Finite element analysis of torsional vibrations in a high-performance hybrid powertrain for LMDh competition

Torsional vibrations in the powertrain can critically affect the performance of race vehicles, potentially leading to rear wheel grip loss, compromising the transmission of power to the ground. This study addresses this issue by developing a one-dimensional finite element model that captures the torsional dynamics of the powertrain, incorporating the stiffness and inertia characteristics of all driveline components and investigating in depth the coupling between the unsprung masses and the torsional vibration of the powertrain itself. Modal analysis is used to identify natural frequencies and mode shapes that align with experimentally observed oscillations at the axle-shafts. Notably, a resonance interaction is found between a critical torsional mode of the powertrain and the vertical dynamics of the unsprung masses. A deep investigation of the coupling between unsprung masses and torsional vibration is carried out. Moreover, to decouple these effects, targeted modifications to axle-shaft stiffness are investigated. The model is further extended to the time domain to simulate driveline excitations during gear shifts, successfully reproducing measured oscillatory behaviour. Both frequency- and time-domain sensitivity analyses demonstrate that reducing axle-shaft stiffness effectively mitigates torsional excitation, offering valuable insights for the design of optimised driveline components aimed at enhancing vehicle performance and reliability.