Automobiles · Vol. III|Automatic transmission|1939 (Hydra-Matic)

Automatic transmission

1939 (Hydra-Matic)

A clutch and a stick ask the driver to be a gearbox. Hydra-Matic, offered on 1940 Oldsmobiles, used fluid coupling and planetary gears to change ratios without a pedal. Automatics spread slowly, then everywhere in some markets. They are a social technology: they lower the skill bar for using a heavy, fast machine.

General Motors (Hydra-Matic) · United States

Automatic transmission — Original plate drawn for this atlas. Not a photograph of a museum object or a copyrighted portrait.

How it works

A fluid coupling or torque converter passes engine torque without a rigid clutch plate.
Planetary gearsets offer several ratios.
Hydraulics or electronics pick a ratio from speed and throttle.

Why it mattered

Made driving in traffic less of a craft.
Widened the market of drivers.
Added complexity that later electronics had to tame.

What it unlocked

1997 (Prius); 2012 (mass-luxury EV landmark)Hybrid and EV platforms

For further study

SAE papers on Hydra-Matic. Design.
GM Heritage. Introduction.

Check

What human task does an automatic take over?