Seat Belt Buckle Release by Inadvertent Contact 2008-01-1236

When an automotive seat belt buckle is believed to have released during a motor vehicle accident, it is typically attributed to one of several potential mechanisms, including inertial release, partial engagement, inadvertent contact, or structural overload. While the majority of literature in the past has focused on the topic of inertial release, little has been written on other release mechanisms. This review paper addresses automotive seat belt buckle release by inadvertent contact between the buckle pushbutton and some other object.

This paper describes the conditions that must be satisfied for inadvertent contact to result in buckle release, including release force, direction, and pushbutton travel. We explain the role of occupant kinematics and the likelihood of contact between and occupant's hand or arm and the pushbutton. Occurrences of inadvertent contact in safety testing and a real world case study are presented. In addition, requirements of United States Federal Motor Vehicle Safety Standards (FMVSS) 208 and 209, United Nations Economic Commission for Europe (UNECE) Regulation 16, and European Economic Community (EEC) Directive 77/541 relating to inadvertent contact will be discussed. Also addressed are the design guidelines that have been adopted by some manufacturers to formalize the design process, including “ball tests”.

Ultimately, the occupant restraint engineer must balance the possibility of release by inadvertent contact with the requirement of easy and rapid removal to maximize safety and promote seat belt usage. We discuss the need for an engineer to consider not only buckle design, but also the vehicle environment in which a buckle will be used, because buckle mounting and location within a vehicle may affect the likelihood of release due to inadvertent contact.