randall

-6.0 Degrees Celcius this morning. Nice big ice patches on the roads around my house. Time to test Quattro!! I positioned the car so that the driver’s side front and rear wheels were on pure smooth ice, and the other 2 wheels were on pavement. Stopped the car. The revved it dumped the clutch (weelll not really “dump it”, but pretty hard). The car JUST GOES. You can feel the antilock kick in (sorry “EDL”) and the car just hooks up. Cool!!<p>Now some questions.<br>I understand that the torsen is the center diff, with the front and rear axles being open diffs, and the slip controlled by the ABS system. This would indicate to me that the front and rear are more of an inclement weather thing, rather than a performance thing. I.E performance u would want a limited slip diff.<p>Why wasn’t the quattro setup with either a limited slip or torsen in the rear? I could see why maybe in corners u might not want limited slip up front, but why not Torsen diff?<p>It seems that some of the marketing blurbs that suggest the quattro is torque sensing are only partially true, since it is only the center diff that is torque sensing. The front and rear diffs are speed sensing through ABS sensors.<p>Comments?<p>1996 a4 2.8 qm<br>

Tony

I also thought that ABS Isn't used at all to regulate power (quattro only). Am I Correct?

randall

i posted on this before and got "Schooled":<p>quatro uses:<br>front axle diff: open with ABS to brake slipping wheel.<br>center diff: torsen torque sensing diff (gleason patent?)<br>rear axle diff: open with ABS to brake slipping wheel.<p><br>1996 a4 2.8 qm

Drew S.

Using ABS to brake a slipping wheel is what traction control is all about. I was led to believe that quattro's did not do this.<p>If the front and rear wheels had ABS sensing slip and braking accordingly, then how is the TorSen supposed to sense torque? That's supposed to be TorSens greatest strength -- that it senses torque and sends more power to the wheels that can use it. If the ABS system is braking wheels to stop spin, then I think the TorSen would mistakenly think that there was not a wheel-spin condition happening, and might think that there is no slip occurring.<p>I think someone has two competing technologies confused and merged here. The ABS traction control and a TorSen work in such different ways that I think they don't make sense to put them together. I hope I'm right about this, otherwise someone is going to have to clear up my confusion.<p>Drew S.<br>

randall

there is only one diff on the quattro that is torsen. check your spec sheet or product lit, or the links at the beginning of this forum!!!<p>also remeber that center diff proportions torque between front and rear axle. <p>and i quote:<br>"Quattro IV - permanently engaged all-wheel drive system with Torsen center differnential and Electronic Differential Lock (EDL)"<p>i was pretty grumpy when i discovered this myself. hence the post.<p>further comments invited<p>1996 a4 2.8 qm<br>

CraigB

My Z3 with traction control uses ABS to control wheel spin. I experienced this in sand/gravel on the road one time. The car basically came to a stop the more I tried to accelerate. However, the same test with quattro results in almost immediate traction and instant acceleration, not braking like the BMW traction control system. I'm not sure how it works, but it doesn't use ABS to control wheel spin. <p>CraigB

dave

EDL is described in A4 service training manual WSP-521-222-00. It states that:<p>"Audi A4's use a traction control system called EDL. EDL stands for electronic differential lock. The EDL system works in conjuction with the anti-lock brake system.<p>If one or more of the driven wheels begin to spin, such as on a low grip road surface, EDL counteracts this by applying the brake to the spinning wheel. This ensures that the remaining driven wheels transmit as much available engine power as possible.<p>The EDL system is activated as soon as wheel spin is detected and will continue to operate as long as wheel spiin is detected up to 25 mph. The EDL system will deactivate if the brake pedal is depressed."

Tony

I think that the FAQ that you read is incorrect. If the Quattro uses ABS to prevent Wheel spin then how come I'm able to spin all four wheels? In the Snow Last year I was in a Parking lot Doing Donuts (Flame me), all four wheels were spinning. Sometimes In the rain while making a slow turn in first gear, I'll Press the Clutch in to free up some revs, After the revs build a little I'll then release the clutch, After that, all Four wheels spin and the rear end kicks out. It's the Best. I wouldn't advice anyone to do this. You have to be a little crazy and a Semi-Decent driver. Can someone settle this? I'll believe Information from Audi.<p>Later fellow A4 People >>Tony<p><p>

Tony

That Applies only to FWD vehicles.

Leszek

The EDL (electronic differencial lock) uses the ABS sensors to detect wheel spin. It does *not* use the ABS brakes to brake that wheel. Instead it *locks* the other wheel, meaning it sends *all* of available torque to the non spinning wheel. This way if both wheels on the EDL start to slip the middle torsen diff can take over.<br>--Leszek