Anti Lock Brakes

[dorey]

Hi every one !!
I'm from India. Well ,currently I'm working on Anti lock brakes.I know that it helps in reducing braking distance,improves steering stability and much more.
But I wanted numbers for it to prove it to my team leader.Actually we have tyre data for coffecient of friction Vs slip ratio. That curve reaches a peak value and remains almost constant at that value. So while we are travelling longitudinally , ABS is not much of use .So now now I'm seeing the effects of ABS on lateral motion of vehicle.I want to see the influence of ABS on lateral force. But I'm not able to get as to how to quantify this influence . Tyre data we are having gives Lateral force vs slip angle only for zero slip ratio.(ie. for zero longitudinal force)
So is there any other way to measure the impact of ABS on lateral force ???

Thank you in advance

[Jersey Tom]

Actually we have tyre data for coffecient of friction Vs slip ratio. That curve reaches a peak value and remains almost constant at that value.

Oh yeah? On what surface? Sandpaper, presumably? How about real, dry asphalt? Wet asphalt? Standing water? Snow? Ice?

Might want to be careful about saying ABS does nothing in a straight line.

[Tim.Wright]

Hi every one !!
Actually we have tyre data for coffecient of friction Vs slip ratio. That curve reaches a peak value and remains almost constant at that value. So while we are travelling longitudinally , ABS is not much of use .So now now I'm seeing the effects of ABS on lateral motion of vehicle.I want to see the influence of ABS on lateral force. But I'm not able to get as how to quantify this influence . Tyre data we are having gives Lateral force vs slip angle only for zero slip ratio.(ie. for zero longitudinal force)
So is there any other way to measure the impact of ABS on lateral force ???

If you are making an FSAE car, ABS is quite an unnecessary distraction/complication that you will be better off without. If you don't know why its there, then don't use it.

Anyway, ABS doesn't really reduce braking distance, it just ensures that you have lateral force capability to maneuver while you are braking.

Put your tyre model in combined lateral/longitudinal mode (see the relevant pacejka equations) and see how much lateral force you have available for maneuvering when your tyres are producing their peak longitudinal force.

[dorey]

Oh yeah? On what surface? Sandpaper, presumably? How about real, dry asphalt? Wet asphalt? Standing water? Snow? Ice?

Might want to be careful about saying ABS does nothing in a straight line.

Well, I'm not saying that Abs is not useful for straight line. The tyre data we are having is such that there won't be much improvement in braking distance of our car by ABS in straight line

[dorey]

If you are making an FSAE car, ABS is quite an unnecessary distraction/complication that you will be better off without. If you don't know why its there, then don't use it.

Anyway, ABS doesn't really reduce braking distance, it just ensures that you have lateral force capability to maneuver while you are braking.

Put your tyre model in combined lateral/longitudinal mode (see the relevant pacejka equations) and see how much lateral force you have available for maneuvering when your tyres are producing their peak longitudinal force.

Yes we are making an FSAE car. I believed that adding ABS would be helpful in improving performance of our car.But lets see how it finally works out ..
You have mentioned about pacejka equations.As I'm new to them , would you suggest some sort of reference for them..

[Tim.Wright]

Do you have a problem with locking brakes/instabilities on your previous car? Have you tried just moveing the brake balance forward??

If you have the tyre data from the TTC, the pacejka equations should be included in that data pack somewhere or on the TTC secure forum.

But again, honestly, forget ABS. You guys need to concentrate on other things which are a million times more important.

[dorey]

I'll talk about Pacejeka equations with the concerned person who handles tyre data for us.

As far as ABS is concerned ,I will surely raise your point among my teammates.
But since I'm working on braking of car ,I felt that introducing ABS would be helpful for our team.Also we are not implementing ABS in this year's car.It has been taken taken up as project for the next year's car.

[matt21]

I would not say, that ABS is not helping in a straight line.
You can use stronger brakes without risking to lock them permanentely.
Just llok at the brakes at sports cars like a 911. If you have no ABS and you brake hard, they will definitly lock without ABS.

BTW, do you have any regulations covering brake size?

[tuj]

It is silly to think that ABS does not reduce straight-line stopping distances. Modern ABS valves can modulate something like 20 times a second, and they can do so for each individual wheel. That is simply not possible with a human and a single brake pedal. Even factory ABS systems are getting good enough for racing. Several years ago at the SCCA runoffs, the C5 Corvettes with ABS enabled dominated the non-ABS cars.

Sometimes drivers do not like ABS because they cannot get a good pedal feel; they have to trust the system. This can make advanced techniques like trail-braking slightly harder, but certainly not impossible.

[Jersey Tom]

It is silly to think that ABS does not reduce straight-line stopping distances.

To be fair, if his data says there's no loss in max braking performance when you lock a tire, there's that... but (a) you have to question that data, (b) if it's a FSAE car I couldn't justify trying to develop this if it's even within the scope of the rules.

[Tommy Cookers]

...... Sometimes drivers do not like ABS because they cannot get a good pedal feel; they have to trust the system. This can make advanced techniques like trail-braking slightly harder, but certainly not impossible.

trail braking is a basic track technique, it's necessary wherever the line radius tightens enough (to make it necessary)
ABS should be helpful in this

[olefud]

With a truly high frequency well balanced ABS there is the advantage that each wheel can independently approach lockup and maximize performance. Regular brakes lock different wheels while the other wheels are not at full brake performance depending on the changing tire loadings with different maneuvers.

[Tommy Cookers]

this means that such a 'good' ABS system would in trail braking brake the outer wheels more than the inners
so tending to oppose the required turn ?

[Greg Locock]

I'd like to see a comparison of straight line braking distances with and without ABS. Last time I looked into it in a straight line a skilled, alert driver in a balanced car could beat the ABS, but since an ABS does your brake balancing for you, handles split mu, allows you to steer etc etc, in practice ABS was a better option most of the time.

You'll never get a straight answer on this from the safety nannies.

On the track ABS is usually seen as an advantage.However for FSAE I tend to agree with Tim, it is an awful lot of work for very small gains.

Tommy - yes ABS tends to be understeer in general

[tuj]

check out table 3.

http://www.msf-usa.org/downloads/imsc20 ... -Paper.pdf

or this sport rider test:

http://www.sportrider.com/sportbikes/ab ... t-stopping