| 摘要 |
PURPOSE:To contrive to prolong the service life of a glow plug, by changing the polarity of current supplied to the glow plug by a current polarity changeover means provided between an AC power source and the glow plug at every times with respect to the operation of a key switch. CONSTITUTION:In case of a changeover means W. as a key switch S is turned on to a preheat contact prior to an engine start, current from an AC power source B is applied to respective glow plugs via a closed contact so as to heat respective cylinders. After an engine is completely explosed, the preheat contact of the key switch S is turned off so that the energizing to the glow plug G is stopped while a switch (a) is opened so that a solenoid device (b) is de- energized and a lever (c) is restored to the dotted line by the attractive force of a spring (b), then in the contact of the changeover means W the energizing polarity is changed over for the next energizing. Therefore, it is possible to suppress the physical and chemical change of the ceramic body forming the glow plug.
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