Fw: torsen tech 101

["JC.NEGRON" <elprofe@isla.net>]

DAVE...GOOD EXPLANATION!!!! I ALREADY READ THIS DABATE ON THE LIST GIVE ME
SOME CONFUSING OF A BASIC POINT IN TORSEN (101)EXPLANATION...NOW I HAVE A
CLEAR IDEA OF "WHAT" TORSEN DO...IF YOU LIKE I WISH TO KNOW MORE OF THAT
"TORSEN TECH 101"
----- Original Message -----
From: Dave Eaton <Dave.Eaton@clear.net.nz>
To: <quattro@audifans.com>
Sent: Wednesday, October 20, 1999 6:52 PM
Subject: torsen tech 101


> orin, eric, others - it is time for me to front up on the technical side
of
> things in the torsen debate.
>
> by way of background, about 12 months ago i got pissed of with the "60
> minutes" tone of the spider debate (and the name calling) and the lack of
> fundamental understanding of differentials which lead to all sort of
claims.
> so i resolved to figure it all out.  i have emailed, written and wheedled
my
> way around various people and organisations to assemble what is probably
one
> of the finest collections of useless information about differentials, awd
> systems, and traction control systems on the planet.  and i have promised
> myself that i would, one day, get my life back.  that time has come...
>
> anyway, for the record, most information in the public domain of the
torsen
> is incomplete.  it is not that it is inaccurate, but simply that people
read
> what they want to in it (not naming names of course).  while summaries
(such
> as eliot lim's) are accurate, they are also incomplete.
>
> earlier this year when scott claimed that the locked diff couldn't
> proportion torque, i twigged that perhaps this was the cause of the
problem.
> scott and jeff believed then that the locker can't do things that it can,
> and conversely that the torsen can do things that it can't.  anyway, i
> digress.
>
> while attempting to understand scotts position and what his "undersanding"
> of the torsen actually was, it is now clear that the issue is simply that
> scott and other do not understand how either the torsen or the locker
> operates.
>
> the major misunderstanding in this debate the assumption that the torsen
> "distributes torque", and that the locker doesn't.
>
> that is incorrect.
>
> both distribute torque in exactly the same manner.  the only input to the
> equation is (as phil has pointed out), the tractive force at either axle.
> they are both dumb devices.  if one gets fooled by slip angles, then they
> both do.
>
> when cornering within the bias ratio of torque distribution the torsen
diff
> is *locked*.  you may need to re-read that statement.
>
> let me say it again in a different form.  the torsen operates as a bevel
> differential until relative slip between the axles occurs.  this causes
the
> differential to *lock*.  until torque distribution across the diff reaches
> the bias ratio.  which is usually 3:1 (25:75) in audi applications, but
can
> also be 4:1 (80:20) depending upon the design.
>
> with the diff locked (within the bias ratio), it is *exactly* the same as
> the locker.  exactly the same.  both shift torque rearwards depending upon
> relative slip when cornering.  the only difference is that the torsen
starts
> of as an open diff (50:50 torque split) on corner entry.  which means less
> understeer than the locker which has a static torque distriution which
> mirrors the weight distribution of the car (60:40).
>
> the other difference in operation is what happens when the torsen hits the
> bias ratio.  while the locker will continue to shift torque rearwards, at
> this point the torsen diff *unlocks* and allows relative axle speed
> differences.  at this point it is acting as an open differential again,
but
> it is operating at the bias ratio (fixed torque split, variable axle
> speeds).  which it maintains (allowing wheel spin) as long as required.
> this is the torsen 4-wheel drift which we know and love.
>
> if you understand these points, you will understand that the issues that
> scott, jeff and othes have with the device are in fact, not technicaly
> possible with a torsen.  it is as simple as that.  the "bite" has to be
due
> to other issues.  the "alignment" thread (pre and post personal attacks)
> gives clear evidence of this causing similar handling (bite) traits on
both
> torsen and non-torsen cars.  which makes it quite clear really.
>
> i hope that this has cleared up the theory and establihed a technical
> baseline for further discussions.  i am happy to expand on these points if
> anyone wishes.
>
> i have found that following are the essential reading on the subject and
> would recommend them for those interested in further study:
> 1) "comparison of the dynamics of conventional and worm gear
differentials"
> freeman
> 2) "the influence of a torsen on the handling of awd vehicles", heibing
> 3) "traction and handling synergy of a torsen", platteau
> 4) "the new torsen ii technology", egnaczak
> 5) "car suspension and design, chapter 10: 4wd", daniels
>
> dave
> '95 rs2
> '90 ur-q
> '89 mb 2.3-16
>
> -----Original Message-----
>
> Date: Wed, 20 Oct 1999 00:49:38 -0700 (PDT)
> From: Orin Eman <orin@wolfenet.com>
> Subject: Re: Torsen theory for Gary
>
> > Now, this whole arguement depends on several factors:
> > (1) Does the torsen in fact redistribute torque to the rear wheels
> >     when powering through a turn?
>
> True.  Since this hasn't been quoted yet, here is an extract from
> the infamous SAE 885140:
>
> [40m radius turn, acceleration of 4 m/s^2, high-grip (uG approx 0.9)]
>
> "...the front wheels follow a wider radius than the rear wheels on the
> circular course, so that 0.2% of forced slip occurs _between_ the
> two axles, which reduces the wheel slip under traction at the front
> wheels, and reduces the slip at the rear wheels.  This results in the
> tractive forces being redistributed towards the rear wheels, so that
> the tractive force distribution is 38/62%.  The extent of this
> redistribution decreases with increasing cornering radii and road speeds.
> With small cornering radii and low speeds the extent of torque
> redistribution can increase to the torque split limit of 25/75%.
> [Orin: that shudder from the rear you feel in parking lot turns.]
> On a high grip surface, the torque limit split is reached at
> a radius of about 15 meters."
>
> So, yes, absolutely, you can get 75% torque rear due to cornering alone.
>
> > (2) Assuming #1 is true, how much does the rearward torque shift
> >     affect the attitude of the car?  (i.e. large or only small affect)
>
> Good question.  This is the question that needs addressing.
> Phil says aligment is crucial.   Tires matter too.
>
>