Study On Bumper Optimization Based On Pedestrian Leg Protection

With the development of our national economy, the independent brands of domestic automobile grow up gradually. The safety of automobile has been getting more and more attention with the increase of automobile possession. It is extremely significant to improve the pedestrian protection performance and reduce the number of casualties in traffic accident. The passenger protection has been researching for decades and the results are obvious. However, pedestrian protection has been little attention. The report of road traffic accident indicates that the proportion of pedestrian casualties has been the second largest category of road accident deaths and injuries. The numbers are only after passengers. It is vital to improve the protection performance of pedestrian. The purpose of this study is to improve the protection performance to the legs by optimizing the bumper and to reduce the injuries of the pedestrian in collision of car and pedestrian. The following are the specific contents of this research.(1) A great number of literatures have been reviewed and summarized. This paper introduces research status and methods of domestic and overseas in this field. The methods of pedestrian protection are also researched. Pedestrian safety regulations, principles of bumper design and pedestrian protection design are analyzed.(2) Finite element models of legform impactor and automobile front structures are established. The range of geometry parameter of automobile front structures is analyzed by the method of orthogonal experiment design. The results indicate that the influence of different geometry parameters of automobile on lower extremities injuries is different. The height of bumper center from the ground has great influence on lower extremities injuries. The tibia of pedestrian will benefit from decreasing the height of bumper. The shear displacement and bending angle of the knee are influenced of the shape and highly of bumper. The bending angle will decrease when the contact position between bumper and pedestrian leg is near the centroid of femur and tibia. The bending angle will increase when the contact position is near the knee. When the collision force is located at two sides of the knee joint, the shear displacement will be decrease. The shear displacement will increase when the collision force focuses on one side of the knee joint. Structural parameters of automobile should be comprehensively considered when bumper is optimized.(3) A specific car is chosen as the simulation model. The simulation is based on EEVC Pedestrian Testing Protocol. The collision analysis between legform impactor and automobile front structures is carried through. The results of the simulation indicate that the values of lower extremities injuries are all over the limit of the EEVC (European Enhanced Vehicle-safety Committee) Pedestrian Safety Regulations. It is necessary to optimize the bumper to enhance the pedestrian protection performance.(4) The paper researches on bumper energy-absorbing foam which affects lower extremities injuries and carries through some methods, such as changing thickness, material, shape and position of energy-absorbing foam. As this research indicates, increasing the thickness of energy-absorbing foam, decreasing the stiffness, ladder energy-absorbing foam instead of the integrated foam, proper increasing the distance between the foam and the covering will improve the pedestrian protection performance. However, the shear displacement of the knee will be little influenced when only the thickness of the foam is changed. The ladder foam precedes the origin. The stiffness of foam influences pedestrian injury. One of the most obvious changes is tibia acceleration. It will decrease when the stiffness of the foam decreases. However, material stiffness cannot be too low. If it is lower than the criterion, it will influence the safety of the passengers. The researches indicate that the methods by changing the foam to improve pedestrian protection performance are feasible. It has little effect on other structures of automobile.(5) The structure parameters of the automobile in the results of orthogonal experiment design are optimized by adopting the method of response surface model. A group of optimal parameter values about the structure parameters are obtained. It can be used for the reference to the vehicle design.In conclusion, based on the analysis of different automobile structure parameters which are designed by orthogonal experiment design, the performances of the lower extremities injuries are predicted. The energy-absorbing foam of the car is improved. The ameliorative foam can decrease lower extremities injuries. The legform impactor in paper accords with the EEVC Pedestrian Safety Regulations. The research can provide reference for pedestrian safety design.