Patent ID: 8212462
Filing Date: 2012-07-03
Classification: H01T

Abstract:
1. A spark plug comprising an insulation member assuming the form of a hollow shaft and having a center electrode disposed at a front end thereof, and a metallic shell surrounding the insulation member and having a ground electrode disposed at a front end thereof and adapted to form a spark gap in cooperation with the center electrode, the center electrode being formed by welding a noble metal tip to a front end of a center electrode base metal in such a manner that laser welding is performed in a circumferential direction along a circumference of a joint surface between the center electrode base metal and the noble metal tip in excess of full circumference, the spark plug being characterized in that when G represents a spark gap between the center electrode and the ground electrode and A represents a shortest gap between a laser weld bead and a line drawn in parallel with an axis X of the metallic shell along an inner surface of a proximal end portion of the ground electrode which faces the center electrode, G and A establish a dimensional relation A≦3G, and when the spark plug is viewed in an axial direction from a front end of the noble metal tip, a vertex of a protrusion formed relatively high in a radial direction in a bead formed by circumferential laser welding does not exist on a straight line which connects a center of the noble metal tip and a circumferential center of a proximal end of the ground electrode, and is located circumferentially away from the straight line.