Redesign of the vehicle bonnet structure for pedestrian safety

Abstract

Redesign of the structure of the bonnet to improve pedestrian head protection has recently received considerable attention from automobile manufacturers and industry institutes. The fatality of a head injury is based on the head injury criterion (HIC) value. This HIC value is calculated on the basis of the resultant acceleration of the head’s centre of gravity (hereafter called the head centre) during head impacts. This study analyses the constitution of and variation in the resultant acceleration in head-to-bonnet impacts, and how each component of acceleration exactly contributes to the resultant acceleration of the head centre. This study also considers how the structural design parameters affect each component of acceleration. The causes that make the characteristic variation in the resultant acceleration differ from the optimal characteristic pulse will be analysed and discussed in detail. Based on the results of this analysis, the sudden increase in K (the curvature of the head centre’s motion) after several milliseconds of the impact process must be eliminated. The sudden increase in K in this duration does not depend on the mass and stiffness of the bonnet but does depend on the characteristics of the reinforcement structure. Therefore, a new design of the bonnet reinforcement structure has eliminated the sudden increase in K. The bonnet reinforcement structure, as well as the bonnet thickness, have been designed to make the resultant acceleration of the head centre close to the optimal acceleration pulse. The results of this study contribute to efforts to design an improved vehicle bonnet structure and to pave the way for developing pedestrian protection technologies.