RE: tt haldex lsc

[Eaton Dave <dave.eaton@minedu.govt.nz>]

chris,

we need to be careful here.  there has been extensive and repetitive
discussions (guilty your honour) about the merits of torque transfers in any
cars, let alone audis.

surfice to say all modern  awd systems shift torque from axle to axle.
early ones, eipcyclic/vc's and tor*en simply responded to driveshaft speed
or torque.  the more recent ones use computers to assist the same
mechanicals to do their job (eg. audi edl tor*en quattro, porker c4).  most
use the abs sensors and "g" sensors.  some also use the throttle position as
well (eg. haldex).

most people would say that these systems are still reactive.  in at least as
much as they respond to vehicle dynamics and attempt to do something about
it by shifting torque.  some shift torque reactively by braking a wheel or
axle, others by active control of the centre diff.  the haldex lsc can
certainly do this through its throttle bleed valve which is under computer
control.  it is not, however, a centre diff.  in the mythical s6 tt v8 app,
with 4 of the suckers, you would then be able to take things one more step.
but still most likely reactive.

full active is a mystical science.  no-one does it, or has done it on
producton cars.  it is state-of-the-art in rally cars, and details are
closely kept secrets.  clearly full active requires the monitoring of
vehicle speed which is quite tricky, and the storing of throttle and diff
maps which modify the torque produced by the engine and the torque shifted
by the diffs (rally cars have active centre and rear diffs, some also active
fronts).  so, using vehicle speed, driver input (throttle, steering), and
vehicle data (lateral g, longtidutional g), the diffs run a particular
torque/traction map.  this can then be modified by reactive data (abs and
'g'  sensors) aka feedback loop.  as you can see, this gets very complex
very quickly.  it looks as though the active thing is being taken one step
further to the dampers in the new wrc cars...

when sorted, the results are stunning.  watching a wrc rally car put down
rubber (literally) onto a loose gravel surface is a sight to behold, and
about as far from the old group 'b' cars as you can get....

formula 1 is also getting up to interesting things with mechanical diffs.
active technology is banned so the top teams have spent millions on
developing fully mechanical diffs linked with braking systems which allow
earlier power applicaiton on corner exit, and better cornering dynamics.
other pioneering work on active setups was done on the class 1 tarmac awd
racers from alfa and opel.

when they go wrong (as they did for colin mccrae on day 2 of the nz
international rally a couple of months ago), the car is pathetic.  when i
spoke to him, mccrae was wanting to stuff the car down the engineers
throat....

btw, harry fergusson would be very unhappy to find that porsche have been
credited with the "invention" of the epicyclic diff/vc arrangement.  he
certainly had this up and going in his 1st prototype just after ww2.  it was
live and installed in a f1 car in 1961.  and in the jensen ff (production) a
few years later.  the 959 is a different matter....

dave
'95 rs2
'90 ur-q

> ------------------------------
> 
> Date: Thu, 8 Oct 1998 02:49:30 EDT
> From: CM1022@aol.com
> Subject: TT Epicyclic?
> 
> Sorry to Dave, I didn't mean to drag on like that but I am new to the list
and
> needed to explain.  I know you already know this stuff, old boy!
> 
> The Epicyclic diff is also called a planetary diff, and it is basically an
> automatic transmission used as a diff.  It has planet, sun, and ring gears
> with many smaller clutches that sit in oil- i.e. a viscousity coupling.
Dave
> is right when he points out the similarity.  It is slip activated, and
Porsche
> is creditied with the invention of it in the late eighties for the Carrera
4
> to my knowledge (after the control clutch center diffless 959).  Does the
TT
> have this?  Is this what the haldex is?
> 
> I know little about "active diffs" used in modern group A.  I would
appreciate
> any info, I would love to learn.  Some of the features of the Porsche
> Epicyclic diff are super fast milli second reaction, and a tested torque
> transfer of 85% on sheet ice.  The Carrera 2 could only transmit
> 65%............
> 
> I regarded the WSS and computer logic control combined with a
> lateral/longitundial G sensor in the epicyclic Porsches as being "active".
> But I guess I was wrong.
> 
> Chris Morlock
> 
> 86 951
> 83 928S
> 81 928
> 81 931
> 70 BMW 2800 CS
> and an HD