Airbag Inflators

Basic Description

The airbag inflator is one of the many components of an airbag system. The main purpose of an airbag is to slow the passenger’s forward motion as evenly as possible in a fraction of the second after a collision. One of the biggest challenges in early efforts to adapt airbags for use in cars was their high price and technical difficulties involving the storage and release of compressed gas. These difficulties included providing sufficient room for gas storage in the car, maintaining the high pressure of the gas during the lifetime of the car, and producing quick and reliable expansion of the bag without causing injuries. These requirements suggested the need to develop an airbag design based on a chemical reaction that would produce nitrogen gas to inflate the airbag. The first automotive airbags developed in the 1970s employed a solid propellant. These airbag inflation systems reacted sodium azide (NaN₃) with potassium nitrate (KNO₃) in order to produce nitrogen gas. The hot blasts of the nitrogen gas inflated the airbag. Because sodium azide is extremely toxic, these gases were widely phased out during the 1990s in favor of more efficient, less expensive, and less toxic alternatives. The alternative propellants may incorporate, for example, a combination of nitroguanidine, phase-stabilized ammonium nitrate (NH₄NO₃) or other nonmetallic oxidizers, and a nitrogen-rich fuel other than azide (e.g. tetrazoles, triazoles, and their salts).

As illustrated in the above figure, when a crash is sensed, the control unit sends an electrical signal to the inflator. The chemical reaction is initiated by the igniter, generating primarily nitrogen gas to fill the airbag causing it to deploy through the module cover. Due to rapid speed change of the vehicles involved in a crash, airbags must inflate rapidly to decrease the risk of occupant injuries by protecting them from hitting the vehicle interior. From the beginning of the crash, the entire deployment process is about 50 milliseconds which is faster than the blink of an eye (about 200 milliseconds). A second later, the gas quickly dissipates through tiny holes in the bag, thus deflating the bag and enabling the occupants to move.

Manufacturers

ARC Automotive, Bosch, Continental, Delphi, Denso, TRW

For More Information

[1] How Airbag Works, Marshall Brain, HowStuffWorks.com, Apr. 1, 2000.

[2] Airbag, Wikipedia.

[3] Inflator Assembly, Lemurzone.com.

[4] Airbag Deployment [Video], Metacafe.

[5] Advances in Airbag Technology, Jeremy Rosenberg, Cars.com, June 18, 2009.