The automatic transmission device of a car and the principle of operation. Automatic transmission types

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

Recently, automatic transmissions are gaining more and more popularity. And there are reasons for that. Such a box is easier to operate and does not require constant “play” with the clutch in traffic jams. In large cities, such a checkpoint is far from uncommon. But the automatic transmission device is significantly different from classical mechanics. Many motorists are afraid to take cars with such a box. However, their fears are not justified. With proper operation, an automatic transmission will last no less than mechanics. But in order to better understand it, you should study in detail the device of the automatic transmission of a car. We will talk about this in our today's article.

Varieties

There are several types of these boxes. So, they distinguish:

• Hydromechanical automatic transmission.
• Robotic (DSG).
• Variator.

What are the features of each of them? Consider below.

ClassicAutomatic transmission

Hydromechanical transmission is the most common type of automatic transmission. The device of such a box assumes the presence of a torque converter, a manual gearbox and a control system. But this design is practiced on rear-wheel drive vehicles. If this is a front-wheel drive car, then the differential is also included in the automatic transmission device, and the main gear.

The torque converter (colloquially known as "donut") is the main unit in this transmission. It serves to change and transmit torque from the engine flywheel to the manual gearbox. The donut also serves to dampen oscillations and vibrations that occur during the transfer of rotational forces from the internal combustion engine.

Torque converter consists of several wheels. This is:

• Turbine.
• Reactor.
• Pump wheel.

The design also includes two clutches - blocking and freewheeling. All these details are enclosed in a separate toroidal case, which looks like a donut (hence the specific name).

The pump wheel is connected to the crankshaft of the motor. Turbine interacts with a manual transmission. Between these two elements is the reactor wheel. It, unlike all the others, is motionless. Each wheel of the automatic transmission hydraulic transformer has blades between which the working ATP fluid passes.

The automatic transmission lockup clutch is designed to block the GTF (donut) in specific operating modes of the internal combustion engine. Clutch free(also referred to as overrunning) rotates the reactor wheel in the opposite direction.

GTF work

It is carried out in a closed cycle. So, ATP liquid begins to flow from the pump to the turbine, and then to the reactor wheel due to the special shape of the blades, the oil flow rate begins to grow steadily. The ATP fluid causes the pump wheel to spin faster. This increases the torque force. By the way, its maximum parameter is achieved at minimum speeds. This is necessary so that the car starts moving smoothly even under load. When the car starts to pick up speed, the clutch engages and the torque converter locks up. In this situation, a direct transmission of torque is performed. It is worth noting that the lockup clutch is activated in the automatic transmission in all gears, including reverse.

Modern cars use a slipper clutch. This mode prevents the mechanism from completely locking up, which has a positive effect on fuel consumption and a smooth ride.

Planetary gear

This assembly functions as a manual transmission. The gearbox can be designed for four, six, seven or eight speeds. In rare cases, a nine-speed automatic transmission is used (for example, on Land Rover cars).

We continue to study the automatic transmission device. The planetary gear consists of several sequential gears. They form a planetary gear set. Each of the speeds includes severalitems:

• The ring gear.
• Satellites.
• Sun gear.
• Carrier.

How is torque change made? Studying the device of the automatic transmission torque converter, it should be noted that this operation is performed using several elements of the planetary gear set. This was the carrier, as well as two gears (sun and crown). Blocking the latter allows you to increase the gear ratio. The sun gear, on the contrary, reduces this ratio. And the carrier changes the direction of rotation of the elements.

Locking is done with clutches. This is a kind of brake that holds certain parts of the gearbox by connecting them to the gearbox housing. Depending on the brand of car (“Mazda” is this or “Ford”), the automatic transmission device assumes the presence of a band or multi-disc brake. It closes with hydraulic cylinders. The latter are controlled from the distribution module. An overrunning clutch is used to prevent the carrier from rotating in the opposite direction.

Electronic system

The device and operation of the automatic transmission of a modern car is impossible without an electronic control system. Includes:

• Control unit.
• Input sensors.
• Automatic transmission selector (we will consider its device later).
• Distribution module.

Note that the list of input elements is quite extensive. So, this includes sensors:

• Gas pedal positions.
• Temperatures of ATP liquid.
• Inlet and outlet shaft speeds.
• Automatic gear selector positions.

The automatic transmission control unit continuously processes the signals that come from these elements and generates control pulses for the actuators. This unit communicates with the engine ECU.

The distribution module activates the friction clutches and controls the flow of ATP fluid in the transmission. This module consists of control spools and mechanically actuated solenoid valves. These parts are enclosed in a separate aluminum case and are interconnected by channels.

An important element in the Honda automatic transmission is the solenoids. They are also called solenoid valves. They are needed to regulate the pressure of the transmission oil. And the spools perform the operation mode of the box. The elements are actuated from the automatic transmission lever.

Since ATP oil is the main working fluid, a gear-type pump is provided in the device of any automatic transmission. It works from the torque converter hub and is the basis of the gearbox hydraulic system. To cool the oil in the Mercedes automatic transmission device, a special heat exchanger is provided. This is a small radiator that is located in front of the car. On some models, it is enclosed with the main engine coolant cooler.

Automatic transmission selector

It is this part that directly controls the automatic transmission. There are several automatic transmission modes:

• Parking.
• Reverse.
• Neutral.
• Drive (move forward).

On some Nissan cars, the automatic transmission deviceassumes the presence of a sports mode. To turn it on, you need to move the gearbox selector to position S. The mode differs in that gear shifting is carried out at higher engine speeds. This results in more torque and vehicle speed. If we consider the Qashqai Nissan, the automatic transmission device also assumes the presence of a manual gearshift mode. Such a box is called "Tiptronic".

DSG robotic transmission

This is a development of the Volkswagen-Audi concern. This checkpoint appeared in the mid-2000s and is installed on most Skoda and Audi cars, as well as on Volkswagens (including the Tuareg).

A key feature of the automatic DSG is fast gear changes without interruption in power flow. This allows you to increase the performance and efficiency of the transmission. Cars with DSG have good acceleration dynamics. At the same time, they have lower fuel consumption compared to classic torque converters.

The device and operation of this type of automatic transmission differs significantly from the previous gearbox. So, there is no usual "donut". The transmission of torque is carried out through the use of two clutches. In addition, an anti-theft device can be installed on this type of automatic transmission.

DSG transmission

It includes:

• Dual mass flywheel.
• Two rows of gears.
• Final drive and differential.
• Electronic control system.
• Doubleclutch.

It's all enclosed in a metal box. If we talk about the dual clutch, it ensures that power is transmitted simultaneously to the second and first row of gears. If this is a six-speed DSG, the box has a drive plate (it is connected to a dual-mass flywheel through an input hub) and friction clutches. The latter are linked to the gear trains via the main hub.

By the way, the type of clutch may differ on the DSG box. If it is a six-speed gearbox, a wet clutch is used in the design. Oil provides not only lubrication, but also cooling of the friction discs. This significantly increases the resource of the aggregates.

If we talk about the seven-speed transmission, a dry scheme is applied here. This significantly reduces the amount of oil used. If in the first case, the operation of the DSG required at least six and a half liters, then in the second - no more than two. The pump that pumps the lubricant is electric. This design, according to experts, is less reliable and does not have a high resource.

As for the gears, the first is responsible for the operation of the reverse and odd speeds. The second is used to control even gears. Each of the rows is a secondary and primary shaft with a specific set of gears. The primary element is complete and coaxial, and the gears are rigidly connected to the shaft. At the same time, the secondary gears rotate freely. Also in the design there are synchronizers. They facilitate the inclusion of a particular speed in the checkpoint. Tothe car could move backward, an intermediate shaft is provided in the DSG box; it is equipped with a reverse gear.

The gear shifting is controlled by electronics. It includes various sensors, a control unit and an electro-hydraulic unit with a mass of actuators. The control module is located in the crankcase of the automatic robotic transmission. During the operation of the gearbox, the sensors analyze the speed of the shafts at the output and input, oil pressure, the position of the gearshift forks, as well as the temperature of the lubricant. Based on these signals, the ECU implements one or another control algorithm.

Thanks to the block, the hydraulic circuit of the gearbox is controlled. This system includes:

• Distributor spools. They are actuated from the gearshift lever.
• Solenoid valves. These elements are used to switch speeds.
• Pressure control valves. Thanks to them, the friction clutch works.

The last two components refer to the actuator controls of the robotic gearbox.

Also, the design of this box provides a multiplexer. It allows you to control hydraulic cylinders with solenoid valves. Remarkably, the number of the former is twice that of the latter. Thus, in the initial position of the element, some hydraulic cylinders are activated, and in the working position, others.

The algorithm of the robotic transmission consists in sequential switching of several gears. So, when the car starts moving on the first, the secondalready engaged with the second disk. After a set of certain revolutions, an instant switching occurs. After all, the system does not need to select one or another shaft - the gears have already started to work.

Where is this gearbox used? Basically, DSG is used on cars of class B, C and D. In many respects, everything depends on the technical characteristics of the motor itself. So, a six-speed box is able to withstand a torque of 350 Nm. And the seven-band DSG is only 250. Therefore, such a box is not installed on powerful cars.

Variator

This is a relatively new type of automatic transmission, although the first copies began to be used as early as 59th year. So, the first car with a variable gearbox was the Daf. Further, this scheme began to be practiced by such manufacturers as Ford and Fiat. However, this box was widely used only 10 years ago. Now this gearbox is used on cars:

• Mercedes.
• Subaru.
• Toyota.
• Nissan.
• Audi.
• Ford.
• Honda.

The key feature is that it has no gears per se. The variator is a continuously variable transmission that provides a smooth change in gear ratios as the vehicle speeds up. The main advantage of such a gearbox is the optimal coordination of the load on the car with the crankshaft speed. This results in high fuel efficiency and productivity. The smoothness of the ride is also noticeably improved, because twitches during dynamic acceleration are excluded here.

The car picks up speed quickly, without jerking, as smoothly as possible. But due to certain restrictions on torque and power, variable automatic transmissions are used only on cars and some crossovers. Also, the cost of the car on the CVT increases significantly, since this transmission is quite high-tech.

Devices and types

There are only two types of these transmissions. This is a toroidal and V-belt variator. The latter is the most widely used. But regardless of the type, they have the same device (Toyota automatic transmission is no exception). So, the design includes:

• CVT transmission.
• Mechanism that transmits torque.
• Control system.
• Mechanism for disengaging the gearbox and for engaging the reverse gear.

In order for the gearbox to perceive and transmit torque, the following clutch mechanisms are activated:

• Automatic centrifugal. Used on Transmatic CVTs.
• Multidisc wet. These are Multimatic variators.
• Electronic ("Hyper" boxes used on some Japanese cars).
• Torque converter. Examples include Extroid, Multidrive and Multimatic transmissions.

The last type of connection is the most popular and resourceful. Note that the variable gearbox drive itself can be belt or chain.

The first type consists of one or two belt drives. also inToyota automatic transmission device includes two pulleys. The latter form some kind of conical disks that are able to move apart and move apart. Thus, the diameter of the pulley is changed. To bring the cones closer together, special springs are provided in the Mazda automatic transmission device (sometimes centrifugal force is used). The conical disk has a 20-degree angle of inclination. This allows the drive belt to move with minimal resistance.

A metal chain is used on Multitronic CVTs. It consists of several plates that are connected by axes. This design has good flexibility. The bending radius is up to 25 millimeters. Unlike a belt variator, a chain variator provides torque transmission with point contact of the plates with the disks. High voltages occur in these areas. Thanks to this scheme, the minimum loss in torque transmission and the best efficiency are ensured. Tapered discs are made of high strength bearing steel.

Due to the design features and arrangement, the automatic transmission valve body is not able to provide reverse movement. Therefore, auxiliary mechanisms are used in the variator to engage reverse gear. This is a planetary gear. It has the same device and principle of operation as in classic torque converter automatic transmissions.

Also in the design of such a checkpoint there is an electronic control system. It provides synchronous adjustment of the variator pulley diameter depending on the current engine speed. This systemprovides and the inclusion of reverse transmission. The variator is controlled through the selector, which is located in the cabin. Control modes are the same as in a conventional automatic transmission. The device and repair of these boxes are also similar. However, we note that many services are afraid to take these cars into work, because they simply do not have the appropriate experience. Such a box appeared in Russia quite recently, and there are many myths about the correctness of maintenance and repair around it. Experts say that for such a gearbox, it is enough just to change the oil on time and not overheat the mechanism itself.

Conclusion

So, we found out what types of automatic transmission are, how it works and how it works. What to choose for an ordinary car enthusiast? Operating experience shows that the best option would be to buy a car with a classic torque converter automatic transmission. Such a box is familiar to many - it can be repaired and serviced in any service. In addition, modern machines of this type are distinguished by a good resource of 300-400 thousand kilometers. As for the DSG robot and the stepless variator, such boxes nurse no more than 150 thousand on our roads. Then problems and serious investments begin. Therefore, you should refrain from buying them.