JP3076150B2 - Pump output control device - Google Patents

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 predetermined output value (horsepower), and the driving load of the engine is maximized. It is known that the engine is used to avoid engine stalls (for example, JP-A-63-272974).

[0003] More specifically, the drive horsepower control of the pump is such that a pressure controlled by a servo regulator is introduced to a tilt cylinder for adjusting a tilt angle of a swash plate of the pump, and the tilt of the pump is adjusted in accordance with the discharge pressure of the pump. The angle is changed so that the relationship between the pump discharge amount and the discharge pressure draws a constant hyperbola.

[0004]

However, since the change in the stroke amount of the tilting cylinder is usually fed back mechanically to the balance lever of the servo regulator, if the specifications of the pump are different, the mechanical characteristics of the servo regulator may be reduced. The feedback control mechanism also needs to be changed accordingly.

[0005] For this reason, the valves constituting the servo regulator must be prepared with different specifications for each type of pump, which lacks versatility and increases the product cost.

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

[0007]

According to the present invention, (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 guided, and a pressure adjusting valve. A regulator mechanism comprising an oil chamber into which pressure is guided, and a means for adjusting the initial deflection of the switching spring of the pressure adjusting valve according to the displacement of the tilting cylinder;
(B) a differential piston that is displaced in accordance with the balance between the control pressure and the spring, a pressure detection piston housed so that its axis 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 in parallel with the differential piston and rotatable about a fulcrum at the base end, and a pressure reducing valve urged by a spring abutting the balance lever from the side opposite to the side where the detection piston abuts. And a passage for guiding the control pressure of the pressure reducing valve switched and controlled via the balance lever to one end of the differential piston, and a control branching from the passage to oppose a switching spring for switching the pressure regulating valve. And a servo valve mechanism comprising a pressure guiding passage.

[0008]

The tilt angle of the swash plate of the pump is controlled in accordance with the displacement of the tilt cylinder, and the discharge rate of the pump increases or decreases accordingly.

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

In this position, the control pressure is settled, and at the same time, the control pressure is fed back to the pressure regulating valve to switch the pressure regulating valve. Therefore, the pressure adjusted via the pressure adjusting valve is introduced into one of the oil chambers of the tilt cylinder, the pressure balance between the two oil chambers is lost, and the tilt 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 a position where the load of the switching spring is balanced with the control pressure, whereby the tilting cylinder stops at a 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 denotes a pump of a variable discharge amount type, and 2 denotes a tilting cylinder for adjusting the discharge amount by changing the tilt angle of the pump swash plate. The cylinder 2 has an oil chamber 3a having a small pressure receiving area. The pump discharge pressure P is directly introduced through the passage 4a branched from the pump discharge passage 5, and the adjustment pressure through the pressure adjustment valve 6 is introduced 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 control valve 6 is switched in response to a control signal pressure Pv supplied from a servo valve mechanism 10 to be described later and a differential force between the feedback spring 7 and, when in the A position, a passage 4a in the oil chamber 3b. And release it to the tank when in the B position. The feedback spring 7 is given an initial deflection 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 above-described regulator mechanism 9 is all provided on the pump side, and is independent of the servo valve mechanism 10 for feeding back the pump discharge pressure.

Next, the servo valve mechanism 10
1, a differential piston 12 is slidably inserted therein, 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. , The differential piston 12 moves.

A pressure detecting piston 15 is slidably accommodated in the differential piston 12 in a direction orthogonal to the axis thereof. The tip of the detecting piston 15 is passed through a side of the differential piston 15 through a cylinder notch 11a to provide a balance lever. 17
Protruding toward. The pressure chamber 16 formed at the base end of the detection piston 15 is provided with a passage 4 b branched from the discharge passage 5.
Is connected through 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 and is rotated about a fulcrum 20 at the base end, the detection piston 15 abuts on the way, and the pressure reducing valve 22 abuts from a direction opposite to the rotation tip side. .

The pressure reducing valve 22 abuts against the balance lever 17 with a predetermined biasing force by a spring 23, and opposes the pressing force of the pressure detecting piston 15. The balance lever 17 is rotated by these moment balances, and switches the pressure reducing valve 22.

That is, when the moment by the detection piston 15 is smaller than the moment based on 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 FIG. Conversely, when the moment due to the detection piston 15 is large, B
Switch to position and connect to 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 is connected to a pressure receiving portion of the pressure regulating valve 6 on the pump side by a passage 25 branched from the passage 24. And the pressure Pv transmitted to the passage 24 with the switching operation via the balance lever 17.
To adjust.

The configuration of the servo valve mechanism 10 has been described above. The servo valve mechanism 10 and the regulator mechanism 9 on the pump side 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 from the state shown in the figure with an increase in load, the discharge pressure P is transmitted to the pressure detection piston 15 inside the differential piston 12 via the passage 4b. As a result, the pressure at 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, and the pressure reducing valve 22 is pushed downward to switch from the A position to the B position. Then, the supply of the discharge pressure of the auxiliary pump P is received, and the control pressure Pv guided from the passage 24 to the pressure chamber 14 increases. Pressure P
The differential piston 12 moves against the spring 13 due to the increase in the distance v, and the balance lever 17 of the detection piston 15 is moved.
And the contact position are brought closer to the direction of the fulcrum 20 of the balance lever 17. The moment of the balance lever 17 is reduced by the movement of the detection piston 15, and eventually the moment of the spring 23 of the pressure reducing valve 22 is balanced.

When the moment is balanced, the pressure reducing valve 22
Switches from the B position to the A position, and the control pressure Pv also stops increasing. 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 manner, 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 changed. It rises as you draw.

On the other hand, the pump discharge pressure P is guided to the oil chamber 3a to the tilting cylinder 2 of the pump 1, and the pressure controlled by the pressure regulating valve 6 is guided to the oil chamber 3b opposed thereto. The tilting cylinder 2 strokes to these balanced positions, and the pump discharge amount is controlled.

The pressure regulating valve 6 is switched in accordance with the balance between the control pressure Pv and the spring 7, and when the pressure Pv rises as described above, A
The pressure is switched to the position, and the pressure P in 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 3a, even if the pressure of 3b is smaller than the pressure of the oil chamber 3a, the tilting cylinder 2 operates in the extension direction due to the pressure receiving area difference, and the tilt angle of the pump swash plate is reduced. To reduce the pump discharge.

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 increased in this manner, the spring 7 eventually balances with the control pressure Pv. When the balance is achieved, the pressure adjusting valve 6 is switched to the B position, and the increase in the pressure of the oil chamber 3b is stopped. At this stop position, the switching to the A and B positions is repeated on and off so that the oil chamber 3
b is maintained 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 increases via the servo valve mechanism 10,
The pressure regulating valve 6 is switched to extend the tilt cylinder 2, whereby the tilt angle of the pump swash plate is reduced, and the pump discharge amount Q is reduced. Thereafter, as the discharge pressure P increases, the pump discharge amount Q decreases.
, The pump drive horsepower corresponding to the product of the two keeps a substantially constant value.

When the pump discharge pressure P decreases, the operation of the servo valve mechanism 10 is reversed from the above description, and the differential piston 12 moves the position of the detection piston 15 to the fulcrum 20 of the balance lever 17. , The control pressure Pv is reduced, whereby the pressure introduced by the pressure regulating valve 6 into the oil chamber 3b of the tilting cylinder 2 is reduced, and the tilting cylinder 2 is contracted to operate the pump swash plate. Is increased, and the pump discharge amount Q is increased.

In the present invention, the servo valve mechanism 1
The servo valve mechanism 10 can be separated from the pump 10 and arranged at any position by connecting the passage 4b and the passage 25 with each other by configuring the pump mechanism 0 and the pump-side regulator mechanism 9 independently of each other and connecting the passages 4b and 25 with hydraulic piping. The degree of freedom in design is increased, and the same servo valve mechanism 10 can be used for pumps 1 having different specifications, and cost reduction can be achieved by using common components.

[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 becomes substantially constant, and the servo valve mechanism and the pump regulator mechanism are combined. Since they are separated and connected by hydraulic piping, the servo valve mechanism can be placed at any position with respect to the pump, increasing the degree of freedom in design and using the same servo valve mechanism differently. It can be applied to pumps with different specifications, and costs can be reduced by using common parts.

[Brief description of the 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 a pump discharge pressure P and a control pressure Pv.

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

[Explanation of symbols]

 Reference Signs List 1 pump 2 tilting cylinder 3a oil chamber 3b oil chamber 4a passage 4b passage 5 pump discharge passage 6 pressure regulating 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 Reference Signs List 16 pressure chamber 17 balance lever 20 fulcrum 22 pressure reducing valve 23 spring 24 passage 25 passage

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F04B 49/00 341 F04B 1/26 101

Claims (1)

(57) [Claims] 1. A tilt cylinder for changing a tilt angle of a pump swash plate, an oil chamber to which a pump discharge pressure of the cylinder is led, an oil chamber to which a pressure adjusted by a pressure adjusting valve is led, A regulator mechanism comprising means for adjusting the initial deflection of the valve switching spring in accordance with the displacement of the tilting cylinder; a differential piston which is displaced in accordance with the balance between the control pressure and the spring; and an axis perpendicular to the differential piston Pressure sensing piston housed in such a manner as to perform the above, a passage for guiding the pump discharge pressure to the base end of the pressure detection piston, and a balance lever extending substantially in parallel with the differential piston and rotatable about a fulcrum at the base end. And a pressure-reducing valve biased by a spring contacting the balance lever from the opposite side to which the detection piston contacts,
A passage for guiding the control pressure of the pressure reducing valve switched and controlled via the balance lever to one end of the differential piston, and a control pressure branched so as to oppose a switching spring for switching the pressure regulating valve by branching from the passage. And a servo valve mechanism comprising a guiding passage.