大型車用ホイールボルトの軸力のばらつきと安全性の評価

概要

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Tire coming-off accidents of large vehicles frequently cause fatal disasters that threaten the safety of civic life. Most accidents were attributed to the fatigue failure of wheel bolts that tighten the rear wheels of large vehicles. Since 2003, a number of guidelines to enhance the joint safety have been issued from the Government and other allied societies and associations. However, a considerable number of accidents are still occurring. In order to achieve a drastic reduction of the accidents, the tightening characteristics of wheel bolts need to be elucidated in greater detail. In this paper, the preload scatter of wheel bolts is comprehensively studied by experiments and FEM. Using a single set of wheel bolted joint, it is shown that a large scatter in bolt preload generates due to its specific geometry. In the next place, simulating the actual tightening operation, eight bolts are successively tightened and the bolt preload scatter among them is quantitatively evaluated. The effect of elastic interaction, which occurs in the tightening process of multiple bolts, is studied by experiments and also analyzed by three-dimensional FEM. Since the scatter of friction coefficient in related threaded fasteners is found to be the primary case for the bolt preload scatter, an improved configuration is proposed by FEM for two kinds of nut loaded surfaces, such as between inner nut and inner wheel and between outer nut and outer wheel.
2009-11-25