| 摘要 |
PROBLEM TO BE SOLVED: To improve ignitability by effectively reducing the number of reflecting times of plasma to an insulator until the plasma is jetted out of a cavity part. SOLUTION: A spark plug 1 includes an insulator 2, a center electrode 5, and a ground electrode 27 which is at least partially arranged closer to a tip side in an axial line CL1 direction than the tip of the insulator 2, and has a cavity part 28 being a concave part formed at the tip of the insulator 2 to open toward the tip in the axial line CL1 direction. A portion of the center electrode 5 is arranged in the cavity part 28, and a portion of the ground electrode 27 is located closer to the axial lien CL1 than an opening of the cavity part 28 to form a gap 29 with the center electrode 5 therebetween. In a cross section including a line segment LS connecting the center electrode 5 and the ground electrode 27 at the shortest distance and parallel with the axial line CL1, at least a portion of a visible outline of the cavity part 28 is a curved line located on an ellipse EL assuming two points on the line segment LS as a focal point. COPYRIGHT: (C)2013,JPO&INPIT |
