Control device of hydraulically driven fan

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 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, 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,
• 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,
• wherein the control means outputs the valve controlled variable to the control valve such that the control valve gradually reaches toward the target valve controlled variable with a prescribed variation per prescribed unit time.

A control method for a hydraulically driven fan using a control device of a hydraulically driven fan which is provided with a hydraulic motor, a hydraulically driven fan driven by the hydraulic motor and a control valve for varying a flow rate of hydraulic oil to be supplied to the hydraulic motor according to an applied valve controlled variable, in which a fan speed command is feedback-controlled according to a control deviation between a target fan speed and an actual fan speed of the hydraulically driven fan, the method comprising:

• a) calculating the target fan speed based on a temperature of cooling water of an engine, a temperature of oil of an oil cooler of the engine and a rotational speed of the engine, detecting the actual fan speed, and calculating a difference between the target fan speed and the actual fan speed as a control deviation,
• b) controlling the control valve by calculating a target valve controlled variable based on the target fan speed when the actual fan speed is zero, and calculating the valve controlled variable to gradually reach toward the calculated target valve controlled variable with a prescribed variation per prescribed unit time,
• c) calculating the fan speed command by using a proportional action based on the control deviation while the difference between the target valve controlled variable and an actual valve controlled variable is not smaller than a predetermined threshold,
• d) calculating the fan speed command by using the proportional action and an integral action based on the control deviation while the difference between the target valve controlled variable and the actual valve controlled variable is smaller than the predetermined threshold, and
• e) controlling the control valve by calculating the target valve controlled variable based on the calculated fan speed command and calculating the valve controlled variable to gradually reach toward the calculated target valve controlled variable with a prescribed variation per prescribed unit time.