Door Latch Integrity: Engineering Analysis and NASS Case Review

The National Highway Traffic Safety Administration (NHTSA) is currently conducting research at the Vehicle Research and Test Center (VRTC) aimed at evaluating door latch integrity. Federal Motor Vehicle Safety Standard (FMVSS) 206 currently consists of a longitudinal tension test, a lateral tension test, and an inertial calculation Several door latch failure mechanisms have been identified that are not properly evaluated by the current FMVSS 206 standard. This being the case, it was decided that an engineering analysis of door latch systems and a NASS case review of accidents with door openings caused by latch or latch/hinge failure should be conducted to determine loading conditions and failure modes of door latch systems in accidents. This paper will provide a presentation of currently identified door latch failure modes and the results of the NASS case review. The identified failure modes include detent lever-fork bolt bypass, structural failure, linkage activation, and inertial unlatching. The NASS case analysis consisted of 97 cases. The loading conditions in these cases were as follows (some cases fall into more than one category): 1) 56 of 97 cases involved compressive longitudinal loading, either alone or in combination with at least one other type of loading; 2) 64 cases involved lateral tension or rotational loading, solely or combined with at least one other loading condition; 3) 14 cases involved longitudinal tensile loading, either alone or combined with at least one other type of loading, and; 4) Most cases involved combination loading. For about 58% of the reviewed cases, the latch was subjected to compressive longitudinal loading. Currently, FMVSS 206 does not address this type of loading.