Patent ID: 7105990
Filing Date: 2006-09-12
Classification: H01T

Abstract:
1. A spark plug for an internal combustion engine comprising: a columnar central electrode; an insulator for holding said central electrode; a housing for holding said insulator; an earth electrode wherein one end thereof is connected with said housing and the other end thereof is opposite to said central electrode, wherein: said earth electrode has a leg connected with said housing and a projection having a cross section smaller than that of said leg, said projection projecting from said leg toward said central electrode; said central electrode has a body held in said insulator and a narrowed portion smaller than said body, said narrowed portion projecting from said body toward said projection; a first border portion between said body and narrowed portion is positioned in said insulator; a length of said projection projecting from said leg is between 0.3 and 1.5 mm, both inclusive; a cross section of said projection is between 0.07 and 1.13 mm said narrowed portion includes a tapered member, the cross section of which is continuously decreased from said body toward said projection; a length of said narrowed portion from a top thereof to an end of said insulator is greater than 1 mm.