| 摘要 |
A plasma jet spark plug is provided which can improve ignitability and durability thereof by forming a part of a spark discharge gap outside the electric discharge space which generates plasma. A cavity (60) surrounded by an inner circumference face of an axial hole (12), which extends from an opening portion (14) of a front-end side of the axial hole (12) of an insulator (10), and a front-end face of a center electrode (20) is formed. Further, a front-end portion (31) of a ground electrode (30) is bent towards a front-end portion (11) of the insulator (10). When a combustion engine runs at high load, a spark discharge occurs in spark discharge gaps (an aerial discharge gap A, an inner creeping discharge gap B and an outer creeping discharge gap C) formed between the ground electrode (30) and the center electrode (20) so as to ignite an air-fuel mixture outside the cavity (60). Further, when a combustion engine runs at low load, plasma generated in the cavity 60 is shot out from the opening portion (14) to ignite the air-fuel mixture. |
