Strategies for weight reduction have driven the noise treatment advanced developments with a great success considering the already mastered weight decreases observed in the last years in the automotive industry. This is typically the case for all soft trims parts. In the early 2010's a typical european B-segment car soft trims weights indeed 30 to 40% less than in the early 2000's years. The main driver behind such a gap has been to combine insulation and absorption properties on a single part while increasing the number of layers. This product-process evolution was conducted using a significant improvement in the simulation capacities. In that sense, several studies presenting very good correlation results between Transmission Loss measurements and finite elements simulations on dashboard or floor insulators were presented.
One may consider that those kinds of parts have already achieved a considerable improvement in performance. But the challenge of weight reduction continues due to up-coming CO2 emissions regulations. To follow this request, one has to move from a single part analysis to an environment dependent approach considering, for example, not only the dash inner insulator but the dash inner coupled with the Instrument Panel. In that sense, recent works increased the studied perimeter considering the Instrument Panel coupled with the dash inner insulator, but without any correlation with coupled reverberant rooms measurements.
In this paper, a numerical finite element study dealing with Transmission Loss simulation of a dashboard insulator with consideration of the Instrument Panel, including absorbing systems behind the Instrument Panel, was carried out in order to predict the insulation performances of a complete front vehicle unit. In the meantime, Transmission Loss measurements were performed in coupled reverberant rooms, in order to check the quality of the model and to assess the quality of the pass-throughs, which are still not taken into account in this paper, but which are driving the global level especially in the high frequency range. Several optimization loops have been carried out in order to define the optimized part depending on the overall targeted performance. This extended module model is then included in a complete vehicle model which is still under investigation.