Patent ID: 6316868
Filing Date: 2001-11-13
Classification: H01T

Abstract:
A spark plug comprising;a center electrode having a front end and a front side;an insulator having a front end, the insulator surrounding and holding the center electrode so as to expose both the front end and the front side of the center electrode out of the front end thereof;a metal housing having a leading end, the metal housing holding the insulator so as to expose the front end of the insulator out of the leading end thereof;a first ground electrode having a leading end and a front end, the leading end of the first ground electrode being fixed to the leading end of the metal housing so as to constitute a first discharge gap between the front end of the first ground electrode and the front end of the center electrode; anda second ground electrode having a leading end and a front end, the leading end of the second ground electrode being fixed to the leading end of the metal housing and the front end of the second ground electrode is positioned radially outside the front end of the insulator so as to constitute a second discharge gap between the front end of the second ground electrode and the front side of the center electrode,wherein dimensional relationships of the center electrode, the first and second ground electrodes, the insulator and the metal housing are respectively in ranges of;0.7 mm.ltoreq.A.ltoreq.1.3 mm,0.3 mm.ltoreq.B.ltoreq.A-0.1 mm1.0 mm.ltoreq.C.ltoreq.4.0 mm,0.5 mm.ltoreq.H.ltoreq.30 mm,-1.0 mm.ltoreq.F.ltoreq.+0.5 mm, and1.0 mm.ltoreq.L1.ltoreq.C+0.5 mm,where A is a distance of the first discharge gap,B is a shortest distance between the front end of the second ground electrode and the insulator,C is an axial length from the leading end of the metal housing and the front end of the insulator,H is an axial length from the front end of the insulator and the front end of the center electrode,F is an axial length from the front end of the insulator to the front end edge of the second electrode, andL1 is a shortest axial length from the leading end of the metal housing to the front end of the second ground electrode.