[torsen] RE: Haldex differential

Dave.Eaton Dave.Eaton at clear.net.nz
Sat Nov 23 02:50:19 EST 2002

1) you're wrong, the haldex lsc in normal operation transfers no torque to
the rear of the vehicle.  quoting directly from the haldex lsc article "the
two shafts are connected via the wet multi-plate clutch, normally unloaded
and thus transferring *no* torque between the shafts" (page 7, "basic
function").  this is *not* a vc, scott, it is a clutch.  there is no
residual shear, as you have in a vc.


2) is the haldex lsc an active clutch?  no - its a reactive one.  an active
clutch uses an external pressure source to supply all the required operating
pressure.  the haldex can't.  not even close.  another simple test.  can the
lsc initiate full lockup without slip?  no, of course not.  therefore it is
not active, because an active clutch can do that.

we're getting nowhere with this.  read the information on the web about the
lsc, or if you'd like i'm happy to email you the information which haldex
has sent me.

i'm done with this.  over and out.

'95 rs2
'90 ur-q
-----Original Message-----
From: QSHIPQ at aol.com
Date: Fri, 22 Nov 2002 08:36:17 EST
Subject: Re: [torsen] RE: Haldex differential
To: quattro at audifans.com
Cc: torsen at audifans.com

[ Picked text/plain from multipart/alternative ]
In a message dated 11/22/02 2:47:54 AM Central Standard Time,
Dave.Eaton at clear.net.nz writes:

>no, with a locked differential the tbr is infinite (the result of dividing
>by 0) as there is no way of controlling the torque shift (the traction
>available does that for you).  with the torsen, the tbr is a *limit*.
>torque will be shifted around up to that amount - whereupon speed
>differentiation occurs.  in other words, with a torsen the tbr is the limit
>up to which the diff will remain locked.  with the haldex there is no tbr
>the normal case, as there is no clutch engagement.

Er, it's 95f/5r to 50f/50r..  The haldex in it's current trim is never fully
decoupled, just like most VC and VCT.  You could say it's negligible in
torque at 5%, but Dave it's not 0r.

A couple things Dave.  Audi could hold rear lock at any point with the ECU,
where I've been trying to lead you and Keith all along, massively
constrasting the strictly mechanical application in the Jeep for example.
throttle valve is controlled electronically, which means that it can hold
lockup or %of lockup as long as the pressure is there.  Put another way, the
throttle valve is a wastegate frequency valve (with a stepper motor no
it can add 100% of piston pressure, or ANY % up to piston pressure.  With no
throttle valve intervention the torque is allocated 95f/5r.  Like a turbo
car, the stepper motor can't create it's own pressure yet.  The addition of
brake bomb or a revision of the piston pressure (make the turbo more
efficient) input could change that.  Changing the turbocharger to a
supercharger if you will.

>fwiw, the porsche 959 system also used a hang-on clutch driven by an axial
>pump powered by the front/rear speed difference - the difference in that
>application was that the difference in tyre size front/rear created the
>pumping pressure to allow clayton's active control.

Which can also be done in the TT.  OR just change the slip to zero, piston
pumps all the time.  With a throttle valve, it doesn't matter that the sytem
is always active, as long as you can bypass 100%.  It might be interesting
understand why the 15% was chosen for activation.  It might be interesting
understand why audi chose 95/5 as well.

>once again, with the clutch fully locked, the haldex lsc has no ability to
>control torque shift, and remember that, once engaged, it cannot
>increase lockup until there is further slip.  what it can do though is to
>monitor wheel speeds and reduce clutch engagement if the rear is sliding.

The clutch is only fully locked if the throttle valve locks it.  As such, it
is controlling lockup all the time.  Again, one should think of the throttle
valve as a WGFV.  Your "cannot effectively increase lockup" should be it
"can't" in current programming.  a series of ck valves could change that, so
could a revision to the pump, or an accumulator.

>the modification to an active clutch would be a good 1st step - but this
>requires a completely different operating principle (why continue to use
>axial pumps?), new software and a powerful external pump.

It IS an active clutch by definition.  It might be a more crude device than
others, but it is active.  Currently, if you have slip, it's fully active in
all senses of the word (like:  if you have boost, the WGFV is *always*
active, without boost -piston pressure, it doesn't matter what you do with
the tvalve).  To make it "better", one could say it needs full lockup
capability all the time.

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