Hydraulic swing motor

Claim 1

A hydraulic swing motor, comprising a casing having an annular center portion and two side plates closing opposite ends of said annular center portion; a shaft journalled in said side plates and being rotatable in said center portion, said shaft defining with said casing a working chamber; vane means subdividing said working chamber into two compartments and including a fixed first vane and a second vane mounted on said shaft for performing a swing stroke having two end positions; a pair of hydraulic fluid inlet and outlet passages each having a first end portion commmunicating with the outside of said chamber and a second end portion, each passage having a port connecting the respective end portion with one of said compartments and positioned to be closed by said second vane as the same approaches the respective end positions; a pair of throttling valves each interposed in one of said passages and each communicating with one of said compartments intermediate said first vane and the respective end positions of said second vane for permitting only throttled escape of hydraulic fluid from the respective compartment subsequent to closing of the port in said compartment by said second vane; and a pair of relief valves, both mounted within one of said side plates of said casing and each communicating with one of said compartments for limiting the maximum fluid pressure therein whereby, due to the pressure buildup resulting from the throttled escape of fluid subsequent to the closing of a port, a rapid braking of the swing stroke of said second vane occurs, but without danger of damage to said motor since the pressure build-up is quickly limited by the respective relief valve due to the location thereof within said one side wall close to the source of increased pressure and the point of initiation of said maximum fluid pressure.