Patent ID: 6321867
Filing Date: 2001-11-27
Classification: B62D,F16H

Abstract:
A hydrostatically driven tractor for sustaining draft loads comprising:a high torque rise engine mounted on a wheeled frame to provide operative power;a variable speed hydrostatic pump driven by said engine and providing operative power to said wheeled frame, said hydrostatic pump having a swash plate movable through variable angular positions to vary the displacement of said hydrostatic pump and thus the power provided to said wheeled frame, said swash plate being operatively connected to hydraulic servos for effecting the movement of said swash plate;an implement hydraulic circuit for providing hydraulic power to an implement connected to said tractor and a first source of hydraulic fluid under a first pressure; anda charge hydraulic circuit providing hydraulic fluid under pressure to said servos, said charge hydraulic circuit including:a charge pump operatively connected to said hydrostatic pump to be driven therewith by said engine, said charge pump providing a flow of hydraulic fluid under a second pressure through an output line for operating said servos, said second pressure normally being lower than said first pressure;a valve associated with said charge pump outlet line for controlling the flow of hydraulic fluid to said servos;a supplemental flow line interconnecting said implement hydraulic circuit with said charge pump outlet line; anda reducing valve in said supplemental flow line, said reducing valve being operable to reduce said first pressure to a predetermined operating pressure, said reducing valve further being operable to prevent the flow of hydraulic fluid from said charge pump outlet line into said implement hydraulic circuit and to limit the flow of hydraulic fluid from said implement hydraulic circuit into said charge pump outlet line when said second pressure is less than said predetermined operating pressure for said servos, whereby adequate charge pressure and fluid flow to said servos are maintained even when the speed of said engine falls off, avoiding stalling of said engine under high draft loads.