Intelligent All Wheel Drive explained

Explanation

Intelligent All Wheel Drive also called automatic all wheel drive is any all wheel drive system that has the ability to automatically vary the amount of torque that is sent to the individual wheels.

Intelligent all wheel drive can improve a vehicle's on road performance and sometimes even assist with off roading. You will need some dedicated off road features for heavy off roading but an intelligent awd system may still help you when you're away from paved surfaces.
Since the vehicle varies or splits the torque between wheels automatically it must receive information from somewhere to decide which are the wheels to remove power from and which are the best wheels to supply power to.
An intelligent awd system may receive data from but not limited to wheel speed sensors, steering angle and yaw rate sensors. This information may then be sent to an ECU which would make the decision as to how to distribute the power from the engine.
There are three types of intelligent all wheel drive systems:

The first type is where only the front wheels are driven. The vehicle functions as a front wheel drive by default and only if the front wheels lose traction then power is sent to the rear wheels. This type is usually referred to as automatic all wheel drive and is very common on crossover SUVs that use a front wheel drive platform.
The second type is where power is sent to the four wheels by default but more power can be sent to the front wheels, rear wheels, left wheels, right wheels or in extreme cases even one wheel if the vehicle starts to lose traction. Power will be sent away from the wheel(s) with traction loss and unto the wheel(s) with the most traction.
The third and least common type is where only the rear wheels receive power. The vehicle functions as a rear wheel drive by default to maintain a sporty character while driving and power is sent to the front wheels only if the rear wheels lose traction.

On the topic of traction loss, a wheel does not have to lose traction until it has 0% grip before power is sent to the other wheels and this applies to all three types mentioned above. The detection of wheel slippage/traction loss and the sending of power to other wheels usually occur in a short space of time, sometimes under a second.
As with any other feature different marques will design their system to function differently with power being transferred at different levels of grip, different reaction times and different amounts of power being transferred.
Some vehicles give more power to certain wheels like the torque split may be 50:50 front to rear in some vehicles and 40:60 front to rear in some vehicles. The rear bias is the intention of the manufacturer and any shifting of torque will occur from that bias.
The second type of intelligent all wheel drive is the type commonly used by high end marques and the one with the big names. One of the most popular and recognised is Audi's quattro but there are also other big names as Mercedes Benz 4-Matic, BMW's X-Drive, Ferrari 4RM and Volkswagen 4-Motion.

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