The torque converter provides a connection between the engine and the drive wheels and is used to change the torque when the car accelerates.
The planetary gearbox ensures the engagement of forward and reverse gears depending on which of its elements are braked or interlocked with each other. The components of the gearbox can be braked or connected by hydraulically controlled friction clutches. The gearbox control elements receive signals from the hydraulic control unit. The pump maintains the required pressure of the working fluid in the gearbox.
The driver controls the gearbox using a selector with seven positions and a four-position switch. The gearbox can operate in "drive" or "hold" mode in the first three gears (for 4-speed gearbox) or in gears 2 through 4 (for 5-speed gearbox). The "drive" (D) mode provides automatic shifting in the entire range of forward gears and is intended for normal driving conditions. The "hold" mode is similar to the previous mode, except that it limits the number of gears that can be engaged. Thus, in the "3" position of the selector, only one of the first three gears is engaged. In the "2" position of the selector, only one of the first two gears is engaged, and so on. This mode is used when driving on a bad road, and also to prevent the inclusion of a higher gear when driving on a winding road.
Using an additional switch, you can select one of three driving modes: "Economy" (economical). "Sport" (sports) and "Manual" (for 4-speed gearbox) or "Winter" (for 5-speed gearbox).
The "kickdown" mode automatically engages a lower gear when the accelerator pedal is fully depressed.
Some models are equipped with the Steptronic system, which allows the driver to change gears by moving the selector lever forward to increase speed or backward to decrease speed.
Since the transmission is fully automatic, any repairs should only be carried out at a specialist service station. This chapter provides only general information and instructions for servicing the transmission, which you can do yourself.
(The original text of the article is available on the resource: BMWMAN.ru)