Power plants – Pressure fluid source and motor – Unsafeness – unreadiness or disarray prevent manual change or...
Patent
1979-06-13
1982-07-27
Cohen, Irwin C.
Power plants
Pressure fluid source and motor
Unsafeness, unreadiness or disarray prevent manual change or...
60436, 60447, 60488, 417218, F04B 4900, F16H 3946
Patent
active
043410731
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a control circuit for selectively varying the displacement of a pump, the circuit including primary control means and override control means for overriding the primary control means independent of actuation thereof.
BACKGROUND ART
Variable displacement pumps, such as those employed in hydrostatic transmissions, are adapted to have the displacements thereof varied between minimum and maximum levels upon adjustment of servo-systems connected to the pumps which are adapted to actuate swash plates of the pumps in a conventional manner. U.S. Pat. No. 3,996,743, assigned to the assignee of this application and issued to Cyril W. Habiger on Dec. 14, 1976, discloses a conventional control circuit for controlling the displacement of pumps of this type.
The control circuit comprises an underspeed actuator which is connected to the servo-systems and further connected to a venturi to receive a differential fluid pressure signal therefrom which is proportional to the speed of a vehicle's engine to automatically control the underspeed actuator for automatically varying the displacement of the pumps under certain conditions of engine operation. The control circuit further comprises a directional control valve movable to a vent and override position to equalize the differential fluid pressure signal whereby the automatic operation of the underspeed actuator may be overriden.
When the control valve is in this position, pressurized fluid is blocked from communicating with replenishing and relief valves of the pump system and also to normally "on" brakes of the vehicle which must be released by fluid pressure. When the control valve is moved from its vent towards its maximum speed position, pressurized fluid is communicated to the brakes to release them and also to the replenishing and relief valves of the pump system to condition the pumps for operation. Simultaneously therewith, the above-mentioned differential fluid pressure signal is re-established to permit the underspeed actuator to control displacement of the pumps automatically, should the need arise.
It has proven desirable, particularly in the application of the control circuit of the present invention to hydrostatic transmissions, to construct and arrange an override control valve as a separate unit from a main control valve which controls the venting and primary control functions of the circuit. In addition to rendering the circuit efficient for expeditious and close control by the operator, the respective control valves and associated components of the control circuit may be arranged for efficient servicing. Also, the main control valve can be maintained operational in its "run" position upon movement of the override control valve from its closed position to its open, override position and back to its closed position.
DISCLOSURE OF INVENTION
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, the control circuit comprises a source of pressurized fluid, a variable displacement pump means for having the displacement thereof varied in response to communication of pressurized fluid thereto, primary control means connecting the source with the pump means for selectively venting pressurized fluid from the pump means or for varying the displacement of the pump means between minimum and maximum values, and override control means for overriding the same when the primary control means is in its actuated condition of operation for selectively varying the displacement of the pump means, independent of actuation of the primary control means.
In another aspect of this invention, the override control means preferably comprises a rotatable valve spool for closely controlling a fluid pressure signal normally utilized to automatically control the displacement of the pump means. In addition to providing close control of the override function, the valve is adapted to provide a much more compact package in comparison with valves adapted for linear movement.
In
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patent: 3898807 (1975-08-01), Habiger
patent: 3952514 (1976-04-01), Habiger
patent: 3990320 (1976-11-01), Habiger
patent: 3996743 (1976-12-01), Habiger et al.
patent: 4041702 (1977-08-01), Habiger
patent: 4106292 (1978-08-01), Habiger
patent: 4211079 (1980-07-01), Saele
Caterpillar Tractor Co.
Cohen Irwin C.
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