| 摘要 |
Resistance to fouling is improved through reliable prevention of adhesion and accumulation of carbon onto an insulator. A spark plug 1 includes a center electrode 5 extending in the direction of an axis CL1, a ceramic insulator 2 having an axial hole 4 which extends in the direction of the axis CL1 and in which the center electrode 5 is provided, a cylindrical metallic shell 3 provided externally of the outer circumference of the insulator 2 and having a support portion 21 formed on the inner circumferential surface thereof, and a ground electrode 27 extending from a front end portion of the metallic shell 3. The insulator 2 has a stepped portion 14 supported by the support portion 21 of the metallic shell 3, and a leg portion 13 formed frontward of the stepped portion 14 along the direction of the axis CL1. A space SP formed between the leg portion 13 of the insulator 2 and the inner circumferential surface 3i of the metallic shell 3 has a volume of 100 mm 3 to 300 mm 3 inclusive. Further, the surface of the leg portion 13 has a centerline average roughness of 1.8 µm or less. |
