| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a spark plug capable of restraining wear of an electrode by restraining flying spark of a base material.SOLUTION: A spark plug for an internal combustion engine comprises: a center electrode 2; an electric insulator 3 for holding the center electrode 2 inside; a housing for holding the electric insulator 3 inside; and a ground electrode 5 forming a spark discharge gap 11 between it and the center electrode 2. The ground electrode 5 has a ground base material 50 connected to the housing, and a ground protrusion part 51 projecting from an opposite face 501 of the ground base material 50 opposed to the center electrode 2. The ground protrusion part 51 has a diameter D of 0.9-1.4 mm. An angle formed by a straight line L for connecting a protrusion corner part 512 that is an edge of a discharge face 511 of the ground protrusion part 51 opposed to the center electrode 2 with a base material corner part 502 that is an edge in a width direction of the opposite face 501 of the ground base material 50 by a shortest distance, and a flat plane M orthogonal to an axial direction of the ground protrusion part 51 is designated asθ[°]. A curvature radius of the base material corner part 502 is designated as R[mm]. At that time,θ≥-53R+49 is satisfied.</p> |
