Lightweight Optimization Of Electric Bus Frame Considering Rear-End Collision And Structural Safety

The mass of the body accounts for too much of the whole electric bus.And when the body mass is reduced,the performance of electric bus is improved.However,the lightweight design of the body is not a simple project,while achieving the goal of weight reduction,comprehensive performance of the bus should also be guaranteed.The research object of this study is electric bus frame,and the finite element(FE)model of the electric bus frame is established.Then the static and modal performances of the bus body under bending and torsion conditions are analyzed.At the same time,the model of moving barrier vehicle and rear-end collision are established,and the collision safety analysis is carried out.The electric bus frame is divided into 20groups according to thickness and area of the components,and then the components’initial thickness are defined as design variable for subsequent optimization.To save calculation time,the top ten groups of design variables that have a great impact on the output response are screened out according to the technique for order preference by similarity to ideal solution(TOPSIS).Design of Experiments(DOE)is completed based on Hyper Study software,and then quadratic polynomial response surface models representing the relationship between design variables and output response are established.A lightweight design scheme of electric bus frame was proposed,where the optimization goal is to minimize mass,and the constraint conditions include the first-order modal frequency,the maximum stress of the unit,and the stiffness of the body under bending and torsional conditions.The deterministic optimization is completed based on the composite differential evolution for constrained evolutionary optimization(C~2oDE).Then,the reliability of the deterministic optimal solution is calculated according to Monte Carlo sampling method.When the reliability is too low,the reliability optimization design scheme is carried out based on the sequential optimization and reliability evaluation method(SORA).Comparing the optimized solution with the initial value,it can be concluded that the mass of body frame is reduced by 50kg and the weight reduction rate is 4.89%under the premise of ensuring no loss of static and modal performance.The top five groups of design variables that separately have great impact on the static performance,modal performance and collision safety performance are combined to study together how to improve the crashworthiness and realize the lightweight of the bus body.The multi-objective optimization is realized based on the non-dominate sorting genetic algorithm (NSGA-).The optimization objectives are to minimize the mass and maximize the energy of the rear wall of the bus frame,and the constraint conditions are the output response representing the static and modal performance,the invasion velocity of the rear wall bottom,the maximum intrusion of the rear wall,and the synthesized acceleration of the passenger compartment center.Then,the optimal solution calculated based on the surrogate model is substituted into the FE model to verify the error and analyze the optimization effect.The results show that the mass of electric bus is reduced by 3.3%,the energy absorption of the rear wall increases by 6.69%without much change in overall performance,which greatly improves the collision safety performance of the tail structure of the electric bus frame,and verifies the effectiveness of the optimization scheme.