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Automatic Transmission
and Evolution Time Line

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Late 1950s: Through the late 1950s, General Motors produced multiple-turbine torque converter transmissions. The Dynaflow and Turboglide are two examples of these multiple-turbine torque converter transmissions. In these transmissions, shifting took place in the torque converter instead of using pressure valves to change planetary gear connections.  With these multiple-turbine torque converter transmissions, each turbine was connected to the drive shaft through a different gear train.  Rather than gear shifts, the different gear ratios were phased in according to speed allowing for very smooth transitions from one gear ratio to the next.

1960s: By the end of the 1960s, the  two-speed and four-speed fluid coupling design automatic transmissions had been replaced with three-speed transmissions all using torque converters.  The use of whale oil in automatic transmission fluid was discontinued at around this time.

Torque converters are still used in modern-day automatictorque converters transmissions.  The images to the right are examples of today's torque converters.

Late 1970s and Early 1980s: In the late 1970s, three-speed automatic transmissions were quickly being replaced by automatic transmissions with overdrive, which provided four or more forward gears.  By the early 1980s, most every automaker offered automatic transmissions with overdrive.  Transmissions with overdrive are more efficient and provide improved fuel economy over three-speed transmissions.  Another improvement in efficiency and fuel economy came with the introduction of the lock-up torque converter at about this same time.  As the name implies, the lock-up torque converter locks the torque converter pump to the turbine of the torque converter once the vehicle reaches cruising speed.  By locking these two components together at cruising speed, slip is eliminated enabling the full power of the engine to be passed through the transmission to the drive wheels.

1980s to Date: The most significant changes (improvements) in automatic transmission design since the 1980s to date are the number of forward gears transmissions now have and the switch from mechanically controlled to electronically controlled transmission operations.

The four-speed automatic transmissions of the 1980s are still available today but are slowly being phased out by the next generation of automatic gearboxes that have five and six forward gears.  In the mid to late 2000s, the first seven and eight speed automatic transmissions were offered on certain high-end vehicles.

arrow In 2003, Mercedes Benz introduced the 7G-Tronic (seven speed) automatic gearbox.  Four years later, in 2007, Toyota unveiled the first 8-speed automatic gearbox which they offered exclusively on their high end Lexus brand, the Lexus LS 460.

Newer, electronically controlled automatic transmissions rely on data received from various electronic sensors and use an electronic control unit (either a dedicated Transmission Control Module (TCM) or the vehicle’s Engine Control Module (ECM) to operate solenoids in the valve body to shift gears.  This process enables timelier, faster and more precise shifts than the shifts produced in a mechanically controlled automatic transmission, which relies on a cable or vacuum operated modulator to determine and effect shift timing and gear shifts.  The time it takes for a mechanically controlled transmission to shift gears is also slower, which causes slipping and increases heat in the transmission.  Slower shifts also increase fuel consumption. 

In addition to the above benefits and advantages, electronically controlled transmissions are also more reliable than mechanically controlled units.

Lastly, the electronically controlled automatic transmission’s ability to gather and process large amounts of information every few milliseconds combined with advanced control strategies based on fuzzy logic (a method of programming control systems using human-type reasoning) gives it nearly limitless capabilities.  Some of these transmissions are already capable of learning and adjusting the way they shift based on travel conditions.  For example, when driving through a mountainous terrain, some electronically controlled automatic transmissions will learn to automatically downshift when going downhill in order to control speed, which adds a measure of safety and reduces wear on the braking system.  Another example occurs when driving through turns where the transmission learns to stay in the present gear through turns rather than continuously upshifting and downshifting every time the car slows down when entering a turn and speeds up after exiting the turn.

arrow Mechanically controlled automatic transmissions have reached their limit in terms of future improvements while electronically (or computer) controlled automatic gearboxes have only touched the surface of the possibilities.

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