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Old 30th May 2013, 08:13   #76
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by supertinu View Post
Yea based on my experience i feel that the system should be smart enough to understand this.
Any control system has to be made smart, this is done by calibration. The input to it is merely the test cases. The limitation of the test set is " have we considered all the real world cases ". No matter having more than 3000 different abuse sets, we can not cover the real world. It is simply too vast.

But these situations only make the next iteration better.
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Old 30th May 2013, 10:38   #77
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by Tejas Ingle View Post

No, there is no minimum threshold speed for deployment.
Consider a scenario where your car is air-borne before it crashes. Your foot will naturally be on the brakes. So the car is sensing the speed is 0kmph since the wheels aren't rotating. But you will need the air-bags when the car lands, right?
Yes, I was wrong
The speed is only recorded as an input to record in the EDR. Deceleration is the parameter which has thresholds set.

Thanks for clarifying many things.
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Old 30th May 2013, 12:29   #78
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by akshay4587 View Post
Wont the mechanical lock activate when the belt is pulled out to its full length?
What i experience is a push back to the seat and the belt tightens around me,not allowing me to move freely on the seat,i guess that is pre tensioner at work and not a Mechanical lock.
No there the mechanical lock that is being spoken about here is not the one the happens when you pull the belt out completely. It is the one that engages when you the belt is jerked.

Try this experiment in your car. Sit on any seat which has a seat belt and pull the seat belt like how you do when you want to wear it. The belt rolls out just fine. Now roll the belt back in and pull it out a little and then pull the belt with a sudden jerk. You will notice that the belt will lock even though it is not completely out. This is the mechanical lock the people are talking about over here. This lock is called an inertia lock.

Last edited by vikram_d : 30th May 2013 at 12:32.
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Old 30th May 2013, 13:52   #79
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by Jeroen View Post

You really should not underestimate the forces on your body even in relatively low speed accidents. My sister T-boned another car, doing about 25 km/h, in a parking lot. She was wearing her seatbelt, but her car at the time had no airbags and she ended up in intensive care. She hit her head onto the steering wheel and front window really badly.

Jeroen
Little OT, was your sister wearing seatbelt? If she was how did she end up hitting the window?
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Old 30th May 2013, 14:25   #80
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Default Re: Airbags deployed after hitting a dog. Understanding why?

Yes she was. It's a while so I can't rmember whether they were fixed seatbelts or the automatic roll up ones.

She was driving a little car, a Fiat I recall and she also sat (to) close to the steering wheel. Always told her she should adjust her seat backwards.

It was clear from her injuries that the seatbelt did really dig into her chest and ribs. Lot of bruising, but even so she still had sufficent slack and forward momentum to smack into the window.

Look at some of the crash test video's on youtube. Even with tensioner it's quite amazing how much forward movement a body will have. Your chest can take a compression of 2 inches easily, you neck/head whips forward.

Here's a sample of a Lada, no airbags, simple seatbelts. If the guy had been sitting closer to the steering wheel he might have hit the window as well.



Jeroen

Last edited by Jeroen : 30th May 2013 at 14:26.
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Old 30th May 2013, 14:31   #81
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by Tejas Ingle View Post
... The purpose of tensioner is that if the occupant has already bent forward before the crash, the conventional mechanical lock will only prevent him from going any further due to th crash, whereas the tensioner will pull the occupant back towards the seat. ...
Thanks for the ESP related information.

But, if the inertia lock is holding the person in place (not moving any further forward), what help would the tensioner provide in bringing the person back? If the driver's mouth hit the steering wheel rim, the teeth are already broken - pulling him back won't save any more? (Sorry for the gory details!). OTOH, in that state pulling the torso back will injure the neck (reverse whiplash), no?

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Originally Posted by Tejas Ingle View Post
... In the end, it says "WHAT IF?" ...
And "What If" means the video is made up?

Quote:
Originally Posted by Tejas Ingle View Post
... Wrong. Air-bag deploying at high speed would be absolutely useless. The car is still at high speed means there is not much impact that may injure the occupants. ...
Err... what kind of ad hoc logic is that?
* Both the airbag and the driver are in the same car traveling at whatever speed
* When the airbag deploys, the speed at which the head travels towards it is independent of the car's speed
* The airbag is meant to protect the head, not any other part of the body
* (I think you meant 'so much impact') If there is a collision, the crumple zones come into effect (if present)
* Despite all that if there is possibility of injury to the rest of the body, what can the airbag do?
So the airbag shouldn't be deployed? Funny!

Quote:
Originally Posted by Tejas Ingle View Post
... There would be no air in the bag when required if the driver is alarmed and blinded by the pop of the bag and hits the median in the process. ...
Didn't understand. Did you mean similar to the filling air in a (plastic / paper) bag and bursting it, scaring someone?

Quote:
Originally Posted by Tejas Ingle View Post
... And in case of such an impact the car wont be travelling at a high speed when the air-bags deploy. ...
So the airbag shouldn't deploy if you brake to a stop only to be hit by an oncoming vehicle? Common scenario in India - I asked this earlier.
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Old 30th May 2013, 15:34   #82
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Default Re: Airbags deployed after hitting a dog. Understanding why?

Thanks for the quite illuminating discussion on dependence of airbag opening on impact intensity . But I had a different question :



Quote:
Originally Posted by supertinu View Post

Next thing I know there is this huge blast or pop, my chest feel crushed and ears are ringing and the car is full of smoke.
Once i got my senses back I immediately opened the windows to release the smoke
1. Why was there smoke inside the cabin ? is it connected to hot air inside the bag?


2. Also while , but I wonder what activates the engine immobiliser? In this case, clearly it was not activated since he drove it after the incident. Also I read somewhere that after an impact the fuel supply to engine is automatically cut off . Did it not happen in this case ?

Last edited by saaicon : 30th May 2013 at 15:36.
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Old 30th May 2013, 15:55   #83
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Default Re: Airbags deployed after hitting a dog. Understanding why?

I was in a similar situation. Driving in Detroit on a cold November morning in my trusty 2003 Civic. Speed was around 30 mph (~50 kmph) when the light turned red. I touched the brakes lightly, preparing to stop but due to a patch of black ice, kept skidding on. It was an empty lane and my vehicle skid for more than 35 meters, into oncoming traffic.
I hit a Jeep Wrangler (front end smacked the passenger door/running board), and out popped the airbags. No damage on my car, not even a scratch on the wrangler. The only signs that there was an accident was the deployed airbags. There was a white powdery smoke in the cabin, and the steering wheel was warm to the touch. The car ended as a writeoff and my insurance renewal was the next biggest pop of my life.

Long story short, I am guessing its the luck of the draw for your collision sensor sensitivity/reaction. Here's another example from youtube -
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Old 30th May 2013, 16:04   #84
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Default Re: Airbags deployed after hitting a dog. Understanding why?

Quote:
Originally Posted by saaicon View Post
Thanks for the quite illuminating discussion on dependence of airbag opening on impact intensity . But I had a different question :

1. Why was there smoke inside the cabin ? is it connected to hot air inside the bag?

2. Also while , but I wonder what activates the engine immobiliser? In this case, clearly it was not activated since he drove it after the incident. Also I read somewhere that after an impact the fuel supply to engine is automatically cut off . Did it not happen in this case ?
A small explosive charge is used to rapidly inflate airbags and this miniature explosion causes the smoke.

Immobilizers are purely theft related, they do not have anything to do with accidents. They are only a deterrent for somebody from stealing a car and driving it away.
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Old 30th May 2013, 16:08   #85
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by vikram_d View Post
A small explosive charge is used to rapidly inflate airbags and this miniature explosion causes the smoke.

Immobilizers are purely theft related, they do not have anything to do with accidents. They are only a deterrent for somebody from stealing a car and driving it away.
Its not just the explosion.
But the layers of powder that are kept between the layers of the airbag that give out an illusion of smoke.

The powder is to help prevent burns.
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Old 30th May 2013, 16:11   #86
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by vikram_d View Post
A small explosive charge is used to rapidly inflate airbags and this miniature explosion causes the smoke.
Thanks Vikram. How about the question on the fuel to the engine being cut off ? Is it not a mandatory safety requirement?
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Old 30th May 2013, 16:28   #87
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by bblost View Post
The powder is to help prevent burns.
Thanks, I completely forgot about the powder.

Quote:
Originally Posted by saaicon View Post
Thanks Vikram. How about the question on the fuel to the engine being cut off ? Is it not a mandatory safety requirement?
To be completely honest I don't know under what conditions fuel cut off takes place.

I know that there is an inertia switch that cuts off fuel in some vehicles, but I don't know about the others.
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Old 30th May 2013, 16:51   #88
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by vikram_d View Post
Thanks, I completely forgot about the powder.



To be completely honest I don't know under what conditions fuel cut off takes place.

I know that there is an inertia switch that cuts off fuel in some vehicles, but I don't know about the others.
Usually, when the airbag controller unit detects a crash has happened and airbags have been fired, it immediately sends a fuel cut off signal. But, I am not sure of this is warranted by every manufacturer. In my opinion it should be.
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Old 30th May 2013, 21:49   #89
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by DerAlte View Post
Thanks for the ESP related information.

But, if the inertia lock is holding the person in place (not moving any further forward), what help would the tensioner provide in bringing the person back? If the driver's mouth hit the steering wheel rim, the teeth are already broken - pulling him back won't save any more? (Sorry for the gory details!). OTOH, in that state pulling the torso back will injure the neck (reverse whiplash), no?
The mechanical lock works when the seat-belt is pulled by a jerk like it happens in an event of a crash. If the car crashes, the jerk will cause the mechanical lock to lock the seat-belt and hold you in whatever position you already are. If you put on the seat-belt and bend forwards slowly, then the seat-belt will allow you to go and touch your forehead on the dashboard or the steering wheel. It wont lock.
So just before the crash, if you are bent forward i.e. away from the seat-back and closer to the steering wheel, the mechanical lock will only lock your torso in the position it already is; close to the steering wheel. You may also get hit by the air-bag deployment or your head may hit the wheel. But the pre-tensioner will pull you towards the seat-back, away from the steering and hold you there firmly. Same with the tensioner. The tensioner is deployed fractionally before the air-bag so that your torso is taken away from the airbag deployment range and you stay planted in your seat.
Ofcourse your head will be whipped forward due to it, but it is going to happen anyways in the crash.

Rally cars are equipped with cables coming out of head restrains and attach to the helmet of the driver. In case of a crash these cables tighten up and prevent the head of the driver from getting tossed voilently.


Quote:
Originally Posted by DerAlte View Post
And "What If" means the video is made up?
Yes. It is an ad made up to promote their website. I didn't get their connection with air-bag though.

Quote:
Originally Posted by DerAlte View Post
Err... what kind of ad hoc logic is that?
* Both the airbag and the driver are in the same car traveling at whatever speed
* When the airbag deploys, the speed at which the head travels towards it is independent of the car's speed

So the airbag shouldn't be deployed? Funny!
Didn't understand. Did you mean similar to the filling air in a (plastic / paper) bag and bursting it, scaring someone?

So the airbag shouldn't deploy if you brake to a stop only to be hit by an oncoming vehicle? Common scenario in India - I asked this earlier.
Here you missed my point by a mile atleast.
Let me put it this way. Consider that a car travelling at 100kmph hits a dog about 50meters before a curve.
The air-bag is deployed and the driver is startled/blinded due to it.
He doesn't notice the curve and drives straight towards the median.
The air-bag will already be losing the air inside it. (It does not hold the air inside it. It deflates within a few seconds)
And when the car will Actually hit the median (when the air-bag would actually be needed) it wont be available because it has already been deployed and the air is now gone.
The driver will be severely injured due to hitting his head.

So the air-bag should be deployed only during a severe crash. A car nannot travel any further (In max cases) after a severe crash. So there will be no chance of losing control due to air-bag deployment.


Quote:
Originally Posted by saaicon View Post
Thanks for the quite illuminating discussion on dependence of airbag opening on impact intensity . But I had a different question :

1. Why was there smoke inside the cabin ? is it connected to hot air inside the bag?

Also I read somewhere that after an impact the fuel supply to engine is automatically cut off . Did it not happen in this case ?
Quote:
Originally Posted by bsksam View Post
There was a white powdery smoke in the cabin, and the steering wheel was warm to the touch.
Quote:
Originally Posted by vikram_d View Post
A small explosive charge is used to rapidly inflate airbags and this miniature explosion causes the smoke.
Quote:
Originally Posted by bblost View Post
Its not just the explosion.
But the layers of powder that are kept between the layers of the airbag that give out an illusion of smoke.

The powder is to help prevent burns.
Vikram, you are partially right. Its sodium azide that is ignited in air-bags and the heat is due to its ignition. But it causes much less smoke than what appears in the cabin. As Bblost pointed out it is the powder which causes the illusion of smoke. It is similar to talc cum powder. It does not prevent burns. Its purpose is to prevent the folded air-bag from sticking together and deploying freely when required. You may have noticed a powder between tyres and tubes or inside the tubes at the puncture shop. Same function .

Quote:
Originally Posted by saaicon View Post
Thanks Vikram. How about the question on the fuel to the engine being cut off ? Is it not a mandatory safety requirement?
I dont think it is mandatory. Some manufacturers have the feature, some dont.
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Old 31st May 2013, 10:47   #90
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Default Re: Airbags deployed after hitting a dog. Understanding why?

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Originally Posted by Tejas Ingle View Post
... Let me put it this way. Consider that a car travelling at 100kmph hits a dog about 50meters before a curve. ...
He doesn't notice the curve and drives straight towards the median. ...

So the air-bag should be deployed only during a severe crash. ...
* The car was at 100Kmph 50m before a curve. And the driver didn't notice it because the airbag deployed? What was he doing 100m before the curve? And he wasn't braking when the dog made an appearance in front of him?
* Do you realize on roads where one can / is allowed to do 100kmph, and wherever visibility is limited or it is dangerous to drive at such speeds, speed limits are imposed to prevent accidents?

How do you propose the 'severity' of a likely crash is measured, to deploy the airbag in <100ms, with an acceleration sensor similar to the ones in smartphones? Please don't propose a system which costs more than the rest of the car.

Last edited by DerAlte : 1st June 2013 at 17:11.
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