This is part of the reason why four speed autos stayed in use for so damn long. You can automatically shift a four speed transmission with a pair of solenoids that turn on/off based on the input values from a couple of basic sensors.
The solenoids control which pair of clutches in the transmission engage, which in turn, determines the gear the transmission is in.
Driveability wise, they were awful, and their overall efficiency was pretty bad. But the fact that it could automatically select the correct gear out of three or four with just one user input (throttle) is still marvelous.
They could also handle insane amounts of power for the era. The GM 3L series came out in 1964 and was the transmission people would reach for when they were putting WWII era plane engines into crazy automobiles.
The solenoids control which pair of clutches in the transmission engage, which in turn, determines the gear the transmission is in.
Driveability wise, they were awful, and their overall efficiency was pretty bad. But the fact that it could automatically select the correct gear out of three or four with just one user input (throttle) is still marvelous.
They could also handle insane amounts of power for the era. The GM 3L series came out in 1964 and was the transmission people would reach for when they were putting WWII era plane engines into crazy automobiles.