Car interior noise performances, such as booming noise and rolling noise, are usually computed in mid-low frequency range by multiplying vehicle vibroacoustic FRFs and the source (powertrain and chassis) blocked force spectrum. Unfortunately, during the early design stages, the cavity as well as some car body parts’ (like panels) are still subject to geometrical changes that do not allow a full vibrocoustic CAE analysis. Nevertheless, it has been shown that even in the low frequency range the vehicle response remains proportional to the mechanical injected power into the vehicle. The Power Frequency Response Functions was introduced in order to link the energy response of the vehicle to the injected power. Then, decreasing the injected power -without any consideration to the panels and cavity coupled responses- will ensure a noise reduction.
The first part of this paper will introduce the injected power and power frequency response functions computation, using vibroacoustic FE models. The comparison of the injected power with the vehicle vibroacoustic response will then demonstrate the relevance of the injected power for the noise control. This relevance is even strengthen when considering the correlation with experiments. Indeed the computed injected power shows a much better correlation than the vibroacoustic response, since it avoids the modeling of the internal cavity and by the way, its sensitive coupling with the body panels. Robust design direction can then be drawn during the early design stages. Finally, a sensitivity analysis of the vehicle frame is presented for which, both vibroacoustic responses and injected power are considered. Again, the injected power and the SPL inside the cavity seem to be provide results with a comparable relevance.