| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug improved in detection capability of an ion current. SOLUTION: This spark plug is composed by facing a tip surface of a grounding electrode 40 to a side surface of a center electrode 30. The area of the tip surface of the grounding electrode 40 is set to 0.07-1.13 mm<SP>2</SP>. By setting the area of the tip surface of the grounding electrode 40 to 1.13 mm<SP>2</SP>or less, electric field intensity across a spark discharge gap<SP></SP>is enhanced to lower a discharge voltage; an arc voltage keeping time, that is, a flame growth time is extended; a combustion residue on the surface of the center electrode is burnt to increase the surface area of a healthy part of the center electrode so that the detection capability of an ion current is improved. By setting the area of the tip surface of the grounding electrode 40 to 0.07 mm<SP>2</SP>or more, the improvement effect of the ion current detection capability can be provided while keeping a practically sufficient level of oxidation wear resistance of the grounding electrode 40. COPYRIGHT: (C)2004,JPO
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