| 摘要 |
<p>The problem addressed by the present invention is to provide a spark plug with superior load life performance. The spark plug is provided with: an insulated body having an axial hole extending along the direction of an axial line; terminal hardware that is provided with an accommodated part that is accommodated in the axial hole, and has a recessed part forming region in which a plurality of recessed parts are formed in the outer peripheral surface of the accommodated part; and main hardware that accommodates the tip end side of the insulated body and holds the insulated body. The spark plug has: (1) a length (H) of the accommodated part in the direction of the axial line of 35 mm or greater; (2) a length (F) for the recessed part forming region in the direction of the axial line of 13 mm or greater; (3) a smooth part of the accommodated part on the outer peripheral surface thereof; (4) a ratio (A/B) for the diameter (A) at the tip of the accommodated part and an inside diameter (B) for the insulated body at that tip of 0.9 <= A/B <= 0.98; and (5) Vickers hardness measured at the center of a cross-sectional surface obtained by cutting the accommodated part in a direction orthogonal to the direction of the axial line of 150 - 350 Hv.</p> |
