| 摘要 |
PROBLEM TO BE SOLVED: To secure the electric continuity between a spark plug and an ignition coil, when detecting an ion current, without covering the surface of a terminal part of the spark plug with an oxidation resistant conductive coating film. SOLUTION: In a general spark plug 14, since the terminal part connected to the secondary side of the ignition coil 11 is formed of an iron-based material, the surface of its terminal part is oxidized, and an insulating oxide film is formed, and this insulating oxide film becomes the cause of causing electric continuity failure when detecting the ion current. As this countermeasure, Zener voltage of a Zener diode 15 is set to 200 V or more so that DC ion detecting voltage charged to an ion detecting power capacitor 17 is set to 200 V or more. Thus, even when flying sparks do not exist (or before the flying sparks), the electric continuity between the spark plug 14 and the ignition coil 11 can be secured, by breaking insulating performance of the insulating oxide film of the terminal part surface of the spark plug 14 by the DC ion detecting voltage of 200 V or more. COPYRIGHT: (C)2008,JPO&INPIT
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