To suppress drive of a ventilation fan when electric generation power is small, by a simple constitution, when ventilation in a cabin using a solar battery is performed.
When the electric generation power of the solar battery is reduced to stop the ventilation fan, a micro-computer sets an interval time TM to a time T1, resets a count value C and stars a timer (step 120-124). Thereafter, when the time T of the timer reaches the interval time TM, the ventilation fan is driven to detect a current value I, and it is confirmed whether the current value I exceeds a reference value Is (step 126-132). At this time, when the current value I does not reach the reference value Is, the count value C is counted up, and when the count value C reaches the defined number Cs, it is updated so as to lengthen the interval time TM (step 134-138). When such a state that the electric generation power is small is continued, the drive frequency of the ventilation fan is suppressed and reduction of durability can be prevented.
Kato Kazunori
Katsuichi Nishimoto
Hiroshi Fukuda