Biomechanics of occupant loading by pre-crash motorized shoulder belt tensioning

Motorized shoulder belt tensioning is a new seatbelt technology that is likely to be incorporated into future vehicles. This technology tightens the shoulder belt in pre-crash situations to reduce automotive crash injuries. Low-level motorized shoulder belt tensioning (<290 N) is well tolerated by vehicle occupants, but optimum performance for a diverse occupant population (6-year-old through 95th percentile male) is unknown.; This research provides data and techniques to optimize motorized tensioning parameters for all occupants. A lack of volunteer data on the biomechanics of occupant pull-back by motorized shoulder belt tensioning and a lack of validated models motivated this research. In addition, the biofidelity of the Hybrid III crash test dummy for shoulder belt tensioning was unknown.; Experiments were conducted with three populations of adult volunteers (5th percentile female, 50th percentile male and 95th percentile male) and the Hybrid III crash test dummy family to measure torso kinematics and kinetics during shoulder belt tensioning.; The volunteer experiments showed that changes in spinal curvature were small and the centre of rotation was within 4.2 cm of the H-point during tensioning. The angular repositioning of the torso was: 54.3° in 0.78 s for the 5 th percentile female, 57.6° in 0.95 s for the 50th percentile male and 42.2° in 0.92 s for the 95th percentile male. The peak shoulder belt forces were 82 N--92 N.; The biofidelity of the Hybrid III dummy was poor for studying shoulder belt tensioning in a relaxed occupant. The rigid pelvis and lower torso assembly lacked the mobility observed in volunteers.; A two and three-dimensional model of shoulder belt tensioning was validated using the volunteer data. The three-dimensional model incorporated pre-impact braking and a DC motor-controller model for the seatbelt tensioner. Applying speed control to the motorized tensioner achieved the best retraction response for the 5th female, 50th male and 95 th male populations during frontal braking. This control scheme shows promise as a single design specification for all occupants.