| 摘要 |
<p>The invention more reliably prevents damage in a rear end portion of an insulating body, even if a rear-end trunk portion is long, or the surface area of a flat portion of the insulating body is small. A spark plug (1) is provided with: an insulator (2) having a shaft hole (4); a body (3) arranged around the outer edge of the insulator (2); a foot portion (6A) passing through the rear end of the shaft hole (4); and a terminal electrode (6) fitted with a head portion (6B) exposed from the rear end of the insulator (2). In the insulator (2): the length (L) of a part exposed from the rear end of the body (3) is between 28 and 34 mm; and the surface area of a flat portion (2F) is no more than 25 mm2. In the spark plug (1) of the abovementioned type, in a range that extends 5.5 mm from the rear end (2) of the insulator, toward a tip, in the direction of an axis (CL1), the thickness (t) of the thinnest wall portion (2A) of the insulator (2) is at least 1.0 mm. Moreover, an area (AR) in which a projected area (PA1) of flat portion (2F) overlaps a projected area (PA2) of flat portion (6F) has a surface area (D) of at least 8 mm2.</p> |
