Methodology to Study the Impact of the Exhaust System on the Vehicle Interior Noise - Identification and Target Setting 2016-01-1826

The transfer characteristics, location of the mounting points, where the exhaust system is attached to the vehicle structure, and the level of excitation forces have a significant contribution to the overall interior noise. The aim of this study is to define targets for the excitation forces of the exhaust line in order to identify its contribution to the overall vehicle interior cabin noise in the early vehicle concept phase when the hardware is not yet available. Furthermore, psychoacoustic parameters are calculated, e.g. the articulation index which provide a representation of the human hearing perception. Therefore a software tool was developed in MATLAB to cascade the interior noise contributions of the exhaust system using the corresponding transfer paths. This tool enables a quick prediction of different combinations (different hanger stiffness and other parameters) to evaluate the potential for improvements. The method combines measured or calculated (FEA) transfer path sensitivity with hanger forces measurements of a similar predecessor exhaust system. To predict the interior noise contributions, the “Mount Stiffness” method is applied in a MATLAB program with a focus on easy use. As the interior noise is a composition of structural noise and tailpipe orifice noise, the predicted noise contribution has been expanded by taking into account the tailpipe noise as well. Moreover, it is possible to import excitation forces directly from CAE codes. The validation has been carried out by recalculating the entire NVH transfer paths and comparing it to noise measurements for different passenger ear positions in a test vehicle.