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.
The invention of Airbag
The airbag specified for automobile use traces its origins to air-filled bladders as early as 1941.
The invention is also credited independently to the German engineer Walter Linderer, and to the American John W. Hetrick who in 1951 registered for the first of his airbag patents. Linderer filed German patent #896,312 on 6 October 1951, which was issued on 12 November 1953, approximately three months after American John Hetrick was issued United States patent #2,649,311 on 18 August 1953. Linderer’s airbag was based on a compressed air system, either released by bumper contact or by the driver. Later research during the 1960s showed that compressed air could not inflate Linderer’s airbag fast enough for maximum safety, thus making it an impractical system.
Hetrick was an industrial engineer and member of the United States Navy. His airbag was designed based on his experiences with compressed air from torpedoes during his service in the Navy, combined with a desire to provide protection for his family in their automobile during accidents. Hetrick worked with the major American automobile corporations at the time, but they chose not to invest in it. Although airbags are now required in every automobile sold in the United States, Hetrick’s 1951 patent filing serves as an example of a “valuable” invention with little economic value to its inventor because its first commercial use did not occur until after the patent expired when in 1971, it was installed as an experiment in a few Ford cars.
In Japan, Yasuzaburou Kobori started developing an airbag “safety net” system in 1964, for which he was later awarded patents in 14 countries. He died in 1975 without seeing widespread adoption of airbag systems.
Safety airbags are commonly referred to as Supplemental Restraint Systems (SRS). When vehicle SRS airbags were first introduced, they were used primarily for frontal crashes. In many modern vehicles, they are used for frontal and side impacts as well as rollovers.
An automobile airbag system is made of three general components:
- The airbag itself, (Air bag module)
- A sensor system (Crash sensors), and
- A deployment mechanism (Electronic control unit).
Crash sensors measure vehicle movement when an impact occurs. As an example, with a side impact the sensors determine the actual movement of the vehicle from the side. Once the sensor detects rapid movement of an impact, it sends a signal to the electronic control unit (ECU). The ECU then decides if the airbag(s) should be deployed. The ECU may also perform other electronic vehicle functions.
Once the ECU determines an impact, it activates the appropriate air bag module(s). The module contains the inflators and the actual airbags. The inflators fill the actual air bag with gases to create a soft cushion barrier between the vehicle occupants and injury causing vehicle components. The air bag modules usually have a cover that matches the interior color and is identified with “SRS” or “Airbag.”
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.
Safety airbags in automobiles have been saving lives since they were first introduced, but how do they work and what is the proper usage of SRS airbags? According to the National Highway Traffic Safety Administration or NHTSA, “Frontal airbags have saved 25,782 lives between 1987 and 2008.” However, there are some things that a car owner should know to help minimize injury to the driver and vehicle passengers.
Safety Tips for Proper Air Bag Usage
Most cars and trucks that are equipped with an SRS have a warning light in the dashboard. The light is normally amber in color and either has the words “air bag” on its face or an identifying symbol. If the light is illuminated or flashing there’s a good chance the SRS is not working and the air bags may not deploy upon impact.
Air bags are not a substitute for seat belts. Seat belts are considered the primary restraint system for vehicle safety; air bags are considered a supplemental system. The SRS for a vehicle are designed to work in conjunction with the safety restraints (seat belts). All occupants of a vehicle should always use safety restraints for maximum protection from a collision.
The placement of child passengers needs special consideration when it comes to airbags. The deployment of an airbag can cause serious injury to smaller children. As a general rule of thumb, the back seat of a passenger car (preferably in the middle of a rear seat) is the safest place for a child. There are also special considerations for the placement of child car seats as it pertains to an airbag system.
For cars and trucks without rear seating, place a child under the age of 12 in the front seat only if the vehicle is equipped with an air bag on/off switch. Ensure that the switch is in the off position when placing the child in the front seat. Always be cognizant to the position of the airbag on/off switch when passengers and children are riding in the vehicle.