Airbag Components and Function
How Airbags are Designed to Save Lives in Automobile Accidents
Airbags have been the largest occupant safety innovation in the automobile industry since the introduction of the lap/shoulder seatbelt.
Automobile airbags are designed to save lives during collisions by cushioning the occupant as he/she decelerates after impact. An airbag is more formally known as a Supplementary Restraint System (SRS), an Air Cushion Restraint System (ACRS), or the Supplemental Inflatable Restraint (SIR).
While airbags were originally installed to protect the driver from impacting the steering wheel or windshield during a collision, airbags are now standard on the driver and passenger side for frontal impacts, and many vehicles have side curtain airbags to protect occupants during side impacts. Airbags use a combination of design, sensor, and chemical technologies to deploy successfully during a collision.
Airbag Components
An automobile airbag system is made of three general components:
- the airbag itself,
- a sensor system, and
- a deployment mechanism.
The airbag itself is constructed of nylon fabric, and each airbag is specifically designed for the specific automobile, and location within the automobile. For example, because the passenger dashboard is further away from the passenger than the steering column is from the driver, the passenger side airbag is larger, and requires more gas to fill it during a collision. Other airbag types include the side air bag, which generally deploys out of the door, and the side curtain airbag, which descends from the roof rail above the door. Several holes are designed into each airbag to slowly expel gas when the occupant strikes the airbag. This action helps absorb the energy of the occupant and prevent the occupant from being bounced backwards.
Deployment of the airbag is controlled by a sensor system, which consists of accelerometers. Gyroscopes may also be part of the sensor package to detect rollover conditions. The sensors send a signal to the deployment mechanism only if a set of conditions are met, including acceleration pulse and pulse duration. These same sensors also control seatbelt pretensioners. The sensors can detect the direction of impact, so front airbags will generally not deploy during side impacts.
The deployment mechanism for the airbag is initiated by the ignition of a pyrotechnic charge. When the sensor system detects an impact, the automobile's microprocessor will send a voltage pulse to the ignition mechanism. The heat of the voltage pulse ignites the pyrotechnic material. The burning propellant generates an inert gas that rapidly fills the airbag.
Airbag Function During a Collision
An automobile collision is a very short event, so airbags have to deploy within a very small time window in order to be effective:
- Time = 0. Automobile makes initial contact with other object.
- Time = 30 ms. Microprocessor decides to deploy airbags. Signal is sent to deployment mechanism.
- Time = 32 ms. Pyrotechnic device ignites, and gas enters airbag
- Time = 60 ms. Airbag is fully inflated
Airbags use a combination of precise design and sensitive components to provide a mechanism to reduce injuries and fatalities in automobile accidents.
Sources
National Highway Traffic and Safety Administration website
eNotes website
United States Patent 5806888
