Automatic Transmission Hydraulic Automatic Transmissions

Most cars sold in the United States since the 1950s have had automatic transmissions. This has, however, not been the case in Europe and much of the rest of the world. Automatic transmissions, particularly earlier ones, reduce fuel efficiency and power. Where fuel is expensive and, thus, engines generally smaller, these penalties were more burdensome. Automatic transmissions have significantly improved in fuel efficiency in recent years, but manual transmissions are still generally more efficient.

Most automatic transmissions have a set selection of possible gear ranges, often with a parking pawl feature that will lock the output shaft of the transmission.

However, some simple machines with limited speed ranges and/or fixed engine speeds only use a torque converter to provide a variable gearing of the engine to the wheels. Typical examples include forklift trucks and some modern lawn mowers.

1 Hydraulic automatic transmissions

The predominant form of automatic transmission today is the hydraulic automatic transmission. This design uses hydraulic pressure to control a set of planetary gears using a series of clutches and bands.

1.1 Parts and operation

The multitude of parts, and the complex design of the valve body make hydraulic automatic transmissions much more complicated (and expensive) to build and repair than manual transmissions. Except in cars for the USA market, they have usually been extra-cost options for this reason.

1.2 History and improvements

Oldsmobile's 1940 models featured Hydra-Matic drive, making this lineup the first vehicles with fully automatic transmission.

Hydra-Matic appeared as an Olds exclusive. It provided true clutchless driving with four forward speeds. Its fluid coupling between engine and transmission eliminated the clutch and its associated foot work. Olds made the Hydra-Matic available on all models for only an extra $57. In the early 50s, Olds produced its millionth Oldsmobile with automatic transmission, demonstrating Hydra-Matic's rapid rise in popularity.

The first hydraulic automatics were introduced by General MotorsGM redirects here. This article is about General Motors . For other uses, see GM (disambiguation). General Motors Corporation also known as GM is a United States-based automobile maker with worldwide operations and brands including Buick, Cadillac, Chevro, Chrysler and Borg-Warner (who produced transmissions for Ford) in the early 1950s. These early models only provided 2 forward speeds, and were not able to handle much torque at first, but 3 speed models followed quickly.

In the 1970s and 1980s, the first big changes to hydraulic automatic transmission designs in years came. The first was the addition of an overdrive capability; fuel economy had become a big concern, and the addition of an overdrive helped increase fuel efficiency considerably on long cruises.

The second was the torque converter clutch or TCC. This concept first appeared in the early 1980s with the advent of engine computers, and involved a solenoid-controlled clutch inside the torque converter, which would lock its input to its output when activated. The idea was to eliminate the drag or inefficiency caused by the fluid in the converter when operating at high speeds. The TCC was an effort to improve fuel economy with a relatively minor modification to the transmission. (A related development was the dual-input (one shaft mechanically driven and one hydraulically driven) in the Ford AOD transmission.)

As the engine computers became more and more capable, even more of the valve body's functionality was offloaded to them. The newest hydraulic automatics remove almost all of the control logic from the valve body, and place it in the hands of the engine computer. In this case, solenoids turned on and off by the computer control shift patterns and gear ratios, rather than the spring-loaded valves in the valve body. This allows for more precise control of shift point s and shift quality, and (on some newer cars) also allows semi-automatic control, where the driver tells the computer when to shift.

2 Automatic Transmission Models

Some of the best known automatic transmission families include: General Motors: Powerglide, Turbo-Hydramatic Ford: FMX, C4, C6, AOD, E4OD, ATX, AXOD Chrysler: Torqueflite

3 Continuously variable transmissions

A different type of automatic transmission is the continuously variable transmission or CVT, which can smoothly alter its gear ratio by varying the diameter of a pair of belt or chain-linked pulleys, wheels or cone s. Some continuously variable transmissions use a variable displacement pump and a hydraulic motor to transmit power without gears. These designs are usually more fuel efficient than manual transmissions, but are very expensive to buy and maintain. The expense reflects the difficulty of manufacturing a reliable product.

4 Manual Valve Body automatic transmissions

Some automatic transmissions have a "manual" valve body. These transmissions are generally limited to sports cars or race cars. A "manual" valve body allows the driver to shift gears at will, similar to a manual transmission, but with no clutch.

Some manual valve bodies are also capable of "semi-manual function". In this case the transmission can function as a standard automatic OR it may be shifted as a manual transmission.

Automotive transmission technologies

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