the directional control valve 3. A pressure oil supply device characterized by having a pushing configuration.