An inflatable belt system in the rear seat occupant environment: investigating feasibility and benefit in frontal impact sled tests with a 50(th) percentile male ATD.

Frontal-impact airbag systems have the potential to provide a benefit to rear seat occupants by distributing restraining forces over the body in a manner not possible using belts alone. This study sought to investigate the effects of incorporating a belt-integrated airbag ("airbelt") into a rear seat occupant restraint system. Frontal impact sled tests were performed with a Hybrid III 50th percentile male anthropomorphic test device (ATD) seated in the right-rear passenger position of a 2004 mid-sized sedan buck. Tests were performed at 48 km/h (20 g, 100 ms acceleration pulse) and 29 km/h (11 g, 100 ms). The restraints consisted of a 3-point belt system with a cylindrical airbag integrated into the upper portion of the shoulder belt. The airbag was tapered in shape, with a maximum diameter of 16 cm (at the shoulder) that decreased to 4 cm at the mid-chest. A 2.5 kN force-limiter was integrated into the shoulder-belt retractor, and a 2.3 kN pretensioner was present in the out-board anchor of the lap belt. Six ATD tests (three 48 km/h and three 29 km/h) were performed with the airbelt system. These were compared to previous frontal-impact, rear seat ATD tests with a standard (not-force-limited, not-pretensioned) 3-point belt system and a progressive force-limiting (peak 4.4 kN), pretensioning (FL+PT) 3-point belt system. In the 48 km/h tests, the airbelt resulted in significantly less (p<0.05, two-tailed Student's t-test) posterior displacement of the sternum towards the spine (chest deflection) than both the standard and FL+PT belt systems (airbelt: average 13±1.1 mm standard deviation; standard belt: 33±2.3 mm; FL+PT belt: 23±2.6 mm). This was consistent with a significant reduction in the peak upper shoulder belt force (airbelt: 2.7±0.1 kN; standard belt: 8.7±0.3 kN; FL+PT belt: 4.4±0.1 kN), and was accompanied by a small increase in forward motion of the head (airbelt: 54±0.4 cm; standard belt: 45±1.3 cm; FL+PT belt: 47±1.1 cm) The airbelt system also significantly reduced the flexion moment in the lower neck (airbelt: 169±3.3 Nm; standard belt: 655±26 Nm; FL+PT belt: 308±19 Nm). Similar results were observed in the 29 km/h tests. These results suggest that this airbelt system may provide some benefit for adult rear seat occupants in frontal collisions, even in relatively low-speed impacts. Further study is needed to evaluate this type of restraint system for different size occupants (e.g., children), for out-of-position occupants, and with other occupant models (e.g., cadavers).