SPARK PLUG FOR LAYERED COMBUSTION TYPE ENGINE

摘要

PROBLEM TO BE SOLVED: To generate normal spark discharge in a mixture in a wide range of condition of use while preventing flashover at the sparking point. ;SOLUTION: This spark plug comprises a center electrode 3 whose tip is located in a combustion chamber, and a main body metal fitting 8 holding an insulator which is mounted on a cylinder. The center electrode 3 is comprised of a columnar part 30 inserted into the insulator and a flange part of which outer diameter is larger than that of the cylindrical part 30 and which is connected to the back end of the cylindrical part 30 and engaged in the insulator. A tip part 31 of the columnar part 30 is comprised of a stepped part 33 having an approximately cone shape tapered toward the tip, and a precious metal tip 34 which consists of an anti-spark wearing member in the form of a disk having the same diameter as a top surface 39, and is coupled to the top surface 39 of the stepped part 33. A boundary 36 between the columnar part 30 and the stepped part 33 is placed outside of the top surface 63, as a base part of the stepped part 33, and provides a radius R in the circumferential direction of the boundary.;COPYRIGHT: (C)1999,JPO