Perturbation Analysis Of Stationary Manifolds Governed By Nonlinear Friction Characteristics In Automotive Drivelines

Torque splitting strategies adopting clutch units are increasingly popular in modern powertrains to improve vehicle dynamics. A significant drawback, however, is represented by the possible occurrence of self-excited vibrations. Therefore, a nonlinear multibody model of a full driveline has been developed to analyze these issues, validating the results with experimental data. The non-stationary behaviour of the driveline is found to be strongly dependent on the nonlinear friction characteristics. Stability maps identified negative friction gradients of the clutch torque splitter as responsible for unstable oscillations, while modal analysis revealed a dominant localization of some modes within the whole transmission. Nonlinear analysis of a minimal model of the transmission revealed the existence of stable limit cycles due to a super-critical Hopf bifurcation. Their amplitude is governed by the magnitude of the equilibrium slip speed inside the clutch unit.