In the automatic transmission for commercial vehicles, there is no clutch pedal and gear shift lever available. It has two planetary gear set which is folded together in a single component and a various set of bands to lock its parts. In this, different gear ratios are produced by a set of gears. Main components of a planetary gear set are: The Ring Gear The planet gear along with the gear carrier The sun Gear The primary job of the automatic transmission in the commercial vehicle is to operate the engine in order to allow it in the speed of narrow range. It also provides a wide range of speed output. Summary: Sometimes it could be seen that the manual transmission for commercial vehicles could not do the work of selecting the right torque and speed for the right load which results in the poor utilization of the power. This could be done perfectly by the automatic transmission. The unit of automatic transmission also has an odd system which is hydraulic and has control of the bands and clutches. A gear pump is also present for the movement of transmission fluid all around. In order to lock the other parts of the gear set, a set of three wet-plate clutches is also present there.  http://www.avtec.in/avtec-automotive-engines-and-transmissions.php