Simulation Study Of Vehicle Engine Hood Based On Pedestrian Head Protection

In vehicle design we should not only consider the protection of the occupants, but also the protection of people outside the car. In traffic accidents, people outside the car, such as pedestrians, cyclists and others, are more vulnerable. Head and thighs of pedestrians are the most vulnerable parts in the process of collision between cars and pedestrians. And the head injuries are most fatal. Adult's head mainly contacts the engine hood in the traffic accident. Therefore, it is practically important to carry out a protection of car engine hood for pedestrians in traffic accidents.The paper mainly focuses on how to release the injuries of pedestrian's head caused by the engine hood from two aspects. One is the parameters of engine hood and the other is the engine hood structure.In the aspect of parameters of engine hood, the shape of the engine hood outer panel has a great impact on head injury. But the shape of engine hood outer panel such as curvature should be consistent with the design of vehicle styling. It is difficult to control the shape of engine hood outer panel, while the thickness of the engine hood is easier to control. On the stage of vehicle conceptual design, we could optimize the thickness of engine hood's sheet, after the determination of the vehicle's shape. The paper discusses how to optimize the thickness of engine hood's sheet to improve the protection of pedestrian's head. The design of the thickness of the engine hood plate is a multi-objective problem. With the purpose of improving the protection of pedestrian head, it should meet lightweight to make the vehicle lighter and should make the first order mode of the engine hood plate meet the requirements and heighten as possible in order to reduce the vibration and noise. The paper hopes to improve the indicators of lightweight and mode with the purpose of protecting pedestrian head.In the paper, the first step is to establish a finite element model of head impactor which must meet requirements of the regulatory. Pedestrian protection regulations vary in different countries and requirements of head impactor are not the same. The selections for materials of head impactor and parameters have a certain degree of blindness. The paper sums up a generally applicable method for determining the material's parameters.In the paper, this paper utilizes computer simulation approach. It will take pretty long time, in the process of optimizing the thickness of engine hood plate, including outer plate, inner plate, stiffener and hinge, due to the continuous variable parameters of thickness and the time that spent on the simulation of the process of a collision between head and the front of vehicle in a computer with 4 cpus is about 7 hours. If we use the finite element model for iterative optimization, 100 iterations would take more than a month. The process is unrealistic in practice. Approximate models are used in the paper and it obtains four variables on the approximate model of the value of head injury, modal and mass. And then this paper uses the approximate model to take place the finite element model to get the answer through the iterative method. To solve this multi-objective problem, the paper adopted the NSGA-Ⅱgenetic optimization algorithm.In the aspect of the engine hood structure, the paper presents an improved structure of hood hinge for the problem that head would bear larger injuries when head collides with the parts of engine hood where the hinges are installed. The improved structure of engine hinge is simple and with practical value.