| 摘要 |
In a spark plug including a cylindrical metal shell whose inner wall has a ledge portion, an insulator having a seat portion which engages with a rear slope surface of the ledge portion to be supported within the metal shell, a center electrode supported within an axial bore of the insulator, and a ground electrode extended from the metal shell to form a spark gap with the center electrode. A dimensional relationship among (A), (B) and (g) is defined as follows: ä(B-A)/2ü >/= 0.8 x (g) or ä(B-A)/2ü >/= 0.9 x (g). Where B (mm) is an inner diameter of a metal shell portion which surrounds an insulator nose, A (mm) is a base diameter of the the insulator nose, and g (mm) is a width dimension of the spark gap. <IMAGE> |
