gk1

True. It still shows the standard quattro system in a 50/50 ice scenario. Would a sports diff equipped car behave identically in the same situation?

swissdrive

if i remember correctly (there was a thread with that vid on a german forum), it's a 3.0TDI

swissdrive

yes, it's this one :

http://www.motor-talk.de/bilder/audi...203326183.html

and there is also an interesting blog about 4 wheel drives and stuff (sorry, german only)
didn't know DSG and 6MT had different center diffs (AAM Trackrite vs Torsen C)

http://www.motor-talk.de/blogs/autos...-t3030917.html

StevehamS4

By the looks of the video it has a conventional differencial. Since the axles are individually locked to the side gears that is where the drive force needs to be transmitted. Therefore the opposing axle would have to turn at a different rate than the other wheel in the opposite direction. That must be where the clutch takes over and allows the inside wheel to "slip". It looks like the only way to get both wheels driving would be to lock the rear end by preloading the weak side.

Kinda like the old drag race days where we used to preload the right rear traction bar by having the rubber bumper higher than the left. If set right it would fool the differencial into thinking the other tire will slip actually locking the side and pinion gears in the carrier. Worked great until the car swayed.

That is of course if the simulation in the video is accurate displaying the "open end" type rear.

helix139

Well in a straight line it doesn't really matter all that much, does it? When wheel speed is not equal, though, that is where the magic happens and the sport diff acts like neither an LSD (which requires a large torque input for a large torque split) or an open differential (which sends power equally to both wheels up to a maximum of whatever torque it takes to make one wheel slip). While those are mechanical, passive systems, the Sport Diff is an active system that can distribute torque on demand (up to 100% will full locking) through the use of the clutches on either shaft as needed, both as an impact to handling or in low-traction situations, determined and identified by a computer analyzing wheel speed, yaw, acceleration (straight line and lateral), steering wheel position, etc.

So essentially, the answer is that it doesn't exactly function like traditional mechanical passive differentials and has the best characteristics of open, limited slip, and locking depending on what is needed at the time.

NWS4Guy

Some info:

This car is a Euro, so it has the 3.0T badge on the rear, likely an '09 though as it seems to have the HUGE side mirrors, but is an S4

- The car does not have Sport Diff, with SD you can nail the throttle and 100% of the TQ would go to the rear tire on the pavement.

- The F/R TQ split is not 50/50 it's 40/60.

- The SD is both a mechanical and electrical diff, as shown in the video, it has a gearset that drives the clutch plates on each side 10% faster than the axles, and the computer can use the clutches to grip the plates, and transfer as much as 100% of the TQ to one side or the other (within tolerance limits, if you really want to know where that limit is I will dig it up, but I don't recall the TQ limit off the top of my head).

gk1

So you are saying that with Sports Diff you would not have the two driver's side wheels spinning like in the video? The car would just giddy up and go since all the torque would switch to the right rear tire? I'd like to see a video of that.

gk1

Right. I understand the theory but I was curious if anyone had any real world proof. The Sport Diff video indicates 100% torque can be given to either shaft, but they never make mention of this occurring in a straight traction situation, only in a cornering situation. They mention "reverse-esp" for safety but again this must only be in cornering situations.

According to what you are saying when one rear wheel spins it will lock the other rear wheel (hydraulically) to aid traction, but I haven't seen any proof this is true. Does the sport diff hydraulic torque transfer action only come into play when turning or will it activate on straight line wheel spin as you mention?

NWS4Guy

I don't have video, but if you are familiar with the Acura equivalent (SH-AWD), there is a nice article here comparing it on their sport ute against a RX350 and Q7 which don't have it on a similar iced road on 1/2 of the car up a 30% grade:

http://magazine.windingroad.com/issue/55/

Here's a video explaining the S4 SD pretty well:

http://www.youtube.com/v/viWJUaakMKs

gk1

Good info, I think I've seen video of that as well. Unfortunately it only proves the Acura system works this way. Still no proof that the Audi Sport Diff function this way as well. It certainly seems like it should but again I've never seen proof.