JPH0599126A - Capacity control device for variable capacity type hydraulic pump - Google Patents

Abstract

PURPOSE:To perform proper control of capacity through simple constitution by providing a load detecting valve to vary a differential pressure between a pump delivery pressure and the load pressure of an actuator according to a differential pressure between positions before and after a throttle in the delivery passage of a fixed pump driven by an engine together with a swash plate type variable capacity type hydraulic pump. CONSTITUTION:A plurality of actuators 23 are connected to a delivery passage 21 of a variable pump 20 respectively through a plurality of direction switching valves 22 and capacity of the variable pump is controlled by regulating the inclination angle of a swash plate 24 by means of a capacity variable cylinder 25. A small-diametered pressure receiving chamber 26 of the capacity variable cylinder 25 is connected to the delivery passage 21 through a passage 27 and a large-diametered pressure receiving chamber 28 is connected to a load detecting valve 30. The load detecting valve 30 is brought into a position where a second force F2 by a differential pressure DELTAPC between positions before and after a throttle 51 located in a delivery passage 49 of a fixed pump 48 is made equal to a first force F1 proportional to a differential pressure DELTAPLS between a pump delivery pressure P0, exerted on a first pressure receiving chamber 38, and a load pressure PLS exerted on a second pressure receiving chamber 44. According to the position, the position of the swash plate 24 of the variable pump 20 is decided.

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 which tilts a swash plate to control the discharge amount per rotation, that is, the displacement.

[0002]

2. Description of the Related Art As shown in FIG. 1, the displacement of a variable displacement hydraulic pump 1 (hereinafter referred to as a variable pump) is such that a pump discharge pressure is applied to a large diameter pressure receiving chamber 4 of a servo cylinder 3 which tilts a swash plate 2. It is supplied by the variable control valve 5, and the servo piston 3 is operated by the pressure receiving area difference from the small diameter pressure receiving chamber 6 to control the torque to be constant. However, in addition to the variable control valve 4, a load detection valve 7 is provided. The load detection valve 7 controls so that the differential pressure between the pump discharge pressure P ₀ and the load pressure P _LS is always constant. The load detection valve 7 is a pump discharge pressure P from the discharge passage 8.
_It is pushed to the supply position A at ₀ , and is pushed to the drain position B at the load pressure P _LS of the actuator 10 from the directional control valve 9 so that the differential pressure between the pump discharge pressure P ₀ and the load pressure P _LS is always constant. ing. That is, when the differential pressure becomes small, the load detection valve 7 becomes the drain position B, the large diameter pressure receiving chamber 4 of the servo piston 3 is connected to the tank 11, the swash plate 2 tilts in the direction of large capacity, and the variable pump 1 Capacity increases, the pump discharge pressure P ₀ increases, and the differential pressure increases. On the other hand, when the differential pressure becomes large, the load detection valve 7 becomes the supply position A, the pump discharge pressure is supplied to the large diameter pressure receiving chamber 4 of the servo piston 3, and the swash plate 2 tilts in the small capacity direction and the variable pump. The capacity of No. 1 decreases, the pump discharge pressure P ₀ decreases, and the differential pressure decreases. By this action, the load detection valve 7 controls the displacement of the variable pump 1 so that the differential pressure between the pump discharge pressure P ₀ and the load pressure P _LS becomes constant. As a result, the pump discharge pressure P
The differential pressure ΔP between ₀ and the load pressure P _LS is ΔP = C ₁ × (Q / A)
² , the flow rate corresponding to the opening degree of the directional control valve 9 can be flowed regardless of the load pressure of the actuator 10, and the variable pump capacity can also provide the required flow rate. Where C ₁ is the flow coefficient, A is the opening of the directional control valve, and Q is
This is the flow rate to the actuator.

[0003]

In the displacement control device provided with such a load detection valve, the pump discharge pressure P ₀ is changed even if the rotation speed of the engine 12 that drives the variable pump 1 is changed.
Since the differential pressure between the load pressure P _LS and the load pressure P _LS is constant, the speed of the actuator 10 does not change with respect to the opening of the directional control valve 9, and the actuator speed corresponding to the set engine speed cannot be obtained. For example, when the engine speed is set to an intermediate speed between the maximum speed and the minimum speed, we want to make it slower than when the actuator is set to the maximum speed. It will be the same as when you did. To solve this, the differential pressure set switching pilot pressure may be introduced to the load detection valve 7 to change the differential pressure set between the pump discharge pressure and the load pressure. In this case, a sensor for detecting the engine speed And an electromagnetic remote control valve for changing the differential pressure set switching pilot pressure are required, resulting in high cost.

SUMMARY OF THE INVENTION 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
The swash plate 24 for increasing or decreasing the discharge amount per revolution of 0, the servo piston 25 for tilting the swash plate 24, the fixed displacement pump 4 driven by the engine together with the variable displacement hydraulic pump 20.
8, pump discharge pressure P ₀ and actuator load pressure P _LS
The pump discharge pressure is changed by the servo piston 2 by the differential pressure of ΔP _LS .
5, the differential pressure ΔP _LS is maintained at a set value to control the capacity, and the pump discharge pressure is controlled by the servo piston 25 with the differential pressure P _C before and after the throttle 51 provided in the discharge passage 49 of the fixed pump 48. A displacement control device for a variable displacement hydraulic pump, which comprises a load detection valve 30 for supplying the pressure difference ΔP _LS to the set pressure difference ΔP _LS .

[0006]

It [created for an engine rotational speed can capacity control while maintaining the set value of the differential pressure △ P _LS between the pump discharge pressure P ₀ at the time of constant load pressure P _LS, fixed pump 4 the change in engine speed
8 is detected as a change in the differential pressure ΔP _C before and after the throttle 51 due to the change in the flow rate, and the set value of the differential pressure ΔP _LS is changed according to the change in the flow rate to the actuator even if the opening of the directional control valve 22 is the same. Since it increases or decreases, the actuator speed can be adjusted according to the engine speed, and the discharge passage 4 of the fixed pump 48 can be used.
It suffices if a throttle is provided at 9, and an engine speed sensor, an electromagnetic proportional valve, etc. are not required and the cost is reduced.

[0007]

[Example] As shown in FIG. 2, a plurality of actuators 23 are connected to a discharge passage 21 of a variable pump 20 through a plurality of directional switching valves 22. 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 load detection valve 30 by a passage.

Next, the specific structure of the load detection valve 30 will be described with reference to FIG. A spool 36 that connects and disconnects the main inlet port 33, the inlet port 34, and the tank port 35 is fitted into the spool hole 32 of the valve body 31, and the main inlet port 33
Is communicated with the first pressure receiving chamber 38 through a small hole 37 formed in the spool 36, and a cylinder hole 39 is formed in the valve body 31 concentrically with the spool hole 32.
A piston 41 having 0 is inserted to form third and fourth pressure receiving chambers 42 and 43, the rod 40 thereof faces the second pressure receiving chamber 44, and the main inlet port 33 has the discharge passage 21 of the variable pump 20. And the inlet port 34 is connected to the servo piston 2
5 is connected to the large diameter pressure receiving chamber 28, the tank port 35 is connected to the tank 45, the second pressure receiving chamber 44 is connected to the maximum pressure detecting means, for example, the shuttle valve 47 through the load pressure detecting path 46,
The pressure receiving chamber 42 is connected to the discharge passage 49 of the fixed pump 48 which is driven by the engine together with the variable pump 20, and the fourth pressure receiving chamber 43 is set to a predetermined pressure by the relief valve 50 and connected to the inlet of a pilot operated valve (not shown) or the like. The third pressure receiving chamber 42
The fourth pressure receiving chamber 43 communicates with a throttle 51 provided on the piston 41.

Thus, the spool 36 of the load detecting valve 30 is set to the drain position where the inlet port 34 communicates with the tank port 35 by the spring force when the variable pump 20 is stopped. The spool 36 of 30 is a pump discharge pressure P acting on the first pressure receiving chamber 38.
_{At 0} , it is pushed toward the pressure oil supply position that communicates the main inlet port 33 and the inlet port 34, and is pushed toward the aforementioned drain position by the load pressure P _LS acting on the second pressure receiving chamber 44, and the spool 36 is pumped. pressurized oil supply position in the discharge pressure P ₀ and the highest load pressure P differential pressure between the _LS △ P pressure difference between the _LS △ P _LS first force F ₁ which is proportional to _{(△ P LS = P 0 -P} LS) Pushed towards. The spool 36 of the load detection valve 30 is pushed toward the drain position by the upstream pressure of the throttle 51 acting on the third pressure receiving chamber 42, and the pressure oil is supplied by the downstream pressure of the throttle 51 acting on the fourth pressure receiving chamber 43. The spool 36 of the load detection valve 30 is pushed toward the position, and the differential pressure ΔP _C (ΔP _C = P _C −
It is pushed toward the drain position with F ₂ with a second force proportional to P ′ _C ).

Next, the capacity control operation will be described. (Operation of load detection valve 30) When the rotation speed of the variable pump 20 is constant. Load detection valve 30 is due to the differential pressure △ P _LS of the second force F ₂ and the pump discharge pressure P ₀ and the maximum load pressure P _LS by differential pressure △ P _C before and after the diaphragm 51 provided in the discharge passage 49 of the fixed pump 48 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 differential pressure ΔP _LS between the pump discharge pressure P ₀ and the maximum load pressure P _LS is the directional control valve 22.
In other words, the differential pressure ΔP _C before and after the throttle 51 is constant because the discharge amount of the fixed pump 48 is constant if the rotational speed of the variable pump 20 is constant. the differential pressure △ P _LS is larger loads first force F ₁ acting on the spool 36 of the detecting valve 30 is the differential pressure △ P _C by the load detection valve 30 is greater than the second force F ₂ when a small The spool 36 is at the pressure oil supply position, and the pump discharge pressure P ₀ is supplied from the main inlet port 33 and the inlet port 34 to the large-diameter pressure receiving chamber 28 of the variable capacity cylinder 25. The discharge flow rate per rotation decreases to decrease the flow rate per unit time, and the flow rate passing through the directional control valve 22 decreases to decrease the difference between the pump discharge pressure P ₀ and the maximum load pressure P _LS. first force F ₁ is low in pressure is reduced And, the position of the swash plate 24 is determined by the first force F ₁ and the second force F ₂ was balanced position. Similarly, when the operation stroke of the directional control valve 22 is large, the difference P _LS is small and the swash plate 24 of the variable pump 20 is small.
The position of is closer to the capacity than 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 suitable for the operation stroke of the directional control valve 22 can be performed regardless of the maximum load pressure. As a result, the fine operability of the actuator 23, that is, the fine controllability can be improved. This is also clear from the following equation. ΔP _LS = P ₀ −P _LS = A ₂ −A ₁ / A ₁ ΔP _C = C ₁ (A ₂ −A ₁ ) (δN / AG / AG × 1000) ² However, P ₀ of the variable pump 20 Discharge pressure, P _LS is the maximum load pressure of the actuator, A ₁ is the pressure receiving area of the rod 40, A _1
2 pressure receiving area of the piston 41, △ P _C is around diaphragm 51 pressure difference, C ₁ is the flow coefficient, [delta] _C is the discharge capacity of the fixed pump (cc / rev), N the engine speed, A _G is stop 51
Area of.

When the rotation speed of the variable pump 20 changes. When the rotation speed of the variable pump 20 changes, the rotation speed of the fixed pump 48 also changes.
Since _C is changed similarly to the differential pressure △ P _LS of the pump discharge pressure P ₀ and the maximum load pressure P _LS, since the position of the swash plate 24 are not changed, the unit time per discharge flow rate of the variable pump 20 is increased or decreased , The flow rate passing through the directional control valve 22 changes due to the change in the rotation speed, and the differential pressure P between the pump discharge pressure P ₀ and the maximum load pressure P _{LS
Since LS} changes by the square of the change in rotation speed, the directional control valve 2
The flow rate passing through for the same two operation strokes changes by the change in the number of revolutions, so that a flow control valve proportional to the number of revolutions of the variable pump 20 can be formed. This is also clear from the following equation. ΔP _LS = C ₁ (A ₂ −A ₁ / A ₁ ) (δ _C / 1000 × AG) N ² = C ₂ (Q / A) ² where C ₂ is the spool flow coefficient of the directional control valve 22, A Is the opening area of the spool of the directional control valve 22, and Q is the flow rate of the directional control valve. For example, the rotation speed of the variable pump 20 is 1 /
When it becomes 2, the differential pressure ΔP _LS becomes 1/4, and the passage flow rate for the same stroke of the directional control valve 22 becomes / 2.

[0012]

When the engine speed is constant, the capacity can be controlled by maintaining the differential pressure ΔP _LS between the pump discharge pressure P ₀ and the load pressure P _LS at the set value, and the change in the engine speed can be controlled by the fixed pump 48. It is detected as a change in the differential pressure ΔP _C before and after the throttle 51 due to a change in the flow rate, and thereby the set value of the differential pressure ΔP _LS is changed to increase or decrease the flow rate to the actuator even if the directional control valve 22 has the same opening. The actuator speed can be set according to the engine speed, and the discharge passage 4 of the fixed pump 48 can be used.
It suffices if a throttle is provided at 9, and an engine speed sensor, an electromagnetic proportional valve, etc. are not required and the cost is reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional example.

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

[Explanation of symbols]

20 ... Variable displacement hydraulic pump, 21 ... Discharge passage, 22 ... Direction control valve, 23 ... Actuator, 24 ... Swash plate, 25 ...
Servo piston, 30 ... Load detection valve, 31 ... Valve body, 3
3 ... Main inlet port, 34 ... Inlet port, 35 ... Tank port, 36, Spool, 38 ... First pressure receiving chamber, 40 ... Rod, 41 ... Piston, 42 ... Third pressure receiving chamber, 43 ... Fourth pressure receiving chamber, 44 ... second pressure receiving chamber, 48 ... fixed pump, 49 ... discharge passage, 51 ... throttle.

Claims (1)

[Claims] 1. A swash plate 24 for increasing / decreasing the discharge amount per one rotation of the variable displacement hydraulic pump 20, a servo piston 25 tilting the swash plate 24, and the variable displacement hydraulic pump 20 are driven by an engine. the fixed pump 48, displacement control to maintain the pump discharge pressure by the differential pressure △ P _LS load pressure P _LS of the pump discharge pressure P ₀ and the actuator to the set value of the differential pressure △ P _LS is supplied to the servo piston 25 In addition, the load detection valve 30 supplies the pump discharge pressure to the servo piston 25 with the differential pressure ΔP _C before and after the throttle 51 provided in the discharge passage 49 of the fixed pump 48 to change the set differential pressure ΔP _LS. A displacement control device for a variable displacement hydraulic pump.