Patent ID: 7449822
Filing Date: 2008-11-11
Classification: H01T

Abstract:
1. A spark plug as comprising: a metal shell; a center electrode disposed within said metal shell with a top projecting from said metal shell, the top having a ground electrode-facing portion on which a cylindrical member is joined; and a ground electrode having a first end portion and a second end portion oposed to the first end portion, the first end portion being joined to said metal shell, the second end portion having a center electrode-facing portion to which a cylindrical member is joined, wherein the cylindrical member of said center electrode extends toward the center electrode-facing portion of said ground electrode to have an end surface facing the center electrode-facing portion, and the cylindrical member of said around electrode extends toward the ground electrode-facing portion of said center electrode to have an end surface facing the end surface of the cylindrical member of said center electrode through a spark gap, wherein diameters of the cylindrical members of said center and ground electrodes are 1.1 mm or less, wherein a longitudinal center line of the cylindrical member of said center electrode extends parallel to a longitudinal center line of the cylindrical member of said ground electrode in misalignment with each other, and an amount of misalignment between the longitudinal center lines of the cylindrical members is 0.05 mm or more and less than or equal to a greater of radiuses of the cylindrical members, wherein a degree of parallelism between the end surfaces of the cylindrical members of said center and ground electrodes is greater than or equal to 1% of the spark gap and less than 1.15mm, and wherein a shortest distance between the end surface of the cylindrical member of said ground electrode and the cylindrical member of said center electrode is between a portion of an edge of the end surface of the cylindrical member of said ground electrode closest to a tip of the second end portion of the ground electrode and the end surface of the cylindrical member of the center electrode.