| 摘要 |
To simultaneously improve voltage resistance, suppress oxidation of a center electrode, and minimize lateral spark leap. A spark plug, provided with an insulating body having an axial hole extending along an axis line, and a center electrode inserted in the axial hole. The insulating body is provided with: a first cylinder part; a truncated-cone-shaped part formed on the distal end side of the first cylinder part, the outer diameter of the truncated-cone-shaped part decreasing towards the distal end side; and a second cylinder part formed on the distal end side of the truncated-cone-shaped part. The center electrode has a diameter (C) of 2.2 mm or less. The total volume (I) of the truncated-cone-shaped part and the second cylinder part, the volume (E) of the center electrode from the rear end position of the truncated-cone-shaped part in the axial direction to the distal end position of the second cylinder part, and the diameter (C) satisfy I/E ≥ 4.2333C2 - 19.79C + 24.869. |
