Multi-objective gear ratio and shifting pattern optimization of multi-speed transmissions for electric vehicles considering variable transmission efficiency

摘要

In the development of electric vehicles, multi-speed transmissions have become an alternative to con-ventional single-speed transmissions. The superior design of multi-speed transmissions requires simultaneous optimization of the gear ratios and shifting patterns. The transmission efficiency of multi -speed structures is inevitably lower than that of single-speed structures; this disadvantage should be considered in the design optimization for multi-speed transmissions. Typically, the transmission effi-ciency varies depending on the torque, speed, and drive gear, and it has a direct effect on the optimal transmission design. Based on the variable transmission efficiency analysis, the design objectives rep-resenting energy efficiency and dynamic performance were defined as the quantified functions. To consider the trade-off between these two objectives, a multi-objective optimization process was implemented, and the surrogate models were utilized for effective optimization. To verify the importance of a variable transmission efficiency, the gear ratios and shifting patterns were optimized by considering a variable and constant transmission efficiencies. The comparison of optimal design solutions and objective-function values clearly highlights the necessity of considering a variable transmission effi-ciency, and the energy efficiency and dynamic performance could be improved to maximums of 12.1% and 10.7%, respectively, compared to those of the electric vehicle with a single-speed transmission. (c) 2021 Elsevier Ltd. All rights reserved.