Analytical Evaluation of Propulsion System Architectures for Future Urban Vehicles

Today, nearly half of the world population lives in urban areas. As the world population continues to migrate to urban areas for increased economic opportunities, addressing personal mobility challenges such as air pollution, Greenhouse Gases (GHGs) and traffic congestion in these regions will become even a greater challenge especially in rapidly growing nations. Road transportation is a major source of air pollution in urban areas causing numerous health concerns. Improvements in automobile technology over the past several decades have resulted in reducing conventional vehicle tailpipe emissions to exceptionally low levels. This transformation has been attained mainly through advancements in engine and transmission technologies and through partial electrification of vehicles. However, the technological advancements made so far alone will not be able to mitigate the issues due to increasing GHGs and air pollution in urban areas. Electrification of propulsion systems may play a significant role in overcoming the challenges associated with personal urban mobility. Electric vehicles are particularly suited for use in urban areas since city transportation is mainly characterized by relatively short driving distances, low continuous power requirements, long idling times and high availability of regenerative braking energy. These characteristics, when carefully incorporated into the design process, create valuable opportunities for developing clean, efficient and cost effective urban vehicle propulsion systems. In this paper, various urban propulsion systems architectures that can address these challenges are presented. These architectures are incorporated into a vehicle math model and they are analyzed. Various advanced propulsion system architectures are presented and their benefits relative to conventional propulsion systems are assessed. Strengths and weaknesses of different designs are assessed relative to conventional propulsion systems on the basis of metrics such as well-to-wheel energy conversion efficiency, GHG emissions and vehicle functionality.