The principle of operation of an automatic transmission. Automatic transmission (automatic transmission) Automatic transmission principle of operation

Nowadays, a large number of motorists use automatic (automatic transmission) and every year there are more and more of them. Automatic transmission not only reduces the burden on the driver when driving a car compared to a manual transmission () during a trip, but also helps the driver reduce fuel consumption by shifting gears at optimal engine speeds depending on the selected driving mode.

Automatic transmission was invented in America, from where it became widespread. Currently, in the US and many European countries, the popularity of manual transmissions is not very high; they are used by about 5% of drivers. However, the demand for cars with automatic transmission in Russia is constantly growing and today they are equipped with automatic transmission.

All automatic transmissions can be divided into several main types:

Variators;
Hydraulic automatic transmissions;

Hydraulic automatic transmission

The automatic transmission, based on the operation of a torque converter, has been seriously modified at the request of the Europeans and at the moment has received several operating modes (winter, sports, economical) corresponding to each.

The number of gears also increases in classic slot machines. In the 90s there were only 4-speed automatics, but now they can be 8-speed.

Components of the automatic box:

torque converter;
Manual Transmission;
working fluid pump;
cooling and control system;
brake band;
planetary gear set (planetary gearbox)

The main units of the automatic transmission are: a torque converter and a mechanical planetary gearbox.

The torque converter changes and transmits torque from the engine to the manual transmission. Located between the engine and gearbox. The torque converter contains two vane machines: centripetal turbine, centrifugal pump. Among other things, the torque converter contains a reactor wheel, a freewheel (overrunning clutch), and a lockup clutch. The pump wheel connects to the engine crankshaft, while the turbine wheel connects to the manual transmission. A fixed reactor wheel is fixed between these two wheels. All torque converter wheels have vanes of a certain shape with channels that provide the passage of the working fluid, because the operation of the torque converter is based on the continuous circulation of the working fluid, which transfers energy from the engine to the transmission. The fluid flow from the pump wheel is transferred to the turbine wheel, then to the reactor wheel. Due to the fact that the reactor blades have a peculiar structure, the fluid flow increases, increasing the speed of the pump wheel. The fluid flow changes its direction after the alignment of the angular velocities of the pump and turbine wheels. The overrunning clutch is activated and the reactor wheel begins to rotate. The torque converter begins to transmit only torque.

The lock-up clutch is designed to lock the torque converter, and the freewheel (overrunning clutch) provides rotation in the opposite direction of the reactor wheel.

The design of a manual transmission is much simpler, allowing you to step change the torque and move in reverse. Often consists of two planetary gearboxes connected in series, modern automatic gearboxes can be performed as six-speed or eight-speed. The advantage of the automatic gearbox is that the planetary gearboxes used in them are more compact and have coaxial operation.

Electronic control system

The electronic control system processes the signals from various sensors and, having processed them, sends control signals to the distribution module.

planetary gear

The main advantage of the planetary gear is its compactness, the use of one central shaft. The planetary gear allows you to switch speeds without jerks, shocks and loss of power. The transmission automatically shifts gears, for this the driver only needs to manipulate the gas pedal, pressing or releasing it.

The constituent elements of the planetary gear set:

sun gear;
satellite;
ring gear;
carrier

The rotation is transmitted under the condition that one or two elements of the planetary gear are blocked. Friction clutches and brakes block these elements. To hold certain elements, a brake is used, and in order to block the elements among themselves, the clutch is activated, ensuring the transmission of torque. Hydraulic cylinders, controlled by a distribution module, actuate the brakes and clutches.

CVT automatic transmission

A CVT is a continuously variable automatic transmission in which the gears do not have a fixed gear ratio.

If you compare the CVT with other automatic transmissions, then its advantage lies in the efficient use of engine power, because the crankshaft speed is optimally coordinated with the load on your car, which ensures quite high fuel economy. Also, when driving a car with a CVT automatic transmission, a high level of comfort is achieved, due to the continuous change in torque, and also due to the absence of jerks.

CVT device

The general arrangement of a CVT automatic transmission:

sliding pulleys;
differential;
V-belt;
torque converter;
planetary reverse gear;
hydraulic pump;
electrical control box

Sliding pulleys look like two wedge-shaped "cheeks" located on the same shaft. The hydraulic cylinder, which compresses the discs depending on the speed, drives them.

The torque converter has the same functions as in a classic automatic transmission, i.e. transmits and changes torque.

The device that distributes torque to the drive wheels is called a differential.

The planetary reverse gear causes the output shaft to rotate in the opposite direction.

In order to pressurize the working fluid, the torque converter starts the hydraulic pump.

The control unit is used to control the actuators of the variator, it depends on the signals supplied from the sensors (crankshaft location, fuel consumption control, ABS, ESP, etc.).

At the moment, the variator cannot be combined with powerful engines, and therefore the variator cannot become a competitor for the classic machine.

Robotic mechanics - a manual gearbox in which there is no clutch pedal, and its functions are performed by an electronic unit.

The robotic transmission combines the comfort of an automatic transmission with the reliability and fuel efficiency of a manual transmission. In most cases, the "robot" is cheaper than the classic automatic transmission. Currently, all leading automakers are trying to equip cars with robotic gearboxes. However, it is worth noting that the so-called "robots" fail faster than other automatic transmissions.

Robotic automatic transmission device

The general device of the robotic gearbox:

clutch;
Manual Transmission;
clutch and gear drive;
control system

Friction type clutch, separate disc or friction disc pack is used. The progression lies in the presence of a dual clutch that ensures the transfer of torque without interrupting the flow of power. A robotic automatic transmission can have either an electric clutch and gear drive, or a hydraulic one. Let's look at the advantages and disadvantages, as well as how each works. The electric motor and mechanical transmission in the electric drive are executive bodies. This drive is characterized by low gear shift speeds, about 0.3 to 0.5 seconds, its advantage lies in low power consumption. Gear shifting in the hydraulic drive is performed by hydraulic cylinders controlled by solenoid valves, using more energy and having a faster shift speed (0.05 - 0.06 seconds on some sports cars). The main disadvantage of a robotic gearbox is the rather long time it takes to shift one gear, which leads to jerks and dips in the dynamics of the car, and also reduces the comfort of driving. This problem was solved with the introduction of an automatic transmission with two clutches (preselective gearbox), gears can be switched without loss of power. With a dual clutch, you can select the next gear when engaged and engage it at the right time without interrupting the operation of the box.

There are two operating modes: automatic and semi-automatic. In automatic mode, the electronic control unit implements a specific box control algorithm using actuators. Operation in semi-automatic mode allows sequential shifting from lower to higher gears (and vice versa), the selector lever and / or paddle shifters assist in gear shifting.

Video - automatic transmission

Conclusion!

At the moment, there are many different gearboxes in the world, differing in their pros and cons. Some are fuel-efficient, others are fast gear changes, and so on. Therefore, each driver will be able to choose for himself and his driving style a gearbox that meets all his criteria.

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Appeared in the 1940s. As you know, the presence of an automatic transmission greatly facilitates the operation of the vehicle, the load on the driver is also reduced, safety is increased, etc.

Note that the "classic" automatic transmission should be understood as a hydromechanical gearbox (hydromechanical automatic). Next, we will consider the box device - automatic, design features, as well as the advantages and disadvantages of this type of gearbox.

Read in this article

Automatic transmission car: advantages and disadvantages

Let's start with the positives. The installation of an automatic transmission allows the driver to not use the gear lever while driving, and the foot is also not used to constantly depress the clutch when switching to a higher or lower gear.

In other words, the change in speed occurs automatically, that is, the box itself takes into account the load on, the speed of the vehicle, the position of the gas pedal, the desire of the driver himself to accelerate sharply or move smoothly, etc.

As a result, the comfort of driving a car with automatic transmission increases significantly, the gear shifts are automatic, soft and smooth, the engine, transmission and chassis elements are protected from heavy loads. Moreover, many automatic transmissions provide for the possibility of not only automatic, but also manual gear shifting.

As for the cons, they are also available. First of all, structurally, the automatic transmission is a complex and expensive unit, characterized by reduced maintainability and resource compared to. A car with this type of gearbox consumes more fuel, an automatic transmission gives less to the wheels, since the efficiency of the automatic gearbox is somewhat reduced.

Also, the presence of an automatic transmission in the car imposes certain restrictions on the driver. For example, the automatic transmission needs to be warmed up before the trip, it is advisable to avoid constant sharp starts and too intense braking.

On a car with an automatic gearbox, it is impossible to slip, it is not allowed to tow a car with an automatic gearbox at high speed over long distances without hanging the drive wheels, etc. We also add that such a box is more difficult and more expensive to maintain.

Automatic box: device

So, even with certain disadvantages, automatic hydromechanical transmission for a number of reasons has long remained the most common solution for changing torque among other types of automatic transmissions.

First of all, even taking into account the fact that the resource and performance of such gearboxes is lower than that of the "mechanics", the hydromechanical gearbox is quite reliable and durable. Now let's look at the automatic transmission device.

The automatic transmission consists of the following basic elements:

Torque converter. The device performs the function of a clutch by analogy with a manual transmission, however, the participation of the driver is not required to switch to one or another gear;
Planetary gear set, which is similar to the gear block in manual "mechanics" and allows you to change the gear ratio when shifting gears;
Brake band and clutches (front, rear clutch) allow you to change gears smoothly and in a timely manner;
Automatic transmission control. This assembly includes an oil sump (box pan), a gear pump, and a valve box;

The automatic gearbox is controlled using a selector. As a rule, automatic transmissions have the following main modes:

P mode - parking;
R mode - reversing;
Mode N - neutral gear;
Mode D - driving forward with automatic gear shifting;

Other modes may also be available. For example, the L2 mode means that only the first and second gears will be engaged when moving forward, the L1 mode indicates the inclusion of only the first gear, the S mode should be understood as sports, there may be various "winter" modes, etc.

Additionally, an imitation of manual control of the automatic transmission can be implemented, that is, the driver can upshift or downshift independently (manually). We also add that the automatic transmission also often has a kick-down mode (kick-down), which allows the car to accelerate sharply if necessary.

The “kick-down” mode is activated when the driver sharply presses the gas, after which the box quickly shifts to lower gears, thereby allowing the engine to spin up to high revs.

As you can see, the automatic gearbox actually consists of a torque converter, a mechanical gearbox, as well as a control system, which together form a hydromechanical gearbox. Let's look at her device.

The principle of operation and design of the torque converter

A torque converter is needed in order to transmit and change torque from the engine to the box. The torque converter also reduces vibration. The torque converter device assumes the presence of a pump, turbine and reactor wheel.

The torque converter also has a lock-up clutch and a freewheel. The torque converter (GDT, often colloquially referred to as a "donut") is part of the automatic transmission, but has a separate housing made of durable material filled with working fluid.

The GDT pump wheel is connected to the engine crankshaft. The turbine wheel is connected to the gearbox itself. Between the turbine and pump wheels there is also a reactor wheel, which is fixed. Each of the torque converter wheels has blades that differ in their shape. Between the blades there are channels through which the transmission fluid passes (transmission oil, ATF, from the English Automatic Transmissions Fluid).

The lock-up clutch is required to lock up the torque converter in some operating modes. The overrunning clutch or freewheel is responsible for ensuring that the rigidly fixed reactor wheel is allowed to rotate in the opposite direction.

Now let's look at how a torque converter works. Its operation is based on a closed cycle and lies in the fact that transmission fluid is supplied from the pump wheel to the turbine wheel. The fluid flow then enters the reactor wheel.

The reactor blades are designed to enhance the flow rate of the ATP liquid. Then the accelerated flow is redirected to the pump wheel, causing it to rotate at a higher speed. The result is an increase in the amount of torque. It is worth adding that the maximum torque is achieved when the torque converter rotates at the lowest speed.

When the engine crankshaft spins up, the angular velocities of the pump and turbine wheels equalize, and the transmission fluid flow changes direction. Then the freewheel is actuated, after which the reactor wheel begins to rotate. In this case, the torque converter goes into fluid coupling mode, that is, only torque is transmitted.

A further increase in speed leads to the blocking of the torque converter (the lock-up clutch is closed), as a result of which there is a direct transmission of torque from the motor to the box. In this case, the blocking of the gas turbine engine occurs in different gears.

It should be noted that in modern automatic transmissions, an operating mode with slipping of the torque converter clutch is implemented. This mode eliminates the complete blocking of the torque converter.

This mode of operation can be implemented if the conditions are appropriate, that is, when the load and speed are suitable for its activation. The main task of slipping the clutch becomes more intense acceleration of the car, lower fuel consumption, softer and smoother gear shifting.

What does the automatic transmission consist of: how the mechanical part of the box is arranged and works

The automatic transmission itself (automatic transmission), like a mechanical one, changes the torque in steps when the car is moving forward, and also allows you to move backward when reverse gear is engaged.

In this case, automatic transmissions usually use a planetary gearbox. This solution is compact, allows you to realize efficient work. For example, a manual transmission often has two planetary gears that are connected in series and work together.

Combining gearboxes makes it possible to obtain the required number of steps (speeds) in the box. Simple automatic transmissions have four speeds (four-speed automatic), while modern solutions can have six, seven, eight, or even nine steps.

The planetary gearbox includes several sequential planetary gears. Such transmissions form a planetary gear set. Each of the planetary gears includes:

sun gear;
satellites;
ring gear;
carrier;

The ability to change the torque and transmit rotation becomes available when the elements of the planetary gear are blocked. One or two elements can be blocked (sun or ring gear, carrier).

If the ring gear is locked, then the gear ratio increases. If the sun gear is stationary, then the gear ratio will be reduced. A blocked carrier means that a change in direction of rotation is taking place.

Friction clutches (friction clutches), as well as a brake, are responsible for the lock itself. The clutch blocks the parts of the planetary gear set between themselves, while the brake holds the necessary elements of the gearbox due to the connection with the gearbox housing. Depending on the design of a particular automatic transmission, a band or multi-disc brake can be used.

The clutches and brakes are closed by hydraulic cylinders. The control of such hydraulic cylinders is implemented from a special module (distribution module).

Even in the general design of the automatic transmission, there may be an overrunning clutch, the task of which is to hold the carrier, which makes it possible to prevent its rotation in the opposite direction. It turns out that the gears in the automatic transmission are switched thanks to the clutches and brakes.

Automatic transmission control and the principle of operation of an automatic transmission

As for the principles of operation of the automatic transmission, the box works according to a given algorithm for turning on and off the clutches and brakes. The control system for such switching on and off on modern gearboxes is electronic, that is, it has a selector (lever), sensors and a gearbox.

The automatic transmission control unit is integrated into and closely linked to the engine control unit. By analogy with the engine ECU, the automatic transmission control unit also interacts with various sensors that transmit signals to it about the gearbox speed, transmission fluid temperature, gas pedal position, selector setting modes, etc.

The transmission ECU processes the received signals, then sends commands to the actuators in the distribution module. As a result, the box determines which gear to turn on in certain conditions (up or down).

At the same time, there is no clearly defined algorithm, that is, the transition point to different gears is “floating” and is determined by the box ECU itself. This feature allows the system to work more flexibly.

The valve body (aka hydraulic block, hydraulic plate, distribution module) actually controls the ATF transmission fluid, being responsible for the operation of the clutches and brakes in the automatic transmission. This module has solenoid valves (solenoids) and special distributors, which are interconnected by narrow channels.

Solenoids are needed for gear shifting, as they regulate the pressure of the working fluid in the box. The operation of these valves is controlled and regulated by the automatic transmission control unit. Distributors are responsible for the choice of operating modes and are activated by means of a lever (selector).

The gearbox pump is responsible for the circulation of hydraulic fluid in the automatic transmission. Pumps are gear and vane, they are driven by the torque converter hub. It is important to understand that the pump together with the hydraulic plate (hydroblock) are the most important parts in the design of the hydraulic part of the automatic transmission.

Given the fact that the box tends to heat up during operation, the automatic transmission often has its own cooling system. In this case, depending on the design, there may be a separate oil cooler of the automatic transmission, or a cooler or heat exchanger, which is included in.

What is the result

Given the above information, it becomes clear that an automatic transmission is a whole complex of mechanical, hydraulic and electronic devices. In this case, the control is carried out both by hydraulics and by an electronic unit.

It should also be noted that the layout of automatic transmissions may differ between front- and rear-wheel drive vehicles, although most of the components are the same.

If we talk about the mechanical part of the automatic transmission, a planetary gear is used in its device, which distinguishes this type of gearbox from the usual "mechanics" (parallel shafts and gears fixed to them, which are engaged with each other, are installed in a mechanical gearbox).

As for the torque converter, this device can be considered a separate element of the automatic transmission, since the gas turbine engine is placed between the engine and the gearbox, performing the functions of a clutch by analogy with a manual transmission.

Also, the oil pump inside the automatic gearbox is driven from the torque converter. The specified pump creates the working pressure of the transmission fluid, which, in turn, allows you to implement control of the box.

Finally, we note that you should not try to start a car with an automatic gearbox without a starter (from acceleration), as is often practiced on cars with a manual gearbox. The fact is that the automatic transmission pump is driven by the engine.

It turns out that while the internal combustion engine is not working, there will be no pressure of the working transmission fluid in the box. This means that without pressure it will not be possible to implement automatic transmission control, and regardless of the position of the selector for selecting the operating mode. Moreover, an attempt to start a car with an automatic “pusher” can lead to serious damage to the gearbox.

Operating modes

To understand how to operate the automatic transmission, you need to figure out what modes exist.

It should be noted right away that the “P”, “R”, “D” and “N” modes are mandatory in each box. To select one of the modes, you just need to move the gear lever to the appropriate position. The difference from a mechanical box is that the movement of the lever occurs in one line.

The mode selected by the driver will be displayed on the control panel. This makes it possible to closely monitor the road and not be distracted to look at the lever.

"P" - parking. Used for long periods of parking. It is from the parking lot that it is desirable to start the car. It is important to completely stop the machine before turning on this mode.
"R" - used to move in reverse. To turn on, you need to completely stop.
"N" - neutral position. When the lever is in neutral, torque is not transmitted to the wheels. Worth using during short breaks.
"D" - movement. When the selector is in this position, the car moves forward. Gear shifting is done independently. The driver only presses the gas pedal.

In cars with a five- or four-speed gearbox installed, the selector has several positions for moving forward: "D", "D3", "D2", "D1". These numbers show top gear.

"D3" - "first 3 gears." It is recommended to use in cases where it is not possible to move without braking.
"D2" - "first 2 gears." The lever should be moved to this position when the speed is less than 50 km/h. Most often used on poor quality roads.
"D1" ("L") - "only 1st gear." Used when the maximum speed is 25 km/h. It is worth moving the lever to a similar position when the car is in a traffic jam.
"OD" - "high gear". You should move into this position when the speed reaches more than 75 km / h, and exit it when the speed drops below 70 km / h. The overdrive makes it possible to reduce fuel consumption when driving on motorways.

Most new cars with an automatic have several automatic transmission auxiliary modes. These include:

"N" - standard, which is used during normal driving.
"E" - fuel economy mode. Helps the vehicle to move at a pace that significantly reduces fuel consumption.
"S" - sport. When the driver switches to this mode, he can make the most of the engine power. It is not surprising that fuel consumption in this mode will be high.
"W" - winter. It is used in those moments when you need to start moving from a slippery road surface.

Of course, there are drivers who could not get used to the automatic transmission, given all its advantages. To meet the needs of these people, the "tiptronic" mode was created. In fact, it involves the imitation of manual control. On the box, it is implemented as a groove for the selector, and is marked with plus and minus signs. Plus makes it possible to upshift, and minus to downshift, respectively.

Basic operating conditions for automatic transmission

In order to start moving on a machine in which an automatic transmission is installed, follow the steps in the following order:

Press the brake pedal.
Move the selector to the "drive" position.
Remove from handbrake.
Release the brake slowly. The car will start moving slowly.
Press the accelerator pedal.
To slow down, you need to throw off the gas. If you need a quick stop, then be sure to use the brake.
To start after a slight stop, you just need to move your foot from the brake to the accelerator.

The basic rule of using an automatic transmission is to avoid sudden maneuvers. If you constantly do them, this will lead to the fact that the gap between the friction discs will increase, and then in the differential. All this will lead to the fact that the car will twitch during each gear change.

Experienced craftsmen believe that the machine needs to be given a short “rest”. This means that the car must be allowed to idle for a few seconds. It is worth noting that even in a car with a powerful engine, sudden movements will significantly reduce the resource of the box.

In fact, this moment is very important, because most of these boxes break in winter. First of all, this is due to a significant drop in temperature and the fact that cars often skid on ice. In order to protect your car from damage as much as possible, you should adhere to the following recommendations:

Before the onset of cold weather, check the quality and level of fluid in the box, and replace if necessary;
Be sure to warm up the car before driving;
If the car is stuck, do not step on the gas in the hope of leaving. It is worth trying to downshift (if possible) or just push;
Before a sharp turn, use only lower gears.

What not to do

What not to do on a car with an automatic transmission:

First of all, you should not heavily load the box if the car has not warmed up to the required level. Even if the temperature is positive outside, the first few kilometers, the movement should be smooth and measured.
Automatic transmission does not like off-road very much. Cars with a gun, it is best to go around roads with poor pavements. If the "iron horse" is stuck, sometimes it is better to resort to the help of a shovel than to put pressure on the gas.
It is not recommended to subject the automatic transmission to high loads. If there were plans to tow a trailer, then it is better to put them out of your head.
It is strictly forbidden to start a car from the so-called pusher. Many people violate this prohibition, but it is worth remembering that this will not pass without a trace for the box.

Of course, we must not forget about the individual features of switching between modes:

you can stay in neutral only if the brake is pressed;
on the "neutral" it is forbidden to turn off the car;
turning off the engine is allowed only in the “parking” position;
when the car is in motion, do not move the lever to the “parking” and “reverse” positions.

Summing up, it is worth noting that the automatic transmission may seem rather "finicky" and having a small resource. In fact, if you use it correctly, it will please its owner for a very long time.

Video: how to use automatic transmission correctly

An automatic transmission (abbreviated as automatic transmission) is one type of vehicle transmission. The automatic gearbox independently (eliminates the direct intervention of the driver in the process) sets the desired ratio of gear ratios, based on driving conditions and various factors.
Engineering terminology recognizes as “automatic” only the planetary element of the assembly, which is directly related to gear shifting and, together with the torque converter, creates a single automatic stage. An important point: automatic transmission always works in conjunction with a torque converter - it guarantees the correct operation of the unit. The role of the torque converter is to transfer a certain amount of torque to the input shaft, as well as to prevent jerks when changing stages.

Options

The automatic transmission is, nevertheless, a conditional concept, because there are its subspecies. But the ancestor of the class is a hydromechanical planetary gearbox. It is the hydraulic machine that is associated with automatic transmission, for the most part. Although currently there are alternatives:

robotic box ("robot"). This is a variant of "mechanics", but switching between steps is automated. This is possible due to the presence in the design of the “robot” of electromechanical (electropneumatic) actuators, which are driven by electronics;
variable speed drive. A subspecies of a continuously variable transmission. It is not directly related to gearboxes, but implements the power of the power unit. The process of changing the gear ratio occurs gradually. The V-chain variator has no steps. In general, the principle of its operation can be compared with a bicycle speed sprocket, which, as it unwinds, gives the bicycle acceleration through the chain. Automakers, in order to bring the operation of this transmission closer to traditional ones (with steps) and to get rid of the mournful hum during acceleration, create virtual gears.

Device

The hydromechanical gearbox - "automatic" consists of a torque converter and an automatic planetary gearbox.

The design of the torque converter includes three impellers:

Each element of the gas turbine engine (torque converter) requires a strict approach in production, synchronous integration, balancing. Based on this, the gas turbine engine is manufactured as a non-separable and non-repairable unit.

The constructive location of the torque converter: between the transmission housing and the power plant - which is similar to the installation niche for the clutch on the "mechanics".

Purpose of gas turbine engine

The torque converter (relative to a conventional fluid coupling) converts the engine torque. In other words, there is a short increase in traction, which is received by the box - "automatic" when accelerating the vehicle.

An organic drawback of the gas turbine engine, following from its principle of operation, is the rotation of the turbine wheel when interacting with the pump wheel. This is reflected in energy losses (the efficiency of the gas turbine engine at the time of uniform movement of the car is no more than 85 percent), and leads to an increase in heat emissions (some torque converter modes provoke a greater heat release than the power unit itself), increased fuel consumption. Now automakers on their cars integrate a friction clutch into the transmission, which blocks the gas turbine engine at the moment of uniform movement at high speed and higher stages - this reduces friction losses of the torque converter oil and reduces fuel consumption.

What is a friction clutch for?

The task of the clutch package is to switch between gears by communicating / disengaging parts of the automatic transmission (input / output shafts; elements of planetary gearboxes and deceleration in relation to the automatic transmission case).

Coupling design:

drum. Equipped with the necessary slots inside;
hub Has outstanding external teeth of a rectangular shape;
set of friction discs (ring-shaped). It is located between the hub and the drum. One part of the pack consists of metal outer lugs that fit into the drum splines. The other is plastic with internal cutouts for the teeth of the hub.

The friction clutch communicates by compression by an annular piston (integrated into the drum) of the disk set. Oil supply to the cylinder is carried out using drum, shaft and body (automatic transmission) grooves.

The overrunning clutch has free slip in a certain direction, and in the opposite direction it is wedged and transmits torque.

Overrunning clutch includes:

outer ring;
separator with rollers;
inner ring.

Node task:

Automatic transmission control unit: device

The block consists of a set of spools. They control the oil flow towards the pistons (brake bands)/friction clutches. The spools are arranged in a sequence that depends on the movement of the gearbox/automatic selector (hydraulic/electronic).

hydraulic. Applies to: oil pressure of the centrifugal governor that interacts with the output shaft of the gearbox / oil pressure that is generated during the depressing of the accelerator pedal. These processes transmit to the electronic control unit data on the angle of inclination of the gas pedal / speed of the car, followed by the switching of the spools.

Electronic. Solenoids are used to move the spools. The wire channels of the solenoids are located outside the automatic transmission housing, and go to the control unit (in some cases - to the combined control unit for the fuel injection and ignition system). The received information about the speed of the car / angle of inclination of the gas determines the further movement of the solenoids through the electronic system / the handle of the automatic transmission selector.

Sometimes the automatic transmission works even with a faulty electronic automation system. True, provided that the third gear (or all stages) is on in the manual mode of controlling the box.

Selector control

Varieties of the position of the selectors (automatic transmission lever):

floor. The traditional location in most cars is on the central tunnel;
stalk. This arrangement is often found in American cars (Chrysler, Dodge), as well as in Mercedes. The desired transmission mode is activated by pulling the lever towards you;
on the center console. It is used on minivans and on some conventional cars (eg: Honda Civic VII, CR-V III), which frees up the space between the front seats;
button. The layout has been widely used on sports cars (Ferrari, Chevrolet Corvette, Lamborghini, Jaguar and others). Although it is now being integrated into civilian vehicles (premium class).

Slots of floor selectors are:

Box operation

How to use the box - "automatic" correctly? Two pedals and many transmission modes can plunge an inexperienced driver into a stupor. At first glance, everything is simple, but there are nuances. Below are explanations of how to use the automatic transmission correctly.

Modes

Basically, the “automatic” box has the following positions on the selector:

P is the implementation of the parking lock: blocking the drive wheels (integrated inside the gearbox and does not interact with the parking brake). An analogue of setting the car into gear ("mechanics") when it is parked;
R - reverse gear (it is forbidden to activate while the car is moving, although blocking is now applied);
N - neutral gear mode (activation is possible during short parking / towing);
D - forward travel (the entire gear ratio of the box is involved, sometimes two higher gears are cut off);
L - activation of the low gear mode (low speed) for the purpose of driving off-road or on such, but with difficult conditions.

Auxiliary (advanced) modes

Present on boxes with extensive operating ranges (the main modes may also be labeled differently):

(D) (or O / D) - overdrive. Economy mode and measured movement (whenever possible, the box switches to the top);
D3 (O / D OFF) - deactivation of the highest stage for active driving. It is activated by braking by the power unit;
S - gears spin up to maximum speed. There may be the possibility of manual control of the box.

Take into account:

The “automatic” with respect to the manual gearbox slows down the engine only in certain modes, while in the rest, the transmission has free slip through the overrunning clutches, and the car “freewheels”.

Example - manual transmission mode (S) provides for motor deceleration, but automatic D does not.

While driving

How to use the "automatic" box correctly in the direction of travel? Modern transmissions allow the transition from one mode to another without pressing the button on the selector lever (except R). And in order not to prevent the arbitrary start of the movement of the machine during a stop, you must press the brake pedal when switching modes.

You also need to know how to properly tow a car with automatic transmission. You must adhere to the following recommendations:

check the oil level in the box for compliance with factory standards;
turn the ignition key, remove the lock from the steering column;
switch the selector to N mode;
towing is recommended no more than 50 kilometers, at a speed of 50 kilometers per hour, and less. When stopping, it is desirable to cool the box;
it is forbidden to start the engine while towing.

Man has always strived for comfort and driving pleasure, as a result of which an automatic transmission was invented, this made it possible to reduce the burden on the driver, it became much easier to drive a car. It was invented in the 40s of the XX century in the concern General Motors.

Automatic transmission is quite complicated and includes the following mechanisms:

torque converter - provides transmission and change of torque from the power unit;
gearbox - converts the force and drives the wheels;
control system - controls the working fluid;
lubrication and cooling system - creates pressure and circulation in the system.

torque converter

It replaces the standard clutch for a manual transmission, and is also located between the gearbox and the engine, attached to its flywheel. Its main task is to smoothly change, transfer torque to the drive shaft of the automatic transmission. Its design includes such elements as: pumping, turbine, reactor wheels, a freewheel and a blocking clutch. The impeller is attached to the torque converter housing and rotates with it. The turbine wheel sits on the drive shaft of the planetary gear. Each of the wheels has blades of a certain shape, when the engine is running, a working fluid begins to pass between them, with which it is filled.

As soon as the engine starts, the pump wheel begins to rotate and its blades pick up the working fluid, directing it to the blades of the turbine wheel, from which it flies off to the reactor wheel (reactor) located between them. The reactor directs the flow of the returning fluid towards the direction of the pump wheel, two forces begin to rotate it, due to which the moment increases. When the speed of the pump and turbine wheels are compared, the freewheel is activated and the reactor begins to spin due to it, this moment is called the clutch point. After that, the torque converter begins to work as a fluid coupling, the rotation from the engine begins to be transmitted to the drive shaft of the planetary gearbox through the working fluid. The exception is the Honda automatic transmission, where instead of the planetary gearbox, shafts with gears are installed as on a manual transmission.

But still not 100% of the energy is transferred from the engine due to the viscous friction of the oil. To eliminate these costs and use it as efficiently as possible, which ultimately leads to a decrease in fuel consumption by the engine, there is a lock-up clutch that is activated at about 60 km / h and more. This clutch is located on the turbine hub. As soon as the car picks up the required speed, the working fluid flows to the wall of the blocking clutch on one side, and on the other hand it comes after the channel is opened by the switching valve, thereby creating a low pressure zone. Due to the pressure difference, the blocking piston is activated, at this moment it is pressed against the torque converter housing, as a result of which the clutch begins to rotate with the torque converter housing.

Transmission

Different manufacturers may differ slightly, but they are all present: a planetary gearbox is also called differential, overrunning and friction clutches that connect all mechanisms with shafts, drums acting as a clutch, and in some models a brake band is used to brake the drums.

It usually consists of several planetary gear sets, clutches and brakes. Each of the planetary gears is structurally made of a sun gear and satellites, they are connected by a planetary carrier. Rotation is transmitted when one or two elements of the gearbox are blocked. When the carrier is blocked, the direction changes, which corresponds to the reverse gear of the car. When the ring gear is locked, the gear ratio increases, and when the sun gear is locked, it decreases, this is gear shifting.

friction clutch

To hold the elements of the gearbox, brakes are used, and friction clutches (friction clutches) are used to fix parts of the planetary gear set. Each such clutch includes a drum on the inside of which there are splines and a hub with teeth on the outside. Between them are placed two types of friction discs, the first with protrusions on the outside that enter the splines of the drum, the second with protrusions inside, where the teeth of the hub enter. The clutch is activated when the disks are squeezed by the piston inside the drum at the moment the working fluid enters it.

Freewheel

It keeps the carrier from rotating in the opposite direction to reduce shock during gear shifting and prevents engine braking in certain modes of operation of the box.

Honda Feature

Two-shaft automatic transmission Honda

It has already been mentioned that Honda boxes are different from all other machines, in fact they are ordinary mechanics with hydraulic control. The advantages of these boxes are reliability, because there is practically nothing to break there, they are easier to repair and manufacture. Such boxes consist of two or more shafts with gears, and by turning on a certain combination of gears, the gear ratio changes.

One gear in each pair is constantly engaged with its shaft, the second is connected with its own through the so-called wet clutch (friction clutch), i.e. all gears rotate, but one of the pair is not engaged with the shaft and, accordingly, the torque and rotation are not are transmitted to the wheels of the car (neutral). The device and principle of operation of the clutch, as in conventional machines. When the disks are compressed, the second gear meshes with its shaft, the corresponding gear is engaged.

The rear is realized on the clutch of one of the gears. On the shaft next to the gear of one gear there is a reverse gear, these two gears are not fixed rigidly on the shaft, between them there is a sleeve with teeth fixed on this shaft, and on this sleeve there is an annular coupling with teeth. And depending on which side this clutch will be moved, that gear engages with the shaft, the annular clutch is displaced using a hydraulically driven fork. The reverse gear changes the direction of rotation, reverse gear is engaged.

Control system

Distributes the flow of the working fluid (ATF), it consists of a set of spools, an oil pump, a valve body. There are two types of systems hydraulic or electronic.

Hydraulic system

Uses oil pressure from a throttle valve, depending on the load at the moment, a centrifugal governor connected to the output shaft of the automatic transmission. The working fluid from these regulators comes to the spool and acts on it from different sides, and depending on the pressure difference, it moves to one side or the other, opening the necessary channels, this determines which gear the box will switch to.

Electronic system

With this system, more flexible operating modes can be achieved that a fully hydraulic system cannot provide. It uses solenoids (solenoid valves), they move the spools. The operation of all solenoids is controlled by the electronic control unit (ECU) of the box, sometimes combined with the engine ECU. Based on the readings from the speed sensor, oil temperature, gas pedal and gear lever, it gives signals to the solenoids. Solenoid valves are divided into pressure regulating, switching control, flow distributing.

Regulators form and maintain the pressure of the working fluid within a given value, which depends on the condition of the car. The shift valves control the gears by supplying fluid to the shift clutches. The distributing streams direct liquid from one channel of the hydroblock to another.

When the automatic transmission mode is selected by the selector lever, a signal is sent to the mode control valve via mechanical or electronic communication. It directs ATF only to those valves that can be actuated to engage the gears allowed in that mode.

Hydroblock

Hydroblock device

The most complex automatic transmission assembly, it consists of a metal plate with a large number of channels and the entire mechanical part of the control system (spools, solenoids). Fluid flows are redistributed in it, and through it ATF is provided with the necessary pressure to all elements of the mechanical part of the box.

Oil pump

It is located inside the gearbox and can be of different types (gear, trochoid, vane), can be fully electronically controlled or have a mechanical connection with the torque converter and engine. It circulates ATF continuously and pressurizes the system. The pump itself does not directly create pressure, but fills the hydraulic system with working fluid, and with the help of dead-end channels, pressure begins to form in the valve body. In modern automatic transmissions, an automatic (electronic) pump is increasingly used to maintain pressure in an optimal way.

Lubrication and cooling system

It is very important for the normal functioning of the gearbox, so it uses a special ATF hydraulic fluid, it is she who lubricates and cools the moving parts. Cooling of the working fluid occurs in the cooling radiator, which can be internal and external. The internal radiator (represents a heat exchanger) is located inside the engine coolant radiator. There are also more complex heat exchangers that have their own liquid cooling, they are installed on the box body. The external one is located separately and is a full-fledged radiator. On some cars, a thermostat is built into the cooling line from the automatic transmission to the radiator, which regulates the volume of oil passing through it. To prevent contamination of the channels of the system with particles that are formed during the wear of moving parts, a filter is installed, it purifies the working fluid.

Automatic transmission with external oil cooler

Automatic transmission with built-in cooling radiator in the engine radiator

Automatic transmission oil cooler with liquid cooling system

The gearbox is controlled by selecting the required operating mode with the selector lever. On different models, there may be a different combination of operating modes:

R(Neutral) – mode for long-term parking;
N(Parking) - for short-term parking or towing;
R(Reverse) - moving backward;
L1, 2, 3(Low) - lowering is designed for driving in difficult road conditions (rough terrain, steep descent or ascent);
D(Drive) - forward movement, is the main mode;
D2/D3– modes limiting gear shifting;
S, P(Sport, Power, Shift) – sports driving mode;
E(Econ) - provides a more economical style of movement;
W(Winter, Snow) - winter mode, provides for a soft start from a higher gear to prevent slipping, gear changes are carried out at low speeds;
+/- - function of manual gear shifting.

Some models have O/D(Overdrive) - a special button that allows you to switch to higher gears, there is also a mode kick-down, which forcibly engages a lower gear when you sharply press the gas pedal, due to which more intense acceleration is provided.

We tried to analyze the automatic transmission device in the most detailed and accessible way, the principle of operation of individual elements and their interaction. But technology does not stand still, perhaps already now they are introducing new principles of work that will appeal to any layman.

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