Table of contents: All-wheel drive ↓ Permanent all-wheel drive ↓
The Torsen differential is based on the principle of a worm drive. The worm drive can be designed to provide a higher or lower degree of locking. The numbers indicate:
- 1 - worm;
- 2 - worm wheel.
All-wheel drive
Until then, all-wheel drive was almost inseparably linked to the concept of a high-performance vehicle. The all-wheel drive concept used in this family of vehicles was simple:
- In addition to the standard drive (front engine, rear drive) a second transmission was simply routed to the front axle by means of a transmission branch and an additional cardan shaft. Normal driving was carried out with the standard drive, and only if road conditions required it, the front drive transmission was connected. This design with a plug-in all-wheel drive is still used today in off-road vehicles.
- Disadvantage: All-wheel drive must be disengaged for driving on hard ground, as the front wheels travel a greater distance than the rear wheels when turning. Different wheel speeds cause transmissions to become overstrained.
- Effect: the car is difficult to control, on turns, to relieve tension from the drive, the wheel rubs with very slight slippage at certain intervals - the car jumps.
Permanent all-wheel drive
When the idea of a permanent all-wheel drive came to mind, it was necessary to come up with a method of alignment that would not allow overstraining of both axle drives relative to each other. This problem is solved by the so-called central differential.
Differentials have long been known in the automobile industry. They divide the forces between the right and left drive wheels. In this case, too, alignment is necessary because, as is well known, on turns, the outer wheel always travels a greater distance than the inner wheel. This alignment is provided by the axle differential. It provides the axle drive while simultaneously allowing both drive wheels to rotate freely relative to each other.
Anyone who has gotten stuck on the road in winter knows the treachery of the object: a wheel standing on ice turns, the opposite wheel on rough ground does not transmit force and stands still.
One thing becomes clear: such a differential is not suitable as a central differential, because exactly the opposite is needed. The force must be directed to where the wheels can carry you to the ground, namely: where there is a road surface with grip. And since this is never known, the distribution of force must be automatic and without delay. After various stages of development of a locking central differential with manual engagement, today the so-called Torsen distribution differential is integrated into the Audi Quattro models.
[The original material is located on the website «AUDImanual»]