Development of Fit Envelopes to Promote Compatibility Among Vehicles and Child Restraint Systems

Abstract

This project developed fit envelopes representing the space occupied by small, medium, and large rear-facing and forward-facing child restraints that can be used as tools for promoting compatibility between vehicles and child restraints. The approach applies the envelope method used by the International Standards Organization (ISO) to the U.S. market, by considering the range of child restraint sizes in the 2014 U.S. market and the more commonly used method of installation with flexible Lower Anchors and Tethers for Children (LATCH). Thirty-one child restraints representing a range of sizes, manufacturers, and product types were scanned and installed in vehicles. The installed positions of the child restraints were measured in 10 late-model vehicles. A comparison of the installed positions of the child restraints in vehicles was done virtually using Hypermesh. Starting with the envelope geometries used by the ISO, envelope shapes were modified to represent small, medium, and large rear-facing and forward-facing child restraints. When possible, envelope dimensions were harmonized with the ISO envelopes. To promote compatibility, child restraints should be able to fit in one or more applicable envelopes at an acceptable orientation when the envelope is rotated 15° relative to horizontal (to represent installed orientations on a typical vehicle seat cushion angle). To promote compatibility from the vehicle side, at least one rear-facing and one forward-facing envelope should be able to be installed in each vehicle rear seating position. Although the evaluation of fit can be performed virtually using computer-aided design, physical representations of the envelopes were also constructed. Four sets of nesting boxes were built. For child restraint evaluation, the largest rear-facing and forward-facing envelope geometry can be modified with foam inserts to represent the medium and smaller sizes. For vehicle evaluation, a wooden base is installed in the vehicle using flexible LATCH belts. Different components are added to represent the small, medium, and large sizes. Test procedures have been drafted to describe setup of vehicles, child restraints, and the evaluation process.