Electrically controlled hydraulic clutch for a front wheel drive

Claim 1

In a tractor having front wheels, rear wheels, an engine and drive means connecting the engine to the front and rear wheels, a front wheel drive system comprising: a hydraulically actuated clutch including a hydraulic actuator operative to engage said clutch when it is supplied pressurized fluid, said clutch being disengaged when pressurized fluid is exhausted from said actuator, a reservoir, a pump connected in fluid receiving relation to said reservoir, a clutch control valve including a housing having an input port connected in fluid receiving relation to said pump, a clutch port connected in fluid delivery relation to said hydraulic actuator of said clutch, a sump chamber connected to said reservoir, a first cylindrical bore and a second bore aligned with said first bore, a fluid flow control spool reciprocatively mounted in said first bore for axial movement between a clutch engaged position in which said input port is connected to said clutch port and a clutch disengaged position in which said clutch port is connected to said sump chamber, spring means biasing said spool toward its clutch disengaged position, an accumulator piston in said second bore and defining therewith an accumulator chamber, and axial thrust transmitting means operatively interposed between said accumulator piston on said control spool, and a pilot hydraulic circuit operable to selectively connect said pump with said accumulator chamber including a solenoid pilot valve having a fluid connection to said reservoir, said solenoid pilot valve including a pilot valve element shiftable between a clutch engaging position in which said pump is connected in fluid delivery relation to said accumulator chamber and a clutch disengaging position in which the accumulator chamber is connected to said reservoir, and a fluid flow restrictor in said circuit, said restrictor and accumulator chamber being proportioned in relation to said spool to effect relatively slow movement of the latter from its clutch disengaged position to its clutch engaged position when said pilot valve element is moved to its clutch engaging position whereby a gradual pressure rise in said clutch actuator is effected.