Effect of various restraint configurations on submarining occurrence across varied seat configurations in autonomous driving system environment

OBJECTIVE: Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Previous studies have shown that the increased risk of submarining exhibited by reclined occupants cannot be fully mitigated by changes in the seat configuration alone. This study aims to investigate the effects of three restraint countermeasures on cases with marginal submarining events and estimate their effect on submarining risk and injury prediction metrics. METHODS: Vehicle environment frontal crash Finite Element (FE) simulations were performed with the two simplified Global Human Body Model Consortium (GHBMC) occupant models: small female and midsize male. The baseline occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor-mounted pre-tensioner and load limiter. Based on submarining thresholds identified in previous studies, three baseline configurations were identified for each occupant size. For each baseline case three restraint system modifications were evaluated. The modifications consisted of the introduction of a pelvis restraint cushion airbag (PRC), the use of a knee airbag (KAB) and the modification of the of the passenger airbag location (PAB). Simulations were performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematic data was extracted from each simulation to investigate how changes in the restraint system configuration affects submarining. RESULTS: Overall, in only one of the investigated cases did the proposed restraint modification prevent submarining occurrence, however each of the restraint modifications reduced the pelvis excursion over the baseline scenario. The presence of the PRC airbag showed the highest reduction in pelvis forward excursion for the female model. The presence of the KAB and the modified location of the PAB also contributed to reductions in excursion to a smaller degree. For the male surrogate, the KAB showed the highest reduction in pelvis forward excursion. The presence of the PRC led to a reduction in the lumbar spine shear force. CONCLUSIONS: Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This suggests that there may not be a single generalizable currently-existing countermeasure able to effectively prevent marginal submarining cases in reclined positions.