Lightweight Optimization Design Of Electric Car Body-in-white Based On Structural Crash Performance

With the energy saving,emission reduction and environmental protection innovation concept deeply rooted in social,the domestic and foreign automotive industry is facing greater challenges and opportunities.Among the new technologies for energy saving and emission reduction,automotive lightweight technology can directly and effectively reduce the vehicle’s energy consumption by reducing vehicle weight while improving vehicle handling and safety.As an important part of the whole vehicle,the structure design of the body-in-white has a great influence on the performance of the whole vehicle and the safety of the occupants.In this paper,the body-in-white of an electric car is optimized for structural multi-objective lightweight under the premise of ensuring its stiffness,mode frequency and structural crash performance.The lightweight optimization of the white body is accomplished through the establishment of body-in-white and the whole vehicle finite element model and completed the analysis,the extraction of the performance indicators of the body-in-white optimization,the division of the white body structure and the selection of design variables and the multi-objective optimization design.Significant lightweight results have been achieved while keeping the body-in-white performance basically unchanged.First,the finite element model of the electric car body-in-white is established,the bending,torsion stiffness and the first 10 order main low frequency elastic modes of the body-in-white are analyzed,and body-in-white lightweight coefficient is calculated.On this basis,by integrating the body-in-white with the chassis,powertrain,four car doors and two car covers,the finite element model of the whole vehicle is further established,and in accordance with the national standard GB11551-2014 and GB20071-2006 test requirements,the simulation analysis and test verification of the vehicle’s frontal and side impact are carried out.The structural crash performance indicators of the white body are extracted,and these indicators are used as the basis for the lightweight optimization design of the body-in-white.Then the body-in-white structure area is divided into non-safety parts,frontal and side impact safety parts according to the characteristics of carrying,crash energy absorption and transmission impact of different parts of the body.Structural sensitivity analysis is carried out on non-safety parts,and structural contribution analysis is carried out on frontal and side impact safety parts respectively.Depending on the analysis,non-safety parts design variables,frontal and side impact safety parts design variables for body-in-white lightweight optimization design are selected.Then,in order to solve the problem of large-scale model and low computational efficiency of the body-in-white lightweight optimization design considering structural crash performance,using radial basis function(RBF)to establish the non-safe part optimization approximation model,the Kriging method is used to establish the optimization approximation model of frontal and side impact safety parts,and completed the accuracy test of each model.Using Non-dominated Sorting Genetic Algorithm(NSGA)and the third Non-dominated Sorting Genetic Algorithm(NSGA-III)to carry out the multi-objective lightweight optimization design of non-safe parts and safety parts respectively and determining its lightweight optimization design scheme.In order to test the performance of the white body after the optimization design variables are rounded,the stiffness,modes and the frontal,side impact structure crash performance of the body-in-white is analyzed,and the corresponding results before optimization are compared.According to the results,the bending,torsion stiffness and the first-order bending,torsion mode frequencies of body-in-white are decreased slightly,but the decrease is less than 5%,which meet the design requirements.Body lightweight coefficient decreased by 1.51%,in the frontal impact,each measuring point intrusion has been decreased,the left and right impact acceleration slightly increased but the increase is less than 5%.Some of the side impact measuring points intrusion and intrusion speed have been increased,the other have been decreased.the impact acceleration increased slightly,but the change was not significant.Overall,lightweight body-in-white in order to meet the stiffness,mode frequency and structural crash performance design requirements.The body-in-white mass is reduced from 228 kg to 216.4kg,11.6kg has been reduced and make a weight loss of 5.1%,resulting in a significant lightweight effect.