Improved head restraint design for safety and compliance
The National Highway Traffic Safety Administration (NHTSA) recently revised Federal Motor Vehicle Safety Standard (FMVSS) 202, which governs head restraints. The new standard, known as FMVSS 202a, establishes for the first time in the U.S. a requirement for the fore-aft position of the head restraint. The fore-aft distance between the head restraint and headform representing a midsize male occupant must not exceed 55 mm when measured with the seat back angle set to 25 degrees. The goal of the rule change is to reduce the incidence of whiplash-associated disorders caused by rear impacts. Moving the head restraint closer to the head prior to impact decreases the amount of relative motion between the occupants’ heads and torsos and is believed to decrease the risk of soft-tissue neck injury. As manufacturers phase in seats that meet the new criterion, some vehicle models are producing complaints from drivers that the head restraint causes discomfort by interfering with their preferred head position, forcing them to select a more reclined seat back angle than they would prefer. To address this issue, an analysis of driver head locations relative to the seat was conducted using a new optimization-based framework for vehicle interior optimization. The approach uses simulations with thousands of virtual occupants to quantity distributions of postural variables of interest. In this case, the analysis showed that smaller-stature occupants are disproportionately likely to experience head-position interference from a head restraint that is rigidly affixed to the seat back. Using an analysis approach that considers both postural and anthropometric variability, design guidelines for the kinematics of an articulated head restraint are proposed. Such a restraint would provide optimal head restraint positioning across occupant sizes while minimizing interference.