No new t*rs*n news

[QSHIPQ <QSHIPQ@aol.com>]

... Yet, at least with this summary
Dave writes:

>for example, the paper states that, in drive mode with the centre torsen, in
a
>slow speed corner, the higher driving torque is sent to the axle which tends
to
>turn slower ie. more torque to the rear and less understeer, until as corner
>speed rises and elastic conditions catchup kinematic conditions, the torsen
>operates as a rigid connection.  at higher speed, either oversteer occurs
(rear
>axle slip ratio increases) and surplus torque is sent to the front, or
>understeer occurs (front axle slip ratio increases), where the torsen sends
>torque to the rear, correcting the understeer.

Ok, a closer look at this in terms of O = oversteer and U = understeer might
clear up this paragraph.  We can look at a quattro as a statically (no power)
understeering chassis, due mostly to that way-front hanging motor.   As we
enter the turn with no power we U.  As power is added, the rear wheels are
slower than the fronts, power goes to the rear = O.  As the speed increases
thru the turn, we either oversteer = O, OR we understeer (I read"rigid
connection" to mean 50/50 split, which in a quattro is) = U, then O
'"correction" follows, according to this paper.  (I would say that "rigid
connection" given the device, is a poor choice of words).

So, to summarize the above with a statically understeering quattro, we see U-
O-O, which is a "good" thing, OR we see U-O-U which is a bad thing.  More
specifically, we see the latter as U-O-U-O as is defined in that paper.  Could
this be the bite?  Keep U-O-U-O-... (ad infinitum), and I see a small problem
turning on power.

>the paper also makes the point that, in coast mode, the centre torsen is
still
>operating and doing good things, although the other way around (higher
braking
>torque is sent to the axle which tends to turn *faster* than the other one). 

The torsen differential is a gear not a freewheeling diff, so the torsen
"always" operates.  Higher braking torque to the faster driveshaft while
coasting thru a turn, may not sound so appealing.  Saying a coasting torsen is
braking the faster driveshaft could have some interesting chassis effects as
speed becomes more significant (i.e. there is effect on the torsen as you
"lift").  Guess the "good" would depend on where you are in the U-0-U-(O)
scenario when you lift.  

>anyway, in the summary to the discussion of the torsen in a centre diff
>application, the conclusion is pertinant to the discussion that we have been
>having about the relevance or not of chassis dynamics: 
>"the ideal centre diff torque bias ratio layout in the 4 operating modes is a
>function of vehicle dimensions (wheel base, track width, centre of gravity
>height, ...), suspension elastio-kinematic design (stiffness front/rear,
>angular variations, ...) and engine torque characteristics for given road
>conditions." 

All these variables are also sitting in the archives, though probably the most
relevent CD issue being in terms of weight shift:
Weight Transfer = (Weight x cg height/ wheelbase) x g

>the reason that the famed spider bite hasn't been seen in an ur-q or rs2 (or
>s4?), but has been seen in a type 44 is given above.  chassis dynamics.

The spider bite "can" happen.  Might think "hasn't been seen" should read
"hasn't been experienced" by Dave and Phil yet.   Chassis Dynamics dictates
only the when, not the if.  Yes the level can be raised with CD.  Not sure we
can make the jump to "eliminated" given the BR of the audi Torsen Center and
all center torsen  designs that "can be" fooled in a turn.  If you look at
what you quoted in the paper, they speak of Bias Ratio "based on chassis
dynamics".  Well, we can look to the audi specifically and see that the Urq
torsen part number is the same as the v8 torsen part number.  According to
this paper, that shouldn't be.  Why?  Because as the paper states: "The ideal
centre diff torque bias ratio layout in the 4 operating modes is a function of
vehicle dimensions..."(wheel base, track width, centre of gravity height,
...), suspension elastio-kinematic design (stiffness front/rear, angular
variations, ...) and engine torque characteristics for given road conditions."
The audi microfiche alone points out, that audi chose BR without consideration
of those specific variables, or the BR's would have been different between the
two units, and they aren't. 

 "... And engine torque characteristics for given road conditions"  sounds
like a couple variables that we specifically don't have control of.  "Engine
torque characteristics" is a plottable set of numbers, a given set of
variables.  "...  for given road conditions" would mean that the significance
of engine torque characteristics increases as cf lowers.  Or conversely, that
as cf increases, more engine torque changes the variables again.  That
statement alone, indicates that best case scenario on all those variables goes
right out the window, as the "given road conditions" change (or HP gets high
enough).  How do you dial "given ALL road conditions" into Chassis Dynamics?
I argue you can't.  

Interesting article.  Should certainly accompany Jeff's for some of the detail
of Center Applications, but Dave's summary hardly contradicts the Chocholek
paper, or what Jeff and I have been proposing all along.  Sure raises some
question as to why Audi chose the BR's they did throughout all chassis lines. 

Happy to review and opin (like you need to ask) on the full Monty Dave.  A
copy or a site to see it would help those of us interested in the "latest"
torsen developments.

Scott Justusson

P.S.   I heard some spider bites were induced at the Stapleton Qclub event
last weekend, by an esteemed member of this list.  Quite successfully in
fact...