JP3084587B2 - Displacement control device for variable displacement hydraulic pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus 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 a variable pump 1) tilts a swash plate 2 to change a displacement, that is, a discharge flow rate per rotation.
In a hydraulic circuit in which an actuator 5 is provided in a discharge path 3 of a variable pump 1 via a directional control valve 4, a variable control valve 6 and a load detection valve 7 serve as a device for controlling the displacement by tilting the swash plate 2. There is known a type in which the discharge pressure P ₀ is supplied to a large-diameter pressure receiving chamber 9 of a 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 high, the pressure oil supply position B is reached 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 to the left 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. reducing the one revolution per discharge flow rate, the pump discharge pressure × 1 the swash plate 2 to increase the spring force is fed back to the spring 10 by the motion mechanical feedback mechanism 13 of the piston 12 as a position commensurate with the pump discharge pressure P ₀ The discharge flow per rotation is controlled to be constant, that is, the torque is controlled to be constant. The load detection valve 7 is provided with a differential pressure ΔP _LS (△ P L) between the upstream pressure P ₀ of the direction control valve 4 and the load pressure P _LS.
When (P _LS = P ₀ −P _LS ) increases, the pressure oil supply position B is reached, 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 decreases, the drain position A is set. Thus, the capacity of the variable pump 1 is controlled in accordance with the opening of the direction control valve 4, that is, the operation stroke, thereby improving the fine operability of the actuator 5, that is, fine control.

[0003]

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

Accordingly, 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 A variable displacement hydraulic pump 2
A variable capacity cylinder 25 for tilting the zero swash plate 24 in the direction of large or small capacity, first means for detecting a change in the flow rate of the variable capacity hydraulic pump 20, a change in the rotational speed of the variable capacity hydraulic pump 20, Second means for detecting a change in pump discharge pressure;
A variable control valve 31 for supplying a pump discharge pressure to a large-diameter pressure receiving chamber 28 of a variable displacement cylinder 25 based on an output signal of the first means and an output signal of the second means; The pressure difference between the upstream pressure of the directional control valve 22 provided in the passage 21 and the load pressure of the actuator;
The load detection valve 32 that supplies the pump discharge pressure to the large-diameter pressure receiving chamber 28 of the variable capacity cylinder 25 based on the output signal of the means, compares the pump discharge pressure of the variable displacement hydraulic pump 20 with the discharge pressure of another hydraulic pump. Variable pressure cylinder 25
A capacity control device for a variable displacement hydraulic pump comprising a high-pressure priority valve 62 for supplying to the small-diameter pressure receiving chamber 26 of FIG.

[0006]

[Operation] The variable control valve 31 is switched according to a change in the flow rate and a change in the number of revolutions of the variable displacement hydraulic pump 20, and a change in the pump discharge pressure, so that the torque can be controlled to be constant without using a mechanical feedback mechanism. The fine controllability of the actuator can be improved by changing the flow rate through the directional control valve in accordance with the number of rotations by switching the directional control valve, and even when the pump discharge pressure of the variable displacement hydraulic pump 20 falls below the swash plate operating pressure, Can control the capacity.

[0007]

[Embodiment] As shown in FIG. 2, a plurality of actuators 23 are connected to a discharge path 21 of a variable pump 20 through a plurality of directional control valves 22, and the capacity of the variable pump 20, that is, the discharge per rotation is changed. The swash plate 24 for increasing or decreasing the amount q is tilted in the direction of large or small capacity by the variable capacity cylinder 25, and the small diameter pressure receiving chamber 26 of the variable capacity cylinder 25 is connected to the passage 27, and the large diameter pressure receiving chamber 28 is connected to the passage 29, Variable control valve 3 at 30
1 and the load detection valve 32. The variable pump 2
A throttle 35 is provided in a discharge path 34 of the fixed pump 33 driven together with 0, and a bypass valve 37 is provided in a bypass path 36 that short-circuits around the throttle 35 in the discharge path 34. Pushed in the closing direction by the spring 38 and pushed in the opening direction by the pump discharge pressure P ₀ of the variable pump 20 acting on the pressure receiving portion 39, the opening of the bypass valve 37 increases in proportion to the pump discharge pressure P ₀ . The discharge path 34 of the fixed pump 33 is connected to a tank 61 via a relief valve 60. A high-pressure priority valve 62 such as a shuttle valve or a check valve is provided between the discharge path 21 and the downstream side of the throttle 35 of the discharge path 34. A passage 27 connected to the small-diameter pressure receiving chamber 26 of the variable capacity cylinder 25 is connected to the output side thereof. The variable control valve 31 has a drain position A and a pressure oil supply position B. 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 a pressure acting on the first pressure receiving portion 41, and is moved toward the drain position A by a pressure acting on the second pressure receiving portion 42. The first pressure receiving portion 41 is connected to the upstream side of a throttle 43 provided in the discharge path 21 of the variable pump 20 via a first pilot passage 44, and the second pressure receiving portion 42 is connected to the second pilot downstream of the throttle 43. pushed toward the pressure oil supply position B are connected by passage 45 by the variable control valve 31 diaphragm 43 before and after differential pressure _{△ P (△ P = P 0} -P 1) first force F ₁ which is proportional to. The variable control valve 31 is pushed toward the drain position A by the pressure acting on the third pressure receiving portion 46 and is pushed toward the pressurized oil supply position B by the pressure acting on the fourth pressure receiving portion 47. The portion 46 is connected to the upstream side of the throttle 35 of the discharge passage 34 of the fixed pump 33 by a third pilot passage 48, and the fourth pressure receiving portion 47
Is connected to the downstream side of the throttle 35 in the fourth pilot passage 49, and the variable control valve 31 changes the differential pressure △ P _C (△ P _C) across the throttle 35.
= P ₂ −P ₃ ) and is pushed towards the drain position A with a _second force F ₂ . The load detection valve 32 has a drain position A and a pressure oil supply position B. When the variable pump 20 is stopped by being pushed to the drain position A by a weak spring 50, the load detection valve 32 is set to the drain position A. The detection valve 32 operates at the pressure oil supply position B by the pressure acting on the first pressure receiving portion 51.
, And 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 via the first pilot passage 54, The second pressure receiving section 52 is connected to the second pilot passage 56 for detecting the load pressure of each of the directional control valves 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. pushed toward the pressure oil supply position B at a differential pressure _{△ P LS (△ P LS =} P 1 -P LS) first force F ₁ which is proportional to the. The load detection valve 32 is pushed toward the drain position A by the pressure acting on the third pressure receiving portion 57, and is pushed toward the pressurized oil supply position B by the pressure acting on the fourth pressure receiving portion 58. The portion 57 is connected to the fixed pump 3 by the third pilot passage 59.
3, 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 across the throttle 35.
Pushed toward the drain position A in _{C (△ P C = P 2} -P 3) second force F ₂ which is proportional to.

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 entire discharge pressure oil of the fixed pump 33 passes through the throttle 35. the by P _C 2 force F ₂ is squeezed 4
The pressure becomes larger than the first force F ₁ due to the differential pressure ΔP of about 3 and the variable control valve 31 is at the drain position A, and the large-diameter pressure receiving chamber 28 of the variable capacity cylinder 25 passes through the passages 29 and 30 to the tank 61. swash plate 24 moves variable volume cylinder 25 in the right direction in the pump discharge pressure P ₀ which acts on the small-diameter pressure bearing chamber 26 from communicating with is tilting in volume large direction, the variable pump 20
Since the discharge flow rate per rotation increases and the discharge rate per unit time increases, the differential pressure across the throttle 43 increases and the first force F ₁ increases, and the first force F ₁ and the second force F ₁ increase. Force F ₂
The position of the swash plate 24 is held at the point where the balance occurs. That is, the differential pressure across the throttle 43 is fed back to the variable control valve 31 as the flow rate detection means of the variable pump 1. 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 and a part of the discharge pressure oil of the fixed pump 33 flows through the bypass path 36, so that the flow rate flowing through the throttle 35 is reduced. The differential pressure ΔP _C across the throttle 35 decreases, and the second force F of the variable control valve 31 decreases.
Since ₂ is less variable control valve 31 pressurized oil supply position B, and the displacement pump discharge pressure P ₀ is the supplied with the pressure receiving area difference to atmospheric径受chamber 28 of variable volume cylinder 25 from the passage 62,29 variable cylinder 25 Moves leftward to tilt the swash plate 24 in the small capacity direction. As a result, the discharge flow rate per rotation of the variable pump 20 decreases, and the discharge flow rate per unit time also decreases. Therefore, the differential pressure across the throttle 43 decreases, and the first force F ₁ also decreases. position of the swash plate 24 is held at the F ₁ and the second force F ₂ are balanced.

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

When the rotational speed changes while the pump discharge pressure of the variable pump 20 is constant. When the rotation speed of the variable pump 20 increases in a state where the position of the swash plate 24 is determined at a certain value of the pump discharge pressure P ₀ , the discharge flow per unit time increases even if the discharge flow per rotation is the same, and the throttle 43 is moved around. Is increased, the discharge flow per unit time of the fixed pump 33 driven together with the variable pump 20 is also increased, and the differential pressure ΔP _C across the throttle 35 is also increased, acting on the variable control valve 31. The first force F ₁ and the second force F ₂ are equal, and the variable control valve 31 remains in balance, so that 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 is the same when the rotational speed of the variable pump 20 is reduced, so that the capacity of the variable pump 20 can be controlled to have a constant torque. That is, the fixed pump 33 and the throttle 35 serve as a variable pump rotation speed detecting means.

(Operation of Load Detection Valve 32) When the rotation speed of the variable pump 20 is constant. Load detection valve 32
The first force 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 is F ₁ is at a position where the swash plate 24 of the variable pump 20 is
Is determined. Rotational speed of 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, the diaphragm 35 before and after differential pressure △ P _C is the variable pump 20 because there is constant if a constant, the differential pressure △ P _LS is larger loads first force F ₁ acting on the detecting valve 32 is the differential pressure △ P _C when the operation stroke is small
Second force F ₂ greater than is the load detection valve by 32 the pump discharge pressure P ₀ to the atmospheric径受chamber 28 of the pressure oil supply position B, and the capacity variable cylinder 25 than the passage 63,30,29
As described above, the swash plate 24 tilts in the small capacity direction, the discharge flow rate per rotation decreases, the flow rate per unit time decreases, and the flow rate passing through the directional control valve 22 decreases. A position where the differential pressure between the upstream pressure P ₁ and the maximum load pressure P _LS is reduced, the first force F ₁ is reduced, and the first force F ₁ and the second force F ₂ are balanced. , The position of the swash plate 24 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 a position in the larger displacement direction than in the case described above. Accordingly, 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 increases when the operation stroke of the directional control valve 22 is large, so that the flow control that matches the operation stroke of the directional control valve 22 regardless of the maximum load pressure can be performed. As a result, fine operability of the actuator 23, that is, 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.
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 by the rotation speed change, and a flow control valve proportional to the rotation speed of the variable pump 20 is formed. For example, when the rotation speed of the variable pump 20 becomes １ ／, the differential pressure ΔP _LS becomes １ ／, and the flow rate of the directional control valve 22 for the same stroke becomes １ ／.

The above description is based on the discharge pressure P _{0 of the} variable pump 20.
Is higher than the discharge pressure P ₂ of the fixed pump 33,
When the discharge pressure P ₀ of the variable pump 20 is lower than the discharge pressure P ₂ of the fixed pump 33, the discharge pressure oil of the fixed pump 33 is supplied from the high-pressure priority valve 62 to the small-diameter pressure receiving chamber 2 of the variable capacity cylinder 25.
6. Thus, the discharge pressure P ₀ of the variable pump 20 when the actuator 23 overruns or moves to or above the discharge flow rate of the variable pump 20 due to external force or the like.
When the pressure becomes extremely low or negative, the swash plate 24 can be controlled by supplying the discharge pressure oil of the fixed pump 33 to the small-diameter pressure receiving chamber 26 of the variable capacity cylinder 25.

That is, if the passage 27 is connected to the discharge passage 20a of the variable pump 20 without providing the high-pressure priority valve 62 and the pump discharge pressure oil is supplied to the small-diameter pressure receiving chamber 26 of the variable capacity cylinder 25, It can not be controlled swash plate 24 can not operate the variable volume cylinder 25 in the reduction direction when the discharge pressure P ₀ of the variable pump 20 is significantly low or negative pressure so.

For example, one actuator 23 is a boom cylinder of a power shovel and another actuator 23
Is a turning motor of a power shovel, and when the boom is lowered with the swash plate 24 at the minimum angle position and the turning acceleration is performed, the pump discharge of the variable pump 20 is reduced when the boom cylinder is reduced by the external force to the discharge flow rate of the variable pump 20 or more. The pressure drops significantly or becomes a negative pressure, and the differential pressure between the load pressure P _LS of the actuator 23 and the pump discharge pressure P ₀ decreases. As a result, the load detection valve 32 is connected to the first and second pilot passages 54,
Since the differential pressure at 56 decreases, the drain position A is set by the differential pressure across the throttle 35 provided in the discharge path 34 of the fixed pump 33. Therefore, the large-diameter pressure receiving chamber 28 of the variable capacity cylinder 25 communicates with the tank 61, and the variable capacity cylinder 25
Must be reduced by the pressure in the small-diameter pressure receiving chamber 26 to operate the swash plate 24 toward the maximum angular position, but when the pump discharge pressure oil is supplied to the small-diameter pressure receiving chamber 26 as described above, the pump because becomes the discharge pressure P ₀ is significantly low or negative pressure is less than swash plate operating pressure can not swing motion to operate subsequently remains minimum angular position uncontrollably the swash plate 24.

On the other hand, if the discharge pressure P ₂ of the fixed pump 33 is supplied to the small-diameter pressure receiving chamber 26 of the variable displacement cylinder 25 by the high pressure priority valve 62 as shown in FIG. When the pressure in the small-diameter pressure receiving chamber 26 becomes equal to or higher than the swash plate operating pressure, the swash plate 24 can be operated toward the maximum angular position.

[0017]

As described above, the displacement of the variable displacement hydraulic pump 20 can be controlled at 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 characteristics do not decrease.
In addition, the flow rate of the directional control valve is controlled in accordance with the change in the number of rotations of the variable displacement hydraulic pump 20, so that the fine operability of the actuator can be improved. Further, even if the pump discharge pressure of the variable displacement hydraulic pump 20 falls below the swash plate operating pressure, the displacement of the variable displacement hydraulic pump 20 can be controlled by operating the displacement variable cylinder 25 with the discharge pressure of another hydraulic pump. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the configuration of a conventional example.

FIG. 2 is a schematic structural explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

20: Variable displacement hydraulic pump, 21: Discharge path, 22: Direction 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 path, 35 ... Throttle, 37 ... Bypass valve, 43 ... Restrictor, 62 ... High pressure priority valve.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-233201 (JP, A) JP-A-58-13202 (JP, A) JP-A-3-37044 (JP, U) JP-A-2- 149881 (JP, U) Actually open sho 59-45302 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F04B 49/00 341

Claims (1)

(57) [Claims] 1. A variable displacement cylinder 25 for tilting a swash plate 24 of a variable displacement hydraulic pump 20 in a direction of increasing or decreasing the displacement, a first means for detecting a flow rate change of the variable displacement hydraulic pump 20, A second means for detecting a change in the number of revolutions and a change in the pump discharge pressure of the displacement hydraulic pump 20, and a large-diameter pressure receiving chamber of the displacement cylinder 25 in accordance with an output signal of the first means and an output signal of the second means. A variable control valve 31 for supplying a pump discharge pressure to a pump 28; a differential pressure between an upstream pressure of a direction switching valve 22 provided in a discharge path 21 of the variable displacement hydraulic pump 20 and a load pressure of an actuator; A load detection valve 32 that supplies a pump discharge pressure to a large-diameter pressure receiving chamber 28 of a variable displacement cylinder 25 based on an output signal of the means, compares the pump discharge pressure of the variable displacement hydraulic pump 20 with the discharge pressure of another hydraulic pump. High pressure Of the variable displacement hydraulic pump, which comprises a high pressure priority valve 62 for supplying the pressure to the small diameter pressure receiving chamber 26 of the variable displacement cylinder 25.