JPS6081502A - Driving device of closed circuit of hydraulic actuator - Google Patents

Abstract

PURPOSE:To improve operatability, by controlling a control valve based on both a pressure difference between two main circuits and operation instructions of a hydraulic actuator. CONSTITUTION:Pressure detectors 15, 16 are provided on main circuits A, B, outputs from the pressure detectors 15, 16 are applied to a control circuit 17 and control valves 11, 12 are controlled based on both a pressure difference between the main circuit A, B and operation instructions of hydraulic actuator 2. With this construction, as it becomes that the size of an operation instruction signal X and the direction of discharge other than the pressure difference between the main circuits A, B are obtained, a sudden change of a rate of the hydraulic cylinder 2 can be prevented and operatability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in 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, and is suitable for hydraulic excavators and the like.

FIG. 1 shows a conventional closed-circuit drive device 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, H. That is, if 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 connects the main circuit B or A on the low pressure side to the low pressure circuit C, and the surplus of the main circuit B or A is passed through the relief 51'4 provided in the low pressure circuit C. Pressure oil is discharged into tank 5. If oil is insufficient in the main circuit B or A on the low pressure side, oil is replenished from the tank 5 via the check valve 6 or 7.

? Referring to Figure J1, when an external force is applied to the hydraulic cylinder 2 in the right direction as indicated by the arrow, if you try to suddenly and violently drive the hydraulic cylinder 2 in the direction in which this external force acts, the piston of the hydraulic cylinder 2 will Due to the delay in the operation of the main circuit B, the pressure in the main circuit B becomes lower than the pressure in the main circuit, and the flushing valve 3
is switched, and the main circuit B is connected to the low voltage circuit C. Therefore, the hydraulic cylinder 2 is rapidly accelerated. and,
When a speed corresponding to the amount of oil supplied from the variable displacement hydraulic pump 2 is reached, the pressures in the two main circuits A and B are balanced, so the flushing valve 3 returns to its neutral position and the main circuits A and B
are both cut off from the low voltage circuit C.

As a result, pressure oil is trapped 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 (% Kaikai 57-
No. 116913) proposed an invention in which one of the main circuits A and B communicates with the low pressure circuit C when the flushing valve is in the neutral position, thereby preventing abnormal confinement pressure. The switching of the lashing valve and the sudden acceleration of the hydraulic cylinder are not resolved. This is due to the fact that the flushing valve 3 is switched only by the pressure difference between the main circuits A and H.

Further, the fact that the seven latching valves are 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 IO is a relief valve for charging.

In FIG. 2, if the hydraulic motor 8 is driven by an external force and the discharge direction of the variable displacement hydraulic pump 1 is on the main circuit B side, the main circuit A will be on the high pressure side, so the 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 capacity hydraulic pump 1 and the 7 latching valve 3 is large because the piping is long or another valve is inserted between them, The pressure in main circuit A is higher than that in main circuit B near flushing valve 3;
Conversely, a situation occurs in which the pressure in the main circuit B becomes higher than that in the main circuit A near the variable displacement hydraulic pump l. In this case, the pressure oil discharged from the variable displacement hydraulic pump 1 into the main circuit B passes through the flushing valve 3 and the relief valve 4 and flows into the tank 5, and the speed of the hydraulic motor 8 increases to the discharge of the variable displacement hydraulic pump l. A problem occurs in that the speed becomes smaller than the flow rate. The shortage of flow rate returned to the suction port of the variable displacement hydraulic pump 1 due to this is caused by the charge pump 9
supplemented by pressure oil from

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 a decrease in external force or a decrease in the speed of the hydraulic motor 8, 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 suddenly 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 cases, but
If the pressure loss in the main circuits A and B is very large, this will occur even when the hydraulic motor 8 drives an external load, especially an inertial load. Such defects significantly impair operability.

To solve this problem, the flushing valve 3 should be placed near the variable displacement hydraulic pump 1, but since the flow also flows to the part of the main circuit that is causing pressure loss, this part should be placed near the variable displacement hydraulic pump 1. will flow, resulting in a large power loss, and if the maximum output after driving the variable displacement hydraulic pump 1 is exceeded, the speed of the hydraulic motor 8 will have to be reduced.

In addition, when the amount of lever operation, 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 H will fluctuate the switching setting pressure of the flushing valve 3. There is a problem that causes a hunting phenomenon in which the power switches frequently.

As mentioned above, only the pressure difference between main circuit A and B concave causes main circuit A to
, B and the low voltage circuit C, various problems occur.

An object of the present invention is to provide a closed-circuit drive device for a hydraulic actuator that can eliminate the above-mentioned problems and improve operability.

In order to achieve this object, the present invention is characterized in that a control means for controlling two on-off valves is provided, and a hydraulic actuator operation command is added as a control input condition.

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

FIG. 3 shows a closed-circuit drive device 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.
b, 12b and pilot pressure receiving chambers 11C+12e, respectively, and open/close the connection between the main circuits A, B and the low pressure circuit C.

The switching valves 13.14 switch the pilot pressure receiving chambers 11c, 12c of the on-off valves 11.12 to the main circuits A, B and the drain. Pressure detectors 15 and 16 that detect the pressure in the main circuits A and H send the detection signal PAr P m to the control circuit 1.
Output to 7. The control circuit 17 performs calculations based on the detection signals PA, PB and the operation command signal X from the operation lever 18, and outputs command signals to the switching valves 13 and 14 and the regulator 19.

The relief valve 4 of the low pressure circuit C also serves as a charging relief valve.

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

In step 20, the signal PA#pHlX is read, and if the hydraulic cylinder 2 is in a stopped state and the pressure difference between the main circuits A and B is less than a predetermined value, in step 21, the operation command signal X is zero. Make a NO decision. In step 22, since the pressure difference IPmu-PB1 is smaller than the predetermined value, N
Make a judgment of O. As a result, in step 26, the control circuit 17 turns off both switching valves 13, 14. Therefore, the switching valve 13114 connects the pilot pressure receiving chambers 11 e e 12 e of the on-off valves 11 and 12 to the main circuits A and B, and the on-off valves 13 and 14 are both closed. and,
In step 28, the command signal for the discharge amount of zero is sent to the regulator 1.
Output to 9.

When the operation lever 18 is operated and the operation command signal X that sets the operating direction and speed of the hydraulic cylinder 2 is input to the control circuit 17, if the rate of change of the operation command signal Even if it is larger, step 2
Regardless of whether it is determined in step 7 that the discharge direction of the variable capacity hydraulic pressure sensor I is on the high pressure side, the pressure difference IPA-FBI 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 20, then from step 23 pressure PA>PR
is determined, and if the main circuit is on the high voltage side, the
4, the switching valve 13 is turned off, the switching valve 14 is turned on, the on-off valve 11 is closed, and the on-off valve 12 is closed. Step 23
If it is determined that the pressure in the main circuit B is high, in step 25, the switching valve 13 is turned on and the switching valve 14 is turned off, respectively, and the on-off valve 11'!・Open the on-off valve 12
to close.

Thereafter, in step 28, a command signal corresponding to the operation command signal X is output to the regulator 19, and the variable capacitor is controlled.

The discharge direction and discharge flow rate of the hydraulic pressure I are controlled.

When an external force is applied to the hydraulic cylinder 2 and the main circuit B is on the high pressure side, when the operating lever 18 is suddenly operated in an attempt to drive the hydraulic cylinder 2 in the same direction as the external force is applied. is YES in step 21 because the rate of change of the operation command signal X is greater than a predetermined value.
In step 27, since the discharge direction of the variable displacement hydraulic pump 1 is on the main circuit A side, the determination is No, and the switching valves 13 and 14 are not switched and are kept in the same state. That is, before the lever operation, the main circuit B was on the h 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 side, the main circuit A
By opening the circuit, the state of communication with the low pressure circuit C is maintained, and sudden acceleration of the hydraulic cylinder 2 is prevented.

When the amount of operation of the operating lever 18 is kept approximately constant and 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, steps 22 to 26 are performed. It performs the same function as a flushing valve.

According to this embodiment, in addition to the pressure difference between the main circuits A and H, the change rate and discharge direction of the operation command signal X are looked at.
Sudden changes in the speed of the hydraulic cylinder 2 can be prevented and operability can be improved.

If the control circuit 17' is configured so that one or both of the switching valves 13 and 14 are turned on by an emergency input to the control circuit 17 in the event of an emergency such as engine trouble, it is possible to turn on the hydraulic cylinder 2 in an emergency. It also has the effect of being able to freely descend, increasing safety.

In FIG. 3, the control circuit 17 controls the switching valves 13, 14, but as shown in FIG. 5, the control circuit 17 directly controls the solenoid valve type on-off valves 29, 30. Good too. Usually, 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 setting pressure of the on-off valves 29 and 30 is not always kept constant like the conventional switching setting pressure, but is changed in consideration of the lever operation amount and the pressure loss of the main circuits A and H. Regarding its operation, the valve opening setting pressure shown in Fig. 7 and the valve opening setting pressure shown in Fig. 8
This will be explained with reference to the flowchart of the control circuit 17 shown in the figure. 31 to 42 indicate steps.

The control circuit 17 reads the operation command signal X and the detection signal P A I P n in step 31 . When the magnitude of the absolute value of the operation command signal
．． 30, and then close the regulator 19.
A command signal corresponding to the operation command signal X is output. Since this state is controlled regardless of the value of the pressure difference ΔP between the main circuits A and B, the hunting phenomenon that occurs when the lever operation amount is small and the external force is also small can be prevented.

If no external force is acting on the hydraulic motor 8 and the high-pressure main circuit near the hydraulic motor 8 and the high-pressure main circuit near the variable displacement hydraulic pump l match, for example, the main Assuming that circuit A is on the high pressure side, the control circuit 17 makes a YES determination in step 34, and reads out the valve opening set pressure ΔPI(X) from the memory in step 35. Opening/closing setting pressure ΔPr (X) of the opening/closing valve 30 when the main circuit A is on the high pressure side
and the opening/closing set pressure ΔP1(X) of the opening/closing valve 29 when the main circuit B is on the high pressure side are determined in advance according to the discharge direction and discharge amount, as shown in FIG. 7, and are stored in the memory. remembered.

When the main circuit A is on the high pressure side and on the discharge side, the valve opening set pressure ΔPI(X) is always constant, and step 3
6, pressure difference ΔPfJ'' - valve opening setting pressure ΔP1 (X)
If it is determined that the on-off valve 30 is larger than the
to be opened. This connects the low-pressure side main circuit B to the low-pressure circuit C, and performs the same function as a conventional seven-lashing valve.

If an external force is acting on the hydraulic motor 8 and the main circuit B is on the discharge side, but the main circuit A near the hydraulic motor 8 is on the high pressure side, in step 35, the valve opening setting pressure is ΔP
When I (X) is read out, its value increases as the value of the operation command signal X increases in the negative direction, as shown in the second quadrant of FIG. That is, 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, ΔP1 (
X). Therefore, in step 36, comparing the pressure difference ΔP and the valve opening set pressure ΔP1(X) is as follows.
This is the same as comparing the pressures in main circuits A and B when there is no pressure loss in main circuit B.

This prevents communication between the main circuit on the discharge side and the low pressure circuit due to the presence of pressure loss, and prevents problems in which the speed of the hydraulic motor 8 becomes lower than the speed commensurate with the discharge flow rate, and furthermore, sudden acceleration. problems that may occur can be resolved.

In this embodiment, in addition to the pressure difference between the main circuits A and H, we are looking at the magnitude and discharge direction of the operation command signal X, and the pressure loss in the main circuits A and B that changes depending on the magnitude. Therefore, it is possible to prevent the hunting phenomenon due to the pressure difference between the main circuits A and B, the speed reduction of the hydraulic motor 8 and the subsequent sudden acceleration, and improve the operability.

In FIG. 6, a pressure detector 1'5.16 is also provided in the vicinity of the variable displacement hydraulic pump 1 in the main circuit A.

The correction for the pressure loss of B may be small, or in some cases, it may be possible to eliminate it altogether.

In the illustrated embodiment, the control circuit 17 corresponds to the control means of the present invention.

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

As explained above, the present invention controls the on-off valve that opens and closes the connection between the main circuit and the low-pressure circuit based on both the pressure difference between the two main circuits and the operation command of the hydraulic actuator. 1- Since a control means is provided and a hydraulic actuator finger command is added as a control input condition, abnormal operation of the hydraulic actuator that is unrelated to the driver's intention can be prevented, improving operability. can be done.

[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. 6 shows another embodiment of the invention. The circuit diagram, FIG. 7 is a diagram showing the valve opening setting pressure in another embodiment of the present invention, and FIG. 8 is a flowchart showing the operation of the control circuit in another embodiment of the present invention. 1... Variable displacement hydraulic pump, 2... Hydraulic cylinder,
4... Relief valve, 5... Tank, 8... Hydraulic motor, 11, t2... Open/close valve, 13.14... Switching valve, 15° 16... Pressure detector, 17. ...Control circuit, 18...Operation lever, 19...Regulator, 2
9.30... Open/close valve, A, B... Main circuit, C...
Low voltage circuit. Figure 1 Figure 2 Here Figure 3 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A variable displacement hydraulic pump is connected to a hydraulic actuator in a closed circuit through two main circuits, and a connection between the circuits is opened and closed between the low pressure circuit that discharges excess pressure oil in the main circuit and the main circuit. In a closed-circuit drive device for a hydraulic actuator provided with an on-off valve, the above-mentioned D11 is
A closed circuit drive device for a hydraulic actuator, characterized in that it is provided with a control means for controlling valve closing.