Motorized Shoulder Belt Tensioning: Modeling and Performance for a Diverse Occupant Population

Motorized shoulder belt tensioning is an occupant protection technology that has promise to reduce automotive crash injuries. The objective of this study was to model the response of a diverse forward-leaning occupant population (6-year-old child, 5th female, 50th male, 95th male) to shoulder belt tensioning during straight line pre-crash braking. The lumped mass model was based on experimental volunteer data for motorized shoulder belt tensioning gathered in a previous quasistatic study. The three dimensional model incorporated the biomechanical properties of the occupant populations, a motorized shoulder belt tensioner (DC motor and controller) and shoulder belt webbing models. Model validation was achieved against the volunteer experiments for angular torso position, torso velocity and shoulder belt moment applied to the torso. The model predicted the motor used in the volunteer experiments was not sufficiently powerful to retract the 50th male or 95th male populations in 0.5 g pre-impact braking. Using a more powerful motor, speed control on the motorized tensioner achieved the best retraction response for the 5th female, 50th male and 95th male population groups. This control scheme shows significant promise for specifying a single criterion acceptable for a diverse population during frontal braking. The angular torso position and velocity response were uniform across all populations and the force applied to each occupant was moderated dependent on occupant size. Applying open loop or force control on the motorized tensioner resulted in much greater kinematic variability in the torso response across populations and applied higher forces to smaller occupants.