PRE-SAFE® in rear-end collision situations

In 2002 the first bridge between active and passive automotive safety was built. The MY03 MercedesBenz S-Class was the first car in the world that implemented preventive measures for occupant protection which took effect before the actual impact occurred. Meanwhile the name “MercedesBenz PRE-SAFE ® System” became well known. Since then many other cars from various car manufacturers have adopted this principle of a “natural protection reflex”. In order to detect dangerous situations or upcoming accidents, various sensor systems are being used in these cars today. In addition to sensors that keep an eye on the driving dynamics or on the driver reaction, the use of radar sensors or cameras has become common during the past few years. Almost all of those systems observe the area in front of the car and therefore address situations with an increased risk for a frontal impact. Very few systems presented up to now are capable to “look” backwards and thus detect an imminent rear impact. This paper presents the Mercedes-Benz approach to integrate this type of accident into the PRE-SAFE ® System. The paper covers the issue of detecting collision objects on the basis of radar data. And it presents a cascade of precautionary actions that can improve occupant protection in rear-end accident situations. In particular, the purpose and benefit of a preventive increase of brake pressure is discussed, as well as taking into account further actuators such as a reversible seat belt pretensioner or an active headrest. In order to substantiate the benefit of such a system several evaluation charts on the reduction of the impact severity, the dummy loads and the estimated risk of whiplash injuries are included. Based on accident simulations there are also evaluations about the reduction of the “accident radius” and thus the risk of a secondary impact. Finally the question of an appropriate electronic architecture for such an integral safety system is touched upon.