Airbags and Bull Bars

[101RRS]

I always thought there were crush cans at the front of cars with airbag sensors in them that set of the airbags in an accident. Hence the hype about fitting an airbag compatible bullbar.

Now I have learned that this is not the case and in fact cars are fitted accelerometers that detect the deceleration in an accident and set off the airbag - in fact if you could decelerate at the required rate without damaging the front, the airbag would still deploy.

If this is all true - why are airbag compatible airbags required. If only rapid deceleration rather than deformation is required surely the style and design of a bar is not relevent.

Any thoughts, wanna set me straight!!

Gazzz

[disconut]

From Overlander on Google.

The Airbag Debate
The next option to consider is how the bullbar is mounted to your vehicle. Some bars completely replace the current bumper from the 4WD, while others incorporate the existing bumper into the design. You'll also need to choose between a bar which uses mounting brackets versus a chassis mount system. Newer bullbars may utilise deformable, impact absorbing mounts to assist with airbag deployment in the event of an accident.

In terms of new car warranty and correct operation of all safety devices on your 4WD, there is no thornier issue than that of bullbars and airbag compatibility. A quick explanation of the airbag concept is necessary to fully understand how an incompatible bullbar could have a serious effect on your vehicle, and your safety.

Current vehicular designs incorporate crumple zones into the chassis, which determines the vehicles 'crash pulse'. The crash pulse is a measure of deceleration, usually taken from the occupants position, when the vehicle hits an obstacle. The front of the vehicle has an almost instant stop, but because the vehicle is designed to crumple, the occupant's rate of deceleration is considerably less. The issue of collision related injury to passengers boils down to the rate of deceleration. The faster an object decelerates, the more load there is on the object and it is this force that can have the most devastating effects on vehicle occupants.

The airbags in a vehicle are designed to deploy at precisely the right moment, timed to the millisecond. Any disruption to the vehicle's crash pulse would have an effect on the timing of deployment of the airbags. With this is mind, it fell to the designers of bullbars, both original equipment and after market, to come up with a system that incorporated the airbag sensors, and didn't disrupt the vehicle's crash pulse. In order for some manufacturers to achieve this goal, it has been necessary to engineer extra crumple zones into the mounting brackets of the bullbars.

Link for more on this:


http://www.overlander.com.au/pg/equipment.php?id=8

Trev.

[seqfisho]

There was a very interesting little segment on 4wd TV last night (Bris31) and they interveiwed ARBs lead design engineer for their front bars and went throught the design process ARB uses to develop new bars and guess what the subject vehicle was 8O no less a new D3 with a prototype bar on the front.

They showed the development of the mounts and how they build the same compression rates into the bar mounts that the manufacturers build into the front of the car, so that the car with a bar will have exactly the same compression graph as the standard front end. They trial both mounts on a computer controlled and monitored press and graph the results.

A very high tech approach to the gear they make and a very interesting segment, makes the few extra dollars you spent on their gear seem worthwhile. :wink:

[101RRS]

Thanks for the information guys - but I would have thought the crash pulse wouold be the same irrespective of the bull bar - but anyway it must be right if it was on TV.

Thanks

Gazzz

[BMac]

I think that with out the crush cans, hitting a solid object like a tree, would produce a much higher deceleration rate then with cans, causing the airbags to deploy at lower speeds than intended. You dont really want them blowing up in your face in a 10kph prang :cry:

Bruce.

[Scouse]

The crash sensors aren't in the crush cans on the MA Discoveries.
If you look in the engine bay & follow the yellow SRS harnesses, you'll see the sensors are mounted at the bottom/front of the engine bay. I would estimate they'd be about 15cm behind the bumper.

Later Discoveries did away with the crash sensors & just used the DCU (decelleration control unit) under the centre console.

[101RRS]

Originally posted by Scouse
Later Discoveries did away with the crash sensors & just used the DCU (decelleration control unit) under the centre console.

Hence I am do not understand the need for airbag compatible bull bars - as a general statement deceleration will be same - well at least close enough for government work!

[Scouse]

Originally posted by garrycol
Hence I am do not understand the need for airbag compatible bull bars - as a general statement deceleration will be same - well at least close enough for government work!So LR can sell a heap of their own "airbag compatible" bull (nudge) bars before the aftermarket guys sell theirs !!
:? :?

I think it was something to do with affecting the crumple zone more than the airbag operation itself.
Something about the airbag deployment being designed as part of the crumple zone operation rings a bell.

[seqfisho]

Originally posted by garrycol+--><div class='quotetop'>QUOTE(garrycol)</div><div class='quotemain'><!--QuoteBegin-Scouse
Later Discoveries did away with the crash sensors & just used the DCU (decelleration control unit) under the centre console.

Hence I am do not understand the need for airbag compatible bull bars - as a general statement deceleration will be same - well at least close enough for government work![/b][/quote]

I know that my S1 disco ARB bar has 3 rippled sections on the mounts and that S2 discos only have 1 on the ARB bar mounts, so that must relate to the type of sensors used.

Most ARB Pootrol and Land Looser bars use the single ripple in the mounts like S2 disco bars.

The mount they showed in the 4wdTV segment for the D3 also only had the single ripple on the mount.

S1 Disco mounts
http://www.aulro.com/albums/red-disco/IMG_0455.sized.jpg

[VladTepes]

I think it must be the cost of the processss (as noted in the post about the 4wdtv segment on arb bar design) that leads to the low (zero?) number of options for bars for low volumen vehicles.

to wit: 1994-5 Range Rover Classic Vogues/LSE's - they are SRS airbag equipped but buggered if I can find an aurbag compatiblr bar for them anywhere. If anyone can help with this PLEASE let me know.

[jase]

yes its "the process" of devlopment that means you can't get bars for lower demand 4wds (cost is just to high unless they can sell thousands)
I "need" a good steel bullbar (and big lights) where I live (to many kangaroos)
I put a DII ARB sahara bar on the wifes P38
yes I needed to mod the mounting holes a little but width ect are the same and as it is airbag compatible (be it for a slightly differant car) I figured it would be good enough.
I'm driving a (don't flame) VW touareg ATM as a daily driver very nice car (not for fwding) unfortunatly I can't get anything in the way of a bullbar for it style_emoticons/<#EMO_DIR#>/sad.gif

Jase
living in kangaroo country cent Vic