JPH0617760A - Output control device for pump - Google Patents

Abstract

PURPOSE:To reduce the cost by means of the degree of freedom in design of a pump and through the use of parts in common with each other by separating a regulator mechanism to effect control of a pump horse power from a servo valve mechanism. CONSTITUTION:A cylinder 2 for inclination to change the inclination angle of a pump swash plate is provided with an oil chamber 3a to which a pump delivery pressure is guided and an oil chamber 3b to which a pressure regulated by a pressure regulating valve 6 is guided, and feedback of displacement of the cylinder 2 for inclination to the pressure regulating valve 6 is performed. A pump delivery pressure is guided to a pressure detecting piston 15 arranged in a state that an axis crosses a differential piston 12, operated responding to a control pressure, at right angles. A pressure reducing valve 22 is brought into contact with a balance lever 17, pressed by the detecting piston, from the opposite side. A control pressure from the pressure reducing valve 22 switched and controlled through the balance lever 17 is guided to the differential piston 12 and the pressure regulating valve 6.

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 output of a plunger pump.

[0002]

2. Description of the Related Art When a plunger pump is driven by an engine, feedback control is performed so that the relationship between the pump discharge flow rate and the pressure does not exceed a certain output value (horsepower) to maximize the engine drive load. It is known that the engine can be used for various purposes and avoiding engine stall (for example, Japanese Patent Laid-Open No. 63-272974).

Specifically, the drive horsepower control of the pump is performed by introducing pressure controlled by a servo regulator to a tilting cylinder for adjusting the tilt angle of the swash plate of the pump, and tilting the pump according to the discharge pressure of the pump. The angle is changed so that the relationship between the pump discharge amount and the discharge pressure is controlled to draw a hyperbola.

[0004]

By the way, normally, since the change in the stroke amount of the tilting cylinder is mechanically fed back to the balance lever of the servo regulator, if the specifications of the pump are different, the mechanical force of the servo regulator is changed. The feedback control mechanism also needs to be changed correspondingly.

For this reason, the valves constituting the servo regulator must be prepared with different specifications depending on the type of pump, which lacks versatility and causes an increase in product cost.

The present invention has been proposed to solve such a problem.

[0007]

The present invention is adjusted by (A) a tilting cylinder for changing the tilting angle of a pump swash plate, an oil chamber to which the pump discharge pressure of the cylinder is introduced, and a pressure adjusting valve. A regulator mechanism including an oil chamber to which pressure is introduced, and means for adjusting the initial deflection of the switching spring of the pressure regulating valve according to the displacement of the tilting cylinder,
(B) A differential piston that is displaced according to the balance between the control pressure and the spring, a pressure detection piston that is housed so that the axis line is orthogonal to the differential piston, and the pump discharge pressure at the base end of the pressure detection piston. , A balance lever extending substantially parallel to the differential piston and rotatable about a fulcrum at the base end, and a pressure reducing valve biased by a spring that abuts the balance lever from the opposite side to which the detection piston abuts. And a passage that guides the control pressure of the pressure reducing valve that is switch-controlled via the balance lever to one end of the differential piston, and a control that branches from this passage to oppose the switching spring to switch the pressure regulating valve. And a servo valve mechanism including a passage for guiding pressure.

[0008]

The tilt angle of the swash plate of the pump is controlled according to the displacement of the tilt cylinder, and the pump discharge amount increases or decreases correspondingly.

When the pump discharge pressure changes, the force with which the pressure detection piston presses the balance lever changes, the moment caused by the balance lever and the pressure reducing valve collapses, and the pressure reducing valve switches. As a result, the controlled pressure changes, and this control pressure acts on the differential piston to displace the differential piston and shift the pressing position of the pressure detection piston against the balance lever to a position where a new moment balance occurs. .

At this position, the control pressure is settled, and at the same time, this control pressure is fed back to the pressure control valve to switch the pressure control valve. Therefore, the pressure adjusted via the pressure adjusting valve is introduced into one oil chamber of the tilting cylinder, the pressure balance between both oil chambers is lost, and the tilting cylinder is displaced. At the same time, this displacement is fed back to the switching spring of the pressure regulating valve, so that the regulating pressure of the pressure regulating valve is determined at the position where the load of the switching spring is balanced with the control pressure, and the tilting cylinder is stopped at the new balance position. Then, the pump discharge amount is controlled corresponding to the changed pump discharge pressure.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 is a variable discharge type pump, and 2 is a tilting cylinder for adjusting the discharge rate by changing the tilt angle of the pump swash plate. The cylinder 2 has a small pressure receiving area in the oil chamber 3a. The pump discharge pressure P is directly introduced through the passage 4a branched from the pump discharge passage 5, while the adjusted pressure is introduced through the pressure adjusting valve 6 into the oil chamber 3b having a large pressure receiving area. The tilting cylinder 2 operates (strokes) to a position where both pressures are balanced.

The pressure adjusting valve 6 is switched in response to a differential force between a control signal pressure Pv supplied from a servo valve mechanism 10 described later and the feedback spring 7, and when in the A position, the passage 4a is provided in the oil chamber 3b. The pressure from is led and released to the tank side at the B position. The feedback spring 7 is initially bent by a lever 8 connected to the tilting cylinder 2, and the spring force changes according to the expansion and contraction of the tilting cylinder 2.

The regulator mechanism 9 described above is constructed on the pump side, and is independent of the servo valve mechanism 10 to which the pump discharge pressure is fed back.

Next, the servo valve mechanism 10 includes the cylinder 1
1, a differential piston 12 is slidably inserted, a spring 13 is applied to one end of the differential piston 12, and a control pressure Pv introduced into a pressure chamber 14 is applied to the other end of the differential piston 12 to balance these positions. The differential piston 12 moves to.

A pressure detecting piston 15 is slidably accommodated in the differential piston 12 in a direction orthogonal to the axis of the differential piston 12. The tip of the detecting piston 15 extends from the side surface of the differential piston 15 through a cylinder cutout 11a to a balance lever. 17
Project toward. The pressure chamber 16 formed at the base end of the detection piston 15 has a passage 4 b branched from the discharge passage 5.
Is connected via a port 18 and a passage 19, and a pump discharge pressure P is introduced. The port 18 formed in the piston 12 always keeps the passage 4b in communication with the passage 19 when the differential piston 12 is displaced in any direction.

The balance lever 17 is a differential piston 1.
5 is arranged substantially in parallel with the reference point 5 and rotates about a fulcrum 20 at the base end, the detection piston 15 abuts on the way, and the pressure reducing valve 22 abuts from the opposite direction to the pivoting tip side. .

The pressure reducing valve 22 is brought into contact with the balance lever 17 by a spring 23 with a predetermined urging force to oppose the pressing force of the pressure detecting piston 15. The balance lever 17 rotates by these moment balances, and switches the pressure reducing valve 22.

That is, when the moment generated by the detection piston 15 is smaller than the moment caused by the spring 23 of the pressure reducing valve 22, the pressure reducing valve 22 is switched to the A position and connected to the tank T side as shown in the drawing. Conversely, when the moment generated by the detection piston 15 is large, B
Switch to the position and connect to the pump P side.

The pressure reducing valve 22 is connected to the pressure chamber 14 of the differential piston 12 via a control passage 24, and a passage 25 branched from the passage 24 serves as a pressure receiving portion of the pressure adjusting valve 6 on the pump side. The pressure Pv transmitted to the passage 24 in connection with the switching operation via the balance lever 17
Adjust.

The above is the configuration of the servo valve mechanism 10. The servo valve mechanism 10 and the pump-side regulator mechanism 9 are connected via a hydraulic pipe.

Next, the operation will be described.

When the discharge pressure P of the discharge passage 5 of the pump 1 rises as the load increases from the state shown in the figure, the discharge pressure P is transmitted to the pressure detection piston 15 inside the differential piston 12 via the passage 4b. The pressure with which the detection piston 15 presses the balance lever 17 increases.

As a result, the balance of the moment acting on the balance lever 17 is lost, the pressure reducing valve 22 is pushed downward, and the A position is switched to the B position. Then, the discharge pressure of the auxiliary pump P is supplied, and the control pressure Pv guided from the passage 24 to the pressure chamber 14 increases. Pressure P
Due to the rise of v, the differential piston 12 moves against the spring 13 and the balance lever 17 of the detection piston 15 moves.
And the contact position with the balance lever 17 toward the fulcrum 20 of the balance lever 17. The movement of the detection piston 15 reduces the moment about the balance lever 17, and eventually balances the moment due to the spring 23 of the pressure reducing valve 22.

When the moments are balanced, the pressure reducing valve 22
Switches from the B position to the A position, and the increase of the control pressure Pv also stops. Then, at this balanced position, the pressure reducing valve 22 is switched on and off to maintain the control pressure Pv at a higher pressure value than before the detection piston 15 moves.

In this way, the pump discharge pressure P and the control pressure Pv change in a relationship as shown in FIG. 2, and when the pump discharge pressure P exceeds a predetermined pressure, a parabola is correspondingly generated. Ascend as you draw.

On the other hand, the pump discharge pressure P is guided to the oil chamber 3a of the tilting cylinder 2 of the pump 1, and the pressure controlled by the pressure adjusting valve 6 is guided to the oil chamber 3b which opposes this. The tilting cylinder 2 strokes to a position where these are balanced, and the pump discharge amount is controlled.

The pressure adjusting valve 6 is switched and operated according to the balance between the control pressure Pv and the spring 7, and when the pressure Pv rises as described above, the spring 7 is compressed and A
Switching to the position, the pressure P of the passage 4a is introduced into the oil chamber 3b having a large pressure receiving area. Therefore, the pressure in the oil chamber 3b of the tilting cylinder 2 increases, and at this time, the oil chamber 3b
Since the pressure receiving area is larger than that of 3a, even if the pressure of 3b is smaller than the pressure of the oil chamber 3a, the tilting cylinder 2 operates in the extending direction due to the difference in the pressure receiving area, and the tilt angle of the pump swash plate is reduced. The pump discharge rate.

The lever 8 is displaced by the extension operation of the tilting cylinder 2, and the initial deflection of the spring 7 is increased.
When the compression force of the spring 7 is strengthened in this way, it eventually balances with the control pressure Pv. When the pressure is balanced, the pressure adjusting valve 6 is switched to the B position to stop the pressure rise in the oil chamber 3b. At this stop position, switching to the A and B positions is repeated on and off, and the oil chamber 3
Maintain b at the same pressure.

Therefore, as shown in FIG. 3, when the discharge pressure P of the pump 1 rises above a predetermined level Po,
The control pressure Pv rises via the servo valve mechanism 10,
The pressure adjusting valve 6 is switched to extend the tilting cylinder 2, which reduces the tilting angle of the pump swash plate and reduces the pump discharge amount Q. After that, as the discharge pressure P increases, the pump discharge amount Q decreases and these P and Q
The pump drive horsepower corresponding to the product of

When the pump discharge pressure P decreases, the operation of the servo valve mechanism 10 is opposite to that described above, and the differential piston 12 moves the position of the detection piston 15 to the fulcrum 20 of the balance lever 17. The pressure adjusting valve 6 reduces the pressure introduced into the oil chamber 3b of the tilting cylinder 2 to cause the tilting cylinder 2 to contract, and the pump swash plate is displaced. The tilting angle of is increased to increase the pump discharge amount Q.

By the way, in the present invention, the servo valve mechanism 1 is used.
0 and the pump-side regulator mechanism 9 are configured independently of each other, and the passage 4b and the passage 25 are connected by hydraulic piping, whereby the servo valve mechanism 10 can be separated from the pump 10 and arranged at a free position. The degree of freedom in design is increased, the same servo valve mechanism 10 can be used for pumps 1 having different specifications, and cost reduction can be achieved by using common parts.

[0033]

As described above, according to the present invention, the relationship between the discharge pressure and the discharge amount can be controlled so that the pump driving horsepower is substantially constant, and the servo valve mechanism and the pump regulator mechanism are combined. Since they are configured separately and connected to each other with hydraulic piping, the servo valve mechanism can be placed at any position with respect to the pump, which increases the degree of freedom in design, and the same servo valve mechanism is different. It can also be applied to pumps with different specifications, and cost reduction can be achieved by using common parts.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between pump discharge pressure P and control pressure Pv.

FIG. 3 is a characteristic diagram showing a relationship between pump discharge pressure P and discharge amount Q.

[Explanation of symbols]

 1 Pump 2 Tilt Cylinder 3a Oil Chamber 3b Oil Chamber 4a Passage 4b Passage 5 Pump Discharge Passage 6 Pressure Adjustment Valve 7 Spring 8 Lever 9 Regulator Mechanism 10 Servo Valve Mechanism 11 Cylinder 12 Differential Piston 13 Spring 14 Pressure Chamber 15 Pressure Detection Piston 16 pressure chamber 17 balance lever 20 fulcrum 22 pressure reducing valve 23 spring 24 passage 25 passage

Claims (1)

[Claims] 1. A tilting cylinder for changing a tilt angle of a pump swash plate, an oil chamber to which a pump discharge pressure of the cylinder is introduced, an oil chamber to which a pressure adjusted by a pressure adjusting valve is introduced, and this pressure adjusting. A regulator mechanism consisting of means for adjusting the initial deflection of the valve switching spring according to the displacement of the tilt cylinder, a differential piston that is displaced according to the balance of control pressure and spring, and the axis line is orthogonal to this differential piston. Pressure sensing piston, a passage for guiding the pump discharge pressure to the base end of the pressure sensing piston, and a balance lever extending substantially parallel to the differential piston and rotatable about a fulcrum of the base end. And a pressure reducing valve biased by a spring that abuts the balance lever from the opposite side to which the detection piston abuts,
A passage that guides the control pressure of the pressure reducing valve that is switched and controlled via a balance lever to one end of the differential piston, and a control pressure that opposes the switching spring that branches from this passage to switch the pressure adjustment valve. An output control device for a pump, comprising: a servo valve mechanism including a guide passage.