Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1980-09-12
1983-05-03
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
417222, F16D 3102, F04B 4908
Patent
active
043816460
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Technical Field
This invention relates generally to a torque and high pressure limiting control for variable displacement pumps and more particularly to modulating means for continuously modulating a fluid pressure signal originating in a fluid actuator to vary the displacement of a variable displacement pump to prevent the system from exceeding a desired horsepower range and pressure level.
Background Art
Hydraulic control circuits employed for controlling the actuation of variable displacement pumps of the type employed in construction vehicles, such as excavators, oftentimes include a so-called "load-plus" valve. The valve generally functions to maintain the discharge pressure of the pump above a minimum pressure level and also above a load pressure generated in a fluid actuator, such as a double-acting hydraulic cylinder. A valve of this type is fully disclosed in U.S. Pat. No. 4,116,587, issued on Sept. 26, 1978 to Kenneth P. Liesener and assigned to the assignee of this application.
The "load-plus" valve functions to sense a load pressure signal and to automatically actuate a swash plate of the pump in response to such signal to maintain a desired pump discharge pressure. Although this control system works quite well, it has been found lacking in the provision of means for limiting system pressures to acceptable levels and obtaining maximum performance efficiency from the prime mover for the pump. In accordance with the teachings of this invention, it has been found that the horsepower required of the prime mover can be limited and closely controlled in an infinite manner by modulating the load pressure signal directly to vary the load pressure signal communicated to the "load-plus" valve.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF INVENTION
In one aspect of the present invention, a fluid circuit having a fluid actuator, a variable displacement pump including a control member, first biasing means for urging the control member towards a first displacement position, and second biasing means for urging the control member towards a second displacement position and in response to a load pressure signal received from the fluid actuator, further includes modulating means for modulating the load pressure signal in the first biasing means to vary the displacement of the pump in response to the magnitude of the signal and the position of the control member.
The improved fluid circuit, incorporating the modulating means therein, will thus provide maximum performance efficiency from the prime mover, such as an internal combustion engine, utilized to drive the pump. The control circuit is torque limiting since the modulated load pressure signal is a function of both pump discharge pressure and pump displacement, i.e., the load pressure signal thus becomes a function of pump torque. This relationship is graphically illustrated in FIG. 4 wherein curve A plots pump flow versus the load pressure signal and wherein curve B represents a horsepower curve for a particular engine.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of this invention will become apparent from the following description and accompanying drawings wherein:
FIG. 1 schematically illustrates a fluid circuit employing a torque and high pressure limiting control for a variable displacement pump incorporating a first modulating valve embodiment of the present invention therein;
FIG. 2 is a longitudinal sectional view through the pump and control therefor;
FIG. 3 is an enlarged sectional view of the modulating valve of the control;
FIG. 4 graphically illustrates a curve A plotting pump flow versus a load pressure signal and a horsepower curve B;
FIG. 5 is a sectional view illustrating a second modulating valve embodiment;
FIG. 6 is a sectional view illustrating a third modulating valve embodiment; and
FIG. 7 is a sectional view illustrating a fourth modulating valve embodiment and an override means associated therewith.
BEST MODE OF CARRYING OUT T
REFERENCES:
patent: 3918259 (1975-11-01), Habiger et al.
patent: 3941514 (1976-03-01), Louis et al.
patent: 3999892 (1976-12-01), Hein
patent: 4034564 (1977-07-01), Johnson et al.
patent: 4116587 (1978-09-01), Liesener
patent: 4129987 (1978-12-01), Blume
"Pump Controls That Save Energy", by H. Sculthorpe, Machine Design, Apr. 21, 1977, pp. 255-259.
"The Search for Credible Design Data", by A. Barrett, Machine Design, Apr. 21, 1977, p. 260.
"Two-Stage Compensator Anticipates Cut-Off Action", by E. J. Stefanides, Design News, Nov. 20, 1978, pp. 74-75.
Ruseff Walter Z.
Schimpf James E.
Caterpillar Tractor Co.
Look Edward K.
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