Explaining engineering: How are intelligent safety and restraint systems developed?

Work on the safety systems of an automobile starts after the first design phase. The engineers provide the safest possible design for the vehicle structure. So-called load paths for distributing impact energy are created, important nodal and connection points are generated from highly stable steels, and potential weak points are provided with additional reinforcement or intelligent crash boxes. In this early developmental phase, system partners such as Siemens Restraint Systems GmbH in Alzenau, Germany, are turned to as consultants. They simulate every possible accident scenario on their high-performance computers to optimize the combination of airbag and safety-belt.

When new materials and processing methods are used, basic research in the form of extensive material tests is necessary. This demonstrates how future components will behave in real life so that a corresponding simulation world can lead to the optimum solution while saving time and money.

Two years before the start of production, the “hot“ phase of safety develop begins. After the first prototype has shown in a crash test that the body structure corresponds to the theoretical values in a real crash, plans for the restraint system are developed in close collaboration between the manufacturer, system developer and supplier. The developers establish the number, volume and position of the airbags and position the crash sensors. The belt system with the belt tightener, force limiter, retention points and belt lengths are specified. Once this has been established, the functions of all the components are tested before the individual systems must show that they can interact smoothly. The airbag igniters, sensors, gas generators, bags and coverings are checked separately before a system test. Only when numerous individual tests have been successfully passed does the entire vehicle return to the crash facility.

In developing safety systems, Siemens Restraint Systems uses a three-stage plan to minimize development time and only destroy as few prototypes as possible. This allows the development cost and time for the safety package to be reduced by up to 50 percent. For this reason, all components, systems and the overall vehicle are first tested in extensive computer simulations. Individual components or assemblies must demonstrate their fitness in a vehicle in more than 1,000 virtual accidents. This requires many thousands of hours of calculations on high-performance computers. New scenarios can be created by the click of a mouse, and alternative constructions can be investigated without the manufacturer or supplier having to create and sacrifice a real component.

When individual variants are particularly promising, the safety development process transitions from the virtual to the real world, although first with limited destructive force on the so-called sled test. In this test, the individual components or subsystems such as the seat system and belts are affixed to a chassis subframe with a reinforced body structure. Elaborate dummies make their first appearance at this juncture. The slide is hydraulically accelerated in a few fractions of a second and braked. The components must survive the force of a real accident. The advantage of this procedure is that although the airbags, belt tighteners or belt force limiters need to be replaced, the expensive body remains unharmed and can be reused. Only when a usually hand-made component has passed the test can the next prototype phase start and preparations begin for series production. However, the final release is only granted when the series parts have run through the entire crash procedure.

If something is remodified after evaluating the sled tests, the process restarts with computer simulation. Otherwise, the crash tests with the entire vehicle begin, approximately 18 months before the start of production. The vehicles are accelerated with a 1,000 horsepower hydraulic system in the Siemens Restraint Systems Crash Center in Alzenau up to 125 km/h, and catapulted in different arrangements against various obstructions. They can be a solid barrier, standing posts or another vehicle. The behavior of a frontal crashes is investigated as well as side collisions, rollovers, crashes against a tree trunk, or rear-end collisions. After the actual crash test, the engineers investigate all the parts. The engineers evaluate the measured values from over 200 sensors in the vehicle and the dummies as well as the kilometers of pictures from ten high-speed cameras. The cameras record the few moments of the crash test at up to 1,000 frames per second.

Before a vehicle is released, European legislators have mandated that approximately 15 different crash tests must be passed. If the vehicle is to be sold in North America and Japan, additional tests are required due to the different laws and standards. Many vehicle manufacturers also test new designs more strictly than required by law and check the accident behavior of vehicles in crash procedures of large consumer organizations. Hence the number of crash tests over the course of vehicle development is frequently far above one thousand. Even in the case of exclusive luxury limousines or extreme sports cars, numerous vehicles must be destroyed in the name of safety.

At the behest of vehicle manufacturers, Siemens Restraint Systems also checks the effects of changes on the safety system after series production starts. The engineers test if new leather seat covers hinder the expansion of the side airbags, or if the crash sensors need to be repositioned or reprogrammed in sport coupes or off-road, all-wheel vehicles to cover all the bases regarding safety.