| 摘要 |
PROBLEM TO BE SOLVED: To prevent falling off of a noble metal tip by an inexpensive method in a spark plug in which difference of a melting point of the noble metal tip and that of an electrode is large, and enable to obtain a sufficient lifetime even in an engine with large wear and tear of discharge face of the noble metal tip. SOLUTION: The noble metal tip 60 in which a recess 61 is formed on a side face is resistance-welded to an earth electrode 40. At that time, the noble metal tip 60 pressurized at an electrode rod 200 invades into the inside of the locally melted earth electrode 40, and the noble metal tip 60 is embedded into the earth electrode 40. Thus, by means of mechanical engagement of the noble metal chip 60 and the electrode 40 in the recess 61, the falling off of the noble metal chip 60 can be prevented. Furthermore, because the diameter of the discharge face of the noble metal chip 60 can be made larger than the diameter of the portion embedded in the electrode 40, the sufficient lifetime can be obtained even in the engine with large wear and tear of the discharge face of the noble metal chip 60. COPYRIGHT: (C)2004,JPO
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