Optimization Of Front Structure Of A Mini-bus For Pedestrian Protection

Traffic accident has caused heavy damage to the society,and the pedestrian accident rate and death toll remain high.As a result,pedestrian protection it should be taken into consideration in the process of vehicle design,and the study of pedestrian protection has important practical significance.This dissertation's research object is based on a certain kind of mini-bus,the pedestrian leg protection and head protection of the mini-bus were studied in order to improve the comprehensive performance of pedestrian protection.The main research work and achievements are as follows:(1)The CAE model of mini-bus was established.The low-speed collision model was established according to laws and regulations,and the simulation of vehicle crash at low speed was carried out.The low-speed collision model was simplified according to the energy conservation.By comparing the whole mini-bus model and the simplified model,the error rates of each collision were within 5%,which proved the accuracy of the simplified model.(2)The pedestrian leg protection performance of front bumper system of mini-bus was analyzed according to the requirements of Euro-NCAP.And two structural optimization schemes of pedestrian protection were put forward on the basis of experimental results and the original vehicle structure,the energy absorbing foam,the energy absorbing thin-walled steel plate and the lower limb support surface sheet metal structure were adopted.In the structural optimization scheme 2,the tibial maximum acceleration decreased 63.6%,the knee joint the maximum bending angle decreased 62.5%,and the maximum knee shear displacement decreased 66.7%,which implies a significantly increase of the pedestrian protection performance.(3)The 5 influential variables,including collider invasion,bumper beam deformation,tibial maximum acceleration,maximum knee bending angle and maximum knee shear displacement,which influence the low-speed collision performance most and injury the pedestrian lower most,were chosen by using sensitivity analysis.The optimal Latin hypercube test method was used to collect the 5 output response samples,and establish the approximate model of the 5 responses.The multi-objective optimization of the approximate model was established using AMGA multi-objective genetic algorithm optimization to approximate the model of multiple objectives,then the optimal value and the simulation results were compared,and the results showed that the maximum error was 3.37%,which verified the accuracy of optimization.After comparing of the final simulation results and the structure optimization,it was found that the maximum tibia acceleration decreased 5.6%,bending angle of the knee joint decreased 4.4%,and knee shear displacement decreased 16.75%,which realized the multi-objective optimization while ensuring low speed crashworthiness of mini-bus.(4)The CAE model of head impactor for children was established,and the dynamic calibration experiment was carried out.The pedestrian head protection performance of original mini-bus model,the modal properties,stiffness and strength of the front panel system were analyzed,and the multi-objective deterministic optimization scheme based on head protection and lightweight cover plate system was put forward.Firstly,the optimal Latin hypercube design method was applied individually to gather sampling points,including the design variables,front cover quality,head injury values(HIC1-3)of three regions,the first three modes(Mode1-3)and three kinds of stiffness(Stiffness1-3),and then establish different response surfaces,and test the accuracy of the approximate model.Afterwards,the multi-objective optimization was done based on the NSGA-II algorithm,the Pareto solution set and optimal solutions were obtained,and it turned out that the optimized quality and three HIC values were significantly decreased.(5)The Monte Carlo sampling was used to analyze the reliability of the optimal solution,and the quality of the optimization result was not satisfied with the 6Sigma.At last,the multi-objective robust optimization scheme for head protection and lightweight cover plate system was put forward,the Monte Carlo sampling method and NSGA-II algorithm were applied to multi-objective robust optimization,robust optimization.After that,the reliability of each static performance were increased to 100%.Finally,the optimization results were substituted into the original finite element model,the total mass of the front panel system of the mini bus was reduced by 1.269 kg,15.087%,and the HIC values of the three regions were reduced by 25.434%,31.028% and 38.628%,respectively.The results hereinbefore showed that our optimization could meet the requirements of lightweight design,improve pedestrian head protection performance,and ensuring the static performance are in line with the requirements.