| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-reliability spark plug for an internal combustion engine having an insulator high in withstand voltage, and also to provide its manufacturing method. <P>SOLUTION: This spark plug for an internal combustion engine is provided with: a tubular main fitting forming an insulator holding hole; the insulator forming an axial hole extending in the axial direction and locked in the insulator holding hole of the main fitting; and a center electrode held in the axial hole of the insulator. The insulator has an organization where, when an optional cross section in a part to be surrounded which is surrounded by the main fitting is formed into an observation surface by mirror polishing, and pores in the observation surface are observed, an area occupied by one or more pores included in an imaginary circle of a diameter of 50 μm is not greater than 40% of the imaginary circle at any position in the observation surface. <P>COPYRIGHT: (C)2007,JPO&INPIT |
