PRE-SAFE Structure: inflatable metal structures
It sounds like science-fiction: concealed metallic structures that wait
patiently in a collapsed, space-saving state until they are required to go
into action. Daimler researchers working together with the gas generator
specialists at Autoliv spent two years actively researching such active metal support systems, and tested a variety of applications. For the very first time, inflatable metal side impact protection can be seen in the ESF 2009.
Imagine an inflatable mattress. When it is not needed, it is rolled up flat and e.g. consigned to a shelf in the attic. When inflated, however, it has a highly resistant structure that can easily carry a man weighing 100 kilograms. Inflatable metallic structures work in the same way: when not in use, the metal section is folded together to save space. Once its protective effect is needed, a gas generator just like those used to inflate airbags builds up an internal pressure of 10 to 20 bar within fractions of a second, the metal section is unfolded and the structure has significantly greater stability.
The advantages are obvious, and mainly involve packaging and weight: more
stable structures can be accommodated within the increasingly tight installation spaces of an automobile, or weight can be greatly reduced while maintaining the same stability. Using the example of the side impact protection member in the doors of the S-Class, the researchers have calculated that around 500 grams less weight per door would be feasible.
Daimler safety researchers examined various applications for these innovative, crash-responsive metal structures, among them side impact protection, the side skirts and the seat cross-members. These have the advantage of being several centimetres away from the impact zone. The gas generator therefore only needs to be activated when a crash has definitely taken place.
One of the still unsolved problems of these protective members is that unlike the PRE-SAFE® measures already in series production, their active deformation is not reversible. Moreover, the activation of protective members installed well to the outside of the bodyshell that can be inflated by internal pressure requires their deployment before the crash. The pre-crash sensor system must therefore provide highly reliable signals.
Another hurdle is the currently still uncompetitive cost level of the required gas generators in relation to the cost requirements for weight-saving measures. These crash-responsive metal structures are therefore still a thing of the future – but the same was also once true of standard safety features like the airbag, ABS or ESP®.