I keep finding articles about Air Bags and how they did or didn’t deploy correctly, and allot of what people are calling defective isn’t at all true. What I hope to do here is help concerned consumers understand the basics on how an automotive Air Bag works in general. This should alleviate some peoples concerns that their air bag didn’t deploy correctly, or why it didn’t deploy at all.
Newer vehicles are being equipped with more and more air bags, like passenger side impact, and curtain style that help protect the head on side impacts. Even motorcycles are being equipped with them.
Lets go through a basic air bag system. There are 3 basic parts to the system,
1) The impact sensors.
There are usually 2 sensors located at the left and right side of the vehicle, and 1 in the Air Bag control Module, typically located in the center of the dash.
2) The air bag Control Module, this controls the air bag deployment and diagnostics of the air bag system.
3) The air bag itself, This is in the center of the steering wheel, and on the passenger side dash, in most cases.
Now in order for the air bag to deploy, 2 of the the 3 impact sensors must meet certain criteria before the control module will set the air bag off.
The impact must cause a certain amount of deceleration force. this is measured by the sensors, by a coil of metal with a contact on the end, “like a butterflies tongue if you will” as the vehicle decells during a accident, the coil will unwind, if the amount of deceleration is hard enough to uncoil 2 of the three sensors “usually one front and the one in the control module, enough where the contacts touch, the control module will set the air bag off.
Now, something you may not know, With the design of the coiled sensor, the only way to get it to uncoil enough to complete the circuit, is if the decel force is in the same direction as the coil, so it can unwind. Like the butterflies tongue, it will only unravel in one direction, forward. The same is true with the impact sensors.
With that in mind, understand that the impact must decelerate the Veh at a pre designed rate, and it must be from the front! If you are hit from the side or rear, the coil will not be able to uncoil “in most cases” and therefore will not complete the circuit necessary to deploy the air bag, still with me ;o)
O.K. lets explain the pre designed deceleration rate that is made into that coil style impact sensor. If you hit something with the front of your vehicle and the airbag didn’t go off, it may be due to the deceleration rate wasn’t high enough, In other words the Veh didn’t slow down fast enough for the coiled sensor to unravel for enough to complete the circuit. This is for your safety!
You will be injured worse if the air bag went off when you hit something going slow.
How to explain this? Hmmmm…. Lets see, your air bag is filled with a solid propellant that when ignited creates a gas that fills the bag in a blink of an eye! “roughly 1/10th of a second”.
I believe that the propellant is the same stuff used in some rockets.
now if your air bag where to go off and you where not moving toward it at a high rate of speed “the forward momentum created during a frontal impact”. BAM! OUCH man thats going to leave a mark! You will get hurt.
This is the reason behind the designed deceleration rate at witch the contact sensor will unravel for enough to complete the circuit. Its a balance between 2 evils, how fast your traveling forward to how fast the air bag deploys. At a certain rate the two “you and the air bag” will actually help prevent injuries from being worse, I mean, a face plant when your body is traveling at 55 mph+ into that hard steering wheel and/or windshield, or a air bag full of expanding gasses, I’ll take the latter of the two.
There is a newer style air bag, its called second generation, what its technoligy brings is this..
The air bag inflation rate is more controlled, therefore it more likely to prevent more injuries than it will cause, since in will inflate slower at slower speeds, so you get less of that punch in the face effect.
Well I hope I’ve helped some, but if your still looking for more information, May I suggest this web site HowStuffWorks This site does a good job of what I tried to do, plus it had pictures :o)