A Comprehensive Evaluation of PU Foam for EV NVH Performance

Low density polyurethane foam was first proposed as an alternative to expandable baffles and tapes for sealing vehicle body cavities towards the end of the last century. In spite of several inherent advantages for cavity sealing, the high equipment cost of dispensing amongst other reasons, this technology has not spread as widely as expected. With the advent of electric vehicles, there is an increased emphasis on controlling higher frequencies from motors, inverters and other components, and polyurethane foam can be a viable solution by providing more robust sealing. Polyurethane foam sealing is already being employed in the new breed of electric vehicles but its NVH advantages have not been fully studied or published in literature. Using an existing electric vehicle with conventional expandable baffles & tape sealing measures, a comprehensive evaluation of NVH performance using the closed-cell polyurethane foam solution was carried out. Testing included component level bench test on body-in-white, body-in-white and full vehicle air leakage tests, vehicle airborne source-to-receiver transfer functions and vehicle on-road performance for wind and road noise. The results indicate that closed-cell polyurethane solution clearly improves NVH performance over the traditional sealing solution at the component level (cavity treatment), system level (body-in-white) and full vehicle level. Compared to existing sealing solution, the total vehicle leakage was improved by 20% and airborne noise sensitivity of the vehicle improved by up to 1 dB. This resulted in on-road vehicle NVH performance improvements of approximately 0.7 dB or 2.5% in the airborne frequency range. With a competitive cost and mass offering, low density polyurethane foam is a formidable alternative to conventional expandable baffles and tapes with clear potential to improve high frequency NVH performance in EVs.