DorsetStrider
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| posted on 26/11/08 at 10:57 PM |
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ABS kitcars and aftermarket ECU's.
Hiya all.
Had a long conflab with one of my tutors the other day regarding ABS brakes.
So long as the master cylinder and calipers/pads are balanced there is no reason why abs (and presumably traction control) won't work on kit
cars. As they are controlled by the ecu and the weight of the vehicle plays no part in the equation.
So my question is this...
Does anyone know if your aftermarket ECU's (megasquirt, emerald etc) allow you to use ABS or traction control? Or would you need to stick to the
ECU from the donor? (assuming your donor had ABS to start with)
[Edited on 26/11/08 by DorsetStrider]
Who the f**K tightened this up!
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Volvorsport
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| posted on 26/11/08 at 11:01 PM |
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vehicle weight plays no part in it ?
what happens to the weight transfer during braking ?
most ecus(aftermarket) and MS does have a limited form of traction control .
www.dbsmotorsport.co.uk
getting dirty under a bus
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DorsetStrider
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| posted on 26/11/08 at 11:06 PM |
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Apparently the abs is controlled by the ecu.
If it senses one (or more wheels) have stopped (or going significantly slower) but others are still turning it tells the ABS to release the locked
wheel till it regains a similar speed to the other wheels. Then the brakes are applied again.
As a result the weight of the vehicle is immaterial. I guess if you managed to lock all 4 wheels at the same time then presumably it wouldn't
kick in at all... but ho woften are you likely to lock both front and rear wheels at exactly the same moment?
Who the f**K tightened this up!
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Volvorsport
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| posted on 26/11/08 at 11:18 PM |
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youve described it in a nutshell , but keep doing research , if it was that easy , wed all have the same ABS ecu .
what happens when all 4 wheels have different co efficient of friction (ie road surface) , what happens when you add forward weight transfer and then
add steering input .
will it prevent the wheels from locking ?
probably.
will it prevent them from locking when you want them to?
hmm , dont know unless your an automotive engineer with specialist knowledge in ABS .
www.dbsmotorsport.co.uk
getting dirty under a bus
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Chippy
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| posted on 26/11/08 at 11:38 PM |
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When I built my car I used the ABS from the donnor XR4X4, and can assure you that it is NOT controlled by the ECU, it has it's own black box
that is totaly independant from the ECU. My main reason for fitting it was not in the hope that the ABS side of it would work, but that the power
assist would give top line braking, which it does. Ford spent thousands developing the ABS system to work on the XR4X4, so thinking that it would work
on a car that weighs less than half is a little optamistic to say the least, mine doesn't, but the braking is bloody fantastic. Cheers Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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DorsetStrider
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| posted on 26/11/08 at 11:40 PM |
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The black box is just a 2nd ecu totally dedicated to ABS. It's still an electronic control unit.
Who the f**K tightened this up!
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DorsetStrider
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| posted on 26/11/08 at 11:47 PM |
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quote:
Originally posted by Volvorsport
will it prevent them from locking when you want them to?
why would you want them to? Unless we are talking about handbrake turns... in which case the handbrake isn't affected by the ABS system anyway.
Remember the ABS system doesn't actually STOP the wheels locking... just releases the brakes momentarily when they do.
Any differences in the co efficients if anything aid the ABS. As makes it much less likely that all 4 wheels would lock up at exactly the same moment
in time. So long as 1 wheel is still turning the ABS ecu (be it seperate to or the same as the engine ecu) know's the car is still in motion.
(or possibly upside down at which point the effectiveness of the ABS becomes a bit redundant  )
[Edited on 26/11/08 by DorsetStrider]
Who the f**K tightened this up!
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MikeRJ
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| posted on 27/11/08 at 02:01 AM |
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The ABS system doesn't just look at speed differences between wheels, it also looks at the rate of change of speed of each wheel.
Beyond some pre-programmed rate of change it will assume the wheel is starting to lock. This limit will be dependant on the weight and general
dynamics of the car it's designed for.
ABS is one of those things that may appear relatively simple on the surface, but the more you learn about it the more complex it looks.
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zetec
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| posted on 27/11/08 at 06:05 AM |
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Emerald were talking about traction control which monitored the rate at which the engine revs were rising, if it was faster than a set rate it would
soft cut the engine. Would do away with the need for any new sensors.
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smart51
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| posted on 27/11/08 at 08:35 AM |
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quote:
Originally posted by DorsetStrider
If it senses one (or more wheels) have stopped (or going significantly slower) but others are still turning it tells the ABS to release the locked
wheel till it regains a similar speed to the other wheels. Then the brakes are applied again.
Shh! I work for an ABS company. Say that kind of thing round here and they'll really put you straight. We don't pay for a permenant
base at MIRA and for ice road testing in Sweeden every year just to get rid of some surplus money.
Things if which to be aware. You can't just put the brake back on for a locked wheel or it will just lock again. You have to apply the
pressure in pulses and build it up "slowly". The size of pulses depends on the weight distribution of the vehicle and the slipperyness of
the road. Speaking of which, you have to deal with split mu surfaces and intermittent mu surfaces.
ABS systems are not just fitted to passenger cars, they are tuned to suit, so the ABS system off a front heavy FWD hatchback won't be ideal for
an evenly balanced RWD kit car.
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iank
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| posted on 27/11/08 at 09:24 AM |
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It's a classic control system problem, the algorithms in the Brake control unit are tuned to the car (mass, cog etc) they're fitted to in
the same way the map in an ecu is tuned to the engine (cam profile, exhaust manifold flow etc).
So say because it's controlled by an ECU doesn't imply for a moment mass doesn't come into the equation, it's been
pre-measured and taken account of. Did this idea come from the tutors?
[Edited on 27/11/08 by iank]
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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smart51
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| posted on 27/11/08 at 11:24 AM |
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It is possible to make an ABS ecu "learn" the vehicle it is fitted to. The first few ABS stops are, shall we say, sub optimal but after a
few goes on different road surfaces, it learns what it has to do.
With the aid of a decelerometer, it can learn how much to back off the rear brakes under a hard deceleration. It can learn how hard or how gently to
treat each wheel, due to tyre grip and weight distribution( a heavily loaded wheel can take more brake force than a lightly loaded one). It will take
on the characterisics of the vehicle. Such a system would suit kit cars. No-one makes them though, probably because there is no call. Mass produced
cars are tuned once then are all made the same. That way you don't have to wait for the ABS to learn its surroundings. You wouldn't want
to crash your brand new car the first time you used the ABS would you?
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DorsetStrider
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| posted on 27/11/08 at 08:58 PM |
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quote:
Originally posted by iank
So say because it's controlled by an ECU doesn't imply for a moment mass doesn't come into the equation, it's been
pre-measured and taken account of. Did this idea come from the tutors?
[Edited on 27/11/08 by iank]
Yeah.
My tutor suggested I fit ABS to the kit. I pointed out about the weight difference and he seemed to think it wouldn't make a big enough
difference for it to be a problem.
Who the f**K tightened this up!
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iank
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| posted on 27/11/08 at 09:08 PM |
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quote:
Originally posted by DorsetStrider
quote:
Originally posted by iank
So say because it's controlled by an ECU doesn't imply for a moment mass doesn't come into the equation, it's been
pre-measured and taken account of. Did this idea come from the tutors?
[Edited on 27/11/08 by iank]
Yeah.
My tutor suggested I fit ABS to the kit. I pointed out about the weight difference and he seemed to think it wouldn't make a big enough
difference for it to be a problem.
Well there's no real harm trying, but I wouldn't hold out as much hope.
The last control system (high speed pan tilt head) where I was involved in removing 50% of the weight went into nasty oscillation and needed a swift
application of the e-stop to avoid shaking itself to bits.
Creating your own controller box that was mappable (MegaStop ? ) would be a good project if you have a software/electronics interest.
Edited to add: Just remembered that the IVA has requirements for ABS if fitted - seems from a first read that it has to comply with Directive
71/320/EEC (whatever that might say)
[Edited on 27/11/08 by iank]
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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