How does the automatic transmission work?

An automatic transmission, or automatic transmission, is a transmission that ensures that the optimal gear ratio is selected in accordance with driving conditions without the participation of the driver. This ensures a good ride smoothness of the vehicle, as well as driving comfort for the driver.

Many motorists cannot master the “mechanics” and the intricacies of gear shifting in any way, so they switch to cars with an “automatic” without hesitation. But here it must be borne in mind that automatic boxes are different and each of them has its own characteristics.

Types of automatic transmission

There are several main types of automatic transmissions - robotic mechanics, variator and hydromechanical transmission.

Hydromechanical transmission. The most popular type of gearboxes, it is known from the old models of the first cars with automatic machines. The peculiarities of this box include the fact that the wheels and the engine do not have a direct connection and the “liquid” of the torque converter is responsible for the transmission of torque.

The advantages of such an automatic machine are the softness of switching, the ability to "digest" the torque of even very powerful engines and the high survivability of such boxes. Cons - higher fuel consumption, an increase in the total mass of the car, the extreme undesirability of towing a car with such a box.

Variator (CVT). This box has big differences over the usual "automatic". Technically, there is no such thing as “shifting” in it, which is why this box is also called “continuously variable transmission”. The gear ratio in such an automatic transmission changes continuously and smoothly, allowing you to "squeeze" maximum power out of the engine.

The main disadvantage of the variator is the monotony of the “sound”. Intensive acceleration of the car occurs with a constant identical engine sound, which not all drivers can withstand. In new models, they tried to solve this problem by creating “pseudo” gears, when the variator seeks to imitate the operation of classic automatic gearboxes. The advantages of the variator include lower weight, efficiency and good dynamics. The downside is the extremely expensive repair of automatic gearboxes, as well as the inability to work with powerful engines.

Robotic mechanics. Structurally, such a box is very similar to a standard mechanical box. It has a clutch (or several) and power transmission shafts from the engine. In the case of a pair of clutches, one of them is responsible for even gears, and the second for odd ones. As soon as the electronics concludes that it is necessary to switch, the disc of one clutch opens smoothly, and the second, on the contrary, closes. The main difference from a manual box is fully automatic control. The driving style does not change either, which remains similar to driving an “automatic”.

The advantages include reduced fuel consumption, affordable price, very high gear shifting speed and low gearbox weight. This box also has some drawbacks. In some driving modes, shifting can be felt quite strongly (especially the first versions of boxes of this type were subject to this). Expensive and difficult to repair in case of failure.

*Volkswagen specialists have created a new, unique roboticth preselective boxу second generation gear - DSG (Direct Shift Gearbox). This Automatic transmission combines all modern transmission technologies of various types. Gear shifting is carried out manually, but electronics and various automated mechanisms are responsible for the whole process.

What does an automatic transmission consist of?

Gearbox manufacturers are constantly improving their design in an effort to make them more economical and functional. However, each automatic transmission consists of the following basic elements:

• torque converter. Consists of pump and turbine wheels, reactor;
• oil pump;
• planetary gear. In the design of gears, sets of clutches and clutches;
• electronic control system - sensors, valve body (solenoids + spool valves), selector lever.

Torque converter in an automatic transmission, it performs the function of a clutch: it transmits and increases torque from the engine to the planetary gearbox and briefly disconnects the transmission from the engine in order to change gear.

The pump wheel is connected to the engine crankshaft, and the turbine wheel is connected to the planetary gearbox through the shaft. The reactor is located between the wheels. The wheels and the reactor are equipped with blades of a certain shape. All elements of the torque converter are assembled in one housing, which is filled with ATF fluid.

Planetary reductor consists of several planetary gears. Each planetary gear includes a sun (central) gear, a planet carrier with satellite gears and a crown (ring) gear. Any element of the planetary gear can rotate or block (as we wrote above, the rotation is transmitted from the torque converter).

To switch a certain gear (first, second, reverse, etc.), you need to block one or more elements of the planetarium. Friction clutches and brakes are used for this. The mobility of the clutches and brakes is regulated through the pistons by the pressure of the working fluid ATF.

Electronic control system. More precisely, electro-hydraulic, because. hydraulics are used to directly shift gears (on / off clutches and brake bands) and block the gas turbine engine, and electronics are used to adjust the flow of the working fluid. The system consists of:

• hydroblock. It is a metal plate with many channels in which electromagnetic valves (solenoids) and sensors are installed. In fact, the valve body controls the operation of the automatic transmission based on data received from the ECU. Passes liquid through the channels to the mechanical elements of the box - clutches and brakes;
• sensors - speed at the inlet and outlet of the box, fluid temperature, selector lever position, gas pedal position. Also, the automatic transmission control unit uses data from the engine control unit;
• selector lever;
• ECU - reads sensor data and determines the gearshift logic in accordance with the program.

The principle of operation of the automatic box

When the driver starts the car, the crankshaft of the engine rotates. An oil pump is started from the crankshaft, which creates and maintains oil pressure in the hydraulic system of the box. The pump supplies fluid to the torque converter pump wheel, it starts to rotate. The vanes of the pump wheel transfer fluid to the turbine wheel, also causing it to rotate. To prevent oil from flowing back, a fixed reactor with blades of a special configuration is installed between the wheels - it adjusts the direction and density of the oil flow, synchronizing both wheels. When the speeds of rotation of the turbine and pump wheels are aligned, the reactor begins to rotate with them. This moment is called the anchor point.

Further, the computer, the valve body and the planetary gearbox are included in the work. The driver moves the selector lever to a certain position. The information is read by the corresponding sensor, transferred to the ECU, and it launches the program corresponding to the selected mode. At this moment, certain elements of the planetary gear rotate, while others are fixed. The valve body is responsible for fixing the elements of the planetary gearbox: ATF is supplied under pressure through certain channels and presses the friction pistons.

As we wrote above, hydraulics are used to turn on / off clutches and brake bands in automatic transmissions. The electronic control system determines the moment of gear shifting by speed and engine load. Each speed range (oil pressure level) in the valve body corresponds to a specific channel.

When the driver presses on the gas, the sensors read the speed and load on the engine and transmit the data to the ECU. Based on the data received, the ECU launches a program that corresponds to the selected mode: it determines the position of the gears and the direction of their rotation, calculates the fluid pressure, sends a signal to a certain solenoid (valve) and a channel corresponding to the speed opens in the valve body. Through the channel, the liquid enters the pistons of the clutches and brake bands, which block the gears of the planetary gearbox in the desired configuration. This turns on / off the desired gear.

Gear shifting also depends on the nature of the speed increase: with smooth acceleration, the gears increase sequentially, with a sharp acceleration, a lower gear will first turn on. This is also related to pressure: when you gently press the gas pedal, the pressure increases gradually and the valve opens gradually. With a sharp acceleration, the pressure rises sharply, puts a lot of pressure on the valve and does not allow it to open immediately.

Electronics has significantly expanded the capabilities of automatic transmissions. The classic advantages of hydromechanical automatic transmissions have been supplemented with new ones: a variety of modes, the ability to self-diagnose, adaptability to driving style, the ability to select a mode manually, and fuel economy.

What is the difference between automatic transmissions?

Many motorists continue to actively look towards automatic transmission, and there is a wide list of reasons for this. Also, traditional mechanics have not disappeared anywhere. The variator is gradually increasing its presence. As for robots, the first versions of these boxes are losing ground, but they are being replaced by improved solutions like preselective gearboxes.

Objectively, even the most reliable existing automatic transmissions cannot provide the same level of reliability and durability as mechanics. At the same time, the manual transmission is noticeably inferior in terms of comfort, and confronts the driver with the need to devote too much time and attention to the clutch and transmission selector.

If you try to look at the situation as objectively as possible, then we can say that in our time it is better and preferable to take a car with a classic. Such boxes are reliable, affordable for repair and maintenance, and feel good in various operating conditions.

As for which gearbox you will be more comfortable, better and more pleasant to drive, then you can safely put in the first place variable speed drive.

Robotic mechanics will suit car owners who prefer a quiet mode of movement in the city and highway, and those who seek to save fuel as much as possible. preselective box (the second generation of robotic gearboxes) is optimal for active driving, high speed and high-speed maneuvers.

Yes, if we take the reliability rating among automatic transmissions, then the first place is probably the torque converter. CVTs and robots share the second position.

Based on the opinion of experts and their forecasts, the future still belongs to CVTs and preselective boxes. They still have a long way to go to grow and improve. But now these boxes are becoming simpler, more comfortable and more economical, thus attracting a large audience of buyers. What exactly to choose, it's up to you.