For several years now, car manufacturers have made significant efforts in the field of thoracic protection. After first limiting the forces in the shoulder belt to 6 kN, these forces are now usually limited to 4 kN, with airbags intentionally designed to absorb the surplus of energy. If this technology is rewarded by a considerable improvement in safety on the road, it remains penalized by the usual biomechanical criteria, when calculated on the Hybrid III and if applied to all restraint systems.

To remedy this problem a new criterion, valid in all the current restraint configurations (belt, airbag only or airbag and belt) is proposed. It is based on the measurement of the shoulder belt forces and of the central deflection and consequently is directly applicable to the current dummy model (Hybrid III). The use of shoulder belt forces allows the separation of the belt and airbag contributions to the deflection. A weighted criterion is calculated from these deflections, taking into account the different risks associated with a belt and an airbag for the same deflection. This new criterion was developed using 65 simulations on the LAB human model and validated by means of 48 sled tests from the literature, consisting of Hybrid III dummy and PMHS tests performed in similar configurations.

This paper describes the logic behind the development of the criterion and gives all the parameters used as well as the elements of validation.