[torsen] RE: Snow Driving

Keith Maddock Keith.Maddock at trw.com
Mon Dec 16 05:00:42 EST 2002

Scott - 

Trg has to equal Teng.

Don't forget that torque going to the axles  has can go to either or both of the following
A) Providing torque to the tire/road interface
B) providing power to accelerate the rotational speed of the rotating drivetrain.

In the case that input torque to an axle exceeds it's friction capability at the tire/road interface (SurfaceMu*NormalForce), the torque "T1" or "T2" doesn't decrease, the excess over Mu*N just goes into making the wheels spin faster rather than pushing the vehicle.  Eventually Teng will decrease because the driver lifts the gas pedal because they see their speedo pegged at 180mph while the vehicle is sitting still (depending on what the speedo uses to detect vehicle speed), or they hear the spinning wheels  (depends on the skill level of the driver :-D  )


Scott First wrote:
  So, my statement appears correct, that Trg is reduced,  cuz by
definition T1(front) +T2 (rear)= Trg, NOT Teng.  As you exceed traction by
spinning a front wheel, T1 is reduced, so then by definition is Trg.  If I
don't have that right, please do help me understand.

Dave then replied:
no, trg cannot change.  as you have stated, trg=t1+t2 (the 2 output shafts).
all that changes is the mix between t1 & t2 - this is, by definition, the torsen
doing its thing.  if the torque can't be supported by one input shaft, it is
sent by the spur gears to the other side.  trg stays the same.

Scott replied back:
Dave, speaking of when a wheel spins at the max BR, trg is reduced (for audi 
awd we can call it Ttos - Torque Trans output shaft).  According to all the 
SAE papers, T1 and T2 are the traction abilities of the front axle and the 
rear axle.  The sum of these two are referred to as Trg.  Think of it as 
Brake specific torque.  Without the brake (traction) Trg is reduced.  The 
only way to have Trg = Teng + gearing is if T1 +T2 (however allocated) = no 

Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com 
** In Arvidsjaur, Sweden,  02-13 December 2003 **
** Direct line: +46 960 /  57 869    Reception  x800  **

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