Patent ID: 8132868

Claim:
A hydraulic regenerative braking system for a vehicle, the vehicle including a shaft connected to at least one wheel, the system comprising: a hydraulic machine operable as a pump configured to be driven by the shaft, thereby increasing the pressure of fluid flowing through the hydraulic machine, the hydraulic machine being further operable as a motor configured to be driven by pressurized fluid, thereby providing torque to the shaft, the hydraulic machine including: a housing including a high pressure fluid port and a low pressure fluid port, a plurality of radial pistons, each of the pistons being configured to reciprocate within a corresponding cylinder in the housing and having a corresponding piston stroke, the pistons pumping fluid when the hydraulic machine is operating as a pump, and providing torque when the hydraulic machine is operating as a motor, each of the pistons including a corresponding cam follower, a cam disposed within the housing, and having a plurality of lobes configured to cooperate with the cam followers to translate rotational motion of the cam into linear motion of the pistons when the hydraulic machine is operating as a pump, and to translate linear motion of the pistons into rotational motion of the cam when the hydraulic machine is operating as a motor, and a valve plate including a plurality of apertures therethrough, at least one of the apertures communicating with the high pressure fluid port and at least one other of the apertures communicating with the low pressure fluid port, the valve plate being configured to connect at least one of the cylinders with the high pressure fluid port and at least one other of the cylinders with the low pressure fluid port, the valve plate being movable relative to the housing to effect a first transition to disconnect the at least one cylinder from the high pressure fluid port and connect it with the low pressure fluid port, and to effect a second transition to disconnect the at least one other cylinder from the low pressure fluid port and connect it with the high pressure fluid port, the valve plate being movable such that the first and second transitions can be effected at a plurality of piston positions within a corresponding piston stroke, thereby facilitating variable displacement operation of the hydraulic machine.