Gearbox: Structure, Classification, Automatic Transmission

Dual clutch gearbox
Latest update date: February 01, 07

Power transmission system - Gearbox: classification, structure, operating principle? Types of automatic transmissions? Damages and repairs

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Introduction Powertrain – Gearbox

The gearbox is an important part of the automotive powertrain. It undertakes the function of changing the torque and the speed of the active wheel to match the torque of the road and the car's speed according to the needs of the user. In addition, it must have the function of allowing the car to move forward or backward, and it must also allow the engine to operate while the vehicle is stationary.

Over many years of development, the gearbox in cars has been divided into many different types from manual transmission to automatic gearbox, and more modern automatic transmission gearbox. The development from manual transmission to automatic transmission will help reduce driver pressure for the user more, users will not get tired when shifting, or operating the car in off-road conditions ... In this article, Thanh Phong Auto will introduce readers useful information about the types of gearboxes fitted on current models.

Powertrain - Gearbox
Powertrain – Gearbox

Sorting of gear boxes

Car gearboxes are classified based on many factors such as:

Number of levels

The number of gears depends on the purpose of use and the type of vehicle, but each car is equipped with a gearbox with different gears.

6 manual gearbox5 manual gearbox

According to the axis number

According to the number of shafts in the gearbox (manual transmission): depending on the position between the engine and the active bridge, the gearbox will be changed accordingly. Most of today's cars are equipped with an engine located in front of the cockpit:

  • If the car has an active front-wheel drive, the transmission is one with two gear shafts inside.

Front-axle manual transmission

  • If the car has an active rear axle, the transmission is the type with 3 inner gear shafts.

rear-wheel drive gearbox

According to the gear control method The transmission will be divided into categories such as manual transmission, automatic transmission and semi-automatic transmission.

6 manual gearboxautomatic transmission

semi-automatic gearbox

Manual transmission (Manual Transmission)

A manual transmission, also known as a regular gearbox, is the oldest type of transmission that is also fitted in cars today. The manual gearbox usually comes with a dry friction clutch, the friction clutch is responsible for switching between the gearbox and the motor. The clutch is controlled via the clutch pedal, when the shifter is shifted, the driver deploys the clutch pedal to stop the rotary movement between the engine and the input shaft (primary shaft) of the gearbox, simultaneously. with the operation of the gear lever to perform gear changes.

Tapered clutch gearbox gear lever lever

The purpose of disconnecting the clutch before shifting is to reduce the speed difference between the input shaft and the output shaft of the gearbox, making shifting easier. A small tip when changing gears to a manual gearbox, during the clutch disconnection, the driver should lightly click the accelerator to increase the engine revs, when the gear is complete, the number of engine revolutions will decrease down to the right working area, helping the car to become more loading and more fuel efficient.

gearbox structure

Advantages of manual gearboxes:

  • More fuel-efficient than automatic transmissions with the same gear ratio because shifting operations with manual transmissions are done manually, while automatic transmissions extract engine power to shift gears.
  • The price of a car equipped with a manual transmission will be cheaper than a car equipped with an automatic transmission.
  • The maintenance and maintenance of the gearbox is also simple and easy, low cost.
  • The gearshift control will help the driver focus more and bring more fun.
  • The manual transmission will help the driver better control the car in situations such as downhill, emergency vehicle speed reduction ...

Disadvantages of manual gearboxes include:

  • Shift control will cause fatigue for the driver, especially in off-road conditions because the driver has to constantly "scroll" or disconnect the clutch continuously.
  • From the above disadvantages, it can be seen that the manual transmission can hardly be increased by too many gears, because it is easy to cause fatigue for the driver, so the fuel economy will be inferior to the automatic transmission. when the gearshift of the automatic transmission is increased.

Automatic transmission with automatic transmission (Automatic Transmission)

Automatic transmission with automatic transmission (Automatic Transmission)
Automatic transmission with automatic transmission (Automatic Transmission)

The automatic transmission with a level is a very popular type of gearbox on the models of Toyota, KIA, MAZDA, HONDA, HYUNDAI, MERCEDES-BENZ, BMW, AUDI, LEXUS, FORD ...

The gearbox has a gearbox that uses planetary gears to make gears, it always comes with a hydraulic torque converter or a clutch to make the motor disconnect. All gear and gear variables are controlled by a controller that automatically switches on and off according to the operating conditions.

automatic transmission throttleDrive automatic gearbox

The gearshift is done by switching wet clutch disc clutches inside the gearbox to fix one of the three components of the planetary gear set: the sun gear, the planetary gear and the gear ring. Each pair of drive gears and pinions will form a gearbox gearbox.

Automatic gearbox constructionAutomatic gearbox constructionAutomatic gearbox constructionAutomatic gearbox construction

+ Note: Cleaning - Car Exterior Maintenance

Advantages of automatic transmission

  • The most obvious advantage is that the automatic transmission brings comfort to the user, the driver will feel less tired when driving on a long route, especially in city road conditions often "off". Street".
  • Because the automatic transmission frees the driver from shifting control, the number of gears can be greatly increased: 9 gears (Mercedes-Benz models such as GLC, E-class, S-class) , 10 gears (Ford models such as Ranger, Everest...); leading to the loading, fuel economy and smoothness of the vehicle will be significantly increased compared to a normal transmission.

mercedes automatic transmission

  • Modern cars also combine engine control in combination with gearbox control to achieve the optimal operating area for power and fuel economy.


  • Fuel consumption is higher than manual transmission for automatic transmissions with fewer gears.
  • Maintenance, servicing and replacement costs are high due to the complex structure of the gearbox.
  • If the vehicle is not equipped with the feature to assist in moving on steep roads, cars equipped with automatic transmission will be very unsafe to move because the driver cannot perform "braking by gearbox" to control. vehicle speed. As a result, the driver will constantly check the brakes and lead to brake failure which is the cause of serious accidents.

automatic transmission

Continuously Variable Transmission (Continuously Variable Transmission)

The reason this automatic transmission is called a stepless gearbox because there is no gear coupling to form a certain gearbox inside the gearbox.

Continuously Variable Transmission (Continuously Variable Transmission)
Continuously Variable Transmission (Continuously Variable Transmission)

CVT gear box uses 2 puly changeable diameter and a belt with special structure connecting 2 puly, a system of hydraulic and electromagnetic pipes and valves designed to be integrated with the pulleys, a The controller will open and close the valves to change the diameter of 2 puly to make a continuous change in gearbox depending on the operating conditions of the vehicle.

CVT gearbox straps

The CVT gearbox operates on friction, so the most important thing for CVT gearboxes is to choose the right gear lubricant. Viscosity of CVT gearboxes must not reduce the coefficient of friction between belt contact surfaces and the pulley below the permissible level to reduce slippage. Each manufacturer will specify a special lubricant specific to their CVT gearbox.

transmission gear CVT hondanissan CVT gearbox lubricantsviscous transmission CVT toyota

Stepless gearbox is an ideal gearbox from the viewpoint of calculation and gearbox design. It allows using the maximum power of the engine on a very long speed range of the car, and the ability to save fuel is also very high compared to other types of gearboxes. It is easy to see that the models are equipped with a CVT gearbox such as NISSAN X-trail; MITSUBISHI Mirage, Attrage; HONDA City, TOYOTA Vios; HYUNDAI Accent ...

CVT gearbox

Advantages of CVT gearbox

  • Because the CVT transmission is an automatic transmission, operating a vehicle equipped with a CVT transmission is gentle and comfortable.
  • The ability to save fuel is very high compared to manual gearboxes and automatic transmissions with levels due to the ability to simultaneously control the engine and change the gear ratio; The engine will run at the best speed and the vehicle speed will change just by changing the gear ratio.
  • A car's CVT transmission allows for the smoothest and fastest acceleration and deceleration.

honda city CVT gearbox

Disadvantages of CVT gearbox

  • The slip inside the CVT gearbox occurs very often, so it easily leads to wear and damage to the gearbox's details.
  • Loud noise when the car accelerates is a huge drawback that causes discomfort to users, even if the car is equipped with a gear simulator.
  • CVT gearboxes cannot be fitted to vehicles with high traction torque due to slip occurring inside the gearbox.
  • In Eco Mode, the CVT gearbox causes a bad feeling for the driver when starting to accelerate, the vehicle speed will not increase according to the speed of the driver's accelerator pedal but will increase steadily according to the control. controller to achieve the best fuel economy.
  • Similar to a leveled automatic transmission, cars equipped with a stepless automatic transmission when traveling on steep passes are very dangerous if the vehicle is not equipped with a support feature for moving on steep roads.

CVT gearbox car downhill

Dual clutch transmission

Dual-clutch gearboxes are also considered as semi-automatic transmissions because the gearbox allows control in both automatic and manual control. As the name implies, the double-clutch gearbox is made up of 2 wet friction clutches that operate separately from each other. One clutch connects the shaft of odd-numbered gears (1,3,5) and the other is connected to the shaft of even-numbered gears (2,4,6).

Structure of double clutch gearbox

The clutch is controlled on and off by the controller via hydraulic-solenoid valves. The gearbox still uses the same synchronous mechanism as the manual gearbox. In principle, the dual-clutch gearbox can be considered as a combination of two manual transmissions into a unified whole.

Dual clutch gearbox


  • Compared to a manual transmission of the same size, cars equipped with a dual-clutch transmission have faster acceleration time, quick and smooth shifting time, creating a sense of excitement for the driver.
  • The torque transmitted to the wheels is not interrupted, so the car runs very fast and does not jerk.
  • The structure is simpler than the AT automatic transmission and the fuel economy of the dual-clutch transmission is 10% more than the AT automatic transmission.


  • The control of a dual-clutch transmission requires a complex and precise algorithm, so it is quite expensive and only suitable for high-end models of Volkswagen, Audi TT, HYUNDAI Veloster, MINI Scopper, BMW 5 series...

BMW dual-clutch gearbox

  • The cost of maintenance, maintenance and replacement of spare parts is quite high.
  • The control algorithm on popular cars such as NISSAN X-trail, FORD, HONDA Civic... sometimes encounters errors such as: sudden acceleration, sudden shutdown, poor response...

The common damage of the gearbox

For manual gearboxes

+ After a long time using the gearbox, it is easy to encounter the error of jamming, the driver cannot change gears.

gearbox repair

+ The gearbox has noise, vibration due to large abrasion of gears.

+ Shift the gear to 0 because the gear lever is pushed and the guide is bent, the synchronous device is worn.

gearbox repair

+ Gearboxes are viscous, lubricant due to openness, excessive amount of oil ...

For automatic transmission

+ The gearbox is overheated, allowing for lack of lubricant or lubricant not in accordance with the prescribed standards.
+ Melting oil at the bottom of the gearbox due to leakage of the gearbox or excessive amount of oil.

gearbox repair

+ Generating loud noise, vibration due to abrasion of planetary gears, or pulley-belts for CVT automatic transmission.

gearbox repair

+ The engine speed is very large while the vehicle speed is very low because of the wrong lubrication for the automatic gearbox, the double-clutch gearbox for wet friction clutch, or it might be due to hydraulic torque variable. (squash) is damaged.

gearbox repair

+ Viscosity of the gearbox automatically changes to black or dark gray due to dirt and dust can quickly erode the gears inside the gearbox.

+ And other damaged errors ...

>>> Suggestions for reference: Signs Of A Broken Gearbox Car

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1 Commentary

  • Tuan Huynh 23/07/2020

    How does the Selectshift gearbox on the FORD FOCUS 2018 have a structural principle? What advantages and disadvantages are there compared to the Powershift gearbox?
    Please Thanh Phong Auto advise to help.
    Thank you very much

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