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]
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 .
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?
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 .
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
The black box is just a 2nd ecu totally dedicated to ABS. It's still an electronic control unit.
quote:
Originally posted by Volvorsport
will it prevent them from locking when you want them to?
) 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.
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.
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.
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]
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?
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]
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.
) would be a good project if you have a software/electronics interest.