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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.

Performance improvements, of catalytic converters, and longer service life can be achieved by improving the flow distribution of exhaust gases. Computational Fluid Dynamics (CFD) is an excellent and relatively inexpensive technique for rapid and efficient optimization of the flow. Studies indicate that a 3D representation is necessary because 2D is insufficient. The computations are confirmed by measurements of steady flow. A number of design parameters are systematically investigated and their effects on an index of flow uniformity established. The parameters include the geometry of the inlet tube and inlet cone, the geometry and placement of the monoliths, and the shape of the exit cone. The difficult flow conditions in close coupled converters are examined. The flow path is improved and the best location of the HEGO-sensor found.