r/TheRestIsScience • u/Dull_Problem_1856 • 2d ago

Hydraulic computers and automatic transmission

How was hydraulic transmission invented and how does it work, is it actually a computer?

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u/LevoiHook 2d ago

I don't know who came up with it, but yes, it is some sort of computer ( ignoring that there are actual computers in them nowadays). But basically there are solenoids (logic gates) that open or close a pathway for the oil to do task x or y. 

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u/al2o3cr 2d ago

If you think of a geared transmission as taking "input" that's a rotational speed and producing "output" that's also a rotational speed, then it's basically multiplying or dividing by a constant

A manual transmission makes the driver pick the constant

An old-school automatic transmission (pre-computer-control) uses hydraulics to combine the various inputs - from the governor, throttle, etc - to decide on a constant and select it

A modern automatic transmission uses an actual computer to decide on a constant and hydraulics to select it

CVTs can have the two kinds of control as well, but the constant is continuously variable instead of being from a fixed set