Audi quattro AWD DIFFERENCES - Torsen vs Centre Differential vs Haldex vs Ultra

Audi Quattro DIFFERENCES - Centre Differential vs Haldex vs Ultra HOW IT'S MADE the AWD Audi System. Audi A1 - A3 - A4 - A5 - A6 - A7 - A8 - Q2 - Q3 - Q5 - Q7 - R8 - 4wd DSG or S-tronc - Manual Gearbox

00:00 - Audi quattro intro
00:45 - Audi quattro Self-Locking crow-gear (Gen VI)
06:52 - Audi quattro ultra
09:46 - Audi quattro haldex
12:55 - Audi quattro Viscous Coupling (R8)

► AUDI A4 - A5 - A6 - A7 - A8 - Q5 - Q7: Audi quattro with self-locking crown-gear centre-differential anq torque vectoring

Audi debuted the 6th generation of quattro in the 2010 RS5. The key change in generation VI is the replacement of the Torsen Type "C" centre differential with an Audi-developed "Crown Gear" differential. With the new "Crown Gear" center differential, up to 70% of the torque can be applied to the front wheels while up to 85% can be applied to the rear wheels if necessary. The net result of this advance in quattro is the ability of the vehicle electronics to fully manage the vehicle dynamics in all traction situations, whether in cornering, acceleration, braking, snow or in any combination of these. This system was later adopted by the A7, latest generation of the A6 and A8.

► AUDI A1 - A3 - Q2 - Q3: Audi quattro with HALDEX

Starting from 1998, the Swedish Haldex Traction LSC unit replaced the viscous coupling. Haldex is used by Audi on the quattro versions of the Audi S1, Audi A3, Audi S3, and the Audi TT. It is also used by Volkswagen in the 4motion versions of the Mk4 and Mk5 generations of Volkswagen Golf, Volkswagen Jetta, and the Golf R32, Volkswagen Sharan, 6th generation VW Passat (also based on the A-platform) and Transporter T5. On the Audis, the trademark holds, and are still referred to as quattro, whereas the Volkswagens receive the 4motion name. The Škoda Octavia 4x4 and SEAT León 4 and SEAT Alhambra 4 also used Haldex LSC, being based on Volkswagen Group models. Curiously, the Bugatti Veyron also utilizes Haldex, though with separate transmission, PTU and front and rear axles.

► Audi R8: Audi quattro with Viscous Coupling

This 4WD system was used only on Volkswagen branded vehicles, and was never used on any Audi cars except Audi R8 model.

A viscous coupling installed instead of a centre differential, with freewheel mechanism to disconnect the driven axle when braking.

Normally a front-wheel drive vehicle (except Vanagon, see above). In normal driving conditions, 95% of torque is transferred to front axle. Because viscous coupling is considered to be "slow" (some time is needed for silicone fluid to warm-up and solidify), 5% of torque is transferred to rear axle at all times to "pre-tension" the viscous coupling and reduce activation time. The coupling locks when slipping occurs and up to near 50% of torque is automatically transferred to rear axle (front in Vanagon). In on-road conditions, the car will not move if one front wheel and one rear wheel lose traction.

The freewheel segment, installed inside the rear differential, lets rear wheels rotate faster than front wheels without locking the viscous coupling and preventing ABS from applying brakes to each wheel independently. Because of the freewheel, torque can be transferred to rear axle only when the vehicle is moving forward. For four-wheel drive to work when reversing, a vacuum-actuated "throttle control element" is installed on the differential case. This device locks the freewheel mechanism when in reverse gear. The freewheel mechanism unlocks when the gear-shift lever is pushed to the right, past the third gear. The freewheel is not unlocked immediately after leaving reverse gear on purpose – this is to prevent the freewheel from cycling from locked to unlocked if the car is stuck and driver is trying to "rock" the car by changing from first to reverse and back.

Disadvantages of this four-wheel drive system are related to actuation time of the viscous coupling.

When cornering under acceleration on a slippery surface, the rear axle is engaged with delay, causing sudden change in the car's behaviour (from understeer to oversteer).

When starting on a sandy surface, the front wheels can dig into the sand before all-wheel drive is engaged.

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