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(11) | EP 1 837 964 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Spark plug for use in an internal-combustion engine |
| (57) A spark plug 100 is comprised of a metal shell 1, an insulator 2, a center electrode
3 and a ground electrode 4. A rear-end face of the ground electrode 4 is welded to
a front-end face of the metal shell 1, and a bent portion 5 located at the intermediated
position in the longitudinal direction is bent toward the center of the spark plug
100. The ground electrode 4 assumes a circular-shape with a diameter of 2mm or less
whereby an inflow of an air-fuel mixture is not disturbed even when the air-fuel mixture
directly flows into a back face of the ground electrode 4. The ground electrode 4
is comprised of an outer layer 4A made of a nickel alloy and an inner layer 4B made
of pure copper with an excellent thermal conductivity, in which a ratio of a cross-sectional
area of the inner layer 4B to the entire cross-sectional area of the ground electrode
4 is 10% or more to 35% or less. Thus, the spark plug 100 which is excellent in heat
sinking ability and can prevent a spring back phenomenon due to a difference in a
coefficient of thermal expansion.
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