quattro evolutions (English, Русский)

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

Type: Full-time all wheel drive.

• Open center differential, manually lockable via switch on center console.¹
• Open rear differential, manually lockable via switch on center console.¹
• Open front differential (no lock).

¹ABS disabled when locked.

Figure: audi quattro evolution 1 differentials lock button

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.

Used 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 (1991-1994) Audi 100/200 quattro, S4.

Type: Full-time all wheel drive.

• Torsen type I 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.¹
• Open front differential (no lock).

¹ABS disabled when locked, automatically unlocks if speed exceeds 25 km/h (15mph)

Figure: audi quattro evolution 2 rear differential lock button

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 this single wheel only and the car will not be able to 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.

Used on Audi V8 starting from 1990

Type: 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 I differential rear.
• Open differential front.

• V8 with manual transmission:
• Torsen type I differential center.
• Torsen type I 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: -

Used from 1994 on Audi A6/S6 C4 (facelifted Audi 100), then on newer generation on Audi A4/S4, A6/S6 C5, A8/S8 with both manual and automatic transmissions (1998 to 2007). Also on VW Passat B5 and Phaeton 4motion.

Type: Full-time all wheel drive.

• Torsen type I center differential, 50/50 split in normal conditions, automatically locking with up to 80% of torque transfer to either axle.
• Open rear differential, Electronic Differential Lock.
• Open front differential, Electronic Differential Lock.

Manually lockable 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 with 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: Good all-weather all wheel drive for on-road use, no driver intervention.

Cons: When both front or both rear wheels are on ice, rollers, or raised in the air, the four wheel drive does not work.

Used on Audi Q7 (2005-), RS4 B7 manual (2005-), S4 B7 manual (2006-), A4 B8 all modifications (2007-), A5, A6 facelift (? 2006- verify)

Type: 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 (2008-) - Torque-Vectoring "active sport differential".
• Open front differential, Electronic Differential Lock.

Figure: Torsen type III center differential on quattro evolution V

Watch how "active sport differential" works (from 2:40):

Figure: Audi active sport differential

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: Good all-weather all wheel drive for on-road use, no driver intervention.

Cons: When both front or both rear wheels are on ice, rollers, or raised in the air, the four wheel drive does not work.

Used on Audi RS5 (2010-...)

Type: Full-time all wheel drive.

• Crown-gear 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. Audi RS5 - rear "active sport differential".
• Open front differential.

Electronic Torque-Vectoring system. This system applies brakes to the inner wheel when the vehicle is turning.

Figure: audi crown gear differential

Figure: audi crown gear differential

Figure: audi crown gear differential

"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."^[1]

"Inside the new center differential are two rotating crown gears that owe their name to the crown-like design of their teeth. The rear crown gear drives the propshaft to the rear axle, and the front one the output shaft that runs to the front axle’s differential The crown gears are driven by four pivot-mounted compensating gears arranged at angles of 90 degrees to each other. They are driven by the housing of the differential, i.e. by the gearbox output shaft.

Under normal driving conditions, the two crown gears turn at the same speed as the housing. Because of their special geometry, they have specifically unequal lever effects. Normally 60 percent of the engine torque goes to the rear differential and 40 percent to the front differential.

If the torques change because one axle loses grip, different speeds and axial forces occur inside the differential and the adjacent plate packages are pressed against one another. The resulting self-locking effect now diverts the majority of the torque to the axle with the better traction; up to 85 percent can flow to the back. In the opposite scenario – if the rear axle has less grip – the same happens in reverse; now up to 70 percent of the torque is diverted to the front axle.

With this broad torque distribution range, the crown gear differential surpasses its predecessors – traction becomes even better. Forces and torques are redistributed without any time lag and absolutely consistently. The purely mechanical operating principle guarantees maximum efficiency and no-delay response. Other strong points of the crown gear differential are its compactness and low weight – at 4.8 kilograms (10.58 lb) it is roughly two kilograms (4.41 lb) lighter than the previous unit.

Audi combines the crown gear differential in the RS 5 – and in other models in which it will subsequently feature – with an intelligent software solution in braking management called torque vectoring. An evolutionary form of the ESP with electronic differential lock that is already standard on many front-wheel-drive models, however it can act on each of the four wheels. The new system makes cornering even more precise and dynamic.

Using the driver’s steering input and desired level of acceleration, the software calculates the optimal distribution of propulsive power between all four wheels. If it detects that the wheels on the inside of the curve, which are under a reduced load, will soon begin to slip, it marginally brakes these wheels – just slight application of the pads on the disks at minimal pressure is all that it takes. This assistance is provided smoothly and continuously. The car remains neutral noticeably longer, and understeer when turning and accelerating is practically neutralized. The ESP intervenes later and more gently – if necessary at all."

Source: DVD quattro® Highlights 2010^[2]

The new system called e-quattro will use a pair of electric motors with a total output of 136 PS to power the rear wheels. The internal-combustion engine would supply power to the front wheels only. Allegedly the new system will be utilized on the next generation of Audi A4 B9 starting from 2014.

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.

Type: Automatic all wheel drive.

• Haldex electronically controlled multiplate clutch installed instead of a center differential.
• Open rear differential.
• Open front differential, Electronic Differential Lock.

This all wheel drive system is based on front wheel drive transmission layout. In normal driving conditions up to 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-...) is proactive and 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 just 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.

The car with Haldex all wheel drive can be towed with one axle lifted, and it is possible to use tires with different wear level, or use the compact temporary spare wheel.

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. All wheel drive will engage even if front wheels have completely lost traction.

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.

Figure: Haldex IV all wheel drive on Audi TT quattro

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• Comparison of Quattro V vs. Haldex.
• 30 years of quattro:http://www.audi-quattro-highlights.com/