Abstract

A rotary actuator is operable under the influence of fluid pressure to rotate a driven member. The rotary actuator includes a drive member which extends into a chamber in a housing. Helical splines interconnect a piston and the drive member to rotate the drive member upon axial movement of the piston in the chamber. The piston is held against rotary movement relative to the housing in one embodiment by a pair of rollers that engage tracks disposed on opposite sides of the piston and in another embodiment by a corresponding oval-shaped configuration of a portion of the piston and an internal portion of the chamber in the housing. In one embodiment of the invention, a rack gear on the piston rotates a pinion to actuate a valve and restrict fluid flow to the chamber when the piston is approaching an end-of-stroke position. A one-way clutch may be connected with the drive member so that the driven member is only rotated in one direction rather than being oscillated upon back and forth movement of the piston.