Mathematical modelling was used to find methods of reducing the forces in the seat belt system in a frontal impact, without jeopardising the protective capacity of the system. One such method was to limit the x-component of the force at the point where the buckle stalk is anchored to the vehicle. In order to further evaluate the method, a physical device which accomplished the desired force-limiting effect was designed and evaluated in sled tests. In both the simulations and the tests, the forces in the different straps of the seat belt, and the injury criteria Chest3ms and Head Injury Criterion (HIC), were significantly reduced without any observed adverse effects such as increased risk of impact of head to the steering wheel. The limiting of the force in this method is progressive, thereby covering a wide velocity range, and it adapts somewhat to impact severity and occupant size. In the range of 30 to 55 kmph impact speed, the force limiter allowed for an increase of up to 25% (on average 13%) of the barrier impact speed before the load to the chest and the abdomen surpassed those obtained with the standard seat belt system. A brief analysis of real-world crashes indicates that the benefit in terms of societal and medical savings of such a reduction of the load to the torso would be substantially greater than the cost for introducing the force-limiting device in the fleet of cars.
Abstract