US Patent 9303633 Over-speed control system and method

A hydraulic power control system includes an engine driving a variable displacement pump. The variable displacement pump is fluidly connected to a first passageway and a second passageway, and has a selectively variable displacement that is adjustable in response to a pump displacement command signal. A hydraulic motor fluidly connected to the first and second passageways operates by a flow of hydraulic fluid originating from the pump. A controller receives an engine speed signal and adjusts pump displacement based on the engine speed signal to reduce the rotation speed of the pump when an overrun condition is present.