Power plants – Pressure fluid source and motor – Having condition responsive control in a system of...
Patent
1980-09-12
1983-04-12
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of...
60452, 417216, 417222, F16D 3102
Patent
active
043793894
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
This invention relates generally to a fluid circuit having a horsepower limiting control for a variable displacement pump and more particularly to a fluid circuit including a "load-plus" valve for modulating an actuator pressure signal during a predetermined range of horsepower consumption of the pump and a horsepower limiting control for modulating the pressure signal in response to a pressure control signal, indicating that the pump has exceeded such horsepower range.
BACKGROUND ART
It is well-known in the arts relating hereto to employ a flow-pressure compensated or "load-plus" valve to maintain the discharge pressure of a variable displacement pump above a minimum pressure level and also above a load pressure generated in a fluid actuator, during a working range of the pump. This type of valve 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 valve functions to sense a load pressure signal and to automatically communicate and modulate an actuator pressure signal for controlling the position of a swash plate of the pump to maintain the pump at its desired displacement.
Should the rating or working horsepower consumption range of the pump be exceeded, it is further desirable to modify the actuator pressure signal to destroke the pump to prevent potential damage thereto and to related components of the fluid circuit. U.S. Pat. No. 3,999,892, issued on Dec. 28, 1976 to Allyn J. Hein, and also assigned to the assignee of this application, discloses a pump control system wherein the actuator pressure signal is vented to tank when such horsepower consumption range is exceeded. This periodic bleeding-off of the actuator pressure signal results in an undesirable loss of system horsepower. Furthermore, the integrated fluid circuit does not adapt the horsepower limiting feature to be incorporated into a module adapted for use with pumps of various sizes.
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 comprises a fluid motor, a variable displacement pump having a control member movable between first and second displacement positions, first biasing means for urging the control member towards its first displacement position, second biasing means for urging the control member towards its second displacement position in response to an actuator pressure signal communicated to it from the pump, and modulating means for modulating the actuator pressure signal in response to variations in a load pressure signal communicated thereto from the fluid motor and during a predetermined working range of horsepower consumption of the pump. The improved fluid circuit further comprises means for blocking communication of the actuator pressure signal with the second biasing means and for venting the actuator pressure signal in response to a pressure control signal indicating that the pump has exceeded its predetermined range of horsepower consumption.
The improved fluid circuit will thus ensure maximum performance efficiency of the prime mover for the pump by preventing undesirable venting of the actuator pressure signal when the rating of the pump has been exceeded. The above improvement also has the advantage of being adapted to pumps of various sizes in modular form.
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, having a pair of variable displacement pumps each associated with a fluid motor, incorporating a horsepower limiting control system embodiment of the present invention therein for preventing each of the pumps from exceeding its rating;
FIG. 2 is a longitudinal sectional view through one of the pumps and the control system therefor;
FIG. 3 is a view similar to FIG. 2, but illustrates a modi
REFERENCES:
patent: 3213617 (1965-10-01), Hallberg
patent: 3732036 (1973-05-01), Busbey et al.
patent: 3918259 (1975-11-01), Habiger et al.
patent: 3941514 (1976-03-01), Louis et al.
patent: 3998053 (1976-12-01), Johnson
patent: 3999892 (1976-12-01), Hein
patent: 4080979 (1978-03-01), Hein
patent: 4116587 (1978-09-01), Liesener
"Hydraulic Systems that Conserve Energy" by R. Henke, Machine Design, Aug. 12, 1976, pp. 81-85.
"Pump Controls that Save Energy" by H. Sculthorpe, Machine Design, Apr. 21, 1977, pp. 255-259.
Caterpillar Tractor Co.
Look Edward K.
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