[torsen] RE: Torsen and Haldex type differentials

Dave.Eaton Dave.Eaton at clear.net.nz
Tue Nov 19 03:40:29 EST 2002


nope - the design of the haldex lsc requires that slip occur before the
clutch can work.  it is intrinsic in the design.  look at the
haldex-traction.com website for a nice schematic of the device.  this is not
new, it has been available (with details on the net) for a number of years.

in other words, short of providing external pumping pressure to activate the
clutch (something which haldex are currently working on), you cannot
actively control the diff prior to traction loss.  once traction loss has
occurred (very soon after if you believe haldex), you have pumping pressure
and a nice electronically controlled pressure valve to control the clutch.
but not before.  if you believe "electronic control" to be all the time -
then you've got fluff in your head.

nice to know that you have discovered the torsen t3 :)

however, you are incorrect in the summary of audi's uses.  audi uses 3 basic
torsen models: 5 speed manual, 6 speed manual and 5 speed automatic. the
manuals are torsen crossed axis with similar bias ratios.  the automatics
use the parallel axis design for the sake of packaging.  there has been no
"evolution" of use away from the t1 to the t2 as you suggest, other than the
packaging issue above - at  least this is what zexel have told me.

also another nit, and one which you keep getting wrong - in a gen 1 quattro
(locker) setup the torque transfer is up to 100% by design when the
transmission is locked.  this means that the transmission has to be built to
allow 100% of the torque to travel to either end - so it is a worse scenario
than that of the torsen which limits torque differentiation by design, and
the one you paint.

back to normal programming?

dave
'95 rs2
'90 ur-q


 -----Original Message-----
From: QSHIPQ at aol.com
Date: Mon, 18 Nov 2002 11:07:36 EST
Subject: Torsen and Haldex type differentials - UPDATE HAC
To: quattro at audifans.com
Cc: torsen at audifans.com

[snip]

>haldex also makes an awd differential, called the lsc.  interested to
>understand how audi could have installed it in "full-time awd" mode?

Well, actually it is now, by definition.  95% of the torque is supported by
the front wheels, electronically.  Electronically, audi could have chosen
any
torque ratio f/r up to lockup (50f/50r).  This is strictly a choice by audi,
the engineers of the device claim it could  have been something other than
synchro.

>certainly the jeep application you mention is the same lsc unit, in the
same
>application as audi use.  nvg started using their haldex lsc-based unit for
>jeep at about the same time as it debuted in vwag applications.  you can't
>call it full-time awd in one, and not the other - because it isn't.

See Keith's comments here, no sense in going thru them again.  To me,
"synchro" isn't full time awd in any stretch of the imagination.

>there is no doubt that an electronically controlled lock-up clutch (which
is
>what the haldex lsc is), it the future of awd systems - cheap, and fully
>controllable.  "torque levels virtually limitless" makes no sense.  the
>haldex lsc has an overload protection valve - but is not operational at
that
>point...

At which point it allows slip, that's different than Trg = 0.

Now, let's take a look where everything has gone in the last 6 years, it
sure
appears the marketing boys have seized some opportunities, and have changed
the engineering boys perspectives some.

Torsen T1/T2 technology allows more torque, which means they were able to
keep audi in line for 1 more car.  This T2 technology isn't without some
sacrifice to the BR.  The really wide T1 BR (I always suspected as part of
it's inherent design problem) has been modified to a much lower BR in the
later audis (1995>).  In fact, torsen recommends that the T1 be used above
2.5BR.  Since we know audi is using the T2, I'd suspect strongly that the T2
torsens don't have the wide BR of the old T1 in the pre 95 cars.

What's really more exciting in my opinion is the T3 technology.  This is
Torsen's attempt at a Torsen limited slip differential lock.  Actually 2
differentials, 1 a fixed split (say 65r/35f), then torsen intervention when
slip occurs up to 30% shift.  This technology has the best chance of
competing with haldex type couplings.  But, given our car engineers (Keith
too:) directives/propensity to have electronic control, Haldex type will be
a
tough nut to crack.





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