Automatic Transmission (AT): Structure, Operating Principle & How to Use

Automatic Transmission (AT): Structure, Operating Principle & How to Use

Most modern car models today are equipped with automatic transmissions by manufacturers.

What is automatic transmission?

Automatic transmission (AT) is a type of transmission that can automatically change the transmission ratio without any control intervention from the driver with the most optimal fuel consumption rate, while changing the direction of engine movement to help the car go backwards easily.

Automatic transmission structure

Automatic transmission works based on adjusting planetary gears to create different input and output ratios. The structure of an automatic transmission includes:

Planetary gear sets

The planetary gear set plays the most important role in the automatic transmission. The structure of the planetary gear set includes:

- Sun gear (or fixed gear): Is the largest gear, located in the center.

- Planetary gears: These are smaller planetary gears that mesh and rotate around the sun gear.

- Outer belt: The outer belt surrounds the entire sun gear and planetary gear. This belt meshes with the planetary gear. In an automatic transmission, the outer surface of the outer belt is designed with many grooves to mesh with the friction plates of the clutch. This helps the friction plates move together with the outer belt.

- Planetary cage: The planetary gear shaft is coupled to a planetary cage (lead rod) coaxial with the sun gear and outer ring.

Hydraulic clutches

Hydraulic clutch kit includes:

- Friction discs

- Friction steel plates

- Spring

- Piston

- The friction disc and friction steel plate are designed to overlap each other.

- The friction disc meshes with the outer belt of the planetary gear set through grooves. When the outer belt moves, the friction discs of the clutch also move. The spring has the task of separating the friction plates from each other when the oil pressure is reduced or absent.

As the oil pressure increases, the spring moves to the right, the friction plates are pressed together. At this time, the planetary gear belt is held back.

Hydraulic torque converter

A torque converter is a fluid coupling that transmits torque from the engine to the transmission shaft. The torque converter is located horizontally between the engine and the transmission. The torque converter consists of:

- Pump gear connected to the motor

- Stator oriented medium

- Turbine connected to gearbox

Electronic controller

The electronic control unit is where input information from sensors is received, then processes the information and supplies current to the valves to open the oil line to the clutches.

How automatic transmission works

Each gear will have a corresponding clutch and planetary gear set such as gear 1 will have clutch number 1 and planetary gear set number 1, gear 2 will have clutch number 2 and planetary gear set number 2... The clutch pairs and corresponding planetary gears are arranged along the gearbox shaft. In addition to the gear clutch, there is also a forward clutch.

Torque from the engine crankshaft is transmitted through the torque converter and from the torque converter to the input shaft of the gearbox. The electronic controller, through the signal from the sensor, will open and close the oil line leading to the clutches. In order for torque to be transmitted to the output shaft of the gearbox, the two clutches must be closed.

- When the vehicle moves forward: the forward clutch and the gear clutch (1st or 2nd gear…) corresponding to the vehicle speed will be engaged.

- When the vehicle is in neutral N: only the second clutch is engaged. The forward clutch is not engaged. This is the reason why torque cannot be transmitted to the output shaft of the gearbox.

- When the vehicle moves in reverse: clutch 2 and clutch 5 are closed (with automatic transmissions with 5 forward gears and 1 reverse gear).

- 1st gear: The 1st gear shift is performed by engaging the forward clutch and the 1st clutch. The forward clutch allows torque to be transmitted from the converter to the input shaft of the gearbox. The 1st clutch is engaged, the torque is transmitted through the planetary gears 1 and 2… and then transferred to the output shaft of the gearbox.

- 2nd gear: The process of shifting to 2nd gear is similar. The forward clutch engages to allow torque to be transmitted from the converter shaft to the gearbox. The 2nd clutch engages to drive the planetary gears 2 and 3, then to the output shaft of the gearbox.

- Reverse: In reverse, clutch number 5 engages, allowing torque to be transmitted from the converter shaft to the sun gear shaft. Clutch number 2 engages, holding the outer ring of planetary gear set number 2 in place. Torque will reverse direction as it is transmitted from the sun gear shaft through planetary gear sets number 2 and 3, then to the output shaft of the gearbox.

Meaning of symbols on automatic car gear lever

Basic symbols

- Automatic gear levers usually have 4 main symbols, including: P, R, N, D arranged in a zigzag or straight line. Each symbol will have a different meaning, so the driver needs to clearly understand the meaning of the symbols on the gear lever, their location and function to ensure safety during driving.

- P (Parking): Represents the parking number, used when starting or stopping the vehicle. The driver can use the P gear lever to pull the handbrake to increase safety and limit damage to the gearbox in case of a rear-end collision.

- R (Reverse): Represents reverse gear and is used when reversing. One thing drivers should note is that they should not use reverse gear when the vehicle has come to a complete stop. Instead, the driver can use their right foot to brake, then shift into gear and slowly release the brake to ensure safety.

- N (Neutral): Indicates that the vehicle is in neutral, meaning the engine is still running but the wheels are not moving.

- D (Drive): This is the forward gear, activated when the vehicle is moving on a flat road and in stable weather conditions. When driving on slippery or steep terrain, the driver should switch to semi-automatic mode to keep the engine healthy and control the speed better.

Extended symbols

In addition to the 4 common symbols above, the automatic gear lever in some car models also has many more symbols with different functions such as:

- M (Manual): Has the same function as a manual transmission vehicle, helping the vehicle shift to gears 1, 2, 3, 4, 5 and vice versa. The letter M usually has a “+” sign (indicating an increase) or a “-” sign (indicating a decrease).

- S (Sport): This is a sport driving mode similar to M with the function of shifting gears according to the driver's wishes. This mode helps the car accelerate quickly, providing a powerful driving experience.

- L (Low): is a low number, used when going uphill, downhill or transporting heavy objects.

- B (Brake): This is a brake gear with the same function as L gear, helping to reduce the vehicle's speed when going downhill.

- OD (Overdrive): is a fast acceleration mode, often used when going downhill or climbing slopes.

- D1, D2 (Drive 1, Drive 2): Used when the driver is moving on uneven, rough roads and needs to drive slowly.

How to use automatic transmission car

Prepare before driving

Before driving, you need to:

 

- Adjust the rearview mirror, right side mirror, and seat to a position that makes you feel most comfortable and visible.

- Check the overall condition of the vehicle before driving to ensure that the control functions are still operating normally.

- Make sure all car doors are closed tightly to avoid the door from opening unexpectedly while driving.

- Wear seat belt properly.

- Check the indicator lights to make sure the vehicle is ready to move.

- When driving, you should keep your phone on vibrate/silent mode or at a low enough volume to avoid distraction.

Steps to start and operate automatic transmission vehicle

To start and operate an automatic transmission vehicle, the driver needs to perform the following steps in sequence:

- Step 1: Insert the key into the correct ignition or press the start button and start the vehicle by fully depressing the brake pedal.

- Step 2: Switch the vehicle to the driving mode that suits your needs.

- Step 3: Brake with your right foot and gradually lower the brake lever. The driver needs to carefully observe through the rearview mirror before moving the vehicle.

- Step 4: Take your foot off the brake pedal and slowly press the accelerator pedal to gradually accelerate the car until it reaches the desired speed, in accordance with road traffic laws.

- Step 5: If you want to park the car, press the brake with your right foot until the car stops completely, then pull the handbrake and put the gear lever in (P) and turn off the engine.

Experience and techniques when using automatic transmission vehicles

After using, users can apply some of the following experiences:

- Brake when starting the car: When starting the car, you should step on the foot brake and leave the gear lever in position P, and pull the handbrake to ensure safety and limit the car from accelerating suddenly.

- Using the right foot to brake or accelerate: Using both feet to brake or accelerate is a habit that can lead to dangerous situations and cause brake pad wear, gearbox damage, tire wear or fuel consumption. In addition, using both feet to brake and accelerate also makes it difficult for the driver to react promptly to emergency situations, even mistakenly pressing the brake or accelerator, causing serious accidents.

- Brake when shifting from P or N: When you want to shift from P or N to another gear, you must brake instead of the accelerator to avoid sudden acceleration and limit loss of control.

- Resting your foot on the brake pedal: Accidentally resting your foot on the gas pedal will make it easier for you to step on the gas pedal and lead to sudden acceleration or loss of control. Therefore, if you do not need to step on the gas pedal, place your foot towards the brake pedal.

Things to keep in mind when driving an automatic car

- For new drivers, driving skills are not much experience, so it is necessary to carefully learn the operations of using automatic transmission vehicles to help you use them correctly and effectively. When driving an automatic transmission vehicle, you need to note the following:

- Do not use your left foot, only your right foot to change from accelerator to brake. Test driving by keeping your heel in the middle so that you can easily rotate the top of your foot to change from accelerator to brake.

- Absolutely do not drive with your left foot on the gas pedal and your right foot on the brake pedal. Because when you are in an unexpected situation, it is easy to panic and mistakenly step on the brake pedal instead of the gas pedal, leading to loss of control of speed and easily causing an accident.

- Always step on the brake pedal when you want to change gears, maintain this habit to keep control of the vehicle speed.

- Do not shift to N while the vehicle is moving, especially when going downhill, because you will lose control of the engine braking.

Advantages and disadvantages of automatic transmission

Some advantages and disadvantages of automatic transmission can be listed as follows:

Advantage

- Simple operation, easy to use because operations such as clutch disengagement, gear selection, balancing transmission ratios between engines are all controlled by mechanical and electronic systems. This feature is extremely useful when driving on urban roads and crowded places, rush hour traffic jams.

- Automatic transmission vehicles only have accelerator and brake pedals, no clutch pedal, so the driver can confidently say "no" to the situation of the vehicle stalling or jerking during use. Controlling the speed of movement is more proactive as well as no more pressure when having to change gears, especially at red light stops or on complex, steep, and rough terrain.

- Less jerking when shifting gears.

- Minimize engine stalling and vehicle rolling downhill when moving on complex terrain.

Disadvantages

- The clutchless design makes the driver heavily dependent on the technology pre-installed on the car. To overcome this drawback, most automatic cars are now equipped with semi-automatic transmission, allowing the driver to flexibly switch to manual transmission mode when needed.

- In highway conditions, automatic transmission vehicles often consume more fuel than in urban areas, due to the complex structure of the automatic transmission and everything is pre-programmed, causing high engine speeds. Although very rare, the risk of mistaking gears or mistakenly pressing the brake pedal for the accelerator pedal during use is still possible. To limit this risk, users need to understand the symbols on the gear lever as well as basic operations when operating the vehicle.

Automatic transmission fluid products from Gartz

To ensure the vehicle's automatic transmission operates efficiently and durably, using quality transmission fluid is very important. Gartz provides automatic transmission fluid product lines such as 9G-HP, ATF G6, ATF G4, 7G Tronic,...

Manufactured with advanced technology, helps protect the vehicle's gearbox system and improve operating performance.

Benefits of automatic transmission

Automatic transmissions offer many benefits to drivers, including:

• Easy to drive:The driver does not need to change gears manually, making driving easier, especially when driving in crowded areas.
   

• Fuel economy:With intelligent control system, automatic transmission helps optimize transmission ratio, thereby saving more fuel.
   

• Reduce fatigue:Not having to constantly change gears helps the driver reduce stress and fatigue while driving, especially on long trips.
   

Conclude

Automatic transmission is an important technology that helps improve the performance and comfort of cars. With the continuous development of technology, automatic transmissions are becoming more and more perfect, providing a better driving experience and saving fuel. Understanding how automatic transmissions work will help you take better care of your car and ensure its efficient operation.