Re: A4 Electronic locking diffs...

[marriott@Summa4.COM]

> In a message dated 96-10-18 01:41:30 EDT, you write:

> .... A locked diff in the center will split torque 50/50....  An open 
diff
> will send more torque to the spinning wheel, hence the locking....  On a
>  side
> to side diff, the lock is rarely 100%, usually more like 70%, even with a
> torsen, hi is 80%....  The locking mechanism on audi GENII is 100% or 
open,
> 100-0-100 to the spinning wheel. Open diffs send more power to the 
spinning
> wheel, limited slips "lock" the other side when wheel slip is sensed.... 
 
>  Me
> thinks you might be confused....
> 
> Scott

i know that a wheel without any traction can't absorb any more torque than 
it takes to accel/decel the wheel in a rotating fashion. for the sake of 
this discussion, put the rear of the car on jackstands (with little wheels 
on the bottom, so you can drive around like that) and leave the front, with 
hot racing tires mounted, on super-grippy asphalt . lock the center 
differential, and even the rear if you wish. let the (virtual) clutch out 
and see that nearly ALL torque goes to the front wheels. not _all_ the 
torque goes to the front because a little is used to speed up the rear 
wheels, axles, driveshaft, differential, hub/rotor, etc, so they rotate at 
the same speed as the front. this is because for a rotating body, newton's 
second law, f = ma, becomes 

T = angular acceleration * mass-moment of inertia

T = torque (newton-meters, ft-lb, etc.)
aa = rad / sec^2, rpm / m, how fast is the velocity changing
mmoi = related to the amount of mass and how far out is is from the 
rotational center

here we see that even though the center diff is locked, the torque split is 
not 50-50. if you wonder, "how often do i drive around on jackstands?" i 
would say pulling out of your driveway (snowy/icy) onto the road 
(salted/dry) would be nearly equivalent.

just my 3 pfennings (@ current exchange)
james


James Marriott, BSME
Manchester, NH, USA
marriott@Summa4.COM
'64 Falcon Sprint Convertible--balanced & blueprinted V-8. GOES great. 
Stopping?
'86 4000S--the better half's commuter
'87 4000CSQ--H-stock auto-x