Powertrain system design optimization is an unexplored territory for battery electric trucks, which only recently have been seen as a feasible solution for sustainable road transport. To investigate the potential of these vehicles, in this paper, a variety of new battery electric powertrain topologies for heavy-duty trucks is studied. Thereby, topological design considerations are analyzed related to having: (a) a central or distributed drive system (individually-driven wheels); (b) a single or a multi-speed gearbox; and finally, (c) a single or multiple electric machines. For reasons of comparison, each concurrent powertrain topology is optimized using a bilevel optimization framework, incorporating both powertrain components and control design. The results show that the combined choice of powertrain topology and number of gears in the gearbox can result in a 5.6% total-cost-of-ownership variation of the vehicle and can, significantly, influence the optimal sizing of the electric machine(s). The lowest total-cost-of-ownership is achieved by a distributed topology with two electric machines and two two-speed gearboxes. Furthermore, results show that the largest average reduction in total-cost-of-ownership is achieved by choosing a distributed drive over a central drive topology (−1.0%); followed by using a two-speed gearbox over a single speed (−0.6%); and lastly, by using two electric machines over using one for the central drive topologies (−0.3%).

One general trend aiming to improve the development of hybrid electric powertrains is the reduction of production cost of powertrains by developing powertrain components that can be used for multiple vehicle segments. The development of these kind of modular powertrain components requires knowledge on the robustness of the performance of vehicles on the sizing of powertrain components, especially for the heavy- duty segment. Therefore, this paper presents a sensitivity analysis of the influence of component sizing on the performance, the costs, and the controls of a long-haul heavy-duty parallel plug- in hybrid electric truck, taking into account the use of a waste heat recovery system.