کیسه های هوا در اتومبیل ها - Air Bags
Air Bag
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INTRODUCTION |
Air Bag, safety device consisting of a large fabric bag that fills with air and provides protection for the head and upper body of an occupant of a motor vehicle during a collision. In head-on collisions, drivers and passengers are thrown forward inside the vehicles. When an air bag is activated, or deployed, it inflates instantly and creates a firm barrier that counters the forward motion of the driver or the front-seat passenger. Air bags are designed to prevent the driver or front-seat passenger from hitting the windshield or dashboard of the vehicle, thereby eliminating injuries or reducing their severity. An air bag is also known as a supplemental restraint system (SRS), or a supplemental inflatable restraint (SIR). Air bags are designed to work in conjunction with seat belts. However, an air bag alone can provide some protection for a vehicle occupant who is not wearing a seat belt. See also Automobile: Safety Features.
In 2002 over 60 percent of all vehicles in the United States were equipped with drivers air bags. The National Highway Traffic and Safety Administration (NHTSA) estimated that by 2002 air bags had saved the lives of over 9,000 people in the United States.
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HOW AN AIR BAG WORKS |
There are several types of air bags. A driver-side air bag is stored inside the steering wheel. It inflates during a frontal collision to prevent the driver from hitting the steering wheel or steering column. A passenger-side air bag is stored inside the instrument panel or dashboard. It inflates during a frontal collision to prevent the front-seat passenger from hitting the windshield. The passenger-side air bag is larger than the driver-side air bag and has a different shape. Some vehicles also have side-impact air bags inside the doors, arm rests, front seats, or rear seats. Side-impact air bags inflate during a side collision. A recent design is a head-restraint system that deploys an air bag from above the side window for added protection in side collisions. Air bags are not designed to inflate or to protect passengers in rear-end collisions or rollovers.
Air bags are made of a nylon or polyester fabric coated with neoprene (a synthetic rubber). Depending on its type, an air bag is folded up inside an assembly located under the steering-wheel cover, inside the instrument panel or dashboard, or in the side panel. The deployment of air bags is controlled by crash sensors and an electronic control module. The crash sensors are designed to detect the sudden deceleration, or slowing down, of a vehicle caused by a crash. When a crash is detected, the electronic control module energizes the air bag inflator. Within the air bag assembly is a metal container with pellets of sodium azide, a chemical that when ignited produces nitrogen gas. When signaled by the sensors, the control module heats a wire that ignites the pellets. A large amount of nitrogen gas is quickly produced and rushes into the bag, causing it to inflate. Deployment occurs extremely fast (in 20 to 35 milliseconds) and with explosive force. The air bag bursts outward at speeds of up to 320 km/h (200 mph) to block the forward motion of the vehicle occupants.
After the air bag is deployed, the nitrogen gas inside the bag is vented through small holes in the back of the bag, allowing the bag to collapse within a few seconds. Talcum powder or cornstarch is typically packed with the air bag to act as a lubricant so that the folded bag doesn’t stick together. A small amount of smoke is created when the nitrogen gas is produced, and the smoke sometimes enters the passenger compartment during deployment. The smoke and the talcum often leave a harmless white coating on the interior of the vehicle.
Air bags that have been deployed as a result of an accident must be replaced when collision repairs are made. Air bag replacement costs range from $400 to over $1,000. Some vehicles also require a new control module and new crash sensors.
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HISTORY |
Safety devices that work automatically in motor vehicles, such as air bags and seat belts that automatically wrap around a passenger, are known as passive restraint systems. Passive restraint systems are required on all new cars sold in the United States. The first air bags were installed on the driver side only. In 1993 passenger-side air bags were introduced. Beginning with 1998 model cars, both types of air bags have been required in new cars sold in the United States. Starting with the 1999 models, all new light trucks and vans also must have dual air bags.
The first air bag was patented in 1953 by American engineer John W. Hetrick. It used compressed air for inflation. The aerospace firm Martin Marietta (now Lockheed Martin Corporation) conducted air bag experiments in the early 1960s to develop a system for protecting pilots and space-capsule passengers from injury, but the system was never produced. In the early 1970s, Ford Motor Company and Eaton Corporation jointly developed an automotive air bag system that also never made it into production. A federal law requiring automobile makers to install passive restraints prompted General Motors Corporation (GM) to introduce the first air bags in 1973. However, these air bags were offered only in 1,000 Chevrolet Impalas. In 1974 GM offered air bags as a $225 option on all its full-size cars, but only about 10,000 units were sold over the next three years. Air bags were discontinued and not offered again as a production option until Mercedes-Benz did so in 1984. Two years later, Mercedes made air bags standard equipment on all U.S. models.
When the federal government began making air bags mandatory in the 1990s, U.S. manufacturers were required to provide air bags that are capable of protecting a full-sized adult weighing 70 kg (160lb) and not wearing a seat belt in a collision at 56 km/h (35 mph). The force with which an air bag deploys has proven deadly to children or small adults in some circumstances, however. Over 80 accidental deaths have been attributed to air bag deployments in relatively minor, low-speed accidents. For this reason, children aged 12 and under, as well as rear-facing infant car seats, should not be allowed in the front seat of a vehicle equipped with an air bag on the passenger side. Adults under 165 cm (65 in) in height who are driving should maintain a minimum distance of 25 to 30 cm (10 to 12 in) between themselves and the steering wheel.
In 1998 second-generation, or depowered, air bags, which deploy with less force, were introduced to minimize the risk of injury during low-speed collisions. Federal law now also permits the installation of a switch for deactivating front air bags when a child or small adult must occupy the front seat.
Contributed By:
Larry W. Carley
