The Hydra-Matic transmissions (Fig. 1), released by General Motors for installation in Oldsmobile models in 1940, are thought to be archetype of automatic transmissions. These were four-speed automatic transmissions using fluid couplings and a drive train consisting of three sets of simple planetary gears. It is possible to see that the clutch, the starting apparatus of manual transmissions, has been replaced by the fluid coupling and the parallel axis gearbox by planetary gears.

Fig. 1 Hydra-Matic	Fig. 2 Dynaflow

Meanwhile, torque converters had long been the subject of research and, though the structure increases in complexity, the conception existed of increasing the torque ratio, improving efficiency and replacing this with the gearbox. It was the Dynaflow (Fig. 2), equipped by General Motors in Buick automobiles beginning in 1948, that grew out of this approach. It was a two-speed automatic transmission using a five-element one-step multiphase torque converter plus one compound planetary gear set.

The “fluid coupling + multi-speed gearbox” and “torque converter + fewer-speed gearbox,” the outcome of entirely different concepts, formed the two cornerstones of automatic transmission technology. The former was inherited by the automatic transmissions of Mercedes-Benz vehicles as well as trucks while the latter was developed for use in the automatic transmissions of most automobiles. Those two flows are currently on the way to converging as the concept of “torque converter + multi-speed gearbox.”

The pacesetter General Motors was joined by Ford and Chrysler in the 1950s for further development, leading to a variety of new models.

The Powerglide, in particular, which was released by General Motors in 1953, was a typical 2-speed automatic transmission, which served as a model for the other companies. Ford announced the Ford-O-Matic (Fig. 3), jointly developed with Borg-Warner, in 1950.

Fig. 3 Ford-O-Matic	Fig. 4 Borg-Warner M-35	Fig. 5 Ford C-4

Chrysler followed with the release of their PowerFlite in 1953.
Successive trial and error efforts continued on from the latter half of the 1950s through the 1960s as the process gradually shifted toward integration. From the perspective of economic viability (cost) and performance and structural simplicity (reliability), a three-element, one-step, two-phase torque converter coupled with a 3-speed planetary gear train emerged as the primary common factor. The most typical models from this period are Chrysler’s 1960 TorqueFlite A904, Borg-Warner’s 1961 M-35 (Fig. 4), the General Motors Super Turbine 400 and the Ford C-4 (Fig. 5), both released in 1964. This system went on to become the global standard during the next several decades.

Evolution of automatic transmission technology in Japan
Motorization started in Japan in the 1950s. Although automobile manufacturers were independently promoting research in automatic transmissions, their technological skills were not sufficiently advanced and they were compelled to rely on overseas manufacturers by purchasing finished products or introducing technological expertise. Automakers moved ahead with the full-scale development of automatic transmissions with the establishment of Aisin Warner (currently Aisin AW) and Japan Automatic Transmission Co., Ltd. (currently JATCO), both specialists in the production of automatic transmissions, in the 1970s. Growth and development persisted at a rapid pace as the manufacturers sought to stay in line with social trends and now Japanese products continue to gradually exceed the products of manufacturers overseas in terms of performance, quality and cost.

From the 1970s to the early 1980s
Shortly after the launch of full-scale domestic production with the cooperation of manufacturers overseas, strong demands arose for resource and energy conservation prompted by the oil crisis in 1973, marking the start of technological innovation for the realization of improved fuel efficiency. The shift point was first of all converted to electronic control and a lock-up mechanism was added. Demands then arose for even better fuel efficiency at the time of the second oil crisis, stimulating the development of multi-speed automatic transmission (from 3-speed to 4-speed). The downsizing of vehicles in turn led to the downsizing of automatic transmissions as well as an increase of front-wheel drive vehicles. The number of vehicles equipped with them rapidly expanded in the domestic market as these innovations improved the performance of automatic transmissions. Whereas fewer than 10% of all vehicles were equipped with automatic transmissions in the early 1970s, this rate grew swiftly to more than 50% by the 1980s.

Early 1990s to date
In the 1990s, importance was placed increasingly on coping with environmental issues and fuel regulations were consequently formulated both in Europe and in Japan. As a result, there were greater demands for the adoption of technologies for the improvement of the fuel efficiency of transmissions. This stimulated manufacturers to seek ways to improve fuel efficiency by promoting the development of multi-stage mechanisms and CVTs while also expanding the lock-up range including slip control. In addition, they also undertook initiatives to reduce both weight and costs by reducing the number of parts and promoting part-sharing while improving materials and manufacturing technologies.
In 1994, Mitsubishi Motors Corporation released the Diamante equipped with the INVECS-II, a tiptronic-type 5-speed automatic transmission, which led to the development of manual shift by other manufacturers. The tendency toward multi-stage transmissions continued to expand with leading manufacturers employing multi-stage systems and expanding their applications. Toyota, for example, adopted a 5-speed automatic transmission system and Honda also began installing 5-speed automatic transmission systems in their automobiles in 1999.
The development and market release of multi-speed transmissions currently continue with 6- and 7-speed automatic transmissions, while the full-scale development of CVTs has also been promoted. Nissan succeeded for the first time in the practical application of steel-belt type CVTs compatible with two-liter engines in 1997. It furthermore introduced toroidal CVTs for three-liter vehicles in 1999 through the adoption of metal rollers in the transmission system. Other manufacturers have also promoted development of CVTs, especially the belt-type, and new vehicle models equipped with CVTs continue to increase year by year.
Meanwhile, the automation of manual transmissions has also now become a focus of attention. With this system, clutch operation is automated using hydraulic pressure to attain both high fuel efficiency and drivability. The development of a new system to automate gear shifts is also under way.
Along with the development and introduction of EV and HEV automobiles, manufacturers are currently developing transmissions compatible with automated manual transmission systems.