The operation of an automatic transmission is explained here with help of animation. Allison-1000 transmission model, which has 6 speed and reverse is used for this purpose.
source/image(PrtSc): Learn Engineering
The video starts with an explanation of planetary gear set. Just by engaging few clutch packs different output speed can be achieved in automatic transmission. A brief introduction of the torque converter is also given here. Watch the video from Learn Engineering for more info:
There is no clutch pedal in an automatic transmission car.There is no gear shift in an automatic transmission car. Once you put the transmission into drive, everything else is automatic.The drive train is coupled to a mechanism known as a torque converter which acts as a fluid drive between the engine and transmission.
Planetary gearsets in the transmission create different gear ratios, allowing the vehicle to shift between different gears based on the communication from the torque converter.As the engine speeds up centrifugal forces acting on hydraulic fluid transmits torque to the turbine—this makes the turning effort.