| 摘要 |
PROBLEM TO BE SOLVED: To prevent pushing breakage of an insulation body and improve wear resistance as well as improving thermal transmission of a center electrode. SOLUTION: The spark plug 1 is provided with an insulating insulator 2 having an axial hole 4 of which top end part has a constant inner diameter and a center electrode 5 or the like which is inserted in the axial hole 4. The center electrode 5 has a flange part 35 which is widened to a base end side, and has a flange bottom part 36 at the top end side of the flange part 35. In the flange bottom part 36, an electrode large diameter portion 37, an electrode small diameter portion 38, and a thin diameter portion 39 having respectively a certain outer diameter are formed in order from the base end. In the constant diameter difference region in which the diameter difference between the outer diameter of the flange bottom part 36 and the inner diameter of the axial hole 4 is constant, when the diameter difference between the outer diameterϕA of the flange bottom part 36 and the inner diameterϕB of the axial hole 4 in the longest constant diameter difference region DL1 is made cb, and the diameter difference between the outer diameterϕD of the flange bottom part 36 and the inner diameterϕB in the second longest constant diameter difference region DL2 is made cf, the value obtained by subtracting the diameter difference cb from the diameter difference cf is larger than 0 mm and 0.06 mm or less. COPYRIGHT: (C)2009,JPO&INPIT |
