Spark plug for internal combustion engine.

摘要

A spark plug for an internal combustion engine is disclosed. The spark plug (1) has a metal shell (4) and an insulator (2). The shell defines a through hole and a shoulder seat (18) and has threads (6) for mounting the spark plug (1) on the engine. The insulator is disposed inside the through hole, fixed on the shoulder seat and holds a center electrode (3) therein. The insulator also has a leg portion (7) extending from the shoulder seat into a combustion chamber of the engine when the spark plug is mounted on the engine. A semiconductor material having a resistance of 5 x 10<2> - 5 x 10<4> M OMEGA /mm is coated or baked in the form of a band (8) on the peripheral surface of a basal part (14) of the leg portion (7) of the insulator (2). Preferably, at least the basal part (14) of the leg portion (7), including the band (8), is covered with a water-repellant insulating coating (9 min ). An inner wall (15) of the metal shell (4) is desirably coated with a water-repellant material (9) at an area facing at least the peripheral surface of the basal part (14) of the leg portion (7) of the insulator (2).