Airbag Serial Lifesavers

In the town of Alfdorf near Stuttgart in Germany, ZF TRW develops passive safety systems such as airbags and seatbelts. Taking a look behind the scenes at the Airbag Test Laboratory.

An ear-piercing horn sounds. With an output of more than 100,000 watts, 48 spotlights bathe the testing facility in a glistening light to ensure ideal photo conditions for the high-speed cameras. The test sled – equipped with a complete restraint system made up of seatbelts and airbags as well as a crash test dummy – sits in front of the hydraulic sled installation. In an instant, a diagonal frontal collision at more than 30 mph is simulated. With a bang, the seatbelts tighten and the airbags fill with a whoosh while the test sled, along with the dummy, is thrown backwards from the power of the impact. This is a daily occurrence at ZF TRW’s crash simulation facility in Alfdorf, the headquarters of the Occupant Safety Systems (OSS) unit. Aside from seatbelts, airbags are the most important element when it comes to passive safety. Both are developed by ZF’s new corporate Active & Passive Safety Technology division in Alfdorf near Stuttgart.

The success story of the airbag began in 1951 when Munich inventor Walter Linderer filed a patent for an airbag prototype. The first airbags were launched on the U.S. market in 1974, but did not arrive in Germany until six years later. The basic principle of the airbag system has barely changed since it was first put into volume production. Pressure and acceleration sensors around the vehicle are analyzed by a control unit. The crash algorithm in the control unit identifies the beginning of a crash and triggers the gas generator via an electrical signal. In a matter of seconds, the stream of gas fills the airbag which then absorbs the kinetic energy of the passengers.

For static tests surrounded by components, the airbag modules are installed in substitute devices which are adjusted to precisely simulate the actual vehicle models.

From idea to production

Depending on whether it is an enhancement to an existing product or an entirely new development, it can take months or even years before an airbag is installed in a production vehicle on the factory floor. This development process has two stages: the core development stage covers the early phases from the initial idea and various concepts to the design of the basic airbag. Near the end of this first stage, enough detailed information is available to present the new product to the customer. The beginning of the second development stage is the volume production order. During application development, the airbag is adapted precisely to the customer’s vehicle specifications.

In Alfdorf, airbag prototypes are produced manually in many work steps.

While innovation management, product planning, and airbag core development are handled centrally by ZF TRW in Alfdorf, application development is done at the locations closest to each customer. “This allows us to provide optimal customer care,” explains Dr. Swen Schaub, Senior Manager of Engineering Strategy & Communication at ZF TRW in Alfdorf. “For our German customers, we also manage application development here in Alfdorf.”

About 1,600 employees work at the Alfdorf facility, with more than 680 involved in the development of seatbelt and airbag systems. They ensure that innovations in the field of occupant safety make daily progress. The airbag portfolio is continuously modified and expanded because engineers are confronted not only with challenges such as new vehicle designs, but also changes to regulations by institutions such as Euro NCAP, the European consumer protection organization. That’s why proven technologies, such as “classic” frontal airbags (airbags for drivers, passengers and knees) and side airbags (including thorax airbags for torso protection and curtain airbags for protecting the head in side-impact collisions) must be constantly modified and enhanced. At the same time, entirely new airbag concepts are also developed in Alfdorf and prepared for volume production, such as the world’s first roof airbag on the passenger side of the Citroen C4 Cactus. This airbag module is not placed in the dashboard, as usual, but rather on or below the roof liner above the windshield. This protects the passenger and provides more cabin space, creating new options for redesigning the vehicle interior.

Occupant Safety Systems Trends

Mr. Schultz, airbags are now an established technology. How much potential is there for further development?

While traffic safety in Germany has risen considerably, the approximately 3,000 traffic fatalities that occur annually on German roads are still too high. Moreover, Germany, or Europe, is only one part of the global market. Today, technologies must become lighter and smaller, and we must also offer greater flexibility in terms of styling.

What airbag innovations is ZF TRW currently working on?

First of all, we’re constantly improving our proven technologies. Weight reduction and better use of space are the drivers behind these efforts. Lighter gas inflators are helping us achieve this. In addition, design engineers are thinking about replacing plastic housings with housings made of industrial textiles. Adaptive systems that adjust to the environment and the occupants are playing an important role in the development of new concepts. Finally, occupant safety in the rear is also becoming increasingly important.

What trends will drive airbag development over the long term?

On the one hand, conventional airbags will continue to penetrate deeper into the market, primarily in developing countries. On the other hand, the question arises of what the automobile of the future will look like. Will we even have steering wheels at all? Where will we put the driver airbag then? The airbag will certainly establish itself to an even greater degree as an inherent component of the car, and along with new features and new technologies, it will be possible to offer even greater improvements to occupant safety.

Innovations such as the center airbag

ZF TRW in Alfdorf is also working on numerous other innovations, such as the center airbag, which deploys between the two front seats and better stabilizes the driver in the event of a side impact, while also ensuring that the driver and the passenger do not collide with one another. “Another major priority are airbags that can be deployed before a crash based on sensor data from radar and camera systems,” adds Dirk Schultz, Director of Engineering for Inflatable Restraint Systems and Inflators at ZF TRW in Alfdorf. “This will help us gain valuable milliseconds. Such pre-crash systems are particularly interesting in the case of side collisions, because there is only a narrow crumple zone between the occupants and the vehicle crashing into them.”

The Alfdorf facility is ideally equipped for the tests required during the development process. In addition to its prototype manufacturing workshop, it has an airbag lab for performing static tests relating to components. “About 1,500 times a month, we test airbags to their limits,” explains test coordinator Armin Abele. “To do this, we install the airbag module in its usual position or an appropriate substitute and store it for several hours in a cold or heat chamber.” Within ten seconds of leaving the chamber, the airbag is deployed so that all parts are still at the desired temperature. To analyze the results, a high-speed camera is used to record all details of the deployment and positioning of the airbag.

Lastly, airbags are tested in dynamic tests in the vehicle environment together with other technologies. The Alfdorf test facilities include two bungee units on which the test sled drives into an obstacle as well as a hydraulic unit in which the test sled is thrown backwards using a hydraulic cylinder. The crash test dummy has come through all of these collisions completely unscathed – thanks to the airbags.

Pictures: Dominik Gigler

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