Quattro Question

The Torsen system used with longitudinally oriented engines (other than the A3/TT) is full-time.

The Haldex system on the A3/TT is front-wheel drive with the rears added once slip is detected.

Expanding on Drew's reply:

The original quattro system was full-time four wheel drive, with a 50/50 torque split between front and rear wheels. Audi engineers were convinced that there were so many advantages of 4WD, and so few disadvantages, that there was no conceivable reason that a driver might want to switch it down into 2WD mode, so they didn't offer the option.

Later in the 1980s, the Torsen diff started to be used, which allowed a variable torque split between front and rear wheels, varying beween 25/75 and 75/25 bias. In an interview at the time in one of the UK car magazines, an Audi engineer said that this change was really made so that they were seen to be updating the technology in the vehicle, and that virtually all the time the torque split would still be 50/50, just the new setup has the possibility to distribute torque differently if it felt it was required.

The Haldex system in the A3/TT is part-time, in that the rear drive is brought in as required.

Mike.

Jep and more specific information about Haldex systems you can find here

-Janne

Related Quattro question: My 2001 A4 (1.8t, Tip, Quattro) got stuck in the snow twice during last years eastern snow storms. The snow was fairly deep with an icy layer under the snow. A push got me going, but while I was stuck, only the rear wheels were turning / spinning. Is my Quattro bad (no known driving or handling issues) or is it normal for only the rears to spin during certain situations? Thanks.

I don't know the definitive answer to your question, but I do know that with

2 wheel drive cars, its common for only 1 wheel to spin. And it that case you don't conclude that its broken and only 1 wheel is working properly. Am I right in thinking that a limited-slip differential is supposed to help prevent this effect? By transfering torque to the wheels that aren't spinning? Well so much for the theory. Anyway, from the sound of it, I would guess your car is behaving normally, but I am no expert.

Chip.

A full time 4WD performance car, as mentioned earlier, needs 3 differentials in order to operate properly. A differential is basically a mechanical device that allows the wheel which sits on the outside (longer radius) of a road bend to spin faster than the wheel on the inside (shorter bend radius). These devices are used on the axles that hold the wheels that are driven by the engine and, in the case of a 4WD car, between axles. If no differential is present then the driven wheels would spin at the same speed in a turn thus rendering the handling of the car very unpleasant. Self-locking differentials add to the classic "free" differential the ability to lock (drive both wheels at the same speed) under certain conditions such as when wheel spin occurs. For instance by locking itself, the differential, allows to avoid the immobilization of the vehicle in situations such as when a wheel sits on snow while the other sits on dry tarmac. In this case, the absence of a locking device would send all engine torque to the wheel that spins faster (the one on the snow) and the car would not be able to extract itself. Locking the differential would split torque distribution on both wheels thus allowing the car to move forward.

Ron

Taken from a website

in theory the quattro has 3 diff's so you should see it spin all the wheels, or it will spin each wheel in turn until 1 wheel stops spinning then it will apply max power to that wheel to get you out and when that one starts spinning agin it changes to another wheel, untill you are free...

Thats whats suppose to happen I think

Ron

In contrast if you were taking a fast corner and needed more purchase on the rear of the car, it should transfer power there to stop the car from sliding out, and then varies between front and back.

A good test is to find a quiet roundabout, when its raining, so slippery and drive flat out round the roundabout, if the back end slides out before you hit 60mph then somthing is up :)

:))

Also try driving on the beach, on the sand, and floor it from standstill, you should'nt get any spin, and should pull away nicely unless you are driving an s4 or a chipped up 1.8T with 200bhp.

The car should pull away fast like your on the road, and not spin like the S4 would as all 4 wheels put down so much power that the 4wd system acts like a 2wd car and digs all 4 wheels into the ground :)

My first Quattro was also an '01 A4 1.8tQTip and I never had such a problem in that car or my current A6 2.7tQTip. It comes to mind that perhaps the snow buildup had "lifted" the chassis so that the tires were no longer in firm contact with the roadway and a push was all that was needed to get you over the hump.

Jon

My error. I meant to state that I was inquiring about the Quattro in the A6

4.2.

Does this make a difference? Is it managed in the same manner as the TT?

Thanks for all of your input thus far.

Jimmy

No, the quattro in the A6 is the torsen system (full time AWD). The quattro in the TT is the haldex system.

Cheers,

Pete

In theory, no. With the rear wheels unloaded (as in not having any grip) the Torsen centre differential should have transfered 75% of the torque to the front wheels which should then have moved the car, or started spinning themselves. A wheel on one side should be prevented from spinning by the electronic differential lock function implemented via the ABS system.

All this assumes that your car does have a Torsen centre diff, and open front and rear axle diffs. I think that some of the automatic cars did have a slightly different arrangement, relying more heavily on the ABS/brakes for transfer of torque. If your car is one of these, then your experience could point to an ABS problem.

I'm quiet unsure about what type of traction control a 2001 A4Q actually has. I'm assuming here: TorSen center diff, open (manually) lockable rear diff. And: NO EDL's!

If it is TorSen, it is not able to split more than say 25/75. So: 0 grip at one axle is 0 x 75 at the other end and that is: 0! Spinning tires. In your case the solution would have been to apply "grip" to the spinning axle: use the handbrake to transfer torque to the rear output shaft of the TorSen. Then 75 x something = something for the front: You would have been rolling.

Unlucky if you have a front tire spinning: No lockable diff and no

*separate* brake for the fronts only either...:( So always point the REAR to the more slippery patch on the ground!

Summary: That problem occurs, if the grip-difference between front and rear is over a specific limit.

So long! Ero.

P.S. If the car is equipped with EDL, that *should* have braked the spinning wheel(s) to let the TorSen transfer some torque to the other axle.

That's possible, but on two occasions I found my car to act differently than I had expected. First one was in the snow, I can do a spin-a-roony if I really want to, the wheels do slip, even when starting from a standstill. But that was no biggie, more concerning is the next case. My A4Q went off the road once, into a ditch. Three wheels were firmly planted on the (hard) ground, while the fourth didn't have as much weight on it, that wheel kept on spinning, no matter what.

I thought with the Quattro system, even if only one wheel had grip, it would be enough to move the car, not too sure I believe that anymore...

Romy

Totally agree on the spin-a-roony, which I've also done on both snow and fine gravel. I can't tell you about any "ditch" situation as you depicted, but I suspect the EDS, i.e., the braking of the wheels is only effective up until a certain amount of torque. If that threshold is exceeded on a low-grip surface the wheels will slip-spin, no matter what.

So, the golden rule of smooth and very gentle acceleration prevails when pulling out of slippery surfaces, I guess.

By the same token, I would hazard an engine with a comparatively low torque - say an 1.8T, might in good hands do better than a mightier one, because it's easier to apply just only the necessary torque so that the wheels won't lose grip.

These are only assumptions but they're based on my experience. I would be curious to know which the torque values are that have been used in pre-programming the quattro-brake-assisted system.

My two cents,

JP

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