| 摘要 |
PROBLEM TO BE SOLVED: To reconcile simplified processability of an Ir alloy chip and security of bondability in laser welding in a spark plug formed by bonding the Ir alloy chip to opposing portions of a center electrode and a ground electrode. SOLUTION: The spark plug has an insulator 20 held within a housing 10. An end portion of the center electrode 30 held within the insulator 20 and an end portion of the ground electrode 40 are opposed to each other with a discharge gap 70 interposed in between. Ir alloy chips 50, 60 each made of a bar-shaped Ir alloy are respectively bonded to the portions of the center electrode 30 and the ground electrode 40 facing toward the discharge gap 70. A cross section perpendicular to the axis of the Ir alloy chips has an imperfect circular shape. In this cross section, where a circumscribed circle having the greatest diameter A among virtual circles tangential to at least three points along the outline of the cross section is assumed and an inscribed circle having the same center as the circumscribed circle and having the greatest diameter B is assumed, the ratio B/A between the two diameters A and B is 0.8 or greater and less than 1.0. COPYRIGHT: (C)2004,JPO
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