AWD discussion, continued...
 

...The merits of different systems have been discussed here at length, with Audi's usually suffering from the supposed limitations of its center diff. Here's a quote from the Audi PR literature (from the AW Geneva show stuff on the new A4 quattro Cabriolet):

"Normally the power is split 50:50 between the two pairs of wheels, but in extreme cases the entire propulsive power can be diverted to either pair."

It also talks about an electronic diff lock to put all the power to one wheel.

Either some of the discussions here have been off-base, or Audi's upped the quattro ante beyond what we've been used to.

Not with a torsen diff it can't...
 

Somebody in Marketing is overspeaking the truth. Seems normal. =)

the new audi magazine has an article on torsen that said up to 66% can be sent to either axle and
 

33% can be sent to one wheel with edl.(think the other 33% is lost in braking the slipping wheel?)

did you see the car and driver review on tv of the new land rover disco 2 off roading?
 

i heard that has torsen center differential and edl and they were lifting tires off the ground while driving offroad and the car continued to move forward.

I thought the Torsen diff was the strength of the system?
 

I've tried to educate myself on this recently and I thought the Torsen diff was as good as it gets.

I thought the weakness was EDL instead of front and rear diffs that could actually redirect torque.

Do I need to go back to school?

Nope, maximum power to any single axle is 67%, maximum power to any single wheel is also 67%.

Missed the review. Would be cool to see. At least one wheel per axel has to have traction unless...
 

The EDL system works to brake <i>both</i> the slipping wheels on an axel - thereby supplying torque to those wheels. Then, some percentage of the torque can be sent to the front wheels. It's what happens on the Hummers for left/right power distribution when one wheel is in the air - Brake Throttle Modulation.

It is a strength in most situations. The Torsen is the quickest acting differential ->
 

for power distribution between axels. We get real fultime AWD becasue of it, and the front/rear power distribution happens as soon as a torque difference is sensed.

The negatives:

a) Speed differences are not sensed. So, if the spinning wheels happen to exert the same drive shaft torque as the non spinning wheels, that is not sensed - though I'm honestly not sure if that's possible.

b) The big one - only a certain "difference" between front and rear torque is supported - limited by the Torsen's bias ratio of 2:1. When that difference in power distribution is exceeded, the differential effectively opens - sending all the power to the wheels with least resistance. So, if you have one axel on asphault, and one axel in the mud, you should get stuck.

April Posted Links to a couple of great articles on allwheel drive systems
 

alot of good information. Oh this was posted on the new a4 forum with in the last couple of days.

How can that be?
 

Our cars have open, non-locking diffs front and rear. By definition, these distrubute an equal amount of torque to each wheel. So it would be impossible to send more then 50% of torque available at that axle (or 33% of the total engine torque) to one wheel.

The EDL can only absorb torque, not redistribute it to the other wheel.

How is my understand wrong?