Lightweight design of an in-wheel motor using the hybrid optimization method

Abstract

An increase in the unsprung mass is a critical issue for an electric vehicle driven by an in-wheel motor. The mass increase will cause the ride quality and comfort to deteriorate. To decrease the unsprung mass, a hybrid lightweight design method including size optimization and topology optimization is employed for the in-wheel motor. The two optimizations are carried out in sequence. First, the finite element method, the response surface method and the particle swarm optimization algorithm are employed in the size optimization design of the in-wheel motor. After this step, the mass of the in-wheel motor is reduced to 2.7448 kg, while its rated torque and losses are almost unchanged. Second, according to the above optimization results, topology optimization using the method of variable density is employed for the supporting frame of the stator of the in-wheel motor, which is the non-magnetic area. The material which is grade 45 steel is analysed. The optimization results show that, after optimization and treatment, the mass of the supporting frame is reduced to 1.069 kg, i.e. 63.11% lighter than before. Then, structural strength verification is carried out. Considering the above two optimization steps synthetically, the total mass of the in-wheel motor with a grade 45 steel supporting frame is reduced by 3.5547 kg, which means that it is 13.623% lighter than the original structure. Calculation of the transient torque and losses show that, after optimization, the total loss is reduced by 1.87%, and the torque by only 1.8%. Therefore, the hybrid optimization method studied in this paper works well for the lightweight design of an in-wheel motor.