[torsen] RE: Torsen differential

Dave.Eaton Dave.Eaton at clear.net.nz
Wed Nov 20 05:40:03 EST 2002

well, i'd say technically and functionally "part-time" awd, and marketing
"full-time" awd :)

the key thing for me is that, in normal operation, there is no engagement
until slip occurs, and therefore no torque distribution until slip.  my
definition of "full-time awd" is a nominal torque distribution in the static
case.  you could achieve it with a haldex lsc, all you need is an integrated
differential.  it interests me that no-one has done one yet.

as i understand it, the pump (called a "feeder pump" by haldex) is used to
prime the clutch on full throttle starts (prior to slip), but is primarily
used (as you've quoted from the haldex web-site) to keep the 2 main
(pumping) pistons closed up to the rollers, to reduce the engagement time.
my description of the use of the feeder pump in abs operation is that the
pump is opened (and presumably disabled) by the ecu on abs operation, as the
throttle valve is connected to it.

however, the feeder pump does not make the haldex an active clutch, not does
it make it capable of "full-time" awd - as per my description above.

i've enjoyed the discussion, thanks.

'95 rs2
'90 ur-q

-----Original Message-----
From: Keith Maddock [mailto:Keith.Maddock at trw.com]
Sent: Wednesday, 20 November 2002 10:19 p.m.
To: Dave.Eaton at clear.net.nz
Cc: QSHIPQ at aol.com; torsen at audifans.com
Subject: RE: [torsen] RE: Torsen differential

I never said it "isn't AWD" :)  Please don't twist my words.  I would
describe the Jeep and Audi units the same in terms of current functionality
as follows:

Pure Technical:  "Part time AWD"
Functionality:  "Full time AWD"
Marketing:  "Full time AWD"

Sure, there is no actual coupling force until slip occurs, hence the pure
technical description as "part time AWD", but since the driver can't ever
disable the AWD feature (at least as delivered from the factory..), it is
functionally and commercially "Full time AWD".

WRT to Haldex, I think the ABS de-clutch is purely acheived with the
throttle valve.  To declutch you have to reduce hydraulic pressure, and the
feeder pump generates hydraulic pressure.  Im curious to hear how the
literature you have describes a de-clutch event being enabled by the


Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com

>>> "Dave.Eaton" <Dave.Eaton at clear.net.nz> 09:59:01 20.11.2002 >>>
ok, good - you agree that the jeep haldex-lsc transfer case (nvg 247) isn't
"awd" as scott asserts.  my posting was prompted by scott's statement that
the jeep was full-time awd using a haldex lsc, and that the audi wasn't
because the audi engineers had turned that capability off.  we agree that
the jeep is a part-time, progressive system, as nvg describe it, as is the
audi unit.

however, i think that we are talking at cross-purposes with regards to the
haldex generation 1 unit.  there is a feeder pump in the lsc, but this is to
allow the clutch to be controlled either during abs braking, or when there
is a full throttle start.  in these cases the clutch is opened and closed
respectively.  this is a normal function of the generation 1 lsc, as fitted
to the audi from day 1.  it is not a full-time awd system, although there
are clearly some aspects of that to it.  nor is this what haldex are
currently working on which is, as i understand it, more of a true "active"
clutch using a similar operating principle.

so, maybe we are in agreement.  i agree that there is a "feeder pump" as
part of the lsc, but the function is as i described - at least according to
the literature that haldex sent me.

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