SPARK PLUG

摘要

Provided is a spark plug having an earth electrode equipped with a needle-like ignition unit for forming a spark discharge gap between the ignition unit and a center electrode. The spark plug is enhanced in its joint strength by forming a molten portion reliably within the projection range of a column portion of the bottom face of an intermediate member integrated with a precious metal member, when the intermediate member is resistance-welded to the earth electrode. An ignition unit (70), which is formed by joining a precious metal member (71) and an intermediate member (75) and which is disposed in a spark discharge gap between a center electrode and an earth electrode (30), is resistance-welded at the bottom face (80) of the intermediate member (75) to the inner face (33) of the earth electrode (30), so that a molten portion (73) is formed at the joined portion. As viewed in a section containing the center line (Q) of the ignition unit (70), the molten portion (73) is reliably formed within the range of the length (D) of a column portion (76) in a direction perpendicular to the protruding direction of the ignition unit (70), and has at least a length (d) of 0.1 times (10 %) or more of the length (D).