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How does an Automatic Transmission work?

The automatic transmission is a critical component that transmits engine power to the wheels. The conventional speed shifting systems installed on most cars have extremely complex, precision structures.
Here, we present an easy-to-understand explanation of how an automatic transmission (AT) works.

1. What is an Automatic Transmission?

An automatic transmission (AT) is installed at a point between the engine's rotation and the point where it is transmitted to the wheels.
An AT automatically changes gear depending on the car's running condition, and transmits rotation from the engine to the wheels.
An AT provides functions that the engine alone cannot perform, such as adding power on slopes, adjusting rotation speed as required during running, decoupling power when stopped, and applying the required opposite rotation when in reverse.


drivetrain
2. Type of Automatic Transmissions

ATs can be categorized into two types: those installed vertically (longitudinal AT) with respect to the automobile and those installed horizontally (transversal AT).
Although the layout of the external and internal components differs depending on the type of engine drive method, the functions basically work in the same way.

Longitudinal engine layout

This type of engine is installed
vertically on the car and has
an elongated shape.
drivetrain
 
Drive methods for the longitudinal engine layout. RWD vehicles (Front engine, rear drive). The engine is mounted on the front end and the rear wheels receive the drive power.
drivetrain
 
4WD vehicles (4-wheel drive, RWD vehicle base). The engine is mounted on the front end and all four wheels receive drive power.
drivetrain

 

Transversal engine layout

This type of engine is installed
horizontally on the automobile
and has a rounded shape.
drivetrain
 
Drive methods for the transversal engine layout. FWD vehicles (Front engine, Front drive). The engine is mounted on the front end and the front wheels receive the drive power.
drivetrain
 
4WD vehicles (4-wheel drive, FWD vehicle base). The engine is mounted on the front end and all four wheels receive the drive power.
drivetrain
MR vehicles (Midship engine, Rear drive). The engine is mounted between the front and rear wheels and the rear wheels receive the drive power.
drivetrain
RR vehicles (Rear engine, Rear drive). The engine is mounted on the rear end and the rear wheels receive the drive power.
drivetrain

3. Automatic Transmission structure and operation

ATs consist of three components: a torque converter that transmits engine rotation to a planetary gear, a planetary gear train that changes rotation speed and transmits it to the wheels, and a hydraulic device that outputs commands to the planetary gear to change speed according to the car's running condition.
Generally speaking, those are the three components of an AT.

 

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The automatic transmission is a critical component that transmits engine power to the wheels. More

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