Difference between EBD and ABS

[Komodo86]

I have been doing a bit of reading into electronic brake force distribution, as I am interested in retrofitting it to my autocross car in an attempt to improve my performance under trailbraking. It would seem that the only physical difference between an EBD system and an regular 4 channel ABS system (rear brake size excepted) is that there is no proportioning valve in the EBD system, as the computer takes this job by monitoring the wheel slip and varying the brake pressure accordingly through the ABS modulator.

Now clearly there must be some different algorithms at play in the progamming, however on the face of it, it would appear that simply removing the proportioning valve from my system would force the ABS to crudely perform the duties of an EBD system. The increased rear brake torque would trigger the ABS on the rear wheels keeping them right on the point of lockup just like the EBD, where the stock system is heavily restricted through the prop valve and so would never normally use the system in this way.

Can anyone enlighten me on what the differences would be between this DIY EBD system and a proper factory fit system?

 

[GregLocock]

Should work. I've only ever seen EBD as an acronym when ESC came in, but it is a separate idea.

The difference between ABS and EBD is that ABS only functions when a wheel is about to skid, whereas EBD also operates at lower braking forces. As a ridiculous example a very bad brake engineer might design the left brake as twice the size of the right brake. So the car would tend to turn left under braking. ABS would not affect this until the left wheel was on the point of locking up, when its pressure would be reduced. EBD could compensate throughout the range of braking forces. However the control side is so bound up with ESC that I can't really suggest how to do one without the other.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[Komodo86]

I see, so where ABS would only be triggered by a lockup, EBD would be monitoring the wheel speeds and compensating before that point. It does sound like a less intrusive system operating in that manner.

I guess my main concern would be a constant ABS judder on the pedal, I'm gathering an EBD car does not have this.

It may be possible for me to graft in the control unit from another model with EBD, however this would be subject to me finding the wiring diagrams, which while easily available for my car are proving elusive for the donor car.

 

[murpia]

Greg,

Would I be right in thinking that EBD operates in an open-loop fashion, by simply reducing brake pressure in response to mapped inputs, while ABS & ESC are closed-loop in their response?

Thanks, Ian

 

[GregLocock]

That /sounds/ right, but I've never really seen EBD without ESC. I suspect they run a very simple model that looks at SWA and speed and acceleration and the wheelspeeds, to decide if one wheel is misbehaving. The trouble is that the SWA sensor is the expensive one, once you add a $2 yaw gyro you have all the hardware you need for ESC.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Komodo86]

What is an SWA sensor?

(I suspect the answer to be glaringly obvious, but it has baffled me so far.)

 

[GregLocock]

Steering wheel angle. SWT= SW torque. yaw sensor senses yaw velocity , irritatingly.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[murpia]

That /sounds/ right, but I've never really seen EBD without ESC.

Well, I had an old Ford built 1998 that claimed ABS + EBD but was way before the ESC era.

Regards, Ian

 

[Komodo86]

Greg - So simple, don't know why I couldn't guess that one.

Honda Accords from 1997 onwards use EBD, while I am not sure on later models, but I believe the <2001 Type R models use EBD exclusively without ESC. It is this system which I am attempting to replicate in my Civic.

 

[GregLocock]

In that case I'd guess they more or less mimic a passive system, ie just ratio the pressures front to rear, up until slip occurs, when the ABS would intervene as usual. If they have a rear axle load sensor then it would work well enough.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Komodo86]

The news release from Honda on this particular system can be found here:

http://world.honda.com/news/1997/c970919d.html

No load sensor so far as I can tell, it simply uses the regular wheel speed sensors to detect lockup and uses the ABS to vary the pressure accordingly in place of the mechanical valve.

This is what has got me thinking that simply removing the mechanical valve in my system might force the computer to act in a crudely similar way?