Research On Optimization Of The Automobile Front Bumper System's Performance Considering Low-speed Collision And Pedestrian Lower Leg Protection

When a vehicle hits pedestrians,the front bumper system first comes into contact with pedestrian's legs.Some of injuries might be irreversible and will accompany the pedestrian a whole life.Meanwhile,in order to reduce the damage of rear body,the bumper should have good crashworthiness.But there is a contradiction between the protection performance of pedestrian leg and low-speed crashworthiness.Therefore,it is of great importance to study the performance of front bumper system considering both low-speed collision and pedestrian lower leg protection.This paper regards the front bumper system of a passenger car as a study case.Through the simulation analysis,it is found that the injury value of the pedestrian lower leg does not meet the requirements of the EEVC regulation.By the multi-objective deterministic optimization,the performance of the pedestrian lower leg protection is obviously improved when the bumper system maintain good crashworthiness.Firstly,the surface stiffness and modal characteristics of bumper skin are analyzed.The results of the surface stiffness analysis show that the deformation amount of the loading points can satisfy the technical specifications of the enterprise,and the accuracy of the simulation model is verified.The numerical modal analysis shows that the first order natural frequency meets the requirements.Secondly,the low-speed crashworthiness and pedestrian protection performance of the bumper system is evaluated.The experimental analysis and simulation analysis are carried out on the front bumper beam with low velocity frontal impact,and the acceleration simulation curve of the collider is in agreement with the experimental curve,and the validity of the finite element model is verified.The results show that the bumper system has good low-speed crashworthiness,but the tibia acceleration at Y400 collision point does not meet the requirements of EEVC regulations.Finally,the multi-objective deterministic optimization design method is used to optimize the comprehensive performance of the front bumper system.The sensitivity analysis determines the four parameters as optimal variables.The optimization results show that the tibia acceleration of the Y400 collision point is reduced by 47.71%,the bending angle and the shear displacement of the knee is reduced by 62.59% and 23.08% respectively,and the bumper still maintains good low-speed crashworthiness.And the bumper system's quality is reduced by 27.57%,achieving lightweight target.The 6Sigma reliability analysis of the optimization results is carried out,and the results meet the design requirements.