Patent ID: 7477007

Claim:
A spark plug comprising: a center electrode having a columnar shape; an insulator accommodating a rear end portion of the center electrode; a metallic shell accommodating the insulator; a ground electrode whose first end is connected to a front end portion of the metallic shell; a first noble-metal tip joined, via a first weld metal zone, to one of a front end portion of the center electrode and a second end portion of the ground electrode; and a second noble-metal tip joined, via a second weld metal zone, to the other of the front end portion of the center electrode and the second end portion of the ground electrode, and forming a spark discharge gap between the first and second noble-metal tips; wherein a projected area S L of the first weld metal zone, obtained by measuring an area of the first weld metal zone projected onto an imaginary plane perpendicular to an axial direction of the first noble-metal tip, is greater than a projected area S S of the second weld metal zone, obtained by measuring an area of the second weld metal zone projected onto an imaginary plane perpendicular to an axial direction of the second noble-metal tip, and an exposed length L L of the first metal tip as measured from the first weld metal zone is greater than an exposed length L S of the second noble-metal tip as measured from the second weld metal zone.