All Wheel Driven - Audi's quattro Evolutions

Used from 1981 to 1987 in Audi quattro turbo coupe, Audi 80 B2 platform (1978-1987), Audi 100 C3 platform (1983-1992), Audi 4000, Audi 5000 on American market.

Full-time all wheel drive.
Open center differential, manually lockable via switch on center console. *
Open rear differential, manually lockable via switch on center console. *
Open front differential (no lock).
* ABS disabled when locked.

When two differentials are locked, up to 100% of torque can be transferred to either axle. The car will not move if one front wheel and both rear wheels lose traction.

Pros: A true solid 4x4, very good for off-road.
Cons: not good for everyday use, needs driver intervention.

quattro II

Starting from 1988 on older generation Audis B2 and C3 platform and Audi quattro turbo coupe until the end of their production and on new generation B3 platform (1989-1992) Audi 80/90 quattro, B4 platform (1992-1995) Audi 80, Coupe quattro, S2, RS2, C4 platform (1991-1997) Audi 100/200 quattro, S4, earlier C4 platform (1995-1998) A6/S6.

Full-time all wheel drive.
Torsen type II center differential, 50/50 split in normal conditions, automatically locking with up to 80% of torque transfer to either axle.
Open rear differential, manually lockable via switch on the center console, located next to the handbrake. *
Open front differential (no lock).
*ABS disabled when locked, automatically unlocks if speed exceeds 25 km/h (15mph)

When rear differential is manually locked, the car will not move if one front wheel and both rear wheels lose traction, but this behaviour occurs only when all wheels are on the ground. Note that, due to the constructive feature of the Torsen (TORque SENsing) differential, if no torque is sensed on one axle the Torsen works as an open differential i.e. if one front wheel is raised in the air the Torsen differential will not lock, all engine power will be transferred to the wheel in the air and the car will not move.

Pros: All-weather all wheel drive with automatic torque distribution front/rear. Manual locking of rear differential is required only in very severe conditions.
Cons: If one front wheel happens to be in the air spinning freely, the all wheel drive will not work.

quattro III

Used on Audi V8 starting from 1990

Full-time all wheel drive. The system varies depending on the transmission being used:

V8 with automatic transmission:
Planetary gear center differential with electronically-controlled multi-plate locking clutch.
Torsen type II differential rear.
Open differential front.

V8 with manual transmission:
Torsen type II differential center.
Torsen type II differential rear.
Open differential front.

The car will not be able to move if one front and both rear wheels lose traction. The Torsen effect with a front wheel raised in the air will not happen on V8 with automatic transmission because it does not feature a Torsen center differential - if front axle loses traction, the multi-plate clutch is automatically locked transferring up to 100% of torque to the rear axle.

Pros: All weather full-time all wheel drive, no driver intervention.
Cons: -

quattro IV

From 1998 to 2007 on Audi A4/S4, A6/S6, A8/S8 with both manual and automatic transmissions. Also on VW Passat and Phaeton 4motion.

Manually locking rear differential was replaced by an Electronic Differential Lock (i.e. limited slip differential imitation - the system detects wheelspin via ABS sensors and applies brakes to spinning wheels, which results in transferring the torque via open differential to another wheel which has more traction). EDL works at speeds up to 40kph (25mph), on more powerful versions (S4/S6/S8) - up to 80kph (50mph). In addition to wheel braking, Audi A8/S8 also limits engine rpm when excessive wheelspin occurs.

EDL controls torque transfer side-to-side. If, for example, both rear wheels are slipping and rotating with the same speed, EDL is not involved. This is the Torsen center differential that controls torque transfer front-to-rear.

This is a superb all wheel drive system for an on-road car. In on-road conditions the car will not be able to move only when all four wheels lose traction. Torsen effect with a front wheel in the air will not happen on quattro IV because Electronic Differential Lock will apply brakes to the spinning wheel and Torsen center differential will transfer torque to rear axle.

In off-road conditions (wheels in the air and an obstacle restricting the vehicle from moving forward) the car will not move further when one front and one rear wheels lose traction. The reason of this behavior is that Electronic Differential Lock system is not a replacement for a mechanical differential lock and it is not able to transfer enough torque to another wheel. The car will end up spinning one front and one rear wheel with crackling EDL trying to stop them from spinning.

Pros: Superb all-weather full-time all wheel drive, no driver intervention.
Cons: -

quattro V

Used on Audi Q7 (2005-), RS4 B7 manual (2005-), S4 B7 manual (2006-), A4 B8 all modifications (2007-), A6 facelift (? 2006- verify)

Full-time all wheel drive.
Torsen type III planetary type center differential, 40/60 torque split front to rear, automatically locking with torque transfer variable from 70/30 to 15/85 front to rear.
Open rear differential, Electronic Differential Lock. Audi S4 - "active sport differential" aka "vectoring quattro system" ?.
Open front differential, Electronic Differential Lock.

A torque split was changed on this vehicle to improve handling. Previous quattro generations were critisized for their unstable behaviour in slippery conditions, where the car's behaviour could suddenly change from understeer to oversteer. Transferring more torque to the rear axle in quattro generation V gives a rear wheel drive-like feel.

In on-road conditions the car will not be able to move only when all four wheels lose traction.

In off-road conditions (wheels in the air and an obstacle restricting the vehicle from moving forward) the car will not move further when one front and one rear wheels lose traction. The reason of this behavior is that Electronic Differential Lock is not a replacement for mechanical differential lock and it is not able to transfer enough torque to another wheel. The car will end up spinning one front and one rear wheel with crackling EDL trying to stop them from spinning.

Pros: Superb all-weather full-time all wheel drive, no driver intervention.
Cons: -

Quattro VI

"Audi did take the time to also point out that the RS5 features new quattro technology: the crown-gear differential. This new differential is a self-locking center differential that Audi says is lightweight and maintains a high efficiency ratio. The front to rear power ratio can be shifted as extreme at 70 percent upfront, or 85 percent out back – depending on where the power is needed. Under normal conditions, the RS5 enjoys a 40:60 front to rear split."

quattro without a torsen differential: Haldex All Wheel Drive.

Starting from 1998, "quattro" has become just a trade mark and it does not guarantee that a full-time all wheel drive system with Torsen differential is used on the vehicle any more. Now, vehicles with transverse engine mounting (Audi A3/S3 quattro, Audi TT quattro) are equipped with Haldex automatic all wheel drive. The same type of automatic all wheel drive is used on VW Golf/Bora/Jetta 4motion (1998-), VW Sharan 4motion (2001-) and other Volkswagen Audi Group vehicles with transverse engine mounting - Seat and Skoda.
All V.A.G. vehicles with longitudinal engine mounting (Audi A6 quattro, A8 quattro, VW Passat 4motion, etc.) continue to use the Torsen-based full-time all wheel drive.

Automatic all wheel drive.
Haldex electronically controlled multiplate clutch installed instead of a center differential.
Open rear differential.
Open front differential, Electronic Differential Lock.

Normally front wheel drive vehicle. In normal driving conditions 100% of torque transferred to front axle. When slipping occurs, Haldex multiplate clutch locks and up to 100% of torque is automatically transferred to rear axle. Haldex Generation I and II clutch offers instant activation - it locks as soon as one driveshaft travels just 1/8 of a turn further than the other. Front wheels do just 1/4 of a turn before all wheel drive is activated. Haldex Generation III and IV clutch (2004-...) does not need to wait for a wheelspin to occur - it has a clutch "pre-tensioning" system, that is activated by the ECU when needed, for example, when accelerating.

Accompanied by EDL on front wheels, in on-road conditions, the car will not move if two front and one rear wheels lose traction. But again, due to limitations of Electronic Differential Lock (see quattro IV description above), in off-road conditions, it is enough for one front and one rear wheel to lose traction and the car will not move.

Haldex Electronic Control Unit disengages the clutch as soon as brakes are applied to allow ABS work properly; it also disengages the clutch when handbrake is pulled to allow "handbrake turns". When performing tight low-speed turns (e.g. parking) the clutch is also disengaged by Electronic Control Unit to avoid wind-up in transmission.

Pros: In comparison to Torsen-based all wheel drive, Haldex clutch offers 100% locking - up to 100% of torque can be transferred to the rear axle. In comparison to viscous coupling based all wheel drive (e.g. Volkswagen Golf Mk II Syncro), Haldex offers instant activation.
Cons: Haldex Generation I and II is a reactive rather than preventive all wheel drive. Torsen-based all wheel drive is always there, offering more stability at high speeds, while Haldex is activated only when needed. However, with introduction of Haldex Generation III and IV, this is not an issue any more. Haldex III and IV has a clutch pre-tensioning feature and is preventive.

There are 11 comments

andre

March 05, 2010 - 08:51

Subject:

www.audiusanews.com

this is the press release about the sport differential a couple of years ago. Most interestingly it is active even when you lift off of the throttle. I wonder how this compares to other systems...??

andre

March 05, 2010 - 08:40

Subject:

www.audiusanews.com

This link was a part of the press release for the 30th year of quattro....which is why it's launching on the RS5. Apparently they say it's lighter and more compact as far as the center differential. They also explain about "electronic torque vectoring" (which Volvo also notes their new S60 has). My only question is - why move from Torsen and develop a system on your own? I thought they were good parterns but I guess they want a proprietary system (the Lexus LS now licenses the Torsen system)....??

Hans Simonsen

February 28, 2010 - 11:43

Subject: Audi RS5

A really good description of all the quatro types!
I read that the new Audi RS5 has a new type of differential but I don't understand how it works.
Any plans on updating this page?

Regards, Hans Simonsen

Reply to Hans Simonsen

awd.ee

February 28, 2010 - 17:27

Subject: Re: Audi RS5

Thanks, I've added this system to the list, but I am still lacking the details, as this is something really new.

allrad

December 07, 2009 - 23:11

Subject: some words to quattro system (Torsen)

As I said before, I've checked that Audi video (test Torsen) some time ago, and I have to say I was very surprised by behaving of Torsen differential. I thought that car will be promptly away from rollers, but he had to accelerate to go away... And now I found this video which I shouldn't see - www.youtube.com !!! Same situation, same result! Can't understand it!

Reply to allrad

awd.ee

December 08, 2009 - 18:31

Subject: Re: some words to quattro system (Torsen)

Yes, this is a very interesting feature of TorSen. The Quattro II description on this page explains why this behaviour is happening.

In this situation, driver has to apply brakes to the spinning wheels and TorSen will transfer torque to the wheels with traction.

Reply to allrad

allrad

December 08, 2009 - 20:45

Subject: Re: some words to quattro system (Torsen)

i think i understood it, according to Torque Bias Ratio of Torsen diff, for example 4,0:1, diff is able to transfer up to 80% of torque to axle with better traction... so the minimal torque on the slipping axle, which can cause limited-slippage, is 20%... if its lower, torsen behaves as open diff and u have to help yourself by park break (in case of slipping rear axle) or lightly pushing break pedal (dunno if it works) (in case of slipping front axle)... in case of torsen in rear axle and one wheel slipping in air, the same process as with slipping front axle (?)...

Reply to allrad

George

January 16, 2010 - 03:49

Subject: Re: some words to quattro system (Torsen)

That kind of video shows how disingenuous some people are.
The coefficient of friction of a [grippy] tire and asphalt is about 1.00
The coefficient of glare is about 0.1 [ice really isn't that slippery, it is the ice-water boundary layer that results forms from contact pressure-ergo Blizzak and other similar tires]
The coefficient of rolling resistance of rollers [with quality bearings] is roughly 0.01.
These roller scenarios equate to having your wheels airborne.
The traction difference, neglecting the front biased weight distribution of an A8, slightly better than 60/40, is FAR outside the TBR of 3:1.

allrad

December 07, 2009 - 22:10

Subject: Superb web sites!!!

I was just browsing web, looking for some 4wd schemes, info, tech specs, images and other stuff, and i found these sites. I'm glad someone made such a good job. I'm also totally all wheel drive addicted, collecting everything about this theme. I'm interested especially in technical side of 4WD's, so I highly appreciated your sites - even though I wasn't surprised by any AWD system presented here (how it works), I enlarged my knowledge at least. I've also checked all videos (that Audi saw some time ago) and also wanted to share some other greats:

www.youtube.com --- full-time 4x4 rulez! (great video!!!!!!!!!!!!!) - why I haven't seen comparison between Subaru AWD and Audi quattro (full-time) yet? :-)
www.youtube.com --- this shows why full-time 4x4 is the best choice - Subaru Outback vs Volvo XC70 AWD - SLOW hill climb!
www.youtube.com --- Subaru symmetrical AWD
www.youtube.com --- quattro rulezzzzzzzzzzzzzzzzzzzzzzzzz!!!!!!!!!

Well, thx again for ur great job and enjoy these videos, if u haven't seen them!

contact:
icq: 300742500
aim: allradx

Reply to allrad

allrad

December 07, 2009 - 22:36

Subject: Re: Superb web sites!!!

PS: Contact me if you want me to provide some schemes you don't have...

Reply to allrad

George

January 16, 2010 - 05:30

Subject: Re: Superb web sites!!!

Those Subaru videos (#1 & 3) were crap.
Marketing propaganda. Lies and non sequiturs.
The snow hill video doesn't make sense [I saw it years ago]. I don't know the year exactly when it was filmed, but the X5, pre 'xDrive'-'04 model year, has the same drivetrain as the 3-series [open front, open 38/62 planetary center, open rear]. So was the performance difference entirely tire dependent. [Weren't those Dunlop SP Winter Sport M2 on the 3-series? If they are, they are pavement oriented winter tires.]
The RX300 has the MF2AV, but the Torsen rear differential was optional. Did that one have it?
Why does it look like the Patrol hits the brakes while still moving forward?

If you want technical, I hope you have read this
www.torsen.com

or find the error is his reasoning that leads him to believe 50/50 torque split.
www.stealth316.com