| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug capable of reducing thermal load charged on an electrical porcelain and a main metal fitting of the spark plug even when the temperature of the spark plug increases. SOLUTION: A galvanized layer mainly containing zinc is formed on a surface of the main metal fitting 5. When the spark plug 100 is attached to an engine head 40, a male screw portion 52 of the metal fitting 5 is screwed with a female screw portion 43 of a plug hole 41 of the engine head 40. The engine head 40 is usually made of aluminum alloy, and the metal fitting 5 is made of steel material. Both coefficients of thermal expansion are different from each other, so that a clearance can occur between the both when the temperature increases with engine driving. However, zinc having high coefficient of thermal expansion thermally expands and deforms to plug the clearance, so that the adhesiveness between the engine head 40 and the metal fitting 5 is maintained, the heat conduction can be performed efficiently, and the thermal load charged on the spark plug 100 can be reduced. COPYRIGHT: (C)2006,JPO&NCIPI
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