SPARK PLUG FOR INTERNAL COMBUSTION ENGINE

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PROBLEM TO BE SOLVED : To provide a spark plug for an internal combustion engine, wherein deterioration in the exfoliation-resistant performance or other property of a rare-metal chip that is caused by a residual stress due to bending of a grounding electrode can be prevented. SOLUTION : A rare-metal chip 32, which is protruding from a front edge face 27s of a grounding electrode 27, forms a gap between itself and a front edge of a central electrode 5. The grounding electrode 27 includes a thick portion 271 provided on a base end side, a thin portion 272 provided on a front end side, and a stepped portion 273 provided on an inner peripheral surface side between the thick portion 271 and the thin portion 272, wherein the rare-metal chip 32 is welded to a flat surface 27f that is an inner peripheral surface on the thin portion 272. When viewed from a side surface of the grounding electrode 27, the rare-metal chip 32 is embedded, thereby forming a bulge portion 51 consisting of the same metal composition as the grounding electrode 27. A relationship of [a protruding height H1 of the rare-metal chip 32 from the inner peripheral surface on the thin portion 272]≥[a protruding height H2 of the bulge portion 51 from the inner peripheral surface on the thin portion 272] is satisfied. COPYRIGHT : (C)2009, JPO&INPIT