Before there were automatic transmissions there were manual ones. Manual transmissions required the driver to shift between gears so that the vehicle can be speeded up or slowed down while the engine rotated within an optimum RPM range. For many decades manual transmissions were good enough for most drivers, but not all. Some just didn’t like the intricate shifting procedure and some, well, just never got the hang of it. The result: during the 1930s, many of the larger car companies began to experiment with transmissions that “shifted themselves”. This was seen a way to capture additional customers.
In 1937, the first semi-automatic transmissions appeared in several General Motors vehicles. GM dubbed these the “Automatic Safety Transmissions”(AST). With planetary gears and a conventional friction clutch, these transmissions allowed easier shifting and required less driving skill. Cadillac and Oldsmobile issued models with AST through 1939. Buick used the AST only in 1938. The AST never inspired the driving public and was not supported by large sales numbers.
The 1938 Oldsmobile was the first model to be outfitted with a true automatic transmission. The Hydro-Matic, developed by GM engineer, Earl Thompson, was advertised as “The greatest advance since the self-starter.” In 1941 the Hydro-Matic was available in most GM models automobiles and it was very popular.
The Hydro-Matic went through continual upgrading and refinements through 1955. Over the years the Hydro-Matic was used in many military applications including the M5 Stuart and the M24 Chaffee light tank. Other auto manufacturers purchased and used the Hydro-Matic. These included Hudson, Frazer Nash, Willys, Rolls-Royce, Nash Rambler, Kaiser, Lincoln, and Bentley
Even into the 1990s, the Hydro-Matic was used, in modified versions, for drag racing and hotrod applications. One company in particular made the “B&M Hydro” a mainstay of hot rodders for decades. Andy Granatelli modified the Hydro-Matic and it was the only automatic transmission to ever be used in Indy Car racing.
Chrysler’s Fluid Drive was introduced in 1939, but this was really a manual transmission that used a fluid coupling to make shifting easier. Chrysler first produced a semi-automatic transmission in 1942 and was late in developing their own true automatic transmission, introducing the two-speed PowerFlite in 1954. BorgWarner engineered the first automatic transmission used by Ford, introduced in 1950.
In the late 1980s, www.keenechryslerjeepdodge.com explains that as onboard computers became prevalent, came the introduction of electronic controls for automatic transmissions. Solenoids and sensors integrate with multiple onboard computers to control shifting and gear ratio in any imaginable scenario.
Five-speed, six-speed, seven, and even eight-speed transmissions are currently being used in automobiles. Such technologies are being tested and deployed in an effort to improve economy and efficiency.
Interesting, the inherent efficiency of manual transmissions has lead transmission engineers back to simpler, more manual designs. The emphasis today is on designs that provide the convenience of an automatic transmission but with high gas mileage.