Already 35 years there is the quattro drive. Audis with this drive were sold about 4 million times. Compared with the first, the current is hardly to recognize. In addition to the bevel gear differential, the hollow shaft unfortunately disappeared, too. Also the manual longitudinal lock no longer exists.
In 1986, 'Torsen' came as 'feeling the torque', self-locking centre differential. Now up to 75 percent were sent no longer towards the fewest traction, but the best possible. In contrast to the viscous clutch, Torsen worked relatively smoothly together with ABS. The quattro drive was available also for transverse engines since 1995. An electrically connectible multiple disk clutch (Haldex) changed the permanent all-wheel drive into one if demanded.
After all, therewith the variable torque distribution was established, here even up to 100 percent to the rear axle. Since 2005 was permanently distributed in principle 40 : 60 in favour of the rear axle, whereby were possible infinitely variable from 60 : 40 up to 20 : 80 percent. Added was a self-locking centre differential as a planetary gear. The highest engine performance of the quattros increased up to 426 kW (580 hp).
Now there was with the R8 and its mid-engine a third quattro concept with viscous clutch at the front axle. It receives as standard 15 and if necessary up to 30 percent torque. From the S models the S4 appeared with the so-called sport differential in 2008, which distributed the engine torques actively between the rear wheels depending on driving conditions.
This is the first step into the so-called 'torque vectoring'. The vehicle is stabilized in extreme cornering no longer by braking, but by specific torque distribution. The driver perceives the ESP intervention no longer as inhibitory. For longitudinal installation of the drive unit, the crown gear differential has prevailed in the meantime. Two crown gears rotate inside the new centre differential which owe their name to their gear geometry. The rear gear powers the cardan shaft to the rear axle differential, the front the output to the front axle differential. The crown gears are engaged with four rotatably mounted differential gears. They are placed at a 90 degree angle to each other and get their drive via the housing of the differential of the transmission output shaft.
Under normal driving conditions, the both crown wheels rotate as fast as the housing. Due to their special geometry arise specifically unequal lever effects: In the basic distribution 60 percent of the engine torque move to the differential of the rear axle and 40 percent up front.
If the torques shift themselves because the grip decreases at one axis, different rotational speeds develop inside the differential - axial forces cause that the neighbouring disc sets are pressed together. Now, the resulting self-locking effect directs the majority of the drive torque to the axle with the better traction, up to 85 percent flow to the rear. In the opposite case - if the rear axle has less grip - this process takes place accordingly, now flow up to 70 percent of the torque to the front axle.
With this even wider torque distribution the crown gear differential surpasses its predecessors - the traction becomes even better. The redistribution of forces and torques is carried out without temporal delay and absolutely homogeneously, the active mechanical mode of operation guarantees the highest efficiency and reactions without time lag. Other advantages of the crown gear differential are its compactness and the low weight - with 4.8 kilogrammes it is about two kilogrammes lighter than the previous unit. 06/15