| 摘要 |
PROBLEM TO BE SOLVED: To maintain excellent ignitability for a long time by preventing a rapid progress of channeling while attaining improvement of ignitability.SOLUTION: An ignition plug 1 comprises an insulator 2 including a shaft hole 4, a center electrode 5 and a ground electrode 27 in which a through hole 28 is formed, and generates spark discharge between the center electrode 5 to which a voltage of positive polarity is applied, and the ground electrode 27. The shaft hole 4 includes a large diameter part 4A and a small diameter part 4B which is positioned closer to a front end than the large diameter part 4A and of which the inner diameter is smaller than that of the large diameter part 4A. A distal end of the center electrode 5 is separated from an inner peripheral surface of the insulator 2 and positioned closer to a rear end than a rear end of the small diameter part 4B. The center electrode 5 includes an edge 32 of which a minimum distance from a center axis CL2 of the small diameter part 4B is smaller than a radius of the small diameter part 4B. An inner diameter of the through hole 28 is larger than the inner diameter of the small diameter part 4B, and a gap is provided between a portion where the through hole 28 is formed, in the ground electrode 27 and the insulator 2. |
