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Old 2nd January 2011, 23:40   #16
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Default Re: ABS - How Failsafe

@SS. Thanks for taking the effort to post.

Quote:
Originally Posted by raju2512 View Post
@ sutripta

What you are talking is about the design of the braking system.
.....
Above all, any new design gets validated before they are approved for production and production parts are routinely subjected to validation tests (endurance, etc) to ensure they meet the required norms.
I Know. What I'm talking about is a system design issue. There are essentially two points.

All engineering is essentially a matter of compromise. Different criteria/ constraints/ philosophies lead to different choices with regard to the balance of this compromise. Would like that full thought process to be out there in the public domain.

Next, in a complex system, can anyone state with authority/ prove that all possible scenarios have been foreseen, and catered to.

After airbags caused a few deaths and injuries, the manufacturers were forced to essentially forced to make public a lot of details which otherwise would have been hidden. White papers, if you please. Something similar for ABS systems is what I wish. But till such time, a discussion amongst ourselves.

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Old 3rd January 2011, 00:34   #17
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Default Re: ABS - How Failsafe

^^ Do you think non-ABS equipped cars are safer than ABS equipped cars? If Yes, Please elaborate.
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Old 3rd January 2011, 09:15   #18
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Default Re: ABS - How Failsafe

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Originally Posted by .anshuman View Post
^^ Do you think non-ABS equipped cars are safer than ABS equipped cars? If Yes, Please elaborate.
Anshuman, there is no debate or thought about whether ABS-equipped cars are safer than non-ABS - they are, and there's no contest. However, what Sutripta is trying to bring out is, whether ABS systems add an element of higher risk of failure during operation, as compared to non-ABS systems.

It is unarguable that the simpler a machine is in terms of engineering, the less likely it is to fail. You have stated yourself that
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Originally Posted by .anshuman View Post
...if the ABS system fails/malfunctions in a car the braking system continues to function just like the non-ABS equipped car. ABS failure will not lead to complete brake failure at all.
...which is just not true, as I have explained in my previous post.
Quote:
(..."false modulation"). Any which way you hit the brakes, the pedal starts juddering, and braking efficiency is much reduced. Got that handbrake working??? Use it...
If anyone on this forum HAS experienced loss of braking efficiency due to an ABS system malfunction, all of us would like to know. Greenhorn already reports one case in a Scorpio, which seems to have been hushed up by the owner, and the car sold to another unsuspecting person. Other cases are improperly identified as a hydraulic system issue rather than an ABS system one, and I have known cars whose entire braking system has been thrown out for no apparent fault in the hydraulics.
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Old 3rd January 2011, 09:56   #19
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Default Re: ABS - How Failsafe

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Originally Posted by SS-Traveller View Post
...which is just not true, as I have explained in my previous post. ...
Incorrect.

No designer in their sane mind would ever do that. Heard of a design time activity called FMEA (Failure Mode Effect Analysis)? Design is NEVER done by one or two designers, it is usually a team of at least 10 people who sit together (multiple sessions) to cover all possibilities - and then rule out any element that has a hint of doubt.

ABS valves are energized to bleed, not energized to supply / block Master pressure to the brake. If it cannot be energized (blown solenoid, for example), it does not impede braking and does not participate in the braking system. ABS systems are designed not to act if ANY of its components are not functioning as designed, and most of the time an ABS ECU keeps performing diagnostics.

Hence, @.anshuman's logic is correct - that on ABS malfunction the brake system acts as if ABS is not present.

Let us not, for intellectual exercise purposes, trivialize automotive system design. What for some is a subject of speculation out of curiosity, is a rather serious subject for hundreds of automotive designers. Sufficient information is available in the public domain on this, not requiring speculation. Of course there will always be many who want to disprove technology and engineering purely on the basis that "compromises are made as a rule in engineering"!
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Old 3rd January 2011, 10:05   #20
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Default Re: ABS - How Failsafe

^^^
Quote:
ABS valves are energized to bleed, not energized to supply / block Master pressure to the brake. If it cannot be energized (blown solenoid, for example), it does not impede braking and does not participate in the braking system. ABS systems are designed not to act if ANY of its components are not functioning as designed, and most of the time an ABS ECU keeps performing diagnostics.
In which case, what is false modulation? Is it an ABS system failure or not? And does it reduce braking efficiency or not?
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Old 3rd January 2011, 22:21   #21
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by .anshuman View Post
^^ Do you think non-ABS equipped cars are safer than ABS equipped cars? If Yes, Please elaborate.
In my lexicon, safe and failsafe are two very different words. So to elaborate, other things being equal,
A) Is a car with ABS safer than a car without ABS? Undoubtedly yes.
B) Is the braking system of a car with ABS more failsafe than if ABS had not been present? No (IMO) Under discussion.

As SS has rightly explained, we are not talking of overall safety. In fact I have said before

Quote:
Originally Posted by Sutripta View Post
Pls. note that I'm not bashing ABS systems. Would love to have it on all my cars. But would also like to know what exactly I'm getting.
@DelAlte. Because something is designed to fail in a certain mode means it can NEVER fail in any other mode?
And in a complex system, one can foresee, and handle every scenario?

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Old 4th January 2011, 10:59   #22
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by SS-Traveller View Post
... what is false modulation? ...
Errr... What IS 'false modulation'?

Quote:
Originally Posted by Sutripta View Post
... Because something is designed to fail in a certain mode means it can NEVER fail in any other mode?
And in a complex system, one can foresee, and handle every scenario? ...
One does not design any system or component to fail in ANY mode - failure is a post-facto observation (or, in a lab or a simulator, controlled introduction of the same to observe effects). FMEA is an exercise to a. examine the effects of single or simultaneous-multiple failures on the rest of a 'system', and b. creating mitigation measures to obviate compromising safety.

As far as "complex system, one can foresee, and handle every scenario" is concerned, yes, that IS the practice of engineering! To an external observer, ANY system can appear complex. To a designer, EVERY so called 'complex' system is an interconnected network of rather simple sub-systems and components. This interconnection is not a 'happening' but a very deliberate scheme to make the system do what it is supposed to do.

Think simple, and you will understand the issue better. 'Foreseeing and handling' is simply the accumulation of all possible scenarios handled at the component level (sub-systems are also an ordered collection of components) during the process of engineering. The tedious task of assembling the n-dimensional matrix of the failure and mitigation ("all scenarios") is made easier when many people work together.
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Old 4th January 2011, 11:23   #23
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by DerAlte View Post
Errr... What IS 'false modulation'?
Maybe this'll help? Automotive chassis: brakes ... - Google Books.

Name:  ABS.JPG
Views: 351
Size:  45.7 KB

I'm outta here... can't carry on an argument on engineering with a DCE-ite!
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Old 4th January 2011, 11:43   #24
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by DerAlte View Post
One does not design any system or component to fail in ANY mode - failure is a post-facto observation (or, in a lab or a simulator, controlled introduction of the same to observe effects). FMEA is an exercise to a. examine the effects of single or simultaneous-multiple failures on the rest of a 'system', and b. creating mitigation measures to obviate compromising safety.
DerAlte - Being from the background (quality assurance), can't help but make this comment. And no I do not really know if i can "reject or fail to reject the hypothesis" i.e. Ha or Ho on this ABS discussion

Coming back to FMEA, at least I haven't come across a single FMEA which a. "uncovered" all probable causes of failure and b. Brought the resultant RPN number to 0 (which we know is not possible) or what you call a mitigation.

so while essentially I appreciate the usefulness and accuracy of FMEA as a tool, I am equally convinced that a product even after going through a near perfect FMEA may still fail during use which will/does force designers to go back to drawing table once again.

PS - And I do hope that ABS does not fail as I drive a car which is equipped with one

Last edited by New.Novice : 4th January 2011 at 11:46.
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Old 4th January 2011, 18:15   #25
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by SS-Traveller View Post
Maybe this'll help? ...
I'm outta here...
Arrey dada, dada, where are you running away?

Thanks! A-ha, 'false modulation' from a p-o-v outside the braking system. What can one say! Is that ABS failure? Kya boss, if Google returns results based on a mistyped word, would that mean Google does not know how to search? Perhaps you are expecting Artificial Intelligence? Even that would fail in such circumstances. Kiska joota, kiska sir, sir.

Quote:
Originally Posted by New.Novice View Post
... Being from the background (quality assurance), can't help but make this comment. ...
Errr... What comment? Where?

Quote:
Originally Posted by New.Novice View Post
... at least I haven't come across a single FMEA which a. "uncovered" all probable causes of failure and b. Brought the resultant RPN number to 0 (which we know is not possible) ...
Correct, @New.Novice sir, not just you, no one else has. What to say to you, what with your background you should know statistical analysis in Quality better than anyone else, sir, that if one says "0 error software", it means 'Errors tending to 0', not 'Errors=0'! In 'uncovering' causes, it is discovery of 'all' till those whose probability 'tends to 0', not N'=0 (all with Probability=0, i.e. no further causes can be discovered)!!! Still, it does not prevent some minds from thinking that N' should be =0.

Quote:
Originally Posted by New.Novice View Post
... that a product even after going through a near perfect FMEA may still fail during use which will/does force designers to go back to drawing table once again. ...
Very true! LOL What is Murphy's Law there for?

Seriously, it has taken close to 30 years for ABS systems to reach the current state of technology, and more importantly, the components in the ABS systems to reach a state of 'failure tending to 0'. Imagine how many cycles it has gone through as you described, and mathematically compute their current MTBF and probability of failure.

And don't worry about ABS failure - all of TBHP members and readers will pray that even if that happens, your brakes and reflexes keep you safe.

Last edited by DerAlte : 4th January 2011 at 18:23.
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Old 4th January 2011, 21:08   #26
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by DerAlte View Post
One does not design any system or component to fail in ANY mode
Surely you are joking (One designs for no failure. But if it does fail, try to see to it that it fails in the least disruptive way)

As far as "complex system, one can foresee, and handle every scenario" is concerned, yes, that IS the practice of engineering!
And of course the engineers always succeed!

Think simple, and you will understand the issue better. 'Foreseeing and handling' is simply the accumulation of all possible scenarios handled at the component level (sub-systems are also an ordered collection of components) during the process of engineering. The tedious task of assembling the n-dimensional matrix of the failure and mitigation ("all scenarios") is made easier when many people work together.

In English I can understand please. I suppose you are saying
Divide and conquer
Experience counts
Many heads are better than one
So I take it that
A) there are no such things as a complex system.
B) every situation can be foreseen. And is.

(There are a lot of software engineers on this forum. Possibly you are one yourself. Transposed into that realm would mean that all programs are simple, can be proven to be correct, and all exceptions are easy to foresee and handle)

And from your other post, tending to zero is the same as zero.

(So a component most unlikely to fail, is the same as the component will never fail.)

As someone once said, "jotodin bachi, totodin sikhi" - (As long as I live, I learn)

Unlike SS, I can't walk away from a thread I've started! Though I'm sorely tempted to. But I can be selective about what I react to.

Regards
Sutripta
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Old 4th January 2011, 23:02   #27
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Default Re: ABS - How Failsafe

ABS is composed of a pump, sensors that feeds its control unit. Like any system it may fail.

But there were cars 70 years before ABS became mainstream.

I personally don't like ABS in cars, in Big SUV and trucks maybe. its doesn't let me do fancy stuff.

You can simulate abs with normal brakes.
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Old 4th January 2011, 23:06   #28
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by DerAlte View Post
Arrey dada, dada, where are you running away?

Thanks! A-ha, 'false modulation' from a p-o-v outside the braking system. What can one say! Is that ABS failure? Kya boss, if Google returns results based on a mistyped word, would that mean Google does not know how to search? Perhaps you are expecting Artificial Intelligence? Even that would fail in such circumstances. Kiska joota, kiska sir, sir.
@ DerAlte: No, I didn't run away! I just took leave of absence, but since you refuse to grant me that with your , I had to come back!

Since false modulation is an issue arising due to a specific component of the ABS system, and does not exist in non-ABS-equipped vehicles, would you still insist it is not ABS failure? Why talk FMEA when you can talk false modulation?

Let's look at it this way... As an uneducated (in terms of automobile engg.) car owner, can one expect even a slightly higher risk of the brakes failing to stop the car when needed, just because the ABS system is fitted? The answer that you and Anshuman give is a resounding NO. You insist that
Quote:
Originally Posted by .anshuman
...if the ABS system fails/malfunctions in a car the braking system continues to function just like the non-ABS equipped car.
Quote:
Originally Posted by DerAlte
... .anshuman's logic is correct - that on ABS malfunction the brake system acts as if ABS is not present.
But since there is clear evidence that an entity called false modulation exists, and is caused by a specific component in the ABS system, and leads to loss of braking power in a vehicle to the point where the non-ABS brakes in a similar car would have stopped it much better, your (and Anshuman's) answers do not hold good. The risk of brake failure in an ABS-equipped car is higher (however minimal that may be) - than if no ABS system was fitted. As for the rest of the argument, I'll let my signature speak for me....
Quote:
Originally Posted by Sutripta View Post
Unlike SS, I can't walk away from a thread I've started! Though I'm sorely tempted to.
Sutripta-da, how could I walk away from you!??!
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Old 6th January 2011, 11:12   #29
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Default Re: ABS - How Failsafe

@SS, 'false modulation' is from an external observers point-of-view, and that is why I gave the example of Google returning results for a mis-typed query - Google is not at fault if the primary search spec was 'not intended'. 'Not intended' is a human concept, for a computer any string presented is a valid string. Also, 'false modulation' was not due to a component in the ABS system, it was due to a component in the 'brake' system of which ABS is a subsystem.

In the example that you gave, the brakes were not to spec, causing the drum & wheel to jam earlier than expected. This is the condition, or rather the rate of angular deceleration of the drum / wheel under these conditions, which the ABS ECU is checking. If more than a set value, it triggers brake modulation. Ergo, it did it's designed job. Would you rather that it do it's job or that it shouldn't do it's job?

In any case, 'false modulation' (unless brakes were bad at all 4 wheels) will only cause 1 wheel to be acted on for a short duration. By logic, 'false modulation' is an incorrect term - the ABS modulated all right, just that for a human looking at it from outside it shouldn't have. Right? Bhai, the ABS ECU is not an artificial intelligence system running on a Cray.

To extend the above, what is the difference between wheel-lock due to wrong-spec brake case and when, however odd it may sound, the wheel goes into a deep pothole and is momentarily not able to rotate? ABS will act correctly in either case, since all that the ABS is doing is sensing an impending 'wheel rotation speed = 0' and switching on modulation. Of course one can write the ABS logic in a way that it compares 4 wheels and then decides whether one wheel is facing a 'wrong' case (as far as humans are concerned), but for all practical purposes that logic would be 'wrong'. It is safer to make the ABS act than not to.

What we are missing in all the discussion is that failure of ABS, intended or not intended, is not going to impede braking. That, I think, is what @Sutripta started questioning. Your example inclusive.

But then, we are assuming danger when the human driver is doing nothing - hands off the wheel, not trying to steer to safety; feet off pedals, not braking hard enough ... So far I have seen only Volvo's City Safety system override / disregard the driver in the interest of safety - it brakes hard automatically when the distance to the next thing you can ram into is less than 6m away.

Last edited by DerAlte : 6th January 2011 at 11:15.
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Old 6th January 2011, 12:03   #30
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Default Re: ABS - How Failsafe

Quote:
Originally Posted by DerAlte View Post
...'false modulation' was not due to a component in the ABS system, it was due to a component in the 'brake' system of which ABS is a subsystem.
DerAlte: The specific component that triggers false modulation is a faulty wheel speed sensor - which IS a component of the ABS system.

Quote:
Originally Posted by DerAlte View Post
...the ABS ECU is checking. If more than a set value, it triggers brake modulation.
The ABS ECU knows that something is wrong, and turns on the ABS light to warn us of failure, when false modulation DOES occur. But the FM that is being performed substantially reduces braking efficiency.

Quote:
Originally Posted by DerAlte View Post
In any case, 'false modulation' (unless brakes were bad at all 4 wheels) will only cause 1 wheel to be acted on for a short duration.
Nope - false modulation happens to all channels despite the fact that only one sensor is triggering it. That's why the car feels like it's trying to brake on loose sand.

Quote:
Originally Posted by DerAlte View Post
...the ABS ECU is not an artificial intelligence system running on a Cray.
No. But as a user who can't stop his car just because the ECU is dumb, I'm going to curse the ABS system as a whole, not be forgiving to the ECU for being handicapped!

Quote:
Originally Posted by DerAlte View Post
To extend the above, what is the difference between wheel-lock due to wrong-spec brake case and when, however odd it may sound, the wheel goes into a deep pothole and is momentarily not able to rotate?
Wrongspec brake is one reason for FM, the other is a messed-up wheel speed sensor (more common cause).

The wheel going into a pothole is a single wheel, which stops being modulated on as soon as it's back on terra firma. When false modulation ends up braking-releasing-braking-releasing all 4 wheels, there's no limit to how long it'll happen. Ergo, the feeling of driving on sand with ABS.

Incidentally, actually driving on sand without ABS allows the wheels to dig in and get some braking - with ABS the feeling of being out of control is rather remarkable. But then you'd be aware of this.

Quote:
Originally Posted by DerAlte View Post
What we are missing in all the discussion is that failure of ABS, intended or not intended, is not going to impede braking. That, I think, is what @Sutripta started questioning. Your example inclusive.
That's precisely what I have been trying to say - false modulation is due to a failure of an ABS component, and it impedes braking. In such a situation, IF there was a switch to turn ABS OFF, one could brake normally.

Quote:
Originally Posted by DerAlte View Post
But then, we are assuming danger when the human driver is doing nothing - hands off the wheel, not trying to steer to safety; feet off pedals, not braking hard enough ...
Try the handbrake?? Downshift? Maybe turn off ignition to tell the ABS ECU to shut up? I dunno...
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