SPARK PLUG AND MANUFACTURING METHOD FOR SAME

摘要

This spark plug includes a resistor in which a connecting portion for electrically connecting a center electrode and a terminal fitting within the axial bore of an insulator has a porosity of 5.0% or less. According to another aspect, this spark plug has a shrinkage ratio ((D - C/D) × 100 of 35% or greater, where fill length D denotes the length from the back end of the center electrode to the back end of a connecting member constituting the connecting portion, and connecting portion length C denotes the length from the back end of the center electrode to the tip of the terminal fitting. This manufacturing method for a spark plug comprises a step in which the terminal fitting is disposed within the axial bore so as to be in contact with a powder for forming the connecting portion, wherein an exposed length H and a powder portion diameter B' satisfy formulae (1) H = -3.1B' + 18, (2) H = -0.85B' + 11, and (3) B = 5, where exposed length H (mm) denotes the length in the axial direction from the back end of the insulator to the tip of a first constituent portion of the terminal fitting exposed from the axial bore, and powder portion diameter B' (mm) denotes the inside diameter in a region of the axial bore where the powder for forming the connecting portion is disposed.