Seat Pan Loading Differences Using a New Test Apparatus

Despite decreases in mortality and overall injury in the last 15 years, in that same time lower thoracic and upper lumbar spine fractures have not decreased, and there is growing evidence that these fractures are actually increasing in frontal impact collisions. Due to the usual upward inclination of passenger seats and structural features added to optimize frontal impact performance, there is a question as to how much the construction of the seat pan might contribute to the incidence of thoraco-lumbar fractures. A seat testing apparatus was designed and evaluated to determine the static stiffness of any vehicle seat when it was loaded in a forward direction. The device used an appropriately pre-weighted seat form to load the vehicle seat and moved the seat form forward relative to the seat cushion. As the seat loading device interacted with the seat, horizontal and vertical forces were generated by the increasing load due to the inclination of the seat and the under cushion structure. While paired same model seats exhibited similar loading patterns and values, there was a variable response from different model seats. Of the five different models tested, maximum vertical loadings varied from 1082 N to 5655 N. After disassembly, structural differences were found between the tested seat models that could account for the difference in seat reaction loads. The device proved that the differences in stiffness between seat models could be evaluated in a nondestructive and timely manner.