Battery Electric Vehicles (BEVs) are extremely sensitive in terms of NVH requirements. While the engine is being replaced with an almost silent electric motor, the transmission noise appears persistent and demands more silent transmission. This has raised demand for improvement in design as well as manufacturing quality. Various innovations are being made to drive an improvement in the NVH.
The following paper will discuss the improvement in NVH achieved through a design optimization of the housing using modal analysis. Firstly, the NVH results were co-related with the modal analysis and the cause for the dominant peak in amplitude of the NVH graph associated with the housing modes were mapped. A simple Excel based correlation matrix is used to map the list of all Eigenfrequencies of housing and its corresponding gear tooth frequency. Further optimization is done in housing design to defer the modal frequencies and another NVH test was run. It was proven that housing design optimization using modal analysis can solve NVH issues and improve the overall performance of the transmission.
It was demonstrated that the electric vehicle NVH is not only critically dependent upon gear geometry and accuracy but also equally impacted by housing design. The best engineered housing design can enhance overall NVH performance of vehicles as well as customer satisfaction.
Background
Regulatory pressures on Internal Combustion Engines (ICEs), combined with technological advancements in electric power trains and batteries, lead to an increase in demand for electric vehicles. Both the traditional carmakers as well as new entrants without ICE legacies are developing and putting new EV models on the market. The dynamics and performance of vehicles have changed significantly because of the switch from ICE vehicles to BEVs. The change in NVH characteristics is among the most noticeable differences. Unlike ICEVs, which generate engine noise that can mask other sounds, BEVs are inherently quieter due to their electric powertrain. This stillness, however, creates special difficulties for NVH since previously muffled sounds- like sounds from the road, wind, and electric motor- become more prominent and may interfere with the driving experience.