Research On The Design And Multi-objective Optimization Of The Front Under-protection Structure Of Commercial Vehicles

With the introduction of national environmental protection policies on commercial vehicles,as well as the continuous increase in commercial vehicle ownership,in order to reduce the emissions of commercial vehicles pollution,improve the fuel economy of commercial vehicles,reduce the fuel consumption of commercial vehicles,commercial vehicles have become a new direction of design optimization.As an important part of the passive safety of commercial vehicles,front underrun protective of commercial vehicles has an irreplaceable role in ensuring the safety of the occupants,but its quality of the front underrun protective is usually too heavy,so its lightweight design plays an important role in the lightweight design of the commercial vehicle.In order to achieve the lightweight design of front underrun protective for commercial vehicles,the "preliminary design and experimental verification-CAE analysis-optimization of design and process implementation improvements" should be used in the entire optimization process.It is divided into the following three parts:(1)According to the classical mechanical theory of commercial vehicles after the simplification of front underrun protective force analysis,according to the deflection theory,the use of the Mohr integral formula to design the section of front underrun protective.After that,constructing the 3D model of the front underrun protective using Proe.Then in order to verify whether the front underrun protective designed according to the theory meets the relevant regulatory requirements,after completing the test of the sample,set up a threepoint static pressure experimental platform,in accordance with the relevant regulations on the sample three-point static pressure experiment,collect the bending deformation of the center of the force in the test,and compare with the prescribed permissible bending range.The results show that the experimental values of the three operating conditions are less than the allowable values of the corresponding operating conditions,which shows that the front underrun protective conforms to the relevant regulations and is designed reasonably.(2)On the basis of the preliminary design of commercial vehicles under the threedimensional model of protection,the establishment of a finite element model,in accordance with the GB 26511-2011 commercial vehicle front and down protection requirements,according to the three-point static pressure experiment requirements for three different operating conditions for the finite element analysis and calculation,and the completed three-point static pressure experiment comparison,The results show that the actual shift error of the center of the force in CAE simulation experiment and the three-point static pressure experiment is not more than 10%.The correct fixation and accuracy of the methods and conclusions of the relevant CAE simulation experiments are shown.Then the front and lower protective main beam of commercial vehicles is free-mode dissotomy,and the first 10 thubar natural frequency is extracted,which lays the foundation for the subsequent multiobjective optimization.(3)Combined with the use of the front underrun protective main beam of commercial vehicles and related regulations,to determine the 3 stiffness sub-targets,in order to extend their service life,determine the 6 natural frequency optimization sub-targets,through the 5unified volume outline to build including stiffness sub-goals and natural frequency optimization sub-targets,the construction of multi-target comprehensive optimization target function.First,the hierarchical analysis method determines the weight coefficients of each sub-target,verifies the weight coefficient sits reasonably by the consistency method of hierarchical analysis,secondly determines the initial value according to the results of the CAE simulation experiment of the rounded rectangle,and finally determines the concrete final multi-target optimization function by integrating the multi-target integrated target function.Optistruct is used to optimize the morphology by setting design domain and nondesign domain,buffer region,multi-objective comprehensive optimization function,etc.,and the morphology optimization results are obtained through 7-step iterative calculation.According to the limitation of the cold roll pressing process,the process feasibility was improved based on the morphology optimization results,and finally a special-section commercial vehicle front underrun protective girder structure was obtained.In addition,CAE simulation experiment was carried out according to the requirements of three-point static pressure experiment for two preset schemes of setting thickness of 2.3mm and 2.1mm.The experimental results show that both of the two schemes can meet the relevant laws and regulations.Combined with the lightweight requirements,the special-section(2.1mm)front underrun protective girder structure of commercial vehicles is finally selected,and the first 10 order natural frequencies are also improved to a certain extent,which can achieve the purpose of extending its service life.Finally determined the program weight reduction 4.66%.