Patent ID: 7821186
Filing Date: 2010-10-26
Classification: H01T

Abstract:
1. A spark plug comprising: a cylindrical metal shell having a leading end surface and a base end, and defining an axial direction; a cylindrical insulator held by the cylindrical metal shell and comprising a leading end surface, a base end, and a protruding insulator portion protruding from the leading end surface of the cylindrical metal shell in the axial direction; a center electrode held by the insulator and comprising a leading end portion and a protruding center electrode portion protruding from the leading end surface of the cylindrical metal shell in the axial direction, the protruding center electrode portion comprising a center electrode leading end portion being column shaped, extending in the axial direction, and having an outer peripheral surface; and an outer electrode comprising: an outer electrode base member having a base end and a distal end; and a columnar outer electrode tip having a distal end surface, the columnar outer electrode tip being welded to the distal end of the outer electrode base member and being narrower than the outer electrode base member, the distal end surface of the columnar outer electrode tip being spaced from the outer peripheral surface of the center electrode leading end portion to define a spark discharge gap, wherein the protruding insulator portion of the cylindrical insulator protrudes at least 1.0 mm from the leading end surface of the cylindrical metal shell, wherein the protruding center electrode portion of the center electrode protrudes at least 3.5 mm from the leading end surface of the cylindrical metal shell, and wherein a following relationship is satisfied: wherein, in defining θ