Team-BHP - Understanding ABS (Anti Lock Braking System)

Quote:

Originally Posted by McLaren Rulez (Post 1713866)

Very interesting video, isn't it? Basically, it is saying that ABS systems are calibrated such that their braking is actually not as effective as threshold braking (i.e. braking at constant force just before the point of lock up).

Well, his methods of testing / simulation are fairly unclear.

IMO theoretical threshold braking will always be better than any kind of ABS.

Quote:

Originally Posted by McLaren Rulez (Post 1713866)

....What we're seeing is that the ABS equipped car's brake pressure graph would probably be an oscillation; first its too much so the wheel locks, then its too little so it has to apply more pressure if the car is to slow down.

Click this diagram to go to another thread where this was just discussed (the same video was also posted there and you have participated in the discussion - though that was not this specific) :

Quote:

Originally Posted by McLaren Rulez (Post 1713866)

The larger x gets, the better the chances of a driver beating the ABS system.

Agreed. In other words - the larger the value of x the worse the ABS system is.
Not all ABS systems are created equal.

Quote:

Originally Posted by McLaren Rulez (Post 1713866)

I know its theoretically possible to beat the system when it comes to braking distance and maintaining steering control at the same time, but is practically achieveable?

Is it achievable and is it easily REPEATABLE? Especially in panic situations.

THATS where i think the differentiator lies.

Add to that - a majority of the car-driving public has no idea about the concept of threshold braking, so there is no questions of them even trying it! Conventional logic says that the harder you press, the faster you stop.

When faced with a sudden braking situation, the conventional logic of the masses fails - and thats where ABS comes in. Atleast thats the way i justify its existence. But that doesn't quite answer your question -- which is also a question i have - that needs to be answered in reality.

cya
R

Quote:

Originally Posted by Rehaan (Post 1718253)

When faced with a sudden braking situation, the conventional logic of the masses fails - and thats where ABS comes in. Atleast thats the way i justify its existence. But that doesn't quite answer your question -- which is also a question i have - that needs to be answered in reality.R

Why not consider race cars, more than 90% of the race cars dont use ABS, the braking under high speeds is usually the job of the driver and it depends entirely on his skills.

If ABS was really so effective the why dont the world famous racing teams with huge R&D teams use it?

Regarding the masses, how many people do you think know the concepts of braking, leave alone braking many can't even drive properly..

Quote:

Originally Posted by McLaren Rulez (Post 1714162)

1) Can drivers can beat the computer and how likely they are to do so?

2) Why are some statistics showing ABS equipped cars being more unsafe?

For question 1, my answer would be 99% of drivers cannot beat the systems on modern cars. I leave the 1% for speculation. The reaction time of a typical system is much lower than that of a human being. This is from experience and witnessing the tests in person. As somebody told earlier in the thread, I cannot reveal more details as it's against IS policy, sorry. When designing systems, we talk in microseconds or 10s of milliseconds, which is too short for a human being.

ABS is not a one stop answer for all the problems. And many of the accidents caused during the initial phases of ABS was due to drivers taking their foot off the brake pedal, when the ABS kicked in. In an ABS equipped vehicle, you should keep the pedal down. There can be considerable back pressure on the pedal and many people take their foot off, once they encounter this. This has caused a lot of trouble, atleast in the beginning.

Quote:

Originally Posted by A350XWB (Post 1718317)

ABS is not a one stop answer for all the problems. And many of the accidents caused during the initial phases of ABS was due to drivers taking their foot off the brake pedal, when the ABS kicked in. In an ABS equipped vehicle, you should keep the pedal down. There can be considerable back pressure on the pedal and many people take their foot off, once they encounter this. This has caused a lot of trouble, atleast in the beginning.

To use ABS effectively first thing is people should know its advantages and drawbacks, then depending on the conditions one can take a safer decision.

Not many people who have ABS in their cars know what ABS stands for and how to use it, Then the question arises is, How will these people learn?

Considering the Indian car learning techniques one is only taught
1. How to control the steering
2. How to change gears
3.

What else does a beginner learns about the cars, If driving the car is only controlling the steering and changing gears, GOD help those people.

I think you got the point which I am trying to explain.

Quote:

Originally Posted by r@CYR@y (Post 1718289)

Let's leave out race cars out of the debate, since they are engineered/driven differently by highly trained/skilled drivers, in a controlled environment.

Like it is pointed out, training/education on the techniques needs to be imparted properly. For example, in my Fiesta manual, nowhere it is mentioned regarding the proper usage of the ABS equipped version.

@ Mclaren : Excellent thread

@ Rahan : Excellent Explaination

We need to understand that in Video what we are assuming is that the driver of NON ABS car knows exactly the threshold where breaking force will be highest but the just little less then tyre lock out. Now to put that in practical scenario difference between the the two would be very very less & to actually guess it everytime keeping all the factors of enviorment in mind is next to impossible & that is why we have errors & cars lock & skid.
Then comes to our rescue ABS, & it caculates the same many times a second the con in it is that imay go a little lesser then ideal but the pro is much more evident that there is no lockout as specified in the Graph above.

Thanks Rehaan. Looks like I stopped following that other thread just as things got interesting. One small question: Shouldn't the ideal force line and lock up line be the same horizontal line? I mean, isn't it so that you have an ideal braking force and any higher would lock the wheel? That aside, I'm glad you see exactly what my question is.

A350WXB, I assume you're involved in some way with ABS manufacturing/research. I wouldn't want you to violate your employer's policy but perhaps you could shed whatever light you can on calibration details without breaking any rules? PM or posting, they're both fine though posting would help others too. I think you're the only one who has facts that prove that ABS beats humans. We all suspect it too, but none of us have the data.

My last area of inquiry is the 30-40% increase in loss of directional control with ABS. It was also found that rollover probability was increased. As I've mentioned earlier, I think its partly due to the risk compensation. However, I suspect that it could also be that the ability to steer in an ABS equipped vehicle is a double edged sword i.e., the driver steers very suddenly and this is what causes him to lose directional control. If this is true, then it can be concluded that ABS+ESP is necessary as ABS alone is insufficient for certain scenarios. If anyone has any ideas/facts regarding this, I'd be most grateful.

Thanks again!

Quote:

Originally Posted by driverace (Post 1719167)

ABS
1. I remember reading that gravel-braking distances is more in ABS-cars as compared to non-ABS cars!
anybody knows a thing or two more about the same?

Yes. In gravel and snow, a locked wheel will cause the gravel/snow to build up in front of the wheel. This slows the car down better than if the wheel were rolling but no material built up in front of the wheel.

Interesting thread. I have some related questions
1) Is ABS only applicable to the front wheels? In most cars, the front wheels have disk brakes and the rear once have drum brakes.
2) If ABS is also used on all the wheels, how does it synchronize?
3) Whenever I hard break on my Scrop, the left rear wheel locks up (I hear the screech from the this wheel). Is this anything to do with ABS. If not does anyone have any idea why does this happen?

Quote:

Originally Posted by CasperRider (Post 1719584)

1) Is ABS only applicable to the front wheels? In most cars, the front wheels have disk brakes and the rear once have drum brakes.

No, it's for all wheels, atleast in modern cars.

Quote:

Originally Posted by CasperRider (Post 1719584)

2) If ABS is also used on all the wheels, how does it synchronize?

The ABS unit is a hardware that fits into the regular brake line and it has an electrical pump to step in. The whole unit is controlled by a computer that reads from ABS sensors in each wheel. The sensors read the rotation count of each wheel. The computer, when braking, will try to match the rotation count of each wheel against the other wheels and if it finds one rotating significantly slower, it'll kick in to control the braking for that wheel.

Quote:

Originally Posted by CasperRider (Post 1719584)

3) Whenever I hard break on my Scrop, the left rear wheel locks up (I hear the screech from the this wheel). Is this anything to do with ABS. If not does anyone have any idea why does this happen?

This can be due to a lot of reasons. The ABS unit will not kick in until it senses a wheel lock. So if you feel your vehicle drags left even under moderate braking, there might be other reasons at work. Check your brakes to see if the the left rear wheel is too tight.

Great Thread Mclaren,

I do have one question, I have experienced ABS being effective while breaking on the dry and smooth highways at high speed. However, in city driving conditions, I have encountered couple of times where I have literally stood on the breaks to stop the car and was afraid that my car would hit the vehicle in front ( speed may be in 45-60 kmph).

Any ideas on this. My car is a palio 1.6 GTX SP :)