SPARK PLUG

摘要

PROBLEM TO BE SOLVED: To provide a spark plug capable of reliably suppressing oxidation of a molten part formed between an electrode tip to be jointed to the tip of a center electrode by sufficiently performing heat dissipation of the tip of the center electrode. SOLUTION: In the direction of the axis line O, a plane P (double dotted line P-P is its cross section) which passes through a position at the rear end of the molten part 95 of the center electrode 20 and is orthogonal to the axis line O, and a plane Q (double dotted line Q-Q is its cross section) which is parallel to the plane P passing through a position 4 mm away from the plane P to the rear end side are assumed. When Va and Vb are volumes of an electrode base member 21 and a core member 25 of the center electrode 20 between the planes P and Q, respectively, and d is the diameter (outer diameter) of the cut surface of the center electrode 20 by the plane Q, the center electrode 20 is superior in heat dissipation, and oxidation of the molten part 95 of the electrode tip 90 can be suppressed if d≤2.1 [mm] and -0.09×d+0.33