-6.0 Degrees Celcius this morning. Nice big ice patches on the roads around my house. Time to test Quattro!! I positioned the car so that the driver’s side front and rear wheels were on pure smooth ice, and the other 2 wheels were on pavement. Stopped the car. The revved it dumped the clutch (weelll not really “dump it”, but pretty hard). The car JUST GOES. You can feel the antilock kick in (sorry “EDL”) and the car just hooks up. Cool!!<p>Now some questions.<br>I understand that the torsen is the center diff, with the front and rear axles being open diffs, and the slip controlled by the ABS system. This would indicate to me that the front and rear are more of an inclement weather thing, rather than a performance thing. I.E performance u would want a limited slip diff.<p>Why wasn’t the quattro setup with either a limited slip or torsen in the rear? I could see why maybe in corners u might not want limited slip up front, but why not Torsen diff?<p>It seems that some of the marketing blurbs that suggest the quattro is torque sensing are only partially true, since it is only the center diff that is torque sensing. The front and rear diffs are speed sensing through ABS sensors.<p>Comments?<p>1996 a4 2.8 qm<br>

I also thought that ABS Isn't used at all to regulate power (quattro only). Am I Correct?

i posted on this before and got "Schooled":<p>quatro uses:<br>front axle diff: open with ABS to brake slipping wheel.<br>center diff: torsen torque sensing diff (gleason patent?)<br>rear axle diff: open with ABS to brake slipping wheel.<p><br>1996 a4 2.8 qm

Using ABS to brake a slipping wheel is what traction control is all about. I was led to believe that quattro's did not do this.<p>If the front and rear wheels had ABS sensing slip and braking accordingly, then how is the TorSen supposed to sense torque? That's supposed to be TorSens greatest strength -- that it senses torque and sends more power to the wheels that can use it. If the ABS system is braking wheels to stop spin, then I think the TorSen would mistakenly think that there was not a wheel-spin condition happening, and might think that there is no slip occurring.<p>I think someone has two competing technologies confused and merged here. The ABS traction control and a TorSen work in such different ways that I think they don't make sense to put them together. I hope I'm right about this, otherwise someone is going to have to clear up my confusion.<p>Drew S.<br>

there is only one diff on the quattro that is torsen. check your spec sheet or product lit, or the links at the beginning of this forum!!!<p>also remeber that center diff proportions torque between front and rear axle. <p>and i quote:<br>"Quattro IV - permanently engaged all-wheel drive system with Torsen center differnential and Electronic Differential Lock (EDL)"<p>i was pretty grumpy when i discovered this myself. hence the post.<p>further comments invited<p>1996 a4 2.8 qm<br>

My Z3 with traction control uses ABS to control wheel spin. I experienced this in sand/gravel on the road one time. The car basically came to a stop the more I tried to accelerate. However, the same test with quattro results in almost immediate traction and instant acceleration, not braking like the BMW traction control system. I'm not sure how it works, but it doesn't use ABS to control wheel spin. <p>CraigB

EDL is described in A4 service training manual WSP-521-222-00. It states that:<p>"Audi A4's use a traction control system called EDL. EDL stands for electronic differential lock. The EDL system works in conjuction with the anti-lock brake system.<p>If one or more of the driven wheels begin to spin, such as on a low grip road surface, EDL counteracts this by applying the brake to the spinning wheel. This ensures that the remaining driven wheels transmit as much available engine power as possible.<p>The EDL system is activated as soon as wheel spin is detected and will continue to operate as long as wheel spiin is detected up to 25 mph. The EDL system will deactivate if the brake pedal is depressed."

I think that the FAQ that you read is incorrect. If the Quattro uses ABS to prevent Wheel spin then how come I'm able to spin all four wheels? In the Snow Last year I was in a Parking lot Doing Donuts (Flame me), all four wheels were spinning. Sometimes In the rain while making a slow turn in first gear, I'll Press the Clutch in to free up some revs, After the revs build a little I'll then release the clutch, After that, all Four wheels spin and the rear end kicks out. It's the Best. I wouldn't advice anyone to do this. You have to be a little crazy and a Semi-Decent driver. Can someone settle this? I'll believe Information from Audi.<p>Later fellow A4 People >>Tony<p><p>

The EDL (electronic differencial lock) uses the ABS sensors to detect wheel spin. It does *not* use the ABS brakes to brake that wheel. Instead it *locks* the other wheel, meaning it sends *all* of available torque to the non spinning wheel. This way if both wheels on the EDL start to slip the middle torsen diff can take over.<br>--Leszek

The FAQ is confusing and/or confused. First, yes, it does mention EDL on each axle of quattro. But, at one point there is the statement:<p><tt><br>"At some speed differential (approximately 25 mph / 40 km/h), the highly sophisticated fifth-generation ABS/EBV actually pulsates the brake momentarily at the spinning wheel, effectively transferring the torque through the open differential to the wheel with more traction."<br></tt><p>Then, in the very next sentence, it says:<p><tt><br>"This system is effective, but due to the stress that it would create on the braking system, it is only used up to speeds of about 25 mph / 40km/h."<br></tt><p>The first statement seems to imply that this action starts at 25 MPH. The second statement seems to imply that this action starts at 0 MPH, and is disengaged above 25 MPH. So which is it?<p>I am not an engineer, but the following would make sense to me. How about if you use the ABS sensors to detect wheel spin, and if detected, send a signal to the EDL to lock the differential. For instance, if the left front wheel starts slipping, the ABS detects it, then signals the EDL to lock the differential, and now the front diff is locked and the torque can be transferred to the right front wheel rather than wasted spinning the left front wheel. I wouldn't be surprised if this is how the ABS/EDL works on our quattros. I also wouldn't be surprised if I were wrong. ;-)<p>Drew S.<br>

Leszek,<p>The brakes (ABS) are used to "lock" the other wheel. There is no piece of hardware called EDL. EDL is a software addition to the Bosch ABS system. The brakes are used to transfer rotation through an open differential. <p>E

> If the Quattro uses ABS to prevent Wheel spin then<br>> how come I'm able to spin all four wheels?<p>Did you hear the ABS pump sound while "spinning four wheels"?? If you did, you did not spin all four wheel simultaneously. Each of the 4 brakes were pulsing very quickly and it appeared to you that you were spinning all four wheels.. If you didn't hear the ABS pump, you were not spinning 4 wheels.<p>E

This is a quote from a brochure authored by AUDI AG Public Relations, Ingolstadt, Germany, in September 1997:<p>If conditions make it very difficult to drive the car away, the electronic differential lock (EDL) will apply the brakes at the driven wheels and, in conjunction with the Torsen centre differential, distribute power to the wheels that have the most grip.<br>EDL makes use of the functions already available in the anti-lock braking system (ABS). If the wheels begin to spin on a surface with differing levels of grip, this is detected by the ABS wheel speed sensors. The spinning wheel's brake is applied until grip is restored. EDL takes effect automatically, and remains available up to 80 km/h. It acts in much the same way as a mechanical limited-slip differential in the front or rear axle, and can cope effectively with even the most extreme starting conditions.<p>

which I read to mean that when a single wheel is spinning so that it's rotation is 25 mph or greater than the wheel that is not spinning, the system is activated. <p>The second sentence refers to actual vehicle speed.

If the EDL only works under 25mph, it needs to measure this speed somehow. I am guessing that it reads it through a non-spinning wheel (which would indicate true vehicle speed). If all wheels are spinning, the computer could get tricked into thinking that the vehicle speed is, in fact, over 25 mph...which would disable EDL. Just a theory...<p>Mike

From the "Active Safety" section of the Audi web site:<br>Anti-Slip Regulation (ASR) all-speed traction control (FrontTrak models except A4 1.8 T) <br> Torsen center differential which reapportions power between the front and rear wheels for the<br> best balance of power (quattro models) <br> Electronic Differential Locks (EDL) in the front and rear distribute power to the individual wheel<br> or wheels with the most traction (quattro models and A4 1.8 T FrontTrak model) <p><br>This specifically says that, while quattro does not use ASR, it DOES use EDL. <p>Miles

The ABS pulses the brakes during startup at much the same rate that it pulses the brakes during the braking operation. Found this out not too long ago on a big patch of glare ice. It sounds and feels much like your taking off on gravel.

The ABS detects differential (one wheel significantly different that the rest) speed, if you've got them all spinning at about the same speed the ABS is not going to brake you, it can't tell the difference between this and normal motion.

I would agree with several of the statements from various people, but mainly e and Randall.<p>The torsen is one of three differentials. It is a wormgear, torque sensitive, center differential. This means that lockup happens only under a torque load (acceleration or spinning) and not in coasting and braking!<p>The front and rear differentials are OPEN! They are no different from yugo diffs. What ADL/EDL are is just the abs sensor system used to activate the BRAKES!!!! There are NO locks or plates in the A4 front and rear differentials (the old q's DID have plate and locking diffs).<p>The torsen just locks the center, so it is important to control the front and back diffs or the other end just spins.<p>This is not idle speculation. Go try it yourself! Take off the abs sensor plug from a wheel and see how the system spins that wheel under acceleration. There are no wires or hydraulic lines to the f/r diffs. It is just the fancy abs system.

It has also been my experience with the car. I think the reason that they wanted to call the function EDL is that older Quattros had diff locks, which are a vacum operated pin that mechanically locks the diff. These are expensive and do not have the variable nature of the EDL. I also think the operation of the center diff and the EDL are complimentary, the diff is balancing the torque from the front to the rear at speed when the road surface is good, maintaining the balance of the car. The EDL's function is much more like the old diff locks, to be used when stuck. The center diff still does it's torque thing so that having both wheels spin on an axle won't stop you. In fact the old ones had a diff lock switch, which was not to be used on dry roads (you could break the driveline). This diff lock switch also turned off the ABS, after all how do you sense differential wheel spin when all the wheels are locked together?

I was confusing EDL with ASR. But You Didn't mention if the Quattros use ABS to prevent Wheelspin. I don't think that they do.

EDL is not a physical differential lock, hence the name electronic differential lock. It applies the brakes, the resulting torque is transferred though the differential to the other wheel.

I never heard the ABS system while I was doing donuts. All four wheels were spinning. Someone was watching and snow was being kicked up from the front tires. While the vehicle was stationary I would gas it and then turn immediately, the rear end would kick around. As long as I kept giving it gas the vehicle would spin time and time again, Just like Alex Zanardi. If ABS is used to prevent wheel spin how can I do this? The Wheels wouldn't spin and the car wouldn't kick around. At least one rear wheel would have to be spinning or I wouldn't be able to Pirouette. In that case why would ABS allow one Wheel to spin and not the others. My ABS works fine just yesterday in the rain I heard it working during a hard stop. If it snows were you live find an open parking lot and try it yourself. I'm sure you will agree that the Brakes are not applied automatically to prevent wheel spin.

I just have to conject at this point, because I too have done donuts in this car, but I have also set the EDL off. I am thinking that rather than looking at the differential speed between all four wheels (which the ABS does) the system may be just checking across the axle, in that fashion the center diff would be left to do it's job independantly of the EDL. Remember that the EDL system does not prevent wheel spin, it just trys to force the speed of the wheels to be similar (a real diff lock forces them to be the same, but you sure can still spin both tires). I am thinking that if your trying to do donuts the system may even be helping, if the diff unlocks on a car without EDL then one of the wheels stops, the other takes off, and the donut stops because the stopped tire just starts making like a plow. You need both tires spinning on the end of the car that is rotating in order to keep the friction down. With the EDL if the diff unlocks and you get a speed differential then the EDL will try and lock the diff back up, keeping both tires spinning. The time I activated the EDL I had stopped on a snow covered puddle (if something about 50 ft across could be called a puddle). I tried to take off as if I were not on ice (not seeing it though the snow) and got a noise and feeling as if I had taken off on gravel. The car did take off, although slowly. I got out and looked, and sure enough glare ice. Made me get out the manual and look up the EDL.

how did u turn on and off??<p><br>1996 a4 2.8 qm

this is a complicated topic.. to really understand it you have to read the torsen<br>paper published by the zexel engineers. the link is on the FAQ page.<p>yes, the a4Q has both torsen and 4 wheel EDL. what some of you are not aware<br>of is that the a4Q has a total of 3 diffs, a conventional front diff, a torsen center<br>diff and a conventional rear diff.<p>ASR refers to the extra electronics to cut power if the brake pumping action<br>of EDL is not coping.. this is implemented only on the FWD cars<p>a simplistic way to understand the interaction of EDL and torsen you should<br>first follow the flow of power. power goes to the torsen diff first before going<br>to the front and rear diffs. the torsen can proactively redistribute torque <br>before any wheelspin occurs. it does this by sensing the "resistance" of its<br>output axles so to speak. the EDL only kicks in as a second stage mechanism<br>to optimize side to side traction; the torsen takes care of front to rear split.<p>also, EDL does not lock 100% (impossible since it pumps rather than locks a<br>wheel solid) so under the most extreme conditions you will have wheelspin.<p>also, if the brake pads get too hot EDL will switch itself off. also if the road<br>speed exceeds 40mph (i think) EDL will also be inactive.<p>feel free to email me eliot@eskimo.com if you have any further questions.

In fact, one of the advantages of TorSen over the locking differential is that ABS can be used simultaneously with all-wheel drive. It's apparently one of the reasons why Audi changed the Quattro system to use TorSen in the center diff instead of a locker.<p>If you want to stir up some real controversy, just post this topic on the Quattro List. They'll love it! ;-)<p>(I'm just kidding here. You'd be totally smoked if you post this subject on the Q-list. However, I'm sure you can find all the opinions you'd want if you do a search on "torsen".<p>Jim

You can spin the tires on an A4Q in the snow or on ice. The front drive is the only version with anti slip for the drive wheels. The quattro shifts traction to the tires with the best traction. I had this conversation with some folks from Audi while in Germany at an Audi event. If quattro had traction control you wouldn't be able to do those fun spin outs in parking lots.

"Quattro system" has anti-spin - it's called EDL. It is a software extension to the ABS system and only works on a per-axle basis. Once Audi introduces yaw control, the system will be intelligent enough to react "beyond the single axle". As EDL stands now, it senses wheel spin, activates the ABS "pump", applies the brake at the spinning wheel to transfer power to the opposite wheel through an OPEN differential. If there is "zero" traction on both left and right wheels of one axle, the brakes are applied back and forth between the two wheels at a high rate. This is the way it works for the front axle and the rear axle. EDL does not lock the open differential - EDL is a misnomer. Locking means that the right and left sides of an "axle" are rotating at the same speed. Audi used to do this on their rear diffs in the PAST.<p>The center differential, which resides in the transmission, is a TORSEN. It also does not lock. It redirects engine "torque" to the axle with the MOST traction. This transfer capability only works if there is some (I forgot the ratio.. maybe 7:1) traction available at the axle with the least traction. If this ratio is not maintained, the TORSEN acts more like an open diff. THIS IS WHY THE BRAKE SYSTEM IS USED.<br>The brake system helps the TORSEN maintain its effectiveness, when traction is near zero on it's open diff "axle". <p>E <p>