Did some more research today and found the information I was looking for. If you are interested about the AWD systems on the CLA and the S3, here's what I found.
Per the literature from mbusa the
CLA uses an AMG performance 4Matic all-wheel drive system. The 4Matic was developed back in 1985 in conjunction with
Steyr-Daimler-Puch (now
Magna Steyr). On the CLA up to 50% of the power can be transferred to the rear wheels on demand.
Pretty thorough write up on wikipedia about 4Matic.
http://en.wikipedia.org/wiki/4Matic
The new S3 uses Haldex.
Starting from 1998, "quattro" has become just a trade mark and it does not guarantee that a full-time all wheel drive system with
Torsen differential is used on the vehicle any more. Now, vehicles with transverse engine mounting (Audi A3/S3 quattro, Audi TT quattro) are equipped with
Haldex automatic all wheel drive. The same type of automatic all wheel drive is used on VW Golf/Bora/Jetta 4motion (199
, VW Sharan 4motion (2001-) and other Volkswagen Audi Group vehicles with transverse engine mounting - Seat and Skoda.
Haldex V is proactive and reacts nearly instantly to any wheel slippage. It also can transfer up to 100% of the power to the rear wheels.
http://www.awdwiki.com/en/quattro+evolutions/
There is some decent info on Haldex on the Borg Warner site. December of 2010 they acquired the AWD Traction Systems of Haldex.
"Haldex Generation V is an electronically controllable all-wheel drive coupling for cars. The Haldex GenV includes an electronic control unit with vehicle dynamics software that can be customized to meet each carmaker's particular desires in terms of driving characteristics.
The front and rear axle of the car is connected via the wet multi-plate clutch which makes it possible to vary the torque distribution between the two axles. As the function of the Haldex GenV is independent of the differential speed between the front and rear axle, full locking torque, if needed, is available at any given time and speed.
When starting the vehicle, the electrical pump in the Haldex Gen V is started, swiftly providing the system with pressurized oil and thereby making the system ready for operation. The pump sets the pressure to the piston which in turn compresses the disc package. The level of pressure set depends on the torque level needed and on the driving situation. In traction/high slip conditions, a high pressure is delivered. In tight curves (i.e. parking) or at high speeds, a much lower pressure is provided."
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