Design Optimization of a Lightweight Electric Bus Body Frame Orienting the Static Performance and Side-Impact Safety

This work aims to perform the optimization of the iron-aluminum lightweight body frame of a commercial electric bus orienting the static performance (e.g., strength and stiffness), side-impact safety, and possible reduction in mass. Firstly, both the static and side-impact finite element (FE) models are established for the electric bus body frame. The body frame is partitioned according to the deformation and the thickness of the square tube beams, and the contribution is analyzed by the relative sensitivity and the Sobol index methods. The thickness of the tube beams in the nine regions is selected as the design optimization variables. After data sampling by the Hamersley method and conducting design of experiments (DOE), the surrogate models for optimization are fitted by the least square method. A multi-objective optimization problem is formulated by selecting the mass of the overall body frame, the maximum vehicle stress and the intrusion of the upper part of the collision area as the objectives of design optimization. The optimization problem is solved by the co-evolutionary constrained multi-objective optimization algorithm. By respectively focusing more on each of the three optimization objectives, three optimization schemes are solved and discussed. The optimization results are finally evaluated by FE simulations, and it is revealed that the stress is reduced by 34.41% and the side-impact intrusion is reduced by 4.48%, while the vehicle mass remained basically unchanged. The proposed optimization method can effectively improve the static performance and the side-impact performance of the iron-aluminum lightweight electric bus body skeleton.