SPARK PLUG HAVING MULTIPOLE OUTER ELECTRODE

摘要

PROBLEM TO BE SOLVED: To provide a spark plug having a multipole outer electrode having an excellent antipollution by setting a space between a tip end inner periphery of each outer electrode and a front end surface or an extending flat surface of an insulator engaged with a main fitting. ;SOLUTION: An outer three-pole spark plug A is provided with a cylindrical main fitting 1, an insulator 2 with a shaft hole 22 engaged with a main fitting while a front end portion (leg portion) 21 is exposed, a cylindrical center electrode 3 engaged with the shaft hole 22 of the insulator 2 while an ignition point is projected, and three outer electrodes 4 having a tip end 41 concentrically opposed to a side surface of the ignition portion 31, a tip end inner periphery 42 disposed in parallel to a front end surface 23 of the insulator and a back end 43 welded to a tip end 11 of the main fitting 1. A space b between the tip end inner periphery 42 of the electrodes 4 and the front end surface 23 or the extending flat surface of the insulator 2 is made 0.3 mm-1.2 mm. Therefore, a spark runs on the front end surface 23 of the insulator 2 and arrives at the electrodes 4 and cleaning is accomplished by itself.;COPYRIGHT: (C)1999,JPO