Extreme out-of-position pre-crash postures may need high-force pre-pretensioner
(PPT) for effective repositioning (Mishra et al., 2023). To avoid applying a high force on the chest, we
hypothesized that in case of these extreme postures the PPT may be activated in
the absence of a pre-crash motion as a cautionary measure. Therefore, the aims
of this study were: (1) to understand the effect of the PPT in repositioning a
forward-leaning occupant in static conditions and (2) to characterize occupants’
kinematic variability during repositioning. Sixteen healthy volunteers (8 males,
8 females, 23.8 ± 4.2 years old) were seated with a 40° forward posture on a
vehicle seat and restrained with a 3-point seat belt equipped with a PPT. Two
PPT seatbelt conditions were examined: low PPT (100 N) and high PPT (300 N).
Head and trunk rearward displacements relative to the initial forward-leaning
position at 350 ms from PPT onset were collected with a 3D motion-capture system
and compared between sexes, repetitions, and PPT levels with repeated measure
3-way ANOVAs (p-level = 0.05). Head and trunk rearward displacements were
greater with the high PPT (head −93.8 ± 9.3 mm, trunk −78.7 ± 6.7 mm) than the
low PPT (head −44.6 ± 8.9 mm, trunk −39.7 ± 7.6 mm) (p < 0.001). There were
no statistically significant differences between sexes (p > 0.19), repetition
(p > 0.28), and no interaction effects (p > 0.18). There was greater
inter-subject variability in the low (head −109.5 to −22.1 mm, trunk −105.0 to
−17.5 mm) compared to high PPT (head −175.0 to −62.5 mm, trunk −128.4 to −54.8
mm). Although no sex differences were found, the high inter-subject variability
suggests that PPT timing and force level might not be designed as
one-size-fits-all. This study shows that triggering the PPT when the vehicle is
traveling at a constant speed could reduce the PPT force needed to reposition
forward-leaning occupants during pre-crash maneuvers.
