US 7,321,187 B2
Spark plug and method for manufacturing the spark plug
Hideki Teramura, Mie (Japan); Tomoaki Kato, Aichi (Japan); and Kazuyoshi Torii, Aichi (Japan)
Assigned to NGK Spark Plug Co., Ltd., Aichi (Japan)
Filed on Jun. 13, 2006, as Appl. No. 11/451,469.
Application 11/451469 is a continuation of application No. 10/465552, filed on Jun. 20, 2003, granted, now 7,084,558.
Claims priority of application No. 2002-181982 (JP), filed on Jun. 21, 2002.
Prior Publication US 2006/0238092 A1, Oct. 26, 2006
This patent is subject to a terminal disclaimer.
Int. Cl. H01T 13/20 (2006.01)
U.S. Cl. 313—141  [313/142; 313/143; 313/144] 9 Claims
OG exemplary drawing
 
1. A spark plug comprising:
a ground-electrode spark portion fixedly attached to a side surface of a ground electrode, which ground-electrode spark portion is disposed to face a center-electrode spark portion made from a noble metal and fixedly attached to a distal end of a center electrode, thereby forming a spark discharge gap between the center-electrode spark portion and the ground-electrode spark portion;
the ground-electrode spark portion is formed from a noble metal which contains Pt as a main component, and is joined to the ground electrode via an alloy layer in which the noble metal that constitutes the ground-electrode spark portion and a metal that constitutes the ground electrode are alloyed with each other; and
the ground-electrode spark portion is configured such that the distal end surface facing the spark discharge gap is smaller in diameter than a bottom surface fixedly attached to the ground electrode; the distal end surface is protrusively located closer to the distal end of the center electrode than is the side surface of the ground electrode; and when the ground-electrode spark portion is viewed in plane from the distal end surface, a portion of a surface of the ground-electrode spark portion is viewed as a peripheral exposed-region surface which is exposed on the side surface of the ground electrode so as to surround the distal end surface,
wherein the entire peripheral exposed-region surface is located closer to the center electrode than is the side surface of the ground electrode,
wherein the peripheral exposed-region surface of the ground electrode-spark portion is formed in parallel with the distal end surface of the ground-electrode spark portion,
wherein, when G represents a shortest distance along an axial direction of the center electrode between a distal end surface of the center-electrode spark portion and the distal end surface of the ground-electrode spark portion, and L represents a length of a line segment connecting, by a shortest distance, a peripheral edge of the distal end surface of the center-electrode spark portion and a peripheral edge of the peripheral exposed-region surface, the following relational expression is satisfied:
1.3G≤L≤3G; and
when, in orthogonal projection on a plane perpendicularly intersecting an axis of the center electrode, A represents a width of the peripheral exposed-region surface, W represents a width of the ground electrode, and d represents a diameter of the distal end surface of the ground-electrode spark portion, the following relational expression is satisfied:
0.15≤A≤{(W−d)/2}−0.4 (unit: mm).