The pressure on reducing polluting elements emitted by vehicles is stimulating the research of alternative vehicle power train technologies. Several solutions are already available on the market ranging from low emission diesel engines to a full hybrid approach, which combines a gasoline engine with one or more electrical motors, achieving higher system efficiency. Gas engines are often used as a dedicated solution in public transport. Such a variety of engines and powertrains entail particular effects on the vibro-acoustic performances of the vehicles. As a consequence, NVH analysis methods and procedures need to account for new noise sources, transfer paths, interior sound quality and exterior pass-by-noise performances. This is discussed through the example of an NVH test campaign carried out on a series hybrid bus.
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