JPH0533775A - Capacity control device for variable capacity type hydraulic pump - Google Patents

Abstract

PURPOSE:To control torque to be constant without using any mechanical feedback mechanism, and improve operability of an actuator. CONSTITUTION:A variable control valve 31 to supply pump discharge pressure to the large diameter pressure receiving chamber 28 of a variable capacity cylinder 25 is switched to the pressure oil supply position B or to the drain position A, by means of pressure difference P across the restriction 43 provided in the discharge passage 21 of a variable capacity type hydraulic pump 20 and pressure difference PC across the restriction 35 provided in the discharge passage 34 of a fixed pump 33 and controlling passing flow by the pump discharge pressure. A load detecting valve 32 to supply pump discharge pressure to the large diameter pressure receiving chamber 28 of the variable capacity cylinder 25 is switched to the pressure oil supply position B and to the drain position A, by pressure difference between the upper stream side pressure P1 and the load pressure PLS of a direction changeover valve 22 and pressure difference across the restriction 35, and flow variation of the variable capacity type hydraulic pump 20 is fed back as a pressure difference across the restriction 43, and rotating speed variation is fed back as a pressure difference across the restriction 35.

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 displacement of a variable displacement hydraulic pump.

[0002]

2. Description of the Related Art As shown in FIG. 1, a variable displacement hydraulic pump 1 (hereinafter referred to as variable pump 1) tilts a swash plate 2 to change its capacity, that is, the discharge flow rate per rotation.
In the hydraulic circuit in which the actuator 5 is provided in the discharge passage 3 of the variable pump 1 via the direction control valve 4, the variable control valve 6 and the load detection valve 7 serve as a device for tilting the swash plate 2 to control the displacement. It is known that the discharge pressure P ₀ is supplied to the large diameter pressure receiving chamber 9 of the variable capacity cylinder 8. That is, the variable control valve 6 is switched between the drain position A and the pressure oil supply position B by the spring 10 and the pump discharge pressure P ₀ , and the pump discharge pressure P _0.
Becomes higher, it becomes the pressure oil supply position B and the pump discharge pressure P ₀
Is supplied to the large-diameter pressure receiving chamber 9 of the variable capacity cylinder 8 and the piston 12 is moved leftward by the pressure receiving area difference from the small diameter pressure receiving chamber 11 to tilt the swash plate 2 in the small capacity direction. The discharge flow rate per rotation is reduced, the movement of the piston 12 is fed back to the spring 10 by the mechanical feedback mechanism 13 to increase the spring force, and the swash plate 2 is set at a position corresponding to the pump discharge pressure P _0. The discharge flow rate per rotation is controlled to be constant, that is, the torque is controlled to be constant. The load detection valve 7 is a differential pressure ΔP _LS (Δ) between the upstream pressure P ₀ of the directional control valve 4 and the load pressure P _LS.
When P _LS = P ₀ −P _LS ) becomes large, the pressure oil supply position becomes B, and the swash plate 2 is tilted in the small capacity direction in the same manner as described above, and when the differential pressure ΔP _LS becomes smaller, it becomes the drain position A. The capacity of the variable pump 1 is controlled according to the opening degree of the directional control valve 4, that is, the operation stroke to improve the fine operability of the actuator 5, that is, the fine controllability.

[0003]

In such a capacity control device, since the mechanical feedback mechanism 13 is required, the structure is complicated and the cost is high, and the control accuracy is increased due to the looseness of the mechanical feedback mechanism 13 and the like. In addition, since the swash plate position is fed back to the variable control valve 6, the efficiency of the variable pump 1 itself deteriorates, so that the actual discharge flow rate per revolution due to the swash plate position causes an error with respect to the theoretical discharge flow rate per rotation, and the output is generated. (Flow rate) characteristics deteriorate.

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

[0005]

[Means for Solving the Problems] Variable displacement hydraulic pump 2
A variable capacity cylinder 25 that tilts the swash plate 24 of 0 in the direction of large capacity and a small capacity, first means for detecting a flow rate change of the variable capacity hydraulic pump 20, a rotational speed change of the variable capacity hydraulic pump 20, and Second means for detecting a change in pump discharge pressure;
A variable control valve 31 for supplying a pump discharge pressure to a variable displacement cylinder 25 by an output signal of the first means and an output signal of the second means, and a direction provided in a discharge passage 21 of the variable displacement hydraulic pump 20. A variable displacement hydraulic pump including a load detection valve 32 for supplying a pump discharge pressure to a variable displacement cylinder 25 by a pressure difference between the upstream pressure of the switching valve 22 and the load pressure of the actuator and an output signal of the second means. Capacity control device.

[0006]

[Operation] Since the variable control valve 31 is switched according to the flow rate change and the rotation speed change of the variable displacement hydraulic pump 20, and the pump discharge pressure change, constant torque can be controlled without using a mechanical feedback mechanism, and the load detection valve 32 can be rotated at the rotation speed. It is possible to improve the fine controllability of the actuator by switching by changing the flow rate of the directional control valve according to the number of revolutions.

[0007]

[Example] As shown in FIG. 2, a plurality of actuators 23 are connected to a discharge passage 21 of a variable pump 20 via a plurality of directional switching valves 22, and the capacity of the variable pump 20, that is, the discharge per rotation The swash plate 24 for increasing / decreasing the amount q is tilted in the large / small capacity direction by the variable capacity cylinder 25, and the small diameter pressure receiving chamber 26 of this variable capacity cylinder 25 is connected to the discharge passage 21 by the passage 27, and the large diameter pressure receiving chamber 28 is connected. Is connected to the variable control valve 31 and the load detection valve 32 by passages 29 and 30. The discharge passage 34 of the fixed pump 33 driven together with the variable pump 20 is provided with a throttle 35, and the bypass passage 36 for short-circuiting the throttle passage 35 in the discharge passage 34 is provided with a bypass valve 37. The valve 37 is pushed in the closing direction by the spring 38, and is pushed in the opening direction by the pump discharge pressure P ₀ of the variable pump 20 acting on the pressure receiving portion 39, and the opening degree of the bypass valve 37 is proportional to the pump discharge pressure P _0. growing. The variable control valve 31 has a drain position A and a pressure oil supply position B, and when the variable pump 20 is stopped by being pushed to the drain position A by a weak spring 40, the drain position A
The variable control valve 31 is pushed toward the pressure oil supply position B by the pressure acting on the first pressure receiving portion 41, and toward the drain position A by the pressure acting on the second pressure receiving portion 42. The first pressure receiving portion 41 is pressed and is connected to the upstream side of the throttle 43 provided in the discharge passage 21 of the variable pump 20 by the first pilot passage 44, and the second pressure receiving portion 42 is connected to the downstream side of the throttle 43 by the second pilot. Connected by the passage 45, the variable control valve 31 is pushed toward the pressure oil supply position B by the first force F ₁ proportional to the differential pressure ΔP (ΔP = P ₀ −P ₁ ) across the throttle 43. The variable control valve 31 is pushed toward the drain position A by the pressure acting on the third pressure receiving portion 46, pushed toward the pressure oil supply position B by the pressure acting on the fourth pressure receiving portion 47, and the third pressure receiving The portion 46 is connected to the upstream side of the throttle 35 of the discharge passage 34 of the fixed pump 33 by the third pilot passage 48, and the fourth pressure receiving portion 47.
Is connected to the downstream side of the throttle 35 by the fourth pilot passage 49, and the variable control valve 31 is connected to the differential pressure ΔP _C (ΔP _C
= P ₂ −P ₃ ), and the second force F ₂ is pushed toward the drain position A. The load detection valve 32 is provided with a drain position A and a pressure oil supply position B, and is set to the drain position A when the variable pump 20 is stopped by being pushed to the drain position A by the weak spring 50. The detection valve 32 is operated by the pressure acting on the first pressure receiving portion 51, and the pressure oil supply position B
Is pushed toward the drain position A by the pressure acting on the second pressure receiving portion 52, and the first pressure receiving portion 51 is connected to the upstream side of the directional control valve 22 by the first pilot passage 54. The second pressure receiving portion 52 is connected to the second pilot passage 56 for detecting the load pressure of each directional control valve 22, and the inlet pressure of the directional control valve 22, that is, the downstream pressure P _{1 of the} throttle 43 and the highest load pressure P _LS. It is pushed toward the pressure oil supply position B by the first force F ₁ proportional to the differential pressure ΔP _LS (ΔP _LS = P ₁ −P _LS ). The load detection valve 32 is pushed toward the drain position A by the pressure acting on the third pressure receiving portion 57, is pushed toward the pressure oil supply position B by the pressure acting on the fourth pressure receiving portion 58, and the third pressure receiving thereof is performed. The portion 57 is the third pilot passage 59 and is the fixed pump 3
3 is connected to the upstream side of the throttle 35 in the discharge passage 34, the fourth pressure receiving portion 58 is connected to the downstream side of the throttle 35 in the fourth pilot passage 60, and the load detection valve 32 is connected to the differential pressure ΔP before and after the throttle 35.
The second force F ₂ proportional to _C (ΔP _C = P ₂ −P ₃ ) is pushed toward the drain position A.

Next, the displacement control operation of the variable pump 20 will be described. (Operation of the variable control valve 31) When the rotation speed of the variable pump 20 is constant and the pump discharge pressure changes. When the pump discharge pressure P ₀ is equal to or lower than the set pressure of the bypass valve 37, the bypass valve 37 is closed and the discharge pressure oil of the fixed pump 33 entirely passes through the throttle 35.
The second force F ₂ due to the differential pressure ΔP _{C between the} front and rear becomes larger than the first force F ₁ due to the differential pressure ΔP before and after the throttle 43, the variable control valve 31 becomes the drain position A, and the variable capacity cylinder 2
The large-diameter pressure receiving chamber 28 of No. 5 passes through the passages 29, 30 and the tank 6
1, the variable displacement cylinder 25 moves to the right at the pump discharge pressure P ₀ acting on the small diameter pressure receiving chamber 26, and the swash plate 24 tilts toward the large displacement direction, and the discharge flow rate per rotation of the variable pump 20. And the discharge amount per unit time increase, the differential pressure before and after the throttle 43 increases, the first force F ₁ increases, and the first force F ₁ and the second force F ₂ balance each other. The position of the swash plate 24 is held in the open. That is, the differential pressure before and after the throttle 43 serves as a flow rate detecting means of the variable pump 1 and is fed back to the variable control valve 31. When the pump discharge pressure P ₀ becomes equal to or higher than the set pressure of the bypass valve 37 in the above-described state, the bypass valve 37 opens to operate and the fixed pump 3
Since a part of the discharge pressure oil of No. 3 flows through the bypass passage 36, the flow rate flowing through the throttle 35 decreases and the differential pressure Δ before and after the throttle 35.
Since P _C decreases and the second force F ₂ of the variable control valve 31 decreases, the variable control valve 31 moves to the pressure oil supply position B, and the pump discharge pressure P ₀ passes from the passages 62 and 29 to the variable capacity cylinder 2.
The variable capacity cylinder 25 is supplied to the large-diameter pressure receiving chamber 28 of No. 5 and moves to the left by the pressure receiving area difference, and tilts the swash plate 24 in the small capacity direction. As a result, the discharge flow rate per one rotation of the variable pump 20 decreases, and the discharge flow rate per unit time also decreases, so the differential pressure before and after the throttle 43 decreases and the first force F decreases.
_{1 is} also reduced, and the position of the swash plate 24 is maintained when the first force F ₁ and the second force F ₂ are balanced.

When the pump discharge pressure P ₀ further increases from the above-mentioned state, the bypass valve 37 is further opened and the flow rate of the passage increases, so the flow rate through the throttle 35 decreases and the throttle 35 increases.
Since the differential pressure ΔP _C between the front and rear becomes even smaller, the variable control valve 3
The second force F ₂ acting on 1 becomes smaller, the variable control valve 31 becomes the pressure oil supply position B, and the variable capacity cylinder 25 moves leftward and the swash plate 24 moves in the small capacity direction in the same manner as described above. The discharge flow rate per rotation decreases and the discharge flow rate per unit time decreases, the differential pressure before and after the throttle 43 decreases and the first force F ₁ also decreases as described above. The position of the swash plate 24 is held when the force F ₁ and the second force F ₂ are balanced. As described above, when the rotation speed of the variable pump 20 is constant, the swash plate 24 is driven by the pump discharge pressure P ₀ .
Is determined and the discharge flow rate q per pump discharge pressure P ₀ × 1 rotation is controlled to be constant, that is, the torque is controlled to be constant.

When the pump discharge pressure of the variable pump 20 is constant and the rotation speed changes. When the number of rotations of the variable pump 20 is increased in a state where the swash plate 24 position is determined by a certain value of the pump discharge pressure P ₀ , the discharge flow rate per unit time is increased even if the discharge flow rate per rotation is the same, and the throttle 43 is located around the throttle 43. Of the fixed pump 33 that is driven together with the variable pump 20 increases, and the differential pressure ΔP _C before and after the throttle 35 also increases, which acts on the variable control valve 31. The first force F ₁ and the second force F ₂ become equal, the variable control valve 31 remains balanced, the position of the swash plate 24 does not change, and the discharge flow rate per rotation of the variable pump 20 does not change. .. This also applies when the rotational speed of the variable pump 20 is reduced, so that the capacity of the variable pump 20 can be controlled to a constant torque. That is, the fixed pump 33 and the throttle 35 serve as a variable pump rotation speed detecting means.

(Operation of the load detection valve 32) When the rotation speed of the variable pump 20 is constant. Load detection valve 32 is due to the differential pressure △ P _LS of the second force F ₂ and the upstream pressure P ₁ and the maximum load pressure P _LS by differential pressure △ P _C diaphragm 35 around which is provided in the discharge passage 34 of the fixed pump 33 The position where the first force F ₁ becomes equal is determined, whereby the position of the swash plate 24 of the variable pump 20 is determined. The upstream pressure P
₁ and the maximum load pressure P _LS differential pressure △ P _LS is the opening of the directional control valve 22, that is proportional to the operation stroke, if the pressure difference △ P _C before and after the diaphragm 35 is a rotational speed of the variable pump 20 is constant Since it is constant, the differential pressure Δ
Since P _LS is large and the first force F ₁ acting on the load detection valve 32 is larger than the second force F ₂ due to the differential pressure ΔP _C , the load detection valve 32 is at the pressure oil supply position B and the passage 63, Three
Since the pump discharge pressure P ₀ is supplied to the large-diameter pressure receiving chamber 28 of the variable capacity cylinder 25 from ₀ , 29, the swash plate 2 is used as described above.
No. 4 is tilted in the small capacity direction, the discharge flow rate per rotation is decreased and the flow rate per unit time is decreased, the flow rate passing through the directional control valve 22 is decreased, and the upstream pressure P ₁ and the maximum load pressure are increased. P
The pressure difference with _LS becomes small and the first force F ₁ decreases, and the swash plate 2 is placed at a position where the first force F ₁ and the second force F ₂ are balanced.
The position of 4 is determined. Similarly, when the operation stroke of the directional control valve 22 is large, the difference ΔP _LS is small, and the position of the swash plate 24 of the variable pump 20 is in the larger capacity direction than in the case described above. As a result, the discharge flow rate per unit time of the variable pump 20 is small when the operation stroke of the directional control valve 22 is small, and is large when it is large, so that the flow rate control that matches the operation stroke of the directional control valve 22 can be performed regardless of the maximum load pressure. Fine operability of the actuator 23
That is, the fine controllability can be improved.

When the rotational speed of the variable pump 20 changes. When the rotation speed of the variable pump 20 changes, the rotation speed of the fixed pump 33 also changes, so that the differential pressure ΔP before and after the throttle 35.
Since _C is changed similarly to the differential pressure △ P _LS of the upstream pressure P ₁ and the maximum load pressure P _LS, since the position of the swash plate 24 does not change, per unit time the discharge flow rate of the variable pump 20 is increased or decreased,
Since flow through the directional control valve 22 is a differential pressure △ P _LS of the maximum load pressure P _LS and the upstream pressure P ₁ is changed by speed change changes by the square of the speed change, directional control valve 22 The passing flow rate for the same operation stroke changes only by the change in the rotation speed, so that a flow control valve proportional to the rotation speed of the variable pump 20 can be formed. For example, when the rotation speed of the variable pump 20 becomes 1/2, the differential pressure ΔP _LS becomes 1/4, and the passage flow rate of the directional control valve 22 for the same stroke becomes 1/2.

[0013]

As described above, the displacement of the variable displacement hydraulic pump 20 can be controlled with a constant torque, a mechanical feedback mechanism is not required, the structure is simple and the cost is low, and the accuracy of the constant torque control can be improved. Even if the efficiency of the displacement hydraulic pump 20 decreases, the output flow rate characteristic does not decrease.
Further, the flow rate of passage of the directional control valve can be controlled according to the change in the rotational speed of the variable displacement hydraulic pump 20, and the fine operability of the actuator can be improved.

[Brief description of drawings]

FIG. 1 is a diagrammatic explanatory diagram of a conventional example.

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

[Explanation of symbols]

20 variable displacement hydraulic pump, 21 discharge passage, 22 directional control valve, 23 actuator, 24 swash plate, 25
Variable capacity cylinder, 26 small diameter pressure receiving chamber, 28 large diameter pressure receiving chamber, 31 variable control valve, 32 load detection valve, 33 fixed pump, 34 discharge passage, 35 throttle, 37 bypass valve,
43 aperture.

Claims (1)

Claim: What is claimed is: 1. A variable capacity cylinder 25 for tilting a swash plate 24 of a variable capacity hydraulic pump 20 in a capacity increasing / decreasing direction, and a flow rate change of the variable capacity hydraulic pump 20. 1 means, a second means for detecting a change in the number of revolutions of the variable displacement hydraulic pump 20 and a change in pump discharge pressure, and a variable capacity cylinder by the output signal of the first means and the output signal of the second means. Variable control valve 31 for supplying pump discharge pressure to 25
And the differential pressure between the upstream pressure of the directional control valve 22 provided in the discharge passage 21 of the variable displacement hydraulic pump 20 and the load pressure of the actuator, and the output signal of the second means for pumping to the variable displacement cylinder 25. A displacement control device for a variable displacement hydraulic pump, comprising a load detection valve 32 for supplying pressure.