[torsen] Re: [s-cars] Torsens is there a difference ??!!

Keith Maddock Keith.Maddock at trw.com
Tue Dec 3 13:50:47 EST 2002

EEEEEEEK! *Keith ducks and runs for cover*

Rob, I don't know what which had me smiling wider:

A) Telling Scott J aka Torsenboy how a torsen works
B) Claiming a Torsen biases torque based on wheel speed differences
C) Claiming that ESP "simluates" a clutch LSD

To address these points

A) Rob, just trust us that Scott knows more about Torsen than most of us ever will.  

B) Torsen LSD's bias torque based on torque difference NOT wheel speed difference.
Bonus quiz of the day:
Where does the name "torsen" come from?
Bonus hint of the day: TORque  SENsing
Re-read that webpage you posted!

C) OK this is a common assumption, and from a functionality standpoint almost close.  A lot of people in my industry  (the ESP industry) and OEM engineers misassume this.

A Torsen, or LSD, or Locker diff is capable of increasing the bias ratio of the "normally open" differential from 1:1 (50/50 normal operation) to a larger number which is limited by the Torsen/LSD/Locker Mechanism.  The amount of bias ratio is dependent on wheel speed difference (normal clutch/viscous LSD), wheel torque difference (torsen), or infinite (100 divided by 0) (Locker).

ESP is incapable of changing the bias ratio of a open differential, and which is fixed at 50/50 (or in some center applications recently, 40/60 or 38/62 IE X5, 03 GMT).  This means the amount of torque going to both individual wheels/axles is directly limited by the wheel/axle with the least traction. Since ESP/EDL can't change the bias ratio, it instead ABSORBS torque of the wheel/axle with less traction, which allows MORE torque to both wheels/axles, including the wheel with more traction.  
**However in no case can the wheel/axle with greater traction ever get more torque than the pre-determined, fixed split of the open differential.**

We'll have several hours weekend after next while building crates to discuss this :-)

Keith "Freezing fingers" Maddock

Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com 
** In Arvidsjaur, Sweden,  02-13 December 2003 **
** Direct line: +46 960 /  57 869    Reception  x800  **

>>> <rbraun at foni.net> 17:54:53 03.12.2002 >>>
Hi Scott:

This is interesting, but I think it would be wise to
distill this done to what a actually Torsen does!

A Torsen works very *similar* to a typical
American V8 limited slip differential. Agreed?

Now, on a limited slip (or Torsen) when one wheel
on the rear starts spinning faster (wheel slippage)
the clutches increase the resistance of that wheel
so that the torque goes to the other wheel until it
too starts slipping. The result is the car will fishtail
as torque goes back and forth between the 2 rear

This happens in Quattros. Accelerate very lightly
and let off the gas. You will feel the car rocking, as
if there is a worn rubber bushing in the driveshaft.
Mr. Kluge, who worked at Audi and designed the
Quattro transmission told me that this rocking you
feel is the Torsen sending torque back and forth.

The Torsen works the same way, but uses the
design of the gears instead of clutches. BTW, the
new cars the ESP use the brakes to electronically
simulate the clutches that are in a limited slip diff.

When speaking of torque split, we should be talking
about Torque Bias Ratio. 80/20 would be a 4:1
Torque Bias Ratio. You mention 3.5TBR, this would
be a 78/22 maximum torque split.

There is nice, short explaination of the Torsen here:


The long and short of it is that the Torsen works
well and if the Torque Bias Ratio is 3 or 4, it really
doesn't matter to the average driver...

Hope this helps.



---- Originalnachricht ----
>Datum: Tue, 3 Dec 2002 11:25:03 EST
>Von: <QSHIPQ at aol.com>
>Betreff: Re: [s-cars] Torsens is there a
difference ??!!
>An: rbraun at foni.net, peter at moreboost.com 
>Cc: s-car-list at audifans.com, torsen at audifans.com 
>   Rob et. al.:
>   I'm not really convinced that this is
>   good information, I suppose it could be,
>   but I doubt it.  The S cars use the
>   "university special" known as the
>   M021-DHU, it's basically the same unit
>   audi used from 1988>.  As far as I can
>   tell, they are all the same, AND the
>   ways to modify them would be steel shims
>   and/or changing friction within the
>   unit.  I'm suspect of the 75% torque vs
>   80% torque, cuz really we are looking at
>   a 5% torque differential here (assuming
>   all cars are equal in terms of torsens,
>   they aren't, they wear immediately and
>   stabilize at something much less than
>   the 3.5TBR).  If you math this out, we
>   are speaking of less than 50ft/lbs of
>   torque, I doubt that's at all
>   significant.
>   751E shows valid for the 5 or 6 speed
>   variants of all 01E based
>   transmissions.  AND this is the
>   "university special" based basket, which
>   means that the differences might be
>   getting TO the unit or coming FROM the
>   unit in terms of splines/size/fitment
>   but the unit itself hasn't changed.
>   Even torsen admits that .7TBR variation
>   *should* be expected as delivered for
>   the "new" university special.  I can't
>   imagine that the "old" one could
>   possibly be better.
>   I'm most intrigued by the infomation
>   that comes from all different sources,
>   including zexel torsen themselves.  Audi
>   started a fine tradition of mystifying
>   this basket of spiders.  I really doubt
>   it's ever been this complicated.
>   Rob, Stasis did some data logging of the
>   driveshaft speeds on the torsen in their
>   race car, it's interesting reading, even
>   if the conclusions might be a bit off
>   (IMO).
>   Right now, I will put forth that the 78%
>   vs 75% vs 80%  (this is the first time
>   I've seen 80% on a center diff
>   referenced, I've seen it as the rear v8
>   torsen) is well within the production
>   tolerance of the device, and "seeking"
>   one over the other isn't time or money
>   well spent.  Audi has published 75 and
>   78% for all 01E based trans (in my
>   library anyway), I wholy consider those
>   to be both valid, since when new either
>   number could be, when used, neither
>   number is.
>   HTH
>   Scott Justusson
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