Re: Haldex and Viscous Couplings

[QSHIPQ@aol.com]

In a message dated 9/10/99 3:23:10 PM Central Daylight Time, 
Dave.Eaton@clear.net.nz writes:

> you're misunderstood the effect of a locked clutch between the axles.  once
>  that sucker is locked, the effect is exactly like a generation 1 locker.
>  solid link, and torque can flow front to rear 100%:0 and visa-versa.
>  depending upon grip of course.  examination of the haldex documentation 
also
>  makes this clear.

Any differential that is physically joined to another is "capable" of 
supporting 100% of engine torque under the right conditions.  This isn't the 
accepted practice of defining a "locking" differential.  You can't have the 
syncro/audi differential actively or  mechanically control locking beyond 50% 
to the rear.   
 
>  certainly edl operating across either axle could limit the torque transfer
>  but for example, picture the front 2 wheels on ice and the rear on tarmac.
>  pretty much 100% torque to the rear regardless of edl operating across the
>  front axle.  only when edl operates across the axles with the torque
>  transfer be limited all the time.

If both front wheels are going for traction on ice, Trg reduces via EDL.  To 
rephrase your argument, 100% of available torque goes to the rear.  The 
difference is, in a locked center  100% of Trg goes to the rear axle, in the 
EDL car (regardless of center diff), it is less, a lot less that 100% of Trg.
 
>  > Again, looking at the comparo, I'm convinced that Haldex should take on
>  the
>  > gen I locker locked in position 2.  I'm not enamored with the Haldex,
>  sorry.
>  > It's a step from the torsen, but 180 degrees from the norm.  One major
>  flaw
>  > in the logistics, IMO.  Audi hasn't had big gains in proving btdt wrong 
in
>  > the torsen arena.  Better luck here?  I'm not as optimistic as you.
>  Another
>  > 6 years of "proving" everyone wrong, that makes a total of 16.  Even if
>  they
>  > prove to be batting 1000 with the Haldex, that's still less than a .500
>  > batting average.  Quattro advantage indeed.
>  
> >> mmm... toyota's performance with a hang-on-clutch in the wrc machine 
would
> >> differ about state-of-the-art.  with their haldex copy they were within a
> >> whisker (500metres) of the world championship last year.

Whoa up here Dave, I think I see your misunderstanding.  You are speaking of 
a Viscous Coupling Differential Lock.  The difference between that and the 
syncro/audi TT application is that a VCDL is a fixed full time 4wd system, 
with an extra center fixed split differential, not found in the vw/aud Haldex 
application.  The vw/audi Haldex is a part time 4wd system, that is to say it 
is not full time 4wd, it is fwd until slip, then UP to 50% of the power can 
go to the rear axle.  

In the Viscous Coupling Differential Lock Device (959 PSK, Toyota WRC, Lancia 
Delta Integrale, Ford Escort RS Cosworth,Scoobie Do Impreza, Mitsu 3k/stealth 
tt) there is a fixed split awd system, usually (in all the cases above) it is 
split somewhere in the 70/30 to 60/40 range.  Then it has a "haldex type 
device (or vc) that either locks the diffs at 50/50 or put the range 
somewhere in between, depending on application.  In the case of the 959, it 
can vary torque from 80/20 r/f to 50/50 r/f, the greatest range yet developed 
from it's static 60/40 r/f distribution (which means the PSK system is 
engaged all the time to get 60/40).  Even if you change the programming of 
the vw/audi Haldex to operate all the time, it's limit is less than 50% to 
the rear, ALL the time, you can add more fwd, you can't add more rwd.  Again, 
Audi has done this the reverse of the rest of the pack, assuming the 
modification.  Statically it's "syncro II" by definition.
  
>  about the haldex, the road testers disagree with you about the experience.
>  interesting call to say that, with sales at 10-year highs, that the punters
>  don't disagree with you as well.  like i've said, lets leave the black 
board
>  and drive the machines.  very big call to pan the technology without having
>  done that methinks...

Sales doesn't mean you have better quattro, it exactly means in fact, that a 
"lesser" quattro still sells cars.  BMW is enjoying a enthusiast and 
performance car sales high, and they have NO quattros (exempting the rover 
purchase I suppose:).  
Maybe given the above, we should understand the basic operation, before going 
for a test drive.  IMO, the part time 4wd system vw/audi has chosen, lacks 
some of the btdt proven application (your WRC example included), which puts 
in perspective, the compromises vw/audi has taken in developing the "new" 
quattro.    

My .02 arbitraged thru the peso

Scott Justusson