How exactly does the STi EBD/ABS work?

[skregg]

The STi has ABS and EBD (I forget what it stand for, E**** Braking Distribution) Anyway, many of you are familiar with the faults of ABS, will EBD correct some of ABS's bad behavior? Or will EBD supplement it in some other way? Will it be possible to pull the ABS fuse, but still benefit from the EBD?

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[ANZAC_1915]

What faults of ABS are you referring to?

I think the "sport tuned" ABS is pretty important, it means the ABS system has been calibrated with stiff suspension and sticky tires in mind.

Glenn

[skregg]

Originally posted by Glenn Wallace
What faults of ABS are you referring to?

Glenn

The fault where your braking power with ABS is only as good as the wheel with the worst traction. Non-ABS, 1 tire skids, the others don't. This typically occurs on loose road surfaces, ice & snow, and the like.

[RafalW]

Originally posted by skregg
The fault where your braking power with ABS is only as good as the wheel with the worst traction. Non-ABS, 1 tire skids, the others don't.

So called 4 channel ABS works independently on each wheel. So it lowers the preassure just on the one which is blocked.

This typically occurs on loose road surfaces, ice & snow, and the like.

Not really. Breaking on loose surfaces is more efficient with bloked wheel because in front it pushes some of this loose stuff slowing it down. In this situation ABS will just make your breaking harder.

[Jon [in CT]]

Here's a better starting point for discussion:
http://Jon.in.CT.home.att.net/2004Sti_EBD.pdf

[skregg]

After reading that, it sounds like the EBD is another way of saying "Improved ABS for cornering", it doesn't add any benefit to bumpy road breaking or straight ahead breaking on loose/slick road surfaces.

There is one spot on my daily commute right at a stop light that can provide an ABS induced heart attack. A little bump in the road 3 car lengths from the stop light. When a car stops for yellow light in front, and my tires bounce over the bump, the breaks shut right off as I head for the reat end of the stopping car. Luckily I don't follow too close, so no collision has occured. If I didn't have ABS, this would be a totally routine, no brainer stop light situation.

Sounds like my STi, whenever I get one, will still be operating without the fuse.

[Balls]

uh... i've probably never driven over that bump but it sounds more like if you didn't have abs... you'd lock the brakes and plow into (or just get closer to) the car in front of you.

[SubyTechMaster]

I was unable to open the PDF linked by Jon so I don't know if he addressed this point or not;

EBD (electronic brake distribution) was introduced on the 2003 Forester 2.5XS. It electronically distributes hydraulic force front/rear using the ABS HCU instead of a conventional Brake Proportioning Valve. This is all it is for. It makes this distribution more acurately and precisely than a proportioning valve can.

Sport Tuned ABS also means it works with the DCCD as well as the stiffer suspension.

[Jon [in CT]]

Originally posted by SubyTechMaster
I was unable to open the PDF linked by Jon ...

Sorry about that. It work's for me, of course. In case this problem is widespread, here's the text from that PDF page (there are also two diagrams):

Super Sports ABS with EBD

The ‘Brembo’ braking system also comes equipped with Super Sports ABS with Electronic Brake force Distribution (EBD). This improves ABS performance during cornering and reduces stopping distances with greater stability under heavy braking.

Super Sports ABS uses input from a lateral ‘G’ sensor to individually control brake pressures more accurately when ABS operates during hard cornering under brakes, leading to reduced understeer.

Normally ABS would jointly control both rear brakes to the same braking force when the inside wheel loses traction, with a resultant increase in stopping distance and cornering understeer. Under these same conditions Super Sports ABS controls rear braking force individually leading to a reduction in stopping distance and cornering understeer.

EBD due to electronic control more accurately regulates brake force distribution between front & rear wheels to the ideal level, thus improving stopping distances and stability.

Conventional braking systems rely on a mechanical proportioning valve to limit the braking force at the rear wheels, to reduce the possibility of rear wheel lock under heavy braking due to weight transfer. A mechanical proportioning valve however restricts rear-braking force to a level well below the ideal limit, requiring the front brakes to take more of the braking load. This leads to increased understeer and under utilisation of the rear brakes.

[MrAWD]

Originally posted by skregg
Sounds like my STi, whenever I get one, will still be operating without the fuse.

This is just another one of the common misunderstanding about the ABS and how it can be beaten by the skilled driver. Very few people can really do that today and it can be done at the very controlled environment and dry grippy surface. The thing is to do a successful braking at the heat of the race, which is far from being ideal. You, my friend, seem to be far from the super driver and you will be benefiting in keeping that fuse where it should be (in a fuse box working as hard as it should be)!


Fedja
__________________
95 AWD #34 SM
"Let boost be with you...
...and bring some timing too!"
http://www.geocities.com/esp_er

[briank]

Originally posted by MrAWD

This is just another one of the common misunderstanding about the ABS and how it can be beaten by the skilled driver. Very few people can really do that ...

Fedja,
Subaru's implementation of ABS on the current WRX has some serious flaws. You can find posts about it if you do a search.
Here's a situation where the ABS really pisses people off:
1) The driver applies brake pressure.
2) The car slows down as expected.
3) One of the tires hits a pot hole in the road. Traction is lost momentarilly and the wheel locks.
4) ABS detects this and reduces brake pressue until traction is regained.
5) A half a second later, the suspension has settled and the road is smooth, but the ABS still is applying reduced brake pressure!
6) The car will continue to limit brake pressure indefinitely, even if the driver presses on the brake pedal harder! The only way to return normal brake pressure is to take you foot off the brake and repress the brake pedal.

Basically with the WRX ABS you still have to pump your brakes in adverse conditions.

I've driven two fords and a chevy with ABS, and have never experienced this loss in braking power under the same conditions. Basically I felt the brake pedal vibrate as the ABS system "pumped" the brakes for me, but the instant maximum traction could be regained, the brakes returned to normal. So to me, the Subaru system seems flawed.

This is probably why skregg has removed his ABS fuse like many other WRX drivers.

-BrianK

[MrAWD]

Originally posted by briank
...
5) A half a second later, the suspension has settled and the road is smooth, but the ABS still is applying reduced brake pressure!
6) The car will continue to limit brake pressure indefinitely, even if the driver presses on the brake pedal harder! The only way to return normal brake pressure is to take you foot off the brake and repress the brake pedal.

This is probably why skregg has removed his ABS fuse like many other WRX drivers.

I didn't know about this problem that WRX has and it sounds pretty bad to me. This might be a problem for all the guys out there with better brake pads. If they press the brake pedal too quick, wheels will exceed to available traction before all of the weights move forward and they might stay at that lover braking threshold even tough with more weight they could be pushed even harder.

If I would have a WRX, I would complain about this all the way to the top!


Fedja
__________________
95 AWD #34 SM
"Let boost be with you...
...and bring some timing too!"
http://www.geocities.com/esp_er

[SubyTechMaster]

To those concerned with the aformentioned "WRX ABS Problem", this is an isolated problem that some of the HCUs had and should not be considered normal operation. I say it is isolated and someone will pipe-up and say "look at all the people here who had the problem". If 100 cars had the problem out of 20,000 it is isolated.
Under normal operation, when the ABS senses a wheel is about to lock-up, it relieves pressure to that wheel until lock-up is no longer imminent, holds pressure, and then restores full pressure to the wheel. This procedure takes approx. 1/10 second and will occur as much as 10 times/second (think you can pump the pedal that fast?). The HCU modulates the pressure ONLY to the wheel that is loosing traction (you can't do that by pumping the pedal).
If you think Subaru designed the ABS system, take a look at the label on the HCU. It is designed and built by Bosch, it is called ABS 5.3i and is the same system used in many German products.

[Balls]

6) The car will continue to limit brake pressure indefinitely, even if the driver presses on the brake pedal harder! The only way to return normal brake pressure is to take you foot off the brake and repress the brake pedal.

I HIGHLY doubt this.... the reduction in pressure happens so fast that it's better described as a pulsing effect. Had it occurred to anyone that the ABS is still active BECAUSE you're applying more brakes?

[Jon [in CT]]

Originally posted by SubyTechMaster
To those concerned with the aformentioned "WRX ABS Problem", this is an isolated problem that some of the HCUs had and should not be considered normal operation. I say it is isolated and someone will pipe-up and say "look at all the people here who had the problem". If 100 cars had the problem out of 20,000 it is isolated.
Under normal operation, when the ABS senses a wheel is about to lock-up, it relieves pressure to that wheel until lock-up is no longer imminent, holds pressure, and then restores full pressure to the wheel. This procedure takes approx. 1/10 second and will occur as much as 10 times/second (think you can pump the pedal that fast?). The HCU modulates the pressure ONLY to the wheel that is loosing traction (you can't do that by pumping the pedal).
If you think Subaru designed the ABS system, take a look at the label on the HCU. It is designed and built by Bosch, it is called ABS 5.3i and is the same system used in many German products.

I have to confess that my WRX ABS now works fine, but only since my ABSCM&H/U (aka ABS Control Module and Hydraulic Control Unit) was replaced under warranty.

[RafalW]

Originally posted by skregg
Sounds like my STi, whenever I get one, will still be operating without the fuse.

It might be harder then you think. In most cars with EBD there is no rear corrector when ABS is disabled. I heard it's not easy to disable ABS in EVO VII and STi might have the same problem.

And I know what you mean cause ABS in my WRX was pissing me off many times.

[briank]

Originally posted by Jon [in CT]
I have to confess that my WRX ABS now works fine, but only since my ABSCM&H/U (aka ABS Control Module and Hydraulic Control Unit) was replaced under warranty.

Oh wow! There's a fix? I guess I should have done a search myself. Only 400 miles left on the warranty, I better make an appointment quick.

Balls,
Come drive my car within the next week, and I can demonstrate for you what happens. Jon [in CT] can vouch for me I'm sure. The problem with the ABS happens exactly as I described it. Like I said, I've driven ABS cars before and know how they should work. I got my car March 2001 (first one at the dealer), so if there was an initial problem with the ABSC&H/U then I've got it.

-BrianK

[emulous]

Originally posted by briank



I've driven two fords and a chevy with ABS, and have never experienced this loss in braking power under the same conditions. Basically I felt the brake pedal vibrate as the ABS system "pumped" the brakes for me, but the instant maximum traction could be regained, the brakes returned to normal. So to me, the Subaru system seems flawed.

This is probably why skregg has removed his ABS fuse like many other WRX drivers.

-BrianK

My Ford SVT Focus has the same problem with the abs, funny though, my Ranger does not do it on the same roads.

[Balls]

okay... threshold vs abs is one thing, threshold v defective abs.... hahaha
Better get that fixed...

Needless to say... this is quite disappointing... all I have to say is that for 32k+ the sti better stop REALLY fast.

[ciper]

I plan to make some of you angry, but above my post you will see even more people who comment on something they dont know about. First you should realize has existed on other subaru besides the wrx. The fix that is mentioned may address a problem but not the problem many of us have complained about so often. I know users on this forum who dont even reply anymore, they have tried to explain it and LOOSERS come and tell them they dont know how to drive or some other stupid comment.

Here is one of the most recent threads.

http://forums.nasioc.com/forums/show...hreadid=310223

[Balls]

You don't know how to drive.

[Balls]

haha.... I'm just joking.....
Listen, the only experience with abs i've had was in my Integra Type R. Maybe the abs is better in the itr than in the wrx... but it seems more likely to me that either you're going too fast or the abs is busted...

[skregg]

Just for the record, I have experienced the tire in air while braking ABS problem on my my 99 Ford F250. This is not a just a "WRX only" problem. It is an inherent fault of ABS.

A wheel in the air will stop turning under moderate brake pressure almost immediately. The ABS will detect that the car is still moving forward and notice that this wheel in the air is no longer spinning. The ABS computes a non-spinning tire as "skidding" and the ABS kicks in. Newer ABS units make corrections so quickly, that it pumps down to almost no brake pressure in the split second before the tire regains contact with the road. Now the vehicle continues forward at this very low break pressure until the driver either manually pumps the breaks or the vehicle eventually stops.

As long as the break pedal is held down, the very weak breaking force will continue to be applied, as the ABS has determined that this is the "maximum force that can be applied without causing the wheel to skid".

The only way to completely eliminate this is to have individual ABS pumps for each wheel. I don't know if there is a car on the road with this feature. 4 channel ABS, I believe simply detects wheels individually, but cannot apply braking force individually.

I was hoping that the EBD would somehow correct this problem.

[skregg]

I am correcting my mistaken comment on 4 channel ABS here. 4 channel ABS is supposed to pump each wheel individually.

Unfortunately, this doesn't seem to help the situation where wheels hit a bump and go airborn momentarily, but should solve the 2 wheels on ice 2 wheels on pavement issue. The EBD, from what I read, treats rear wheels as a set, and possibly front as well.

[ANZAC_1915]

Unfortunately, this doesn't seem to help the situation where wheels hit a bump and go airborn momentarily,

Did you not read or understand anything of what was posted or referenced above?

The "sport tuned" aspect of the new system should take into account the suspension and tire combo and be much better at dealing with bumps.

Just for the record, I have experienced the tire in air while braking ABS problem on my my 99 Ford F250. This is not a just a "WRX only" problem. It is an inherent fault of ABS.

It is not an inherent fault of ABS. It is a software tuning issue. Wheels won't stop the car in the air so it doesn't matter much what the ABS does then, once the wheel lands, it depends on the suspension and tire grip as to how quickly it spins up. There is some threshold (in terms of the wheel speed being below the other wheels) that the ABS will still actuate.

4 channel ABS is supposed to pump each wheel individually.

I don't think pump adequately describes what ABS does. There is a valve block with four valves (one for each wheel). I believe the solenoids on some systems (haven't looked too closely at the WRX) can basically go open, close, recycle.

I know users on this forum who dont even reply anymore, they have tried to explain it and LOOSERS come and tell them they dont know how to drive or some other stupid comment.

For some reason Americans have problems spelling "lose" and "loose". Loose is the opposite of tight, lose is the opposite of win.

Glenn