Occupant Protection in Rear-End Collisions Preceded by Autonomous Emergency Braking Deployment

The safety of vehicle occupants has evolved recently due to the market implementations of new sensing technologies that enable predicting and identifying hazardous road traffic situations and thus actively prevent or mitigate collisions. The obvious benefits of the active safety systems has also been recognized and acknowledged by the regulatory and consumer bodies responsible for transportation, and as a result, the new standards, regulations and public rewards are being introduced. The active safety systems can prevent or mitigate collisions by controlling the motion of the vehicles through autonomous actuation of either: braking, steering or both simultaneously. The autonomous control of the vehicle inevitably affects the motion of the travelling occupants with respect to the vehicle interior. Depending on the severity of the maneuver, the occupant motion may lead to non-optimal postures for the in-crash phase if the collision is unavoidable. This consideration creates the direct need for developing the active systems together with passive systems with the ultimate objective to best protect the occupants. This paper presents a simulation methodology for developing new automotive safety systems in an integrated manner that ensures optimal exploitation of benefits of predictive sensing and occupant restraints. It also demonstrates the application of the above methods, to investigate and optimize the occupant whiplash protection in rear-end collisions occurring during the autonomous emergency braking of the collided vehicle. The investigation was performed using simulation techniques (MADYMO software). The driver occupant is initially exposed to the low-g longitudinal acceleration resulting from emergency braking, during which the rear-end acceleration pulse is applied, representing the collision conditions (following the High Severity Sled Pulse of Euro New Car Assessment Program (NCAP) Whiplash testing protocol). Two different models of anthropometric test devices are used and compared: BioRID-II facet Q model and Active Human Model (AHM) to predict occupant motion while braking and assess injury risk as a result of the rear-end collision. The results obtained showed the severity of the out-of-position occupant posture created by the autonomous braking maneuver, and its effect on injury risk in the consecutive collision. It was observed that the occupant motion resulting from braking is more pronounced in case of AHM than BioRID-II. Increased occupant travel during prebraking impairs significantly the effectiveness of occupant rear-end protection restraint systems, thus increasing the whiplash injury risk. Further study demonstrates conceptual, pre-crash deployed safety solutions that alleviate the negative effects of the out-of-position postures created by pre-braking. The study shows the need for developing the new safety systems in an integrated manner. It was performed based on the numerical simulations and some of the model components were not fully validated. The simulation methods and techniques will play a significant role in the integrated safety systems development processes, allowing testing the conditions of high complexity in order to represent the real life scenarios and thus ensuring better occupant protection.