How Does Your Car's Airbag System Work

November 13, 2013

Learn about the inflator and crash sensors that form the key components of an airbag system; also answers to frequently asked questions about airbags.

Airbag System In Action

The airbag system is one of the most important parts of your vehicle's safety components. Proper airbag deployment can ensure that you and your passengers survive a crash that you may have otherwise experienced serious injury or death as a result of. Airbag deployment has saved thousands of lives through the years. But how exactly do they work? The airbag system is extremely complex and needs to activate within milliseconds after a crash occurs to ensure the protection of the driver and passengers.

What Are Airbags?
Airbags are stretchable fabrics or other materials that are tightly packed in various locations throughout your vehicle. There are airbags at the front of the dashboard in most cars, and many vehicles have airbags along the side of the car as well. These bags are compressed and kept in a small area. When there is an accident, the airbags fill up with air very quickly to provide a cushioning system for the people in the car so that they are not thrown around in the event of a crash. While this does not necessarily prevent total injury or death, it can be very helpful in cushioning the passengers in a car in many cases.

Crash Sensors
The most important parts of the success of the airbag system are the crash sensors. These small pieces of electronics are designed to tell when the vehicle has been damaged in an accident. They respond to several different sets of stimuli, including sudden stopping, increased pressure as pieces of the car are moved due to the force of the collision, and more.

Different types of sensors measuring wheel speed, seat occupant status, brake pressure and impact, and other vehicle status indicators are monitored by the airbag control unit located in the front portion of the cabin. The sensors relay signals to the airbag control unit, which analyzes the data and can orchestrate safety features like seat belt lock, automatic door locks, as well as airbag deployment.

Two types of airbag sensors used in cars are electrical and mechanical. Electrical sensors vary in design. Some use an electromechanical "ball and tube" mechanism, which basically consists of a small tube containing a circuit switch and ball that's held together by a small magnet. If a collision occurs, the ball is dislodged from the magnet and rolls forward in the tube, hitting a switch that completes the electrical circuit. Other electrical designs are similar in principle, using a metal roller or spring loaded weight instead of a ball, or in newer cars, an accelerometer to trip the sensor. Mechanical sensors work independent of the electrical system and respond similarly to the electrical sensors, with a design that actuates a firing pin triggering a small explosion after a crash. Since a mechanical sensor does not require a power source, it cannot be deactivated like an electrical sensor can when the battery is disconnected.

The success of the airbag system relies upon the crash sensors working not only accurately but also extremely quickly, so the most expensive and technologically advanced part of the airbag system are here.

Once the control unit determines there is an accident, it sends a signal to the inflator system. The inflator sets off a chemical charge, producing an explosion of nitrogen gas, filling up the airbag. As the airbag fills up, it bursts through the paneling that contains it and enters into the space of the car in order to protect you.

This all happens in an instant, usually within 25 or 50 milliseconds. That translates to almost 200 miles per hour. The airbag then will deflate itself on its own once it deploys.

Related Questions and Answers

How Fast Does an Airbag Deploy?

An airbag can deploy in about 55 milliseconds, according to engineering study. This is about the same amount of time it takes you to blink your eyes or sneeze. In other words, airbag deployment is very quick. Authorities have noted that if you are out of position when an airbag deploys, you can be injured. How can you get out of position? Airbags should be used in conjunction with seatbelts, and if you drive without your seatbelt fastened, then it is possible for the airbag to fire, and for you to slide under the airbag just far enough so that you can receive a nasty blow to the face or head.

Which Airbag Sensors are Better, Electrical or Mechanical?

The jury is still out on the best airbag sensors system. For example, Toyota and Jaguar use electromechanical airbag igniters in which a small switch senses a crash force. If it is great enough, an igniter pin drives into the sodium azide packets used to inflate airbags. Other automakers use small tubes that break over a certain pressure, freeing a gold ball that completes the circuit, igniting the airbag. A third type--piezoelectric sensors--are used by several automakers. These electrical systems rely on switches located outside and inside the vehicle. If the sensors agree that there is enough force, then the airbag inflates.

How Much Does an Airbag Cost?

A common question asked is, 'How much does an airbag cost?'. If you need to replace or repair an airbag in your vehicle, the cost will vary depending on the type of car you are driving, as well as which airbag needs to be replaced. In most cases, budget between $400-800 for a driver's side airbag. A passenger side airbag can cost up to $1,000. Curtain airbags tend to be a bit cheaper, but are still fairly expensive. Replacing an airbag is a complicated repair, and it must be done by a professional. The labor costs are what makes up the majority of the bill when it comes to replacing an airbag.

How Do I Know If My Car Has Faulty Airbags?

If your vehicle has an airbag light, and it is lit up, this could indicate faulty airbags or a problem with the airbag system. If the vehicle does not have an airbag indicator light there is no real way of knowing if the vehicle has a faulty airbag. If the airbag light comes on, it is best to have the vehicle checked out by a professional. Airbags and the sensors that monitor them are complicated and must be repaired by a professional. This light comes on if the system senses a fault or problem with the airbag system. As the airbag system may save your life, it is best to get it checked out as soon as possible.

Where Can I Buy Used Airbags for Sale?

There are a number of places that have used airbags for sale. Used airbags are much cheaper than brand new ones, and if they have never been deployed, they are just as safe as new ones. Used airbags are removed from dead vehicles. Airbags can be salvaged and refurbished if necessary. It is best to check with your insurance company before having used airbags put in. There are policies that void coverage if used airbags are installed. Check with local junkyards and part recyclers. Doing a Google search for used airbags brings up a number of listings. Airbag Center is one of the leading providers of used and new airbags.

What is the Speed of an Airbag Deployment?

The speed of an airbag deployment will vary depending on the vehicle and the seriousness of the accident. In most cases, the airbag will come out at a speed of between 100 to 220 miles per hour. At this speed, an airbag can cause significant damage to a person, so it is important to be at least 10 inches away from the airbag when it deploys. This is why wearing a seatbelt is extremely important. Even when driving a car equipped with airbags. There have been cases of children being killed by a deploying airbag, so it is vital that the airbag be turned off if a child is in the front seat.

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