JPH0518364A - Controller for volume of valiable capacity type hydraulic pump - Google Patents

Abstract

PURPOSE:To control capacity of pump accurately with a constant torque and reduce costs by changing over a control valve with the total of pump discharge pressure and force corresponding to flow rate and the total of spring mounting load and the number of rotation of pump, thereby controlling the discharge flow rate per one rotation of cylinder pump to increase and decrease. CONSTITUTION:A variable control valve 9 is pushed to a drain position A with a first thrust F1 by the mounting load of a spring 20, a second thrust F2 of a first pressure receiving part 21 by pressurized oil, a third thrust F3 to a second pressure receiving part by pressurized oil. The valve 9 is also pressed to a supply position B with fourth and fifth thrusts F4, F5 of third and fourth pressure receiving parts 23, 24 by pressurized oil, F1+F2+F3 and F4 +F5 are turned into balanced conditions. To control a variable pump 1 to have a constant torque irrespective of the number of rotation thereof, a relation of pump discharge pressure P0kg/cmX discharge amount (q) per one time is made constant. Pressure difference P before and after a restriction 27 by discharge flow amount Q per unit time is expressed by a formula: P=nuX(Q0/A0)<2>, where nu is a coefficient determined by a flow amount coefficient and A0 is the opening area of a restriction 26.

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 a device for controlling a displacement of a variable displacement hydraulic pump (hereinafter referred to as a variable pump), that is, a discharge flow rate per one rotation, for example, a device shown in FIG. 1 is known.
That is, the displacement of the variable pump 1 is changed by changing the angle of the swash plate 2, and the angle of the swash plate 2 is changed by the piston 4 of the variable displacement cylinder 3. The pump discharge pressure P ₁ is always guided to the rod-side pressure chamber 5 of the variable capacity cylinder 3 via the first pilot passage 6, and the variable control valve 9 to the bottom-side pressure chamber 7 via the second pilot passage 8. The output pressure of is guided. The variable control valve 9 receives the first thrust force toward the drain position A by the spring 10,
The second thrust force toward the supply position B is generated by the pump discharge pressure P acting on the pressure receiving portion 11, and the seat surface of the spring 10 is connected to the piston 4 of the variable capacity cylinder 3 via the link 12 to form the feedback mechanism 13. is doing. In FIG. 1, 14 is a directional control valve, and 15 is an actuator. Next, the operation will be described. When the pump discharge pressure P is low and the second thrust acting on the variable control valve 9 is smaller than the first thrust due to the mounting load of the spring 10, the variable control valve 9 is in the drain position A, and the bottom side pressure of the variable capacity cylinder 3 The chamber 7 is connected to the tank 1 through the second pilot passage 8 and the third pilot passage 16.
Connect to 7. Therefore, the piston 4 of the variable capacity cylinder 3 is contracted by the pump discharge pressure P of the rod side pressure chamber 5, and the swash plate 2 is tilted and held in the large capacity direction. In this state, if the pump discharge pressure P exceeds the set pressure, the variable control valve 9
The second thrust acting on the
Becomes larger than the thrust of the variable control valve 9 to the supply position B, and the pump discharge pressure P passes through the fourth pilot passage 18, the variable control valve 9 and the second pilot passage 8 and the bottom side pressure chamber 7 of the variable volume cylinder 3 Is supplied to the piston 4, the piston 4 extends, and the swash plate 2 tilts in the capacity decreasing direction. At the same time, the link 12 moves together with the piston 4 so that the mounting load of the spring 10 increases in proportion to the moving amount of the piston 4 and the variable control valve 9
Of the swash plate with respect to the pump discharge pressure P, that is, the variable control valve 9 is held at a position where it is balanced with the second thrust of the pump discharge pressure P acting on the pressure receiving portion 11. Since the discharge flow rate per rotation is determined, the pump discharge pressure P × the discharge flow rate q per rotation is controlled to be constant. Therefore, by combining a plurality of springs 10, as shown in FIG. The capacity can be controlled by the characteristic D that approximates the output characteristic C in which the discharge flow rate q per one rotation is constant.

[0003]

In such a displacement control device, the mechanical feedback mechanism 13 feeds back the increase / decrease in the discharge flow rate q per rotation due to the change in the pump discharge pressure P to the variable control valve 9 to change the torque of the variable pump 1. Since the mechanical feedback mechanism 13 is controlled to be constant, the structure is complicated and the cost is high. In addition, the angle of the swash plate 2 is fed back instead of actually feeding back the discharge flow rate q per rotation. Variable pump 1
Due to the decrease in the efficiency of the pump itself, the discharge flow rate per revolution actually discharged is smaller than the value determined by the swash plate angle, so the accuracy of the pump discharge flow rate deteriorates.

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 1
Variable cylinder 3 that increases or decreases the discharge flow rate per revolution of the
And a variable control valve 9 for supplying pump discharge pressure to the pressure chamber on the small variable pump capacity side of the variable capacity cylinder 3, and the variable control valve 9 is provided with a spring 20 and a force proportional to the pump rotation speed. Capacity of the variable displacement hydraulic pump configured to be pushed toward the supply position B at the pump discharge pressure P ₀ and pushed toward the supply position B with a force proportional to the square of the discharge flow rate. Control device.

[0006]

[Operation] The variable control valve 9 switches to operate by the sum of the forces according to the pump discharge pressure and the discharge flow rate, the mounting load of the spring 20 and the sum of the forces proportional to the pump rotation speed, and the variable capacity of the variable cylinder 3 Since the discharge flow rate per rotation of the hydraulic pump 1 is controlled to be increased or decreased, the capacity of the variable displacement hydraulic pump 1 can be controlled based on the pump discharge pressure regardless of the pump rotation speed to control the torque to be constant, and mechanical feedback is possible. No mechanism is needed.

[0007]

EXAMPLE An example of the present invention will be described with reference to FIG. It should be noted that the same members as those in the related art have the same reference numerals. The variable control valve 9 has a first thrust F ₁ due to the mounting load of the spring 20, a second thrust F ₂ due to the pressure oil of the first pressure receiving portion 21 and a third thrust F ₃ due to the pressure oil of the second pressure receiving portion 22. It is pushed toward the drain position A, and is pushed toward the supply position B by the fourth and fifth thrusts F ₄ and F ₅ by the pressure oil of the third and fourth pressure receiving portions 23 and 24, and F ₁ + F ₂ + F ₃ and F ₄ + F ₅ are in a balanced position. The first pressure receiving portion 21 is connected to the downstream side of the throttle 27 provided in the discharge passage 26 of the variable pump 1 through the first passage 25, and the second pressure receiving portion 22 outputs a pressure proportional to the variable pump rotation speed. 28, and the third and fourth pressure receiving portions 23, 24
Is connected to the upstream side of the throttle 27 through the second and third passages 29 and 30, and the inlet side of the variable control valve 9 is connected to the upstream side of the throttle 27 through the fourth passage 31. The means 28 is, for example, a fixed displacement hydraulic pump driven by an engine together with the variable pump 1, a sensor for detecting the rotational speed of the variable pump 1, and a fixed displacement hydraulic pump that operates in proportion to the detected rotational speed. It is composed of a proportional pressure reducing valve or the like that increases or decreases the discharge pressure of the.

Next, the operation will be described. First, the variable control valve 9
The relationship between the thrust acting on and the balance is explained. When the pump discharge pressure is P ₀ and the pressure receiving area of the fourth pressure receiving portion 24 is A ₄ , the fifth thrust F ₅ is F ₅ = A ₄ × P ₀ . When the downstream pressure of the throttle 27 is P ₁ and the pressure receiving areas of the first and third pressure receiving portions 21 and 23 are A ₁ and A ₃ , the second thrust F ₂ is P ₁ × A
₁ , the fourth thrust F ₄ becomes P ₀ × A ₃ , and the variable control valve 9 due to the differential pressure ΔP (ΔP = P ₀ −P ₁ ) before and after the throttle 27 is pushed toward the supply position B. Thrust F ₆ is F ₆ = P ₀ ×
Since A ₃ −P ₁ × A ₁ , the first and third pressure receiving portions 21 and 2 are
If the pressure receiving areas A ₁ and A ₃ of ₃ are the same, F ₆ = A ₁ × △
P. Since the sixth thrust F ₆ and the fourth thrust F ₄ both push the variable control valve 9 toward the supply position B, the sixth thrust F ₆ + the third thrust F ₄ is the mounting load of the spring 20. When the first thrust force F ₁ + third thrust force F _{3 is} smaller than the first thrust force F ₃ + the third thrust force F _{3, the} variable control valve 9 is in the drain position A, and the pressure oil in the bottom side pressure chamber 7 of the variable capacity cylinder 3 is in the second pilot passage 8 It flows out into the tank 17 through the three pilot passages 16, the piston 4 is contracted, and the swash plate 2 is tilted and held in the direction of large capacity. When the pump discharge pressure P ₀ becomes high in the above-mentioned state, the fifth thrust F ₅ increases and the fifth thrust F ₅ increases.
₅ + 6 first thrust F ₁ + third pump discharge pressure P ₀ becomes greater than the thrust F ₃ variable control valve 9 is a pressure oil supply position B of by mounting load of thrust F ₆ spring 20 is It is supplied to the bottom side pressure chamber 7 of the variable volume cylinder 3, and the piston 4 is generated by the difference in pressure receiving area between the bottom side pressure chamber 7 and the rod side pressure chamber 5.
And the swash plate 2 tilts in the direction of small capacity. As a result, the discharge flow rate per revolution of the variable pump 1 is reduced, so that the discharge flow rate per unit time of the variable pump 1 is reduced even if the number of revolutions of the variable pump 1 is the same, and the differential pressure Δ before and after the throttle 27 is reduced.
Since P becomes smaller and the sixth thrust F ₆ becomes smaller,
Thrust force F ₅ + sixth thrust force F ₆ becomes smaller, the variable control valve 9 is pushed back toward the drain position A by the first thrust force F ₁ + third thrust force F ₃ due to the mounting load of the spring 20, and the spring 20 is pushed back.
It is held at a position balanced with the first thrust F ₁ + third thrust F ₃ due to the mounting load. Because of this, if the variable pump 1 is kept in the same rotation state, the swash plate angle can be adjusted according to the pump discharge pressure P ₀ without mechanically connecting the piston 4 of the variable capacity cylinder 3 and the variable control valve 9 by a feedback mechanism. Can be controlled to control the torque of the variable pump 1 to be constant by setting the discharge flow rate per one rotation of the variable pump 1 to a value corresponding to the pump discharge pressure P _0. Even if there is, the discharge flow rate per unit time changes and the sixth thrust F ₆ due to the differential pressure before and after the throttle 27 changes, so the torque of the variable pump 1 cannot be controlled to be constant.

Next, constant torque control of the variable pump 1 will be described. To control the constant torque of the variable pump 1 regardless of the variable pump speed, the pump discharge pressure P ₀ kg / c
As shown in FIG. 4, m ² × the discharge flow rate q may be constant regardless of the number of revolutions. Here, the differential pressure ΔP before and after the throttle 27 is ΔP = ζ × depending on the discharge flow rate Q ₀ per unit time.
It is represented by (Q ₀ / A ₀ ) ² and is as shown in FIG. However, ζ is a coefficient determined by the flow coefficient, and A ₀ is the throttle 26
Is the opening area of. From the above, the sixth thrust F ₆ = A ₁ × ΔP acting on the variable control valve 9 is F ₆ = A ₁ × ΔP
= ΖA ₁ × (Q ₀ / A ₀ ) ² and P ₀ × Q ₀ = C, Q ₀ = C / P ₀ , and the sixth thrust F ₆ = ζ
XC ² × A ₂ / A ₀ ² ÷ P ₀ ² = K / P ₀ ² , and the force F _B for pushing the variable control valve 9 to the supply position _B is F _B =
A ₄ P ₀ + K / P ₀ ² , and this force F _B changes depending on the rotation speed of the variable pump 1. Further, the force F _A to press the variable control valve 9 to the drain position A, F _A = first thrust + third thrust F ₃ becomes, and this force F _A and the force F _B so that the balanced. As described above, the third thrust force F ₃ is linearly proportional to the rotation speed. If the first thrust force F ₁ << the third thrust force F ₃ and the rotation speed is ½, the force F is reduced. _A also becomes approximately 1/2, and the pump discharge pressure P _{0 with} respect to the balance point of the variable control valve 9 also becomes approximately 1/2, and the set horsepower changes in proportion to the rotational speed. That is, the set horsepower P _S αP × Q = P × q × N, and the set horsepower P _S
Is proportional to the rotation speed N, P × q = constant, the torque T of the variable pump 1 is T = P × q / 200π = constant, and constant torque control can be performed. The relationship between the first thrust F ₁ due to the mounting load of the spring 20 and the third thrust F ₃ due to the pressure that changes depending on the number of revolutions is, for example,

[0010]

[Table 1]

When the rotation speed N becomes 1/2, the force F _A
= F ₁ + F _{3 is} also approximately 1/2, and the operating pressure of the variable control valve 9 is also approximately 1/2. To summarize the above, when the rotation speed of the variable pump 1 increases when the pump discharge pressure P ₀ is constant, the discharge flow rate per unit time increases and the sixth thrust F ₆ increases. At the same time, since the third thrust F ₃ increases, the variable control valve 9 continues to be held at the initial position, and if the number of revolutions of the variable pump 1 decreases, the discharge flow rate per unit time decreases and the above-described sixth control. Although the thrust F ₆ becomes smaller, at the same time, the third thrust F ₃ becomes smaller, so that the variable control valve 9 is held at the initial position, and even if the rotation speed of the variable pump 1 changes, the discharge flow rate q per rotation q P ₀ without changing
Since xq = constant, the torque of the variable pump 1 can be controlled to be constant. The pressure before and after the predetermined length of the discharge line of the variable pump 1 may be detected and supplied to the first and second pressure receiving portions 21 and 22 of the variable control valve 9. In this way, since the pressure loss of the pipe according to the law of Hagen Poiseuille can be fed back as a flow rate ^{change, Q = πD 4 / 128μl ×} △ P where, D is the pipe inside diameter, mu is viscosity coefficient, l is the pipe length Therefore, since the flow rate Q and the pressure difference ΔP are linear functions, the flow rate Q and the pressure difference ΔP can be controlled more accurately along the constant horsepower curve. Also,
A proportional solenoid that pushes the variable control valve 9 toward the drain position A is provided, and a current proportional to the number of revolutions is applied to the proportional solenoid so that the third thrust F ₃ that directs the variable control valve 9 toward the drain position A is set to the number of revolutions. You may make it proportional.

[0012]

The variable control valve 9 is switched and operated by the sum of the forces according to the pump discharge pressure and the discharge flow rate, the mounting load of the spring 20 and the force proportional to the pump rotation speed, and the variable capacity cylinder 3 changes the variable capacity. Since the discharge flow rate per revolution of the hydraulic pump 1 is controlled to be increased or decreased, not only the capacity of the variable displacement hydraulic pump 1 can be controlled with a constant torque, but also a mechanical feedback mechanism is not required and the cost can be reduced. Since the capacity is controlled based on the discharge flow rate and the pump rotation speed, it is possible to accurately control along the constant torque curve.

[Brief description of drawings]

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

FIG. 2 is a chart showing a relationship between a discharge flow rate per one rotation and a pump discharge pressure.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a chart showing the relationship between the discharge flow rate per rotation and the pump discharge pressure.

FIG. 5 is a chart showing the relationship between flow rate and differential pressure.

FIG. 6 is a chart showing forces acting on a variable control valve.

[Explanation of symbols]

1 variable displacement hydraulic pump, 2 swash plate, 3 variable displacement cylinder, 9 variable control valve, 27 throttle.

Claims (3)

[Claims] 1. A displacement control cylinder for increasing / decreasing a discharge flow rate per revolution of a variable displacement hydraulic pump 1, and a variable control valve for supplying pump discharge pressure to a pressure chamber on the small side of the variable pump displacement of this displacement control cylinder 3. 9, the variable control valve 9 is pushed by the spring 20 toward the drain position A, is pushed by the pump discharge pressure P ₀ toward the supply position B, and has a discharge flow rate of 2
A displacement control device for a variable displacement hydraulic pump, wherein the displacement control device is configured to be pushed toward a supply position B by a force proportional to a power and further pushed toward a drain position A at a value proportional to a pump rotation speed. 2. The variable displacement hydraulic pump 1 according to claim 1, wherein the discharge passage 26 is provided with a throttle 27, and the variable control valve 9 is pushed toward the supply position B by the differential pressure before and after the throttle 27. Variable displacement hydraulic pump capacity control device. 3. The variable displacement hydraulic pump according to claim 1, wherein the variable displacement hydraulic pump 1 is pushed toward the supply position B of the variable control valve 9 by a predetermined differential pressure across the discharge line of the variable displacement hydraulic pump 1. Capacity control device.