Setup torque ratio for AWD vehicles

Question

I'm trying to model some AWD cars but are confused about their "advertised" torque split ratio.

For the Ford Focus RS Mk4, "a maximum of 70 per cent of the drive torque can be diverted to the rear axle", does that mean I'm going to use a torque splitter, with 0 preload and 0.7 stiffness?

For Subaru DCCD,  41/59 split,.. Utilizing a planetary mechanical limited slip differential as well as an electronic differential that the driver can lock up when needed, does that mean it's going to be a center viscous differential with 0.6 stiffness and rear axle as primary? Or a torque bias with 0.6 bias?

Sometimes it's just, for example, 40/60 split, does it mean it's an open center differential but with asymetrical torque split?

Thank you.

Answer 1

The differential with asymmetric torque distribution (also planetary differential) hasn't been incorporated to the vehicle controller yet. This is planned for a future update (can't estimate any date, sorry).

UPDATE: A convenient way of configuring asymmetric torque distribution in AWD vehicles is setting up different gear ratios at front and rear differentials (more info). This has the same effect as using a planetary differential. However, at this moment this requires writing a custom vehicle controller, as the standard VPVehicleController doesn't expose a procedure for setting up different front-rear differential ratios. This is planned for a future release.

Currently you may emulate the torque distribution by using a center viscous differential or a torque splitter. For those cases, I'd start by trying a viscous differential without preload, then finding a stiffness that shows a similar torque distribution. Watch the Telemetry (column Td) for the torque values actually sent to each wheel:

• The viscous differential sends the same torque to both shafts, but when one rotates faster than the other then some torque is routed to the slower rotating shaft. The amount of routed torque is based on the stiffness and the preload.
• The torque splitter sends the torque to the primary shaft, but when this shaft rotates faster than the secondary then some torque is routed to it. The amount of routed torque is based on the stiffness.

Stiffness is a sort of locking ratio. 

• A stiffness of 0 means no locking at all. A differential will behave as open. A torque splitter will apply torque to the primary shaft only.
• A stiffness of 1 means fully locked, like a rigid rod. Both shafts are forced to rotate at the same exact rate. Both the differential and the torque splitter behave as locked center differentials.
• A stiffness of 0.5 is half way between both situations.