Rotational dynamics of timing belt drives comprising non-circular pulleys

Abstract :

Timing Belt Drives (TBD) of automotive internal combustion engines are subjected to a very harsh vibratory environment. Various excitation sources such as crankshaft acyclism and fluctuating load torques applied to driven pulleys, generate vibratory phenomena that may affect the TBD dynamic performances and life. In particular, two phenomena require careful monitoring and need to be minimized: rotational vibrations of the transmission axes and tension force fluctuations in the belt spans.

Within the objective of reducing these phenomena, car manufacturers now commonly design TBD comprising Non-Circular (NC) pulleys. When rotating, a NC pulley causes periodic elongations of its adjacent belt spans. Hence, it behaves like an exciter that may generate a corrective rotational excitation able to counteract the other excitations acting on the TBD. However, designing efficiently a TBD with NC pulleys remains hard to accomplish and requires numerical tools able to predict the rotational dynamics of such transmissions.

The presented work aims at assessing the predictive capability of a recently developed rotational dynamic model for TBD comprising NC pulleys. This 0D/1D model based on a Lagrangian-Eulerian approach is applied to a simplified TBD of a 4-cylinder car engine. Simulations performed on the transmission show that the rotational velocity and span tension variations caused by the fluctuating camshaft torque can be counteracted by using an elliptical crankshaft pulley. In parallel, the transmission has been reproduced experimentally. Comparative analyses have shown that the numerical results obtained from the model are in good agreement with the experiments.