| 摘要 |
<P>PROBLEM TO BE SOLVED: To stably generate plasma by more reliably preventing current leakage while suppressing a variation in position of a ground electrode relative to an insulator and overheating of the ground electrode. <P>SOLUTION: A spark plug 1 includes: an insulator 2 having an axial bore 4 extending along an axis CL1, a central electrode 5 inserted in the axial bore 4, a main fitting 3 disposed on an outer circumference of the insulator 2, and a ground electrode 27 fixed to the main fitting 3, and has a cavity portion 29 formed by an inner circumferential surface of the axial bore 4 and a tip end face of the central electrode 5. Support portions 31 to 34 are interposed between the insulator 2 and the ground electrode 27, and a space formed radially outward of the support portions 31 to 34 and a space formed radially inward of the support portions 31 to 34 are interconnected. On an imaginary plane orthogonal to the axis CL1 on which an outline of the opening of the axial bore 4 and outlines of the support portions 31 to 34 are projected, points A on the outlines of the support portions 31 to 34 at the shortest distance to the axis CL1 are situated radially outward of the outline of the opening of the axial bore 4. <P>COPYRIGHT: (C)2012,JPO&INPIT |
