>> "...sends power away from the slipping wheel(s)..."
Exactly this. The best ones are entirely mechanical, without any fancy computers or even viscous couplings. Audi sold (sells?) IMHO the most sophisticated AWD system on the market, which uses a system of crossed helical gears to continuously and instantaneously redistribute torque proportionally to wheel traction, up to a roughly 80-20 split. There are no computers and the whole thing is mechanical. The differential is a minor mechanical miracle sold under the trade name Torsen, short for "torque sensing." Despite Audi's German-engineering themed marketing, the differential was actually designed by an American.
In the 80's, the station wagons even had a manually-actuated center locker, which was eventually replaced by a servomoter driven locker. I don't know what the new ones have.
Audi Quattro is great, although IIRC, it also eats a bit tires on tight turns like anything but an open diff would. I also like the viscous clutch on the jeep, although it definitely is less on-road friendly (A tight 90 degree turn is enough to hear the tires, 180 and you can almost feel the car get lower). My worst system was my 98 explorer - it engages the clutch completely when front axle falls behind, waits a second, disengages to check if axle is still behind, if so, reengages... It's jumpy as hell when turning, and sucked no matter what. You could mod it for pure 2WD operation by switch, but stock was awful.
However, I don't think you should underestimate electric systems. I mean, I hate car software with a passion, but when they work, they actually have really good characteristics. Things like LSD's where the pump is electrically enabled give quite smooth transitions, and can simulate the response of both on and offroad mechanic systems. Response time is also nearly instant. If car computers weren't bloody black boxes (or at least leave only important things to the black box!), these systems often end up being much simpler than their purely mechanic black voodoo counterparts.
Exactly this. The best ones are entirely mechanical, without any fancy computers or even viscous couplings. Audi sold (sells?) IMHO the most sophisticated AWD system on the market, which uses a system of crossed helical gears to continuously and instantaneously redistribute torque proportionally to wheel traction, up to a roughly 80-20 split. There are no computers and the whole thing is mechanical. The differential is a minor mechanical miracle sold under the trade name Torsen, short for "torque sensing." Despite Audi's German-engineering themed marketing, the differential was actually designed by an American.
In the 80's, the station wagons even had a manually-actuated center locker, which was eventually replaced by a servomoter driven locker. I don't know what the new ones have.