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Before a physical proto-vehicle is assembled, various components or subsystems are ready by Tier-I or II suppliers. During final design judgement of the vehicle thru’ CAE or Mule-vehicle testing, performance target compliance need be assured for all these components to meet the Vehicle-level NVH targets. The work here studies some of the major components of a passenger car. Their individual NVH response can be critical to be cascaded for meeting the final targets for the vehicles running over roads. Conclusions of the study challenge some of traditional beliefs or generic targets. Often the component level response deviating from its own targets may not have an adverse influence on NVH of the vehicle facing multiple excitations from tyre/road, wind and power-train in a frequency band of interest.

This technical paper presents a study to eliminate 6.5 kHz to 8.0 kHz abnormal whistle noise created by the exhaust at engine rpm ranging from 2000 rpm to 4000 rpm. The abnormal noise to a customer has a high level of repeatability during highway driving. Vehicle level experiments were carried out to root cause the noise source and identify optimization, which will not impact other parameters like exhaust back pressure, emission and vehicle pass-by noise. The study was focused on perforated pipes in mufflers internals with different perforation patterns, hole sizes, hole shapes and addition of glass fiber mat.