The Thorsen differential is based on the principle of a worm gear. The worm drive can be designed to provide a more or less high degree of blocking. The numbers indicate:
- 1 - worm;
- 2 - worm wheel.
Plug-in all-wheel drive
Until then, four-wheel drive was almost inextricably linked to the concept of a cross-country 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 laid to the front axle by retracting the gear and an additional cardan shaft. The movement in the normal mode took place with a standard drive, and only if the road conditions required it, the front drive transmission was connected. This plug-in all-wheel drive design is still used today in off-road vehicles.
- Disadvantage: All-wheel drive must be disengaged to drive on hard ground, as the front wheels travel a longer distance than the rear wheels when cornering. Different wheel speeds lead to overstressing of the transmissions.
- Effect: the car is difficult to steer, on turns to relieve stress from the drive, the wheel rubs with very little slipping at certain intervals - the car bounces.
Permanent all-wheel drive
When the idea of permanent all-wheel drive came to mind, it was necessary to come up with an alignment method that would not allow both axle drives to overvoltage relative to each other. This problem is solved by the so-called center differential.
Differentials have long been known in the automotive industry. They share the forces between the right and left drive wheel. In this case, alignment is also necessary, because, as you know, on turns, the outer wheel with respect to the turn always covers a longer distance than the inner wheel. This alignment is provided by the axle differential. It provides axle drive with simultaneous possibility of free rotation of both drive wheels relative to each other.
Anyone who got stuck on the road in winter knows the insidiousness of the subject: 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 one, since just the opposite case is needed. The force must be directed to where the wheels can take you to the ground, namely where there is a pavement with traction. And since this is never known, the distribution of power must be automatic and without delay. After various stages in the development of a manual locking center differential, the Audi Quattro now incorporates a so-called distribution torque differential.
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