Locking Torsen

[Lawrence C Leung]

On Thu, 14 Dec 2000 12:39:08 +0100 (MET) Jens =?ISO-8859-1?Q?R=F6sner?=
<jens.roesner at gmx.de> writes:
>Hi Lawrence!
>
>I have posted some kind of FAQ dealing with all that some weeks ago, I
>hoped this was not CWOB...
>
>> Any Quattro (not including the TT) is full time all wheel drive
>And not including the A3/S3: All "quattros" with transverse mounted
>engine.
>BTW: The Haldex is IMO between full-time and part-time, I don't want 
>to
>revive that discussion.
>
>> is full time all wheel drive, which 
>> means that approximately 50% of the torque is directed to one front
>axle,
>> the other 50% is directed to one rear axle. 
>As long as there is no serious slippage on the axles.

True - that's why the approximately. It's only certain to be 50/50% when
quattro1's center diffy is locked


>> Any non-limited slip front or
>> rear drive car has approximately 100% of it's torque directed to one 
>of
>> the two driven axles 

Was trying to figure out how to say that without adding too many
sentences.....

An open diff RWD car will direct approximately 100% of the engine's
torque to one rear wheel, especially in a slippage situation.
Unfortunately, the wheel that gets that 100% is the wheel that is (or
will be) slipping. 

An open diff FWD car will direct approximately 100% of the engine's
torque to one front wheel, especially in a slippage situation. Again the
wheel that gets the 100% is the wheel that is (or will be) slipping. 

>And where did you get that from?

Standard operating procedures for an open diffy.

>And what do you mean with "non-limited slip front or rear drive"? Do 
>you

Meant open differentials, which are standard in most RWD and FWD cars, as
well as the front and rear diffys of all quattros, and the center diffy
of Quattro 1 cars. Quattro 1's, however provide the means to lock the
center and rear ones, later quattro's use various means to "lock" the
center and rear ones. 
>
>> quattro system has an even distribution between front and rear axles 
>and
>> at least two driven wheels at one time (vs one driven wheel for FWD 
>or
>> RWD).


>If slippage occurs, the equal torque distribution changes.

Again, true. Trying to provide the simplest case, to limit WBW. Finding
that my economies of English are somewhat less than successful. 
>
>> The purpose of the locks is to guarantee the front rear 
>distribution. 
>> For quattro 1 <snip> this is accomplished by a true mechanical 
>locking 
>> mechanism, as the center diffy is an open diff, so in extreme
>situations, 
>> it is possible to one wheel drive even a Q1 without the lock. 


>I think early quattros have two diff locks, one center one rear, 
>right?

Correct.

>You need two diff locks to always get out of µ-split. If left is 
>pavement
>and right is ice, only a locked center diff won't help you very much, 
>the
>right wheels would turn on the ice. With an additional left-to-right
>diff-lock, your car will start to move. If of course three wheels are 
>on ice, and
>only one on pavement, you'd need three diff locks to start moving in 
>all
>circumstances. 

True. In engineering terms, it's called degrees of freedom (D.O.F.).
Mercedes and BMW (and now Acura) use the brakes to overcome this
difficulty, as the brakes serve to lock the wheels across and along the
car body. So, all 4 wheels can be capable of providing torque, and
actually, you can get three wheels stuck on ice, and ALL of the torque
can be forced to go to the one wheel on pavement. I don't know what the
allroad does for this, but I'd bet it's similar.  

And if all four are on ice, well...
>(wet ice has about µ=0.1 and below, down to 0.05, dry asphalt has up 
>to
>1.2, motorcycle tires are capable of reaching 1.4)
>...you will start moving slowly, very slowly.
> 
Only if you can seriously control your torque application via clutch
and/or throttle. Here's where I'd bet an auto may actually be a bit
better, i.e. creep. You can't afford wheel spin, remember m for sliding
friction is lower than static friction. That's why locked wheels don't
stop as well as threshold braked (or ABS braked) wheels. 

>> In later quattros, (excluding
>> your V8Q) it's accomplished with a viscous coupling called T_rs_n, 
>This is NO viscous coupling!! It is purely mechanic! That's why it is 
>so
>great, IMO.

Oops, you are correct. And agreed, the viscous coupling is what I hate
about Subes. My mistake. Planetary gears of the same fashion as the
Quaife. That's what you get for typing late at night!
>
>> which
>> "senses" slip at one end a redirects torque to the other end up to a 
>(I
>> think, list may correct the %ages) 30-70% or 70-30% split. 
>AFAIK, some are 30/70//70/30, some different?! 

Same.

>
>> As for your V8Q auto, there is a slightly different function (V8 
>owners,
>> or V8listers help). AFAIK, the center diffy of the autobox V8Q's has 
>an
>> electronic center lock that senses slip via the ABS sensors, and a
>T_rs_n
>> rear diffy lock, making the entire system automatic at all times. 
>There
>> is no decision making for the driver to do. Again, both the front 
>and
>> rear axles of the car are (attempted to be) driven at all times, and
>> again there are no factory controls designed so that the car could 
>be
>> made an on demand FWD car. 
>100% correct, I would say.
>Having a manual V8 would change the center diff to Torsen.
>(Yeah, I said Torsen, not T-thing or T_rs_n or Nesrot, simply Torsen 
>like
>in TORqueSENsing) 
>
>CU
>Jens
>
>http://www.AudiStory.com
>Member of the AFOSAT
>(Association for open speech about Torsen)
>
>-- 
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>