It was initial launched in 1939 for vehicles. It consists of the fluid coupling and 3 planetary gears. They collectively make a few forward and 1 reverse speed. There is not any clutch for engagement and disengagement from the engine. Torque converter does a similar function the clutch does https://spencernopmg.anchor-blog.com/14101272/a-simple-key-for-gearbox-unveiled