Automatic Transmission: Definition, Functions, Components, and How It Works

Do you use automatic vehicles? Then, of course, you know about functions, components, and how automatic transmission works. Maybe now, most people have driven this type of car to support their daily activities.

automatic transmission shifter paddle in a car
automatic transmission shifter paddle in a car

Some people prefer to use a car with an auto transmission because they find it easier to drive than a car with a manual trans.


Not surprisingly, one of the main advantages of an automatic transmission is the ease of operation of the vehicle because you don't need a clutch pedal.

automatic transmission images
automatic transmission images

You should know about the functions, components, and how the automatic transmission works because in addition to the smoother operation of the vehicle, lately, the number of cars with automatic transmission is increasing.

Also, the automatic transmission has a softer gearshift than a manual trans, so you will be more comfortable when driving.

Unlike in manual transmission vehicles, with automatic transmission, you will not feel the pounding when switching gears so that the car will run smoothly. Once you understand the functions, components, and how automatic transmission works, you will have a better idea for the maintenance of your car.

Although many people often use cars with automatic transmissions, it seems that many of them do not know about the functions, components, and how automatic transmission works correctly.

automatic transmission maintenance and components
automatic transmission maintenance and components

You may have occasionally read information about automatic transmissions, but you don't understand it. If you know what is in it, including functions and how the auto transmission works, then it will be easier to find a solution if there is a problem with it.

You will also know how to operate it and what you need to avoid so that the transmission can last longer and function properly.

Also, you will know exactly the advantages and disadvantages of automatic transmission. Although the operation seems more straightforward, the automatic transmission has many components that have an essential role in supporting the mechanical performance to run smoothly.

It might be too complicated if you imagine how the transmission system works on your vehicle. Therefore, we will help you to understand it by providing information related to functions, components, and how automatic transmission works.

Definition of Automatic Transmission


Automatic transmission or A / T is a type of transmission with gears that can perform self-switching automatically based on the engine load, which comes from the amount of gas pedal pressure and vehicle speed.

The operation is different from the manual transmission, which requires shifting gears using a gear shift paddle.

Through automatic transmission, the gears can move by themselves to adjust to road conditions and varying the amount of load.

automatic transmission parts
automatic transmission parts


Unlike the manual transmission, the automatic transmission is equipped with a torque converter or twisting modifier which functions as an automatic clutch. In an automatic transmission, transmission oil has a dual function. It not only lubricates and cools but also shifts gears as well as the clutch fluid automatically.

Thus, the amount of transmission oil must always be sufficient to be able to function correctly. You should change the transmission oil regularly because when the mileage increases, the quality will decrease.

Automatic Transmission Function

You can distinguish the automatic transmission function based on the type. Fully hydraulic automatic transmission controls the gearshift times or locks up entirely hydraulically, and the automatic transmission Powertrain Control Module (CPM) functions to regulate the time of the gearshift or lock up electronically.

automatic transmission gears and parts
automatic transmission gears and parts

Besides using data in the form of shift and lock pattern on PCM as a controller, this type of automatic transmission also has a diagnostic and fail-safe function.

Although the functions of the two types of transmission are the same, the way they work is different because one relies on hydraulic power while the other relies on electronics.

Automatic Transmission Components


The following are the auto transmission components:

  1. Torque Converter
    The torque converter is an auto transmission component contained in the transmission shaft input and is bolt tightened to the flywheel crankshaft.
    automatic transmission torque converter
    automatic transmission torque converter



    This component is usually filled with automatic transmission oil (ATF), which is useful to enlarge the moment of the engine and will proceed to the transmission section. It also functions as an automatic clutch to move or break the engine moment to the transmission. The torque converter also works to smooth the engine work, reduce vibration, and run the oil pump.

  2. Planetary gear unit
    The planetary gear unit is a component that functions to increase and decrease the moment of the engine and vehicle speed. This automatic transmission component is used to produce power and drive vehicles that have heavy loads with light power.
    automatic transmission planetary gear, torque converter, and other parts
    automatic transmission planetary gear, torque converter, and other parts



    An essential part of the planetary gear unit is the brake that moves to obtain the required gear ratio, and this is an automatic transmission component that operates with hydraulic pressure.

  3. Hydraulic control unit
    The hydraulic control unit is an auto transmission component that functions to control the work of the brakes and clutch by utilizing pressure from the oil pump. The oil pan in the hydraulic control unit is useful as a fluid reservoir. There is also an oil pump to increase hydraulic pressure as well as a variety of valves and pipes that will flow the transmission oil to the clutch, brake, and other parts of the automatic transmission component. Most hydraulic control unit valves are in the valve body assembly under the planetary gear.

  4. Manual linkage
    Even though the automatic transmission makes automatic shifts, it still has two ties that allow it to be operated manually by the driver connected to the automatic transmission. Manual linkage is an auto transmission component in the form of a selector lever with cable, accelerator, and throttle cable.

  5. Automatic transmission fluid (ATF)
    Automatic transmission fluid is a special oil that is mixed with various additional materials. Automatic transmission must use certain ATF as a lubricant. If you use different specifications, the transmission capacity will decrease. Regular oil level checks are needed to ensure the transmission is working correctly. Perform automatic transmission component checks when the engine is idling, the trans is at standard operating temperature, and the paddle is in the P position.

Automatic transmissions come in several types and are made in different ways. Even so, the essential functions and components of the automatic transmission are the same.

Each element in the transmission must work correctly and in good condition so that the overall performance can run smoothly.

How Automatic Transmission Works


The following is how an automatic transmission works:

automatic transmission diagram components
automatic transmission diagram components


  • The torque converter functions as a mechanical clutch. Through this component, torque is transferred by the pump and turbine mechanism. The first propeller in the torque converter works as a pump and is coupled directly using the engine. The second propeller mills the turbine with a planetary gear directly. Meanwhile, the latter serves as a stator to develop a two-propeller system into three propellers. When the automatic transmission system runs, the propeller coupled to the engine will spin to pump the transmission oil in an enclosed space. Then the oil pressure is used to drive the turbine, and this system makes the torque in the turbine rise with increasing engine RPM.

  • Planetary gear functions the same as the gear ratios in a manual transmission: changing the rotation ratio of the turbine on a wheel, this is the same case to the gear paddle used to run a car. The difference lies in the physical design because planetary gear does not have two rows of gears connected with different ratios. However, planetary gear only has a gear, and there are many small gears around it. Meanwhile, in other parts, there is gear inside, and the valve body will change the planetary gear ratio hydraulically.
Thus an explanation of how automatic transmission works are widely available in modern cars today. This type of transmission is designed with particular components that have the same function as in a manual transmission such as a torque converter and planetary gear.