All-Wheel Drive

The illustration shows a sectional view of the Torsen center differential.
1 – drive gear (drive to front axle);
2 – hollow shaft (drive from transfer mechanism);
3 – differential housing;
4 – flange/driveshaft (for rear axle drive);
5 – rear axle final drive worm;
6 – spur gears;
7 – worm wheel axle;
8 – worm wheels;
9 – front axle final drive worm.

If any company is to be credited with introducing all-wheel drive into series-production passenger cars "for polite society", it is undoubtedly Audi.

The Audi 80 quattro illustration clearly shows the rear axle drive train with the driveshaft, the rear axle final drive and the rear axle drive shafts.

The off-road vehicle "VW Iltis", developed by Audi for Volkswagen on behalf of the Bundeswehr, most likely served as the seed for the quattro (all-wheel drive) idea. The legend goes:

during a winter trip in northern Sweden, a modest "Iltis" far outpaced much more powerful and faster front-wheel-drive Audis. Afterwards, the then chassis test manager wished for "an all-wheel-drive vehicle with sufficient power" as an everyday car. And since it is well known that nothing is stronger than an idea whose time has come (and this idea seemed to be exactly that), the concept was worked on until the legendary Audi quattro was presented.