Patent ID: 7841307

Claim:
A cooling fan drive system for a travel type working machine including an engine, an acceleration pedal for instructing a target engine rotational speed of said engine, a cooling fan for cooling an engine coolant, a hydraulic pump driven by said engine, and a hydraulic motor actuated by a hydraulic fluid delivered by the hydraulic pump for rotating the cooling fan, wherein said cooling fan drive system comprises: engine speed control means for controlling a rotational speed of said engine such that the rotational speed of the engine decreases to a low-speed idling speed when said acceleration pedal is not operated and the rotational speed of the engine increases from said low-idling speed to a maximum rotational speed in accordance with an operation amount of the acceleration pedal when the acceleration pedal is operated; temperature detecting means for detecting the temperature of the engine coolant; rotational speed detecting means for detecting the rotational speed of the engine; and cooling fan control means for controlling the rotational speed of the hydraulic motor on the basis of the detection values of the temperature detecting means and the rotational speed detecting means so that the rotational speed of the cooling fan is increased as the temperature of the engine coolant increase and the increase of the rotational speed of the cooling fan is limited not to exceed a limiting value that increases as the rotational speed of the engine increases when the travel acceleration in which the rotational speed of the engine increases is performed by operating the acceleration pedal; and said cooling fan control means controls the rotational speed of the hydraulic motor such that the rotational speed of the cooling fan decreases to a lowest rotational speed regardless of the temperature of the engine coolant, when the acceleration pedal is not operated and the rotational speed of the engine decreases to said low-speed idling speed.