Occupants in vehicles equipped with automated driving systems (ADS) may sit in various seating positions (e.g. forward facing, rear facing, oblique facing) and at different seatback recline angles. Since forward facing impacts have been studied in detail, the objective of this study was to: A) analyze rear impacts using finite element (FE) human and seat models; B) update the seat model based on lessons learned from part A and then analyze the injury metrics trend for the 50 th percentile male occupant: i) at various seatback recline angles, and ii) in different carriage style seating configurations; and C) investigate a potential countermeasure for reducing injury metric values. For analyzing rear impacts, the Total Human Model for Safety (THUMS) FE model along with a FE driver seat model of a Toyota Yaris was used. Simulations were carried out at both low (Delta-V=15 mph) and high (Delta-V=35 mph) speeds to understand the effect of seat hinge stiffness on THUMS kinematics at both speeds. Other design changes such as integrated seat belts and active head restraints were also evaluated. Then injury metrics were analyzed for the 50 th percentile male occupant at various seatback recline angles and in different carriage style seating configurations. For this part of the study, Global Human Body Models Consortium (GHBMC) 50 th percentile simplified (M50-OS) male FE model was used along with a Honda Accord FE driver seat model. Head Injury Criterion (HIC) and Brain Injury Criterion (BrIC) were used as injury metrics for the head/brain, while max chest deflection was used as the chest injury metric. A potential countermeasure for reducing BrIC was investigated for the seating configuration with the highest BrIC value. From the rear impact study, it was found that having a rigid seat hinge, an integrated seatbelt, and an active head restraint help in reducing the injury metrics. Higher BrIC values were observed at higher seatback recline angles for both frontal and rear impacts. Chest deflection was also higher at higher seatback recline angle for frontal impact but showed an inverse trend for rear impact. For occupants experiencing frontal/oblique-frontal impacts, the BrIC and chest deflection values ranged from 0.75 to 0.81 and from 33 to 45 mm respectively whereas for occupants experiencing rear/oblique-rear impacts, the BrIC and chest deflection values ranged from 0.23 to 0.93 and from 17 to 24 mm respectively. HIC 15 values were below 300 for the various recline angles and seating configurations investigated except one instance where the head contacted the knee. The potential countermeasure (redesigned head restraint) investigated was effective in reducing BrIC by a third for the case with the highest BrIC value (0.93).
Keywords: Automated driving systems (ADS); human models; head/brain injury; chest injury; carriage style seating configurations