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Automatic Transmission 10
Four-wheel Drive

Please see if you can find out, what the main difference is between the two drive-train concepts. It will surprise you, just how much they have in common, although the Audi four-wheel drive was developed from a front- wheel drive and Mercedes from a rear-wheel drive. If we disregard the specifics of the V8-engines and the amount of gear-speeds (Audi: 6, Mercedes: 7) of the particular automatic transmissions, the outcome is that there are hardly any differences at all.

Indeed, it does get a bit more exciting. Mercedes has stayed with the constant power ratio which delivers 45% of the torque to the front- and 55% to the rear wheels. A pre-tensioned multi-disc clutch locks up to a maximum of 50 Nm. Audi, on the other hand, controls the rear axle through a Torsen-differential. In both systems, the electronics has only the possibility of braking intervention.

That's it then. Now you can admire the different constructions of the drive-shafts to the front axle. In Mercedes only the two universal joints are sealed, in Audi they are completely encased and the gear-teeth have an interesting slant. In the meantime, even the engine overhang, past the front axle, is almost the same in both cars, this is because Audi places the clutch or the torque converter behind the front axle differential.

Not only is the similarity between the two systems important, but also that in the course of time, the mechanics have become more simple. The Mercedes 4matic once started out with an externally operated limited- slip. It's function has now been taken over by the ESP. It has a surprisingly low extra weight of only 75 kg for the S-Class, however, it is only available in combination with automatic transmission.

Audi, in the meantime relies exclusively on Torsen, with the classical longitudinal locking right at the beginning and torque distribution through a planetary gearbox, although in a partially simplistic form. As far as the torque distribution of 40% to the front and 60% to the rear is concerned, a change of thinking has taken place. 05/10

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