What is Automatic Transmission : Types and How it Works

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In Automatic Transmission driver does not require to press the clutch and change gears very frequently. Therefore It provides comfort to the driver while moving around the city busy roads. In this article we will discuss what is automatic transmission, various technologies available and how they work?

What is Automatic Transmission?

Automatic gear system does not require user to shift gears very frequently

Automatic Transmission is a type of transmission that automatically changes vehicle gears ratio according to speed and load requirements. 

For example, when you drive a manual transmission car. You need to change gears according to road conditions and your vehicle speed. But in AT vehicles, There is no need to change gears. Vehicle gear ratio changes automatically.

It is also known as Auto, self-shifting, m-speed automatic or AT transmission.

Automatic-Transmission Technologies

AT technologies are evolving with time. Following are some of the technologies available in existing vehicles.

  • Automated Manual Transmission (AMT)
  • Continuously Variable Transmission (CVT)
  • Dual Clutch Transmission (DCT)
  • Automatic Transmission (AT)
Automated Manual Transmission (AMT)

It is a type of semi-automatic transmission or clutchless transmission. AMT is similar to manual transmission. But Clutch press and gear shift operation is performed by a set of sensors and actuators. It is the simplest type of automatic-transmission available and low in cost.

Automated manual transmission is similar to manual transmission.

AMT vehicles does not require driver to apply clutch, Vehicle is controlled using accelerator and brake pedal. If required, the driver can also manually shift gears up or down. 

Automatic Manual Transmission Types
  1. Single Clutch AMT
  2. Dual Clutch AMT
How AMT Works?

AMT transmission utilizes sensors and hydraulic actuators to press the clutch and shift gears. Hydraulic actuators gets input car ECU and work accordingly. ECU provide input according to vehicle RPM.

Advantages of AMT
  • Low Cost
  • Fuel Efficient
Disadvantages of AMT
  • Performance is not good in hilly terrain or at low Speed.
Continuously Variable Transfer (CVT)

CTV transmission does not have gears. It utilizes variable diameter pulley-belt drive to transfer the power from engine input shaft to the wheels of the car. Car ECU electronically control the shifting of belt from one shaft to another.

CVT transmission cars have parking, reverse. neutral, drive and low drive shifts.

How Continuously Variable Transfer Works?

CVT transmission system utilized variable diameter pulley belt to change car speed. In this belt length is constant. Sheaves are used to change pulley diameter. When sheaves of driven pulley are at distance. Pulley diameter increases, that reduces car speed.

Whereas when shelves of driven pulley are at small distance. Car goes in high gear and car speed increases.

Advantages of CVT Transmission
  • Low Cost
  • High Fuel Efficiency
  • Smooth Ride
Disadvantages of CVT Transmission
  • High Maintenance Cost
  • When acceleration is applied, increase in speed in slow
Automatic Transmission (AT)

It is a type of completely automatic transmission. Vehicle gear ratio changes as it moves on the road. Driver do not require to change gears or press clutch.

How AT Works?

Automatic-transmission consists of three major components.

  1. Planetary gear are used to achieve speed variation of output shaft. It has two inputs and one output. Output shaft is connected to Planet carrier. Whereas input are connected to ring and sun gear. Input shaft at ring and sun gear is rotated at different speeds in order to achieve different speed at the output shaft. For example, when the sun gear is rotated and ring gear is stationary, Planet gear rotates at relatively small speed. Whereas when ring gear is also rotated along with sun gear, Planet gear rotates at relatively high speed 
  2. Hydraulic Coupling / Torque Converter is a coupling between the engine and transmission and used to transfer power from engine to transmission. It is also used to lock and unlock planetary gears and works similar to clutch in manual transmission.
  3. Hydraulic Controls are used to control hydraulic coupling. They get input from car ECU.
Advantages of AT
  • Great driving performance.
  • Hill Assist Feature
Disadvantages of AT
  • High Cost


To sum up, Automatic transmission provide greater driving comfort. AMT, CVT and AT are various technologies used in automatic transmission.

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