Car occupant seat belt fit; the effect of belt pre-pretensioning

Abstract

In the event of a crash, the seat belt should load the occupant’s pelvis, thorax, and clavicle. A shoulder belt segment routed distal of the shoulder, i.e. positioned on the arm, may cause chest and abdominal injuries during a crash. The overriding aim of this study was to investigate if an improperly positioned shoulder belt can be repositioned to a proper position on the clavicle, with the help of a pre-pretensioner for front seat occupants. More specifically, the aims were to investigate if the location of the belt attachment points, occupant body characteristics, belt geometry, belt fit, and friction of clothing affected the ability of the pre-pretensioner to reposition the shoulder belt and from which distances down the arm it was possible. A volunteer study was conducted to investigate if the shoulder belt could be repositioned for a nominal belt geometry similar to a Volvo S60 and for a belt-in-seat geometry in an adopted test rig. Several anthropometric, belt geometry, and belt fit measurements were collected and analyzed to identify why the belt did not reposition for some individuals compared to others. In addition, the ability of the prepretensioner to reposition the shoulder belt for different fore-aft seat positions, Dring heights, and a belt-in-seat installation were investigated. 17 male and 18 female volunteers were tested. The study found that the location of the belt attachment points affected belt repositioning, since the shoulder belt was not repositioned for the majority of the volunteers in the belt-in-seat installation. The belt repositioned for all volunteers in the most common seat positions while the rate of unsuccessful repositionings increased for more forward seat positions. A high D-ring made belt repositioning possible for all volunteers. Measurements identified as influencing belt repositioning were a taller shoulder height (measured while seated) and a smaller abdominal depth in seat positions forward of the mid position and for the belt-in-seat installation. The belt did not reposition with the lower friction clothing material in the belt-in-seat installation but repositioned for some in a forward fore-aft position. The repositioning commonly failed from positions close to the acromion on the arm. The results indicate that the upper body shape influences belt repositioning. It could be linked to combinations of upper body measurements, shoulder belt routing, and different belt geometries. Based on the results, future studies should investigate shoulder belt repositioning for additional belt geometries and dynamic scenarios as well as the possibility to implement belt fit warning interventions.