Small Occupant Dynamics in the Rear Seat: Influence of Impact Angle and Belt Restraint Design 2005-01-1708
Catastrophic head and spinal injuries have been reported to older children, properly restrained in the back seats of motor vehicles. The interaction of small stature occupants in contemporary, rear restraint systems has not yet been reported in controlled frontal oblique sled test conditions. Such data is fundamental to understanding potential mechanisms of injuries and effective countermeasures.
The purpose of this study was three fold: (1) to conduct a series of controlled sled tests to determine the critical angle at which torso roll-out from the shoulder belt occurs in 6 year old Hybrid III (H3-6C) and 5th percentile female Hybrid III (H3-5F) dummies, (2) to compare dummy injury measures to the standard Injury Assessment Reference Values (IARVs) as a function of impact angle, and (3) to assess the influence of belt pretensioners and anchorage geometry as countermeasures to submarining and torso rollout dummy kinematics.
A series of sled tests were conducted from 0 to 60 degrees in 15 degree increments on a rebound sled at velocities of approximately 35 kph. The dummies were positioned in the right (far-side) outboard seats of a sled buck constructed from a late 1990's model year large SUV.
The second row seat was initially fitted with an OEM adjustable upper belt anchorage and C-pillar mounted retractor. The third row restraint system included a fixed upper anchorage with an OEM roof-rail mounted retractor.
Kinematic targets were mounted on the dummies' head, shoulder and pelvis. Test instrumentation included: lap and shoulder belt load transducers, triaxial accelerometers at the center of gravity of the head, triaxial accelerometers and a deflection gauge in the chest, and a six-axis force (and moment) transducer in the upper neck of the dummy. Tests were digitally recorded at 1000 frames per second using high speed digital video cameras placed around the test fixture. Cameras were set up on the left side of the buck for video analysis. In addition, pre- and post test images were taken using still digital photography. Sensor signals were filtered according to SAE specifications.
The kinematic data was compared to the earlier work of Horsch (1980) that reported the shoulder belt retained the upper body of a 50th percentile male dummy for impact angles up to 45 degrees. Moreover, he reported for mid-size male dummies, “…significant kinetic energy was removed from the upper body before escape, even for full lateral deceleration.” In contrast, this study revealed that H3-6C and H3-5F dummies began to roll out of their shoulder belt at 15 and 30 degrees, respectively. Complete loss of torso support was seen at 45 degrees without significant kinetic energy dissipation.
A retractor pretensioner with 7 ms fire time prevented torso rollover of the H3-6C child dummy at impact angles up to and including 45 degrees. Elimination of submarining kinematics for the H3-5F; however, required significant modification of the OEM belt system's inboard buckle and anchorage geometry, even in the presence of a retractor pretensioner.