Dynamic Optimization Method for Speed Ratio of Electric Vehicle's Transmission System Based on NMOPSO Algorithm

In order to achieve the best vehicle economy performance, on the basis of static optimization on the speed ratio of transmission in a pure electric vehicle and in view of its defect of without adopting corresponding gear-shift schedules for different speed ratio, a dynamic optimization scheme on transmission speed ratio with consideration of changing gear-shift schedules is proposed based on shifting point judgment rule. An objective function of minimizing the sum of all speed ratios of transmission is also put forward based on lightweight design principle. Then an ISIGHT-MATLAB/Simulink co-simulation is conducted on objective functions by adopting niche multi-objective particle swarm optimization (NMOPSO) algorithm, which can avoid local convergence. The results of optimizations (both static and dynamic) achieve certain effects: compared with the optimization without considering gear-shift schedules, the energy consumption of vehicle reduces by 1.09%~1.35%, the sum of speed ratios lowers by 8.06%~9.76%, but 0-100km/h acceleration time increases by 1.90%~2.11%, probably because the weighting of objective function still preferring on fuel economy. Compared with the optimization considering static gear-shift schedules, with dynamic optimization, the reduction percentage of the sum of speed ratios increases by 0.95%~1.7%, but the energy consumption of vehicle is basically maintained the same as that with static optimization, not showing the expected effects of adopting different gear-shift schedules for different speed ratios in optimization. This requests further in-depth exploration in subsequent research.