Control device for hydraulically driven fan

A control device for a hydraulically driven fan, comprising:

• a cooling fan rotated by a hydraulic motor and carrying out a ventilation for cooling a working fluid that is involved in an operation of an engine;
• first detecting means for detecting a temperature of the working fluid;
• adjusting means for adjusting a rotating speed of the hydraulic motor in correspondence to a result of detection of the first detecting means;
• second detecting means for detecting whether a working mechanism actuated by the engine is in a stopped state by determining whether a working machine lever has been operated;
• and
• control means for controlling an operation of the adjusting means in correspondence to a result of detection by the second detecting means thereby adjusting the rotating speed of the hydraulic motor in such a manner that a resonance between the cooling fan and the engine is suppressed, wherein if the working machine lever has not been operated and a temperature of the working fluid is lower than a predetermined value, the control means causes the adjusting means to operate in such a manner that a rotating speed of the cooling fan is lowered;
• wherein, when at least one of the working machine levers is switched to an operating position from a state in which all the working machine levers are at a neutral position, the control means controls the operations of the engine and the hydraulic motor in such a manner that the rotating speed of the engine is immediately increased from a low rotating speed range to a normal range, and that the rotating speed of the cooling fan is gradually increased in a predetermined time.