Hydraulic motor having multiple speed ratio capability

Abstract

A multiple speed ratio gerotor motor having first ( ) and second ( ) gerotor gear sets as the displacement mechanisms, and a commutating valve member ( ) of the well known type. In one embodiment (FIGS. ) there is provided a selector valve section ( ) disposed between the first and second gerotor gear sets, and in a low speed mode (FIG. A), fluid flows from the commutating valve member ( ) through the first volume chambers ( ), then through the selector valve section, then through the second volume chambers ( ). In a high speed mode (FIG. B), flow out of the first volume chambers ( ) is blocked by the selector valve section ( ), and fluid in the second volume chambers ( ) flows through the selector valve section to the case drain region ( ). In a free wheel mode (FIG. C), both the first and second volume chambers are open to case drain. In another embodiment (FIG. ), the selector valve section ( ) is disposed between the commutating valve member ( ) and the first gerotor gear set ( ), and can permit, or block, fluid communication to either gerotor gear set separately, thus providing three speed capability. In either embodiment, the relative speed ratios which can be achieved are determined by the relative axial lengths of the two gerotor gear sets, thus providing much greater flexibility in the choice of high-speed, low-torque speed ratios.