[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Torsen 103

Dave writes:
>in re-reading my last post "torsen tech 102", i realise that i have not made
>something as clear as i should have.
>when the torsen reaches the bias ratio and then "opens" or "unlocks" to
>allow axle speed differentiation, it is now operating as an open diff would,
>but the torque outputs *remain* at the bias ratio.  they do not change.  so
>while an open diff will allow different output shaft speeds but equal
>torque, the torsen will told the bias ratio torque outputs to each shaft,
>but also allow shaft speeds to change.
>surplus torque gets turned into wheel spin.  as in the 4-wheel drift.
>thus it is *impossible* for the torsen when at the bias ratio to "apportion
>torque" front to rear as some are assuming.  at the bias ratio, it is acting
>as a bevel diff with fixed torque outputs (albeit at different levels).

No, not true.  In your 885140 "...With tighter radii the differential starts 
to accomodate different speeds of rotation at the two axles.  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 resulting from the vehicles circular path."  

This expressly means, if you are forcing slip do to steering, and it causes a 
traction input, traction input rules over slip angle input.  In the case 
above, if the rear breaks traction torque shifts forward, and immediately.  
If that overloads the tractive ability of the fronts, then torque shifts 
rearward again.  We are getting close to the bite phenomenon.  Given the 
above turning scenario, the ONLY thing that could shift torque forward is a 
traction input rear.  It will shift and suddenly = U, it's a different and 
priority torsen input.  However, if you haven't added any steering and 
restored traction to the rear, the torsen will default to the rear bias = O 
due to slip angle differences.  Each time the rear loses traction, torque 
goes forward.  Each time the rear gains traction, torque goes rearward due to 
slip angle.  Can happen by lowering cf, or raising Trg.

Think of it this way, if *all* you have is a slip angle argument on dry 
pavement, you can make the above claim.  The problem is, a car with 75% of 
it's torque on the rear wheels could very much induce a traction input to the 
torsen (increase trg or decrease cf).  In which case, slip angle differences 
become secondary to the input and output of the torsen's appropriation of 

Scott Justusson