Hydrostatic transmission check valves with automatic unloading

Claim 1

In a vehicle having an engine and traction wheels with a hydraulic transmission and a hydraulically actuated implement means operatively connected there-between including a pump and motor, first conduit means connecting the pump outlet with the motor inlet and second conduit means connecting the motor outlet with the pump inlet so that the pump supplies fluid under pressure to drive the motor, and a variable angle swash plate mechanism in the pump operable for varying the transmission ratio of the transmission and for controlling direction of fluid flow between pump and motor according to desired vehicle movement, and a fluid charge pump driven by the engine and communicatively connected to a fluid source, the combination therewith of automatic, valving means communicatively interconnectable between said charge pump and the first and second conduit means interconnecting said pump and motor and operable in one position for porting fluid flow from said charge pump selectively to the first and second of said conduit means, and in another position for by-passing fluid between the said first and second conduit means, said automatic valve means including housing means having first and second power chamber means, said first power chamber being controlled by pressurized fluid from said charge pump means, said second power chamber being controlled by said pump and motor means, whereby pressure changes in said power chamber means cause movement of said valve device means resulting in communicatively connecting or disconnecting said charge pump means and said pump and motor means.