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7.1.1. Torque transmission

At a car start of motion driving wheels need considerable torque while the engine develops the small moment on low turns. In this case you include the 1st transfer, and thanks to its transfer number the torque increases, and rotation of wheels in comparison with the frequency of rotation of the engine is slowed down.
At movement along the high-speed highway on the 5th transfer there is the return. Its transfer number such is that the frequency of rotation of the engine at torque transmission increases by driving wheels. Thus, with almost invariable frequency of rotation of the engine the desirable speed of rotation of wheels is reached.
However, kinematic communication between the engine and the transmission can be interrupted — for example when you launch the engine, stand on the traffic light with the working engine or want to switch transfer. On cars with a mechanical box of gear shifting this task is carried out by coupling. Thanks to it also perhaps smooth start of motion as it levels the frequency of rotation of a bent shaft and leading shaft of a box of gear shifting. On automatic transmission function of coupling is performed by the hydrotransformer. Main advantages of automatic transmission following: the engine does not become deaf, there is no need of gear shifting that facilitates driving.