SPARK PLUG

摘要

A spark plug wherein the structural configuration of a melted section formed at the joint portion between a discharge section and a pedestal section, which form an igniting section projecting from a ground electrode, is specified to suppress the occurrence of cracks and separation. In the outline of a cross-section of an igniting section (80) including the center axis (P) thereof, the exposed surface (88) of a melted section (83) is connected to the side surface (82) of a discharge section (81) and to the side surface (85) of a pedestal section (84). Also, the external angle (?) of the angle which an imaginary line (Q) passing through the position (X1) of the boundary between the melted section (83) and the pedestal section (84) and through the position (X2) of the boundary between the melted section (83) and the discharge section (81) forms at the intersection (C) at which the imaginary line (Q) intersects the center axis (P) satisfies 135° = ? = 175°. In addition, the proportion (T/S) of the depth (T) of formation of the melted section (83) to the outer diameter (S) of the discharge section (81) satisfies T/S = 0.5.