Investigation of Inflatable Belt Restraints 912905

Studies conducted in the 1970's suggested that inflatable belt restraints might provide a high level of occupant protection based on experiments with dummies, cadavers and volunteers. Although inflating the belt was one factor which contributed to achieving these experimental results, much of the reported performance was associated with other features in the restraint system. Exploratory experiments with the Hybrid III dummy indicated similar trends to previous studies, belt inflation reducing dummy response amplitudes by pretensioning and energy absorption while reducing displacement. The potential advantage of an increased loaded area by an inflatable belt could not be objectively demonstrated from previous studies or from dummy responses.

Clearly, belt inflation can be one component of a belt restraint system which tends to reduce test response amplitudes. However, other belt system configurations have demonstrated similar test response amplitudes. Additionally, packaging and comfort issues for inflatable belts have not been completely resolved. Thus inflatable belts do not appear competitive with other approaches to achieve belt restraint system performance.

IN THE EARLY 1970's, Allied Chemical developed an inflatable belt restraint to achieve FMVSS 208 performance [1]. They suggested that inflatable belts might be a superior restraint system compared with belts or air bags, by providing lower dummy response amplitudes than conventional belts or air bags in frontal tests. In lateral and oblique crashes, and potential ejection situations the inflatable belt could perform better than air bags and at least as good as belts. They suggested that inflatable belts might cost less than an air bag system and have lower replacement costs, less stringent triggering requirements, and fewer inflations based on a higher inflation threshold because of the protection provided by the uninflated restraint. However the belt would need to be “used” to protect an occupant.

Allied Chemical conducted various general and specific development efforts. These efforts included volunteer tests sponsored by the NHTSA and conducted at Southwest Research Institute in which no significant injury was noted in sled tests to 32.5 mph. Sled tests with dummies achieved HIC and chest acceleration well below “208” limits at 32.5 mph. Other efforts chose inflatable belt restraint systems for front or rear seating positions in Research Safety Vehicles with good test results well above 30 mph barrier crash severities [1].

In spite of these favorable demonstration efforts, the system never achieved sufficient development to be placed in a fleet of experimental vehicles. Unresolved design and packaging issues, and the use of other technologies to achieve protection may be among the reasons that inflatable belt design never reached a fully developed product.

Based on the previous test results, the trend of increased belt usage, and the increase of elderly car occupants who generally have lower tolerance to belt loading, a study was undertaken at the General Motors Research Laboratory in the mid-1980's to evaluate inflatable belts. The study's objective was to review the state-of-art for inflatable belts in terms of performance and design by reviewing the literature and conducting exploratory sled tests with current dummies and advanced injury assessment techniques.