| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug having a reduced diameter stably sparking at a regular spark discharge plug when not sputtering, securing an ignition property even when sputtering and creeping discharge is generated. SOLUTION: A spark plug has a mounting screw 12 of a mounting fitting 10 of M10 or smaller, and satisfies relations; (X + 0.3Y + Z)/G≥2, Y1 (mm)≥1, W/Z≥4 and 1.25≤Z (mm)≤1.55, wherein X is a distance between insulating glass 20 and a center electrode 30 at the tip 21 of the glass 20, Y is a creeping distance of the surface of the glass 20 outside the fitting 10, Y1 is a protrusion amount of the glass 20 from the fitting 10, Z is a pocket gap, G is a distance of a spark discharge gap 50, and W is a length on the surface of the glass 20 up to a site at which a distance between the glass 20 and the fitting 10 inside the fitting 10 becomes G or less. COPYRIGHT: (C)2005,JPO&NCIPI
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