Quote Originally Posted by itix View Post
To answer your first question. An active center diff locks up the differential at will with some form of clutch arrangement. When the clutch is closed it will be like having no diff at all. When open, it will behave like a standard open differential.

The benefit from this is that the engine torque will always go where there is grip when the diff is locked. For instance, if you had your back wheels on ice and front wheels on tarmac and an open diff, your rear wheels would spin and you'd go nowhere. If you could lock the diff all of the torque would go to the front wheels and you'd move forwards.

It is the same concept in the WRC cars. Under acceleration the diff would lock up and you'd gain more torque on rear wheels due to the front wheels lifting from acceleration (therefore the rear wheels having better grip).

I am not in any way an expert in how they make their diff maps and based on what sensors, angles, positions etc etc... That's for the real brains to work out but at least I gave you one scenario where it would be beneficial.
Hello Itix

Everything you have described can be done - and is done - with a passive diff.
The potential in the active diff (an active centre diff in the WRC17) is that you can regulate power transfer any way you want, any time you want, on the background of the mapping.

So with these new active centre diffs the engineers can map the diffs to distribute power between front and rear as they want. And they will use certain sensors to get the raw data (speed, rotation, gear, throttle, braking, etc), and they will map the diff to distribute power in a certain way according to the parameters they set, and the "numbers" they get from the sensors.

The advatage of the active diff is that it is fully adjustable, so a driver can make the car suit him better in stead of battling it (if he has that kind of problem.) And the diff can react before its needed, so its ready from the second its needed, in stead of having the delay of the passive diffs.