| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine which has a grounding electrode of a circular cross-section and can control wearing of the electrode due to oxidation corrosion and sparking wear and can improve a durability of the grounding electrode and moreover can prolong a life of the spark plug. SOLUTION: The spark plug 1 is provided with an insulator 2 with an axial hole 4, a central electrode 5 inserted into the axial hole 4, a main metal fitting 3 provided around an outer circumference of the insulator 2 and a grounding electrode 27 provided on the main metal fitting 3. A precious metal chip 31 is jointed on a top end of the central electrode 5 and between the precious metal chip 31 and the grounding electrode 27, there is formed a spark discharging gap 33. A cross-section of the grounding electrode 27 is circular and a surface of the top end portion of a base metal matrix composing the grounding electrode 27 is covered by a precious metal covered portion 34 composed of at least either of the precious metal or an alloy containing the precious metal. COPYRIGHT: (C)2008,JPO&INPIT
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