Patent ID: 7199511

Claim:
A spark plug comprising: a metal shell; a center electrode disposed within said metal shell with a top portion thereof projecting from said metal shell, said center electrode having a noble metal chip laser-welded to the top portion; a ground electrode having a first end portion, a second end portion, and a middle portion between the first and second end portions, the first end portion being welded to said metal shell, the second end portion having a center electrode-opposed surface on which a noble metal chip is laser-welded, the middle portion being bent to have the noble metal chip face the noble metal chip of said center electrode through a spark gap; and fused portions formed around an interface between the noble metal chip and the center electrode-opposed surface of said ground electrode, said fused portions creating welds between the noble metal chip and said ground electrode and being formed by materials of said ground electrode and said noble metal chip melted together by emitting laser beams around the interface between the noble metal chip and the center electrode-opposed surface of said ground electrode, wherein the noble metal chip of said ground electrode has a given length and projects toward said center electrode from the center electrode-opposed surface by 0.3 mm or more in a longitudinal direction thereof, wherein fused portion sectional area centerlines, each defined as a line extending inward of the noble metal chip of said ground electrode through a center of a sectional area of a respective said fused portion, at the interface between the noble metal chip and the center electrode-opposed surface of said ground electrode, lie outside an angle θ 1 , angle θ 1 being defined as the angle between lines extending from the noble metal chip on the ground electrode, before it is bent, in a plane of the center electrode-opposed surface of said around electrode to respective edges of said metal shell opposed in a widthwise direction of said metal shell, and wherein a transverse sectional area A of a portion of the noble metal chip of said ground electrode closest to said fused portions, as taken perpendicular to the length of the noble metal chip of the ground electrode, and a transverse sectional area B of an unfused portion of the noble metal chip of said ground electrode, as taken over the interface between the noble metal chip and the center electrode-opposed surface of said ground electrode, have values such that an unfused portion sectional area percentage, defined as a percentage of the sectional area B in the sectional area A is 50 or less.