Establishment of mathematical optimization modelDetermination of optimization variablesWe determined the basic parameters of the vehicle and the parameters of the drive motor. The total speed ratio of the transmission system will eventually affect the power and efficiency of the battery electric vehicle,19 and thus, it is particularly important for optimizing the transmission ratio.20 In this study, the main reduction ratios of the transmission system as well as the first-gear and second-gear transmission ratios were taken as the optimization variables, and the design variable was expressed as follows: