Hello and thank you for using just answer!
What year and Model Lexus are we discussing here?
The all wheel drive systems on the new models is much more complex and better controlled then on the older models.
I am sure you have read about the benefits of VSC, ABS, skid control, Traction control and Brake force distribution (EBD), these are all incorporated into the ABS system on this car and it also works with the all wheel drive system.
The is250 and Gs350 use the exact same setup, just different size cars with different engines and transmissions.
Basically the rear wheel drive works the exact same on both of these as they do on a regular 2wd model, with all wheel drive there is a differential bolted to the transmissin to supply power to the front wheels.
On the AWD models they use a full-time transfer differential.This transfer uses a planetary gear type limited slip center differential. A wet type multi-disc clutch is used
as the center differential limiting device, and the silent chain is used for transferring driving force to the
front wheels.This transfer also adopts the AWD control system. Based on driving conditions, this system optimally
distributes driving force to the front and rear wheels. Distribution of the driving force is done by electronic
control of the center differential limiting device.
So when driving on a smooth dry road you will have about 80% power to rear and 20% to front.
When you get into low traction the system can divide power up to 50/50 between front and rear.
The system also uses the traction control and ABS to kep traction, so lets say for example you get onto ice or mud, if one wheel is slipping not only will the transfer differential split power 50/50 but the car will also use the brakes to control wheel slip, so brake force is applied to the slipping wheels a needed to keep traction on the wheels that can grab. So basically you can keep your foot on the gas in low traction control and the car will do what it needs to do in order to move. The throttle is also electronic on this car, so if needed to get traction the engine output is reduced. It is really interesting to experiment with these cars in low traction, I once got onto an icy hill with one of these, I felt a wheel try to slip, I floored the gas pedal and then car did all the work, the engine stayed at about 2,000 rpms as the abs cycled to switch power to the gripping wheels and the car slowly climbed the hill at about 5 mph.
Are there any technical specifications or specific questions you have on this system?