Airbag Deployment Systems

Basic Description

Airbags are passive safety devices that are mandatory on all vehicles sold in the United States. Airbags are a critical part of the Supplemental Restraint System (SRS) in most vehicles. The objective of the airbag, which is deployed when the vehicle suddenly decelerates (as in a collision), is to prevent the vehicle occupants from hitting any rigid surfaces and cushion the forces on their heads and upper bodies. Airbags are typically made of nylon fabric and are hidden behind panels at various locations in the vehicle, including the steering wheel.

Depending on the crash severity, the rate at which the airbags are deployed is decided by the airbag control unit. In event of a crash, the crash sensor (an accelerometer) sends a signal to the airbag control unit. This control unit triggers the inflation device, which generates nitrogen gas by igniting a mixture of sodium azide (NaN₃) and potassium nitrate (KNO₃). From crash detection to complete deployment of the airbag, takes about 0.05 seconds. The airbag speed is about 200 mph, which itself can be harmful in certain cases, this has given rise to a new solution called dual-stage airbags that use two inflators.

Dual-stage airbags have the capability to produce either a low-level or high-level deployment. A sensor on the track of the driver's seat determines whether the seat is adjusted forward or rearward. If the seat is forward on the track, the occupant will be closer to the air bag module, and the control system inhibits the high-level deployment. The deployment algorithm also uses other parameters, such as crash severity and seat belt use, to determine the level of deployment. Alternatively, if the crash is of high severity, both stages of air bag inflation may be initiated to produce a high-level deployment.

In the front passenger seat, most systems use a weight sensor to determine if the seat is unoccupied in which case deployment of the passenger air bag will be inhibited. The weight sensor can also discriminate between children and adults who may be occupying the seat. Typically, air bag deployment will be suppressed if the sensor identifies a low-weight condition.

Sensors

Accelerometers, wheel speed sensors, brake pressure sensors, seat occupancy sensor

Actuators

Airbag inflation device, passenger airbag ON/OFF indicator

Data Communications

• Serial Data link to the vehicle data bus
• Control unit communication: CAN bus

Manufacturers

Bosch, Delphi, Denso, Continental, Mitsubishi, Tokai Rika, Takata, TRW

For More Information

[1] Questions and Answers about Air Bag Safety, National Highway Traffic Safety Association (NHTSA) website.

[2] Car Airbags - Explained, YouTube, 2008.

[3] Airbag Deployment in Slow Motion, YouTube, 2008.

[4] Advanced Air Bags, The Canadian Association of Road Safety Professionals, CARSP/ACPSER.

[5] The History of Airbags, About.com.

[6] History of Airbags, Motorvista.

[7] How Airbags Work, Marshall Brain, HowStuffWorks.com, Apr. 1, 2000.

[8] Airbag, Wikipedia.

[9] Vehicle Safety Airbag Control System, U.S. Patent No. 6,273,461, Aug. 14, 2001.

[10] Volkswagen Golf IV Crash Test, YouTube, 2009. (in German)