Optimizing protection for rear seat occupants: assessing booster performance with realistic belt geometry using the Hybrid III 6YO ATD

Abstract

A series of sled tests was conducted to examine the performance of booster seats under belt geometries representing the range found in the rear seats of current vehicles. Twelve tests were performed with the standard 6YO Hybrid III ATD and 29 tests were performed with a modified version of the 6YO ATD. The modified dummy has a pelvis with more realistic shape and flesh stiffness, a gel abdomen with biomechanically-based stiffness characteristics, and a custom neoprene jacket. Shoulder belt upper anchorage was set at the FMVSS No. 213 belt anchorage location and 64 mm inboard and outboard from this location. Lap belt anchorage locations were chosen to span the range of lap belt angles permitted under FMVSS 210, using the FMVSS No. 213 belt anchorage locations and forward belt anchorage locations that produce a much steeper lap belt angle. Four booster seats that provide a range of static belt fit were used. The ATDs were positioned using either the standard FMVSS No. 213 seating procedure or an alternate UMTRI procedure that produces postures closer to those of similar-size children. Kinematic results for the standard and modified dummies under the same test conditions were more similar than expected. The current version of the modified 6YO is less sensitive to lap belt geometry than the prototype version of the dummy. The seating procedure had a greater affect on kinematic results. The UMTRI seating procedure produced greater knee-head excursion differences and less forward torso rotation than the FMVSS No. 213 procedure. Shifting the shoulder belt upper anchorage 128 mm laterally produced minimal variations in kinematics for a given booster seat/lap belt condition, likely because the belt-routing features of the booster seats limited the differences in static shoulder belt score to less than 10 mm. Moving the lap belt geometry from rearward (shallow angle) to forward (steep angle) produced less desirable kinematics with all booster seats tested. The forward position of the lap belt anchorage allows greater forward translation of the booster and ATD before the belt engages the pelvis. Steeper belt angles are associated with better lap belt fit for children sitting without boosters, so designing rear seat belts for children who sit with and without boosters may involve a performance tradeoff.