Patent ID: 8162621

Claim:
A hydraulic machine arrangement including a hydraulic machine having high and low pressure sides and being operable in at least one of two modes, a first mode being a pump mode, wherein the hydraulic machine can be driven by mechanical energy to increase the pressure of fluid flowing through the hydraulic machine, and a second mode being a motor mode, wherein the hydraulic machine can be driven by pressurized fluid to provide output torque, the hydraulic machine arrangement comprising: a port housing including a high pressure fluid port on the high pressure side of the hydraulic machine and a low pressure fluid port on the low pressure side of the hydraulic machine; a cylinder block in fluid communication with the port housing and including a plurality of cylinders therein; a plurality of radial pistons, each of the pistons being configured to reciprocate within a corresponding cylinder in the cylinder block, the pistons pumping fluid when the hydraulic machine is operating in the pump mode, and providing torque when the hydraulic machine is operating in the motor mode, each of the pistons including a corresponding cam follower; a cam having a plurality of lobes configured to cooperate with the cam followers to translate relative rotational motion between the cam and the cylinder block into linear motion of the pistons when the hydraulic machine is operating in the pump mode, and to translate linear motion of the pistons into relative rotational motion between the cam and the cylinder block when the hydraulic machine is operating in the motor mode; 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 and the cylinder block being movable relative to each other 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 relative to the cam 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, the valve plate being further configured such that during the first transition, the at least one cylinder is partially connected to the low pressure fluid port before it is fully disconnected from the high pressure fluid port, thereby providing overlap between oncoming and offgoing connections of the at least one cylinder with the high and low pressure fluid ports, and inhibiting occurrence of a hydraulic lock.