Multi-Objective Lightweight Optimization Design Of Steel-Aluminum Hybrid Body For The Full-Load PHEV Bus

With the development of the bus and the environmental protection more and more important,the lightweight design of bus is of great significance to save fuel consumption,reduce emissions,improve the range and battery life.Therefore,based on the National Key R& D project of “High performance-to-price ratio commercial vehicle hybrid power system development and vehicle integration”(2018YFB0105900),this paper completes the subproject of “Research on lightweight technology of multi-material composite structure plug-in bus body”,the light weight optimization design is carried out for a certain bus,and the weight reduction effect is achieved while the performance of the frame is guaranteed.In this paper,we use TRIZ theory to find the proper parameters in “39 engineering parameters” and analyze the conflict property of optimization problem.Then we use “40invention principles” to find the idea that can guide the whole optimization design,combining with the engineering practice,the optimal design scheme is determined.The finite element model of the bus frame is established,and the strength,stiffness and free mode analysis of the bus frame under bending,torsion,steering and braking conditions are completed,which verifies the accuracy of the model,and provides the condition for the lightweight design later.The original steel is replaced by aluminum alloy material according to the principle of equal rigidity for the frame of the front,back,left and right sides of the bus body.Then the variables of the frame are grouped and the relative sensitivity analysis is completed to screen the design variables.The thickness and shape of the beam section are optimized by the orthogonal test design method,which improves the performance of the bus frame and lays a foundation for the light weight optimization design.Two-step sensitivity analysis was carried out to screen the variables for the bus bottom frame structure.Firstly,all the variables were grouped according to the thickness and the relative sensitivity was analyzed to complete the first variable screening.Secondly,the selected variables are grouped according to symmetry and functionality,and the optimal design variables are determined by the second relative sensitivity analysis.The Latin hypercube design method is used to find the sample points,and the sample space is established by simulation.After fitting the Gauss process regression approximation model with the sample data,the Pareto optimal solution set satisfying the optimization requirements can be found and the optimal results can be obtained by particle swarm optimization combined with the mathematical model of optimization problem.Finally,the stiffness and strength of the optimized bus frame are analyzed under four typical operating conditions,and the free mode frequency and the formation are calculated.The results show that the stiffness and strength of the optimized bus frame can meet the requirements while the weight is reduced by 327 kg and the weight reduction rate reaches13.24%,which means the light-weighting effect is obtained.