Hysteresis Effects on Driveline Torsional Vibrations 951293
A major challenge in predicting driveline torsionals is the modeling of major energy dissipation mechanisms in the driveline. Primary candidates for such mechanisms are viscous dampers and dry friction (hysteresis) dampers which are specifically included by the designers to disperse the energy of torsional vibrations. The inherent structural and other internal damping in the components of the driveline is small as compared to those of viscous and dry friction dampers.
Past attempts to model clutch hysteresis have repeatedly resorted to the classical approach of modeling that has been reported many years ago. However, such an approach is oversimplified and assumes, for instance, that the hysteretic effects are independent of the frequency. In addition, the motion of the damper is assumed to be purely harmonic. Also, such studies rely solely upon the static hysteresis characterization of the elements, particularly within the clutch. Such assumptions are not appropriate, given that the level of participation of the hysteretic phenomenon may vary significantly at various operating frequencies. The present work reevaluates ways of mathematically modeling dynamic hysteresis in order to develop practical, engineering criteria for the description of damping properties of clutch dampers. An experimental approach to this issue and some empirical results are presented and recommendations for future tests discussed.
A new approach has been formulated in this work wherein an energy based criterion is proposed to determine the equivalent viscous damping effect based on the angular speed fluctuations across the clutch damper. The work done by dry friction forces is equated to energy dissipated within a viscous damper during the same relative rotation of the clutch damper in both cases. Values for an equivalent viscous damping effect will be iteratively improved until the torsional response of the system is also seen to converge. A new parameter is proposed which is the level of participation of this damping effect as a function of damper angular deflection and the operating frequency. This new parameter is to be determined based on extensive testing and verification of the clutch damping effects.
A computer simulation (TORAN™) has been developed wherein the algorithm will also detect a potential lock-up condition when the clutch torque is less than the hysteresis torque limits of the clutch elements. At this point, the clutch lock-up is automatically simulated and the corresponding results are reported for the frequency response. Experimental studies have been conducted on a truck driveline and the vibratory response of the driveline has been recorded. Results from both the studies are presented in this paper.