RE: torsen tech 101

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

dave, thanks for your input.  i hope that i've addressed those issues with
"torsen tech 102" recently posted, where i specifically address the
low-speed manoeuvring issue.  but, it is as you say, it was just that i
didn't cover that case specifically in "torsen tech 101".

with regards to the locker having a static torque bias of 50:50, you need to
understand that the locker has no method of apportioning torque.  in other
words, it has no idea of what 50% is.  unlike the open diff which is of
course fixed at this figure.  once you accept that, then you will see that
the locker in an audi moving in a straight line at constant speed
proportions torque based on chassis kinematics, which mirror the weight
distribution (in this situation).  this point is made in the jeff daniels
book.  the torsen in this same scenario is, like the open diff, operating at
a 50% torque bias to either axle.

what i would consider "essential" references are the list i included,
although the "torsen ii" paper is just in there to show how torsen design
has changed over the years...

dave
'95 rs2
'90 ur-q
'88 mb 2.3-16

-----Original Message-----
From: Lawson, Dave [mailto:dlawson@ball.com]
Sent: Friday, 22 October 1999 11:28
To: Dave.Eaton@clear.net.nz
Cc: quattro list
Subject: Re: torsen tech 101


Dave,

>anyway, for the record, most information in the public domain of the torsen
>is incomplete.

What documents are needed to create a complete set of information by
which someone can better understand the Torsen operation? Is it the list
(1-5) identified in your post? Just wondering...


>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.

I would add that others have stated this same thing. The available tractive
force does include the effect of relative slip angles.


>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.

It appears when you use the term *lock* in this context, you are
associating the torsen behavior to that of a locked differential, which
you mention in the next paragraph. If that is so, then the locked
differential has the characteristics of equal speed of output shafts
with variable torques to the output shafts. In AUTOTECH 95,
C498/30/144 (your reference (3)), Figure 6 shows that
the torsen doesn't behave *exactly* like a locker, at *low* lateral
accelerations, the torsen does allow wheel speed differences. Then
there is the region which they call *Medium* lateral accelerations
in which the torsen does behave like a locked differential where
both output shafts have the same speed, albeit with different
allocated torques.

>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 "static torque distriution which mirrors the weight distribution of the
car (60:40)" for a locked differential is only true when the allocated
torque
to a given axle has exceed tractive force of that axle. If the allocated
torque
is less than the tractive force and all wheels are rotating at the same
speed
on the same surface, the torque distribution is 50:50, just like the open
differential and torsen differential.


More to come.
-
Dave Lawson