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Concept
Automatic transmission
Résumé
An automatic transmission (sometimes abbreviated AT) is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions.
The most common type of automatic transmission is the hydraulic automatic, which uses a planetary gearset, hydraulic controls, and a torque converter. Other types of automatic transmissions include continuously variable transmissions (CVT), automated manual transmissions (AMT), and dual-clutch transmissions (DCT).
The 1904 Sturtevant "horseless carriage gearbox" is often considered to be the first true automatic transmission. The first mass-produced automatic transmission is the General Motors Hydramatic four-speed hydraulic automatic, which was introduced in 1939.
Globally, 43% of new cars produced in 2015 were manual transmissions, falling to 37% by 2020. Automatic transmissions have long been prevalent in the United States, but have only started to become common in Europe much more recently. In Europe in 1997, only 10-12% of cars had automatic transmission.
In the United States, over 80% of new cars had automatic transmission by 1957. Automatic transmission has been standard in large cars since at least 1974. By 2020 only 2.4% of new cars had manual transmission. Historically, automatic transmissions were less efficient, but lower fuel prices in the US made this less of a problem than in Europe.
In the United Kingdom, a majority of new cars have had automatic transmission since 2020. Several manufacturers including Mercedes and Volvo no longer sell manual transmission cars. The growing prevalence of automatic transmission is attributed to the increasing number of electric and hybrid cars, and the ease of integrating it with safety systems like Autonomous Emergency Braking.
The most common design of automatic transmissions is the hydraulic automatic, which typically uses planetary gearsets that are operated using hydraulics.
Source officielle
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