Spark plug

摘要

In a spark plug, at least one of a center electrode and a ground electrode has a cover portion and a core portion having a different thermal expansion coefficient. The core portion has a concave portion and a convex portion formed at a front end thereof. The convex portion is such that, in a cross section passing through a barycenter of a front surface of the electrode and also passing through the convex portion, an area of the convex portion delimited by a line perpendicular to a bisector of the convex portion and passing through a point 0.2 mm shifted from a front end of the convex portion in the direction of the bisector is smaller than an area of a triangle formed by connecting the front end of the convex portion and intersections of the line perpendicular to the bisector and a contour of the convex portion.

主权项

1. A spark plug comprising a center electrode and a ground electrode which forms a gap between the ground electrode and the center electrode,
wherein, when a side toward the gap is taken as a front side of the center electrode or the ground electrode, at least one of the center electrode and the ground electrode has a cover portion and a core portion covered with the cover portion and formed of a material having a thermal expansion coefficient different from a thermal expansion coefficient of the cover portion, the core portion of the at least one electrode has a concave portion and a convex portion formed at the front side of the core portion, and the convex portion is such that, in a cross section passing through a center axis of the electrode and also passing through the convex portion with a line along the cross section perpendicular to a bisector of the convex portion and passing through a point 0.2 mm shifted from a front end of the convex portion in a direction of the bisector, the line intersecting a contour of the convex portion at two points, a cross-sectional area of the cross section passing through the convex portion delimited by the contour of the convex portion and the line perpendicular to the bisector is smaller than a triangular area of the cross section having vertices at the front end of the convex portion and each of the two points of intersection of the line perpendicular to the bisector and the contour of the convex portion.