Effect of reactive car seats and active head restraint system in rear-end collision and safety mechanisms to reduce whiplash injuries
A car seat should be designed in such a way to reduce occupant acceleration in rearward and rebound motion so that minimum neck abrupt motion and neck forces occur. The reactive car seats have become quite popular by automatic reclining mechanism and its ability to reduce injuries in rear impacts. An example is the Whiplash Protection System (WHIPS), which absorbs crash energy by controlled motion of the seat. A car seat without an Active Head Restraint (AHR) system exhibits poor performance in low-speed rear impacts. According to the Federal Motor Vehicle Safety Standards (FMVSS) test procedures, the Neck injury criteria (Nij) typically exceeds the limiting injury values without an AHR system. The AHR system can recognize rear collision and adjust the head restraint with respect to the motion of occupant's head. The goal of this study is to develop a reactive car seat system, which would reduce the neck motion of an occupant in rear collisions, and to develop a seat with an Active Head Restraint system. In this thesis, the LSDYNA non-linear finite element (FE) solver is utilized to analyze the structural crash response of different cars and obtain the acceleration pulses. The MADYMO biodynamics code is then used to design the car seat interior model, and to examine the occupant neck responses and kinematics of a Hybrid III 50th percentile male dummy model as well as a human model. The results are compared to achieve optimum head restraint position and seatback angle, which reduce neck loads and bending moments. The reactive car seat systems and the Active head restraint systems are further examined to identify the optimum seat design to reduce neck injuries. The results from this study show that a seat with reclining properties and most suitable position of seatback and head restraint, considerably reduces the neck extension motion of an occupant in the car. The results also demonstrate that, whiplash injuries with an AHR system are much less expected, when compared to the seat system with a normal head restraint.