| 摘要 |
PROBLEM TO BE SOLVED: To provide a technology which can improve a durability of an electrode and control an increase in discharging voltage. SOLUTION: A spark plug includes a central electrode 20 extending in an axial direction of the spark plug, a central electrode precious metal chip 90 adhered to a top end portion of the central electrode, and a grounding electrode 95 having an end surface to face a side surface of the central electrode precious metal chip. When an area of the end surface of the grounding electrode is Sa, and a shortest distance form the end surface of the grounding electrode to a side surface of the central electrode precious metal chip is G, and an area, in which crossing surface specified by a crossing of a virtual plane surface which has a distance 1.05G from the end surface of the grounding electrode and is parallel with the end surface of the grounding electrode and the central electrode precious metal chip is projected to the end surface of the grounding electrode and the end surface and the crossing surface are overlapped, is Sb, the spark plug satisfies a relation formula of Sb/Sa≥0.75. COPYRIGHT: (C)2009,JPO&INPIT
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