I worked in the airbag industry for years and was in charge of laser fabric cutting equipment as well as brining in the sewing and module assembly equipment for the late 90s Dodge trucks and other Chrysler vehicles.
the inflators use a small amount of rocket fuel that heats a cylinder of compressed inert gas. This inert gas expands rapidly and a disc is ruptured filling the bag. This minimizes the amount of explosive used in the inflator.
The inflation rate and amount is determined by measuring the impact impulse produced by the cars. Small cars like the Suzuki Samurai at the time had large impulses and required fast, aggressive inflators while the big dodge trucks were softer.
We had to track every part with bar codes, every nut and every rivet and rivet head. Rivets and heads were counted electronically. One time we came up short on one rivet and unloaded and scanned and disassembled an entire truckload to finally find the one rivet folded up in a bag.
The standing dark joke at our company was a riddle "Know what they call a missing rivet on an air bag?" Answer: " A bullet through the head".
We manufactured what I called "pillowcases inflated by hand grenades"
Video of rivets tearing through crash dummies' heads' was always enlightening.
It is amazing the amount of technology packed into today's cars. While I'm in favor of protecting lives, I don't believe that it's the government's job to enforce what safety devices an automobile must have. I for one would be more than happy to wear a 5-point racing harness instead of a typical shoulder/lap belt with all the airbags. If it's good for race cars to use a 5-point harness, why not for road use at much slower speeds? I would even be wiling to wear an open face helmet which attaches to the seat to protect my neck in case of an accident. The cost of all the airbags is astronomical (as added to the cost of the car purchase price), the added weight to the car robs fuel efficiency and cabin/cargo space, the increased system complexity affects reliably and service costs, malfunctioning airbag can cause injuries, and there is no guarantee that all systems are functioning properly each time I get in the car. US is supposed to be a free country where people can make their own decisions, not shoved something down the throats. Give the car makers freedom to build what the consumers want. I for one, want a small, light, simple, fuel efficient enclosed trike for commuting with a racing harness, not a 3 ton SUV with thousands of dollars in airbags, rear view cameras, proximity sensors, lane keeping sensors, ABS, traction control, tire pressure sensors, and countless other needless gadgets that make cars prohibitively expensive.
I've never been in an accident where airbags have deployed, but I have seen them in salvage yards after deployment, and in the classroom in their undeployed state.
In 1989, I took a GM training course on SIRs (Supplemental Inflatable Restraints). I learned a lot, and at that time, GM was using solid rocket fuel contained in a wafer-shaped disc about 3" in diameter and 1/2" thick for the driver's airbag in the steering wheel.
Several asked the instructor if one could be deployed, but we were denied repeatedly. Apparently the sound and mess was not something they wanted inside the classroom or training center, which was understandable. They did show us some videos, however...
I wonder what type of fuel is in the airbags of today.
A friend of mine who rebuilds automobiles said they are about $500 a bag to replace and they are dealer only part. The control module for these, usually under driver seat has to be reset by the dealership on genises system if bags where deployed.
Bags are inflated with a chemical reaction. My understanding is that compressed air was too slow.
Al: There is a lot of effort to move some of the crash testing to simulation as opposed to physical crash tests. Not that physical crash testing will be wholly eliminated. But it is expensive and it does wreck a car every time you do it. The idea is to use simulation to do repeated testing during the design optimization stage when evolving the air bag design and positioning, the crumple zone, etc. Once the design is optimized and tested in the virtual world of simulation, traditional physical testing is then employed to validate the design and do final safety evaluation.
As part of the move to enable virtual crash tests, there is also work underway to create virtualized crash test dummies, in all shapes and sizes and to accommodate different ethnicities. With more valid human crash test dummy models, you can do more valid crash testing.
Ann: I don't know the answer about small versus big cars, and whether the size of the crumple zone is generally taken into account when figuring out how many airbags to deploy. I can point to one isolated case, however. The GMC Acadia does not have kneebags because the large crumple zone in the front absorbs sufficient crash energy without the use of a kneebag. Regarding whether new structural materials are less crash-resistant: Most of the new structures are actually better, as I understand it. Big vehicles in the old days had more volume in front to absorb the energy, but they weren't designed for optimization of structural loads. Vehicle structures today absorb more energy. Finite element analysis, and understanding of load paths, has played a big role in the creating structures that absorb crash energy more effectively.
I can't give exact statistics on the effect of airbags in small cars, Alex, but I can take a stab at how airbags compare with other safety systems. In the early days of airbags, it was said that three-point seat belts would prevent about about 42% of fatalities and the use of airbags would bump that figure up to 47% (at the time, that would have come to about 2,000 fatalities per year prevented by airbags). More recent studies based on vehicles with multiple types of airbags have set the airbag number at 3,000 per year, which is still well below seat belts. By way of comparison, electronic stability control is estimated to cut the annual number of fatalities by 10,000 per year (based on a NHTSA study of vehicle crashes in Florida, Illinois, Maryland, Missouri and Utah between 1997 and 2003). And NHTSA predicts that vehicle-to-vehicle communications will save more about 24,000 per year. The bottom line is, airbags probably save fewer lives than the public expects.
Two reasons for the odd shape, Beth: First, it's not a full frontal bag and therefore doesn't need to catch the full width of a person. It's really just there for head protection, so it has to be tall. Second, it has to pop out of a seam in the seat, so it has to be skinny.
Good question about the size and shapes of the various bags, Beth. I would guess there is some size and bulk determination based on providing protection while still allowing emergency personnel to get to the person from the side. The ability to exit after a crash has to be a major consideration is slimming down the size for side bags.
Wow, that's an amazing amount of airbag types. Like Beth, I've never had a reason to seen an airbag operate so I don't know what they look like either. I think Alex's question is interesting. I'd guess that the number of airbags have increased at least because cars have gotten smaller, and also that they may have increased as more plastics and lighter metals are incorporated in car designs. Those lighter materials are, AFAIK, crash-optimized, but I wonder if there have been any tradeoffs: are they less crash-resistant psi than the metals they replace and are more airbags deployed as a result?
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This year, Design News is getting a head start on the Fourth of July celebration. In honor of our country and its legacy of engineering innovation -- in all of its forms -- we are taking you on an alphabetical tour through all 50 states to showcase interesting engineering breakthroughs and historically significant events.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.