2006-02-07 Airbag and belt tensioner
Airbag and belt tensioner – world premiere in 1981
The 1981 Mercedes-Benz S-Class, the world’s first car with airbag and belt tensioner
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Rocket technology for passive safety
Initially an option, today a permanent integrated safety feature
Stuttgart, Feb 05, 2006
In 1981 the W 126 series Mercedes-Benz S-Class attracted a great deal of attention at the Geneva Motor Show with a new item of optional equipment: the airbag and belt tensioner – two passive safety innovations – were celebrating their world premiere in the flagship Mercedes model. The combination of a driver airbag and a front passenger belt tensioner was initially only available for the 126 series from July 1981, as an optional extra costing 1,525.50 DM (equivalent to around 780 euros) for the sedan and coupe.
During the first year no less than 2,636 S-Class buyers opted for this new safety feature, ushering in the triumph of the airbag. More than twelve million Mercedes-Benz cars were equipped with airbags in the first 25 years of this new technology, with other brands following suit. An optional extra for the driver of 1981 has developed into a restraint system which now protects vehicle occupants with a system of airbags, belt tensioners and belt force limiters during an accident.
A protective air cushion for car drivers
The first ideas for an air cushion which would protect drivers from impacting on the steering wheel during a collision were already aired in the 1950s. At the time it was not however possible to translate this idea into reality with the mechanical sensors and control systems available. The idea of the airbag was given a new impetus when the United States announced plans to prescribe automatic occupant protection systems for passenger cars in 1969, and in 1973 the driver airbag was even to become compulsory for new vehicles. The solutions presented came in for a great deal of criticism, however, and the introduction date was repeatedly postponed. Most of these projects eventually ended with no concrete result.
These developments were paralleled by continuous efforts on the part of Mercedes-Benz researchers. Work on a practical airbag already commenced in Stuttgart in 1967. The researchers and developers had numerous hurdles to overcome in the first few years. The sensor system had to be newly developed, as did the gas generation technology and the woven material for the airbag itself. The first tests relied on compressed air and Freon to inflate the airbag. But the best technical solution proved to be a fabric bag which could be inflated within milliseconds by a pyrotechnical charge during an accident, gently cushioning the driver. The developers adopted the sodium azide explosive charge from rocket technology.
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In 1971 Mercedes-Benz was granted patent number DE 2152902 C2 for the airbag. Many details of this new restraint system needed to be improved and tested before it was ready for series production. The airbag proved its reliability during more than 250 impact tests using complete vehicles, more than 2,500 sledge impact tests and thousands of tests on individual components. At the same time 600 vehicles entered long-term trials in on-road and off-road operations to en-sure that the airbag would not be activated during normal driving.
The evolution of the air cushion in the dashpot
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The airbag presented for the S-Class in Geneva in 1981 was still rather voluminous; therefore the dashpot of the S-Class equipped with an airbag was larger than the standard steering wheel boss. And when the first front passenger airbag was presented at the International Motor Show (IAA) in Frankfurt in 1987, the system still occupied the entire glove compartment. Airbag modules became increasingly smaller, however. This was made possible by continuous technical development, and also led to the creation of sidebags which would protect vehicle occupants from injury in lateral impacts.
Mercedes-Benz was already able to present a side airbag as a study in 1993, and in 1995 the side airbag became available as an optional extra for the E-Class. In 1998 the windowbag supplemented the comprehensive protection system of the E-Class, and in 2001 Mercedes-Benz presented the head-thorax side airbag for convertibles and roadsters. In 1992 the driver airbag became standard equipment in all Mercedes-Benz models, and in 1994 the front passenger airbag joined the list of standard safety features.
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In the W 221 series S-Class, adaptive airbags are part of the safety philosophy known as PRO-SAFE™. The airbags are activated in two stages, depending on accident severity and the personal data of the vehicle occupants. Future airbag generations will be able to adapt even better to the individual occupants. As a next technical step Mercedes-Benz developers are testing the integration of airbags into the preventive protection system PRE-SAFE®. In this case the airbags are not activated only when a collision occurs, but slightly in advance so that the occupants are supported and held in place when the impact takes place.
From the pyrotechnical belt tensioner to PRE-SAFE® The belt tensioner presented in conjunction with the airbag also became a permanent passive safety feature, having been introduced in Geneva in 1981. In an accident this support system uses a pyrotechnical charge to tension the inertia-reel seat belt worn by the front passenger within a few milliseconds. In this way the safety technology in the W 126-series S-Class reliably fixed the front passenger in place, even if the seat belt had initially been fastened too loosely.
From 1984 all Mercedes-Benz models were equipped with front seat belt tensioners as standard. In 1995 the belt tensioners in all models were combined with belt force limiters to adapt the action of the restraint system to individual requirements. In 2002 the pyrotechnical belt tensioner was supplemented with an electronic belt tensioner on the introduction of the preventive occupant protection system PRE-SAFE®. This tensions the seat belts when PRE-SAFE® detects a critical situation and prepares the vehicle for a potential impact. In contrast to the pyrotechnical belt tensioner the electronic system is reversible: the belt is loosened again if no impact occurs.
Airbag and seat belt as an entity
The airbag is intended as a complement to the seat belt, by no means as a replacement. This was already clear to the developers at Mercedes-Benz when they began their research for the airbag in 1967. It is only the joint effect of the belt and airbag that provides the best possible protection against serious injury in an accident. Since the 1981 debut of this safety technology in the S-Class, airbags combined with seat belts have literally saved thousands of human lives.
Mercedes-Benz has continued to improve its integrated safety systems with numerous innovations. In today’s Mercedes cars the airbags and seat belts combine with the belt tensioners and belt force limiters to create a complex restraint system for fully integrated safety. In 1992, in order to demonstrate the operational reliability of the restraint system even years after first delivery, Mercedes-Benz used the occasion of the one millionth airbag to be installed in one of its vehicles to conduct a crash test with a Mercedes-Benz 500 SEL produced in 1981 at the crash-testing center in Sindelfingen. The airbag deployed exactly as it was designed to do. The service intervals recommended to ensure perfect operation are normally shorter, however.
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