| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug capable of improving pollution resistance and an ignition property by bringing the position of a first spark discharge gap close to the position of a second spark discharge gap. SOLUTION: By using a tip surface 15 of a tip 11 of an insulator 1 as a reference in the direction of an axial line O, a projection amount D by which a tip surface 22 of a tip 21 of a center electrode 2 is projected toward the tip direction is set to -0.5 to 0.3 mm. A noble metal chip 65 formed as a projection part from the inside surface 61 of a main grounding electrode 60 has at least a part having a diameter not smaller than 1.2 m and a height not smaller than 0.4 m. In addition, a distance of an in-air discharge space (space B) in an auxiliary spark discharge gap and a distance of a main spark discharge gap (space A) are set to 0.4-0.7 mm and 0.7-1.3 mm, respectively. By virtue of this structure, the first and second spark discharge gaps are brought close to each other and an ignition property including that in cleaning can be improved. COPYRIGHT: (C)2006,JPO&NCIPI
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