What types of automatic gearbox's are available?

Automatic gearboxes explained

Automatic gearboxes can be more efficient than manuals
British car buyers are falling in love with the automatic gearbox. The old stereotypes about poor fuel economy and sluggish manners are a thing of the past.
Several modern day automatics can be bought  which are more fuel efficient than the manual  versions.


Automatic-gearbox technologies
The market for automatic gearboxes has never been more compelling. But with all the automatic gearbox technology out there, it is also baffling.

Here, we cut through the confusion and show why there’s never been a better time to choose an automatic gearbox.

Conventional automatic gearbox
How does a conventional automatic gearbox actually shift gears?
In a car fitted with a conventional automatic gearbox, the engine is connected to a torque converter  which allows the engine to rotate even when the road wheels are still.
There are two ‘sun’ gears and two ‘planet' gear carriers rotating around them, all within a central ring gear. By varying which components rotate, different gear ratios are achieved.
Are conventional automatic gearboxes smooth?
The best automatics are the smoothest gearboxes around; gear changes are almost imperceptible. They are usually reliable, too.
What are the most common names for it?
Automatic or automatic gearbox

CVT/stepless automatic gearbox
How does a CVT gearbox or stepless automatic gearbox actually shift gears?
Very simply. A belt or chain is connected to two pulleys that move in and out such that the belt runs at different heights in its groove. This alters the gear ratio – and, as there aren’t fixed ‘steps’, a CVT gearbox has a theoretically infinite gear ratio.
Is a stepless automatic gearbox smooth?
As it is stepless, the ‘feel’ of a CVT automatic gearbox is smooth, but the engine revs rise to optimum-power revs and stay there until the car’s speed ‘catches up’, so it feels a bit like a slipping clutch.
Common name? 
CVT (continuously variable transmission)

Clutchless manual gearbox
How does a clutchless manual gearbox actually shift gears?
With a clutchless manual gearbox, electric motors take the place of the driver’s left arm and leg in shifting gears. Often, the driver has easy manual override, by either a lever or steering-wheel paddles.
Is a clutchless manual gearbox smooth?
Clutchless manual gearboxes are the least smooth automatic gearboxes you can buy. Computers lack the finesse of a human, so gear changes can be jerky.
What are the most common brand names?
Citroën SensoDrive, Ford Durashift EST, Honda iShift, Renault Quickshift, Toyota Multimode MMT, Volvo Easytronic

Twin-clutch automatic gearbox
How does a twin-clutch automatic gearbox actually shift gears?
Two clutches are connected to a special transmission shaft, with ‘inner’ and ‘outer’ parts. Odd-numbered gears use one shaft, and even ones the other. When, say, second gear is engaged, third is ‘pre-selected’ by a computer. Changing is a matter of shifting from one clutch to another, via hydraulics.
Is it smooth?
Seamless. Gear shifts happen so fast they are barely perceptible.
What are the most common brand names?
Ford/Volvo PowerShift, Porsche PDK, VW Group DSG