The "Quattro system" has anti-spin traction control - it's called EDL. It is a software extension of the ABS system and only works on a per-axle basis. Once Audi introduces yaw control, the system will be intelligent enough to react "beyond the single axle". As EDL stands now, it senses wheel spin, activates the ABS "pump", applies the brake at the spinning wheel to transfer power to the opposite wheel through an OPEN differential. If there is "zero" traction on both left and right wheels of one axle, the brakes are applied back and forth between the two wheels at a high rate. This is the way it works for the front axle and the rear axle. EDL does not lock the open differential - EDL is a misnomer. Locking means that the right and left sides of an "axle" are rotating at the same speed. Audi used locking on their rear diffs in the PAST.<p>The center differential, which resides in the transmission, is a TORSEN. It also does not lock. It<br>redirects engine "torque" to the axle with the MOST traction. This transfer capability only works if there is some (I forgot the ratio.. maybe 7:1) traction available at the axle with the least traction. If this ratio between the axles is not maintained, the TORSEN acts more like an open diff. THIS IS ONE REASON WHY THE ANTI-SPIN BRAKE-BASED SYSTEM (EDL) IS USED. The brake system helps the TORSEN maintain its effectiveness when traction is near zero on it's open diff "axle".<p>E <br>

 

Let's assume that traction was identical and near zero at every wheel. The TORSEN would split torque equally between the front and rear "axles" since the load presented by the front axle is identical to the load presented be the rear axle. On each "independent" axle, EDL would transfer wheel rotation back forth from the left wheel to the right at it maximum designed rate.<p>E

 

Let's assume that your A4 was travelling faster than 25 mph before you wanted to accelerate on this sheet of ice. EDL is off. The load presented to the TORSEN by the front and rear axles are identical. The TORSEN would split the torque equally between the axles. Since the A4 has an OPEN diff in the front and the rear, ONE wheel at EACH axle would spin at one time. <p>E

 

If traction is near zero, and <i>identical</i>, I doubt any system available today would be able to help. I suppose the computer could detect the unrealistic acceleration. One way or the other, you're pretty much stuck.<p>

 

Would EDL still be needed if one used Quaife differentials?

 

Agreed, Just for illustration

 

I believe that quaifes have some "drag" designed in them to improve their effectiveness. Although in a low traction situations, quaiffe owners usually apply brakes to transfer torque (if the quaife is used as a center diff). Quaiffes also require that the traction difference between the front and rear axles be less than TORSEN to work.<p>E

 

The reason I'm asking is because Quaife now offers Front and Rear diffs for the A4...

 

The information I gave you pertains to older Quaifes - mid 80's 4K quattro. I have not researched any of the new offerings. If you have any info, please let me know.<p>Thanks,<br>E

 

<br>I looked this up because a friend of mine is trying to do a mass order of Quaifes directly with Quaife to drop the prices.<p>He's getting one for his GTI.<br>He mentioned a lower price due to quantity.<br>He wanted to know if I knew of any interested buyers and told me about the A4 application.<p>Kev<br>1990 Jetta GTX w/VR6 swap<br>1.8TQMS was due in earliy March... now looks like mid April...<br><ul><li><a href="http://www.autotech.com/qdiff.htm">Quaife info... follow the link to the new applications.</a></li></ul>