Electric powertrain transmission design including NVH performance using specialized software

In recent years, due to the sadly well-known environmental problems concerning air pollution, the automotive field is moving towards greener solutions: the electrification of vehicles is becoming more and more important, even exceeding most forecasts. The electrification of vehicles is spreading worldwide only recently, and the NVH (Noise, Vibration, Harshness) problem should be completely reconsidered, since the main noise and vibrations sources are changed with respect to conventional ICE (Internal Combustion Engine) vehicles. Furthermore, many noises that were totally inaudible in ICE vehicles, moving to electric vehicles can become really annoying since the masking effect of the engine is missing. Therefore, the aim of this thesis is to propose a method to investigate in depth all the aspects concerning the NVH of electric powertrains, by exploiting the features of a commercial specialized software, Romax. Before performing any dynamic analysis, static analyses are required, to understand if the system can bear the required loads of the duty cycle. Different versions of the model are evaluated, focusing on macro and micro-geometry modifications of the gears of the transmission system. It has been proved that the life of the components remarkably increases moving from spur gears to helical. Moreover, adding proper microgeometry modifications it possible to even enhance the static performance, also centring the contact patch, which is another important goal of static evaluation. Then, the dynamic analysis can be done, considering as excitation source the transmission error (TE) of both gear sets composing the transmission system, the unbalance of the rotor and the electromagnetic excitation coming from the electric motor. Considering the model with spur gears, it has been verified the supremacy of the vibration response due to TE excitation, rather than due to the other sources. Moving to helical gears, it is possible to strongly reduce the vibration response and the emitted noise caused by the TE excitation. Only adding proper microgeometry modifications, the response to electromagnetic excitation becomes the only relevant one, leading to almost negligible vibrations and noises produced by TE. Finally, a sensitivity analysis on the electric motor is performed, too, mainly considering modifications of the parameters of the motor, modifying the number of poles and slots. As regards the dynamic analyses, not only results in terms of amplitude of forces and acceleration response are available, but also results directly related to sound and acoustic are obtainable, which are particularly important to gain information about the directivity of the sound. The last considered aspect concerns the efficiency: it is indeed possible to compute the losses of both the mechanical and the electric components of the powertrain. It is demonstrated that microgeometry can also strongly help in enhancing the performance of gears even from the efficiency viewpoint. This thesis represents a starting point useful to understand how to use the features of this commercial software to study in a pretty complete way all relevant aspects of the design of an electric powertrain. Future steps could require moving beyond just the simulation world, trying to correlate the results obtained by the software with some experimental data coming from an existing model. Further optimizations of the transmission system and other methodologies to reduce noises and vibrations caused by the electric motor can be studied.