Patent ID: 8459959

Claim:
A control device of a hydraulically driven fan provided with a hydraulic motor, a hydraulically driven fan driven by the hydraulic motor and a control valve for varying a flow rate of a hydraulic oil supplied to the hydraulic motor according to a valve controlled variable, wherein a fan speed command is feedback-controlled in a manner that at least a proportional action and an integral action are used with respect to a control deviation between a target fan speed and an actual fan speed of the hydraulically driven fan, the control device comprising: first command value calculation means for calculating the fan speed command by using, from a proportional term and an integral term, only the proportional term only while a difference between a target valve controlled variable and an actual valve controlled variable is not smaller than a predetermined threshold, wherein the integral term is an intergration of the control deviation between the target fan speed and the actual fan speed, second command value calculation means for calculating the fan speed command by using both of the proportional term and the integral term while a difference between the target valve controlled variable and the actual valve controlled variable is smaller than the predetermined threshold, target valve controlled variable calculation means for calculating the target valve controlled variable of the control valve based on the calculated fan speed command, and control means for outputting the valve controlled variable to the control valve such that the control valve reaches the target valve controlled variable.