ABS discussion
01-09-2003, 10:33 PM
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ABS discussion
There was an ABS discussion on a non-Porsche forum. I thought I'd share my reply to a writer that disconnected the ABS from his truck because he thought he could do it better ... yes there are those people still out there.
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Perhaps if everyone understood how ABS works then they would know how to use it and feel safer using it.
People panic if they don't understand the feel of the brake pedal during ABS operation, often they let off pressure and pump the brakes. I suggest going to an open lot when it is damp or snowy and use the ABS to get the feel. Keep doing it until it feels natural. It is very hard to convince your wife or sig-other to do this, they just don't like it. However, unless they learn they may NOT use ABS to it full efficiency. IMHO this is the major problem that people have with ABS. Because of improper ABS usage, Mercedes and other cars now have a system that senses how fast you stomp on the brake, and the system senses a panic stop it then applies maximum braking even if the driver doesn't. This ensures that ABS is used.
ABS has a valve assembly for each brake circuit (it could be each wheel for a 4-channel system or for each front wheel and the rears combined for a 3-channel system). NOTE: 928s use a 3-
channel system, so the rear wheels brake together.
The valve has three settings
- pressure-buildup
The braking circuit is open and braking operates just as if there were NO ABS, i.e. the operator foot pressure determines how much pressure is on the brakes
- pressure-hold
The controller senses that if there were more pressure, wheel lock would occur so no further pressure is allowed to the brake cylinder, however pressure is held at the current level.
- pressure-reduction
The controller senses that the wheel is about to lock or has locked and releases pressure from that braking circuit. Once sufficient pressure has been discharged from the wheel-brake cylinder, the system returns to either "pressure-hold" or "pressure-buildup"
Other systems:
- Return pump: as pressure is released from wheel-brake cylinders, the return pump moves the brake fluid through the accumulator back into the master cylinder.
- Accumulator: acts to temporarily absorb the brake fluid flow surges that occur as brake fluid is discharged during the pressure release phase. [This is where the strange pulsing feeling in the pedal comes form from during ABS usage. This shows ABS is working ... KEEP YOUR FOOT IN IT.]
With ABS, there is never MORE brake pressure than what the driver creates by pushing on the brake pedal. So, if you DON'T push hard enough to engage ABS, you are in the "pressure-buildup" mode but are not getting maximum braking effect.
If you unplug the ABS unit, then you are only operating in the "pressure-buildup" stage ... since the valve is open pressure also freely releases, so you have braking with no ABS.
What about large tires???? This is a good question. It is likely that Ford and the ABS manufacturers don't do engineering testing on trucks that are raised high in the air and have much larger tires. Therefore ABS may not work properly. I don't know this for a fact, and if you asked Ford they'd probably just say "Use standard size tires." So, for those who feel the need to venture into non-standard configurations you go at your own risk.
How do I know this stuff? I interfaced with Bosch during their development of traction control (the next step beyond ABS). I drove in cars on their test track. If you try to stop on a split-mu surface (slippery on one side and traction on the other) you will spin very quickly. This doesn't happen with ABS ... it provides a very graphic illustration of what ABS can and does do for you.
Other than drivers NOT pressing as hard as possible on the brake so ABS doesn't work as intended, there is a problem where drivers feel invincible and drive too fast for the road conditions. If there is no traction, you can't stop. ABS can't change the laws of physics; it just stacks the deck in your favor. Is it perfect, no. Is it better than 98% of drivers in most situations, I think so. On a split-mu surface I'd say it is better than 100% of drivers because you aren't given the ability to change braking force on each side of the car.
I hope this helps! Remember, just MASH the brake pedal as hard as possible and HOLD IT DOWN!!!!!
---------------------
Perhaps if everyone understood how ABS works then they would know how to use it and feel safer using it.
People panic if they don't understand the feel of the brake pedal during ABS operation, often they let off pressure and pump the brakes. I suggest going to an open lot when it is damp or snowy and use the ABS to get the feel. Keep doing it until it feels natural. It is very hard to convince your wife or sig-other to do this, they just don't like it. However, unless they learn they may NOT use ABS to it full efficiency. IMHO this is the major problem that people have with ABS. Because of improper ABS usage, Mercedes and other cars now have a system that senses how fast you stomp on the brake, and the system senses a panic stop it then applies maximum braking even if the driver doesn't. This ensures that ABS is used.
ABS has a valve assembly for each brake circuit (it could be each wheel for a 4-channel system or for each front wheel and the rears combined for a 3-channel system). NOTE: 928s use a 3-
channel system, so the rear wheels brake together.
The valve has three settings
- pressure-buildup
The braking circuit is open and braking operates just as if there were NO ABS, i.e. the operator foot pressure determines how much pressure is on the brakes
- pressure-hold
The controller senses that if there were more pressure, wheel lock would occur so no further pressure is allowed to the brake cylinder, however pressure is held at the current level.
- pressure-reduction
The controller senses that the wheel is about to lock or has locked and releases pressure from that braking circuit. Once sufficient pressure has been discharged from the wheel-brake cylinder, the system returns to either "pressure-hold" or "pressure-buildup"
Other systems:
- Return pump: as pressure is released from wheel-brake cylinders, the return pump moves the brake fluid through the accumulator back into the master cylinder.
- Accumulator: acts to temporarily absorb the brake fluid flow surges that occur as brake fluid is discharged during the pressure release phase. [This is where the strange pulsing feeling in the pedal comes form from during ABS usage. This shows ABS is working ... KEEP YOUR FOOT IN IT.]
With ABS, there is never MORE brake pressure than what the driver creates by pushing on the brake pedal. So, if you DON'T push hard enough to engage ABS, you are in the "pressure-buildup" mode but are not getting maximum braking effect.
If you unplug the ABS unit, then you are only operating in the "pressure-buildup" stage ... since the valve is open pressure also freely releases, so you have braking with no ABS.
What about large tires???? This is a good question. It is likely that Ford and the ABS manufacturers don't do engineering testing on trucks that are raised high in the air and have much larger tires. Therefore ABS may not work properly. I don't know this for a fact, and if you asked Ford they'd probably just say "Use standard size tires." So, for those who feel the need to venture into non-standard configurations you go at your own risk.
How do I know this stuff? I interfaced with Bosch during their development of traction control (the next step beyond ABS). I drove in cars on their test track. If you try to stop on a split-mu surface (slippery on one side and traction on the other) you will spin very quickly. This doesn't happen with ABS ... it provides a very graphic illustration of what ABS can and does do for you.
Other than drivers NOT pressing as hard as possible on the brake so ABS doesn't work as intended, there is a problem where drivers feel invincible and drive too fast for the road conditions. If there is no traction, you can't stop. ABS can't change the laws of physics; it just stacks the deck in your favor. Is it perfect, no. Is it better than 98% of drivers in most situations, I think so. On a split-mu surface I'd say it is better than 100% of drivers because you aren't given the ability to change braking force on each side of the car.
I hope this helps! Remember, just MASH the brake pedal as hard as possible and HOLD IT DOWN!!!!!
01-10-2003, 03:17 AM
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Good info! Very kewl post!
However:
I'm trying to decide which will take longer: Me changing out the left front ABS sensor on my '85, or deleting from my mind the reflex to reach for the central warning system cancel button whenever I've just started my car and have rolled past 10 mph-
Normy!
'85 S2 5 Speed
However:
I'm trying to decide which will take longer: Me changing out the left front ABS sensor on my '85, or deleting from my mind the reflex to reach for the central warning system cancel button whenever I've just started my car and have rolled past 10 mph-
Normy!
'85 S2 5 Speed
01-10-2003, 05:32 AM
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Awesome information! We had this discussion back in Germany in the late 80ies. Lots of press coverage, including detailed feature tests and comparisons. But there are still people who don't get it. Same story as using the safety belt...
In case you wonder, why there are so few original Audi Quattro cars left - they did not have ABS. People did not realize that accelerating faster on ice does not mean you can stop faster.
In case you wonder, why there are so few original Audi Quattro cars left - they did not have ABS. People did not realize that accelerating faster on ice does not mean you can stop faster.
01-10-2003, 02:08 PM
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The most important thing is that you must use your ability to steer during ABS engagement; try to avoid acting like the deer with the headlights in its eyes! People tend to stare at the back of the car in front of them & plow right into it. If you are in a panic situation and the ABS is doing its job, do yours & steer to safety.
Nicole, don't fool yourself; ABS won't stop you that much quicker on slick ice! Agreed, the advent of 4WD probably contributed to a lot of early model "incidents" since people would more readily drive beyond their means (and they still do today). But with or without ABS, slick ice will getcha.
Nicole, don't fool yourself; ABS won't stop you that much quicker on slick ice! Agreed, the advent of 4WD probably contributed to a lot of early model "incidents" since people would more readily drive beyond their means (and they still do today). But with or without ABS, slick ice will getcha.
01-10-2003, 04:02 PM
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Question then. OT as it's not relevent to 928s, but...
On some first round ABS instilations, such as on my and my Dad's old pick up, there were ABS sencors on the rear wheels, but no ABS sencors on the frought wheel. You stop on the brake, lock the frount wheels and you can basicly turn the frount wheels stop to stop. The truck never turns, but goes almost perfectly straight.
I know, I did it, just to see what it was like. Now I wasn't stupid enough to turn the steering wheel stop to stop, I get exactly 0 control from it.
With that set up, what do you do? If you act like it's a traditional system, the rear wheels don't brake fully. If you act like it's a ABS system, you get no control, and the frount wheels don't brake very well.
I always figured just act like it's a traditional system, and use the most important wheels, the frount ones. That away you won't lose control.
I was seriously thinking about disableing the ABS, but sold it to my brother before I got to it.
On some first round ABS instilations, such as on my and my Dad's old pick up, there were ABS sencors on the rear wheels, but no ABS sencors on the frought wheel. You stop on the brake, lock the frount wheels and you can basicly turn the frount wheels stop to stop. The truck never turns, but goes almost perfectly straight.
I know, I did it, just to see what it was like. Now I wasn't stupid enough to turn the steering wheel stop to stop, I get exactly 0 control from it.
With that set up, what do you do? If you act like it's a traditional system, the rear wheels don't brake fully. If you act like it's a ABS system, you get no control, and the frount wheels don't brake very well.
I always figured just act like it's a traditional system, and use the most important wheels, the frount ones. That away you won't lose control.
I was seriously thinking about disableing the ABS, but sold it to my brother before I got to it.
01-10-2003, 05:22 PM
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U do what you did; trete it lyke a tradisionl systum & dont wurry about the reer breaks. They dont do muck breaking anyway & U jus dont want themm to lokup.
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01-10-2003, 09:13 PM
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Old & New, be nice (that was funny though).
Viribus, c'mon man - 'frought' wheels?
Rennlist installed the spell check feature at considerable expense, but after this I'm now thinkin' that you are a master of the written word who is having a joke on us.
Viribus, c'mon man - 'frought' wheels?
Rennlist installed the spell check feature at considerable expense, but after this I'm now thinkin' that you are a master of the written word who is having a joke on us.
01-10-2003, 11:37 PM
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Old & New,
That is the funniest thing I have seen on the web except for this Lexus chat room thread:
<a href="http://www.is300.net/forum/viewtopic.php?t=13317178" target="_blank">http://www.is300.net/forum/viewtopic.php?t=13317178</a>
That is the funniest thing I have seen on the web except for this Lexus chat room thread:
<a href="http://www.is300.net/forum/viewtopic.php?t=13317178" target="_blank">http://www.is300.net/forum/viewtopic.php?t=13317178</a>
01-12-2003, 11:57 AM
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I was afraid he might not be able to read it, otherwise. Sorry, Viribus <img src="http://www.is300.net/forum/images/smiles/icon_redface.gif" alt=" - " />
Actually, it was sort of liberating...
Actually, it was sort of liberating...