Simulation models of dual mass flywheels

Abstract

Heavy duty trucks are faced with strict requirements regarding exhaust emissions and fuel efficiency. The demands are achieved through downsizing and downspeeding. This introduces torsional vibrations in the powertrain which, if not dealt with, will decrease life and comfort. One solution that deals with these vibrations is the Dual Mass Flywheel that absorbs the vibrations. The goal of this thesis is to develop and verify different computational models of a Dual Mass Flywheel and in particular study how the friction between the arc-spring and the primary ywheel affects the system. Modelling is done in Python using the Newmark- method combined with Newton's method for numerical simulations. The same model is also created in AVL Excite for verification. The friction between the arc-spring and the primary flywheel channel is modelled using the Coulomb friction model or an inverse tangent function. It has been verified that the two computational models give similar results. A method to approximate Coulomb friction has been developed in order to make the computational model more stable. The friction depends on both spring compression and centripetal force due to the rotation of the Dual Mass Flywheel. For a truck's operating speed the spring compression is the largest factor to frictional losses with current selection of geometrical and structural parameters. The results show that with low friction and low viscous damping resonance is not a significant problem even if it occurs at low engine speed. A study about the number of masses needed to solve the friction model have been performed. It is concluded that the friction moment has not converged using five spring masses. A method of achieving accurate results with few masses is presented. For a final conclusion about the dynamics of the Dual Mass Flywheel, the developed computational models need to be validated using experimental data. Modifications of geometrical and structural parameters should be done to fit the experiments.