| 摘要 |
In a first embodiment a spark plug satisfying the relations: t>=0.3 mm and St/Sw<=7 in which t is the axial-direction shortest distance between a leading end surface (41a) of a precious metal tip ( 41 ) and a joint portion, St is the surface area of the precious metal tip ( 41 ) and a joint portion ( 43 ) between the precious metal tip ( 41 ) and the ground electrode body (4a), and Sw is the area of the joint portion ( 43 ) between the ground electrode body (4a) and the precious metal tip ( 41 ). In a second embodiment, the spark plug satisfies the relations t>=0.3 mm and La>Lb; and in a third embodiment the spark plug satisfies the relations t>T and La>Lb, where T, La and Lb are as defined in the specification. The relation t>=0.3 mm is specific to the first and second embodiments, and the relation St/Sw<=7 is specific to the first embodiment only.
|
