Patent ID: 7967574

Claim:
A pump or hydraulic motor comprising a drive shaft with a first axis of rotation rotatably mounted in a housing, first plungers connected to the shaft and rotatable around the first axis of rotation, a port plate mounted in the housing and provided with a port plate surface with a high-pressure port at a first radius and a low-pressure port at the first radius each connected to a respective pressure line, a second axis of rotation which intersects the first axis of rotation in a centre plane, first cylinders rotatable around the second axis of rotation and sealingly fitted around the first plungers for forming chambers with the first plungers, each chamber having a volume that in a full rotation of the first plungers and the first cylinders changes according to a stroke volume, a plurality of cylinder channels, each cylinder channel rotatable with a respective first cylinder and connected to a respective chamber and ending in a valve surface, wherein the valve surface abuts and is rotatable relative to the port plate surface for connecting the chambers through respective cylinder channels with the high-pressure port or the low-pressure port, whereby a bearing supports each port plate in the housing, wherein by rotating the port plate in the housing around a third axis of rotation the stroke volume can be changed using a port plate positioning drive, wherein the third axis of rotation is perpendicular to the centre plane and intersects the first axis of rotation and the second axis of rotation, wherein the port plate positioning drive is located in the centre plane and exerts a force on the port plate and comprises a first hydraulic actuator and a second hydraulic actuator acting on the port plate in a direction parallel to the second axis of rotation and counteracting each other.