Patent ID: 6864623
Filing Date: 2005-03-08
Classification: H01T

Abstract:
1. A spark plug comprising a tubular metallic shell, an insulator disposed in the metallic shell such that a distal end portion the insulator of protrudes from an end surface of the metallic shell, a center electrode disposed in the insulator such that a distal end portion of the center electrode protrudes from an end surface of the insulator, and a ground electrode which has a proximal end joined to the end surface of the metallic shell and a distal end portion which faces said distal end portion of the center electrode to thereby form a spark discharge gap, wherein, if a side of the spark plug toward the spark discharge gap along a direction of an axis of the center electrode is defined as a front side, a front end portion of the center electrode is formed as a circular cylindrical center-electrode noble-metal ablation resistance portion whose radius r (mm) and length l (mm) are determined so as to satisfy 5≦l/r the ground electrode is an ignition-performance-improving ground electrode in which a distal end portion thereof is bent in a direction toward the center electrode; a rear end-edge of a distal end surface of said distal end portion is located frontward in relation to a front end surface of the center-electrode noble-metal ablation resistance portion; and, in an orthogonal projection on a projection plane perpendicularly intersecting said axis of the center electrode, the rear end-edge is located outward in relation to the front end surface of the center-electrode noble-metal ablation resistance portion; and a portion of the ignition-performance-improving ground electrode which includes at least the rear end-edge is a ground-electrode noble-metal ablation resistance portion.