Power plants – Pressure fluid source and motor – Unsafeness – unreadiness or disarray prevent manual change or...
Patent
1979-06-13
1982-08-10
Cohen, Irwin C.
Power plants
Pressure fluid source and motor
Unsafeness, unreadiness or disarray prevent manual change or...
60433, 60447, 60449, 60468, 60488, F16H 3946
Patent
active
043431500
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a hydraulic circuit for controlling and preconditioning the operation of a hydrostatic transmission or the like.
2. Background Art
Variable displacement pumps of the type employed in hydrostatic transmissions are adapted to have the displacements thereof varied between minimum and maximum levels upon adjustment of servo-systems operatively connected to the pumps for actuating swash plates thereof in a conventional manner. The control circuit therefor may comprise 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 control automatically the underspeed actuator and thus the displacement of the pumps under certain operating conditions of the engine.
U.S. Pat. No. 3,952,514, assigned to the assignee of this application, and issued to Cyril W. Habiger on Dec. 27, 1976, discloses a conventional control circuit of this type. This control circuit further comprises a direct speed control and vent valve having a spool thereof sequentially movable from a "vent" position whereby the control circuit is deactivated with the vehicle brakes being retained in their normally "on" condition of operation, a "zero" speed condition whereby the control circuit is preconditioned for operation and then to a "run" position whereby the brakes are released and the control circuit is activated.
When the spool is moved to its "zero" speed position, pressurized fluid is communicated to a second spool to move it to a position whereby brakes may be released and pressurized fluid may be communicated to a replenishing and relief valve of the control circuit. Should the operator move the first-mentioned spool too fast, the preconditioning of the brakes for release thereof and further preconditioning of the replenishing and relief valve may not occur. Furthermore, control circuits of this type are somewhat complex and require very close calibration for efficient operation of the control circuit and its associated hydrostatic transmission.
DISCLOSURE OF THE INVENTION
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of this invention, a fluid control circuit comprises a source of fluid, fluid actuating means for being placed in an activated or deactivated condition of operation, first valve means movable between first and second positions, second valve means movable between a first position blocking communication of fluid to the fluid actuating means when the first valve means is in its first position and a second position communicating fluid to the fluid actuating means, and third valve means movable between a first position blocking communication to the second valve means and a second position when the first valve means is in its first and second positions. The second valve means is responsive for movement to its second position by positioning of the first valve means in its second position and positioning of the third valve means in its second position.
In another aspect of this invention, the fluid actuating means comprises a variable displacement pump and associated circuitry of a hydrostatic transmission. The control circuit further comprises control means connecting the source of fluid with such circuitry for automatically controlling the displacement of the pump thereof between minimum and maximum levels and override control means for selectively overriding the same.
In still a further aspect of this invention, an operator control arrangement is adapted to be mechanically connected to a control valve of the control circuit and includes snubber means for alerting an operator when a control lever has over-traveled the "run" condition of the control circuit.
The control circuit of this invention is relatively non-complex in structure and operation, provides for the efficient control of the fluid actuating means and exhibits a continuous preconditioning functi
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Shuler Lucien B.
Spivey, Jr. William J.
Caterpillar Tractor Co.
Cohen Irwin C.
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