Influence of belt pretensioning on dummy responses in 40 km/h rear-impact sled tests

This study compares dummy kinematics and biomechanical responses with and without belt pretensioning in matched rear sled tests.

Two rear-impact sled tests were run at 40 km/h (25 mph) rear delta V with a lap-shoulder-belted Hybrid III 50th percentile male dummy on Ford F-150 driver seats. One test was with the standard lap-shoulder belts and the other with a buckle pretensioner activated at 20 ms. The head, chest, and pelvis were instrumented with triaxial accelerometers. The upper and lower neck, thoracic spine, and lumbar spine had transducers measuring triaxial loads and moments. Lap and shoulder belt loads were measured. High-speed video recorded different views of the dummy motion. Dummy kinematics and biomechanical responses were compared to study the influence of belt pretensioning.

The dummy kinematics and biomechanical responses were essentially similar with and without belt pretensioning in the rear-impact sled tests. There were higher belt loads with pretensioning, but they did not result in different dummy lumbar loads or pelvic, chest, and head accelerations. In a rear impact, the dummy moves rearward away from the belts that wrap around the chest and pelvis. The occupant loads the seat, which yields rearward restraining dummy motion. Though pretensioning caused a transient increase in belt load, it was of short duration and there was no sustained effect on occupant dynamics until late in rebound.

The matched tests showed no difference in occupant restraint with and without buckle pretensioning in 40 km/h (25 mph) rear-impact sled tests. Belt pretensioning did not influence occupant responses in these rear impacts because the seat supported the occupant.