Optimal drivetrain design methodology for enhancing dynamic and energy performances of dual-motor electric vehicles

Abstract

Electric vehicles (EVs) are a dominant transportation trend towards a low-carbon future. However, there is a lack of systematic studies for full-electric off-road vehicles in terms of drivetrain design and energy management issues. This paper proposes a novel methodology to develop a drivetrain system for a four-wheel-drive (4WD) dual-motor off-road EV. The obtained design delivers high performance in both driving performance and energy efficiency of a desired vehicle using the two electric motors with their multi-speed gearbox. The proposed approach is to minimize the power envelope (force-speed characteristic) difference between a targeted model and the system under study. As a result, the objective function finds an optimal solution for a proper set of gear ratios and constant power speed ratio (CPSR) through a two-layer hierarchical scheme. The upper layer sets the targeted power envelope based on the expected driving measures. The lower layer minimizes the gap of the power envelope characteristics between the targeted vehicle and the dual-motor vehicle. In parallel, two optimization loops are implemented at the lower layer. The outer loop determines the proper value of CPSR, meanwhile, the gear ratios corresponding to the selected CPSR are optimized by a particle swarm optimization (PSO) algorithm in the inner loop. The results verify that the dynamic and energy performances of the studied dual-motor vehicle are enhanced over critical testing scenarios. In a comparison with the single-motor single-speed gearbox configuration, the optimized design shows that the top speed is 55% higher; the acceleration time to 45 km/h is reduced by 55.83%; and the gradeability is improved by 162.5%. Moreover, the test under a typical off-road cycle reveals a 1.9% overall efficiency increase compared to the dual-motor drivetrain using the same non-optimized gear ratio. The proposed comprehensive design approach has the potential to be applied to a wide range of vehicle areas.