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NVH refinement is an important aspect of the powertrain development and vehicle integration process. The depletion of fossil-based fuels and increase in price of gasoline have prompted most vehicle manufacturers to embrace propulsion technologies with varying degrees and types of hybridization.Many different hybrid vehicle systems are either on the market, or under development, even up to all-electric vehicles. Each hybrid vehicle configuration brings unique NVH challenges that result from a variety of sources. This paper begins with an introductory discussion of hybrid propulsion technologies and associated unique vehicle NVH challenges inherent in the operation of such hybrid vehicles. Base: 1700 kg, 150 kW, EU-IV HEV w/ On Board Charging AER: All Electric Range Mild HEV (+ Power Assist + Opt. Operating Strategy) 50 60 70 80 90 100 Otto MPI Diesel Belt Driven Generator (Start/Stop + Recuperation)

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Powertrain noise is a significant factor in determination of the overall vehicle refinement expected by today's discriminating automotive customer. Development of a powertrain to meet these expectations requires a thorough understanding of the contributing noise sources. Specifically, combustion noise greatly impacts the perception of sound levels and quality. The relevance of combustion noise development has increased with the advent of newer efficiency-driven technologies such as direct injection or homogeneous charge compression ignition. This paper discusses the application of a CSL (Combustion Sound Level) analysis-a method for the identification and optimization of combustion noise. Using CSL, it is possible to separate mechanical and combustion noise sources. Combustion noise is then further classified as direct combustion noise (directly proportional to the combustion gas pressures), indirect combustion noise (proportional to rotational forces as well as combustion-induced piston side forces) and flow noise. During the development stage of new powertrains, benchmarking testing and analysis helps to identify the state-of-the-art. Incorporation of the CSL process into the benchmarking process facilitates a more in-depth comparison of powertrains, providing valuable information to drive potential design improvements. In this investigation, two benchmark four cylinder engines were compared using the CSL process. This provided a comprehensive comparison of the noise shares as well as the combustion excitation levels. In addition, the paper compares engine specific combustion noise share weighting functions to obtain insights into the relative strengths and weaknesses of each benchmarked engine.

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