How does a automatic gearshift work?

Question

I think i heard, that they are hydraulic, but how does the gearbox “know” when to shift and how does it change gears?

In: 2

Answer 1

There’s a torque converter to cut and connect the power between engine and gear-box.

While gear-box is controlled by an ECU when to shift gear using various parameters e.g. speed, rpm, paddle position etc.