A Comparison Study of Active Head Restraints for Neck Protection in Rear-End Collisions

Neck injuries caused by rear-end collisions havebecome a major problem in traffic safety over the last two decades, however, surprisingly little effort has been made
so far to improve car seat and head rest design. Several studies have shown, that whiplash injuries can be reduced by minimizing the gap between head and head restraint during the first phase of a rear-end impact. On the other hand, the requests for comfort from the car passengers limit the reduction of this distance. Various publications show that generally neither drivers nor passengers are aware of the necessity to adjust current head rests to the their head position. The conclusion is, the head rest should either be large enough to protect all occupants or should be automatically adjusted to protect all occupant sizes.
This study shows a comparison of different active head restraint concepts, which guarantee a reduction of the distance between head and head rest during a rear-end
collision. In addition the size of the head rest is enlarged. Different concepts were validated by sled tests using Hybrid-III Dummies equipped with the newly developed
TRID-neck. Also volunteer tests were performed to prove the effectiveness of the new concepts. From these concepts, the inflatable head rest has proven to be the most efficient system. It is big enough to protect occupants up to the size of the 95’h-percentiIe male, independently from the preadjusted position. If the head rest is positioned too low the upward increase in volume will be sufficient for occupant protection, whereas if the head rest is positioned too high the downward
increase in volume will fill the gap between seat back and head rest. Thus the inflatable head rest concepts will be appropriate for almost all occupant sizes, independent from the preadjusted position.
The results have shown that relative motions between head and neck, as well as neck loads, were reduced significantly at all impact velocities and in all occupant
positions. The inflation noise was reduced to a level that was hardly audible for the volunteers, at least when compared to the crash noise. Further sound pressure
measurements in the cabine alpha showed a 99.99 % probability, that no hearing damage will occur. This report shows that the inflatable head rest is a promising new concept that can reduce Whiplash Associated Disorders (WAD) following rear-end impacts especially in low speed collisions. It allows a comfortable head rest position and is suitable for almost all occupant sizes without the need for adjustment.