External damping of roller bearings and its effect on the acoustics of an e-mobility gearbox

This study analyses the effect of external damping of roller bearings on the acoustic behaviour of gearboxes in electric powertrains. The increasing adoption of electric vehicles has increased the importance of mitigating gearbox noise, as the lack of masking noise from internal combustion engines and the higher operating speeds of electric motors exacerbate the acoustic challenges. Gearbox noise, which is primarily caused by tooth mesh excitation and its transmission through shafts and bearings, requires strategies to minimise its impact on vehicle comfort and performance. External damping is introduced via adapters integrated into the outer bearing ring, which are used to modify the vibrational behaviour of the bearing assembly and reduce both structure-borne and airborne noise emissions. A systematic approach using Design of Experiments (DoE) methodology is used to quantify the effects of this damping. This approach allows the analysis of critical parameters including material properties, stiffness and oil pressure of the damping adapters. Physical experiments are conducted on a high-speed gear test rig, specifically designed to measure key variables such as noise emissions and vibration characteristics. The test rig ensures reliable data acquisition, allowing a comprehensive analysis of the interactions between damping properties and noise reduction mechanisms. The experimental results are systematically compared with reference measurements conducted under standard bearing conditions. This comparison enables the quantification of the damping effect and ensures that the observed noise reduction is attributable to the external damping elements. The results provide valuable insights into the dynamic behaviour of the gearbox housing with externally damped bearings. These findings contribute to the optimisation of gearbox designs for e-mobility applications.