| Power transmission belt drives have numerous advantages over such other mechanical components as gear trains, chain drives, and linkages. Key features include simplicity, ease of installation and maintenance, and the capability for absorbing shock. Mechanical imperfections in belt drive systems are unavoidable, just as in other machine components, but they can significantly affect the belt's noise and vibration characteristics, as well as its operational life. Squeal noise, excessive vibration, and fatigue failure problems are generated and/or accelerated by such imperfections. This thesis investigates dynamic effects in power transmission belt drives with a view towards developing design guidelines for improved performance and efficiency, and for understanding the underlying physical phenomena. The following specific issues are addressed and form the primary contributions of this work: (1) The role of pulley eccentricity arising from manufacturing and installation imperfections is examined in the context of the belt's transverse vibration. Laboratory measurements, perturbation analysis, and numerical simulation demonstrate the importance of non-linear jump and hysteresis phenomena in the belt's resonance and near-resonance regions. Non-contact laser interferometry is used to measure the belt's response over a wide range of operating speeds. A convenient "frequency crossing diagram" is introduced to predict resonant operating speeds, it is analogous to the Campbell diagram as used for rotating machinery. A modal perturbation solution is developed through the asymptotic method of Krylov, Bogoliubov, and Mitropolsky for a general continuous, non-autonomous gyroscopic system with weakly non-linear stiffness, and that solution is directly applied to the belt problem at hand. (2) The source of squeal noise that arises when v-belt pulleys are misaligned is examined next using both theoretical and experimental means. A fine time scale "sawtooth" boundary motion is observed at the belt/pulley interface, and this motion is identified to be a key contributor to belt squeal noise. This friction-induced, self-excited, motion also contributes to belt wear. Stick-slip frictional behavior as the belt mates with the pulley is modeled analytically to predict the frequency of squeal, which in turn depends on the belt's initial tension and bending stiffness, friction coefficient, operating speed, pulley radius, and the pulley's wedge angle. A comparison with laboratory measurements shows that the predictions provide a useful predictive tool for characterizing the belt drive's acoustic performance. |
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