Comparing restraint system sensitivity between the thor and the hybrid iii , and potential implications in restraint optimization

Restraint system optimization is affected by the sensitivity of dummies to relative loading between the seatbelt and airbag. Differences in design between the THOR and Hybrid III dummies may affect the mechanisms of interaction with the various restraint system components, and the factors that influence compression measured in the dummy’s chest. Previous studies have compared dummy responses in sled tests representing select specific configurations. The goal of this study was to compare the mechanisms of chest compression in the THOR and Hybrid III, and sensitivity to loading by various restraint system components, in full vehicle crash tests. The NHTSA full-vehicle crash test database was queried to find cases of matched tests with the THOR and the Hybrid III. Four cases of matched tests were found one with a sub-compact hatchback, one with a compact sedan, one with a mid-sized sedan, and one with a full-sized pickup. All were 56 km/h frontal-impact, rigid barrier tests, with the dummy seated in the driver position. The vehicles were matched based on make, model, model base year, and restraint system characteristics (e.g., observed belt force limit). Shoulder belt forces, chest deflection time histories, and frame-by-frame videos were examined to restraint system interaction and factors influencing compression measured in the chest. In all four cases the shoulder belt force time histories were similar between the THOR and the Hybrid III. In one case the chest compression in the Hybrid III appeared to be predominantly dependent on force limiting in the shoulder belt, while the THOR exhibited a greater sensitivity to combined loading by the belt and airbag. In two cases the results were mixed, with both the dummies exhibiting some sensitivity to both belt and airbag loading (though the airbag appeared to contribute to a greater degree with the THOR). The nature of chest compression appeared most similar in a case of an apparent digressive force limiter, with both dummies exhibiting a plateau associated with a transition to airbag loading with a drop belt force limit. These results suggest that the relative sensitivity to belt and airbag loading can vary between the THOR and the Hybrid III, depending on the specific characteristics of the restraint system and vehicle being studied. The THOR is more flexible, tends to experience greater forward excursion into the airbag, rides up higher on the airbag, and is capable of measuring deflection in the upper chest where a majority of the airbag loading occurs in some cases. As a result, in some cases the THOR appears to be more sensitive to loading by the airbag than the Hybrid III. Sensitivity to loading by the various restraint system components will likely affect optimization of the restraint systems, affecting the perceived optimal apportionment of load between the belt and the airbag. These results suggest that the two dummies may lead to different strategies for restraint system optimization in some cases, and that the relation of restraint system interaction between the THOR and Hybrid III may vary in the fleet.