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Re: Torsen stuff/Torsen Threads <*all*>

Phil says:
>I still find it bizarre that a phenomenon that occurs (AFAIK) on only
>two cars out of Audi's production of many hundreds of thousands of
>vehicles is causing this discussion.

No, there are two people claiming to have done it on every torsen they've
tried to do it on.  Big difference.

Scott says about what Phil says:
>>  The Torsen doesn't care about corners.  It can't 'see' corners - it
>>  has no sensors whatever.  All it has is an input shaft supplying
>>  torque and two output shafts to which it delivers that torque.
>NO.  Phil, you can't be anymore wrong.  885140 "Vehicle Behavior When 
>Acclerating in a Turn: (.9cf, max load, 80q) "...  However, the front
>follow a wider radius that the rear wheels on the circular course, so that 
>.2% forced slip occurs between the two axles, which reduces the wheel slip 
>under traction at the front wheels. and increases the slip at the rear 

Sorry Scott, but Phil is correct.  The example of slip being given here
seems to be the slip in the differential (i.e. difference in speed of the
two outputs) because of the difference in circumference of the turn at the 2
ends of the car.  The slip in the differential reduces the forced slip of
the wheels that would be required if the differential were locked and had no
slip.  The difference in speeds of the front vs. the rear is *exactly* the
same as might occur if the fronts were on ice.  Power is being applied, yet
the fronts spin faster, therefore more torque is allocated to the rear.  It
can't see corners, only differences in output shaft speed (which equates to
wheel speed indirectly through another front or rear differential) as a
result of the application of torque.  To the extent that slip affects
traction, it can see it because of torque's affect on the slipping tire.

>  This results in the tractive forces being distributed towards the 
>rear wheels, so that the tractive force distribution is 38/62%....  On a
>grip surface the torque split limit (75/25) is reached at a radius of about


Hah!  The answer to the bite?  Greg: Cockamamie theory 17 -- Phil's
roundabout and Scott's track turns are on different sides of this radius.

>  However, if the wheels of one axle reach the limit of adhesion, 
>the drive torque is diverted to the other axle (within the range of the 
>torque split limits), independent of the forced slip rsulting from the 
>vehicles circular path."

Because of the sudden drop in torque-force required to spin the wheel that
has just reached the limit of adhesion, obviously.  (Or, because of the
sudden increase in wheel speed for that given application of torque.)

>There are two inputs to torque allocation in a Torsen diff:  1)  Traction
> 2)  relative slip angles.  This is a basic torsen center differential 

Sorry, but traction and relative slip angles only affect the amount of
torque required to drive the wheel, or rather, the speed the wheel turns for
a given torque input, and that torque/speed-difference is the only possible,
conceivable thing the diff can be detecting.  You must have missed the irony
of Phil's NASDAQ reference.  Please explain how a dumb device can know about
slip angles vs. traction vs. no traction.  It can't.  There is no difference
between them except for the result.  The torsen can only see the result --
how all those things affect torque/wheel-speed.

Jack Rich