Spark plug with improved ground electrode joined to metal shell

摘要

A spark plug has a metal shell and a ground electrode joined at a base end portion thereof to the metal shell and includes a surface layer and a core higher in thermal conductivity than the surface layer. The core includes a first core member and a second core member. A weld region, where the ground electrode is joined to the metal shell, has an undulating shape. A distance between frontmost and rearmost ends of a part of the weld region in contact with the first core member in the axis direction is 0.15 mm or more.

主权项

1. A spark plug, comprising:
a rod-shaped center electrode extending in an axis direction of the spark plug; an insulator having an axial hole formed in the axis direction so as to retain the center electrode in the axial hole; a metal shell circumferentially surrounding and retaining the insulator; and a ground electrode having a base end portion welded to the metal shell to define a weld region and a distal end portion facing an axially front end portion of the center electrode with a gap left between the distal end portion of the ground electrode and the front end portion of the center electrode, the ground electrode including a surface layer defining a surface of the ground electrode and a core located inside the surface layer and having a higher thermal conductivity than that of the surface layer, the surface layer having a thickness of 0.2 mm to 0.4 mm at a specific position that is located 1 mm from the base end portion in a direction toward the distal end portion along an outer shape of the ground electrode, wherein the core includes a first core member located on an inner side thereof and a second core member located on an outer side thereof so as to circumferentially surround the first core member and having a higher thermal conductivity and a lower hardness than those of the first core member; wherein the first core member has a protruding shape that protrudes to a rear of the second core member in the axis direction; wherein the weld region has an undulating shape that undulates according to the protruding shape of the first core member; and wherein a distance between frontmost and rearmost ends of a part of the weld region in contact with the first core member in the axis direction is 0.15 mm or more.