So, a well engineered AWD system actually sends power away from the slipping wheel(s) and towards the wheels with traction, which makes more sense.
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.
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.
When it goes to the wheels with traction, it helps get the car un-stuck. This is usually what you want when you're doing serious off-roading, stuck in snow, etc... Also, in this scenario you're usually going very slowly/not moving, so the sudden change of direction won't be a problem.
Modern AWD does a bit of both - it'll send power to wheels with traction, but will also compensate by sending power to a wheel on the other side of the car. For example, if there's no traction on your left front tire, it'll send power to your right front tire and left rear tire, and reduce power on your right rear tire to keep you going strait.
I had an old Toyota Tercel 4WD station wagon and it was very difficult to steer sharply at low speed with 4WD engaged because of the lack of a differential. It would lurch and I had to press harder of the accelerator to get straightened out and pop it back into 2WD. It was my first car so I didn't know any better. Fun fact: In 4WD, you got an 'extra low' gear below 1st and that car could very nearly climb trees. The gear ratio was insane. No ground clearance but I used to scare the crap out of friends by going up very steep inclines in extra low gear with 4WD engaged. They would have to park their pickup trucks at the bottom of the hill and ride with me, and this caused them some embarrassment. Good times.
One time in college I was turning too sharply while parking and the axle actually popped out of the right front. Loose axle would just spin in 2WD but switching to 4WD enabled me to make it to the nearby Mech E. building and get help. :)
One day, I think, even 80's and 90's Toyotas will be collectors items. I know some of them are collectors vechicles now, but I feel the 80's to 90's vechicles will see a huge boost in interest.
I think you just said the opposite of the guys above you while saying you agree. 4WD should not have a problem on slippery terrain.
An AWD car has _3_ diffs, one in the middle that splits power F/R, and then one at each axle that splits it L/R.
Highend 4wd setups can lock the diffs so all wheels spin at the same speed all the time - essentially on slippery ground, but very counterproductive when you actually have traction.
The term the are talking about when traction is applied to the wheel with the most binding to the ground and away from the one that has the least traction is called a Limited Slip Differential and by virtue of the slipping of the low traction wheel it will spool the high traction wheel and bind it transferring torque to it. This can also be done by what is called a locker, either electronic or manual but manual lockers can be dangerous at high speed if you are not used to their manor. You generally only see manual lockers and welded differentials in offroad trucks. Limited Slip differentials and electronic lockers are available in both 4WD and AWD vehicles.
The term they are talking about to apply power to both the front and rear wheels is not a differential but rather a transfer case and it is not always at a 50:50 ration man times they run 60:40 or 70:30. Both 4WD and AWD have a transfer case, 4WD's allow you to select whether they are engaged or not.
The term they are talking about when they talk about adjusting power front to back is called a Traction Control Unit and is handled by a Body Control Module that may or may not also communicate with the Engine Control Unit or the Transmission Control Unit to defuel or detorque the powertrain, as well as adjust torque via electronic lockers in the differential to the wheels that need it and away from the ones that do not. As well as engage or disengage front and back axles via the transfer case. Many newer AWD systems have this but it is also available in most newer 4WD vehicles.
TLDR is 4WD and AWD can be virtually identical depending on the subsystems but the article confuses a lot of those subsystems as being unique to one or the other. Though the upper end of 4wd's have more "hardcore" options not generally found or offered in AWD vehicles.
4wd without lockers means you can still get stuck (been there) because front and rear each have their own diffs. One wheel in each diff will be spinning and then you need to get a tug from a friend. The rule of thumb is always have 3 points of contact if you don't have a locker -- then one diff can spin while the other pulls you along.
I have a Dodge 2500 4x4 diesel and even with all that torque (about ~600 ft-lbs) it still bucks if I turn too tight even on ice.
I'm guessing it's due to the transfer case my truck doesn't have a center differential.
Here I am in snow no buck I guess no tight turns https://www.youtube.com/watch?v=zdK75UmoRMY
LSD's front and rear makes this worse, but center is the most important when it comes to on-road maneuverability.
At one point I remember there was a workaround mentioned by the Hummer engineers (I believe) to apply the brake simultaneously with the gas if you ran into the "one wheel spinning in the air" problem. This is a simply a manual application of the same physical solution of creating at least some resistance everywhere.
Hummers have torsen diffs, which have a pair of worm gears where a conventional open diff would have single star gear. As a result, the torsen diff sends some fixed multiple (changes with model) of the torque used by the easier to spin side, to the harder to spin side.
Of course if one wheel is spinning in air, the easy side uses effectively 0 torque, and 0 times anything is still 0, hence the brakes.
Applying the brakes increases the torque requirement of all wheels by a fixed amount, but the hard to spin wheels get More than that amount of extra torque.