An idea that triggered a revolution
- 13 years of development involving pioneering work in numerous fields
- Automotive engineers as blasters and canaries as testers
- 250 crash tests and seven million kilometres of testing
- Airbags that protect against side impacts since 1995
A wide area around the proving ground at Stuttgart-Untertürkheim was cordoned off. Crouching behind thick walls, the Mercedes-Benz engineers waited with bated breath. Not a sound could be heard, not a breeze stirred the air. All of a sudden there was an ear-splitting bang. Shreds of fabric and plastic flew everywhere, causing birds to flutter nervously from the trees. The engineers emerged from their sanctuary behind the walls, jumping for joy: the “explosives” had gone off just as planned. The Mercedes-Benz safety experts had just taken another step towards reaching their ultimate goal: the car airbag.
“We used missile technology,” remembers Helmut Patzelt, one of the founding fathers of the airbag and an expert in pyrotechnics. “A missile receives its thrust from discharged gas, and we applied this very principle. The only difference is that we trapped the gas – in an airbag.”
It was with this type of triggering test that Mercedes-Benz began to develop the idea of the airbag in 1967, prompted by two developments which affected traffic policy: the rapidly spiralling number of accidents during the sixties and a resultant series of new laws in the USA, one of which prescribed an automatic occupant protection system for every car in the USA from 1969 onwards. “We can no longer tolerate unsafe automobiles,” said the then US President Lyndon B. Johnson, making car safety a matter for decision at the top level.
And so it was that previously ignored inventions – for which patent applications had been submitted by the German Walter Linderer and the American John W. Hedrik as early as 1953 – suddenly took on a whole new meaning. “A folded, deployable receptacle which inflates automatically in the event of danger” was a fascinating idea yet, at that time, the technology required to make it happen simply did not exist. This was the cue for the automotive engineers to commence their explosive experiments. In 1970 the pressure on the developers increased when the newly formed US highway-safety authority stipulated that driver airbags would be a legal requirement for all new cars – starting as early as January 1, 1973.
No sooner had it been made a requirement than the airbag became the subject of a long-running dispute. “The airbag will kill more people than it saves,” claimed the new critical voices entering the debate in the USA. As a consequence, the introduction date was put back until 1976. And even after that, the production launch had to be postponed on several other occasions. The airbag – was it all really just a lot of hot air? Hansjürgen Scholz, the then project manager for passive restraint systems at Mercedes-Benz, remembers only too well: “When a fatal accident involving an airbag occurred in the USA in 1974, most of those involved deserted the project like a sinking ship.” All of a sudden the Mercedes developers were left on their own without any outside support. Other German manufacturers also failed to see the potential of the life-saving airbag at the time.
Those who advocated the airbag philosophy at Mercedes-Benz were very much left to their own devices. But they were not about to give up. “We had recognised the enormous potential of the air cushion. And we were not going to throw away our trump card,” says Professor Guntram Huber, the former director of development for passenger car bodywork at Mercedes-Benz, who would later be awarded the “Safety Trophy” by the American Department of Transportation for his role in the introduction of the airbag. And so it was that, in 1974, Mercedes‑Benz decided to go ahead and develop the airbag for production, regardless of happenings in the US market. What is more, it would be aimed at the world market. Airbags have only been a requirement in the USA since 1993, not 1973.
The technological challenges that had to be overcome when developing this innovation, which finally led to the unveiling of the world’s first driver airbag in December 1980, were immense. A new product had to be created entirely from scratch. Problems that required solutions included the sensor-triggered deployment mechanism, the gas generation process, the tear-resistance of the airbag fabric, the effects on health and hearing, functional reliability and the issue of how to prevent unintentional activation. Given the intrepid test methods employed – they were, after all, based on missile technology – the authorities were quick to offer resistance, at first putting the triggering mechanism used to inflate the airbag in the same category as fireworks. For this reason, all those involved in the development of the airbag had to attend an explosives course. Following initial tests with liquid gas cylinders, the breakthrough was finally achieved by using a solid fuel for firing the airbag.
Toxicologists also had their say, querying the emissions left behind in the car after deployment of the airbag. But the developers were able to allay these fears as well, since the solid fuel pressed into tablet form – consisting of sodium azide, calcium nitrate and sand – left behind predominantly non-hazardous nitrogen gas and small quantities of hydrogen and oxygen.
Crash tests with canaries
In their efforts to overcome the technical hurdles before them, many of the ideas the engineers came up with were highly unconventional. Since the sound of the deploying airbag was above the pain barrier but only lasted for ten milliseconds, the effect on the eardrums could not be clearly ascertained at first. The engineers therefore installed a cage containing 15 canaries in the test car to determine the harmful effects of the noise, gas emissions and air pressure during deployment of the airbag. Not only did all the canaries survive the test, they also remained their usual lively selves. Yet another step in the right direction.
Some 250 crash tests on complete vehicles, around 2500 sled tests and thousands of component tests provided the airbag pioneers with invaluable knowledge to help the airbag on its way to full series production.
The primary concern in all the tests was stopping the car airbag from deploying unintentionally – a horror scenario for the developers. In early tests, the airbag would sometimes go off when the vehicle was at a standstill, meaning that the engineers also had to develop the electronic system from scratch. The sensor only had a few milliseconds in which to deploy the airbag – still very much a utopian idea in those days. As if that were not enough, the sensor had to be able to function reliably for several years at extremely low and very high temperatures with constant fluctuations in humidity.
Some 600 test cars took part in road tests, off-road trials and rally events, clocking up in excess of seven million kilometres, in order to ensure that the sensor could perform its vital, life-saving function. In addition, the engineers, technical experts and office staff had to put themselves in the firing line, sitting at the wheel to gauge the effects of the airbag in an emergency, all under the watchful eye of the project team who recorded the results. Last but not least, another issue which had to be resolved before the first airbag was allowed to see the light of day in a production car in December 1980 was disposal, in other words what to do with the airbag when the car reached the end of its life.