Innovations in Driving: The Automatic Transmission

Automatic Transmission vestman via flickr.

Have you ever looked at a diagram of an automatic transmission? If not, check this out:

Diagram of an Automatic Transmission:

I defy anyone who isn’t a mechanical engineer or who doesn’t work in the transmission industry to make sense of this schematic. There are, of course, plenty of things about cars that are hard to understand. Wiring looms, for example. The innards of limited-slip differentials. How the with a bicycle, a car is fitted with several gears offering various ratios to maximize the efficiency of the engine. The only fundamental difference between the two is that, in a car, a so-called friction clutch is used to briefly disengage one gear from the engine before the next gear is selected. Naturally, manual transmissions contain lots of slick complications – synchromesh cones, for instance, to allow shifting without matching revs and double-clutching. But it’s essentially the same system about which automotive pioneer Rene Panhard once declared (in French), “It’s brutal, but it works.”

Many drivers don’t want – or don’t know how – to shift gears manually. And especially before synchomesh was commonplace, only a small percentage truly mastered the technique. So as early as Panhard’s time, at the beginning of the 20th century, manufacturers began experimenting with various methods to make the process of shifting gears easier. Crude first appeared on the 1940 Oldsmobile. During World War II, the tranny was used in American tanks that saw action in the European Theater. After the war, GM’s “battle-tested” Hydra-Matic was an immense hit with consumers. (Here’s an exhaustive history of the Hydra-Matic’s development.) Ford brought out its first automatic, actually created by Borg-Warner, in 1950, and Chrysler belatedly followed suit in 1954. Before long, manual transmissions were an endangered species here in the States, though they remained the norm overseas. In fact, it wasn’t until 1962 that Mercedes-Benz became the first foreign automaker to develop its own automatic transmission in-house.

Unlike manual gearboxes, automatic transmissions don’t contain individual gears. On the contrary, they’re built around what are known as planetary gearsets that can be configured to produce multiple gear ratios. Instead of a friction clutch, a hydraulic torque converter is used to swap ratios. Automatic transmissions also entail the use of components such as stators, clutch packs, lockup clutches, bands, pumps, turbines, etc. Fortunately, you don’t have to understand how the technology works to use it. But for the technically inclined, here are some insights to the inner workings of an automatic transmission. And this site offers additional details and some spectacular animations.