| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug which has almost the same flame extension property as a spark plug of which a cross sectional shape of a ground electrode is circular, even against a main metal fitting with which only a ground electrode of a small thickness having a small thickness of a top end face can be connected, and moreover has an ultra fine precious metal chip and an effective thermal conduction of the ground electrode. SOLUTION: The sparkplug is provided with a plane face 401 formed in an extension direction of the ground electrode and on the both ends of the plane face 401, an arc part 402 is formed, and this arc part 402 is extended virtually to draw a circular arc VX nearer the side of the central electrode 10 than the plane face 401, and the top end face of the external chip is projected to the side of the central electrode 10 over the crossing point of this virtually extended circular arc VX. Thus, a flame-out due to the ground electrode 40 can be made minimal and an excellent flame growing property is obtained and furthermore, a thermal conduction is excellent. COPYRIGHT: (C)2007,JPO&INPIT
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