ANALYSIS OF THE PRE-CRASH BENEFIT OF REVERSIBLE BELT PRE-PRETENSIONING IN DIFFERENT ACCIDENT SCENARIOS

摘要

The goal of active belt systems is to reduce occupant movement in highly dynamic driving situations to increase both safety and comfort. In this paper the ability of such systems to reduce occupant displacement is quantified and the resulting increase in occupant safety is analyzed for different accident scenarios. These scenarios are characterized by the direction of occupant displacement as it results from vehicle dynamics prior to the accident such as braking or evasive steering and by the impact direction. To identify the occupant displacement as initial condition for the chosen accident types, the inertial forces prior to the accident are reproduced in a test vehicle for the chosen scenarios. Different levels of reversible pre-pretensioning are used within these tests. A conventional belt system (no pre-pretensioning), a belt system with reactive pre-pretensioning (activation based on vehicle dynamics data) and a belt system with predictive pre-pretensioning (pre-triggered based on environmental sensors) are being compared. The occupant displacement is measured during these tests. The results show, that a significant reduction of occupant displacement is possible using active belt systems. For instance forward head displacement during panic braking scenarios can be reduced significantly with reactive pre-pretensioning and even further with pre-triggered pre-pretensioning in comparison to the same scenario with a conventional belt system without pre-pretensioning. The effect of reduced occupant displacement is studied using crash simulation and sled tests. In both cases the dummy is positioned according to the measured displacement values as initial condition. Characteristic injury values of these crash simulations and sled tests are compared to identify the effect of different levels of occupant displacement on injury probability. Both simulation and sled tests demonstrate that a modified initial occupant position may result in an altered injury mechanism during the crash. The rapid deceleration in the tested panic braking situations for example leads to a forward displacement of the occupant that in case of a subsequent front crash may result in a bag slap (caused be the reduced distance between occupant and instrument panel). The improved occupant position using an active belt could decreases the probability of a bag slap for the same scenario. Lateral displacement with a subsequent frontal collision could have even more severe consequences on occupant injuries. The simulation results show that because of the lateral displacement of the occupant the contact with the frontal airbag may be misaligned and therefore airbag effectiveness could be reduced. As a worst case scenario the probability for a contact to the instrument panel could increase. This effect is intensified as the routing of the belt is influenced by lateral occupant displacement, which may reduce the effectiveness of the belt system in a crash. Reduced occupant displacement can avoid or mitigate the risk of such an injury mechanism. In case of a rear impact with initial forward occupant displacement the changed occupant position results in injury rating values many times higher than those in nominal position. Again, reduced occupant displacement can mitigate this effect. In conclusion reversible pre-pretensioning allows the reduction of occupant displacement and proves to have a direct effect on occupant safety in the examined scenarios.