| 摘要 |
PROBLEM TO BE SOLVED: To provide a sparkplug for an internal combustion engine having excellent productivity and a long life, in which a center electrode base material is securely bonded to an Ir alloy chip. SOLUTION: The sparkplug for the internal combustion engine includes a mounting fitting, an insulator, the center electrode 3, and a grounded electrode. The center electrode 3 is formed by bonding the Ir chip 32 in the form of an almost square pole to the tip face of the center electrode base material 31 in the form of an almost cylinder. The base material tip part 312 of the center electrode base material 31 has a diameter D2 smaller than the diameter D1 of a base material body part 311. When, among the diagonal lines of an almost quadrangle forming a cross sectional shape perpendicular to the axial direction in the Ir alloy chip 32, an circumscribed circle C<SB>A</SB>having the length of the longer diagonal line as its diameter is assumed, its diameter is set as A, the minimum inscribed circle C<SB>B</SB>inscribing at least two confronting sides of the almost quadrangle while having the almost same center as that of the circumscribed circle C<SB>A</SB>is assumed, and its diameter is set as B, this sparkplug has the relation of D1>A>D2>B. COPYRIGHT: (C)2007,JPO&INPIT
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