Influence of initial belt torso contact on the kinematics and kinetics of booster-seated ATDs in frontal-oblique impacts

Abstract

Objective

Varying initial belt torso contact (i.e., belt gap) on belt-positioning boosters may have implications for potential shoulder belt slip-off in low-speed evasive vehicle maneuvers and differences in dynamic outcomes in frontal sled tests. This study evaluated the influence of initial booster belt gap and belt fit conditions on the kinematic and kinetic outcomes during frontal oblique impacts.

Methods

Frontal oblique (+15° from frontal) sled tests (n = 18; 23.6 ± 0.1 g at 12.4 ± 0.1 ms) were conducted using the Q-Series 6-year-old (Q6) and 10-year-old (Q10) and the Large Omni Directional Child (LODC) anthropomorphic test devices (ATDs). Various initial belt fit and belt gap conditions were investigated by evaluating each ATD on 2 high-back (HB), 3 low-back (LB), and 1 low-profile (Low) booster. Initial belt fit and belt gap were quantified, and boosters were categorized as “smaller gap” or “larger gap” for comparison.

Results

Larger-gap boosters produced greater peak lumbar FY and MZ (HB: −23.2 ± 8.8 Nm, LB: −23.6 ± 9.7 Nm) compared to smaller-gap boosters (HB: −12.6 ± 4.4 Nm, LB/Low: −12.4 ± 7.2 Nm) for the LODC and Q10. Peak axial torso rotations were also observed for larger-gap LB (38.6°) compared to smaller-gap LB boosters (23.8°), and the LODC experienced greater peak thoracic rotations on larger-gap boosters compared to smaller-gap boosters. These results suggest that ATDs on larger-gap boosters experienced greater torso rotation and lumbar MZ due to lack of initial contact between the shoulder belt and inferior torso. No ATDs experienced complete shoulder belt slip-off; however, larger-gap boosters displayed more visual evidence of outboard shoulder belt positioning at the time of peak forward head excursion.

Conclusion

This study provides a novel investigation on the role of initial belt fit and belt gap metrics on the dynamic response of booster-seated ATDs in frontal oblique impacts. Larger-gap boosters allowed the torso to undergo greater axial rotation before restraint was provided by the shoulder belt to the lower torso. Increased shoulder rotations may indicate greater propensity for shoulder belt slip-off in more severe crashes, in oblique maneuvers, or with variations in initial occupant posture. These results suggest the importance of continued evaluation of the implications of initial belt gap provided by boosters and the importance of evaluating lumbar FY and MZ and useful metrics for discrimination of differences in ATD response across booster designs.