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Discover how an automatic transmission system works



Did you ever experience driving both manual transmission and automatic transmission cars? Then, you will be able to know the big differences between the two. But how does an automatic transmission system work in a car?

That’s a good question!

There are two big differences between these two systems and we will discuss them here. We will also feature how the automatic transmission is put together, the types of automatic transmissions, to learn more about how the controls are best used, and to discuss some of the sophistication and complexities in controlling a transmission.

But most importantly, this article will also educate you and let you discover how an automatic transmission system works in vehicles and some good things about this system. So here goes!

Two main differences between manual and automatic transmissions

  • In an automatic transmission, there is no gear shift manually. Everything else comes automatically once you put the car’s transmission into drive.
  • An automatic transmission system doesn’t have a clutch pedal like in a manual transmission.

These two transmission systems of a vehicle do the same thing in your car. They both control the gears to accelerate or decelerate the vehicle. However, a manual transmission uses a clutch pedal to do this thing, while an automatic transmission uses a torque converter to accomplish the same task

Moreover, each system does it in a lot of different ways. But the automatic transmission (also known as auto, AT, self-shifting transmission, or n-speed automatic) can enable the driver to change gear ratios as the car moves. Interestingly, the automatic transmission gear system that comprised an AT, will free the driver from having to shift gears manually.

Also, unlike a manual transmission car, a self-shifting transmission will not lock the steering wheel while the vehicle is in the drive (say, at 70mph) when you suddenly turn off the key.

What is P, R, N, D (1-2-3), and L in an automatic transmission?

how an automatic transmission system works automatic transmission

The automatic vehicle gear system may be more complex than a manual transmission type, but once you become more used to it, everything will come smoothly. Knowing how hot your car engine could be is more difficult to determine than discovering how easy it is to drive an automatic transmission.

Most automatic transmission cars feature a series of letters (sometimes with numbers) that spell out P-R-N-D-L. These letters sound out phonetically as ‘Prindle’, which what engineers call the automatic gear shifter system. However, each letter stands for an individual setting within the AT.

We know that drivers who use a vehicle with an automatic transmission are surely aware of the corresponding letters and numbers associated with the system. For the benefit of those who are still grinning and just starting to drive an auto transmission vehicle, here are what those letters and numbers mean in a car’s AT:

P: The ‘P’ stands for ‘Park’ setting. If the gear shifter is in ‘P’ position, the gears are locked that keep the wheels from spinning forward or backward. Many drivers use this setting as a brake, which is one of the main purposes of this setting. 

R: The ‘R’ stands for ‘Reverse’ or the gear chosen to drive your car backward when parking or changing direction, etc. Shifting the gear spindle from P to R, the auto transmission reverse gear is actuated that spins the drive shaft backward.

N: The ‘N’ stands for ‘Neutral’. At this position, the transmission and rear wheels are disengaged which allows the vehicle to roll freely but can’t go anywhere under its power.

D: ‘D’ stands for ‘Drive’. When you shift to this setting, the auto transmission is activated. When you accelerate, the drive gear will administer power to the wheels which could be continuously shifted into higher gears as the engine speed (RPM) attains the intended level.

When the vehicle begins to decelerate, the auto-drive gear will down-shift to the lower gears. However, if your car’s auto transmission has a series of the number after the ‘D’, it indicates manual gear positions for the drive gear operation. Here are the different variations of the ‘D’ settings:

  • D1: Used for more challenging terrain, such as mud and sand that increase torque.
  • D2: Helps the vehicle in steep climbs, such as hilly terrain. D2 also aids in a quick engine boost just like in a manual transmission.
  • D3: The D3 is sometimes called or shown as an OD (overdrive). D3 revs up the engine for an effective overtaking. The OD gear ratio enables the wheels to rotate faster than the speed of the engine.

L: The ‘L’ (for Low) is specified as the lower drive gear (lowest possible gear ratio) in an automatic transmission vehicle. In other modern auto transmission cars, the L is replaced with ‘M’, which means that the transmission is on a ‘manual shifted’ option. 

The mode can be used in uphill or downhill roads, which need a stable, steady, and a lower speed.

What are the different types of automatic transmission?

The convenience and hassle-free gear shifting make the n-speed automatic transmission as the prime choice of many car lovers all over the world. The evolution and innovation of this modern automobile transmission propelled this system as the transmission of choice for increasing efficiency and performance. 

But did you know that there are at least 6 variations of the modern automatic transmission system? Let us take a look at each type.

  • Traditional Automatic Transmission (TAT)

The TAT is widely known as the torque converter automatic. This type of auto transmission is the most common in vehicles. The transmission uses hydraulic fluid coupling or a torque converter instead of a clutch. Its engine control unit (ECU) is directly connected to this device allowing a smooth and flawless engine control of your car.

  • Automated-Manual Transmission (AMT)

Also known as a semi-automatic transmission, the AMT uses a regular clutch and gear configuration. However, it uses more electronic devices like sensors, processors, actuators, and pneumatic to mimic manual gear use.

AMT’s are ‘notorious’ for shaky or jerky engine drive during low speeds and difficult acceleration but can get high fuel mileage over a long haul.

  • Continuously Variable Transmission (CVT)

CVTs commonly used belts and pulleys in place of the traditional steel gears. This system is a continuous and variable transmission for efficient gear shifting with various ratios that are dependent on the engine’s RPM. However, this system could sometimes produce a loud noise from the engine but provides maximum efficiency and fuel economy.

  • Dual-Clutch Transmission (DCT)

The DCT is a combination of an automatic and manual transmission in one system, Additionally, the DCT has no torque converter, instead, it uses two distinct shafts, each has its clutch for shifting gear. One shaft is used for even-numbered gears while the other is utilized for odd-numbered ones.

The system could get loud and noisy when shifting from a higher or lower gear but the transmission is seamless.

The shifting can get rough after wear as the DCT is a dry transmission that does not need changing the gearbox fluid. The system lets the clutches dry but eventually wears out over time.

  • Direct Shift Gearbox (DSG)

The DSG transmission is similar to the DCT system where it uses two clutches that disconnect alternately when shifting gears. This system allows for a quick-shifting and flawless acceleration. 

This is a wet transmission, which could give long-lasting service as long as the fluid is changed regularly. Interestingly, modern car models with this kind of transmission provide fuel efficiency that exceeds manual gearboxes.

  • Tiptronic Transmission

The Tiptronic transmission is also known as ‘manumatic’ and is usually used in car racers and other sports-oriented vehicles. The transmission system was popularized by Porsche in the 1990s and functions like a manual gearbox but uses a torque converter instead of a clutch pedal.

How the car transmission system works

how an automatic transmission system works

An automatic transmission seems too complicated to some, but like what we have stated before, this system could be your ‘best friend’ on the road once you are used to it.

So, how does an AT works? Just like a manual transmission, the automatic transmission’s foremost job is to permit the engine to operate in its limited range of speeds while allowing a wide range of output speeds.

Most automatic transmissions use sensors to know when it should shift gears, then, changes them using internal oil pressure. The key components of an automatic transmission system are the torque converter and planetary gear sets. 

In shifting gears, the transmission must be momentarily disconnected to the engine. Compared to a manual transmission, shifting gears is done by pressing a clutch pedal, but on an automatic, the job is done by the torque converter.

Moreover, the torque converter acts as a flywheel of the car, and it is located inside the bellhousing of the transmission. There are 2 fan-shaped elements inside the torque converter (filled with transmission fluid); the impeller (connected to the engine’s driveshaft), and a turbine which is attached to the transmission input shaft.

When the engine is turned on, the blades move the fluid causing the turbine to turn. A third component, a fan-shaped element called the stator, helps direct the movement of the fluid flow. When you press the gas throttle, the fluid spins the turbine faster sending more power to the transmission. 

  • Planetary gear system at work

Once the power has been delivered to the auto transmission input shaft, the planetary gears can do their thing. A central gear (also called the sun gear), is held in a ring called a planet carrier; while smaller planet gears revolve around it. The sun gear and the other smaller gears are surrounded by a large toothed ring gear and are harmonized with the planetary gears in their housing.

The automatic transmission’s various speeds are consummated by using the various combinations of gears. The sun, planetary, and ring gears are actuated in various combinations; such as the outer ring gear turns while the inner sun gear remains stationary. The auto transmission is realized with very little friction clutches that engage the gears for spinning, and bands, which keep them out of the way so they won’t turn. The clutches and bands are driven by pins and valves that are actuated by high-pressure transmission fluid.

The transmission is powered by the engine that increases or reduces it on its way to the output shaft, sending power toward the wheels. This is realized by creating different gear ratios.

Some auto transmissions utilized coolers to regulate the fluid’s temperature. When you are frequently using your vehicle for towing, you may consider adding a heavy-duty cooler if your car/vehicle is not equipped for heavy workloads.

What are automatic transmission problems?

While an automatic transmission system is easy to operate, certain problems may arise in its use. One of the most common problems is the thickening or dirty and burnt automatic transmission fluid (ATF). Once this happens, you will have a hard time operating the clutches and bands.

So you better check the ATF once a month and change it.

Watch this video on how an automatic transmission works: 


Do you find this article interesting?

It is better to know how an automatic transmission system works in a car so you can have ideas if it can provide you more convenience or problems once you buy one. An automatic transmission is a modern concept that we should never afraid to try. 

The system might best work for your driving needs. So, discovering the usefulness of an automatic transmission is all about safety and convenience.

If you like this article, please share it. Your comments (please write below) are welcome. 


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