| 摘要 |
A spark plug 1 includes a tip 31 joined to a center electrode 5. The coefficient of linear thermal expansion of the center electrode 5 is greater than that of the tip 31. The tip 31 has a gap-forming portion 31X having a maximum width of 1.2 mm or greater and forming a gap 28 in cooperation with the ground electrode 27 and a to-be-joined portion 31Y joined to the center electrode 5. At a position A which is shifted 0.1 mm from the forward end of the outer surface of the fusion portion 33 toward the forward end side, the width of the to-be-joined portion 31Y measured on the cross section is smaller than the width of the gap-forming portion 31X. The to-be-joined portion 31Y satisfies Dtw/Dw ‰¤ 1.1, where Dtw represents the width of the to-be-joined portion 31Y at the position A, and Dw represents the width of the fusion portion 33 at the forward end of the outer surface thereof. |
