Mowry 1 REDUCING RIB DEFLECTION IN THE IIHS TEST BY PRELOADING THE PELVIS INDEPENDENT OF INTRUSION

A cooperative research project with the National Highway Traffic Safety Administration (NHTSA) was conducted to evaluate the capability of a Tubular Thoracic Cushion (TTC) airbag concept to significantly reduce rib deflections for the SID-IIs dummy in the Insurance Institute for Highway Safety’s (IIHS) side-impact barrier test. The concept of the TTC airbag was to efficiently distribute a majority of the crash force to the pelvis, which is more able to tolerate forces from side-impact crashes. The characteristic of the airbag to develop tension when deployed appeared to offer additional opportunities for occupant restraint in the IIHS side-impact environment. Computer analysis confirmed that an approach of interposing an inflatable cushion between vehicle occupants at the ribs and a vehicle’s intruding side structure may be problematic when attempting to limit rib deflection, particularly for small-stature occupants. NHTSA analysis of NCAP side-impact tests suggested that pelvic lead (pelvic loading prior to the loading of the rib cage) lessens severity of thoracic injury [1]. Simulations of the IIHS side-impact barrier test utilizing this approach of pelvic lead with the TTC device showed reductions in rib deflection to a 5 percentile female dummy when airbag inflation was limited only to the pelvis region. Due to the characteristic of the TTC airbag to develop tension when deployed, a strategy of applying an inboard lateral "pre" load to the pelvis region of the SID-IIs dummy prior to intrusion was developed. This further reduced rib deflection in dynamic simulations and was validated in dynamic sled testing. The tensioning characteristic of the TTC airbag concept demonstrated pre-loading the pelvis of an occupant in the IIHS side-impact environment provided significant reduction in injury risk. BACKGROUND Side-impact crashes represent the most hazardous crash mode of all planar crashes. Based on 1999 US NASS data, the frequency of these crashes comprises approximately one fifth of all planar crashes. However, 1999 US FARS data indicates more than a third of all occupants fatally injured are disproportionately represented in side-impact collisions. There are several reasons why side-impact collisions have the highest injury potential over frontal impact crashes. Unlike frontal crashes, side crashes involve considerably less crush space between the point of impact from the striking vehicle and the struck passenger [2]. Consequently, this very limited crush space increases the protection requirements on the vehicle side-structure, interior padding, and other countermeasures such as side airbags. During a side-impact crash, the door of the struck vehicle intrudes into the passenger compartment with the velocity of the striking vehicle. The occupant in the struck vehicle remains motionless relative to the intrusion until the distance between the occupant and the intruding door come together and the door accelerates the occupant. The struck vehicle is accelerated as a result of the stiffness of the side structure. The intrusion of the door is complete when the velocity of the door is equal to the velocity of the vehicle. Later in the crash event, the velocity of the occupant becomes greater than the intrusion velocity and the occupant separates from the intrusion. However, the highest risk of injury is likely to occur much earlier in the crash event [3]. Changes to U.S. Vehicle Fleet A significant shift in the United States' vehicle fleet composition appears to be greatly increasing the hazards associated with side-impact crashes [3]. This shift is due to increased popularity of sport utility vehicles, vans and light trucks.