For years, the entire worldwide production of BMW passenger cars has been equipped with 3-point belts installed in the front seats. It has been proven, through many theoretical and experimental investigations, that the ideal location for the lower seat belt anchorage points, is the seat frame itself rather than the conventional mounting to the chassis. In the case of seat frame mounting, the lower belt portion stays fixed in relation to the occupant in all seat adjustment positions, and accordingly provides optimum comfort and protection to the occupant. Additionally, a lap belt angle of approximately 60° from the horizontal has been proven to be the most effective.

This technical paper describes BMW's research of an alternative installation location for the upper shoulder belt anchorage point and its influence on occupant protection and comfort. The first part of the investigation reviews the results of theoretical examinations, taking well known parameters into account. As a result of theory, in the second part an anchorage point in the upper seat back was further examined, using computer simulation models as well as a series of experimental frontal impact tests. The corresponding dummy load data are compared with those of conventional belt geometry. Finally, a short overview of additional safety features of a seat integrated belt system in the overall crash scenario is presented.