ok. For all of u who want to argue about what the quattro uses, i am quite comfortable with the following: (but i have a question at the bottom)<p>3 diffs required to proportion torque to all 4 wheels.<p>power first goes to center diff which is torsen (torque sensing) to front and back axles.<p>Side to side torque proportioned on both axles using open diffs. To limit slip, elctronics uses the brakes to limit spin on a specific wheel. EDL is euphamism (sic) for using the brakes/ABS. There is not physical locking of the differentials using mechanicals, or otherwise.<p>The electronic pseudo "limited slip" drops out of operation beyond a certain overall vehicle speed (45KPH or whatever)<p>-----<br>so:<br>To me the system (aside from the torsen) seems biased more to safety then performance. I mean u probably want a limited slip to lay down available power, rather than "brake" one of the wheels (posi-track, et al).<p>why not use a mechanical limited slip or torsen in the rear? I suppose u might not want to do it at the front because of the wheels steering and differnent distance traveled, etc. But isn't a rear limited slip/torsen better than an open diff?<p>i am all for not using clutch packs etc (delayed response, mechanical failure) but is a limited slip prone to the same problems?<p>Comments invited.<p>1996 a4 2.8 qm

Randall,<p>Fine synopsis. And a great question, IMHO. Yes, the system is biased more toward safety. But, the penalties are really fairly minor.<p>The pros of Audis set up: 50:50 FR proportion is THE safest for ice/snow (proven by 12 years of pro rally). Open front differential allows for great steering properties. EDL/abs is a safetynet, it slows the car to match the actual friction of the surface. Torsen is perfectly progressive and doesn't break or wear (amazingly).<p>This setup is biased towards worst case safety. For all out racing I want a 30F:70R bias, and torsens at each diff (available for 2500usd). No stupid sunroof, and 400ft.lbs torque...<p>Is it too much of a compromise?! Nope, this car is highly competitive in SCCA Gstock. I can drive 90 mph all day and it gets 31mpg! I want the safety end for when I screw up, the rest is up to me.<br>

The V8 quattro manual, and I believe the 91 200 quattro/S4/S6 have center AND rear torsen diffs. The handling is great on the road, but they suck trying to navigate a parking lot. The torsens, with the excellent turning radii of these cars, causes the driveline to bind. That said, I can only reference high mileage examples. I wouldn't expect this to be due to wear, but it could be. It is my understanding that torsens can also be designed across a range of "tightness". Don't expect any to show up in the aftermarket arena though. I did see someone mention Quaiffes, but I don't remember what type they are.<p>You are corect about the quattro system in the A4, although I thought it was active to 80MPH (seems a little high).<p>Todd W

I am trying to get some work done so I can go on vacation....but NO, you gotta post these thought provoking "quattro" threads...that actually make me think....Please refrain from these kind of posts until I get my essential work done. Thanks for understanding. :-P<p>Still at Work Steve<br>97 2.8QM < - - - - - audi content<br>

And they claim that 100% of torque can now be transfered to 1 wheel. From my quick read of the brochure, the center differential appears similar to Torsion(?), but I didn't get into it enough to figure out side to side transfer. FYI.<p>Tom<br>1.8TQMS Silver/Ecru

Actually I don't believe this is mechanically possible with their system. They use a variety of pressure-activated limited-slip friction (wet) disks. Even torsen doesn't have 100% lockup (see latest Grassroots Motorsports).

And I quote:<p>"In many 4x4s, two wheels on a wet or slippery<br>surface on the same side of the vehicle would<br>mean a call for help. In a Grand Cherokee<br>equipped with Quadra-Drive, the Vari-Lok front<br>and rear progressive axles transfer engine torque<br>to the wheel or wheels with the most traction,<br>giving you plenty of power to continue your<br>journey.<p>Designed to provide outstanding responsiveness<br>and make maximum use of traction, Quadra-Drive<br>sends virtually all engine torque through the<br>transfer case to the rear axle and wheels under<br>normal driving conditions.<p>The moment a rear wheel loses grip, however, the<br>system can respond in a number of ways. For<br>instance, a gerotor coupling in the rear Vari-Lok<br>progressive axle transfers torque to the other rear<br>wheel (side to side). If that wheel does not have<br>sufficient traction, a gerotor pump in the<br>Quadra-Trac II™ transfer case supplies<br>instantaneous pressure to a multidisc clutch pack<br>that progressively transfers torque to the front<br>Vari-Lok axle (rear to front). There, a gerotor<br>coupling can transfer 100 percent of the developed<br>engine torque to just one front wheel (side to side).<p>This reaction and torque transfer is continuously<br>monitored and maintained by Quadra-Drive<br>regardless of which wheel experiences loss of<br>traction -- and it is done progressively, silently and<br>smoothly."<p>Miles

a little about how AWD/automatic breaking works. The Porsche allows the driver to turn the EDL off.

after being on this web site for 5 months, we finally got a direct internet connection at work.<p>It was driving me nuts how fast u guys respond to posts. <p>I had to dial up, (everyone hears the modem connecting), and i had no access to my extension when connected to the internet!!!<p>Actually not on vacation yet, but i had way too much fun this morning (read other post on handbrake)<p>1996 a4 2.8 qm (RED, concert, r-28 on order)

Jeep: Under normal driving conditions, the Quadra-Trac II transfer case transfers most of the power and torque to the rear wheels. The moment a wheel loses traction, a speed variation between the front and rear axle occurs and a gerotor pump applies hydraulic pressure to a multi-disc clutch pack. This bridges the coupling, minimizes speed difference and sends power to the front axle. The vehicle maintains traction and control.<p>The gerotor pump is similar to an engine oil pump. The rotor is driven by the front drive shaft and the case by the rear drive shaft which creates a<br>pressurized oil flow to the clutch pack in proportion to their speed variation. As with the pump, clutch discs are alternately splined to the front and rear drive shafts.Power transfer in a Vari-Lok differential is proportional to wheel speed difference rather than torque difference as is typically the case in mechanical<br>limited-slip systems. Because conventional limited-slip differentials are initially pre-loaded to assure torque transfer, normal use tends to cause wear that reduces the ability of the differential to transfer torque over time. By design, the Vari-Lok differential is virtually wear free.<p>ErikR: Chrystler uses one of the two kinds of gerotor, the speed sensitive version. From Gerotor: Conventional torque sensitive limited slip differentials in highly powered two wheel drive vehicles, lose directional stability under hard acceleration due to differential lockup and commensurate spin at both rear wheels. GERODISC will also spin both wheels but at slightly different rates, thus preserving lateral stablity. As in Option 1, the GERODISC coupling provides a virtual torque split ratio continuously variable between 10:90 to 50:50.<p>NOT 100% lockup!!!!<p>Note, with front locking hubs, If desired, a locking feature may be incorporated into the TWIN-DISC front axle shafts...<p><br>http://www.media.chrysler.com/wwwprkt/25de.htm<br>http://www.ashacorp.com/gerodisc.html<ul><li><a href="http://www.ashacorp.com/gerodisc.html">Gerotor</a></li></ul>

The electronic differential locking (EDL) operates both the front and rear differentials. The system detects and limits wheel spin and redistributes the drive torque from side-to-side to take advantage of available traction. The ABS system (brakes) are not part of the EDL system (although I think the same Bosch controller for the ABS system may be used). The EDL operates automatically at speeds up to 45mph like previously mentioned. <p>This, combined with the front-to-rear power distribution capability of the TORSEN (TORque SENsing) center differential that distributes up to 66% of the traction to whichever axle has the most traction, can theoretically help get the car underway with traction to only one wheel.<p>There is also VW/Audi's ASR (Anti-Slip Regulation) system that limits wheel spin through the ABS system on FWD A4s (and 1.8T Passat models).<p>More alphabet soup anyone?<p>-jamie

One of the articles mentioned by name the same units used in the new Jeep as the units that will be utilized on the TT. Can someone confirm this?<p>Mike

Similar concept, but no diff and electronically controlled in the TT. I have not heard of any similarities of manufacturers.

EDL clamps calipers on brakes, thereby controlling the diffs. I don't know why they have a different name for the FWD version.

i think ASR can cut power in addition to braking wheels (EDL). <p>biggest reason why they use EDL instead of another torsen is COST. a torsen<br>is expensive, EDL is practically free if you already have ABS.. it uses all the ABS<br>hardware you simply need to program the ABS controller to do EDL.. EDL is<br>just inverse ABS if you think about it.<p>i prefer the system in my v8 (clutch pack center, torsen rear) compared to<br>what i have on the a4 now.

<br>A friend of mine is ordering a mass number of them.<p>I don't know if the Quaifes qualify (say that 10 times fast) as torsen type diffs but I know that they are indispensible on FWD autocrossers etc.<p>I would imagine if the Quaifes could balance torque mechanically, the EDL would probably not get used as frequently.<p>The Quaifes also firm up steering feel in FWD (increase the effort) which may or may not be beneficial for the A4. I've heard that the A4's steering is a little light and I personally think it could be a little heavier.<p>Anyhow anyone want to add any input to this?<p>Kev<br>1990 Jetta GTX w/95 VR6 motor swap<br>1.8TQMS now due in April I'm told (ordered from B status on Nov. 21)

Some more info regarding the use of Torsen or Quaife diffs in the front or rear:<p>1. Torsens (and Quaifes) require that the "slippery" side have at least some traction available. If the torque bias ratio is not met on an axle (about 4:1- 6:1), the Torsen will act as an open diff. This does not happen with EDL (ABS based anti-slip control). EDL can transfer 100% rotation with 0 traction on the "slippery" side.<p>2. Using Torsens in the front will affect steering unless a very low bias ratio is used, one approaching an open diff. Also, Torsen bias ratios vary when accelerating and deaccelerating - not good up front.<p>3. Torsen and Quaifes do have additional drag. Quaifes have a greater drag or pre-load.<p>E

<br>If you look at the diagram long enough you'll see how it works.<ul><li><a href="http://www.autotech.com/qdiff.htm">Click Me</a></li></ul>

Was I wrong, or did they find a loophole in the patent (or has the patent expired)?