Audi 80/Avant (B4)

since 1991-1995 release

Repair and operation of the car

On an illustration the distributive Torsen-differential in a section is presented.

1 – the leading gear wheel (the drive to the forward bridge); 2 – a hollow shaft (the drive from the transmission gear); 3 – differential case; 4 – the flange/driveshaft (for the drive of the back bridge); 5 – worm of the main transfer of the back bridge;	6 – cylindrical gear wheels; 7 – axis of worm wheels; 8 – worm wheels; 9 – worm of the main transfer of the forward bridge.

If establish authorship of any firm in a question of introduction of the four-wheel drive for the serial cars "in decent society", then it will be given, undoubtedly, by Audis.

The identikit of the Audi 80 quattro car demonstrates transmission to the back bridge with the driveshaft, the main transfer of the back bridge and the leading half shafts of the back bridge.

The VW Iltis SUV developed by request of the Bundeswehr by Audi for Volkswagen, most likely, served as a germinal cage for the idea of quattro (four-wheel drive). The legend says:

during a winter trip in Northern Sweden one modest "Iltis" far overtook much more powerful and bystry front-wheel Audis. After that the head of tests of that time of a running gear wished to have "the all-wheel drive car with a sufficient power" as the daily car. And as it is known that nothing is be stronger than the idea which time came (and this idea, appear, was such), worked on the concept until legendary Audi quattro was presented.

Concepts of the four-wheel drive

The connected four-wheel drive

Until recently the concept of "the all-wheel drive car" was almost inseparably linked with a concept of "the off-road car". The concept of the four-wheel drive of the last was quite simple: one more drive was simply attached to the standard drive (the engine ahead, the drive back), namely to the forward bridge one more transmission via the transfer case and the additional driveshaft conducted.

Trips were carried out usually with the standard drive and only if it was demanded by situation on the road, the forward drive was connected. This design with the connected four-wheel drive and is today usual for cars of the increased passability (SUVs).

Lack of similar system: at trips on a hard coating the four-wheel drive has to be switched-off because on turns forward wheels pass longer way, than back. Various frequency of rotation of wheels result in difficulties with management.

Constant four-wheel drive

So if the idea to create the constant four-wheel drive, permanent on all four wheels came to mind, then it is necessary to create the device preventing wheel slip. This problem is solved by so-called interaxal differential.

Differentials in automotive industry are known for a long time. They distribute torque between the right and left driving wheels.

There too it is necessary to counterbalance forces because, as we know, the external wheel passes on turns longer piece of a way, than internal. The role of the balance weight undertakes axial differential. It allows to give the moment to both driving wheels depending on the angular speed of each of them.

The design of Torsen-differential is based on the principle of the worm gear. The worm gear can be calculated in such a way that it will possess big or smaller coefficient of blocking. 1 – a worm, 2 – a worm wheel.

In the winter, for example, happens so: the wheel standing on ice is turned, and the opposite wheel on a rough covering does not transfer any force and therefore costs. One is clear: the similar differential does not suit for a role interaxal because it is necessary to achieve opposite effect. Force has to be transferred there where wheels will be able to move the car. Namely there, where the paving possesses good coupling. And as the driver never foreknows it, distribution has to happen automatically.

After various development stages, including the interaxal differential blocked manually, the all-wheel drive Audi quattro models are completed today by so-called Torsen-differentsialom.