Fuel Savings of a Medium-Duty Hybrid Electric Truck With Varying Electric Axle Efficiencies

The cost of truck electrification can be offset by significant fuel savings, making the efficiency of components critical. Among these, electric axle efficiency is a key factor in achieving fuel savings. This paper quantifies the impact of electric axle efficiency on fuel savings in hybrid electric trucks. The electric axle studied consists of an inverter, electric machine, gearbox, and control unit. For fair comparison, the speed range of the electric axle and the mechanical drivetrain parameters are kept constant. An accurate forward model of the truck is coupled with optimal energy management strategies, organized by the energetic macroscopic representation (EMR), enabling a flexible analysis of different scenarios. The study reveals that, although electric axle efficiency improves by up to 6%, fuel savings for long-haul transportation are minimal (less than 0.7%). In contrast, urban trips (e.g., delivery trucks) see fuel savings of up to 5%, regardless of whether a 20Ah or 40Ah battery is used. Additionally, in the case of plug-in hybrid trucks, fuel savings can reach 12% during inter-urban trips with a 100Ah battery. The development of more efficient electric axles for hybrid trucks is most beneficial for specific usage scenarios and depends on the level of hybridization.