DCT vs CVT vs AMT | Choose The Best Transmission

CVT transmission

Nowadays, we are spoilt for choices when buying a new car. The search for a car usually begins with you seeing a new car advertisement and realising its something you might wanna get. Then the search for other more interesting alternatives begin. But, every car has a permutation and combination of features and sometimes it gets a bit frustrating to understand what’s what and what’s not. It is even said that the Nasa’s Apollo 1 had lesser features as compared to the modern car. Take, for example, deciding on the choice of the car transmission available.

An automatic car transmission

Well, worry not! I’ll try to help you out in your journey of buying a new car by explaining which automatic transmission is best suitable for you. But first!

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How does an automatic car transmission work?

Before we delve into the types of automatic transmission we need to know how does an automatic transmission work, to get a better understanding of the different types. The very basic knowledge that everyone has that an automatic transmission changes gear automatically and doesn’t need a gear stick or clutch operation by the driver.

Allow me to explain an automatic gearbox in brief. The engine connects to a Torque Converter which is then connected to a gear system and then to the transmission. The gear system is called a Planetary Gear system which consists of a gear in the middle called Sun Gear and three gears around it called planetary gears which are covered by a ring gear (thus the name). These parts in combination make an automatic transmission.

What is a Torque Converter?

An Automatic Transmission Torque Converter

A Torque Converters is a vital component of an automatic transmission. It working is a bit complicated but I’ll word it as easy I can.

Inside the Torque Convertor, there are parts that work in tandem with each other.

A Torque Converter Mechanism

The outermost side of a Torque Converter has the flywheel which is connected to the engine. This flywheel rotates the entire structure. The rotation makes the pump push out fluid at high speed. This fluid makes the turbine rotate. The fluid keeps on rotating in a counterclockwise direction separated in two sections and is kept rotating with the help of a stator in the middle. The turbine is connected to the shaft which connects to the rest of the system.

The pump and turbine have grates in them, holes if you may and these holes help with the movement. In the pump, the fluid goes in one of the holes and is then ejected at the speed at which the engine is rotating, and for the case of the turbine, the fluid goes into the hole and pushes the turbine at a speed which the fluid was ejected in. The turbine rotates in the opposite direction thus absorbing the torque that the liquid carries. After the fluid is left with almost no energy of its own it goes to stator which pushes it towards the pump. The energy is then transferred to the gear system.

Looks simple! Right? Well, fellas, I got something better for you. Working of the planetary gear system.

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How does the Planetary Gear system work?

Personally I believe this to be one of the best inventions in the automobile area as it made automatic transmission possible. So how does it work?

Planetary Gear System

As I said earlier it is called planetary because it’s the same as what happens in the universe. A star is followed around by the planets and rotate around it at respective speeds. In planetary gear system, it has a sun gear, three planet gears one ring gear which covers them and is connected to the three planet gears and one carrier which takes the output.

There are some cases as to how the gear system works. Basic understanding of gear is helpful here but I’ll cover it anyway. Where two gears are connected they need to have the same speed as having uneven speed will destroy the gear system as the teeth will cross over. Now if two gears need to have same contact velocity that means if the size is uneven the smaller one will move faster. This is a major point in the working of the gear system.

The planetary gears are smaller than the sun gear. The speed at which sun gear rotates will be slower than what the planet gear rotates, in turn, making the ring gear rotate faster than the sun gear. This allows for multiple velocities with only one possible input this is one of the possible cases.

The second possible case is when the ring gear stays stationary and the sun gear moves. This will force the planet gear to both move and turn, as the ring gear can’t be moved.

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There are few more cases but these two should be enough to help you get an understanding of how the system works. We still need to talk about the comparison of the subtypes of Automatic Transmission.

What are the different types of an automatic car transmission?

Now there are two types of transmission systems. Manual and Automatic. And there are types of Automatic transmission which I’ll be explaining in depth.

There are three types of automatic car transmission:

  1. Dual Clutch Transmission (DCT)
  2. Continuously Variable Transmission (CVT)
  3. Automatic Manual Transmission (AMT).

DCT (Dual Clutch Transmission)

DCT or dual-clutch transmission is a really interesting piece of hardware. It is a bit on the heavier side as it has a lot of moving parts and gears. I’ll explain how it works below:

A DCT (Dual Clutch Transmission)

Take the case of 6 gears DCT. It has two clutches that control even and odd gear ratio with the first one getting an odd set of gear. It also has two transmission shafts that control those gear ratios which are already divided the odd one being inside the even and longer. It also has a part named dog clutches which are close to the gear and engage when the gear ratio respective of them needs to be used.

When the car starts and the engine is fired up, and the mode is shifted to drive mode, ECU engages gear one. This means the First clutch will act and the dog clutch on the first gear will engage. Now the interesting part is that the dog clutch the next second gear is also engaged however it won’t rotate its own shaft because the clutch for it the second gear is not engaged ( there are two clutches, the main and the dog). This process keeps on-going and this is how the dual-clutch transmission works

The advantages are the driver comfort and efficiency. The gear switch is so smooth that you will not feel a jerk while changing gears. And as there are no breaks in transmission it has better efficiency. People that prefer manual due to fuel efficiency can pick this up and be carefree. DCT is also the fastest and is used on high-end cars and racing cars.

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CVT (Continuously Variable Transmission)

A CVT (Continuously Variable Transmission)

CVT is soulless. Not my words but most motorheads consider it bad. Why? Because it doesn’t give any output. What do you mean by output? Ever rev a car and feel the speed increasing, that moment when you shift the gear when the RPM is just right and the sound it makes. If you like those things and haven’t driven a CVT, you’ll hate it too.

CVT has a pulley system. This pulley system makes it have an infinite gear ratio which allows it to have the best efficiency in the automatic transmission systems better than DCT. Depending on the speed of the crankshaft the pulley length changes changing the gear at the same time. Even an mm shift in the pulley means there is a new gear ratio in play basically giving it an infinite ratio.

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AMT (Automated Manual Transmission)

An AMT (Automated Manual Transmission)

AMT is the most successful automatic transmission system in India. Maruti Suzuki sold over 6 lakh cars that were equipped with AMT. Does it mean its the best of all three? Actually not, it is one of the weaker systems and the only advantage it has over others is that it is cheaper. So what does it have over others that make it cheaper?

Pressing a clutch disengages the engine from transmission allowing for a gear change and this process happens every time you change speed. The clutch disengaging happens automatically using hydraulic actuators. Different gear ratios are changed accordingly 


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Which is the best automatic car transmission?

Go for DCT. It is costlier and higher-end cars have it but it’s well worth it if you crave speed and smooth rides with a bit of fuel efficiency sprinkled in. it could almost be considered a jack of all trades but being a bit on the costlier side it is not. Is it worth the cost? Absolutely!

What should you choose

If you wanna go for efficiency choose CVT as its more efficient. With almost no delay in gear shift and less moving parts with almost no downtime, it has better efficiency than the other two systems and is a good choice some people might not like it as they require the car giving an output while they are driving to fully enjoy the experience. But if you use cars to get from point A to point B consider CVT.

If you want the feel of gears changing and getting an output from the car and quick acceleration DCT is better than the rest. It has decent efficiency on its own but compared to CVT it lacks behind.

AMT is a good choice and is easily available as more of the entry-level cars have it and is cheaper compared to DCT and CVT. Not as smooth as CVT and as fast as DCT it still has its uses.

Every transmission has its own advantages and disadvantages. I hope I was able to help you understand how all of these works so you can make a better and informed decision.

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