| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine, capable of sufficiently preventing the occurrence of noises when detecting an ion current, while securing normal spark discharge in a spark discharge gap.SOLUTION: The spark plug 1 for the internal combustion engine includes a fitting 2, an insulator 3, a center electrode 4, a main ground electrode 51 forming the spark discharge gap between the center electrode and itself, and a sub ground electrode 52 forming a corona discharge gap between a front end outer peripheral angle portion 311 at an insulator front end 31 and itself. The insulator has a conductive coat formed on at least part of the outer surface opposed to the fitting. The front end outer peripheral angle portion has a curvature radius of 0.5 mm or smaller. A close point 521 of the sub ground electrode is arranged at the side of the front end beyond a front end face 312 of the insulator. G1≤G2, H1≤1.4 mm, and H2≤0.5 mm are satisfied, where H1 is a radial distance between an intersection Q and the close point, H2 is an axial distance, G1 is the size of the spark discharge gap, and G2 is the size of the corona discharge gap. |
