Displacement controlling circuit system for variable displacemen

Details Displacement controlling circuit system for variable displacemen Displacement controlling circuit system for variable displacemen

1992-03-10

1993-07-13

Bertsch, Richard A.

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

60452, F04B 4900

Patent

active

052268004

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The present invention relates to a circuit system for controlling a variable displacement pump.


BACKGROUND ART OF THE INVENTION

As a system for controlling a variable displacement pump in displacement, for example as shown in FIG. 6, one so controlling as to keep a difference between a delivery pressure and a load pressure constant is known.
Namely, a displacement control member 2 of a variable displacement pump 1 is actuated in a displacement reducing direction by means of a large piston 3, and actuated in a displacement increasing direction by means of a small piston 4 so that: a pressure chamber 3a of the large piston 3 is so controlled through a load sensing valve 5 as to be connected with a tank side and a delivery passage 1a; and a pressure chamber 4a of the small piston 4 is connected with the delivery passage 1a.
The above-mentioned load sensing valve 5 controls the variable displacement pump 1 in displacement in a manner such that: under the influence of a pressure or delivery pressure P.sub.1 in the delivery passage 1a of the pump 1, the load sensing valve 5 is moved into a first position I in which the pressure chamber 3a of the large piston 3 communicates with the delivery passage 1a, and, under the influence of a pressure or load pressure P.sub.LS in an outlet side of an operated valve 6, the load sensing valve 5 is moved into a second position in which the pressure chamber 3a communicates with a tank; and, when a difference (P.sub.1 -P.sub.LS) between the delivery pressure P.sub.1 and the load pressure P.sub.LS increases, the pressure in the pressure chamber 3a of the large piston 3 is increased to actuate the displacement control member 2 in the displacement reducing direction so that a delivery flow rate/revolution is reduced to lower the delivery pressure P.sub.1, and when the difference (P.sub.1 -P.sub.LS) between the delivery pressure P.sub.1 and the load pressure P.sub.LS decreases, the pressure in the pressure chamber 3a of the large piston 3 is reduced to actuate the displacement control member 2 in the displacement increasing direction so that a delivery flow rate/revolution is increased to increase the delivery pressure P.sub.1, whereby the variable displacement pump 1 is controlled in displacement so as to keep always the difference (P.sub.1 -P.sub.LS) between the delivery pressure P.sub.1 and the load pressure P.sub.LS constant.
In FIG. 6: 7 is a pressure compensating valve; and 8 is a shuttle valve for detecting a higher load pressure which is detected by the shuttle valve 8 when a plurality of the operated valves 6 are simultaneously operated, the pressure being adapted to act on the above-mentioned load sensing valve 5 and each of the pressure compensating valves 7.
In such displacement control system: since the difference between the delivery pressure P.sub.1 and the load pressure P.sub.LS is controlled so as to be constant, a delivery flow rate/unit time does not vary even when an engine 9 varies in rate of revolution, provided that the operated valves 6 are kept constant in opening.
For example, when the rate of revolution of the engine 9 decreases to cause the variable displacement pump 1 to be decreased in rate of revolution and in delivery flow rate/unit time, the difference between the delivery pressure P.sub.1 and the load pressure P.sub.LS decreases so that the displacement control member 2 is actuated in the displacement increasing direction by means of the small piston 4 so as to increase the delivery flow rate/revolution and the delivery flow rate/unit time, whereby the difference between the delivery pressure P.sub.1 and the load pressure P.sub.LS is kept constant, and, therefore the delivery flow rate/unit time does not vary even when the rate of revolution of the engine 9 varies. For example, in a condition in which the operated valves are opened to the maximums, it is kept constant as shown in FIG. 7 with A.
As a result, for example, when it is applied to a hydraulic circuit for a work unit of a construction machine, since a

REFERENCES:
patent: 4081223 (1978-03-01), Fricke
patent: 4600364 (1986-07-01), Nakatani et al.
patent: 4637781 (1987-01-01), Akiyama et al.
patent: 4710106 (1987-12-01), Iwata et al.
patent: 4904161 (1990-02-01), Kamide et al.
patent: 5111789 (1992-05-01), Moriya et al.
Patent Abstracts of Japan; vol. 6, No. 232, Nov. 18, 1982.

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