US 4,431,379 AGranted

Valve piston for constant displacement pump

AssigneeJ. I. Case Company

InventorJohn E. Langdon

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Abstract

A variable volume pump for satisfying the requirements of a hydraulic system while limiting fluid flow when the full volume of fluid displacement from the pump is not required by the hydraulic system. The pump includes one or more lines of reciprocable pumping pistons mounted radially around a crankshaft. The rotation of the crankshaft results in centrifugal flow of fluid through crankpin apertures for filling the pumping pistons. Each pumping piston reciprocates within a pumping chamber and the fluid volume filling the piston is directed through a discharge port to the hydraulic system. A valve piston is mounted within the pumping chamber in spaced apart opposing relationship to the pumping piston. The valve piston is normally seated against a valve seat when the pressure level in the hydraulic system is below that necessary to reduce flow. When the pressure in the hydraulic system reaches a predetermined level, compensating pressure is communicated against the valve piston which results in the movement of the valve piston towards the pumping piston. At a maximum desired system pressure, the valve piston contacts the pumping piston and follows the pumping piston during its suction stroke thereby limiting or blocking the fluid flow out the discharge port. Thus, the fluid flow from the pump is reduced in proportion to increased system pressure until a maximum desired output pressure is reached with minimum fluid flow.

A variable volume pump for satisfying the fluid flow requirements of a hydraulic system while limiting fluid flow when the full volume of fluid displacement from the pump is not required by the hydraulic system, said pump including at least one reciprocable pumping piston, said pumping piston including a tube portion which is movable within a pumping chamber, means for filling the pumping piston tube portion with fluid during a suction stroke by said pumping piston, said pumping piston being slidably mounted by a free riding slipper member on a rotatable substantially hollow crankpin having an aperture, said pumping piston including an enlarged spherical head with an axial drilling therethrough, and fluid being fed through said aperture and axial drilling into said pumping piston for filling said piston tube portion, means for dicharging the fluid filling said pumping piston tube portion through a discharge port to said hydraulic system when the fluid pressure in said hydraulic system is less than the fluid pressure in said pumping piston tube portion,

a reciprocable valve piston mounted within said pumping chamber in spaced apart aligned opposing relationship to said pumping piston, said valve piston including a tube portion which is normally seated against a cover when the pressure level in said hydraulic system is below that necessary to reduce fluid flow, a spring mounted within said valve piston tube portion in abutting engagement against said cover for biasing said valve piston towards said pumping piston, spring means mounted within said pumping piston tube portion and said spring means engaging one end of said valve piston, means for communicating compensating fluid pressure through an opening in said cover and into said valve piston tube portion for unseating said valve piston when the pressure in said hydraulic system reaches a predetermined level, and said valve piston being movable towards said pumping piston for engaging and following said pumping piston during its suction stroke when the pressure in said hydraulic system reaches said predetermined level whereby said valve piston limits or blocks fluid flow out of said discharge port.

Abstract

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