Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1996-01-16
1997-10-07
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60422, 60430, 60452, 137884, F16D 3102
Patent
active
056735570
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a displacement control system for a variable displacement type hydraulic pump.
BACKGROUND ART
As a displacement control system for a variable displacement type hydraulic pump, a system performing control with a pump discharge pressure and a load pressure, as shown in FIG. 1, for example, has been known.
Namely, a direction control valve 3 is provided in a discharge path 2 of a variable displacement type hydraulic pump 1 (hereinafter referred to as variable hydraulic pump) and then a pressurized fluid is supplied to an actuator 4 via the direction control valve 3. A displacement control cylinder 6 is provided for driving a displacement control member 5, such as a swash plate and so forth of the variable hydraulic pump 1. One chamber 6a of the displacement control cylinder 6 is connected to a discharge path 2 via a first circuit 7. The other chamber 6b is selectively connected to a second circuit 9 (connected to the discharge path 2) via a pump port side of a displacement control valve 8 and to a tank circuit 10 via a drain port side of the displacement control valve. A first pressure receiving portion 11 of the displacement control valve 8 is connected to the second circuit 9, and the second pressure receiving portion 12 is connected to a load pressure detecting circuit 14 which is connected to the actuator 4. The displacement control valve 8 is forced to a communicating position A by a pressurized fluid (pump discharge pressure P.sub.1) acting on the first pressure receiving portion 11, and to a drain position B by a pressurized fluid (load pressure P.sub.LS) acting on the second pressure receiving portion 12 and a spring 13. It should be noted that a circuit for returning the pressurized fluid from the actuator 4 to a tank is neglected for simplification of the drawing.
With the displacement control system, the displacement control valve 8 is placed at the communicating position A when a pressure difference .DELTA.P.sub.LS between the pump discharge pressure P.sub.1 and the load pressure P.sub.LS becomes higher to actuate the displacement control cylinder 6 in X direction to operate the displacement control member 5 in a direction for smaller displacement, and is placed at the drain position B when a pressure difference .DELTA.P.sub.LS between the pump discharge pressure P.sub.1 and the load pressure P.sub.LS becomes lower to actuate the displacement control cylinder 6 in Y direction to operate the displacement control member 5 in a direction for greater displacement. In practice, the displacement control member 5 is controlled for establishing equilibrium between the pressure difference .DELTA.P.sub.LS of the pump discharge pressure P.sub.1 acting on the first pressure receiving portion and the load pressure P.sub.LS acting on the second pressure receiving portion 12 and the load of the spring 13. Namely, the displacement of the variable displacement pump 1 is controlled so that the pressure difference between the pump discharge pressure P.sub.1 and the load pressure P.sub.LS is maintained constant.
With such displacement control system, when the open area of the direction control valve 3 is reduced while a constant flow rate of pressurized fluid flows (at this time the pressure difference .DELTA.P.sub.LS is maintained constant), the pressure difference .DELTA.P.sub.LS becomes greater. Therefore, the displacement control member 5 is actuated in the direction for smaller displacement until the .DELTA.P.sub.LS returns to the initial value. On the other hand, when the open area of the direction control valve 3 is increased, the pressure difference .DELTA.P.sub.LS becomes smaller. Therefore, the displacement control member 5 is actuated in the direction for greater displacement until the pressure difference .DELTA.P.sub.LS returns the initial value. Accordingly, the displacement of the variable hydraulic pump 1 becomes a value depending upon the open area of the direction control valve. Namely, the displacement is controlled to maintain a pressure l
REFERENCES:
patent: 4561341 (1985-12-01), Aikawa
patent: 5115835 (1992-05-01), Ueno
patent: 5148676 (1992-09-01), Moriya et al.
patent: 5243820 (1993-09-01), Shimoura et al.
patent: 5454223 (1995-10-01), Tschida et al.
Honda Nobuhisa
Karakama Tadao
Yoshida Nobumi
Komatsu Ltd.
Nguyen Hoang
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