How does an automatic transmission work
In: Engineering
In a modern automatic, a computer monitors road speed and engine speed (and also how hard you’re pressing on the accelerator pedal). It will then activate [electric solenoids](https://sciencing.com/a-solenoid-work-4567178.html) in the transmission to turn on or off certain [hydraulic circuits](https://www.e4training.com/hyd_newbie/basic_comp1.php), which then release or apply particular [clutches and bands](https://www.freeasestudyguides.com/transmission-brake-band.html) to obtain the optimum gear ratio (1st for slow speeds, 2nd for faster, etc) in the [planetary gearset](https://www.youtube.com/watch?v=ARd-Om2VyiE).
You can see the hydraulic circuits, clutches, bands, and solenoids in most of the transmission rebuild videos on this YT channel: https://www.youtube.com/user/click482003
Also: https://auto.howstuffworks.com/automatic-transmission.htm
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