Patent ID: 6956319
Filing Date: 2005-10-18
Classification: H01T

Abstract:
1. A spark plug comprising: a metal housing; a porcelain insulator installed in said metal housing; a center electrode retained within said porcelain insulator, said center electrode having a length and a tip portion projecting from a tip of said porcelain insulator; a shoulder formed on a side wall of said center electrode to define a large-diameter portion and a small-diameter portion of said center electrode, said shoulder tapering off to the tip portion of said center electrode and having a boundary leading to the large-diameter portion located inside said porcelain insulator; a first ground electrode being installed on said metal housing which has an end portion opposed to the tip portion of said center electrode to define a first spark gap between; a noble metal chip being disposed on the tip portion of the center electrode which faces the first ground electrode; a second ground electrode installed on said metal housing which has an end arranged outside the tip of said porcelain insulator and opposed over the tip of said porcelain insulator to a portion of the side wall of said center electrode to define a second spark gap in which sparks are to be generated to burn away carbon adhered to a surface of the tip of said porcelain insulator, resulting in a decrease in insulation resistance offered by said porcelain insulator; and a wear resisting member provided on said portion of the side wall of said center electrode for offering resistance to wear caused by the sparks generated in the second spark gap, said wear resisting member being different from said noble metal chip disposed on the tip portion of the center electrodes, wherein an interval between an inner wall of said porcelain insulator and the side wall of said center electrode is defined as d, and a circle is defined which has a center on an inside corner of the tip of said porcelain insulator facing said center electrode and a radius R defined on a plane including a longitudinal center line of the spark plug, the radius R is the interval d plus 0.1 mm, and said wear resisting member is located at least inside the circle.