tozoM8

US 97-99 4.2 quattro don't have EDL.

ThaboTheWuff

Apparently, wuffman knows jack Shyte about EDL, thanks you silverDtoo for pointing this out in a most gracious Souther hospitality esque manner. My understanding of traction control, I never had it in a car cos I've always has older Audi beaters, is that it'll cut the throttle rather than let the wheels spin so perhaps EDL is an older implementation of this. The FWD Audis do have a ASR light, look at the A8 manual it's in there. Would be know if the system were applying the brake or the diffs were intervening - not sure.

SH-Awd from that appliance maker Honda is actually better than the standard Quattro system right now (sans the sport diffed S4 and upcoming S7 s6) but well'll all be getting vectoring AWD systems in the near future. See our beloved Quattro fail - http://www.youtube.com/watch?v=FJZxVefta68 - makes perfect sense and sure the Q7 is heaver - outer wheels are only getting 50% of power per axle and the Acura is getting more. The new systems will have vectoring on both axels, can't want till only one wheel has traction and it gets 100% of the power - round and round we go ......

As for my I want to retrofit my A8 with stability control, should be quite simple, a little Arduino $30, some messy code, an accelerometer $30 and a way to pluse each caliper individually with a little blip of braking

troverman

Interesting video. However, it'd be extremely rare for a driver to encounter this type of situation. To design an AWD system for this would be crazy. I much prefer a design like a Mercedes G-Class. Full-time 4WD with open differentials and always active traction control with brake and throttle control. If this situation were ever encountered, the driver could simply engage the front, center, and rear diff locks and arrive at the top. Cheaper and simpler, and the ultimate at maximizing traction. Obviously no handling advantage like torque vectoring diffs.

silverd2

I have no hands-on knowledge of the "first try" 97-99 D2's...just reading the standard features here:

https://www.audiworld.com/model/a8/99/a8.shtml

AudiWorld couldn't be wrong could they?

silverd2

EDL is still used and is much more effective than just throttle intervention, which is useless alone and only kicks in when other systems are not enough.

Most (all?...certainly D2's) Audi Quattro's have regular open diffs at each end (torque biasing in the middle). EDL applies measured ABS braking to the spinning wheel. It is the nature of an open diff to transfer MUCH more power (%?) to the other side when one side is held in place, rather than spinning...while that side is allowed to spin, nothing goes to the other side...that's how a standard diff works. Some scoff at EDL (since it's not a true mechanical lock-up diff), but it works quite effectively.

This same "antique" EDL system is exactly the same principle and system that applies one brake at a time for stability corrections in ESP.

An older mechanical lock-up diff can only do 50/50%...the center torsen diff in existing Quattros, can bias 65/35% (I think that;s the %...certainly way better than 50/50 lock up) front to rear as needed, mechanically.

BY the way, Audi does have a new design diff that can bias 85% to one (or front to rear) side when needed...not sure what this is found in (optional or in use yet? ...not sure).

troverman

I will agree that a torque-biasing center differential is generally superior to a 50-50 lock. On flat ground, in vehicles with approximately equal weight distribution, a 50-50 lock will accelerate just as quickly as a vehicle with a torque-biasing center diff. However, the advantage goes to the biasing center diff as soon as the vehicle is on an incline. Weight transfer to the rear when the vehicle is moving up an incline causes some of the torque to be wasted in the 50-50 lockup vehicle as the front wheels scrabble a bit for grip. Because there is actually more traction available then usual over the rear wheels in this situation, the biasing diff can actually reallocate the torque, causing the vehicle to accelerate faster up the slope.

Handling is another advantage for the bias diff. Being able to "unload" the front wheels of an AWD vehicle by sending more torque to the rear causes less understeer and thus better handling. This is why many AWD vehicles are set by default to a 35-65 biasing ratio from the factory.

The problem with with the torque biasing diffs is that they generally cannot vary the torque past 50% to the front wheels. Typically, they can do a 50-50 split or vary all the way down to 10-90 front to rear. However, usually they cannot vary in the reverse direction...i.e. move from a 50-50 to a 90-10, front to rear. And many that are set by default at the factory to a 40-60 or 35-65 front to rear cannot ever apply more torque than that to the front wheels. This leaves them at a disadvantage for traction over those that can go 50-50.

Now for traction control. I have never seen a system that "solely" uses throttle intervention. The early systems (late 80's Benzes and Bimmers) used brake intervention on the rear wheels only. When e-throttle started to be used, that's when the throttle intervention started. It 'can' be effective. Obviously you'll take off better with less wheelspin. Of course, you could just use less throttle! Many cars of the mid late 90's had a "winter" button on the transmission that caused the vehicle to start off in 2nd gear, limiting torque to the wheels. Audi's needed no such thing since they had twice the available traction to get started vs a FWD or RWD vehicle.

Some manufacturer's started thinking they could use traction control in place of mechanical differential slip control methods. The idea was to have open front center and rear diffs, and use a sophisticated TC system that could operate in two modes simultaneously. First, the system would act as a center diff torque bias. If wheels on one 'axle' turned faster than wheels on the other, the TC would brake that the wheels together on that axle until the opposite axle engaged to the desired bias rate, be it 50% or other amount. Simultaneously, if individual wheels slipped than individual brakes would be applied slightly more than the rate of the axle brakes. Theoretically this would move the vehicle forward even if only one wheel had traction. And there was no problem with wheels off the ground (vs Audi's Torsen setup which will send all the power to just the one wheel off the ground...not that Audi's are finding their wheels off the ground too often!) I know that the late 90's to mid 2000's 4-matic systems used this type of traction control system and 1999-2003 Land Rover Discovery II's used this as well.

From first-hand experience I can tell you this doesn't work that well. Brakes are used up much more quickly, the system shuts down after repeated hard use due to overheating the brakes, and it is purely a reactive system. Another disadvantage is the need for heavier-duty axle and diff components. When a traction control brake pulse is applied, its like a shock to the axle shaft and diff.

But note, the torsen in the quattro is a reactive system as well. (albeit a very good one) It can only bias torque after traction is lost. A 50-50 mechanical lock can be applied before slippage occurs. Of course, if there is rapidly varying traction surfaces, a 50-50 lock system would be hard to use locked up.

Anyway, just my two cents. I think the quattro system is very good, but still has its drawbacks. I'm disappointed the '97 to '99 A8's don't seem to have EDL (TC).

ThaboTheWuff

Hmm. lots of snow and ice driving experience here and I too have never experienced anything that seems like traction control. If I'm in deep snow and hit the throttle all the wheels just spin, snow tires and all. The cars with ESP had true traction control I believe.