JPH0154561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an improvement of a closed-circuit drive device for a hydraulic actuator that drives a hydraulic actuator such as a single-rod hydraulic cylinder or a hydraulic motor in a closed circuit;
In particular, it is suitable for hydraulic excavators, etc., with regard to improvements in on-off valves with a flushing function (on-off valves that discharge part of the oil in the main circuit from the low-pressure side main circuit to a tank).

FIG. 1 shows a conventional closed-circuit drive system for a single-rod hydraulic cylinder. A variable displacement hydraulic pump 1 is connected to a hydraulic cylinder 2 in a closed circuit by two main circuits A, B. A flushing valve 3 is connected between the main circuits A, B and the low pressure circuit C, and the flushing valve 3 operates according to the pressure difference between the main circuits A, B. That is, when there is no pressure difference, the flushing valve 3 is in the neutral position, cutting off both the main circuits A and B from the low pressure circuit. When the main circuit A or B becomes the high pressure side, the flushing valve 3
Alternatively, A is connected to a low pressure circuit C, and excess pressure oil in the main circuit B or A is discharged to a tank 5 through a relief valve 4 provided in the low pressure circuit C. When there is a shortage of oil in the main circuit B or A on the low pressure side, oil is supplied from the tank 5 via the check valve 6 or 7.

In Fig. 1, when an external force is applied to the hydraulic cylinder 2 in the right direction indicated by the arrow, if you try to suddenly drive the hydraulic cylinder 2 in the direction in which this external force acts, the piston of the hydraulic cylinder 2 will be delayed in its operation. Therefore, the pressure in the main circuit B becomes lower than the pressure in the main circuit A, the flushing valve 3 is switched, and the main circuit B is communicated with the low pressure circuit C. Therefore, the hydraulic cylinder 2 is rapidly accelerated. Then, when the speed reaches a speed commensurate with the amount of oil supplied from the variable displacement hydraulic pump 1, the pressures in the two main circuits A and B are balanced, so the flushing valve 3
returns to the neutral position, and both main circuits A and B are cut off from low voltage circuit C. As a result, pressure oil is closed in the main circuit B, the speed of the hydraulic cylinder 2 suddenly changes, and an impact is generated.

The applicant of this application is Japanese Patent Application No. 56-1614
No. 116913) proposes an invention in which a flushing valve is structured to communicate one of main circuits A and B with low pressure circuit C in a neutral position, thereby preventing abnormal confinement pressure. However, switching of the flushing valve and sudden acceleration of the hydraulic cylinder have not been solved. This is due to the fact that the flushing valve 3 is switched only by the pressure difference between the main circuits A and B.

Further, the fact that the flushing valve is switched only by the pressure difference between the main circuits A and B causes another problem in a closed circuit drive system for a hydraulic motor. FIG. 2 shows a conventional closed circuit drive system for a hydraulic motor. 8 is a hydraulic motor, 9 is a charge pump, and 10 is a charge relief valve.

In FIG. 2, if the hydraulic motor 8 is driven by, for example, an external force and the discharge direction of the variable displacement hydraulic pump 1 is on the main circuit B side, then the main circuit A is on the high pressure side. Flushing valve 3 connects main circuit B to low pressure circuit C. Here, if the pressure loss between the discharge port and suction port of the variable displacement hydraulic pump 1 and the flushing valve 3 is large because the piping is long or another valve is inserted between them. In this case, a situation occurs in which the pressure in main circuit A is higher than that in main circuit B near the flushing valve 3, whereas the pressure in main circuit B is higher than that in main circuit A near the variable displacement hydraulic pump 1. . In this case, the pressure oil discharged from the variable displacement hydraulic pump 1 to the main circuit B is transferred to the flushing valve 3.
This causes the problem that the speed of the hydraulic motor 8 becomes smaller than the speed commensurate with the discharge flow rate of the variable displacement hydraulic pump 1. The resulting shortage in the flow rate returned to the suction port of the variable displacement hydraulic pump 1 is compensated for by the pressure oil from the charge pump 9.

Furthermore, from this state, when the pressure difference between the main circuits A and B near the flushing valve 3 becomes smaller than the switching setting pressure of the flushing valve 3 due to the external force becoming smaller or the speed of the hydraulic motor 8 decreasing, the flushing valve 3 returns to the neutral position, and the flow of pressure oil from the variable displacement hydraulic pump 1, which had been flowing into the tank 5, is abruptly stopped. Therefore, high pressure is generated in the main circuit B, and the hydraulic motor 8 is rapidly accelerated. This phenomenon typically occurs in the above case, but if the pressure loss in the main circuits A and B is very large, it also occurs during normal operation when the hydraulic motor 8 drives an external load, especially an inertial load. Such defects significantly impair operability.

This problem can be solved by arranging the flushing valve 3 near the variable displacement hydraulic pump 1, but another problem arises. In other words, the flow rate that was diverted from the low-pressure side main circuit to the low-pressure circuit C by the flushing valve 3 also flows to the part of the main circuit where pressure loss is occurring, so a large flow rate flows through this part. In addition, the power loss becomes large, and if the maximum output of the prime mover that drives the variable displacement hydraulic pump 1 is exceeded, the speed of the hydraulic motor 8 must be reduced.

Furthermore, when the lever operation amount, that is, the actuator drive flow rate is small, and the external force is also small, the pressure difference between the main circuits A and B will fluctuate above and below the switching setting pressure of the flushing valve 3, and accordingly, the flushing valve 3 will be activated frequently. There is a problem that causes a hunting phenomenon.

As described above, if the connection between the main circuits A and B and the low voltage circuit C is switched only based on the pressure difference between the main circuits A and B, various problems occur.

An object of the present invention is to provide a closed circuit drive device for a hydraulic actuator that can prevent problems caused by undesirable switching of an on-off valve having a flushing function and improve operability. It is.

In order to achieve this object, the present invention provides a pressure difference detection means for detecting a pressure difference between two main circuits, an operation command detection means for detecting an operation command for a hydraulic actuator, and a pressure difference detection means for detecting a pressure difference detected by the pressure difference detection means. control means for controlling the on-off valve based on both the pressure difference detected by the operation command detection means and the operation command detected by the operation command detection means; It is characterized by adding:

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 3 shows a closed circuit drive system for a single-rod hydraulic cylinder, which is an embodiment of the present invention. Components similar to those in FIGS. 1 and 2 are designated by the same reference numerals. The on-off valves 11 and 12 are of the poppet valve type and have poppets 11a and 12a, springs 11b and 12b, and pilot pressure receiving chambers 11c and 12c, respectively, and open and close the connection between the main circuits A and B and the low pressure circuit C. do. The switching valves 13 and 14 switch the pilot pressure receiving chambers 11c and 12c of the on-off valves 11 and 12 between the main circuits A and B and the drain. Pressure detectors 15 and 16 that detect pressures in main circuits A and B output detection signals P _A and P _B to control circuit 17 . The control circuit 17 performs calculations based on the detection signals P _A and P _B and the operation command signal X from the operation lever 18, and operates the switching valve 1.
3, 14 and the regulator 19. The relief valve 4 of the low pressure circuit C also serves as a charge relief valve.

Next, the operation will be explained with reference to the flowchart of the control circuit 17 shown in FIG.

In step 20, read the signals P _A , P _B , and X.
Hydraulic cylinder 2 is stopped and main circuits A and B
If the pressure difference is less than the predetermined value, step 21
Now, since the operation command signal X is zero, the determination is NO. In step 22, the pressure difference |P _A −P _B
Since | is smaller than the predetermined value, the determination is NO.
As a result, in step 26, the control circuit 17
turns off both switching valves 13 and 14. Therefore, the switching valves 13 and 14 connect the pilot pressure receiving chambers 11c and 12c of the on-off valves 11 and 12 to the main circuits A and B, and both on-off valves 13 and 14 are closed. Then, in step 28, a command signal indicating a discharge amount of zero is output to the regulator 19.

When the operating lever 18 is operated, the operating command signal X that sets the operating direction and speed of the hydraulic cylinder 2 is
When inputted to the control circuit 17, the discharge direction of the variable displacement hydraulic pump 1 is set to the high pressure side in step 27 when the rate of change of the operation command signal In either case, the pressure difference |P _A −P _B | is determined in step 22. If a pressure difference occurs between the main circuits A and B during normal startup or operation of the hydraulic cylinder 2, step 23 turns P _A
>P _B is determined, and if main circuit A is on the high voltage side,
In step 24, switch valve 13 is turned off and switch valve 1 is turned off.
4 is turned on, the on-off valve 11 is closed, and the on-off valve 1 is turned on.
Open 2. As a result, the main circuit B on the low voltage side
is connected to the low pressure circuit C, and excess pressure oil is discharged to the tank 5. If it is determined in step 23 that the pressure in the main circuit B is high, in step 25, the switching valve 13 is turned on, the switching valve 14 is controlled to be turned off, the on-off valve 11 is opened, and the on-off valve 12 is turned on. Close it. Thereafter, in step 28, a command signal corresponding to the operation command signal X is output to the regulator 19, and the discharge direction and discharge flow rate of the variable displacement hydraulic pump 1 are controlled.

When an external force is applied to the hydraulic cylinder 2, the main circuit B
If the operating lever 18 is suddenly operated in an attempt to drive the hydraulic cylinder 2 in the same direction as the direction in which an external force is applied while the hydraulic cylinder 2 is on the high pressure side,
In step 21, it is determined as YES because the rate of change of the operation command signal However, the switching valves 13 and 14 are not switched and are kept in the same state. That is, before the lever was operated, the main circuit B was on the high pressure side, so the switching valve 13 was on and the switching valve 14 was off, and this state is maintained. Therefore, even if the main circuit A suddenly becomes high-pressure, the state in which the main circuit A is connected to the low-pressure circuit C by opening the on-off valve 11 is maintained, thereby preventing sudden acceleration of the hydraulic cylinder 2. be done.

The amount of operation of the operation lever 18 is kept approximately constant,
When the magnitude relationship between the pressures in the main circuits A and B changes due to a change in the load applied to the hydraulic cylinder 2, the operations of steps 22 to 26 are performed, so that the same function as a conventional flushing valve is achieved.

According to this embodiment, in addition to the pressure difference between the main circuits A and B, the change rate and discharge direction of the operation command signal X are checked, so sudden changes in the speed of the hydraulic cylinder 2 are prevented and operability is improved. can be done.

Although not within the technical scope of the present invention, it is possible to turn on one or both of the switching valves 13 and 14 by an emergency input to the control circuit 17 in the event of an emergency such as engine trouble. With the configuration of the control circuit 17, the hydraulic cylinder 2 can be freely lowered in an emergency, and safety can be improved.

In FIG. 3, the switching valves 13 and 14 are connected to the control circuit 17.
However, as shown in FIG. 5, the control circuit 17 may directly control the solenoid valve type on-off valves 29 and 30. Normally, in this case, check valves 6 and 7 for charging are required.

FIG. 6 shows a closed circuit drive device for a hydraulic motor, which is another embodiment of the present invention. Components similar to those in FIGS. 2 and 5 are designated by the same reference numerals.

In this embodiment, the opening set pressures of the on-off valves 29 and 30 are not always kept constant like the conventional switching set pressures, but are changed in consideration of the lever operation amount and the pressure loss of the main circuits A and B. The operation will be explained with reference to the valve opening setting pressure shown in FIG. 7 and the flowchart of the control circuit 17 shown in FIG. 31-4
2 indicates a step.

The control circuit 17 reads the operation command signal X and the detection signals P _A and P _B in step 31 . When the magnitude of the absolute value of the operation command signal _X is smaller than the predetermined value | Outputs a command signal according to the In this state, main circuit A,
Since the control is performed regardless of the value of the pressure difference ΔP of B, the hunting phenomenon that occurs when the amount of lever operation is small and the external force is also small can be prevented.

When no external force is acting on the hydraulic motor 8 and the high-pressure side main circuit near the hydraulic motor 8 and the high-pressure side main circuit near the variable displacement hydraulic pump 1 match, for example, the main circuit Assuming that A is on the high pressure side, the control circuit 17 makes a YES determination in step 34 and sets the valve opening set pressure ΔP ₁ (X) in step 35.
Read from memory. The opening setting pressure ΔP ₁ (X) of the on-off valve 30 when the main circuit A is on the high pressure side and the opening setting pressure ΔP ₂ (X) of the on-off valve 29 when the main circuit B is on the high pressure side are , as shown in Figure 7,
It is determined in advance according to the ejection direction and ejection amount and is stored in the memory.

When the main circuit A is on the high pressure side and on the discharge side, the valve opening setting pressure ΔP ₁ (X) is always constant,
In step 36, the pressure difference ΔP becomes the valve opening set pressure ΔP ₁
If it is determined that it is larger than (X), in step 37,
The on-off valve 30 is opened. As a result, the main circuit B on the low pressure side is communicated with the low pressure circuit C, and performs the same function as a conventional flushing valve.

An external force is acting on the hydraulic motor 8, and the main circuit B
is on the discharge side, so if the main circuit A near the hydraulic motor 8 is on the high pressure side, step 35
When the valve opening set pressure ΔP ₁ (X) is read out, the value increases as the value of the operation command signal X increases in the negative direction, as shown in the second quadrant of FIG. In other words, the flow rate flowing through the main circuit B increases, and the pressure loss in the main circuit B also increases accordingly, so by adding up this increase in pressure loss, ΔP ₁
(X). This pressure loss correction is shown by a dotted line in FIG. The pressure loss generated in the main circuit is determined depending on the flow rate of the pressure oil flowing therethrough, that is, the discharge capacity of the hydraulic pump (when the pump input shaft rotation speed is approximately constant). Therefore, in step 36, the pressure difference ΔP and the valve opening set pressure ΔP ₁
(X) is the same as comparing the pressures in main circuits A and B when there is no pressure loss in main circuit B. In other words, the pressure in main circuit B is higher than the pressure in main circuit A near the variable displacement hydraulic pump 1, but the pressure in main circuit A is higher than the pressure in main circuit B near the hydraulic motor 8 due to pressure loss. In this case, the pressure difference ΔP becomes smaller than the valve opening set pressure ΔP ₁ , and the on-off valve 30 is maintained in the closed state. Then, as the external force becomes larger and the pressure in the main circuit A becomes higher than the main circuit B even near the hydraulic motor 8 (the hydraulic motor 8 performs a pump action and the variable displacement hydraulic pump 1 performs a motor action), the pressure The difference △P becomes larger than the valve opening setting pressure △P ₁ , and the opening/closing valve 30
is controlled to be open. Thereby, it is possible to solve the problem that the speed of the hydraulic motor 8 becomes smaller than the speed commensurate with the discharge flow rate, as described in the explanation of FIG. 2, and the problem that the hydraulic motor 8 is suddenly accelerated thereafter.

According to this embodiment, in addition to the pressure difference between the main circuits A and B, the magnitude and discharge direction of the operation command signal X and the pressure loss in the main circuits A and B that change depending on the magnitude are looked at. Therefore, it is possible to prevent a hunting phenomenon due to the pressure difference between the main circuits A and B, a decrease in the speed of the hydraulic motor 8, and a sudden acceleration thereafter, and improve operability.

In FIG. 6, if the pressure detectors 15 and 16 are installed near the variable displacement hydraulic pump 1, the main circuit A,
It is possible to make only a small amount of correction for the pressure loss of B, or in some cases, it may be completely omitted.

In the illustrated embodiment, the control circuit 17 corresponds to the control means of the present invention, and the step 22 of the control circuit 17 corresponds to the control means of the present invention.
(FIG. 4) and step 33 (FIG. 8) correspond to the pressure difference detection means together with the pressure detectors 15 and 16.
The portion that performs steps 35 and 38 (FIG. 4) and steps 35 and 38 (FIG. 8) corresponds to the operation command detection means.

Note that a differential pressure detector can be used instead of the pressure detectors 15 and 16.

As explained above, according to the present invention, the pressure difference detection means detects the pressure difference between the two main circuits, the operation command detection means detects the operation command of the hydraulic actuator, and the pressure difference detection means detects the pressure difference between the two main circuits. control means for controlling the on-off valve based on both the pressure difference detected by the operation command detection means and the operation command detected by the operation command detection means; By adding this feature, it is possible to prevent problems caused by switching the on-off valve having the flushing function in an undesirable state, and to improve the operability.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional closed circuit drive device for a single rod hydraulic cylinder, Fig. 2 is a circuit diagram of a conventional closed circuit drive device for a hydraulic motor, and Fig. 3 is a circuit diagram showing an embodiment of the present invention. , FIG. 4 is a flowchart showing the operation of the control circuit in one embodiment of the present invention, FIG. 5 is a circuit diagram showing a modification of the embodiment of FIG. 3, and FIG.
The figure is a circuit diagram showing another embodiment of the present invention, Figure 7 is a diagram showing the valve opening setting pressure in another embodiment of the present invention, and Figure 8 is the operation of the control circuit in another embodiment of the present invention. This is a flowchart showing the following. 1...variable displacement hydraulic pump, 2...hydraulic cylinder,
4...Relief valve, 5...Tank, 8...Hydraulic motor,
11, 12...Opening/closing valve, 13,14...Switching valve, 1
5, 16...Pressure detector, 17...Control circuit, 18...
Operation lever, 19... Regulator, 29, 30...
On-off valve, A, B...main circuit, C...low pressure circuit.

Claims (1)

[Claims] 1. A variable displacement hydraulic pump is connected to a hydraulic actuator in a closed circuit by two main circuits, and a low pressure circuit and a main circuit that discharge part of the oil in the main circuit toward a tank. In a closed circuit drive device for a hydraulic actuator, which is provided with an on-off valve that opens and closes a connection between the circuits, a pressure difference detection means for detecting a pressure difference between the two main circuits, and an operation command for the hydraulic actuator are provided. and a control means for controlling the on-off valve based on both the pressure difference detected by the pressure difference detection means and the operation command detected by the operation command detection means. A closed circuit drive device for a hydraulic actuator. 2. A closed-circuit drive device for a hydraulic actuator according to claim 1, which uses a single-rod hydraulic cylinder as the hydraulic actuator, wherein the operation command detection means detects the speed of change of the operation amount and the operation direction. , a hydraulic actuator in which the control means is configured to switch between on-off valve control based on the pressure difference between the two main circuits and on-off valve maintenance regardless of the pressure difference, depending on the detection result of the operation command detection means; Closed circuit drive. 3. The operation command detection means detects the operation amount and the operation direction, and the control means changes the opening setting pressure of the on-off valve according to the detection result of the operation command detection means, and controls the pressure of the two main circuits. A closed-circuit drive device for a hydraulic actuator according to claim 1, which performs open/close valve control based on a difference.