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Airbags – woven protective shields

The purpose of airbags is to slow an occupant's motion as evenly as possible in a fraction of a second in a crash. Airbags are supplemental restraints and work best in combination with seatbelts.

The airbag consists of a folded textile cushion designed to inflate quickly inside the vehicle immediately after a collision. Most airbags are inflated pyrotechnically and can only be deployed once.  

There are four main parts in an airbag module (from right to left): 

  1. An inflator that produces sufficient gas to inflate the folded bag.
  2. A textile cushion made of thin, woven nylon or polyester fabric. 
  3. A housing for storing the folded bag and the inflator. The housing can be made of steel, plastic or even textile.
  4. A cover that opens as the cushion inflates.

The airbag is controlled by the passive safety electronics unit that is normally located in the middle of the vehicle, where it is well protected. This "electronic brain" decides if and when each of the airbags should be deployed. It also controls the seatbelt pretensioners, providing the best protection for the vehicle’s occupants. The ECU receives information from sensors, such as accelerometers, mounted in key locations inside the vehicle. By measuring deceleration, accelerometers activate the airbag depending on the severity of the collision. Airbags are designed not to activate during sudden braking or while driving on rough or uneven pavement. In fact, the most severe braking is only a small fraction of the deceleration necessary to activate the airbag system.
 

   

The Airbag deployment



Frontal airbags are deployed in less than 50 milliseconds. Airbags for side protection have to be fully inflated within 15 milliseconds, which is eight times faster than the blink of an eye. Once an airbag deploys, deflation begins immediately as the gas escapes through vent holes in the fabric.  A frontal airbag is empty after approximately one second.

 

Advanced Airbags 
 
Frontal airbags can be designed to inflate with variable volume depending on the severity of the crash and system requirements as well as the occupant's size and distance from the airbag. Many of these variable volume airbags use multi-stage inflators that deploy less forcefully in moderate crashes than in very severe crashes.
 
Multi-stage driver airbag  

Occupant sensing devices can determine the occupant’s seating position, whether the person is an adult or a child and whether a seatbelt or child restraint is being used. Based on this and other crash severity information, the airbag is deployed more aggressively, less aggressively, or perhaps not at all.

  

What happens after a crash?