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Originally Posted by Jeroen I don't want to get caught in semantics, but are you saying there is a difference between tensioners and pre-tensioners? Either the belt is working normally, ie it locks/doesn't unwind or it gets (pre) tensioned.
Actually, I think the term pre-tensioning is a bit misleading in the first place; There is actual tensioning happening when this system kicks in. But it is before your body starts actually moving forward. Maybe that's why the call it pre?
Jeroen |
There is a difference between tensioner and pre-tensioner.
I am coming to that point.
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Originally Posted by DerAlte Err... what is the connection between Seat Belt and Electronic Stability Program? Is the seat belt expected to hold you in the seat if you swerve the car??? -ive g produced due selective braking by ESP is way below the trigger threshold.
The time between seat belt (pre)tensioning and airbag firing can be detected only in an appropriately equipped test facility - the driver cannot figure it out
Right on all counts, @Jeroen. 'Pre' is used by some to denote active belt tensioning by the 'tensioner' before the seat belt latch/lock engages. |
Yes, there is a connection between the ESP and seat-belts, in high end cars. Please read in detail about Mercedes-Benz Pre-Safe system. It is standard on all Mercs of today.
I will put it here in short.
Suppose a driver swerves at high speed in order to avoid something:
1. The car will lose stability and the ESP will be activated and it will try to stabilise the car.
2. The pre-safe feature will sense instability and a potential accidental situation based on data received from ESP.
3. So it starts preparing the car for a crash before it actually happens.
4. The seat-belt "pre"-tensioner is actuated (It is reusable and does not need replacement)
5. If the seats are reclined, they are straightened.
6. If the rear head restrains are folded, they pop out.
7. All the open windows are rolled up. (But not completely. About 2 inches of gap is left as the occupants tend to hold the edge of the window in panic. Closing the window completely would crush their fingers) Same happens with an oppen sunroof.
All this happens together.
I have been through this experience several times in a row and I definately felt the pre-tensioners pull me back on every single occasion.
The car may travel some distance in this mode and then crash which will deploy the air-bags. So there would be a lot of time between "pre"-tensioner and air-bag.
However, There is no time gap in tensioners (I have not used pre here) and air bags.
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. Quote:
Originally Posted by lucifer1881 On a related note, what would have happened if a car at 80kmph does not brake and hits a dog or a deer or some other animal? I am assuming due to impact the speed would decrease to say 50-60 kmph or even 20-30 kmph, and the car would keep moving. Would an airbag deploy in such a case? And would it not be extremely dangerous for an airbag to deploy when the car has not come to a complete stop? Do manufacturers build in any logic to not deploy an airbag if the car is moving above a threshold speed? |
You have hit the exact point. All air-bags are designed keeping this in mind and air-bags are never deployed like that. This is a case of faulty deployment.
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Originally Posted by MotoNanu Every manufacturer would have set a minimum threshold for the vehicle speed. For example: 30 kmph. Only if the vehicle speed is above this and the system detects a crash, the airbags would deploy. If the speed is less than the threshold, airbags won't deploy. |
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?
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Originally Posted by DerAlte The video that @vikram_d posted shows that, doesn't it? It wasn't a simulation or Photoshop modification - the car was stationary when the airbag deployed. |
Yes, the video is made up. In the end, it says "WHAT IF?"
Air-bags dont deploy because of a hand bag hitting the grill.
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Originally Posted by DerAlte Err ... why would the driver lose steering control? Forget to steer in panic is different! Also, the harm due to airbag deployment is - at any speed - much less than the harm it's absence would have caused, right? |
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.
Also the air bag inflates and deflates in a matter of seconds. See what Bblost is pointing at in the post quoted below. 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.
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Originally Posted by bblost A bunch of retards crashing into a traffic jam.
You can see how fast the airbags inflate and deflate. Accident happens at 53 seconds. By 58 seconds the camera is back to normal and you can see the airbags have been deflated. |
Please understand that air-bags never deploy by such a small impact. Please see the video that I have posted two paages back. The airbags deployed after the bumper, bonnet, fender were all damaged and the front wheel almost locked due to the damage. A massive impact is needed for deplyment of the air-bag.
And in case of such an impact the car wont be travelling at a high speed when the air-bags deploy.
I hope I was able to explain my point correctly.