| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug capable of being prevented from causing bending breakage when subjected to impact from the outside. SOLUTION: In a spark plug of this invention, a main metallic shell 50 and an insulating porcelain 10 are integrally fixed with an outer packing 6, an inner packing 7 and talc 9 tightened inside by bending the top portion 60 of the tightening portion 53 of the main metal shell 50. The outer packing 6 is shaped in a ring with a circle cross-section, and the minimum inner diameter portion of the tightening portion 53, which is most close to the outer circumferential surface 17 of the trunk portion 18 of the insulating porcelain 10, is positioned so as to lie on the center line of the outer packing 6 or to lie inside the center line in radial direction with respect to the axis O. Further, the tightening portion 53 does not contact to the insulating porcelain 10, but the outer packing 6 abuts against the insulating porcelain 10. By making the hardness of the outside packing 6 lower than that of tightening portion 53, the insulating porcelain 10 is prevented from causing bending breakage when subjected to impact from outside. COPYRIGHT: (C)2006,JPO&NCIPI
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