To enhance the reliability in a heating capacity variable type heating unit which is operated by the driving force of an external driving source and also having a minimum heating capacity, not a zero.
A solenoid on-off valve 45 is interposed on a heating channel 131 lying between a viscous heater 22 and a radiator 21. In addition, a bypass channel 46 is connected to this heating channel 131 between the viscous heater 22 and the radiator 21 so as to have a parallel relation with the solenoid on-off valve 45. A passing sectional area in the bypass channel 46 is made to be smaller than that at the side of the heating channel 131. In a state that a heating switch 44 is turned off, the solenoid on-off valve 45 is closed, whereby water being delivered out of the viscous heater 22 flows in the bypass channel 46.
SUZUKI SHIGERU
MORI HIDEFUMI
HIROSE TATSUYA
