Quaife for the 01E transmission?

[Lee]

ATB are not locking when off the throttle.

True. If your application requires this function then that is appropriate to go this way. The guys who have done this, what are they setting their cars up for? Gravel, Mud or tarmac? The requirements are different for all. I have no requirement for off-throttle locking in my S2.

PS I have no desire to ever enter a scooby Forum!

[Lee]

To get three lsd is just matter of the fact that somebody has to do it, but I have no resource to buy atb just see if it fits.

I would never suggest this. I would take standard diffs to Quaife and get them to make one that is a direct replacement rather than buy an existing solution just to 'try it out'...that would be bonkers.

[Lee]

All 4WD are the same in that they transfer engine power to 4 wheels. But, when it comes to solving a handling issue you cannot take what other people have done and copy it as it is a lot more complex than that. Optimisation for different conditions will produce varied results and you are forgetting that suspension, tyres and driving style play a massive part in power transfer to the wheels. Everyones preference will be different.

To solve a problem, first you must understand what the problem is and the consequences of various potential solutions.

[S2central.net]

AFAIK, the S2 has the following setup -

Front Diff - Open
Centre Diff - Torsen
Read Diff - Open

Here's a good start for bedtime reading...

http://www.everything2.com/index.pl?node_id=943580&lastnode_id=1391595

I already think that a Quaife ATB is a bit like a Torsen. Only difference I see is that the ATB has no limits whereas the Torsen is limited to a maximum of 70:30 torque split.

The LEGO suggestion is a good one actually !


Paul

[Lee]

ATB is available in various ratios IIRC. Let me check. Up to 6:1 rings a bell but I will dig out the info.

The late S2s follow that convention for torsen centre only but I am not sure about earlier ones or URs.

[Billman]

The Rs2 's are also open -torsen- open ??

[S2central.net]

Summarising this with the basics we have:

Open Diff
Main advantage is simplicity and cost
Biggest drawback for driveability is the 'infinite slip' scenario when one wheel is significantly unloaded during fast cornering, with the consequence of poor traction.
Another disadvantage is when one wheel is stuck in mud/snow which results in excessive spinning of the other wheel.

A limited slip differential (LSD)
Main advantage is 'limited slip' (funny enough) in that improved traction is available when cornering. This is done by funky gears and friction plates which limit the torque transfer to the unloaded wheel. Really tricky LSDs are now available with software control from wheel speed sensors and whotnot.
Main disadvantage is cost, complexity and wear & tear.

Torsen is a special type of LSD
Main advantage is the ability to transfer torque to the wheels which have most grip. A hugely ingenious piece of mechanical engineering its actually more reliable than a traditional LSD as it doesn't have friction plates or any electronic gubbins to go wrong.
Main disadvantage is cost.
Another disadvantage is that the torque split is limited by gearing such that a 70:30 configuration is typical on Audis. Guess different gears could be more radical ?
Another disadvantage of Torsen is that it cannot be locked !

ATB - Automatic Torque Bias - seems to be a special cousin of Torsen
Main advantage I can see is it doesn't have the 70:30 limitation of Torsen. ie It can transfer all torque to one side.
Disadvantages ? - Cost presumably of getting custom installations.


OK so far, but here's another question - If the UR quattro's 016 gearbox had a lockable centre differential for pure 50:50 torque split - what sort of differential is that - just a mechanical LSD with locking facility ?

Paul

[porkkis]

Torsen has also the disadvantage that it "leaks" all the power if the other side has virtually no grip at all. In our cars raising the other axle would make this happen.

And yes, traditional 016 setup is mechanically fully locked or when unlocked it acts just like normal open diff. 88 onwards there were also 016 torsens (urq, 200).

ATB=Torsen. The different values might be caused by different spring discs that a torsen unit has in its middle part.

[S2central.net]

Torsen has also the disadvantage that it "leaks" all the power if the other side has virtually no grip at all. In our cars raising the other axle would make this happen.

This 'leaking' business. Is this what you call the phenomenon Iget on the S2 on wet roundabouts ?

The scenario is that you approach a wet roundabout (or corner) with too much power (sorry torque) being applied... Then the car starts to understeer and *start* to spin the front wheels if you keep your foot in... Then Mr.Torsen transfers the torque to the rear wheels (as long as you keep your foot in) and soon enough you need some opposite lock on the steering to get the drifting car back into shape. Et voila the art of 'Torsen-ing' a quattro... Dunno if I'll ever master the art, as I don't find a very predictable thing to judge on new territory and much depends on the road surface and weather and tyres of course.

Lifting off the gas when the front starts slipping simply reduces the understeer and you get no torque transfer to the rear for that slightly sideways moment.

Is this what you mean ?



Paul

[NoNonsense]

OK so far, but here's another question - If the UR quattro's 016 gearbox had a lockable centre differential for pure 50:50 torque split - what sort of differential is that - just a mechanical LSD with locking facility ?

Paul

Lockable diffs are open diffs, just like what we have on the rear of our cars. When the UrQ doesn't have the center locked, it can send 100:0 power to front or rear....so if you break the tires loose when launching, it would take the path of least resistance and you'd really light up the front tires.

[S2central.net]

And yes, traditional 016 setup is mechanically fully locked or when unlocked it acts just like normal open diff. 88 onwards there were also 016 torsens (urq, 200).

The 016 had an OPEN centre diff which was lockable ?

So without locking centre diff, you could get such a system into trouble by getting both front or rear wheels stuck in the mud/snow as the other axle will just spin.

When we talk about locking the UR centre differential - does it force a 50:50 torque split, or force both axles to rotate at the same speed ?

Reason I ask is that a system with front & rear axles locked to the same speed would be OK to drive on gravel & snow but would be unsuitable for tarmac.

I'm coming to the conclusion that a system with THREE Torsens (or ATBs) would be best as it would provide reliable LSD functionality for all conditions.

Is a Quaife ATB lockable ?

Does Quaife simply call it an ATB to avoid copyright/branding issues with the manufacturers of Torsen ?

Paul

[NoNonsense]

I have been thinking about trannys and diffs for a long while now. Think about this senario:
You are doing some rally-type driving down a snow-packed road...you are taking a right turn at speed with trees on your left. When you start to drift it a little in a controlled manner, the center TorSen is going to transfer power to the wheels with more traction...so while you were controlling your drift, the power suddenly shifts to the front wheels...this would slow then down and you'd quickly loose traction as they lock up before they begin to spin slowly. By now, you've just crapped your undies because the trees are too close for comfort.
If you have a center diff that is locked, you wouldn't have to worry about that as the power between front/rear is equal.
I may be going this route in the near future and run a tranny from a 4000Q. It had lockable center and lockable rear with open front. I, however, may add a quaife up front and add the rear diff from a 94 V8 which is TorSen....

[NoNonsense]

The 016 had an OPEN centre diff which was lockable ?

So without locking centre diff, you could get such a system into trouble by getting both front or rear wheels stuck in the mud/snow as the other axle will just spin.

When we talk about locking the UR centre differential - does it force a 50:50 torque split, or force both axles to rotate at the same speed ?

Reason I ask is that a system with front & rear axles locked to the same speed would be OK to drive on gravel & snow but would be unsuitable for tarmac.

I'm coming to the conclusion that a system with THREE Torsens (or ATBs) would be best as it would provide reliable LSD functionality for all conditions.

Is a Quaife ATB lockable ?

Does Quaife simply call it an ATB to avoid copyright/branding issues with the manufacturers of Torsen ?

Paul

Paul,
On the UR with locking center, it splits torque 50:50 between axles and turns the axles at the same speed because of it. Then, it is up the the front and rear diffs to decide which corner(s) to send the power. With open diffs, this could mean that only the right side of the car will loose traction, or the left side accordingly.
The other advantage to a lockable center diff is better braking power, especially on slick surfaces. When you jam the brakes, the rears will have to slow down just as fast as the fronts, so it'll decelerate much quicker. Also, it makes it much more difficult to lock up the brakes with a center locked diff.
Rally cars usually have center diffs that are always locks or even welded closed. If you ever look at a rally car, the front and rear brakes are the same size...no bias either.
This is why I am thinking of a 4000 Q center differential. I don't drive like a maniac on the streets, so an open center is fine for me, but when I race, I could lock up the center and "increase my brakes" as well as limit the amount of torque steer on corner exits.

edit: quaife is not user lockable. It may lock when torque loads make it lock, but it'll unlock as soon as torque disappears (ie..foot off of the GO pedal). The quaifes only take about 3/4 of a rotation of spin to lock up too...

[S2central.net]

OK & understood.

What we really want then is a lockable Torsen centre diff - Can Quaife do that with their ATB technology ?

Paul

[S2central.net]

Heeheh Joe - our posts are wee bit of sync... Kinda like delay on a satellite phone

Am I correct in saying that the UR (with locakable centre diff) is easier to drive on the limit as you don't get the mindf*ck with the Torsen switching ends when the front starts slipping ? Your heart says 'lift off' but your brain says 'keep your foot in'.

Given the impossiblity of a lockable Torsen or ATB, then I'm swaying back to the lockable centre diff from a UR or 200 (4000/5000) in keeping with your thoughts.

Means its normally open in the centre until you need to lock it for the traffic light grand prix, the odd snow day or getting stuck in the beach. I think the benefit of Torsens or ATB for front and rear diffs would outweigh have a Torsen in the centre. Ultimately I feel this might be the easiest and most fun to drive...

Trouble is we'll have to pay lots of money to find out for ourselves !!!!!!


Paul