NVH Refinement of Structure borne tonal noise in electric vehicle

Globally all OEMs are moving towards electric vehicle to reduce emission and manage fuel cost. Customers expect highest level of refinement and sophistication in electric vehicle. At present, the customers are sensitive to high pitched tonal noise produced by electric powertrain which gives a lot of challenges to NVH engineers to arrive at a cost-effective solution in less span of time Higher structure borne tonal noise is perceived in electric vehicle at the vehicle speeds of 15 kmph and 60 kmph. The test vehicle is front wheel drive compact SUV powered by motor in the front. The electric powertrain is connected to subframe with help of three mounts. Transfer path analysis (TPA) using blocked forces method is carried out to identify the exact forces of the powertrain. Powertrain mount is characterized by applying the predicted forces and dynamic stiffness at problematic frequency is measured. By reducing the dynamic stiffness of powertrain mounts, the noise levels are reduced by ~ 5 dB (A). To reduce the noise levels further, Operation deflection shape (ODS) analysis is performed on electric powertrain, subframe and body to identify the resonating components at the problematic frequency. Based on the outcome of ODS, it is identified that higher deflections are observed on electric motor casing, electric powertrain mounting bracket and bracket connection on body. The dynamic stiffness of motor casing and electric powertrain connection bracket is increased which reduced noise by ~ 3 dB (A) . The dynamic stiffness at powertrain mount connection point on body is increased by ~ 2 times which reduced noise by ~ 3 dB (A). With all the modifications, noise levels are considerably reduced by ~ 10 dB (A). NVH Criteria which should be considered to avoid the structure borne tonal noise is also elaborated.