Airbags

Technical discussion on converting internal combustion to electric
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parscheese
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Airbags

Post by parscheese »

Hi everyone!

Long time lurker, first time poster.

I'm going to convert a car to electric drive. Woo! Cheer! :)

However on approaching a VASS engineer I have been advised that it is difficult (impossible?) to convert a car *with airbags* to electric drive as there is no way to test the airbag... well almost no way ;)

Has anyone had any experience in converting a car with an airbag(s) to electric drive? I'd especially like to hear from anyone in Victoria as this is my home state.

Thanks guys.

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Richo
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Airbags

Post by Richo »

Some cars have the airbag seperate to the computer system.
So during an eV conversion this wiring is not altered.
You would need to check the wiring for the car you want to convert to see if it uses the ECU for the airbags.

So the short answer is NO but the long answer is YES.
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Squiggles
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Post by Squiggles »

Richo, are you suggesting that some cars have airbag systems that relay on the ECU. If so I am astonished. I always imagined that air bags had separate controllers with accelerometers in them.

evas
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Post by evas »

Hi Parcheese,

We are looking at doing an airbag car in Victoria. The engineer you should speak with is Laurie Sparke - sparkengineering@bigpond.com

He should be able to help you.

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Richo
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Post by Richo »

Well they may not rely on it but may communicate with it over can bus.
The point I was suggesting is to check to make sure it is NOT.
Since the airbag system is not touched during the conversion there should be no need to test it.

The one I have is seperate.
So during a conversion the airbag is not touched, changed or adjusted in anyway.
So saying you can't do a conversion because it has an airbag is a joke.
Why should the airbag be tested if the engine is changed?
The only reason is if the ECU is connected to the airbag and the ECU is removed during the conversion.
Or some of the parts connected to the ECU ie the petrol engine.

So the short answer is NO but the long answer is YES.
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EV2Go
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Post by EV2Go »

Not being any kind of electrical guru like some on here I wouldn’t have thought setting up / testing an air bag wouldn’t be that big of a job.

I would have thought (and I stand corrected) that it would be as simple as some form of G force switch to sense the accident like those offered by some members of this forum.

Wired to a relay that passes the correct voltage (found in a service manual) to the air bag. The air bag doesn’t need the ECU to work it only needs voltage, by creating a simple circuit and bypassing the ECU it can still work.

Testing is just as easy...

Unplug the air bag (because you don’t want it to go off) plug a volt meter on the wire that goes to the air bag and give the G force sensor a whack, if you get the right voltage reading the air bag should work.

As I say correct me if I am wrong but I don’t see why it needs to any more complicated than that.

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Post by Tritium_James »

With newer cars, it's more complicated than that. They detect the extent of the impact, and can fire various airbags, seatbelt pretensioners, etc, depending on what it things is necessary. eg lower speed crash will probably fire seatbelts but not airbags. Side impact is more likely to fire side bags, etc, etc

The engineer may also be worried that the structural mods to the car with battery boxes will change the crumple characteristics of the car, which changes the response (inflation rate, delay times) that is required for the airbag system.

Airbags aren't just airbags, the inflation rate and firing delays are tuned to each model of vehicle using crash testing.

parscheese
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Airbags

Post by parscheese »

Tritium_James wrote: The engineer may also be worried that the structural mods to the car with battery boxes will change the crumple characteristics of the car, which changes the response (inflation rate, delay times) that is required for the airbag system.

Airbags aren't just airbags, the inflation rate and firing delays are tuned to each model of vehicle using crash testing.


Thanks for your responses guys. This is the critical fact. For an airbag to work effectively it needs to inflate and start deflating at exactly the correct time. Too early and it'll deflate before you come in contact with it. Too late and it may hurt you.

Thanks evas.. I'll contact Laurie.

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EV2Go
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Post by EV2Go »

parscheese wrote:
Tritium_James wrote: The engineer may also be worried that the structural mods to the car with battery boxes will change the crumple characteristics of the car, which changes the response (inflation rate, delay times) that is required for the airbag system.

Airbags aren't just airbags, the inflation rate and firing delays are tuned to each model of vehicle using crash testing.


Thanks for your responses guys. This is the critical fact. For an airbag to work effectively it needs to inflate and start deflating at exactly the correct time. Too early and it'll deflate before you come in contact with it. Too late and it may hurt you.

Thanks evas.. I'll contact Laurie.
Yeah TJ I forgot for a moment that the air bags are factored into the safety rating of the vehicle. Your right it is a little more complicated than I represented it.

If you were adding a single air bag to an older car that wasn't designed to have them it might be a little more simplistic.

parscheese: agree having experienced an accident only a couple of years ago where it didn't trigger properly it is vital they work properly.

I hit a gutter square on which triggered the air bag in the steering wheel but by the time I hit the brick fence several seconds later it had already been up and down, leaving me with a fractured vertabrae in my lower back.

Mind you that kind of proves even with it wired up proerly doesn't mean it is going to work as intended.
Last edited by EV2Go on Thu, 01 Oct 2009, 17:37, edited 1 time in total.

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