The transmission is the part of your car that changes gears based on your speed. Most cars come with an automatic transmission these days, or at least they have the option. This type of transmission is much more common because it’s so much easier to use, so how do automatic transmissions work?
Automatic transmissions are actually pretty complex. There are tons of small moving parts in an automatic transmission, but most simply, you just need to know a few.
One is the torque converter. This connects the transmission to the wheels and joins fluids that let it act the same way the clutch does in a manual transmission: the fluid, which is pushed through by the engine, turns the turbine, which causes the torque converter to send torque to the transmission.
This also drives the transmission fluid pump, which is what delivers fluid to the planetary gear set and makes it turn. The planetary gear set, which is made of many moving parts, operates on the principle that the clutch and brakes will stop certain parts of it from working, which changes the gear ratio. Before automatics, you’d have to manually change the gear ratio by pushing the clutch yourself.