| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine capable of preventing degradation of ignitability by suppressing influx inhibition of an air-fuel mixture, and of improving durability. SOLUTION: This spark plug 100 is provided with a main fitting 1, an insulator 2, a center electrode 3 and a ground electrode 4. The ground electrode 4 is provided with: a cross-sectionally nearly-oblong base part 41 joined to a tip surface of the main fitting 1 and having a certain width; a cross-sectionally round narrow part 42 located on the tip side relative to the base part 41; and a tapered part 43 located between the base part 41 and the narrow part 42 and having a cross-sectional shape gradually changing along the longitudinal direction. The cross-sectional area of the base part 41 is not smaller than 3 mm<SP>2</SP>, and the width (diameter D) of the narrow part 42 is 1.0-2.0 mm. A partγout of the narrow part 42 closest to the base part 41 side is set to be located between a tip surfaceαof the insulator 2 and a tip surfaceβof the center electrode 3 in the axial direction. COPYRIGHT: (C)2007,JPO&INPIT
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