SPARK PLUG FOR STRATIFIED COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide a wide-range plug by enhancing heat resistance and pollution resistance even in an engine adopting a stratified combustion method with an auxiliary gap. ;SOLUTION: A main gap 6 is formed between a center electrode 3 and a grounding electrode 5 with a main metal fitting 4 connected, and an auxiliary gap 9 is formed between the center electrode and an inner protruding rim 8 of an opening end 7 of the main metal fitting 4. Infiltration of combustion gas with high temperature is reduced and thermal load to insulator is reduced by tapering off a diameter of an inner wall surface 11 lower than a shelf part 10 of the main metal fitting 4 toward a tip of the main metal fitting 4 at least by not less than 0.6 mm and by making a space formed by the inner wall surface 11 lower than the shelf part 10 of the main metal fitting 4 small, and also pollution is prevented by reducing infiltration of carbon. Thereby, heat resistance and pollution resistance are enhanced and a wide-range plug can be obtained.;COPYRIGHT: (C)1999,JPO