Speed override control for hydraulic motors

Claim 1

A hydraulic control system including speed override control means for rotary output radial piston hydraulic motors, comprising: a primary source of pressurized fluid; means including a directional control valve and conduit means for selectively directing fluid from said source to a reversible multi-speed hydraulic motor; a pilot operated speed-control valve operative to selectively control the flow of fluid in said conduit means to thereby selectively control the speed of said motor wherein said speed-control valve is a two-position valve operative in a first position to direct pressure fluid sequentially to all of said pistons for low-speed high-torque operation, and operative in a second position to direct pressure fluid to one-half of said pistons for high-speed operation; and an override control valve responsive to fluid pressure in said conduit means to alter said pilot signal to override said speed-control valve; a speed selector valve is operative to selectively control said speed-control valve by means of a pilot signal; said conduit means includes a first conduit for directing said fluid to one side of said motor for operation of said motor in one direction and a second conduit for directing said fluid to the other side of said motor for reverse operation thereof; and each of said first and second conduits includes a branch conduit controlled by said speed-control valve for controlling the speed of said motor.