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Re: Oversteering with a locked center diff...



In a message dated 11/9/99 5:34:06 PM Central Standard Time, 
Steven.Buchholz@kla-tencor.com writes:

> Speaking of which, I guess it still isn't clear to me how having a definiive
>  agreement about whether or not it is possible to induce oversteer in a car
>  with a locked center diff is essential to the continuation of discussions
>  about torsen diff behavior.  

My thinking is this Steve.  We had an early impass with Dave Eaton on the 
torsen discussion, which left a void as to the reason/methods to procede.  My 
own thinking is we should use this list to discuss all differential operation 
that applies to quattros:  Locked, open, torsen, then maybe proceed to those 
diffs with open, locked, torsen edl, rear diffs.  Looking to baseline the 
operation of all the differentials, and their corresponding behavior.  In the 
case of the locked center, most that have come to this list, visualize that a 
locked center *can* oversteer.  I go on record that it doesn't, in fact, 
claim most don't (if not *all*).  Looking to the locked diff specifically in 
regards to the chassis dynamics issue, which really are my only 
claims/interest wrt to the torsen. 

This torsen list is a different instrument to many of us here.  I'm not 
convinced that we can chomp all the variables listed to specify *when* and 
*where* the bite occurs, I'm frankly quite content with the *can* happen.

So where to go from here.  Well, I think Dave L and I are looking to develop 
some models and formulas extending 885140 conclusions.  Then maybe explore 
some other differentials.

>  
>  I'm still not able to concentrate on this stuff too much, but it seemed as
>  though there were some questions about Torsens differentiating.  I have two
>  right angle torsens (one installed and the other sitting on the bench) and
>  could do some empirical studies if it made any sense.  One thing that comes
>  to mind would be to mark the tires with the car sitting still (here again
>  we're talking about a rear torsen on a V8Q) in a parking lot, and then
>  driving through an arc at a particular radius using as little engine torque
>  as possible and then seeing if the tires are lined up at the end of the 
arc.
>  Is this worthwhile?  If so, would the radius of the tun matter?

Well, I've thought of that exact experiment.  The best (and only) way I can 
see the above is with a video camera.  Because, once torque is no longer 
applied the BR changes, which could include axle differentiation.  So that 
poses the problem exactly how to do an practical experiment, when you have to 
stop the car to measure.  Not valid results.  We may call upon you to do some 
*bench* testing (thanks for the offer), tho bench testing means we need some 
way to apply torque to the axle which would change in the real world (think 
of a torque curve of a given motor, as torque falls off as rpm increases, the 
bias ratio changes for that torque variable)

So, we don't have all the differential discussions ironed out, there are 
plenty to discuss and come to agreement on.  If we can get some common 
understanding and baseline 885140, I think we can go many places from there, 
since it presents some intrinsic and expressed methodology to isolate some 
variables in a very complicated BR matrix.  Then, proceeding with self 
imposed caution (since we don't have Dave anymore), draw some conclusions 
about these diffs in relation to quattros and quattro handling.

Is whether a locked diff capable of O relevent?  I think if we come to a 
baseline agreement that it can't in any quattro, we have made some progress.  
I'm still a little shell shocked that Dave E couldn't hold up under fire 
here, given his voracity on this torsen issue for the last 2+ years.   Both 
sides lose.  But that shouldn't present this list with an *impass*, we just 
need to actively give this discussion direction.

Thoughts?

Scott Justusson