Evolution of Airbags

The advent of airbags, when the first production car fitted with one, an S-Class Saloon, rolled of the production line at Mercedes Benz after 13 years of development work, heralded a new era in passenger car safety. According to accident research, the airbag has saved over 14,200 human lives in the USA to date; in Germany, meanwhile, the airbag has prevented over 2,500 fatal injuries to car occupants since 1990. Airbags are also set to become an integral part of the PRE-SAFE anticipatory occupant protection system, equipped with new, anticipatory sensors which will enable them to deploy in advance of a possible accident so as to reduce the forces exerted on the car occupants both before and during any impact. For the same reasons, the airbags of the future will also take into account individual parameters such as the body size, sex and age of the occupants.

Here's a look at the evolution of this vital component of passenger car safety.

Development History

▪	13 years of development involving pioneering work in numerous fields
▪	250 crash tests and seven million kms of testing
▪	Airbags that protect against side impacts since 1995
▪	Windowbags make their debut in 1998

 
The development of the airbag began in 1967. Although, the idea for an air cushion of this kind had been around since the early 50s, engineers had been unable to transform the vision into reality. The Mercedes team had made great progress with a discriminating sensor system and a gas generator capable of deploying the airbag in just 30 milliseconds. Missile technology was used by the pioneers, based on the principle that discharged gas was the thrust provider for the missile. The only difference was that the gas was trapped in an airbag.

It was with this type of triggering test that engineers 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 60s 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.

The airbag becomes a bone of contention

No sooner had it been made a requirement than the airbag became the subject of a long-running dispute. Some people were of the opinion that the airbag would kill more people than it would save. As a consequence, the introduction date was put back until 1976. 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. But they were not about to give up. It was their trump card and they were not about to throw it away. So in 1974, Mercedes-Benz decided to go ahead and develop the airbag for production, regardless of happenings in the US market. What was more, it would be aimed at the world market.

The technological challenges that had to be overcome when developing this innovation, were immense. Problems 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, 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 soothe 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 performed to allay fears

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. 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. The sensor also 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. Another issue which had to be resolved before the first airbag was launched in a production car in December 1980 was disposal - what to do with the airbag when the car reached the end of its life.

From airbag to windowbag

The Mercedes engineers built on their lead in the airbag development stakes and continued to further improve the system. The world premiere of the driver's airbag was followed by the launch of the front-passenger airbag in 1988 and the first side airbags for passenger cars in 1995.

The next milestone in airbag history - the windowbag - was also achieved in 1998. In the event of a side impact, it inflates across the side windows to form a curtain, its large dimensions providing a wide area to protect the heads of both the front occupants and the rear passengers. Windowbags can prevent the head from hitting the side window, roof pillars or roof frame and are also capable of catching any fragments of glass or other objects propelled into the interior following a collision or subsequent roll-over.

Since the design of some of the cars made it impossible to install windowbags, a side airbag was thus developed to protect both the head and the upper body. This head/thorax bag, as it is known, is located in the front seat backrest and deploys within milliseconds following a side impact, forming an asymmetric air cushion whose upper edge spreads further upwards when inflated, thus reducing the risk of the occupant's head hitting the side window or coming into contact with any object penetrating the car interior. At the same time, the lower section inflates between the door and the occupant, creating a large surface protective shield for the chest area.

Two-stage triggering

The front airbag has also developed into a highly complex and sensitive electronic system - a high-tech product that adapts to suit the seat occupant and the accident situation, responding accordingly before the driver has even had time to fully register any precarious accident situation. This lightening-fast reaction time is down to electronic triggering sensors and newly developed gas generators which allow the front airbags to deploy in two stages, depending on the severity of the accident: in the event of a minor frontal collision, the ECU only fires one chamber of the two-stage airbag gas generators. As a consequence, the airbags are deployed with a lower internal pressure. However, if the control unit detects a severe frontal impact, it also fires the second chamber of the gas generator to produce a higher internal pressure, thus affording the seat occupant the ideal level of protection for the accident situation in hand.

Personalised safety for large and small front passengers

Equipment on board the new cars include a computer which, in addition to gauging the severity of the accident, also takes into account the size of the front passenger. If the sensor system housed in the seat upholstery detects a small front passenger, it initially only triggers the first airbag stage, depending on the type of accident, meaning that less air is injected into the airbag. If the system senses a larger front passenger, however, both airbag stages are triggered.

Occupant protection before impact

The year 2002 saw the advent of the PRE-SAFE anticipatory occupant protection system. The innovative system, further enhances the effectiveness of the seat belts and airbags by identifying situations which might turn into accidents and preparing the occupants and vehicle for a possible collision. As a precaution, PRE-SAFE tensions the front seat belts, moves the front-passenger seat into the optimum position and, if applicable, automatically closes the sunroof. These preventive pre-crash measures ensure that the occupants are in the best possible sitting position should an impact occur, allowing the seat belts and airbags to do their job as effectively as possible.

Tests carried out by the Mercedes engineers show just how effective the PRE-SAFE functions are: inflatable air cushions housed in the seats, support and hold the driver, front passenger and rear occupants in the ideal position before an imminent accident, thus considerably limiting the dangerous oscillating motion of the upper body. As a result, the distance between the shoulder and the door's interior panelling is increased, enabling the sidebag to offer even better protection in the event of an impact.

Accident Research

▪	Sharp decline in the number of serious and fatal injuries
▪	Airbags have saved more than 14,200 human lives in the USA

 
Right from the start, the Mercedes experts designed the airbag to work in tandem with the seat belt, hence the term Supplemental Restraint System (SRS) which appears on the steering wheel's impact absorber. In the event of a frontal impact, maximum occupant protection can only be assured if all the safety systems work in unison.

Today the merits of this approach are undisputed, and the airbag has been universally acknowledged as a safety-enhancing innovation. Thanks to seat belts, belt tensioners, airbags and other safety measures, the number of car occupants fatally injured in road accidents in Germany has fallen by more than half since 1970 whilst, during the same period, the number of vehicles on the road has more than doubled.

Effective interaction between the airbag, seat belt and other protective systems

Ever since the eighties, when the seat belt tensioner and the airbag made their debuts in passenger cars, the number of drivers seriously or fatally injured in frontal collisions has been falling constantly. Aside from a small number of catastrophic accidents - so severe that no protective measures would have been effective in any case - the safety experts have not recorded any instances of serious or fatal injuries to drivers involved in frontal collisions since the nineties.

Based on these and other findings, the accident researchers at Mercedes-Benz have estimated that the airbag alone has saved the lives of more than 2,500 car occupants involved in road accidents in Germany since 1990.

Outlook

Vision: Airbag as an integral part of the PRE-SAFE anticipatory occupant protection system

Given that every fraction of a second counts when it comes to offering the best possible level of protection for car occupants in advance of a collision, this form of anticipatory crash analysis represents a further step on the road towards improved occupant safety - and an important addition to the pioneering PRE-SAFE system unveiled by Mercedes Benz in 2002. New sensors could work alongside the current PRE-SAFE belt tensioners, giving rise to PRE-SAFE airbags which are deployed earlier, less abruptly and more "softly" in accordance with the accident situation. In this sense, "earlier" means during the PRE-SAFE phase, that is to say before certain frontal collisions.

If the airbags have more time to do their job, they can be inflated with even more air at a slower rate, enabling them to cushion the driver and front passenger at an earlier stage and hold them in the best possible seating position, thus reducing deceleration distances both before and during the impact. The end result is lower forces exerted on the occupant's body and more effective protection against injury.

Individualisation is also high on the development agenda: tomorrow's protection systems will be even more precisely configured to take into account the seat occupant's size, weight, sex and other parameters. In other words, "personalised" safety will be the order of the day.

By way of example, it would be conceivable for the driver, front passenger and rear occupants to program the on-board computer with personal details such as size, weight, sex or age before commencing a journey. Based on these biometric data, the computer would then adjust the degree of airbag inflation and deflation, the force exerted by the belt tensioners, the performance of the belt force limiters and the position of the steering column in line with individual requirements in the event of an accident. In addition, PRE-SAFE functions such as automatic seat positioning in advance of an accident could be controlled based on the size of the occupant concerned.