| 摘要 |
PROBLEM TO BE SOLVED: To provide spark plugs for internal combustion engine, having superior ignitability which as well as discharging sparkling gas, also in case of fouling, recover from the fouling by discharging along its surface and eliminating carbon on the tip of insulators with discharge sparks, and which have superior ignitability. SOLUTION: A spark plug for an internal combustion engine is composed of a first grounding electrode 5 to form a first discharge gap A with the tip side of a center electrode 4, and second grounding electrodes 6 and 7 to form a second discharge gap with the side of a center electrode 4. The first discharge gap A, the diameter direction thickness B of the tip side of an insulator 3, shortest distance C between the insulator 3 and the second grounding electrodes 6, 7, shortest distance D between a starting point X of the small diameter section of the center electrode 4 and edge of the inner circumference of the insulator, and a creepage discharge distance H on the insulator 3 at the spark discharging between the center electrode 4 and the second grounding electrode are respectively set within the fixed value ranges. According to this constitution, the task can be achieved.
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