Cooling fan drive system for travel type working machine

A cooling fan drive system for a travel type working machine having an engine, an acceleration pedal for instructing a target engine rotational speed of said engine and a hydraulic pump of a working hydraulic system driven by the engine, said cooling fan drive system including a cooling fan for cooling a coolant of the engine and a hydraulic fluid of the working hydraulic system, a hydraulic pump driven by the engine, and a hydraulic motor actuated by the 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;
• first temperature detecting means for detecting the temperature of the engine coolant;
• second temperature detecting means for detecting the temperature of the hydraulic fluid of the working hydraulic system;
• 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 first and second temperature detecting means and the rotational speed detecting means so that the rotational speed of the cooling fan is increased as any one of the temperature of the engine coolant and the hydraulic fluid of the working hydraulic system increases, 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 temperatures of the engine coolant and the hydraulic fluid of the working hydraulic system, when the acceleration pedal is not operated and the rotational speed of the engine decreases to said low-speed idling speed.

A cooling fan drive system for a travel type working machine having an engine, an acceleration pedal for instructing a target engine rotational speed of said engine, a hydraulic pump of a working hydraulic system driven by the engine and a travel device driven through a torque converter by the engine, said cooling fan drive system including a cooling fan for cooling a coolant of the engine, a hydraulic fluid of the working hydraulic system and an operating oil of the torque converter, a hydraulic pump driven by the engine and a hydraulic motor actuated by the 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;
• first temperature detecting means for detecting the temperature of the engine coolant;
• second temperature detecting means for detecting the temperature of the hydraulic fluid of the working hydraulic system;
• third temperature detecting means for detecting the temperature of the operating oil of the torque converter;
• 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 first, second and third temperature detecting means and the rotational speed detecting means so that the rotational speed of the cooling fan is increased as any one of the temperature of the engine coolant, the hydraulic fluid of the working hydraulic system and the operating oil of the torque converter increases 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, the hydraulic fluid of the working hydraulic system and the operating oil of the torque converter when the acceleration pedal is not operated and the rotational speed of the engine decreases to said low-speed idling speed.

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;
• first engine speed detecting means for detecting the target rotational speed of the engine;
• second engine speed detecting means for detecting the actual 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 first and second engine speed detecting means so that the rotational speed of the cooling fan is increased as the temperature of the engine coolant rises up and the increase of the rotational speed of the cooling fan is limited not to exceed a limiting value that is lowered as the rotational speed difference between the target rotational speed and the actual 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.