Airbags not work without seat belt?

[CHCRandy]

I was just driving down the road earlier and car starts beeping and flashing warning me that seat belt wasn't hooked up and no air bags or something like that. I never wear seat belts but I am usually in my F250....and it beeps then shuts up, as did this car, but the warning light caught my attention and got me to thinking about airbags deploying. I remember once in my truck when plowing snow I hit an object in a parking lot...we hit hard enough that it shoved the plow thru the bumper busting my AC/Radiator, broke my plow off my truck and threw the wife into the windshield giving her a concussion....but no airbags deployed.

What makes an airbag activate? Do you have to have seat belt hooked up for them to go off? Do you have to be hitting brakes? Any of you guys have any ideas or experiences with em?

 

[Bennettjh]

There are usually sensors on the radiator support that have to get smashed to ground out then it'll deploy the bags. I work in a body shop so I've had to tangle with those little devils. Has to hit just right.

 

[M67]

I thought there were sensors under the seat too that measured the g force.

But I don't know for sure. The 1 time I had air bags deploy...it was called for

 

[Nojoy621]

Most pickup trucks have a switch for passenger airbags to turn them off, that could have been the cause.

 

[yeti rider]

What Bennettjh said. I have worked in a body shop and now own one after 25 years. I still sometimes think there is no rhyme or reason. You'll see some cars with them deployed and wonder why they came out, and then the next one will be smashed to hell and you'd think they should have deployed. We had a General Motors product where the passenger bag deployed and the driver one did not. The car had never been in an accident prior to this particular one. GM sent an engineer to check that situation out. I think the owner of that particular car got a little extra cash and a totaled car that was otherwise repairable. The car has to have very specific parameters that the computer measures before they will deploy.

 

[hoosierdoc]

Our passenger seat has a scale in it. If you're over a certain weight it turns on the airbag and flashes the "seatbelt not engaged" warning for a bit. My son figured out if I'm leaning my arm on the seat he can activate it by putting his feet hard into that back.

If I am transporting something heavy in passenger side it beeps and tells me to buckle up

if you don't need the airbag you don't want the airbag. Breaks thumbs, wrists, noses. But saves lives.

look at the acceleration (deceleration) formula. You wAnt to slow down over a distance. If your deceleration distance (time) is how far your face sinks in when you hit something that exponentially increases the force compared to slowing down over the distance of an airbag.

or slowing down over the time the car crumples if you're belted in instead of hitting the dash

 

[churchmouse]

I was told these were G-Force meters that deployed the bags.

 

[CHCRandy]

Doc may be onto something...when I drove by myself, I don't remember that beeping. There must be some type of weight sensor in the seat to let it know whether the passenger needs to buckle up or not. These cars now days are something else..........almost too many gadgets.

I really should start wearing a seat belt....I can see how they can save a guys life!

 

[phylodog]

If I sit my backpack on the passenger's seat in the Taurus the passenger air bag light comes on. I believe most modern vehicle have this feature to prevent infants in car seats from being launched out the back window in an accident (or something to that effect).

 

[thunderchicken]

Most modern vehicles (especially with side curtain air bags) have seat pressure sensors in the passenger seat. The seatbelt pretensioner is also wired into the air bag system. In the event of a crash a small pyrotechnic ignites and causes the seatbelt to instantly lock the shoulder harness in place. If the air bag warning light is on the air bags aren't supposed to deploy.

 

[thunderchicken]

If I sit my backpack on the passenger's seat in the Taurus the passenger air bag light comes on. I believe most modern vehicle have this feature to prevent infants in car seats from being launched out the back window in an accident (or something to that effect).

Thats from the seat pressure sensor. It's fun when one gets stuck. Then you have to get weights to stack in the seat to recalibrate the sensor. Hang it from the back rest or buckle the seat belt

 

[russc2542]

From memory from my auto tech classes a few yrs ago

-Back in the late 80s/early 90s, driver airbags were mandated. one out was to use automatic seatbelts (or the door mounted seat belts) which was the source of those joys.
-Early-mid 90s, passenger airbags were mandated
-Shortly thereafter, someone realized there are situations where a person might not want the passenger airbag to go off: pickups with no back seat and a child carseat. You DO NOT want the airbag to hit the carseat. hence most trucks can manually disable the passenger airbag.
-Late 90s "advanced airbags" that have a high and low setting show up because different speeds=different force
-Early 00s: more advanced airbags incorporate a passenger seat weight sensor to vary the airbag force based on passenger mass. under 100lb passenger may force the low setting or no airbag at all.
-Late 00s: side curtains and side impact airbags commonplace. driver seat weight sensors too to vary driver airbag power.

I'm not aware of any mfr disabling the airbags if the seatbelts are unbuckled but not exactly something I've looked for.

The oft-quoted number is hitting a solid object, squarely, above 15-20 mph. obviously there are a LOT of variables involved and driving into a brick wall at 20mph doesn't simulate most accidents: what if you're at an angle, an offset, what if the object is smaller (like a sign post) and impacts the bumper a foot from the sensor, what about offset impacts, rear impacts, above/below the bumper... the idea of airbags is to improve the situation in at least some circumstances without the detriment in other circumstances tipping the balance. As such there are a lot of compromises and some times when it isn't ideal but what in a car is perfect in all situations?

As for how they're mounted...it varies. Different ways have been tried and different manufacturers prefer different methods. ALL will have sensors somewhere around the perimeter (quantity and locations depend on newness), GM I know liked mounting an additional sensor under the center console with the controller. others skipped the central sensor and could mount the control unit almost anywhere (usually under the dash or seats though). Legal mandates specify the end result and certain criteria along the way. It leave the engineering to the car companies.

Things like plows and bull-bars really jack up airbag deployment. The airbag sensors (early versions were a weight that had to move a certain distance, like a ball bearing stuck to a magnet: hit it soft and it stays stuck, hit it hard enough and it'll fall. newer models use solid-state accelerometers) are mounted on the bumper support while plows and bullbars are mounted to the frame for strength. If you hit something with one mounted, you have to collapse it and/or the frame before the bumper contacts something and the airbag sensor sees enough acceleration, meanwhile the truck and it's contents have been decelerating a while, by the time the sensor hits a solid object or is jostled, much of the acceleration/deceleration is done.

Without a plow or bar, the sensors mounted to the bumper would (ideally) be the FIRST thing to contact an object and would trigger the airbags to go off before the crumple zones have begun to come into play. With the plow or bar, the sensors are about the LAST thing to contact an object and if they trigger the airbag, it'll be far far too late, (and this part is conjecture) possibly even dangerously so if the occupants have already moved forward into the deployment path (people are supposed to hit the inflated airbag, airbag hitting people while inflating is BAD)



Other mandated tidbits:
mid 90s? any car sold with run-flat tires must have TPMS.
04: 30% of passenger cars/light trucks must be sold w/ TPMS
06: 60%
08: 100%

'16 or '17: all passenger cars/light trucks must have stability control. In order to meet this they basically have to have 4-channel ABS and throttle-by-wite. Yay.

 

[BugI02]

A little dry, perhaps, but maybe worth the read/skim

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256779/

Evaluation of Advanced Air Bag Deployment Algorithm Performance using Event Data Recorders

 

[DoggyDaddy]

Doc may be onto something...when I drove by myself, I don't remember that beeping. There must be some type of weight sensor in the seat to let it know whether the passenger needs to buckle up or not. These cars now days are something else..........almost too many gadgets.

I really should start wearing a seat belt....I can see how they can save a guys life!

You really should. As a survivor of two head-on collisions (both back in the pre-airbag days), I can say without a doubt that I would have been seriously injured in both cases without the belt. In the second one, I was injured but the injury was to my right foot (saw the truck coming into my lane and had my foot on the brake). In both cases the car was totaled. In the first one ('73 Plymouth Satellite Sebring), I came out without a scratch. Actually that car was what got me in the habit of using the belt (lap belt only back then I believe), because unlike modern cars, that little "warning bell" wouldn't stop going off until you fastened the belt.

 

[BugI02]

Having done a fair amount of racing (SCCA) I would have worn belts even w/o it being in the rules. When you're on a road course they're essential to keeping you in position and the vehicle under control under lateral Gs. Since I drive ... spiritedly ... wearing the belts just naturally carried over. They provide the same advantage on the street

 

[bwframe]

...I really should start wearing a seat belt....I can see how they can save a guys life!

Does your wife wear hers, after nearly going through the windshield?

 

[churchmouse]

Does your wife wear hers, after nearly going through the windshield?

Good question.
Being a racer from a very young age I have always worn mine if the car was so equipped. It keeps my butt square behind the wheel in adverse situations. It keeps my face away from the windshield. I have tested this theory before and it does work.

I used to tell people to buckle up when they got in the car with me. The way I drove pushed a few to do so out of survival instincts. My younger brother refused to do so. I picked him up from school one day (he was a junior I believe) and rolling home a car failed to yield and I had to evade. In this we hit a light pole. The car bounced off but my brother went straight into the windshield. His glasses were transformed into contacts and his nose was reshaped. He bled all over the interior.
Seriously "P"d me off as all of that injury could have/would have been avoided. Plus all the blood.

After that incident no one was allowed to ride unless they buckled up. More than one ended up walking. This rule is still in effect.

 

[PGRChaplain]

The Bags on a late model Ford Taurus do. Last Saturday a young lady hit a Utility Ploe in my Neighbors front yard. She put the Pole right behind the driver side front tire. Windshield had the tell tale Shatter at the top right above the steering wheel. Front Air Bags Deployed, may have pushed her upward during the sudden stop. No Indication she tried to Break before Impact. Broke the Pole and its only a couple years old.

 

[WanderingSol07]

Seat belts should lock due to a mechanism that is based on speed of seatbelt movement. Try this, pull on the seatbelt really fast, it should lock into place.

Read an article from GM several years ago, if they could they would rather assume everyone is always seatbelted in, this way they could tailor the inside trim and airbag deployment to be better/safer for all. But because they cannot rely on the occupant using the seatbelt we have more aggressive airbags and wasted space to allow it to deploy.

 

[CHCRandy]

Does your wife wear hers, after nearly going through the windshield?

She wears hers most of the time but not always. She usually has it on when I am plowing, pulling a trailer, bad weather, etc.....but we never put them on to just cruise down the road. I need to try changing my habits on that, but I am just so use to not wearing it.