Analysis and Refinement of Road Boom Noise in Electric Vehicles

Nowadays, customers are expecting higher level of refinement in electric vehicle. Since the background noise is less in electric vehicle in comparison with ICE, it is challenging for NVH engineers to address even minor noise concerns without cost and mass addition. Higher boom noise is perceived in the test vehicle when driven on the coarse road at the speed of 50 kmph. The test vehicle is rear wheel driven vehicle powered by electric motor.. Multi reference Transfer Path Analysis(TPA) is conducted on the vehicle to identify the path through which maximum forces are entering the body. Based on the findings from TPA, solutions like reduction in the dynamic stiffness of the suspension bushes are explored which resulted in reduction of noise. To reduce the noise further, Operational deflection shape (ODS) analysis is conducted on the entire vehicle to identify the deflection shapes of all the suspension components and all the body panels like floor, roof, tailgate, dash panel, quarter panel, doors at the problematic frequency. Based on ODS, the components having higher deflections at the problematic frequency is identified. Modifications are proposed to improve the dynamic stiffness of the structure at the problematic frequency and the contribution of each modifications for cabin noise reduction is discussed. Alternate solutions like tuned mass dampers (TMD) on suspension components and body panels are explored and the critical parameter which should be taken into account to get maximum reduction in noise with TMD is also discussed. Effect of tire stiffness reduction in the noise is also explored. With all the modifications, the noise levels are reduced by 6 dB (A) at problematic frequency. NVH criteria which should be considered related to suspension and tire system to avoid boom noise concern in electric vehicle is also discussed.