FAN CONTROL SYSTEM WITH ELECTRO-HYDRAULIC VALVE PROVIDING THREE FAN MOTOR OPERATIONAL POSITIONS

摘要

A fan control system (25) includes a tank (30), a pump (32), a hydraulic motor (34), a fan (15), and a control valve (40, 140). The control valve (40, 140) is adapted to selectively direct a flow of hydraulic fluid from the pump (32) through the control valve (40, 140) into a pressure control chamber (81) of the hydraulic motor (34) or from the pressure control chamber (81) to the tank (30) to vary the control pressure therein to move the hydraulic motor's swashplate (85) between forward and reverse positions. The control valve (40, 140) is adapted to selectively direct hydraulic fluid from the pump (32) into the pressure control chamber (81) such that the control pressure therein is pressurized to an idle pressure to move the swashplate (85) to an intermediate position between the forward and reverse positions such that the output shaft (75) rotates at an idle rate which is less than the rotational speed of the output shaft (75) when in the forward mode.