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it uses a fluid clutch setup in the drivetrain.

 

Panza,
The torque split is determined by the centre differential. The centre diff comprises an epicyclic gear assembly in conjunction with a viscous coupling.
It is important to appreciate the specific purpose of each component -
The epicyclic differential (more of this later) is what transmits and splits the engine torgue to front and rear transmissions. It is an ingenious arrangement that allows a differential speed between input and output (ie front and rear) when need be, but under normal conditions when everything runs at the same speed, it provides the predetermined torque split front-rear.
The viscous coupling has absolutely nothing to do with the torque split, but applies a viscous "connection" between the front and rear drives, which acts to limit the potential SPEED difference between the two ends under poor traction conditions (a form of 'limited slip' if you like)

If you want to make your brain hurt, have a read through the following link, which explains how the epicyclic gear mechanism works and how it produces the torque split (it's all about the relative diameters of the sun and planet gears )

http://home.earthlink.net/~graham1/M...plitDevice.htm
Don't worry about the fact it's talking about the Toyota Prius sytem, it is the principle that is the same - the last section is the most relevant to the torque split issue.

Hope this helps

 

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I've uploaded some pages from the Technician's Manual HERE it's not brilliantly clear, but it might help visualise it better