Vertical Occupant Loading in Car Crashes; Test Methods and Countermeasures

Vertical loading can cause thoracic and lumbar spine injuries to a car occupant. Crashes potentially causing occupant vertical loads include; rollover events or free flying events when the car lands on its wheels, and run off road events when the car goes into the ditch and collides with an embankment. To date, there is no standardized test method evaluating this occupant loading mechanism. The aim of this study was to develop test methods addressing vertical occupant loading for car occupants and to evaluate countermeasures for reduction of such loads. Based on real world run off road crashes, representative test track methods were developed. These complete vehicle test track methods were used to provide input to a simplified and repeatable rig test method. The rig test method comprises a dummy positioned in a seat attached to a frame and exposed to a vertical acceleration. Vertical pelvis acceleration is monitored, as an indication of potential loads through the spine. Two different seat designs are compared. The modified seat concept includes a deformation element which is built into the rear part of the seat connection to the seat frame. The deformation element allows for a controlled deformation of up to 25 mm. The space under the seat is cleared to allow for total occupant movement up to 150 mm. During this movement, energy is absorbed by the deformation element as well as the springs and seat cushion material. Compared to the reference production seat, the dummy pelvis vertical acceleration is reduced by 25-32% in the situations tested in this study.