Patent ID: 7225721

Claim:
A hydraulic motor comprising a cam and a cylinder block that are suitable for rotating one relative to the other about an axis of rotation, the cam comprising a plurality of cam lobes each of which has a rising ramp and a falling ramp, and the cylinder block having a plurality of cylinders slidably receiving pistons that are suitable for co-operating with the cam, the motor further comprising a fluid distributor that is constrained to rotate with the cam about the axis of rotation and that includes distribution ducts connected via distribution orifices to a feed or to a discharge and suitable for communicating with the cylinders while the cylinder block and the cam are rotating relative to each other, each distribution orifice being disposed in register with a ramp of a cam lobe such that a cylinder whose piston is co-operating with a rising ramp can be connected to the feed and such that a cylinder whose piston is co-operating with a falling ramp can be connected to the discharge, the instantaneous angular positions in which the pistons co-operate with the cam while the cylinder block and the cam are rotating relative to each other being such that the motor is a substantially constant-velocity motor; wherein, in any relative position of the cylinder block and of the cam, there is at least one cam lobe that is unused and with which no piston co-operates, and wherein the angular spacings between consecutive cylinders are mutually different and differ from a multiple of the smallest angular spacing between consecutive cylinders, said angular spacings being determined so that the resultant of the forces exerted by the pistons on the cam is small or substantially zero.