| 摘要 |
<p>A corner of a distal end of a ground-electrode-side noble metal tip of a spark plug is taken as a first corner; a corner of a leading end of a center-electrode-side noble metal tip is taken as a second corner; a corner formed at a starting point where a diameter of the center electrode is reduced is taken as a third corner; a corner of the ground electrode is taken as a fourth corner; a corner closest to the third corner of the corners on the distal end of the ground-electrode-side noble metal tip is taken as a fifth corner; a length of a virtual flying spark path defined between the first corner and the second corner is taken as L1; a length of a virtual flying spark path defined between the third corner and the fourth corner is taken as L2; a length of a virtual flying spark path defined between the third corner and the fifth corner is taken as L3; and L2 or L3, whichever is shorter, is taken as L4, the spark plug fulfills a relational expression of L4/L1 ‰¥ 0.9.</p> |
