| 摘要 |
PROBLEM TO BE SOLVED: To satisfy heat resistant property and breakage resistant property of a ground electrode, in a spark plug equipped with a ground electrode narrowed down so as to secure high ignition property even at a high mixed gas stream velocity. SOLUTION: The spark plug is provided with a metal fitting 10, an insulator 20 fixed inside the metal fitting 10 so that an end part 20a protrudes from an end part 10a of the metal fitting 10, a central electrode 30 fixed inside the insulator 20 so that an end part 30a protrudes from an end part 20a of the insulator 20, and a ground electrode 40 having a bent part 42 at a middle part with an end part 41 fixed to the metal fitting 10 and the other end part 43 opposed to the end part 30a of the central electrode 30 through a spark discharge gap 50. The ground electrode 40 is made of Ni or Fe as main component with Cr, Al added as additive, with a cross-section S of not less than 2 mm<SP>2</SP>and not more than 3 mm<SP>2</SP>, and an average value D of a crystal particle size in a thickness direction at least at the bent part 42 of 100μm or more. COPYRIGHT: (C)2006,JPO&NCIPI
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