Assessing lightweight layouts for a parallel Hybrid Electric Vehicle driveline

The presence of multiple power sources and the several possible architectures that can be designed when referring to hybrid electric vehicle (HEV) powertrains complicate the identification of an optimal HEV configuration. Among the diverse parameters that can be chosen in design and sizing processes of a parallel full HEV, the number of gears and the gear ratios in the transmission are considered as fulcra of this case study. For this scope, five different transmissions have been sized while assessing drivability and acceleration performance along with the fuel economy capability. A dynamic programming-based approach algorithm has been utilized for controlling the HEV, thus providing reliable outcomes and enhancing the consistency of the study. The results obtained in the sizing process suggest that the presence of an electric machine may mitigate the effect of the lower number of gears and enhance the fuel consumption efficiency even when reducing the number of gears in the transmission to 2 or 3. More precisely, even though they might be associated to slightly higher fuel consumption and, in turn, operative costs compared with the other considered configurations, these drawbacks can be overcome by the higher savings in production costs, thus suggesting parallel full HEVs with a reduced number of gears as an appealing design option.