Abstract
The demand for decarbonization across all automotive industries is growing, and therefore improving fuel economy and reducing emissions have become top priorities in powertrain technology development. Although battery and fuel cell electric powertrains can be widely deployed to aid decarbonization in many sectors, medium- and heavy-duty (MHD) off-road applications present challenges that are difficult to address with these powertrain approaches. For example, off-road applications require high power ratings, low dwell/refuel times, and robustness to extreme environmental conditions. Additionally, the efficiency of traditional engine-based powertrains for these applications is limited due to the peak load requirement and highly transient operation. Hybridization for heavy-duty off-road powertrains is a viable de-carbonization pathway, replacing or supplementing engine operation with tailored electrification solutions that can also enable the use of low life-cycle carbon fuels that have problems covering the full operating map.
In this study, a novel high-power low-voltage (HPLV) hybrid architecture is employed for medium and heavy-duty off-road applications, featuring a downsized engine, an integrated electric motor, and an energy storage solution that utilizes ultracapacitors for high energy capacity and rapid energy discharge. A modeling approach is presented, as well as a system analysis that compares off-road vehicles with powertrains using internal combustion engines, high-voltage hybrid systems with batteries, and the low-voltage hybrid system investigated here. The analysis shows that, among all available electrification options for MHD off-road vehicles, the low-voltage system with ultracapacitors provides the best synergy with the ICE powertrain, both technologically and economically. Furthermore, the results demonstrate a 17% reduction in powertrain weight through engine downsizing and a payback period of 33 months compared to the conventional diesel powertrain vehicle. Additional simulation results with a real-world mission profile indicate a fuel economy improvement and greenhouse gas emissions reduction of up to 15.5%, and a decrease in criteria emissions of up to 15% are possible, illustrating the emissions benefits of the HPLV hybrid system.
