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A mathematical model has been developed for the investigation of mechanical vibrations of an exhaust system under road load excitation. For practical reasons, the vehicle body and the exhaust system has been considered as masses connected by springs and dampers. Non-linear damping characteristics of the vehicle tires and the exhaust isolators have been included in the model. Equations of motion have been solved in the MatLab environment, and transfer functions of the system and response to input signals representing the power spectrum density (PSD) of the road profile have been obtained for each mass in the system. The model developed has been verified through comparisons to the acceleration time history recordings on a proving ground and has been used for the parametric studies. The paper describes a comparison of model results with experimental observations, and predictions of parametric studies.

Road inputs are one of the most significant components of operational loading of motor vehicles and their exhaust systems. Even if road profiles remain the same, the response spectrums measured on exhaust system components vary for different vehicle and exhaust system combinations. Existing exhaust system product development and design approval procedures require multi-channel data acquisition on vehicles under specified driving conditions and at proving grounds to cover all representative customer usage events. After analysis and reduction, damage relevant sections of this data package will be used for test lab simulation purposes. This vehicle instrumentation and data acquisition process is very time consuming and cost intensive. The method presented here is based on the calculation of the dynamic characteristics of each road segment, or road events using road measured acceleration time histories, and lab measured transfer functions of vehicle body and suspension.