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.
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.
the end of the 1960s, the two-speed and four-speed fluid
design automatic transmissions had been replaced with three-speed
transmissions all using torque converters. The use of whale
in automatic transmission fluid was discontinued at around this time.
converters are still used in modern-day automatic transmissions.
The images to the right are examples of today's torque converters.
Late 1970s and Early
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
offered automatic transmissions with overdrive. Transmissions
with overdrive are more efficient and provide improved fuel economy
over three-speed transmissions. Another improvement in
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
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:
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.
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
mid to late 2000s, the first seven and eight speed automatic
transmissions were offered on certain high-end vehicles.
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.
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
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
addition to the above
benefits and advantages, electronically controlled transmissions are
also more reliable than mechanically controlled units.
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
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
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.
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.