| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug using a high-melting-point metal chip mainly composed of Ir or the like and having an outer diameter D of an attaching screw part of 12mm or less, and solve a trouble such as horizontal jump, and insulation breakdown. SOLUTION: By making a thickness C at a tip part of an insulator 2 at 1.1 mm or more, withstanding voltage at the tip part of the insulator 2 is increased, so that intensity against insulation breakdown or the like can be improved. And also, by appropriately setting a value of a gas volume width E, generation of horizontal jump between a center electrode 3 and a main fitting 1 can be prevented very effectively. Since the spark plug is structured by an ignition part 31 with the high-melting-point metal chip mainly composed of Ir, even if an outer diameter A of the center electrode is set to be as thin as 2.0 mm or less to worsen heat length, ablation of the ignition part 31 dose not proceed very much. As a result, a space inside the main fitting 1 of the space is increased as much as the center electrode 3 is thinned, it is extremely effective to prevent horizontal jump of sparks. COPYRIGHT: (C)2007,JPO&INPIT
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