JPH0220474Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate control device for a variable displacement pump.

Generally, a variable displacement pump is equipped with a constant output control device that controls the pump output to a constant level by changing the discharge flow rate according to changes in the discharge pressure. It is also practiced to change the discharge flow rate by the command pressure regardless of the command pressure. Its configuration is shown in Figures 1 and 2.
As shown in the figure, the pump flow rate of the variable displacement pump a is controlled by the operation of a control piston d, which is connected to a pump displacement changing mechanism such as a swash plate via a rod c and has different pressure receiving areas at both ends. A pressure chamber e on a small diameter pressure receiving surface of the control piston d is connected to a discharge circuit f, and a pressure chamber g on a large diameter pressure receiving surface is selectively connected to a discharge circuit f or a tank i via a servo valve h. . Further, the servo valve h is connected to the first piston l via a control rod k having a control spring j interposed between it and the control piston d, and a second piston m is provided superimposed on the first piston l. It will be done. The discharge pressure _P1 of the pump a acts on the first piston l in a direction to deflect the control spring j, and the second piston m also deflects the control spring j via the first piston l. An external command pressure P ₂ acts in the direction.

In this configuration, if there is no action of command pressure _P2 ,
The first piston l is pump a as shown by curve V in _FIG .
Performs constant output control. That is, when the discharge pressure P ₁ is low, such as when the pump a is under no load, the control piston d is at a position where the pump flow rate is maximized by the force acting on the small diameter pressure chamber e and the force of the control spring j, and the discharge pressure P ₁ increases and the force acting on the first piston l becomes greater than the load of the control spring j, the servo valve h moves to introduce the discharge pressure _P1 into the large diameter pressure chamber g,
The control piston d moves in a direction to reduce the pump flow rate due to the force caused by the difference in pressure receiving area between its two ends.
This movement of the control piston d causes the control spring j
When the force is deflected and the force overcomes the force of the first piston l, the servo valve h is pushed back by the return spring n, and the load of the first piston l becomes equal to the loads of springs j and n, and the servo valve h moves to close the pressure chamber g, and the control piston d stops.

When the discharge pressure _P1 decreases, the load on the first piston 1 decreases, and the first piston 1 and the servo valve h
The control piston d is pushed back by the springs j and n and connects the large diameter pressure chamber g to the tank i, so that the control piston d moves in the direction of increasing the pump flow rate.

This movement reduces the load on the control spring j, and the control piston d stops when the load on the first piston l and the loads on the springs j and n are balanced.

By decreasing the pump flow rate Q by increasing the discharge pressure _P1 and increasing the pump flow rate Q by decreasing the discharge pressure _P2 , it is possible to maintain the output of the pump a almost constant. pressure
If P ₂ is applied, the load on the first piston 1 increases, and the pump flow rate can be reduced within the constant output control range, regardless of the discharge pressure P ₁ . In this case, if the pressure receiving area of the first piston l is A ₁ and the pressure receiving area of the second piston m is A ₂ , then the command pressure P ₂ applied to the second piston m is A ₁ /A ₂ ×P ₁ . Moreover, since P ₁ changes from P′ ₁ to P″ ₁ ,
The command pressure P ₂ must be selected within the range of P′ ₂ to P″ ₂ accordingly.The relationship between the discharge pressure P ₁ and the command pressure P ₂ is as shown in the third diagram, and the discharge pressure P If the range of change ΔP _{1 is} large, the command pressure P ₂ correspondingly increases.
The range in which ΔP ₂ should change also increases. Moreover, when the command pressure P′ ₂ is determined, P″ ₂ becomes large, and a large amount of energy is required to generate a large P″ _2. Therefore, when the discharge pressure P ₁ is low, the pump flow rate Q is reduced to reduce the consumption of pump a. The purpose of aiming for an energy-saving effect by reducing power diminishes, and conversely, if the command pressure P″ ₂ is set small, P′ ₂ becomes small, and the operating pressure of the control device is not guaranteed, resulting in unstable operation.

The purpose of the present invention is to provide a flow control device for a variable displacement pump that can perform flow control operation using a command pressure with a relatively narrow range of change without impairing the constant output control function. The pump flow rate is varied by the discharge pressure of the pump 1 acting on the control piston 3 via the servo valve 2, and the servo valve 2 is operated by the discharge pressure acting against the control spring 4. The first piston 5
and a second piston 6 that slides with a command pressure that also acts against the control spring 4, with a second piston 6 at the opposite end of the first piston 5 from the control spring 4. Two pistons 6 are placed over each other, and the second piston 6 is provided with a second spring 7 that resists the command pressure.

As shown in FIGS. 4 and 5, the control piston 3 is formed to have different pressure receiving areas at both ends, and is connected via a rod 8 to a pump displacement changing mechanism such as a swash plate of the variable displacement pump 1. The pressure chamber 9 facing the small diameter pressure receiving surface of the control piston 3 is connected to the discharge circuit 10, and the pressure chamber 11 facing the large diameter pressure receiving surface is connected to the discharge circuit 1 via the servo valve 2.
0 or tank 12. The servo valve 2 is connected to a first piston 5 via a control 13 having a control spring 4 interposed between it and the control piston 3, and a pressure chamber 14 on which discharge pressure acts is interposed in the first piston 5. A second piston 6 is provided.

The above configuration is not particularly different from the conventional one,
Discharge pressure acting on the pressure chamber 14 of the first piston 5
The control piston 3 is actuated depending on the strength of P ₁ to control the pump flow rate and keep the pump output constant, and the pressure chamber 15 of the second piston 6 is controlled.
Controlling the pump flow rate by operating the control piston 3 by applying the command pressure P ₂ to the pump is similar to the conventional one, but in the present invention, the second piston 6 is applied to the second piston 6 to resist the command pressure P ₂ . A second spring 7 is provided to provide an arbitrary command pressure P ₂ with a narrow range of change.
to control the pump flow rate.

The second spring 7 is provided between the machine casing 16 and the flange 6a of the second piston 6, and the pressure receiving areas of the first piston 5 and the second piston 6 are A ₁ and A ₂ , respectively, and the second spring 7 is If the spring force is F, the command pressure P ₂ and the discharge pressure P ₂
As shown in the straight line W shown in Figure 6, the relationship is a gentle slope that takes into account not only the area ratio of A ₁ and A ₂ but also F, and the command pressure corresponding to the range of change ΔP ₁ of the discharge pressure P ₁ . The range of change in P ₂ ΔP ₂ can be made relatively narrow, the minimum required command pressure P′ ₂ for pump flow rate control can be determined, and ΔP ₂ can be arbitrarily determined regardless of ΔP ₁ . Since the pressure required for pump capacity control operation can be guaranteed and the command pressure P″ ₂ for minimizing the pump flow rate can be kept low, the control energy can also be reduced.The command pressure P ₂ is A ₁ /A ₂
It is obtained from the relationship ×P ₁ +F/A ₂ .

In this way, according to the present invention, the second piston 6 on which the command pressure acts is placed over the first piston 5, and the second piston 6 is supported by the second spring 7 against the command pressure. The pump flow rate can be controlled without impairing the constant output control performed by the first piston 5 with a command pressure in a range smaller than the pressure change range, and the maximum pressure of the command pressure can be reduced, so that the pump flow rate can be controlled. The energy required is also reduced, and by changing the force of the second spring 7, the pump flow rate can be conveniently controlled in accordance with any change in the discharge pressure.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the conventional example, Fig. 2 is an enlarged view of the main parts thereof, Fig. 3 is a diagram of the conventional flow rate and output control relationship, Fig. 4 is an explanatory diagram of the embodiment of the present invention, FIG. 5 is an enlarged view of the main part thereof, and FIG. 6 is a flow rate and output control relationship of the present invention. 1...variable displacement pump, 2...servo valve, 3...
...Control piston, 4...Control spring, 5...
...first piston, 6...second piston, 7...second spring.

Claims (1)

[Scope of utility model registration request] The pump flow rate of variable displacement pump 1 is controlled by servo valve 2.
The first piston 5 is varied by the discharge pressure of the pump 1 acting on the control piston 3 via the control spring 4, and the first piston 5 slides with the discharge pressure acting against the control spring 4 to act on the servo valve 2. control spring 4
The first piston 6 is controlled by a second piston 6 which is slid by a command pressure acting against the second piston 6.
A flow rate control device for a variable displacement pump, comprising a second piston 6 placed over the end of a piston 5 opposite to the control spring 4, and a second spring 7 for resisting command pressure provided on the second piston 6.