| 摘要 |
PURPOSE:To prevent misfire on low rotation side and deterioration of pre-ignition resistance on high rotation side and improve voltage resistance by forming the insulator of a spark plug by Si3N4 sintered body followed by heating in oxidizing atmosphere. CONSTITUTION:The insulator 11 of a spark plug 10 is formed by use of Si3N4 sintered body, and then heat treatment is conducted at a determined temperature and time in oxidizing atmosphere having an increased oxygen partial pressure. The insulator 11 is formed of Si3N4 sintered body, whereby the insulator leg part 11a is lengthened to prevent the misfire on low rotation side by carbon adhesion. The cooling property of the electrode part is improved because of satisfactory heat conductivity of the sintered body, and deterioration of pre-ignition resistance on high rotation side can be avoided. Further, free Si in the sintered by is oxidized by the heat treatment is oxygen atmosphere to form stable SiO2 which is an insulating material. Hence, voltage resistance of the spark plug is improved. |
