JPH05172107A - Capacity control device for variable hydraulic pump - Google Patents

Abstract

PURPOSE:To stabilize the cutoff function at the time when the delivery pressure of a variable pump has become a set pressure by controlling the pressure oil to be supplied to a servo-cylinder for controlling the tilting angle of the swash plate of the variable pump by which the delivery pressure oil is supplied to a plurality of actuators, by means of two control valves having different control modes. CONSTITUTION:In a hydraulic circuit in which the delivery pressure oil of a variable pump 1 is supplied to a plurality of actuators 3 through operation valves 2 and pressure compensating valves 5, the pump delivery pressure PO is always supplied to the small- diameter chamber 13 of a servo-cylinder 12 for changing the tilting angle of the swash plate 11 of the variable pump 1, while the delivery pressure PO is supplied to the large-diameter chamber 14 thereof through first and second control valves 15, 16. The first control valve 15 controls torque by the delivery pressure PO and a feedback link 18, so as to be constant; while the second control valve 16 controls the capacity of the variable pump 1 by the delivery pressure PO and the maximum load pressure so that the delivery pressure PO becomes higher than the maximum load pressure by a given value. And the first control valve 15 is operated by a solenoid 21 in the direction the capacity is reduced when the delivery pressure PO is a set pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the capacity of a variable hydraulic pump used in a hydraulic circuit that supplies the hydraulic fluid discharged from one variable hydraulic pump to a plurality of hydraulic actuators.

[0002]

2. Description of the Related Art In order to supply the hydraulic fluid discharged from one hydraulic pump to a plurality of hydraulic actuators, a plurality of operating valves are provided in the discharge passage of a variable hydraulic pump, and by switching the operating valves, the pressure is applied to each hydraulic actuator. Although it is sufficient to supply oil, when supplying pressure oil to multiple hydraulic actuators at the same time, pressure oil is supplied only to the hydraulic actuator with a small load and pressure oil is supplied to the hydraulic actuator with a large load. It will be gone. As a hydraulic circuit to be solved by this, for example, the one shown in Japanese Patent Publication No. 2-49405 has been proposed.

A schematic diagram of such a hydraulic circuit is shown in FIG. That is, the discharge passage 1a of the variable hydraulic pump 1
A plurality of operating valves 2 are provided, and a pressure compensating valve 5 is provided in each circuit 4 connecting each operating valve 2 and each hydraulic actuator 3, and the pressure of each circuit 4, that is, the highest pressure in the load pressure is checked by a check valve 6 To the load pressure detection path 7 with
The detected load pressure acts on the pressure receiving portion 5a of each pressure compensating valve 5 to set the pressure corresponding to the load pressure, and the pump discharge pressure is supplied to the displacement control portion 9 by the control valve 8 to supply the variable hydraulic pump 1 Is set to a value commensurate with the load pressure, the outlet side pressure of each operation valve 2 is made equal, and when each operation valve 2 is operated simultaneously, pressure oil is applied to each hydraulic actuator 3 at a diversion ratio proportional to the opening area of each operation valve. Is available.
In the above description, the capacity of the variable hydraulic pump 1 is the flow rate discharged after one rotation.

With such a hydraulic circuit, the function of the pressure compensating valve 5 allows the flow rate distribution to be proportional to the opening area of the operating valve 2 regardless of the load of each hydraulic actuator 3, so that the discharge of one hydraulic pump 1 can be performed. The pressure oil can be supplied to each hydraulic actuator 3 in proportion to the operation amount of the operation valve 2. Further, the control valve 8 controls the pump discharge pressure P ₀ and the load pressure P _LS.
The pump discharge pressure P ₀ is set to be higher than the load pressure P _LS by a constant value by controlling the displacement of the variable hydraulic pump 1 by the switching operation.

[0005]

In such a capacity control device, a relief valve 10 is provided in the load pressure detection path 7 to provide the load pressure P _LS.
Has a so-called cut-off function that minimizes the displacement of the variable pump 1 by generating a differential pressure above the relief valve set pressure. However, the relief valve 1
In addition to the outflow rate from 0, there are many factors such as errors such as leakage, and the pressure when the capacity of the variable pump 1 becomes the minimum is not constant and the cutoff function becomes unstable.

Therefore, an object of the present invention is to provide a displacement control device for a variable hydraulic pump, which can solve the above-mentioned problems.

[0007]

A first control valve 15 to the displacement of the variable hydraulic pump 1 to the torque constant control by the pump discharge pressure P ₀ and the feedback link 18. Means for Solving the Problems], variable between the pump discharge pressure P ₀ by the said maximum load pressure The second control valve 16 for controlling the displacement of the hydraulic pump 1 so that the pump discharge pressure P ₀ is higher than the maximum load pressure P _LS by a constant value, and the first control valve 15 are set in the direction of small displacement regardless of the pump discharge pressure. A displacement control device for a variable hydraulic pump, comprising a solenoid 21 that operates and a controller 22 that energizes the solenoid 21 when the pump discharge pressure of the variable hydraulic pump 1 is a set pressure.

[0008]

[Operation] When the pump discharge pressure P ₀ reaches the set pressure, the cutoff can be made stable and the cutoff function is stable, and the pump discharge pressure P ₀ at the time of cutoff can be arbitrarily changed.

[0010]

[Example] As shown in FIG. 2, the capacity of the variable pump 1 is increased / decreased by changing the tilt angle of the swash plate 11 by the servo cylinder 12, and the small diameter chamber 13 of the servo piston 12 is changed.
When pressure oil is supplied to and slides in the direction of arrow a, the capacity increases, and when pressure oil is supplied to the large diameter chamber 14 and slides in the direction of arrow b, the capacity decreases. The pump discharge pressure P ₀ is constantly supplied to the small diameter chamber 13 of the servo piston 12, and the large diameter chamber 14
In the first control valve 15 and the second control valve 16, the pump discharge pressure P
₀ is supplied, the first control valve 15 is pushed to the communication position A by the pump discharge pressure P ₀ acting on the first pressure receiving portion 17, and is pushed to the drain position B by the feedback link 18 connected to the servo piston 12. The variable hydraulic pump 1 has a first capacity
The control valve 15 controls the product (torque) of the pump discharge pressure P ₀ and the capacity to be constant. The second control valve 16 is pushed to the supply position C by the pump discharge pressure P ₀ acting on the first pressure receiving portion 19, and is pushed to the drain position D at the load pressure P _LS acting on the second pressure receiving portion 20. 2 Control valve 16 pump discharge pressure P ₀
Is higher than the load pressure P _LS by a constant value.

As a result, the capacity of the variable pump 1 becomes as shown by the solid line in FIG. 3, but since it does not have a cutoff function, a solenoid 21 is provided in the first control valve 15 as shown in FIG. By energizing the controller 22, the first control valve 15 is pushed to the supply position A and the swash plate 11 is set to the minimum angle to provide the cutoff function. The controller 22 receives the pump discharge pressure P ₀ from the pressure sensor 23 and energizes the solenoid 21 when the pump discharge pressure P ₀ reaches the set pressure. This allows
The capacity of the variable hydraulic pump 1 becomes minimum when the pump discharge pressure P ₀ is the set pressure as shown by the dotted line in FIG. 3, and has a cut-off function. In FIG. 2, the second control valve 1
Reference numeral 6 has a third pressure receiving portion 23 to which pressure oil is supplied from the outside, and by supplying pressure oil to this third pressure receiving portion 23, the differential pressure between the pump discharge pressure P ₀ and the load pressure P _LS can be changed. Is done.

[0011]

The pump discharge pressure P ₀ can be cut off when the pump discharge pressure P ₀ reaches the set pressure, the cutoff function is stabilized, and the pump discharge pressure P ₀ at the time of cutoff can be arbitrarily changed.

[Brief description of drawings]

FIG. 1 is a conventional hydraulic circuit diagram.

FIG. 2 is a diagrammatic configuration explanatory view showing an embodiment of the present invention.

FIG. 3 is a chart showing a relationship between pressure and capacity of a variable hydraulic pump.

[Explanation of symbols]

1 ... Variable hydraulic pump, 1a ... Discharge passage, 2 ... Operation valve, 3 ...
Actuator, 4 ... Circuit, 5 ... Pressure compensation valve, 7 ... Load pressure detection path, 15 ... First control valve, 16 ... Second control valve, 21
… Solenoid, 22… Controller.

Claims (1)

[Claims] 1. A plurality of operating valves 2 are provided in a discharge passage 1a of a variable hydraulic pump 1, a pressure compensating valve 5 is provided in a circuit 4 connecting each operating valve 2 and an actuator 3, and a load pressure of each actuator 3 is provided. In the hydraulic circuit in which the load pressure detection path 7 for detecting the maximum pressure in the above is connected to the pressure receiving portion 5a of each of the pressure compensating valves 5, the capacity of the variable hydraulic pump 1 is set to the pump discharge pressure P ₀ and the torque constant by the feedback link 18. The first control valve 15 for controlling, and the second control for controlling the displacement of the variable hydraulic pump 1 by the pump discharge pressure P ₀ and the maximum load pressure so that the pump discharge pressure P ₀ is slightly higher than the maximum load pressure P _LS. Valve 16
And a solenoid 21 for operating the first control valve 15 in a small capacity direction regardless of the pump discharge pressure, and a controller 22 for energizing the solenoid 21 when the pump discharge pressure of the variable hydraulic pump 1 is a set pressure. Variable hydraulic pump capacity control device.