Piston pump assembly having load responsive controls

Claim 1

In a piston pump assembly having a housing, an angularly adjustable swash plate for controlling the volume of fluid discharged from the pump, a servo valve having a biasing means and being positioned in contact with the swash plate at a location sufficient for biasing the swash plate toward one of a maximum or minimum fluid discharge position, and means positioned in contact with the swash plate at a location sufficient for biasing the swash plate toward the other fluid discharge position, said means being in communication with fluid discharging from the pump for biasing the swash plate toward the other fluid discharge position, said means being in communication with fluid discharging from the pump for biasing the swash plate in response to the pressure of the discharging fluid, said discharge pressure being reduced, the improvement comprising: means for controllably reducing operating load pressures and forming a modified load-pressure control signal, passing the modified load-pressure control signal to the servo valve, and imparting a biasing force on the servo valve in response to said modified load-pressure control signal, said modified load pressure signal being of a value less than the value of the reduced discharge pressure acting upon the biasing means of the swash plate.