Abstract

A hydraulic device with fluid pockets formed by a gerotor gear set, including a rotatable and orbital rotor, has a special commutation valve structure for valving fluid flow to and from the fluid pockets in timed relation to the movement of the rotor. The gear set is disposed between a pair of housing members. One end face of the rotor and the face of the adjacent housing member cooperate to define separate pressure areas which are continuously communicated with high and low fluid pressures, respectively. The other end face of the rotor has a circular array of openings which number twice the number of teeth of the rotor. A series of passages extending through the rotor communicate all of the openings of the circular array with the separate pressure areas, alternate openings being communicated with areas at different pressures. The face of the housing member adjacent the other end face of the rotor has radially extending, generally T-shaped recesses facing the fluid pockets. The circular array of openings in the rotor and the recesses in the housing member cooperate to valve flow and direct flow to and from the pockets at the interface of the rotor and housing member as the rotor rotates and orbits.