The Different Types of Automatic Transmissions

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With fewer manual cars available, and the sales of automatic vehicles being the vast majority, you might or might not know that not all automatics are made equal.

They say simplicity is the utmost sophistication, and when all you have to do is sit in the driving seat and move the gear lever to drive, it’s not difficult to see why. You never have to be nervous about stalling or tiring out your left leg, all while what’s effectively magic goes on beneath you.

The auto transmission accomplishes the same results as a manual transmission and its clutch but in a few separate ways. The purpose of a gearbox is to allow the engine to provide a wide range of output speeds even though the engine itself has a narrow window of speeds. Without a manual or auto transmission, cars would be limited to one gear that enables them to drive at one desired top speed. Thus, a transmission applies gears to make more effective usage of the engine’s torque to allow the engine to work at an optimal speed.

Another comparison of a manual transmission and a conventional automatic transmission would be the manual transmission locks and unlocks various gears to the output shaft to attain different gear ratios. In contrast, the conventional automatic transmission uses the same set of gears to process all of the other gear ratios. The part that allows this process to work in an automatic transmission is called a planetary gearset.

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Planetary Gearset

One of the big components of an Automatic Transmission would be the Planetary Gearset. When dissecting an automatic transmission, you will see the planetary gearset in the centre. This is the part that enables the gear ratios to increase and decrease automatically. The planetary gear set consists of 3 different parts working:

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  • A Sun Gear

It’s at the centre of the planetary gear set.

  • The Planet Gears

They are three to four small gears that surround the sun gear and work with the sun gear. Like the planets, they spin but also rotate in orbit around the Sun gear.

  • The Ring Gear

The outermost gear is the ring gear that surrounds all the other gears. It works with the Planet gears.

These three components form the Planetary Gearset that gives your reverse movement and five different levels of forward driving. This relies on which of the gears is set or holding stationary. To find out more in-depth details of how the Planetary gearset works would be a bit more technical and complicated and deserves an article on its own.

Different Types of Automatics

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There are a few main types of automatic gearboxes: Torque Converter Automatics, Continuously Variable Transmissions (CVT), Automated Manual Transmissions (AMT), and Dual Clutch Transmissions (DCT). You may be thinking at this point, “I’ve heard it before, but like what’s the big difference?” Well, you’re about to find out.

Torque Converter

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A Torque Converter Automatic is the most common form of automatic gearbox. It sits between the engine and the transmission and works by replacing the functions of a clutch that is used to engage and disengage the engine’s torque from the gearbox. The torque converter works with the planetary gearset and is hydraulically controlled to enable movement of the vehicle.

If you’d like us to write a full article on how this works, let us know in the comments (so I can go get my engineering degree first because frankly, this is basically voodoo to me). Decades of improvements and mass manufacturing have brought down costs significantly and because of it being cheap and reliable it is seen used in cars the world over.

Continuously Variable Transmissions (CVT)

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Next, we have the Continuously Variable Transmission or CVT for short. It sounds cool and it works exactly like its name suggests, a CVT keeps the engine spinning with maximum efficiency as it is able to vary the drive ratios continuously. The CVT is one of the most reliable gearboxes, fuel efficient and smooth when it comes to driving.

However, while the pros of a CVT gearbox are plentiful, many drivers find it annoying and uninspiring to drive because the engine does not sound or drive like a traditional engine. Despite that, the pure efficiency of CVTs are a big lure to manufacturers hence many cars are still released with CVTs in them.

Automated Manual Transmission (AMT)

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Third, the Automated Manual Transmission or AMT is also known as a clutchless manual because the mechanics of it is similar to a manual transmission. The AMT allows the car’s clutch and gear selection to be controlled electronically. One pro to the AMT is that it's cheap because there is no need for manufacturers for developing or even having a separate assembly line for building the AMT.

The electronic gubbins to make the AMT work are simply added onto the standard manual gearbox. With sensors and computerised actuation, the AMT can also be more fuel efficient than the same vehicle with a manual gearbox. However, some AMTs can be less refined resulting in jerky shifts and slow reactions to driver inputs. AMTs usually function by electronically operating either just the clutch or the entire shifting process, which means some AMTs may shift gears by itself or some might still require driver input to request a different gear.

Some cars that have used an AMT include Ferrari’s ‘F1’ transmission on its road cars and the ‘E-gear’ range of transmissions from Lamborghini.

Dual Clutch Transmissions (DCT)

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Lastly, we have the the most expensive and complex option among all the gearboxes, the Dual Clutch Transmissions or DCT. This is regarded as a premium option because it is offered to continental car brands and models like Mercedes, Audi and Porsche among many others but they are becoming an increasingly popular choice of gearbox for new cars.

The DCT gearbox is complex as it works like an Automated Manual but with two clutches as well as complicated software, hence the name. This allows cars with a DCT to make seamless shifts, one clutch dealing with odd numbered gears while another clutch deals with the even numbered gears. The pros to the DCT are its efficiency and seamless shifts as well as its good fuel efficiency. On the other hand, due to the complexity of the DCT, it can be very costly to fix when there’s something wrong with it.

While the benefits of auto transmissions are plentiful, such as providing a hasslefree ride in the city, fuel economy, and even faster lap times on track, you just can’t escape the fun that is rowing your own gears and we hope the manual ‘box doesn’t die out any time soon.

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