Development of Airbags

Airbags, like lap belts/shoulder belts, are a type of automobile safety restraint system designed to mitigate injury in the event of an accident. These gas-inflated cushions, built into the steering wheel, dashboard, door, roof, and/or seat of your car, use a crash sensor to trigger a rapid expansion of nitrogen gas contained inside a cushion, that pops out on impact to put a protective barrier between passengers and hard surfaces. The National Highway Traffic Safety Administration (NHTSA) says that frontal airbags have saved over 2,000 lives each year federal legislation mandated frontal air bags in 1998.




Types of Airbags

The two main types of airbags are designed for frontal impact and side impact. Advanced frontal airbag systems automatically determine if and with what level of power the driver-side frontal airbag and the passenger-side frontal airbag will inflate. The appropriate level of power is based on the readings of sensor inputs that can typically detect occupant size, seat position, seat belt use of the occupant, and severity of the crash.


Side-impact airbags (SABs) are inflatable devices designed to help protect the head and/or chest in the event of a serious crash involving impact with the side of a vehicle. There are three main types of SABs: chest (or torso) SABs, head SABs, and head/chest combination (or "combo") SABs.



History of the Airbag

The airbag idea was conceived in 1941. However it took the public over 30 years to get on board with the idea. The first airbag was made in 1952 by John W. Hetrick. He applied the airbag invention in the Navy when he was repairing a torpedo with a canvas covering. This reminded him of an airbag because when the compressed air was released it quickly inflated the canvas shooting it to the ceiling. He was able to patent his design on August 5, 1952. His design of airbags is similar to the airbags today (see diagram, below). However, his airbags would have never worked. It would take years and years of designing and testing to get to where we are today.



After Hetrick patented the idea, Ford and General Motors (GM) began to experiment with the design. However, they did not go far with the idea because they realized the complexities that would be involved. Also there were two initial obstacles that would have to be overcome. One was the accuracy and reliably of detecting a collision. The second one was inflating the airbag within forty milliseconds.



Airbags became popular again in 1966 because of the successful testing of new detonating valve created by the U.S. Army. This design was similar to Hetrick's design, because it consisted of a 9'-10' nylon bag that attached to a container holding nitrogen gas. The detonator for the airbag exploded with the power of a .22-caliber rifle shell. Since the tests were successful, Ford decided to use the safety device, in 1971, in its line of full-sized Fords and Mercurys. However, the plan was shot down by Ford's chief body engineer due to two major issues. One was a performance problem in the components intended for mass production. The second reason was that child size dummies would receive fatal blows from the airbags during the crash tests. Also, airbags were not effective in angular crashes and the windshield often broke when the bags were deployed. (See “Crash Test Dummies” article).

During Ford's design and testing, GM was working on their airbags, too. GM also faced difficulties like unacceptable sound and the need to completely redesign the car's interior in order to accommodate the bags. AC Electronics, a company owned by GM, developed crash sensors. After developing an effective airbag system they installed them in a fleet of 1973 Chevrolet Impalas—for government use only. The 1973 Oldsmobile Toronado was the first car with a passenger airbag sold to the public. GM later offered an option of driver-side airbags in 10,000 full-sized Oldsmobiles and Buicks in 1975 and 1976, respectively. Cadillacs became available with driver and passenger airbags options during those years, as well. GM, which had marketed its airbags as the "Air Cushion Restraint System," discontinued the ACRS option for the 1977 model year, citing a lack of consumer interest. They would not be back until eight years later.


1973 Olds Tornado

Airbags came back because they were offered as an option in 1984 models by Mercedes-Benz. Within two years of airbags coming back, they became standard equipment on all of Mercedes-Benz's automobiles. Ford and GM subsequently spent years lobbying against airbag requirements, arguing that the devices were simply not viable. Eventually, however, the automobile giants realized that the airbag was here to stay. Ford began offering them as an option on their 1984 Tempo. Because of this success, they were standard on their 1986 Tempo and Mercury Topaz models.


1984 Mercedes Benz


1984 Ford Tempo

While Chrysler made a driver-side airbag standard for its 1988-1989 models, it wasn’t until the early 1990s that airbags found their way into the majority of American cars. In 1994, TRW began production of the first gas-inflated airbag. Airbags have been mandatory in all new cars since 1998.


1988 Chrysler New Yorker

In 1990 the government passed a law that requires all cars sold in the U.S. had to be equipped with either airbags or automatic seat belts. Then, in 1991, Congress enacted the Inter modal Surface Transportation Efficiency Act. This ordered the National Highway Traffic Safety Administration to require both driver's side and passenger side airbags in all new vehicles by
1998.

Airbag Inflation

Seat sensors determine how a two-stage airbag inflates. The primary stage is for smaller occupants or less severe crashes. Both stages can be triggered simultaneously for larger passengers, unbelted occupants or high intensity crashes.

Airbags rely on lightning quick chemical reactions. A spark bridges two wires to light the initiator, which creates a small flame that ignites the booster- a fast-burning granular material that triggers a large pool of guanidine nitrate- a rocket propellant. The resulting hot gases- primarily carbon dioxide, water vapor and nitrogen- fill the bag in as little as 0.025 seconds. Sidebags react even quicker and inflate in 0.01 seconds, based on a single pressure sensor within the door- they cannot wait for forces to build and for multiple accelerometers to agree that a crash is occurring.



To work effectively and avoid injury, lap belts/shoulder belts must be used in conjunction with airbags. They lock down whenever the car exceeds 0.50g of force. When a crash is detected, pre-tensioners use pyrotechnics to pull in about four inches of seat belt. Over the last decade, the load-limiting seat belt has become the norm. These devices use a torsion bar in the retractor to allow the belt to unwind in a controlled manner at forces generally between 300 and 1,500 pounds.