Monday, December 16th, 2013

Air Bags in Today’s Automobiles

Aside from being a song that ran wild in the sixty’s and the theme song of a famous movie starring Sidney Poitier released in 1967 of the same name. It also stands for Supplemental Inflation Restraint system. It is also called SRS, which stands for Supplemental Restraint System. But to the average Joe it is just called the “Air Bag”. In a following article we’ll talk about other “Air Bags in today’s automobiles.

  • Multiple Air Bag Patents

Surprisingly enough there were multiple patents for air bags ranging from the early 50’s in Germany, the United states and Japan, all using compressed air as the inflation product. Unfortunately it became very obvious that compressed air could not be produced or stored on the vehicle to efficiently inflate and deflate quickly enough or to be valued as a safety device.

  • First Contact with an Air Bag

In 1967 Allen K. Breed invented the ball- in- tube crash sensor which was a mechanically based system. Interestingly my first contact with an air bag was in 1968-1969. I was working for Gaylin Buick in Union N.J. while I was still in school. The body shop was a few blocks away next to Multi Chevrolet. Now I cannot remember if the vehicle we were pushing into the shop was a Buick or a Chevrolet, but the total front left corner of the vehicle was totally smashed.

  • Blow the Bag

The front left wheel was so damaged that we had to pick up the front of the vehicle with a floor jack and we all got behind the car and pushed while someone “steered” with the floor jack. Apparently we were pushing too fast or the guy in charge of steering was not quick enough, but we did in fact hit the side of the building with the front right fender and KABOOM the air bag that we didn’t know was in the vehicle went off. Needless to say all the estimates had to be redone and with the amount of damage done to the left side and it didn’t “blow the bag” left us as non- believers in this new system.

  • Ball-in-Tube Sensor

The beauty of the ball-in-tube sensor was the simplicity and pure physics used in its design. As every physics buff knows that a body at rest tends to stay at rest, and body in motion tends to stay in motion.

Simply explained, a steel ball was held by an electromagnet and when the sensor was jarred hard enough the ball would break loose and touch a pair of contacts and“blow the bag”. Now these bags were not being inflated with compressed air but with Sodium Azide, which was the precursor to rocket fuel.

  • Accidental Air Bag Inflation

This was all very rudimentary and the biggest fear was accidental inflation so there were a number of redundant safety measures installed to prevent just that. So just to make this very simple I am going to walk you through a “Crash”.

  • Upon Impact

Just as you were driving down a dark and deserted road, that “TREE” ran right out in front of you forcing you to hit it. (It’s a proven fact that there are a tribe of rogue trees that live to do this). Upon impact the front crash sensors deploy and they yell out to the Air bag control unit, “we’ve crashed! deploy, deploy”.

  • Air Bag Control Unit

Now the Air bag control unit, which we will now refer to as the ACU, is far wiser and less apt to make a decision on impulse. The first thing it does is to see if the manifold vacuum is at its highest point and if the accelerator has been released and the brake pedal depressed.

It looks for a rapid deceleration and checks the wheel speed sensors and the ABS control module for activity such as skidding or lock up. Then and only then, it communicates with the ECM, the mother of all modules and reports “We seem to have collided with something should I deploy the air bag? The ECM will look at the criteria and then give its permission to deploy.

  • The Firing Mechanism

At that point the ACU will talk to the firing mechanism in the steering column and tell it to fire. Now the airbag will explode through the horn pad at about 400 miles per hour and break your wrists or forearms if they were not in the 10 o’clock and 2 o’ clock position, smack you in the face and push you back away from the steering column and back into the seat as it is quickly deflating and spewing this talc like dust all over everything.

  • Whole Passenger Air Bags

This whole process from, or as we like to name it as an event, start to finish would have taken about 500 mili seconds. YES the whole event takes less than half of a second, and that is phenomenal. Is there any reason why the major manufacturers are now enveloping the whole passenger compartments air side bag, top bags seat belt bags etc? The sad truth is that air bags are passive restraints and they fire without your knowledge and or permission.

The only active restraint system is the seat belt which the nut behind the wheel must put on, yet many do not. Just one more instance of which the manufacturer tells us, the consumer that we are not smart enough to drive our own vehicles and the vehicles should drive us.

Let’s Fill The Trolley!

P.S: Remember those that are less fortunate than us and drop off a new unwrapped toy at the shop for the Marine Corps Toys For Tots campaign. I vowed to fill the trolley again this year, please don’t let me down!!


Gregg’s Automotive Maintenance & Repair Center

236 S. Tamiami Tr.
Punta Gorda, Fl. 33950
Auto Repair, A/C Repair, Oil Change, Brake Repair & Transmission Services