Assessing the restraint performance of vehicle seats and belt geometry optimized for older children

Abstract

In a previous study, a computational model of child occupants 6 to 10 years old (YO) was validated using data from a sled test series with the 6YO and 10YO Hybrid‐III ATDs. Simulations using this model were used to identify characteristics of a vehicle seat and belt geometry that would improve occupant protection for older children not using booster seats. The current report presents a series of sled tests to examine the effects for other occupants using vehicle seats optimized for 6‐ to 10‐year‐old children. Tests were conducted with a 12MO CRABI seated in a Graco SnugRide rear‐facing infant restraint and a Hybrid III 50th male ATD. Seat cushion length was set to 450 mm, 400 mm, and 350 mm. Lap belt conditions included one representing the mid‐range of FMVSS No. 210, “Seat belt assembly anchorages,” allowable seat belt anchorage conditions as well as one more forward but closer to the vehicle seat H‐point. Shoulder belt conditions included the standard FMVSS No. 213 shoulder belt anchorage as well as one positioned closer to the adult male shoulder. Vehicle seats from a 2008 Dodge Town and Country were used, and some tests included modifications to make the front support structure of the seat cushion stiffer. The tests with the midsize adult male ATD showed no negative consequences from design changes intended to improve protection for children. Kinematics were similar among all conditions tested. For the rear‐facing infant restraint, none of the tests exceeded the 70° rotation angle requirement of FMVSS No. 213, although shorter cushion length and more forward belt locations produced larger rotations. The three tests with the more forward lap belt geometry slightly exceeded the 3‐ms‐chest clip acceleration limit of 60 g, but a review of all chest acceleration curves suggests that the vehicle seat may produce higher chest accelerations than the FMVSS No. 213 test bench. In tests with the shortest seat cushion length, the infant seat showed acceptable kinematics even though less than 80 percent of the child restraint base was initially supported on the vehicle seat. These preliminary tests with rear vehicle seat configurations selected to optimize protection for older child occupants produced good restraint kinematics for infants in a rear‐facing only child restraint and for adult mid‐size males. Additional research to identify possible negative consequences for other types of child restraints should be conducted. If shorter cushion lengths are chosen as a safety countermeasure for older children, the current child restraint installation requirement to have at least 80 percent of the base contacting the vehicle seat will need to be addressed.