Challenges in NVH for electric vehicles

Abstract

ERTRAC predictions currently show EV growing their market share to around 20 % of new vehicles sold by 2030, to meet these demands NVH engineers will be challenged to define and refine the sound, comfort and feel of tomorrow's automobile without hindering the drive for more efficient vehicles. Often though, improvements in efficiency such as those gained by weight reduction bring extra challenges to the NVH engineer as their concerns become secondary to performance and efficiency gains. This paper aims to show how NVH activities can positively aid efficiency gains for electric vehicles with examples of some recent simulation and test work carried out on electric vehicles. NVH Engineering takes on a new focus for Electric Vehicles with the removal of broadband internal combustion engine (ICE) noise, significant differences are found in the noise spectrum when comparing an Electric Vehicle (EV) with an ICE vehicle. EV noise is characterised by tonal harmonic noise related to the number of poles on the electric motor. Results from vehicle benchmarking tests together with analysis highlight the relative quietness in the low/mid frequency range (<1 kHz). An example of how this can offer opportunities for weight reduction is shown using NVH simulation tools to demonstrate that early application of NVH engineering can aid weight reduction while maintaining acceptable interior sound levels and quality. The choice of electric motor is often dictated by technical, financial and logistical limitations, increasingly in the automotive industry is researching alternative motor configurations that do not permanent magnets such as switched reluctance motors which do not contain magnetic materials which are expected to become increasingly expensive and scarce as demand grows. The drawback of SRM is increased noise and control complexity. A methodology using a combined 1D multi-physics approach and 3D finite element analysis approach is shown with initial results that can help optimize the mechanical design and controls of the SRM in parallel, maximising power without impairing the acoustic performance. Finally with a quieter powertrain a challenge facing vehicle manufacturers is how to alert vulnerable road users to the presence or movement of the electric vehicle, pedestrian warning systems are seen as the best solution but how can you optimize these systems, Fast Multipole BEM tools can help simulate the propagation so sound and the effect of the environment around it, results for such a study are presented to demonstrate its potential. This paper highlights the evolving NVH demands from the emergence of electric vehicles and demonstrates how NVH analysis methodologies can be applied to optimize key vehicle NVH attributes. Analysis of NVH benchmarking data for electric and ICE powered vehicles show the potential needs for NVH engineering focus on electric vehicles. Results of vibration and acoustic simulation tools applied to EV body weight, electric motor performance and warning sound are shown to demonstrate where NVH analysis can aid electric vehicle development without hindering the search for efficiency gains. © 2013 Springer-Verlag.