[torsen] RE: differential/torque sensing

QSHIPQ at aol.com QSHIPQ at aol.com
Mon Mar 31 07:52:03 EST 2003


Andre:
Let's back up a second here...  Back to your "bike" analogy:
turn the bike upside down, pedal it so that wheel accelerates to 20 miles per 
hour.  First, that takes a lot of force to do so, even on an unloaded wheel 
in first gear.  But as you accelerate faster, you reach the limit of how fast 
you can turn your hands = redline.  Now, after you have reached that 20miles 
per hour, stop pedalling, and have a friend put his hand on the wheel and 
rotate around the circumference of the wheel opposite the direction of 
travel.  The reverse force is now on the "other" side of the gear (torsen 
basket).  At a certain point that negative force generates negative rotation. 
 Nothing has changed to do so in terms of load on the gear.  The more 
negative force you place on the gear, the faster these events will occur, but 
there isn't a different force in terms of braking vs reverse accelerating.

Over to the torsen, this reverse torque sends the helix gear to the "other 
side of the basket", so that more torque is allocated to the faster spinning 
axle.  If you actually put the car in reverse while you are coasting forward, 
more reverse torque is applied.  Eventually the car will come to a stop, then 
it will start to accelerate backwards.  From a standstill, this force will 
follow inversely weight distribution.  So, from a resting 50/50 state, slip 
increases at the rear wheels relative to the fronts backing up, and more 
torque goes to the wheels with more slip, up to the maximum bias ratio of the 
differential in reverse drive mode.  

So, in the above "unlocking" scenario, we know that torque is going to the 
unloaded axle.  When does that change when in "reverse drive" mode?  I argue 
it doesn't.

Thoughts?

SJ

 
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