Real-world steep drive cycles and gradeability performance analysis of hybrid electric and conventional class 8 regional-haul truck

Gradeability is a key determinant for powertrain component sizing of class 8 heavy-duty (HD) trucks; thus, knowing real-world steep roads along with their grade profiles are essential for design and performance analysis of commercial HD trucks. This paper refines the traditional gradeability criterion established by the SAE J2807 standard for conventional HD trucks, tailoring it to address the testing requirements of hybridized HD trucks with downsized internal combustion engines (ICE). To achieve this, grade–distance profiles of 14 steep highways worldwide from the U.S., Canada, Europe, and China used by HD trucks are introduced. These profiles serve as benchmarks for assessing the gradeability performance of both conventional and pre-transmission parallel hybrid class 8 truck models. The optimal component sizing of the conventional and hybrid models is refined using each newly identified steep highway as the gradeability criterion. Results show that the equivalent fuel consumption of the parallel hybrid truck models, with the refined component sizing, is 3.4% to 8.9% lower than the conventional counterpart, over a representative highway drive cycle. This superiority is attributed to the hybrid’s ability to maximize engine efficiency, reduce engine-on time, and utilize regenerative braking.