Pass by Noise Reduction on an Intermediate Commercial Vehicle 2018-01-1535

A major activity of any new vehicle development program, is to meet legal requirements of local markets. Pass by noise (PBN) test is one of the standardized tests and is used to certify new vehicles/variants for their Noise emissions. Certification for noise emissions of commercial vehicles is achieved by measuring external sound levels according to procedures defined by standards such as IS: 3028 for Indian market. Before a physical proto-vehicle is assembled, various systems and subsystems are readily made available by suppliers off the shelf. During final design validation of the vehicle by mule-vehicle testing, PBN target compliance need be assured for all these systems in order to meet overall PBN target. The PBN on an Intermediate commercial vehicle (ICV) migrated to the latest Exhaust emission standard, was the subject of this study. This vehicle emitted PBN greater than accepted threshold. Significant design changes on proprietary components from supplier(s) is not feasible considering cost and time to market implications. A quick and accurate method of source identification as well as countermeasure development that would meet the cost, quality and delivery requirements of the program was therefore paramount. The overall approach is to identify the dominant frequency bands of PBN and identify main noise contributors for those frequency bands through selective near source noise measurements and windowing techniques. This method is reliable and quickly reveals significant noise contributors. Improvements on the main identified noise sources are verified for its effectiveness on overall PBN reduction. By implementing those modifications on the respective system(s), the required noise reduction was achieved and the vehicle met the PBN target.