| 摘要 |
<p>A spark plug (1) includes a center electrode (5), a ground electrode (27), and a tip (31) joined to the center electrode (5) and forming a spark discharge gap (33) in cooperation with the ground electrode (27). The tip (31) is joined to the center electrode (5) via a fusion zone (35), and the fusion zone (35) has an exposed surface (35E) exposed to the external environment. In a section which contains an axis (CL1) and the center (CP) of the exposed surface (35E), the relational expression C - B ‰¥ 0.02 is satisfied, where C (mm) is the distance on the side surface of the tip (31) between the fusion zone (35) and the distal end of the tip (31), and B (mm) is the distance between a distal end surface (31F) of the tip (31) and a portion of the fusion zone (35) located closer to the axis (CL1) than the side surface of the tip (31) and located closest in the fusion zone (35) to the distal end surface (31F) of the tip (31). By virtue of these features, exposure of the fusion zone (35) to the spark discharge gap (33) can be restrained over a long period of time; accordingly, durability can be improved.</p> |
