JPH06105081B2 - Hydraulic control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydraulic control device in which a hydraulic pump and an actuator are connected via a closed center type control valve, and an unload valve is connected to a discharge circuit of the hydraulic pump. It is about.

2. Description of the Related Art In the above-mentioned hydraulic control device, when the pump discharge amount becomes smaller than the control valve required flow rate, the pressure becomes below the pressure compensation function minimum working pressure and the compensation becomes ineffective, so it is necessary to increase the pump discharge flow rate. is there. On the other hand, when the hydraulic pump discharges more than the required flow rate of the control valve, as shown in FIG. 4, the load pressure gradually rises according to the lever stroke of the control valve, but the pump pressure rises to the relief pressure and the pressure rises. Control becomes impossible. Therefore, unnecessary pump pressure is generated and the force cannot be controlled.

From the above, there is one in which a variable relief valve is used as an unload valve in the discharge circuit of the hydraulic pump (JPT / SE82 / 00299).

In this conventional example, the feed back control is performed so that the set pressure is (pump pressure)-(load pressure) = (control valve passage differential pressure) always constant.

For this purpose, a load sensing circuit, which is means for detecting the pump pressure and the load pressure, is provided.

Problems to be Solved by the Invention The above-mentioned conventional example has the following problems.

(1) Since feedback control is performed, hunting or vibration may occur when the load pressure fluctuates.

(2) In order to prevent this, it is effective to restrict the pressure feedback circuit, but there is a problem that the response is deteriorated.

(3) Even if the actuator tries to control the pressing force, a pressure difference of zero does not occur at the flow rate of zero, so the pressure rises infinitely, and the force fine control cannot be performed.

Means and Actions for Solving Problems The present invention has been conceived in view of the above, and hunting or vibration does not occur even if the load pressure changes, and the fine control of the pressing force by the actuator is possible. The purpose of the present invention is to provide a hydraulic control device which is configured to open and close the upstream port and the drain port by opening and closing a pilot circuit that communicates the closed chamber with the drain port. The poppet valve and the pilot valve interposed in the pilot circuit so as to open the pilot circuit by pushing with an actuator such as a solenoid against the pushing force by the pressure of the upstream side port, The upstream port is connected to the discharge circuit of the hydraulic pump, and the pilot valve is connected by an actuator such as a solenoid. By operating, the poppet valve is opened and closed to control the pressure of the discharge circuit of the hydraulic pump, and the pressure of this discharge circuit is controlled in proportion to the operating force of the actuator.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

In FIG. 2, 1 is a hydraulic pump, 2 is a cylinder which is an actuator, and 3 is a closed center type control valve interposed in a hydraulic circuit 4 which connects the two. An unload valve 5 is connected to the pump side circuit of the hydraulic circuit 4.

The unloading valve 5 is as shown in FIG.
The upstream port 6 connected to the pump side circuit and the closed chamber 7
When a predetermined differential pressure occurs between the upstream side port 6 and the drain port 8, the poppet valve 9 that opens the upstream side port 6 and connects the upstream side port 6 and the closed side chamber 7 via a variable throttle,
The poppet valve 9 comprises a pilot valve 10 for controlling the differential pressure by being interposed in a pilot circuit connecting the closed side chamber 7 and the drain port 8.

The poppet valve 9 includes an upstream port 6 and a drain port 8
And a valve seat 11 provided between the valve seat 11 and the valve seat, the poppet opening and closing the valve seat 11 by reciprocating.
12, a spring 13 interposed in the chamber 7 on the closing side for pushing the poppet 12 toward the valve seat 11, and a slit-shaped opening 14 fitted in the poppet 12 and provided in the poppet 12 to close the poppet 12. Metering pin that forms a variable throttle with the side chamber 7
It consists of fifteen. The upstream port 6 and the closed chamber 7 of the poppet 12 are squeezed and communicated with each other by the metering pin 15, and the throttle opening is gradually increased by the opening operation of the poppet 12. .

The pilot valve 10 includes a back pressure chamber 16 communicating with the upstream side of the poppet valve 9, a pilot inlet port 17 communicating with the chamber 7 on the closing side of the poppet valve 9, and a pilot outlet port 18 communicating with the drain port 8. The spool hole 19 is provided, a pilot spool 20 fitted into the spool hole 19, and a solenoid 21 for moving the pilot spool 20 against the pressing force acting on the back pressure chamber 16. A step portion is provided at the tip of the pilot spool 20, and the step end surface 20a faces the back pressure chamber 16. Further, when the spool 20 is moved by the pressing force on the back pressure chamber 16 side to the outer periphery of the intermediate portion, the pilot inlet port 17 and the pilot outlet port are provided.
A groove 22 communicating with 18 is provided. Reference numeral 23 is a spring that lightly biases the pilot spool 20 in the opening direction. Although not shown, a spring for urging the pilot spool 20 in the opening direction may be provided on the pilot outflow port side.

In the above structure, the cylinder 2 is operated by switching the control valve 3, and the pressure P in the hydraulic circuit 4 at this time is set by the pilot valve 10 of the unload valve 5.

That is, in FIG. 1, the pump discharge pressure is P, the thrust of the solenoid 21 is Fs, the mounting load of the spring 23 is Fo, the spring constant is K, the area of the step end face 20a of the pilot spool 20 is S, and the stroke of the pilot spool 20 is S. Is X, the pilot opening area is A (x), the flow amplifier gain is α, the pilot flow rate is q, and the unload flow rate is Q. When the unload flow rate Q is small, the pump discharge pressure P acts on the pilot spool 20. It is determined by the balance of the forces to be applied, and P · S = Fs− (Fo + K · x)

At this time, if K · x <<<< Fs and Fo << Fs, then P = Fs / S, and the pump discharge pressure P is controlled in proportion to the thrust of the solenoid 21.

The unloading valve 5 having the above structure is represented by a general hydraulic symbol as shown in FIG.

With the above operation, the pressure P in the hydraulic circuit 4 can be controlled to a pressure proportional to the load pressure while maintaining a pressure higher than the load pressure by the lever stroke of the control valve 3 as shown in FIG.

EFFECTS OF THE INVENTION According to the present invention, the control of the unload valve 5 is controlled not by the feedback control by the load pressure but by the thrust force Fs of the solenoid 21, so that hunting or vibration does not occur even if the load pressure changes. . Further, since the zone for changing the pressure is provided in accordance with the lever operation of the control valve, the fine control of the pressing force by the actuator can be performed. In addition, the poppet valve 9 constituting the unload valve 5 is internally provided with a metering pin 15 whose opening degree is gradually increased by the opening operation of the poppet valve 9, so that the pressure in the hydraulic circuit 4 is reduced. Is paid and
Stable unloading without chattering

[Brief description of drawings]

FIG. 1 is a sectional view showing an essential part of the present invention, FIG. 2 is a circuit diagram,
3 and 4 are diagrams showing changes in the pump discharge pressure with respect to the lever stroke of the operation valve. FIG. 3 shows an example of the present invention, and FIG. 4 shows a case of a conventional example. 1 is a hydraulic pump, 2 is a cylinder, 3 is a control valve, 5 is an unload valve, 6 is an upstream port, 7 is a closed chamber, 8 is a drain port, 9 is a poppet valve, 10 is a pilot valve, 21
Is a solenoid.

Continuation of the front page (56) Reference JP 60-37401 (JP, A) JP 60-196402 (JP, A) JP 56-18803 (JP, B2)

Claims (1)

[Claims] 1. A hydraulic control device in which a hydraulic pump 1 and an actuator are connected via a closed center type control valve 3 and an unload valve 5 is connected to a circuit on the discharge side of the hydraulic pump 1, wherein the unload is performed. The valve 5 has a poppet valve 9 configured to open and close the upstream side port 6 and the drain port 8 by opening and closing a pilot circuit that connects the closed side chamber 7 and the drain port 8, and the pressure of the upstream side port 6. By pushing the solenoid 21 against the pushing force by the pilot valve 10, the pilot circuit is opened so as to open the pilot circuit, and the poppet valve 9 is provided with the pilot valve 10. A hydraulic control device having a metering pin 15 in which the throttle opening is gradually increased by the opening operation of 9.