Spark plug

摘要

A spark plug, comprised of: an insulator having an axial bore extending in the direction of an axis, a first inner circumferential surface extending at a forward side of the axial bore, a second inner circumferential surface extending at a rear side of the axial bore and having a diameter greater than that of the first inner circumferential surface, and a ledge connecting the first inner circumferential surface and the second inner circumferential surface; a center electrode having a head supported by the ledge and extending in a space surrounded by the second inner circumferential surface, and a circular columnar leg extending continuously from the forward end of the head in a space surrounded by the first inner circumferential surface; and a seal material for holding the center electrode in the axial bore.

主权项

1. A spark plug comprising:
an insulator having an axial bore extending in a direction of an axis, said axial bore having
a first inner circumferential surface extending at a forward side of the axial bore, a second inner circumferential surface extending at a rear side of the axial bore and having a diameter greater than that of the first inner circumferential surface, and a ledge connecting the first inner circumferential surface and the second inner circumferential surface;a center electrode having a head supported by the ledge and extending in a space surrounded by the second inner circumferential surface, and a cylindrical columnar leg extending continuously from a forward end of the head in a space surrounded by the first inner circumferential surface of said insulator; anda seal material charged into a space surrounded by the ledge, the second inner circumferential surface, and the head to thereby hold the center electrode in the axial bore;wherein, assuming a position P1, P1 is a position on the center electrode where an outside diameter of the center electrode begins to increase, beyond an outside diameter H of the leg, from the leg toward a rear end of the center electrode,when an axial distance E along the axis from the position P1 to a forward end of the center electrode is 15 mm or more, an axial distance A along the axis from the position P1 to the rear end of the center electrode is 3.8 mm or more.