| 摘要 |
PURPOSE:To lower the average temperature of a glow plug and reduce the operation frequency of relay switches by transferring the relay switches in response to the detected temperature for a short time in serial connection when the engine temperature is low and for a long time when it is high. CONSTITUTION:A control unit 7 turns the first relay switch 2 on and the second relay switch 4 off initially after a key switch 5 is turned on, connects a glow plug 1 in parallel, and applies the battery voltage as it is to perform quick preheating. When the preset temperature is attained and the start signal is turned off, it turns the first relay switch 2 off and the second relay switch 4 on and connects the glow plug 1 in series, and about a half of the battery voltage is applied to start a heat reserving state. Next, when the start signal is turned on, a shorter time in serial connection is set as the temperature becomes lower based on the detected temperature of a water temperature sensor 6, and individual relay switches are transferred from the serial connection to the parallel connection when this time elapses. When the preset temperature is attained, the serial connection state is resumed. Accordingly, the average temperature of the glow plug 1 is lowered, and the operation frequency of the relay switches is reduced.
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