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

Kirby Smith kirby.a.smith at verizon.net
Tue Dec 3 23:13:51 EST 2002


As a point of reference on limited slip differentials (why am I doing
this?), on the Corvair Positraction, the torque required to force
differential slip was 80 lb-ft.  The engine could generate (in my Turbo
Corsa) 280 lb-ft, IIRC.  This would be multiplied by the gear ratio and
the differential ratio (3.39?).  Thus, in slush, ice, sand, the diff
would act as if it were locked.  Otherwise, using reasonably sticky
tires (I used to drive on Firestone rain race tires), the engine could
easily overpower the clutches and the torque to the wheels would be
relatively independent (like the suspension).

kirby

rbraun at foni.net wrote:
> 
> 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
> wheels.
> 
> 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:
> 
> http://www.howstuffworks.com/differential8.htm
> 
> 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.
> 
> Rob
> 
> *****
> 
> ---- 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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