Patent ID: 9318878
Filing Date: 2016-04-19
CPC Classification: H01T

Claim Text:
1. A spark plug comprising: a center electrode extending in a direction of an axis; a ceramic insulator having an axial bore extending in the direction of the axis and holding the center electrode in the axial bore; a metallic shell provided externally of an outer circumference of the ceramic insulator; and a ground electrode having an extending portion extending in the direction of the axis, attached to the metallic shell at one end, and forming, at the other end, a gap in cooperation with the center electrode, at least one of the center electrode and the ground electrode has an electrode base metal; a columnar noble metal tip disposed in such a manner as to face the other electrode; and an intermediate member disposed between the electrode base metal and the noble metal tip, said intermediate member having a first surface and a second surface the first surface of said intermediate member being in contact with the noble metal tip and the second surface of the intermediate member being in contact with the electrode base metal, said second surface of said intermediate member having an area greater than that of a cross section of the noble metal tip defined by a plane cut parallel to the first surface; said intermediate member attached to said electrode base member by a nugget that is formed through fusion and solidification resulting from welding at least a portion of the boundary between the intermediate member and the electrode base metal; and in a section of the spark plug cut by a plane which passes through the center of gravity of the intermediate member and is in parallel with a facing direction between the extending portion and the center electrode, a relational expression S1/(D1×H1)≧0.005 is satisfied, where S1 is a total area of the nugget, H1 is a height of an end surface of the noble metal tip from a disposition surface of the electrode base metal where the intermediate member is disposed, and D1 is a maximum width of the noble metal tip.