A well-known disadvantage of SUVs is the need to turn on rear-wheel drive only when driving over rough terrain. When driving on a flat roadway, this drive must be turned off, because when making a turn, the radius of movement of the front wheels is greater than the rear wheels, and the car becomes difficult to control.
In AUDI 80 quattro vehicles, this problem is solved by the so-called distributive (interaxle) differential (Torsen distribution differential), developed by Gleason, which provided permanent all-wheel drive. The operation of this differential is based on the principle of a worm drive (see illustration 2.0a).
The designation Torsen was assigned to the differential not by chance, but is derived from two words, which can be translated from English as «torque sensing». This is true, because when driving on poor quality roads, the Torsen differential automatically directs the main traction force to those wheels that have the best grip on the road surface. When driving on a road with a flat hard surface, on which the wheels and the rear and front suspensions have the same degree of adhesion, there is an even distribution of the driving force and there is no need to turn off the differential, as is done with SUVs.
Due to the specified differential, it was possible to solve the problem of handling when cornering. Due to the fact that the radius of movement of the rear wheels when making a turn is less than that of the front wheels, and, accordingly, the number of their revolutions is also less, the distribution differential transfers more traction to them, keeping the car on the desired trajectory. If, when cornering at high speed, there is an accelerated rotation of one of the rear wheels, then the differential immediately redistributes traction and directs it to the slower rotating front wheels at the moment. This fast differential response causes the front wheels to pull harder at this point, and this stabilizes the vehicle.
Quattro vehicles - operating instructions
The drive does not act on the raised front or rear axle. The same applies to the raised rear wheel if the differential is not engaged. When the cardan shaft is disconnected from the gearbox, the drive does not work.
The rear and front brakes can be checked alternately on a conventional stand, the speed of which is approximately 6 km / h. The drive to the wheels must perform the stand. Do not engage the differential lock or gear when checking the brakes.
The power test should be performed only on a stand that ensures the vehicle is placed on all four wheels.
The car must be equipped with wheels of the same size and it is desirable that all tires have the same profile depth of the pattern. Dynamic wheel balancing is only possible with all wheels raised. The drive of the wheels must be carried out from the engine, and not from the machine. Attention! Do not apply the parking brake while doing this. Winter tires are also recommended for quattro models. Snow chains should also be installed if necessary.
Transportation of an emergency vehicle AUDI quattro is carried out in the usual manner, if it is operated and it is on all four wheels. If at least one wheel does not turn or is raised, then the car is recommended to be transported by loading. Transportation in tow with a raised defective wheel is allowed if it is carried out for a distance of not more than 50 km and at a speed not exceeding 50 km/h. The differential does not need to be turned on. If these limits are exceeded, the gearbox may be damaged due to a lack of lubrication.
The rear-wheel drive differential on quattro vehicles has a wheel speed lock. This lock allows both rear wheels to turn at the same speed, thus preventing one of the wheels from spinning. The lock is intended primarily as a starting aid, especially on snowy, icy or muddy roads. When the vehicle reaches a speed above 25 km/h, the lock is automatically deactivated.
It is necessary to turn on the lock when the car is stationary using the switch located on the center console. This command is executed by the electronic control unit. Located under the rear seat, it opens the low pressure air supply or, when the vehicle reaches a speed of over 25 km / h, it closes the air supply, thereby disabling the lock. Low pressure air intake comes from the intake manifold (see illustration 2.0b).
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