An Automatic transmission is one of those parts on your car that you just don’t think too hard about unless it’s broken. That’s the beauty of an automatic transmission; you press the gas pedal and the car goes. Anyone who has had the dubious pleasure of driving a manual transmission in heavy traffic can tell you how wonderful it can be not having to think about shifting gears. Though the very first “automatic” transmission was invented just a few years after the first car, it’s only in the past few decades that it’s really taken over—especially in the U.S. According to the New York Times about 99% of cars sold in the U.S. today have a manual transmission, up from about 65% in 1980.
“Automatic” Transmissions: The Early Years of Motoring
The device usually cited as the first automatic transmission was made way back in 1904—the Sturtevant “horseless carriage gearbox.” It was a fairly simple affair that was controlled with engine driven flyweights that shifted the car into one of two gears depending on the speed that the car was going. It was also prone to dramatic failure due to the abrupt gear changes.
From these humble beginnings, a number of other patents were developed. These ranged from the unhelpful—like Alfred Horner Munro’s compressed air powered automatic transmission from 1923—to the game changing—like the first use of planetary gearsets in the 1904 Wilson-Pincher Automobile. What a majority of the early developments in automatic transmission technology had in common was that even though they made shifting easier, or did the shifting when the car was in motion, they didn’t actually make it fully automatic yet.
No Clutches: The First Truly Automatic Transmissions
It wasn’t until Oldsmobile’s 1939 Series 60 and 70 that there was a truly automatic transmission option that was mass produced. The Hydra-Matic Drive automatic transmission was the combination of decades worth of developments, using a fluid coupling instead of a clutch to put the car in gear, and a hydraulic planetary gearset for the different ratios required to get the car moving. Though it was an expensive $57 (well over $1,000 today with inflation) add-on in the beginning of its life, the Hydra-Matic became pretty popular over the years, especially after WWII.
When you can say to the American consumer that a product was “battle-tested,” especially in the post-WWII years, that product was sure to be a bestseller. Since the Hydra-Matic was used and refined during the war years in both the M5 Stuart Tanks and M24 Chaffee Light tanks, car salesmen could tell consumers about the toughness and reliability of this relatively new technology. In as soon as 1948, 70% of the Pontiacs sold in the US had Hydramatic automatic transmission technology.
No Clutch for Me: How Do Automatic Transmissions Work?
There is no simple way to fully describe how an automatic transmission functions, but the main idea is that the transmission uses a number of gears—in this case set up in what is called a planetary gearset—to change the narrow range of speed that can be produced from output of the engine’s crankshaft into a wide range of gear ratios. The transmission itself is a series of gears hydraulically connected to the crankshaft that automatically changes the gear ratios in relation to the speed that the car is going and the torque needed to get it there.
Automatic transmissions have a lot of parts that need to be working perfectly in tandem with one another to be fully functional. That’s why it is so expensive for a transmission to be rebuilt. If you want to know more about guts of an automatic transmission, a great explanation with helpful diagrams can be found over at How Stuff Works.
Even Smarter Transmission Technology for the Modern Age
Since the 40s, there have been many upgrades and refinements to the form and function of the automatic transmission. The widespread introduction of the torque converter in the 60s allowed for the multiplication of torque in certain scenarios. The addition of electronics to the mix has also allowed for smoother and more intelligent shifting as well as to the ability to manually shift your car with an automatic transmission.
In the past two decades, the typical 4-speed automatic transmission has given way to the first 6-speed transmission in the 2002 BMW 7 Series, and the first 7-speed by Mercedes in 2003. Toyota pushed the envelope even more with an 8-speed developed in 2007, a 9-speed in 2013 and 10-speed in 2017.
Continuously variable transmissions (CVT) are seeing increasing use in the auto industry, especially in the world of hybrid cars. Instead of the finite number of ratios in a traditional automatic transmission, a CVT can cycle through an unlimited number of these ratios, making shifting absolutely seamless.
Though modern all-electric engines no longer need traditional transmissions, as long as there are gas powered engines, the form and function of our cars’ transmissions will surely continue to change and be refined with the times.
