| 摘要 |
In a side ground electrode type of spark plug, sizes of discharge members are optimized to reduce a useless portion in discharging to improve discharge wear resistance. A first discharge member mainly comprising Ir alloy is welded to the central electrode. A second discharge member comprising Ir metal circle plate is welded to the ground electrode, wherein a side surface of the first discharge member confronts a surface of the second discharge member to form a spark discharge gap G>=0.2 mm, D(a width of the first discharge member)>=1.6 mm. |A-D|<=(G+0.5 mm). A is a width of the second discharge member. Moreover, D<=5.0 mm. A maximum cross-sectional area of weld portion between the first discharge member and the central electrode <=8 MM<2>. This weld portion has distance L to the second discharge member. L>=G.
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