Override control system for a controlled slippable clutch

A control system for a drive train having an engine-driven power input member and auxiliary equipment coupled with the power input member for operation by the prime mover and having at least momentarily substantial power requirements relative to available power from the prime mover, a power output member and a hydraulically-operated slippable clutch operatively coupling the power input member and power output member in order to vary torque transmission therebetween, comprising

• a source of fluid under pressure,
• a control valve arranged in communication with said source and the hydraulically-operated clutch, said control valve including a spool means for alternately providing a fixed flow condition of fluid at a predetermined maximum pressure for fully engaging the clutch and a variable flow condition of fluid at an adjusted pressure lower than the predetermined maximum pressure for variably engaging the clutch,
• manually operable override means operatively coupled with said spool means in said control valve, said spool means in said control valve means including means responsive to operation of said override means for operating said spool means to alternately communicate to the clutch the predetermined maximum pressure in the fixed flow condition and the adjusted pressure in the variable flow condition, and
• adjustment means operatively coupled with said spool means in said control valve means for selectively establishing the adjusted pressure independent from response of said spool means to said override means, said adjustment means comprising a load piston means resiliently coupled with said spool means and a manual control element coupled with said load piston means to vary resilient force applied upon said spool means by said load piston means.