Electrode structure for a spark plug

摘要

A spark plug having a center electrode comprises a ceramic insulator whose leg portion is shaped at the tip in a bag form so as to close the insulator bore. A firing tip is provided at the bag-shaped tip in a face-to-face relation with a side electrode by fixing an electrode element made of a sinter of a ceramic powder containing particles of a size between 10 and 200 mu m which are coated with a noble metal to a thickness of 0.1-20 mu m. An electrode axis extends from the top end of the plug and is inserted through the insulator bore.