How an automatic transmission works, the device and types of automatic transmissions used in modern cars

Each motorist has his own preferences regarding the gearbox – for someone it is vital to have full control over the power of the car, someone else likes more comfort and the absence of unnecessary movements. Today we will talk about the automatic transmission, its features, the principle of operation, advantages and disadvantages. This is a review article. In more detail on the work of each type of automatic transmission we will talk separately. If the automatic transmission and other parts of the machine are badly damaged, it makes sense to think about turning the machine in for recycling:

The work of the automatic transmission

Automatic transmission gearbox (automatic transmission) assumes an independent choice of transmission gear ratio without the involvement of the driver. Its main components are the control unit, torque converter and planetary series. The torque converter is installed next to the engine.

The turbine wheel, pump wheel and stator are located in its housing. The pump wheel and the crankshaft are connected to each other. The rotating impeller of the pump wheel directs the oil flow to the turbine wheel, thereby spinning it. The energy that remains after the torque transfer is directed by the stator back to the impeller, thereby further increasing its rotation and, consequently, the torque. The energy of the reversible oil flow depends on the speed difference between the pump wheel and the turbine wheel.

The speed of rotation of the pump wheel is always greater than that of the turbine wheel, and this difference decreases with increasing vehicle speed, as does the slippage of the turbine wheel relative to the pump wheel.

When the oil flow begins to rotate the stator, the torque stops increasing, and the torque converter essentially operates as a fluid coupling. In this case, the efficiency is practically less than 85%, and a lot of thermal energy is released; to cope with this, there is a locking mechanism for the pump and turbine wheels, which is activated by a command from the control device.

The planetary rows are systems of gears mechanically linked together, which transmit the rotation from the input shaft to the wheels. They are necessary for reverse travel and increased torque. Planetary gears use only one center shaft, are fairly compact, and shift gears by locking and unlocking the elements of the row. This process is regulated by a control mechanism, so that the shifting is smooth, without jolt or loss of power.

How a variator gearbox works

The variator gearbox consists of a variator gearbox, a neutral translation mechanism, a mechanism which is responsible for driving in reverse, and a control unit. It is based on two pulleys that are connected by a belt, each consisting of two conically shaped discs that can shift and move apart, changing diameter.

When the master pulley has the discs apart, it has a small diameter (low engine speed). At the same time, the idler pulley discs are compressed. When the speed increases, the diameter of the idler pulley becomes smaller while that of the driven pulley increases; the gear ratio changes. The variator maintains the RPM of the motor at which maximum power can be obtained.

Changing the pulley diameters and gear ratios allows you to reduce or increase the speed of the vehicle. Due to this design, the variator gearbox is characterized by smooth, stepless gear shifting and economy.

Robot transmission operation

Robotic gearbox in terms of its use by the driver does not differ much from mechanical boxes: the main difference – the choice of transmission is provided by servo drives (electric motors with an actuator and gearbox), which are controlled by an electronic block.

When operating in automatic mode, the computer is responsible for gear changing, which gives the appropriate command after processing the data on the engine speed, driving speed and information of the onboard systems. In manual mode, the driver increases or decreases the speed thanks to the selector.

The main disadvantage of this type of gearbox is the slowness during shifting, which results in increased fuel consumption.


The Tiptronic transmission when working in automatic mode resembles a hydraulic automatic gearbox, but there is also a manual control mode, which allows you to set the range of gears, manually turn on a certain speed. For this purpose, a lever is provided which is moved to a special position and moved by short jerks to the “+” and “-” signs.

The operation of the automatic transmission is different from the mechanics, especially it is noticeable in the cold season. The car with such automatic transmission should be well warmed up, the box itself, and when driving, if possible, use manual shift mode or driving mode in ice. If the car is stuck in the snow, it will be more difficult to get out, so you will have to carefully plan the route.

Leave a Reply