Design Selection of Multi-Mode Power-Split Hybrid Electric Vehicle Powertrains

The new challenges of reducing the fuel consumption and the pollutant emissions are leading the transport sector towards a paradigm shift. Among the sustainable alternatives to the carbon fossil dependency the electrification is one of the most appealing solutions. In fact, the technological progress, especially in the power electronic field, is making ectrified vehicles increasingly attractive for the mobility scenario. Nevertheless, some know-how limitations, as the ones related with the battery energy density, represent the current obstacle for a massive penetration of the fully electric vehicle (EV). Consequently, in the near future the market will be likely dominated by the hybrid electric vehicles (HEV). In this case both the internal combustion engine and the electric components can contribute to the propulsion with a significative efficiency improvement. Among the HEV state of art possible design architectures, the power split HEV are the most interesting for the market. Indeed, they can exploit the advantages of both parallel and series configurations. These types of transmissions typically use the planetary gear sets as power split devices to divide the engine power in an electrical and a mechanical path. Typical current market applications are the transmission of Toyota Prius 2010, Chevrolet Volt II Generation, Ford Fusion and Chrysler Pacifica. Moreover, the addition of clutches allows to greatly improve the powertrain flexibility enabling multi-mode operations. Being for this type of HEV the design stage a crucial activity the aim of the whole project is to create a tool capable to select the best design and sizing providing the right compromise solution among fuel economy, emissions and vehicle performances. This thesis deals with the first step of the tool development, which is related to the selection of the best design candidate on the base of the fuel consumption value fixing as input parameters the components dimension. For this purpose, the selection of the proper energy management strategy (EMS) is crucial. A design instrument, called “Analytical Transmission Design Tool” (ATDT), has already been built in MATLAB, using as EMS the “Power-weighted Efficiency Analysis for rapid sizing” (PEARS) algorithm. Since the results produced have been found to be in some cases far from the optimal benchmark, the scope of this dissertation is to find a new and more suitable optimization algorithm for the design analysis. First, the “Slope-Weighted Energy-Based Rapid Control Analysis” (SERCA) is implemented in the ATDT. Subsequently, after some consistency analysis, another strategy called SERCA+ is introduced. This algorithm, which represents the main intellectual contribution of this research, is obtained combining the strengths of PEARS and SERCA. Finally, some case studies are presented to confirm the value of the proposed methodology.