Crash Tests with Automatic Pre-Crash Braking Cars

摘要

Secondary safety systems to protect occupants have attained a very high level over the past decades. Further improvements are still possible, but increasingly minor progress is only to be had with a high degree of effort. Today, integrated safety is the key aspect to improve overall safety in manifold accident situations. This is already implemented in the development of new cars. But so far, the testing and assessment of new cars still involves using tests which do not take into account the significant additional potential of integrated safety measures. An example is given with automatic pre-crash braking functions, which are newly available in state-of-the-art cars. Using reliable information on an imminent crash, such measures act already in the pre-crash phase and can result in a significantly high decrease of the accident outcomes. Such preventive measures are the key to a further substantial reduction of the figures of crash victims on our roads. This paper aims to illustrate the pre-crash braking approach for cars of the BMW 5 series. These measures can contribute to lessening the consequences of a crash by creating an optimal interplay of measures in the fields of primary and secondary safety. Already available are driver assistant systems that warn the driver of an imminent front-to-rear-end crash. The next step is to support his reactions or, if he fails to react sufficiently, to even initiate an automatic braking when the crash becomes unavoidable. Automatic pre-crash braking can, in an ideal situation, fully prevent a crash or significantly reduce the impact speed and thus the impact energy (which directly influences the severity of the accident). If a vehicle is being braked in the pre-crash phase, the occupants are pre-stressed by the deceleration. This is true for pre-crash braking activated by the driver as well as for automatic pre-crash braking. The information available about the imminent crash can be used to activate reversible belt tensioners and other secondary safety systems in the vehicle just before the impact. The pre-crash deceleration also causes the front of the vehicle to dip. Conventional crash tests are unbraked. Such tests do not take into consideration specific impacts of pre-crash braking. As a consequence, the influences of dipping of the vehicle front and possible pre-crash displacements of the occupants are not recorded in the test results. Furthermore, a reproducible assessment of the additional benefit of vehicle safety systems, which prepare the occupants for the imminent impact, is not possible. In order to demonstrate some prototype functions of automatic pre-crash braking and to investigate the differences during crashes as a consequence of altered occupant positions as well as of altered force applications at the vehicle front, DEKRA teamed up with BMW to carry out joint crash tests with the latest BMW 5 series vehicles. The vehicles involved braked automatically from 64 km/h initial test velocity down to different impact velocities. The tests were run by the new intelligent drive system at the DEKRA crash test facility. This required several modifications to be made to the test facility as well as to the vehicle. The paper will describe and discuss some relevant details and results of the crash tests. In addition, the possible benefits of such systems to real-world accidents will also be considered. The tests supplemented the work of the vFSS (advanced Forward-looking Safety Systems) Working Group.