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The necessity of an adaptive vehicle structure to optimize deceleration pulses for different crash velocities
Published June 04, 2001 by National Highway Traffic Safety Administration in United States
To minimize injury to the occupants, the frontal vehicle structure must absorb much more energy in the first deformation phase in case of a high-speed collision. Depending on the crash situation, an intelligent system must regulate the structure stiffness yielding additional energy absorption by means of friction. Concept ideas are mentioned to achieve different crash pulses at different crash velocities within the available deformation length.
An independent search for optimal deceleration pulses at several crash velocities is necessary, because the usually found structure-based pulses are not obviously the optimal pulses for minimal injury to the occupants. Therefore, in this paper the more interesting case of the reverse question is answered: which crash pulse gives the lowest injury levels with an already optimized restraint system, instead of finding the optimized restraint system for a given crash pulse. For this research, a method is described in which a numeric model of an interior and a FEM dummy has been used to find the levels of the injury criteria. To compare the results of different crash pulses, an overall severity index has been used. From a described research an optimal pulse has been found after several considered pulse variations at a crash speed of 56 km/h. This pulse, used as example, gives as it seems much lower injuries. During the first 18 cm deformation length the deceleration level must be high, then a low deceleration interval is required, and at the end (dummy is restrained by belt and airbag) the deceleration must be high again. Also for other crash velocities, pulses are mentioned with adapted pulse characteristics for optimal results.
The only way to generate an optimal crash pulse at different collision speeds is variable structure stiffness. After detection of the crash velocity, the optimal stiffness of the front structure should be realized. Solutions are presented based on controllable energy absorption by additional friction or based on controllable hydraulic flow restriction. With this new design, an optimal vehicle deceleration curve is possible for each velocity over the entire frontal collision spectrum, yielding the lowest levels of the occupant injury criteria, also in case of compatibility problems.