| 摘要 |
In a spark plug for use in an internal combustion engine, an elongated insulator is provided in which a center electrode is supported. A cylindrical metal shell is provided in which the insulator is supported, and an ground electrode extended from the metal shell to form a spark gap with a front end of the center electrode. The front end of the center electrode has a tapered-off step section whose front end surface has a spark erosion resistant portion, and having a boundary between a columnar portion of the center electrode and the tapered-off step section. The boundary of the tapered-off step section is located into a front end surface of the insulator, and a front end surface of the tapered-off step section being positioned outside of the front end surface of the insulator. The front end of the center electrode defines a conoidal configuration positioned coaxially with the center electrode, and inscribes a front periphery of the insulator while maintaining an apex angle of the conoidal configuration to be 110 degrees or less. <IMAGE> |
