Caterpillar Tractor Co.

Walter Z Ruseff

James E Schimpf

Howard L Johnson

Allyn J Hein

William D McMillan

Gilbert Tribley

Pump control with fluid responsive standby pressure

A 'load-plus' valve is oftentimes utilized in the servo-system for a variable displacement pump to maintain pump discharge pressure above a minimum pressure level and above a load pressure in a fluid actuator. Valves of this type normally employ a spring interconnected between a modulating spool and a piston which is responsive to load pressure to modulate a control pressure, controlling the displacement of the pump. Valves of this type thus provide a constant discharge pressure margin over load pressure while also providing the pump's minimum stand-by pressure. However, valves of this type further provide pump packages which are somewhat bulky in design. The improved load-plus valve (22) of this invention provides a spool (49) movable between a first position communicating a control pressure (P.sub.C) from a pump (11) to a control chamber (24) and a second position at least partially venting the control chamber (24), and a piston (57) movable between a first position isolating the piston (57) from the spool (49) to enable the spool (49) to move independently of the piston (57 ) and a second position engaging and moving the spool (49) to modulate the control pressure (P.sub.C) in response to variations in a load pressure (P.sub.L) in a fluid actuator (13).

Load-plus valve for variable displacement pumps

Torque and high pressure limiting control for variable displacement pumps

Unloading means for flow-pressure compensated valve

Variable displacement pumps are each provided with internal biasing means which adjusts displacement in response to spring forces, discharge pressures and net swivel torque forces in order to limit output pressure and to avoid overtaxing the power output capabilities of the motor which drives the pumps. In a system where a plurality of such pumps each supply a separate fluid-operated device but are driven by a single motor, the internal displacement control means of each pump may be arranged to be responsive in part to the discharge pressure of each other pump. The pumps may operate at different power output levels and if one experiences a relatively heavy load, the displacements of the others also reduce if necessary to avoid exceeding the power limitations of the drive motor from a total system overload.

Pressurized fluid supply system

A piston pump having a housing and an angularly adjustable swash plate for controlling piston displacement and the flow of fluid discharged from the pump has improved control means for controllably positioning the swash plate in response to a modified load pressure signal.

Piston pump assembly having load responsive controls

A three-section pump including a variable displacement piston pump and an additional rotary pump arranged in axial alignment upon a common drive shaft together with a centrifugal pump, the output for the centrifugal pump being connected to the input for the piston pump in order to assure positive filling. Preferably, the output for the centrifugal pump is also connected with the input for the additional rotary pump in order to also assure its optimum operation. The three-section pump includes a specially configured housing permitting compact assembly of the three-section pump and providing a bearing mount for the common drive shaft of the three-section pump.

Supercharged three-section pump

A pump control assembly for a variable displacement pump has adjustable biasing means for providing improved control of the pump.

Growing community of inventors

New Lenox, IL, United States of America

Walter Z Ruseff