| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent a rise at a tip of a ground electrode while achieving high ignitability. <P>SOLUTION: A spark plug 1 includes a main metal fitting 3 having a screw 15 whose screw diameter is M10 or smaller, a center electrode 5, and a ground electrode 27 bent at a bent part 27B to form a spark discharge gap 28 with the center electrode 5. In a cross section perpendicular to an axial line CL1 at a base end part of the ground electrode 27, an angle θ of a corner located on the side of the ground electrode 27 between corners formed by two tangents TL1 and TL2 drawn on a contour line of the ground electrode 27 from the axial line CL1 is 30° or less. In a cross section perpendicular to a center axis CL2 of the ground electrode 27 at a part being the closest to the tip of the ground electrode 27 in the bent part 27B, the center of gravity GP of the ground electrode 27 is located closer to a surface 27S than the position of 1/2 of thickness of the ground electrode 27, and a distance in the thickness direction between a center CP and the center of gravity GP of the ground electrode 27 is 4% or more of the thickness of the ground electrode 27. <P>COPYRIGHT: (C)2013,JPO&INPIT |
