Wheel creep control of hydraulic hybrid vehicle using regenerative braking

A system according to this invention opposes creep in a hydraulic hybrid motor vehicle. An accumulator contains fluid at high pressure, and a reservoir contains fluid at lower pressure. An engine produces positive torque at the wheels during an engine idle condition, and a pump/motor, driveably connected to the wheels and the engine, has a variable volumetric displacement pumps fluid to the accumulator from the reservoir. A control system determines a magnitude of negative torque transmitted from the wheels to the pump/motor that would exceed the magnitude of positive torque, determines the volumetric displacement of the pump/motor corresponding to the magnitude of negative torque, changes the displacement of the pump/motor to the required displacement, and operates the pump/motor as a pump driven by negative torque from the wheels to pump fluid from the reservoir to the accumulator.