Operational transfer path analysis of high frequency noise in electric vehicles: air-borne and structure-borne contributions from electric front and rear axle drive units

Abstract

Transfer Path Analysis (TPA) has been a major NVH refinement framework utilized in the automotive industry for years. Traditionally, classical TPA has been used to conduct Source-Path-Receiver based investigations. However, its time-consuming nature and the inability to maintain complete vehicle boundary conditions limit its application to vehicle development stages. Over the recent years, shorter vehicle development cycles have led to the evolution of more practical TPA techniques. Operational TPA (OTPA) is one such efficient and time-saving method, which even ensures the maintenance of boundary conditions over the complete vehicle. However, OTPA results are extremely sensitive to instrumentation and hence, it demands greater care for the inclusion of all coherent transmission paths within the vehicle. OTPA has been proven to be an efficient troubleshooting tool over the conventional Internal Combustion Engine (ICE) vehicles. However, there still remains a vast scope for its implementation in modern electric vehicles due to the high frequency nature of their propulsion noise. This Master Thesis deploys OTPA to study high frequency noise and vibration propagation from the electric propulsion units inside a prototype Battery Electric Vehicle (BEV). Upon a detailed inspection of the potential air-borne leakages and structure-borne transfer paths from the electric motor bays into the vehicle, measurements were conducted on a chassis dynamometer inside a semi-anechoic chamber. Next, individual path transmissibilities to the response, i.e., the Driver Ear Level (DEL), were estimated upon Cross-talk Cancellation (CTC) using Singular Value Decomposition (SVD) and Principle Component Analysis (PCA), and a detailed Path-Receiver based vehicle model was formulated. Moreover, the critical paths responsible for high frequency noise propagation inside the vehicle were detected. To conclude, validation studies were conducted in order to verify the estimated path contributions. The investigation also revealed some challenges in frequency distinction between the air-borne and structure-borne contributions.