RE: torsen 101 questions

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

>Date: Sun, 31 Oct 1999 09:27:18 -0800
>From: "David G" <daveglu@hotmail.com>
>Subject: Re: torsen 101 questions
>
>  For simplicity lets discuss a torsen in a rear diff in a front engined,
> rear drive car (as in camaro) (I don't have one!)(don't have a mustang
> anymore either)
>   I don't recall the torque limits but's lets assume this torsen operates
up
> to a 75/25 split.
>
> #1    If driving this theoretical car around our virtual corner (sorry
hard
> to resist) without nearing the torque limit or traction limit (driving
3/10)
> is the torque split 50/50???
>

no, with the torsen static torque split is 50:50 (straight ahead driving in
your scenario).  however, the torque split is determined by the tractive
inputs of both tyres.  torque will bias to the wheel which is travelling
slower, but in your scenario (before the bias ratio is reached), there will
be little or no axle speed differences.  the torsen is acting as a locked
differential would.

btw, you should remember that the torsen design for a centre diff and for an
axle diff are different, because in an axle differential application, it is
desirable to reach the bias ratio earlier than in a centre application....

> #2  If pushed harder to the point the inside tire slips (or would in an
open
> diff) would I be correct in my understanding that it will spin at the same
> rate as the outside tire (acting as if locked)???
>

no, once traction is lost on one wheel, the torsen is at the bias ratio and
will allow axle shaft speed differences, while holding the torque
differences between the shafts at the bias ratio level.  once at the bias
ratio either or both wheels can spin up.  the one much more likely to spin
is the one already overloaded with torque (the inside).  in other words the
bias ratio is forcing more torque to the *least* tractive axle than that
axle can bear (by definition) - hence the axle is already slipping (by
definition).  this is a very important distinction because it has a
fundamental effect on handling dynamics.

> #3 (an easy one I assume) past that point both tires will spin at the same
> rate as long as the torque split does not exceed 75/25  and if exceeded
the
> torsen is uncapable of working and will operate as an open diff.
correct???
>

no.  the torque spit will not exceed 27:75 (or visa-versa).  ever.  once at
the bias ratio, the torsen operates as a open diff except that, rather than
the fixed 50:50 torque allocation of an open diff, it is a 75:25 (or 25:75)
allocation.  but axle speed differences are allowed.

hth,
dave
'95 rs2
'90 ur-q
'88 mb 2.3-16