23 october 2016

A car's automatic transmission is designed to transfer engine power to the wheels. It selects the gear that best suits the current driving speed. The automatic transmission eliminates the need for manual gear changes. The car's computer uses sensors to determine at what moment it is necessary to change the speed and sends a signal electronically to turn the gear on or off.

The main elements of an automatic transmission

A car's automatic transmission mechanism is a system of levers and gears that transfer power to the drive wheels, allowing the engine to operate at its best.

The box is assembled in an aluminum casing called a crankcase. It houses the main components of an automatic transmission:

1. A torque converter that acts as a clutch, but does not require the driver to directly control it.
2. Planetary gearbox that changes the gear ratio when shifting.
3. Rear, front clutches, brake band, directly carrying out gear shifting.
4. Control device.

How does a torque converter work?

The torque converter consists of the following main elements:

• pump or impeller;
• turbine wheel;
• blocking plates;
• stator;
• overrunning clutch.

To understand how an automatic transmission works, you need to imagine its overall structure. So, the pump is mechanically connected to the engine. The turbine wheel is connected to the gearbox shaft using splines. When the impeller rotates with the engine running, an oil flow is created that rotates the turbine wheel of the torque converter.

In this case, the torque converter plays the role of a conventional fluid coupling, by means of liquid only transmitting torque from the engine to the automatic transmission shaft. When the engine speed increases, no significant increase in torque occurs.

To convert torque, the automatic transmission circuitry includes a stator. The principle of operation is that it redirects the flow of oil back to the pump impeller, causing it to rotate faster, increasing the torque. The less the speed of rotation of the turbine wheel in relation to the pump, the more residual energy is transferred by the stator through the returned oil to the pump. Accordingly, the torque increases.

Turbine and automatic transmission pump basics

The turbine always runs slower than the pump. The maximum ratio of pump and turbine rotation speeds is achieved when the vehicle is stationary, decreasing with increasing vehicle speed (TC). The stator is connected to the torque converter through an overrunning clutch that can rotate in only one direction.

The turbine and stator blades are specially shaped so that the oil flow is redirected to the underside of the stator blades. In this case, the stator wedges and, remaining stationary, it transfers the greatest oil energy to the pump inlet.

Due to this operating mode of the torque converter, maximum torque transmission is ensured. It increases almost threefold when the car starts to move.

When the vehicle accelerates, the turbine relative to the pump slips less and less until the moment when the stator wheel is picked up by the oil flow, starting to rotate in the direction of the freewheel clutch. At the same time, the device starts to work as a conventional fluid coupling, does not increase the torque. In this mode, the efficiency of the torque converter does not exceed 85%. This mode of operation is accompanied by the release of excess heat and increased fuel consumption.

Purpose of the blocking plate

This drawback is eliminated with the help of a special device - a blocking plate. Despite the mechanical connection with the turbine, it is structurally designed so that it can move to the right and left. This device is activated when the vehicle reaches a high speed. On command, the control unit changes the oil flow so that it presses the blocking plate against the converter housing on the right.

In this case, the turbine and pump are mechanically connected to each other. To increase traction, a special friction layer is applied to the inner side of the converter housing. Thus, the engine is connected to the output shaft of the automatic transmission. Naturally, this blocking is immediately turned off even with slight vehicle braking.

Above, only one of the methods for blocking the torque converter was described. However, any other method has the same goal - to prevent the turbine from slipping in relation to the pump wheel. Typically, the described mode of action in various sources is called Lock-Up.

It will be easier to understand the operation of a torque converter for dummies if, instead of a turbine and a pump, imagine two simple fans, one of which is powered by the network, and the other rotates due to the air flow created by the first fan. Only, instead of air, oil appears here, and the blades of the first fan (pump in the case of an automatic transmission) are set in motion not due to electricity, but due to a mechanical connection with the car engine shaft.

Planetary rows

The torque converter can increase torque, but only up to a certain limit. An automatic transmission device for a more significant increase in torque, for example, when overcoming hills, as well as for reversing, provides planetary gears. The planetary gear also provides smooth gear shifting while driving without loss of engine power. Thanks to it, shifting occurs without the jolts that occur during the operation of a conventional transmission.

The planetary row includes the following elements:

• sun gear;
• satellites;
• epicycle;
• drove.

The planetary row is called because the friction wheels rotating simultaneously around their axes and moving with these axes are very reminiscent of the planets of the solar system. It depends on their relative position which gear is currently on.

How are gears shifted in an automatic transmission?

Shifting gears or changing the gear ratio in the planetary gearbox is carried out by locking and unlocking the elements of the planetary gear set by means of brake bands and clutches. In the hydraulic system of an automatic transmission of a car, gear changes are directly carried out by a valve. The three-speed gearbox has two such valves, one of which switches from first gear to second, the other from second to third. The four-speed box already has three valves.

Other types of automatic transmission

In addition to the hydraulic transmission considered, other types of automatic transmissions are widely used today:

1. CVT automatic transmission. In this type of transmission, there is no fixed gear ratio for gears. Therefore, such an automatic transmission is called continuously variable. The principle of operation is that, unlike other "automatic machines", it uses engine power more efficiently. As a result, cars equipped with this type of transmission are more economical and comfortable.
2. Robotic checkpoint. Such a box can be called automatic conditionally, since in fact it is an ordinary "mechanics", where the function of the clutch pedal is assigned to the electronic unit. Cars with which gearboxes are also quite economical, but less comfortable, since gear changes in automatic mode are often accompanied by jerks.

Thus, in addition to the most common hydraulic automatic transmission, there are several types of automatic transmissions that differ in their design. They differ in price, efficiency, comfort of car driving. The common thing is that the driver is relieved of the need to independently select and change gears.

An automatic transmission is a part of a transmission capable of regulating the torque and speed of a vehicle. This means you no longer need to calculate when to engage and release the clutch and manually shift gears.

In this article, we will consider the principles of the mechanism.

The history of the creation of an automatic transmission

Transmission automation has historically taken place in three phases. The first attempt to make the car more independent was made by Henry Ford in the early twentieth century. The Ford T had a planetary gearbox that required fewer gear shifting skills from motorists than a conventional mechanical gearbox.

At the next stage, cars with semi-automatic transmissions entered production. In them, automation is aimed either at self-changing gears, or at refusing to use the clutch, which greatly facilitated driving a vehicle.

Did you know? This semi-automatic transmission is still used on scooters.

The last stage in the transition to automatic transmission was the system proposed by the developers of the American company General Motors. It was based on the planetary model previously used at the Ford plant, as well as the hydraulics, which itself turned on at the moment when it was necessary to change the gear. Both principles are at the heart of modern automatic transmissions.

Arrangement of units and mechanisms

An automatic transmission conventionally consists of three main parts:

1. Mechanical. Her responsibilities include changing the speed of the vehicle, as well as direct gear shifting.
2. Hydraulic. This part of the automatic transmission transmits torque between the components of the gearbox without any driver action.
3. Electronic. This component is the brain of the gearbox, which monitors the operation of the mechanical and hydraulic systems, and also transmits signals to other parts of the car.

Components of the automatic gearbox:

Did you know? In the USSR, the first torque converters began to be used on such cars as "Chaika", "Volga", ZIL, as well as some other vehicles.

Principle of operation

Any automatic transmission works on the basis of a planetary gearbox, which consists of a sun gear and, united by a carrier and a ring gear. There are as many of these nodes as the speed of the car.

Principle of operation:

1. All pulses to the gearbox are fed through two inputs connected to the ring and sun gears, and are transmitted through one output, which is provided by the rotation of the carrier.
2. When a pulse arrives at the input to the sun gears, they begin to rotate, which causes the carrier to rotate.
3. The carrier, in turn, forces the ring gear to move, which entails a constant increase in the speed of the carrier at the exit.
4. If the driver needs to go to reverse, the sun gears will move in the opposite direction.

The automatic transmission has no direct connection between the input and output shafts. They are united by an intermediate shaft, on which two packs of friction discs are closed in working condition, which are connected to a gear.

Did you know? Over the past year in Europe, 80% of all purchased cars operate on an automatic transmission. On the territory of the CIS countries, purchases of cars with automatic transmission account for only 10% of the total number of vehicles sold.

It is these discs that transmit power. Friction discs at the inlet have a smaller diameter than the outlet. This is due to the increase in rotational power during the transmission of the pulse from input to output.

Pros and cons

Let's take a look at the pros and cons of using a car with an automatic transmission.

Pros:

• convenience.No more distractions of gear shifting and clutch use. The driver can fully concentrate on the road;
• easier to get under way. Responsible for this process in an automatic transmission is the electronics, and not the correct pressing of the clutch or the gas pedal;
• vehicle components have a longer service life due to electronic control. Very often, drivers, especially beginners, do not switch gears on time, which leads to a malfunction of the engine, or they delay the clutch, or work without it at all, which leads to its burnout.

Minuses:

• cars with automatic transmission are expensive. Moreover, they are also more expensive to maintain than vehicles with a manual transmission;
• there are difficulties in bad weather. The main way to get out of a skid or mud is "swing", which is impossible when using an automatic transmission.

Important! When changing gears using the selector, do not press the gas pedal.

A car with an automatic transmission is designed for people who value comfort. To determine which type of transmission is right for you, you should practice driving with both manual and automatic transmissions.

The principle of operation of an automatic transmission: video

Driving a car equipped with an automatic transmission is quite simple, difficulties arise for beginners who are not familiar with the principle of operation of an automatic transmission and its design features.

Have you driven a car with a manual transmission and do not belong to "dummies"? Then, at first, when driving an automatic transmission, watch the position of your left foot. The acquired habit of pressing the clutch pedal, which is absent on cars equipped with automatic transmissions, can interfere with driving. Obviously: before driving a car equipped with a selector, learn to use only one foot - quickly move your right foot from the gas pedal to the brake, without remembering the clutch.

The gearshift lever in vehicles equipped with automatic transmission is called a selector; it is additionally equipped with an unlock button that prevents incorrect gear shifting. The main advantage of the specified type of boxes is the ability to select the gear ratio by electronics, corresponding to the driving conditions, without the participation of the driver. There is no need to learn how to smoothly change gears: the "smart" box copes with this task on its own.

Driving a car equipped with an automatic transmission begins with studying the main operating modes of the unit, which have the appropriate designations:

1. "R" - parking, used to start the engine. The selector switches to this position when the vehicle is completely stopped or when the handbrake is used. Some manufacturers of vehicles with automatic transmissions in the operating instructions of the machine indicate the need to use the handbrake when applying the position "Parking".
2. "D" - move forward, allows the car to move forward. The gears will be selected automatically depending on the degree of pressing the gas pedal and the driving conditions of the vehicle. While in this mode, a vehicle standing on an incline will not roll back unless the incline is too steep.
3. "R" - Reverse, allows the car to move backward. This position is turned on after a complete stop of the car, plus when the "brake" pedal is depressed.
4. "N" - neutral, used to warm up the engine in the cold season, it is not recommended to switch the selector to the specified position while the machine is moving. Provides idle operation of the power unit without transmitting torque to the wheels.
5. "D2" (or S) - downshift, used on descents, ascents. Stopping the car in this mode will be more effective than in position "D". The box will use only two gears - first and second.
6. "D1" (or L) - the subsequent range of reduction of the gear, is used when icing roads, mountain serpentine, in some cases can be used for engine braking. In this mode, the car will always move in first gear.

Switching the selector from position "D" to position "D3" (D2), "D2" (D1) is performed when the machine is moving. Advanced automatic gearboxes have additional acceleration modes:

• economical - "E";
• normal - "N";
• sports - "S".

Workshops

Set the selector to the desired mode by doing the following:

1. Start the engine (you can only switch the lever when the engine is running).
2. Depress the brake pedal.
3. Press the desired mode button located on the selector (if necessary).
4. Select the position corresponding to the required direction of movement of the machine: "D" - the vehicle will go forward, "N" - neutral, the car will stand still, or roll downhill, "R" - will go back. When turning on the gear selected by the driver, the car will not start moving, and when you release the brake pedal, the car will go. Consider this nuance, do not take your foot off the "brake" ahead of time in order to avoid an accident.

Automatic transmissions recognize the driver's commands by pressing the accelerator pedal: smooth acceleration, gradual gear shifting is provided by pressing with little effort. Intensive acceleration required when overtaking is achieved by pressing the gas pedal to the floor, while the automatic transmission will first turn on the gear lower, then the car will start to accelerate. Consider: from the moment you press the gas pedal to the acceleration of the vehicle, there is a small delay, about one second, this time is imperceptible when driving slowly, and in overtaking conditions it can be fatal.

Having decided to stop the movement of the car, press the brake pedal. In case of a short stop, at a traffic light, do not move the selector from the “D” position - extend the life of the automatic transmission internal mechanisms.

Keep the brake pedal depressed after stopping the machine in situations:

1. Long stops (traffic jams), pressing the brake pedal will allow the engine to rest, the fuel will not be burned in vain, use the “N” position.
2. The machine is standing on a slope, the selector is not moved to the "P" position.

The above instructions for "dummies" will allow you to drive a car with an automatic transmission. Please note: it is better to immediately learn how to drive correctly so as not to harm the automatic transmission. It is difficult to correct bad driving habits.

Additional modes

Additional modes of automatic transmissions include:

1. Winter mode has the designation "*", "W", "SNOW", "HOLD", "WINTER". According to it, slipping is excluded during gear shifting and when the vehicle starts moving. The machine starts moving from the second gear. Switching to other gears occurs at lower drive speeds - this allows you to exclude drops in the operation of the box during acceleration, and reduces the likelihood of a car skidding. Experts clarify: you should not use this mode in the summer - you can get the box overheating due to the maximum load on the unit.
2. The "D" position sub-modes limit acceleration beyond a certain gear range:

• "S" or "З" - ensuring the inclusion of a transfer not higher than the third. These positions are used on road sections that require increased attention from the driver. When driving, use the "Z" mode, while watching the tachometer readings, its arrow should not fall into the red zone.
• "2" - limiting the inclusion of gears not higher than the second, the car moves at a speed of no more than 80 km / h. It is used on steep slopes, slippery roads.
• "1", "L" - used for heavy machine operating conditions: off-road driving, steep slopes. Only transmission, speed no more than 40 km / h.

Additional modes of operation of automatic boxes allow you to control the machine under adverse conditions. Consider: accidental activation of sub-modes "1", "2" at high speed will lead to a sharp slowdown in the movement of the car, provoke a skid of the vehicle.

An inexperienced driver can operate the automatic transmission, the following recommendations will extend the resource of the automatic transmission:

1. Do not put heavy loads on an unheated box. Transmission oil warms up more slowly than engine fluid. When driving a car with the specified type of transmission, drive several kilometers at low speed.
2. Avoid wheel slip: do not press hard on the accelerator if the road surface is not uniform.
3. Try not to tow trailers, other cars.
4. Refuse to engage neutral when the vehicle is moving.

Correct operation of the automatic transmission allows you to enjoy driving and prevents premature damage to the unit, allowing the mechanism to work normally.

How to check the oil in the gearbox Automatic transmission pulls the car when changing gear

Recently, more and more vehicles are equipped with automatic transmissions. It is lighter and easier to use and is ideal for beginners and city traffic with regular stops.

What is automatic transmission and its types

An automatic gearbox is one of the types of transmission, in which, without driver intervention, the required gear ratio is set, matched to the driving mode and other factors.

From a technical point of view, an automatic transmission is considered only the planetary part of the unit, which is directly related to the gear change, and together with a hydraulic transformer forms a single automatic unit.

It is customary to refer to automatic transmissions as a classic with a torque converter, a robotic gearbox and a variator.

Classic automatic transmission

The torque converter transmission is a popular and classic transmission model found on most vehicles currently off the line.

The automatic transmission consists of a planetary gear reducer, a control system and a hydraulic transformer, which gave it the name - a torque converter gearbox. It is installed on both passenger cars and trucks.

Robotic checkpoint

The robot box is a kind of alternative to a manual gearbox, only gear shifting is automated by means of electrical mechanisms driven by an electronic unit.

The only similarity between a robotic gearbox and a classic automatic gearbox is the presence of a clutch in the case itself.

Variable speed drive

CVT is a device for smooth, stepless transmission of torque to the wheels.

Provides a reduction in fuel consumption and improves dynamic performance, sparing the state of the vehicle engine compared to automatic transmission or manual transmission.

Variators are belt, chain and toroidal. Of the variators, the most common with a V-belt.

The principle of automatic transmission

Several types of automatic gearboxes with their own characteristic features are installed on vehicles.

Simplified, the mechanism of operation of a classic automatic transmission consists in transmitting torque from the engine crankshaft to the transmission devices, while the gear ratio varies in accordance with the position of the selector lever and the conditions of movement of vehicles.

When the engine is started, working fluid enters the hydraulic transformer, the pressure increases. The blades of the centrifugal pump begin to move, the reactor wheel and the main turbine are stationary in this mode.

When you switch the selector lever and supply fuel using the accelerator pedal, the pump blades increase the speed. The increasing speed of the vortex flows begins to rotate the turbine blades. The vortices of oil are thrown to the stationary reactor, then they return back to the turbine, increasing its efficiency. The torque is transferred to the wheels and the car starts moving.

Upon reaching the required speed, the impeller and the vane central turbine move at the same speed, while the vortices of the transmission fluid hit the reactor wheel from the opposite side (movement is possible only in one direction) and it begins to rotate. The unit changes to a hydraulic clutch.

If the reaction on the wheels increases (upward motion), the reactor wheel stops rotation and adds torque to the centrifugal pump. When the required speed and torque is reached, the gear changes in the planetary unit.

The electronic control unit transmits the command, as a result of which the brake band and friction discs slow down the downshift, and the increased movement of fluid flows through the valve accelerates the overdrive and gear changes are provided without reducing power.

When the machine comes to a complete stop or the speed decreases, the pressure of the working fluid decreases and a downshift occurs.

When the engine is switched off, there is no pressure in the torque converter, therefore it is not possible to start the car with a push.

Automatic box device

A classic automaton consists of four main components:

• Hydraulic transformer - replaces the clutch, converts and transmits torque to the wheels. Consists of a centrifugal pump, a vane turbine and a reactor, providing smooth and precise torque changes. The pump is connected to the crankshaft, and the turbine is connected to the gearbox shaft. The transformation of energy is carried out due to fluid flows and the pressure generated by them. The torque converter changes the rotation speed and torque in a small interval, so a planetary unit (box) is added to it.
• Planetary reductor consists of a central gear (sun), satellites, a ring gear and a planetary carrier. It makes gear shifting by blocking some gears and unblocking others.
• The brake band, rear and front friction discs provide direct gear shifting.
• Control system consists of a gear pump, oil sump, hydraulic unit and electronic control unit (ECU). The hydraulic block consists of channels with solenoids (valves) and plungers that carry out control and management functions. The ECU carries out control through information from sensors that collect a variety of indicators.

Robotic checkpoint is a more advanced version of the manual transmission with highly efficient control systems.

AT variator the transformation of the gear ratio is performed by a mechanism that includes a driving and driven pulleys through which the V-belt passes.

How to use an automatic transmission

According to car mechanics in the service station, the main malfunctions of automatic transmissions appear due to violation of the rules of operation and untimely maintenance of the box.

Operating modes

There are different automatic transmission modes depending on the type of automatic transmissions. Each position of the selector lever or buttons on it are designed for different driving conditions with their own characteristics.

The main types of automatic transmission modes and their effect on the operation of the car:

• R (parking) - blocking of driving wheels, box shaft, used only when in the parking lot and warming up;
• N (neutral) - the shaft is not blocked, the car can be towed, it is equivalent to neutral gear at the manual transmission;
• D (drive) - movement under normal conditions with automatic gear selection;
• L (D2) - low gear for driving in difficult conditions - off-road, steep descents and ascents, speed less than 40 km / h;
• D3 - downshift at small descents and ascents;
• R(reverse) - movement in reverse, it is switched on at full stop and the brake pedal is pressed;
• O / D - inclusion of the fourth gear when driving at high speed;
• PWR - sports mode, to improve dynamic qualities, the gear is increased at higher engine speeds;
• Normal - for a smooth and economical movement;
• Manu - manual mode of shifting gears, recommended for use in winter.

How to start a car automatically

Features require a competent launch. Degrees of protection have been developed to protect the box from misoperation and subsequent damage.

At the time of starting the car, the selector must be in the "P" (parking) or "N" - neutral position. Only in such positions will the protection system give a signal to start the engine. In other positions of the lever, turning the key will not work or there will be no changes after turning the key.

For the start, it is better to use the parking mode, since the driving wheels of the vehicle will be blocked and this will not allow it to roll. Neutral mode should only be used for emergency towing.

In addition to choosing the correct mode, to start the engine in most cars with automatic transmission, it is necessary to depress the brake pedal, which is also a protection and saves from accidental rollback of the car when the selector is in neutral mode.

Most modern cars are equipped with a steering wheel lock and anti-theft lock. If, when all the previous actions are performed correctly, the steering wheel does not turn and the key does not turn, the protection is activated. To unlock, you need to insert the key into the ignition lock and try to turn it gently while turning the steering wheel in different directions. If these actions are synchronized, the lock will be released.

How to drive an automatic transmission and what not to do

Competent driving in a car with automatic transmission will increase the operational resource of the box and save a lot of money and nerves.

To ensure the long-term operation of the automatic transmission, it is necessary to correctly select the modes depending on the operating conditions.

For correct driving with automatic transmission, you should:

• get under way after a jolt showing full engagement of the gear;
• in conditions of slipping, turn on a lower gear and, working with the brake pedal, control the slow rotation of the wheels;
• using different modes, you can apply engine braking or limit acceleration;
• it is possible to tow vehicles with the engine running at a speed not exceeding 50 km / h in the "neutral" selector position and at a distance not exceeding 50 km;
• it is not recommended to tow another vehicle, if necessary - the towed vehicle should not be heavier than the towing one, the mode must be D2 or L and the speed is up to 40 km / h with smooth movement.

What not to do when driving with automatic transmission:

• it is forbidden to turn on the "P" mode - parking while the car is moving;
• movement in neutral downhill;
• push start;
• when stopping for a short time (at a traffic light, in a traffic jam), select parking mode or neutral, this reduces the resource of the automatic transmission;
• for a long stop in city mode, the selector must be put in the "parking" position;
• it is forbidden to engage reverse gear from the “drive” mode or to a complete stop;
• it is impossible to put the parking mode on the slope first, when parking the car on a slope, first put on the hand brake, and then in the parking selector position, to start moving off the slope, first the brake pedal, then removing the car from the parking brake, and only then select movement.

How to operate automatic transmission in winter

Severe weather conditions in winter bring a lot of worries and problems to owners of cars with automatic transmission.

• correct warming up of the box - a few minutes after starting the vehicle should warm up, before starting to move, it is recommended to turn on all modes one by one with the brake pedal depressed to accelerate the heating of the transmission oil;
• the first 5-10 km after the start of the movement, sharp acceleration and wheel slip should be avoided;
• to get out of the snow or ice, you must turn on a lower gear and, using alternate work with the brake and gas pedal, carefully drive out;
• swinging is not recommended, as this method will have a detrimental effect on the torque converter;
• use of low gears or semi-automatic mode for engine braking on a more or less dry road surface, and on slippery slopes, use the brake pedal;
• on icy uphills, wheel slip and sharp pressing on the accelerator pedal should be avoided;
• short-term, but clear and accurate, the transition to the "neutral" mode helps to stabilize the machine by aligning the wheel rotation and getting out of the skid.

Pros and cons of an automatic transmission

There is a fan for every type of transmission. In connection with the increasing distribution of automatic transmissions, it is necessary to outline their pros and cons for competent selection for the needs of the car owner.

The advantages are:

• automatic gear shifting, in which you do not need to be distracted, which is especially important for novice drivers;
• facilitated starting off process;
• more gentle operation of the chassis and engine thanks to the operation of the torque converter;
• improved flotation in most conditions.

The disadvantages include:

• not suitable for fans of fast acceleration;
• lower throttle response compared to a similar vehicle with manual transmission;
• impossible to start with a push;
• towing is undesirable and is possible only under certain conditions;
• improper operation leads to breakdowns;
• expensive repair and maintenance.

With the correct operation of a car with automatic transmission, the resource of the box is quite high and is practically not inferior to the manual transmission. Driving comfort, especially in urban conditions, will bring you many pleasant minutes.

At the moment, there are several types of transmissions in the automotive world. But the most popular are only two. It is automatic and mechanic. The latter appeared ...

From Masterweb

15.05.2018 21:00

At the moment, there are several types of transmissions in the automotive world. But the most popular are only two. It is automatic and mechanic. The latter appeared earlier, but now it is gradually being replaced by automatic transmission. The machine is much more convenient to use, and in terms of reliability, this box is no worse. Today we will pay special attention to this type of transmission. The device, the principle of operation of an automatic transmission and much more - further in our article.

Characteristic

So what is an automatic transmission? This is a device used to change the torque that is supplied from the engine to the drive wheels of the car. Automatic transmission is also referred to as hydromechanical transmission.

What brands is this transmission installed on today? At the moment, almost every car manufacturer practices the installation of automatic transmissions. Here are the brands on which the automatic transmission is installed:

• "Toyota".
• Audi.
• BMW.
• Nissan.
• Volkswagen.
• Skoda.
• Renault.
• Citroen.
• Peugeot.
• Mercedes.
• Chevrolet and many others.

Moreover, this mechanism has approximately the same structure and principle of operation. So, this node consists of:

• Torque converter.
• Planetary row (manual transmission).
• Control systems.

If we talk about front-wheel drive cars with an automatic transmission, the unit also includes:

• Differential.
• Main gear.

These elements are located directly in the box, and are not separate units, as in rear-wheel drive cars. So, let's take a closer look at the automatic transmission device.

Torque converter

This element serves to change and transfer torque from the flywheel of the internal combustion engine to a manual transmission. In addition, the torque converter helps to reduce vibrations that occur when starting the movement and when changing gears. The GDF design includes:

• Reactor wheel.
• Turbine.
• Freewheel clutch.
• Blocking clutch.

The converter has blades of a certain shape. Between them are channels for the circulation of the ATP liquid. As for the last item on the list, it serves to block the GTP in certain vehicle modes. And the freewheel allows the reactor wheel to rotate in the opposite direction. All elements of the GTP are enclosed in a single body. Inside it, there is always an ATP liquid.

Principle of operation

The torque converter operates in a closed loop. Thus, the flow of ATP fluid is transferred first to the turbine and then to the reactor wheel. Since both have certain blade shapes, the flow rate increases. The liquid is directed to the impeller and increases its speed. This also increases the torque. The highest torque values \u200b\u200bare usually achieved at minimum speed (that is, when the first gear is engaged).

With an increase in engine speed, the speed of rotation of both wheels becomes equal. This activates the blocking clutch. In this case, power is transferred directly to the manual transmission. The torque converter is locked in each gear when the rotation speed of the turbine and reactor wheels is equalized.

Note that in some automatic transmissions, the locking principle is somewhat different. So, in the automatic transmission there is a mode with a slipping clutch. It prevents complete blocking. Where is this mode used? This is necessary in conditions of acceleration and high loads. Also, this mode allows you to reduce fuel consumption and with it a smoother gear shifting is carried out.

Planetary row

This is the same manual transmission that is part of the automatic transmission. What is this node for? It allows you to change the gear ratio, thereby adjusting the amount of torque and vehicle speed. The mechanical gearbox consists of two planetary gearboxes. They are connected in series with each other. It is necessary for them to work together and to ensure the required number of steps. Previously, only four-speed automatic transmissions were practiced on cars. Now the number of steps has increased to six (and some manufacturers practice nine-speed boxes).

Each planetary gear consists of:

• Crown gear.
• Drove.
• Sun gear.
• Satellites.

Torque transmission is only possible if one or two of the above elements of the planetary gear set are blocked. So, thanks to the stationary sun gear, the gear ratio is reduced. And when blocking the crown, it, on the contrary, increases. The very blocking is carried out by the clutches and brakes. The latter allow you to hold certain parts of the automatic transmission gearbox due to the connection to the transmission housing. Brakes can be tape type or multi-disc. They are closed together with the clutch by means of hydraulic cylinders. Also, the automatic transmission device has a clutch that holds the carrier and does not allow it to rotate in the other direction.

Thus, the principle of operation of an automatic transmission is based on a specific algorithm for disengaging and activating different clutches and brakes.

Automatic transmission control system

Most modern boxes have an electronic control system. It includes:

• Electronic control unit.
• Input sensors.
• Selector lever.
• Distribution module.

A number of additional sensors are also involved in the automatic transmission system:

• Temperatures of the ATP liquid.
• Rotation frequencies at the inlet and outlet of the box.
• Gas pedal and automatic transmission selector positions.

The automatic transmission ECU processes the incoming signals from the sensors and then activates the actuators. It is worth saying that the electronic unit of the box closely interacts with the engine ECU.

Valve body

The distribution module is also called a hydraulic block. This unit controls oil flows and provides clutch brakes. The valve body consists of:

• Solenoid valves (solenoids).
• spool valves. They are mechanically driven and housed in an aluminum housing.

Solenoids are used to switch gears in an automatic transmission by changing the fluid pressure. For this, their device has two-position valves. These elements act on the basis of signals from the electronic control unit. As for the spools, they serve to select the operating modes of the box. They are controlled by the automatic transmission selector itself.

Pump, cooling

In order for the working fluid to circulate in the system under pressure, the automatic transmission device has a gear-type pump with internal gearing. Some boxes use a paddle element. But regardless of the type, the pump is driven by the GTP hub.

During the operation of the automatic transmission, the fluid heats up significantly. In view of this, a cooling system is provided in the box design. It assumes the presence of a special heat exchanger, which is included in the engine cooling system. In some cases, a separate ATP fluid radiator is used, placed in the front of the car.

Benefits of automatic transmission

Let's consider the main advantages of this transmission. Why did she become so popular? First of all, automatic transmission is relevant for its ease of use. So, it is much easier to learn how to operate this gearbox (we will consider how to drive a car with an automatic transmission a little later). The driver can fully concentrate on the road conditions without worrying about grip and what speed to apply. Everything happens automatically. It is especially convenient to use a car with an automatic transmission in large cities, where frequent traffic jams are possible. The driver is much less tired as there is no need to play with the clutch.

The next plus of the automatic transmission is its smooth running. Such a box works smoother than mechanics. The movement starts without jerking. Also, many transmissions have various auxiliary modes and additional functions. It is worth noting the winter as well as the sports mode. Some cars have a mode for driving through mud and other surfaces. The box adapts itself to the given conditions.

Disadvantages of automatic transmission

But there is also a downside to the coin. First of all, it is worth noting the expensive maintenance. Take, for example, the price of an ATP liquid. One liter of it costs from a thousand rubles, while for mechanics, oil will cost 3-5 times cheaper. Expensive repairs should also be noted. The automatic transmission is more complicated than the mechanics. Therefore, the cost of repairs will always be 2 times higher.

The next disadvantage concerns operating restrictions. Thus, a car with an automatic transmission must not be towed by a cable or in any other way. This leads to breakdowns in the automatic transmission. If the car breaks down on the way, you only need to call a tow truck.

There is one more disadvantage. This is fuel consumption. This is especially true for old four-band automatic transmissions. They are practically not used now, but you can still find them on Logans and other budget cars. So, one and the same engine on the machine will consume 10-15 percent more fuel than with mechanics. Modern six-speed gearboxes have less difference in consumption. However, owners of four-speed automatic transmissions take a long time to get used to the expense. It is not uncommon for a 1.6-liter "Logan" to spend up to 14 liters of gasoline in the city on such a machine. With mechanics under the same conditions, the car consumes no more than ten.

And perhaps one of the main drawbacks is the overclocking dynamics. It is for this reason that many abandon automatic transmission in favor of mechanics. So, a car with a gun will always be half a second slower than with the same engine, but mechanically (meaning acceleration to one hundred kilometers per hour). Yes, some boxes have a manual shift option as well as a sport mode. But if we talk about B-class cars, all the same, this does not bring the acceleration speed much closer to the manual transmission.

Maintenance and repair of an automatic transmission

It should be noted that each automatic transmission, regardless of the year of manufacture and the number of steps, needs periodic maintenance. This operation involves changing the oil. In an automatic transmission, it is subjected to higher loads because it circulates under pressure in the system and allows the transmission of torque. the regulations for each manufacturer are different. However, on average, an oil change should be carried out every 60-70 thousand kilometers.

How can you make a replacement? There are two methods in total:

• Partial. In this case, the oil does not change completely. So, first, old fluid is poured out of the drain hole. Typically, its volume is no more than 50 percent of the filling. After that, new oil is poured into the box through the dipstick. Its volume must be identical to the one that was leaked earlier. The advantage of this method is that you can do it yourself. All you need is a pit and an extension tube. But there is also a drawback. Due to the fact that the oil is not completely drained, it must be replaced twice as often. Thus, in the event of a partial replacement, the box requires attention not every 60, but 30 thousand kilometers.
• Complete. In this case, special vacuum equipment is used. The pump pumps out the entire volume of oil from the system, simultaneously driving new oil. This is a more correct replacement method, but it has a couple of drawbacks. So, this method cannot be applied with your own hands. In addition, the cost of such a replacement will be several times higher. Indeed, in addition to the cost of the work of the master, you will need to purchase more ATP liquid. Typically, with a filling volume of 8 liters, about 12 liters are required for replacement.

Now about the repair. The most harmless operation is the replacement of oil seals and gaskets. As a rule, the wear of the sealing elements is evidenced by oil leakage on the box body. One of the most common operations is replacing the automatic transmission oil pan gasket.

There are also more serious repair methods. So, over time, the valve body may become dirty. This is usually dirt from the clutch packs. As a result, the spools stop functioning normally and the box starts to kick. The repair technology consists in disassembling the valve body and replacing the failed spools. In some cases, only cleaning the hydraulic plate helps.

Repair may be required even if the solenoids are defective. The reason for their failure is trivial. These are small deposits in the oil that somehow got from the filter to the valves. As a result, the latter begin to jam and malfunction. The repair consists in replacing the bronze bushings and solenoid rings.

If this problem is not eliminated in time, the gap between the ring and the shaft housing will increase. This will cause oil to seep into the gap. And since the pressure in the block will drop, the pump is forced to pump oil more intensively (in order to compress the clutches). This happens until the automatic transmission pump is completely exhausted. A characteristic sign of a worn pump is an increased hum and howl when the automatic transmission is operating.

The electronic control unit of the box can also fail. Because of this, the electronics cannot correctly send signals to the actuators. The box is not able to change gear at high revs, or the gear changes are jerky. Also, the box can get up in emergency mode. Automatic transmission repair in this case consists in replacing the block or restoring the loops in case of damage.

As for the cost of repairing a transmission, the price depends largely on the nature of the breakdown. But often the price ranges from 30 to 90 thousand rubles.

About replacing automatic transmission

When is it advisable to replace an automatic transmission? This operation may be required in case of failure of large elements. It could be a planetary gear set. Also, replacing an automatic transmission is relevant if several systems fail at once. Repair in this case will be expensive, and buying a whole box for disassembly is cheaper. But as a rule, such actions are resorted to in the case of a high mileage of the box (300 or more thousand kilometers).

How to use an automatic transmission?

Automatic transmission has differences not only in the principle of operation, but also in use. So, consider driving a car with an automatic transmission. First, we need to start the car. The gear selector should be in the "Parking" position. Next, we squeeze the brake pedal (with the right foot) and turn on the mode we need. Recall that there are only a few of them:

• "Parking".
• "Reverse" (reverse gear).
• "Neutral"
• "Drive" (moving forward).

To start driving, you should move the gearbox selector to the "Drive" position. After that, move your foot to the accelerator pedal. Do not forget to remove the car from the parking brake first, if it was previously installed on it.

Driving with an automatic transmission has its own nuances. So, beginners are wondering whether it is necessary to transfer the selector to "neutral" mode when the car is stationary (for example, in a traffic jam or at a traffic light). Experts give the following answer. It is worthwhile to transfer the automatic transmission selector to neutral mode only when the car has been parked for a very long time (more than a minute), and keeping your foot on the brake constantly is already problematic. If the stop is short, do not switch to neutral mode. Indeed, in this case, the box is significantly loaded: the friction packs are opened, the shafts are disengaged and the solenoids are closed. And when you switch to "drive" mode, this whole process is repeated.

Thus, switching the automatic transmission to neutral should only be done in case of prolonged downtime. Otherwise, the transmission suffers significant loads. It is worth knowing that the principle of operation of an automatic transmission, in contrast to mechanics, is different, and here it will not be possible to just throw the lever into "neutral". This is especially not worth doing on the go, trying to coast. This can lead to irreversible consequences. As a result, the box kicks and the clutches slip. Yes, this does not happen immediately. But if you constantly operate the transmission like this, you can soon get to its expensive repair. There are a lot of cases when one and the same box drove 100 thousand kilometers for some owners, and 300 for others without repair. The reason for such a high resource is trivial. This is the correct operation of the transmission and its timely maintenance.

Conclusion

So, we found out what an automatic transmission is and how to use it. No matter how scolded this transmission, cars with an automatic transmission are gradually replacing mechanics. Automatic transmission is more relevant in large cities. It is chosen even on the condition that the consumption with it is 5-10 percent more than on the mechanics.

Kievyan street, 16 0016 Armenia, Yerevan +374 11 233 255