Variator, mechanic or automatic. What's better? What is an automatic transmission (automatic transmission) and how it works How does an automatic transmission work and work

Automatic transmissions are widely used in the design of cars because they make it easier to drive a vehicle. Machine owners need to know how to use the automatic transmission, since the resource and reliability of the product depends on the correct operation.

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The device and principle of operation of the automatic transmission

The automatic transmission includes:

• hydraulic transformer;
• planetary mechanical gearbox (or shaft);
• hydraulic control system;
• electronic control system;
• differential (in front-wheel drive boxes);
• main pair (for front-wheel drive).

The torque converter is housed in a toroid-shaped housing, earning it the nickname "donut" among mechanics.

Torque converter automatic transmission

The hydraulic transformer is a mechanism with the transmission of torque by fluid flows. The device is placed between the engine flywheel and the mechanical part of the transmission. As a working fluid, oil is used, which has a low foaming ability and a viscosity that is stable from temperature and service life. The transformer acts as a clutch and changes the amount of torque taken from the flywheel of the power unit. The photo below shows the general arrangement of the box.

Schematic diagram of the automatic transmission

The structure of the torque converter includes:

• a drive wheel equipped with pump blades, which is rigidly connected to the flywheel;
• a driven wheel equipped with a turbine impeller, rigidly mounted on the input shaft of the mechanical part of the box;
• additional bladed reactor (stator);
• frame.

The design of the wheels provides for minimal gaps between the working elements; seals are additionally installed to prevent fluid from escaping. At the moment of the start of the movement, the pump vanes create a flow of oil. The resulting centrifugal force brings the oil to the outer radius of the wheel. Then the flow enters the turbine wheel, transmitting torque to the gearbox input shaft associated with it. After that, the flow is directed to the reactor, after passing through which the liquid returns to the inlet channels of the pump impeller. If the reactor is removed, the design will turn into a conventional fluid coupling, which cannot control the amount of torque.

The reactor operates in two modes - stationary and rotational. At the initial stage of the box, the reactor does not rotate, its blades are used to hold the liquid flow reflected from the turbine. When the reactor is removed, this flow will enter the pump, slowing it down and reducing transmission efficiency.

By holding the flow, the reactor increases the fluid pressure on the turbine wheel, thus regulating the torque. After alignment of the pump and turbine speeds, the reactor wheel begins to rotate. The moment the reactor begins to act is called the point of adhesion. The reactor wheel rotates at a frequency corresponding to the turbine speed.

However, the reactor does not allow the torque to be controlled over a wide range. In addition, the design of the transformer does not provide a reverse gear.

A visual representation of the principle of operation of a transformer in an automatic transmission

Planetary automatic gearbox

To expand the transformation range and ensure reverse, mechanical gearboxes are used. The most widely used are planetary mechanisms that provide a wide range of gear ratios with small overall dimensions. The gearbox consists of a central (sun) gear, around which satellites mounted on a common carrier rotate. Another gear (epicycle or crown) is installed on the peripheral part of the transmission.

The planetary gearbox in the automatic transmission is complemented by friction and brake clutches, as well as band brakes. Automatic transmissions have several planetary gearboxes that are used when switching gears. The number of gearboxes is one less than the number of speeds in the box. For example, a 4-speed gearbox is equipped with three planetary gears with different gear ratios.

The clutch consists of a set of discs and plates installed alternately. The plates are rigidly fixed on the drive shaft, and the discs are connected to the parts of the planetary gearbox. Clutch control is hydraulic. The discs are made of soft friction material, the plates are made of steel. A band brake includes a friction surface (drum) mounted on a shaft and a brake band. The tape is fixed on the box crankcase and on the hydraulic actuator.

Planetary reductor

Automatic transmission hydraulics

A hydraulic drive is used to control the speed change, which allows automating the process. In modern transmissions, hydraulics are supplemented by electronic control units that control the operation of the system.

The hydraulics of the box include:

• an oil pan equipped with a magnetic element for collecting wear products of parts;
• oil pump with centrifugal pressure regulator (spool type);
• filter for cleaning fluid from contamination;
• channels for supplying the working fluid to the actuating elements:
• valve distributors.

The oil in the box is used not only to drive the actuators, but also to lubricate and cool the components. There are two holes in the crankcase - for level control with a dipstick and a ventilation breather.

When operating an automatic transmission, it is necessary to maintain the fluid level in the sump. The resource of the box and the reliability of operation depend on this parameter.

The pressure regulator allows you to maintain the flow rate within the specified limits. Modern boxes are equipped with solenoid valves, which are controlled by an electronic unit. The block changes the flow intensity depending on the speed of the car, the throttle opening angle, resistance to movement and other parameters. Solenoid valves are used to control the flow in one or more lines, and also in gearshift drives. The valves are placed in a separate box located in close proximity to the pump. The body of the box is a so-called hydraulic plate - a part with a large number of channels for the liquid.

Hydraulic plate of automatic transmission

Hydraulic cylinders are used as actuators, converting oil pressure into mechanical work. A special case of a hydraulic cylinder is a booster used to control the operation of a disc brake or a locking mechanism.

The device of an automatic box on the example of a Toyota node is shown in a video filmed for the AvtoMaster TechCenter channel.

Scheme of the box

The principle of operation of the four-speed box:

1. Torque is supplied to the central gear from the torque converter. At the same time, the carrier of the satellites is blocked. In any automatic transmission there are at least two planetary gears, so the rotation from the first is transferred to the second. The output shaft of the box receives torque from the second planetary gear.
2. The second gear works with the help of two planetary gears. In first gear, the crown is blocked by a band brake, the carrier rotates with the satellites. From this node, the moment is supplied to the second gearbox, in which the central gear is stopped by the clutch. The output shaft of the box receives torque from the crown of the second gearbox. The gear ratio of the second gear is calculated by multiplying the gear ratios of the first and second gearboxes.
3. In third gear, the ring gear and carrier of the first gearbox are stopped. Due to this, the gearbox works as a whole, without changing the speed.
4. The fourth gear is overdrive. Operation is ensured by brake stop of the annulus, the torque is transmitted through the central gear.
5. To turn on the reverse gear, the satellite carrier is held in the second gearbox. Torque is applied to the center gear of the second gearbox, which is then transmitted to the center gear of the first gearbox.

What are the benefits of an automatic transmission?

Automatic transmission has several advantages:

1. Automatic gear shifting simplifies the process of driving, as the number of pedals is reduced. The driver does not need to control the engine speed and the gear engaged.
2. The cross-country ability of a vehicle equipped with an automatic transmission is higher. The increase in cross-country ability is achieved by eliminating the break in the flow of power and torque when switching speeds.
3. Reducing the dynamic loads transmitted to the power unit and transmission units.
4. Protection against starting when the gear is on. The control system built into the box blocks the starter when the selector is in positions other than park and neutral. Modern vehicles only allow starting in the park position.

The disadvantages of automatic transmissions usually include:

1. Loss of power in the torque converter, which leads to an increase in fuel. On modern multi-speed gearboxes, this disadvantage is eliminated by ensuring the optimum engine speed and the introduction of a computer-controlled torque converter lock-up.
2. Slightly reduced dynamics of a car with automatic transmission. The problem is solved on gearboxes with two clutches, which provide fast gear changes.
3. Inability to tow the car or start the engine by towing.
4. Rapid wear of working elements in stepless variators. Impossibility with power plants developing a torque of more than 300 N / m.
5. A stuck car cannot be freed by swinging (by quickly switching first and reverse gears), since the automatic transmission fails from such manipulations.

Types of automatic transmissions

Modern cars use several types of automatic transmissions. Boxes differ in design and method of transmitting torque from the incoming shaft to the outgoing one. The most common transmission options are discussed below.

Hydromechanical gearbox

The structure of the box includes three main components:

• hydraulic transformer;
• mechanical box;
• switching and control system.

There are two types of hydromechanical transmissions that differ in the design of the mechanical part:

• with shafts (used on trucks or buses);
• with planetary gear (for passenger cars and minibuses).

Gear shifting in boxes equipped with shaft gearboxes is carried out by multi-plate friction clutches of the "wet" type, i.e., working in an oil bath. A gear clutch can be used to engage first or low gear. A similar clutch is used to engage reverse gear. The use of friction clutches ensures smooth gear shifting, without impacts and torque breaks. The disadvantage of the shaft box is its large size and noisy operation. On the other hand, a massive design allows you to transmit significant torque without the risk of failure of the components.

In a planetary hydromechanical transmission, shifting is performed by clutches and band brakes. A design feature is the slipping of the clutches and tapes of the box when switching any speed. Because of this, there is a decrease in the efficiency of the box. The advantage of the transmission is reduced dimensions and weight, but the cost of the product is higher, as is the complexity of repair and maintenance.

The transformer installed on hydromechanical transmissions can be blocked. This mode of operation is referred to as Lock Up Torque Convertor Clutch. In this mode, the torque from the engine is supplied directly to the planetary gearboxes, turning the box into a mechanical unit. Locking and unlocking are performed automatically.

Hydromechanical planetary box Ford in section

Variator (CVT)

The variator is a gearbox with an infinitely variable gear ratio. The change in the number occurs depending on the external load and engine operating conditions, which makes it possible to effectively use the characteristics of the power unit.

Two types of variators are used on cars:

• V-belt;
• friction.

The design of the V-belt variator consists of two adjustable pulleys and a steel belt. The belt links have a cross section in the shape of a trapezoid. Each pulley consists of two parts, the side surfaces of which form the working surface. Parts can move relative to each other, shifting the working surface along the radius.

When the halves of the drive pulley are shifted, the belt is forced out to the outer radius, which leads to an increase in the gear ratio. The displacement occurs according to the principle of a wedge caught between two surfaces. Therefore, the design was called V-belt. When breeding the pulley halves, the belt goes between the parts to the minimum point, reducing the gear ratio.

To achieve direct transmission, it is required to set the same working radii on the pulleys. The steel belt can have a different design - in the form of a chain or consist of a set of steel plates. The diagram clearly shows how the V-belt variator is arranged.

V-belt variator Mercedes-Benz

Designation of nodes on the variator diagram:

• 1 - input shaft;
• 2 - chain drive of the hydraulic system pump;
• 3 - starting torque converter;
• 4 - differential;
• 5 — ;
• 6 - driven pulley;
• 7 - the secondary shaft of the box;
• 8 - planetary gear reverse gear;
• 9 - drive pulley.

The composition of the V-belt variator includes a small-sized clutch or torque converter, which are used at the time of the start of movement. After the start of the variator, these nodes are blocked. The pulleys are directly controlled by servo drives that receive signals from an electronic control unit and sensors.

A friction or toroidal variator is a set of coaxially arranged discs and rollers that transmit torque. The toroidal device got its name for the shape of the working surfaces of the driven and leading element.

The gear ratio is adjusted by rearranging the rollers along the side surface of the discs. Due to the significant force of pressing the roller to the disk, movement is possible with the help of special mechanisms.

Other constructive solutions are also possible. An example would be the Nissan Extroid assembly, in which the roller is pulled out of place by a hydraulic drive. After that, it moves independently (due to the shift relative to the axis of the disk). The principle of operation of the toroid mechanism is well understood by the diagram below.

The principle of operation of the Nissan toroidal variator

Robotic mechanics

This type of transmission is a conventional mechanical gearbox with gear shifting by a robot, i.e. without driver intervention. Vehicles with a robot are not equipped with a clutch pedal, the shift selector is similar to the automatic transmission assembly.

Manual VAZ with robotic clutch

The disadvantages of robotic boxes are:

• low smoothness of work;
• poor dynamics (partially corrected by switching to the "manual" mode);
• problems when driving on long climbs;
• overheating of the clutch discs when driving in traffic jams.

Another variant of the robotic gearbox is a dual-clutch transmission, first introduced into production by Volkswagen under the trade designation DSG. The box uses two clutches, one of which serves even gears, and the second - odd.

• with a "wet" type clutch, which causes power loss;
• with dry discs.

Brief description of working principle:

1. At the moment of starting the movement, the clutch of the first gear is engaged, transmitting torque, the second one is in the open state.
2. When a certain engine speed is reached, the electronic control unit disengages the first clutch and engages the second.
3. After that, the first clutch is rebuilt to control the third gear and waits for the moment of switching.

Sectional view of a seven-speed DSG box

The traditional advantages of the box include a very fast shift procedure, the box provides more dynamic acceleration than a conventional mechanical transmission. Computer control of the box operation allows to reduce fuel consumption by 10-12%. The main disadvantage of the transmission is the accelerated wear of the clutches, especially the “dry” type, due to which shocks begin when switching

Cam gearbox

The transmission is mechanical, the car has a clutch pedal. The cam type gearbox does not have synchronizers in the design; switching is carried out using cam clutches. The clutch is used when starting off, further shifts are performed at a reduced throttle opening angle. The shift lever moves in two directions - including high or low speed. Such a mechanism is called sequential, it resembles a gearshift device on motorcycle boxes.

For switching, a clutch is used, equipped with several large cams (no more than 5-7), which engage with the cams mounted on the transmission gear. The engagement has a significant backlash, which allows to accelerate the inclusion of speed. The disadvantage of the box is the shock loads on the engine and other transmission components. To reduce axial loads in boxes, spur gears are used.

Cam boxes are used on small-scale sports and modified cars. Serial production is not equipped with such units.

Cam gear set for Subaru gearbox

Operating modes of automatic transmissions

To select the mode of operation of the box, a selector is used, which is associated with . The box has a switching mechanism that is responsible for turning on the modes. The selector is surrounded by a frame with applied icons indicating the mode of operation. Icons can be backlit. The photo shows the basic version of the selector without the possibility of manual switching.

Typical diagram of automatic transmission switching and control modes

Main functionality

During the operation of the automatic transmission, several basic modes are used, the features of which are discussed below.

The driver must know the features of operation and control of each mode:

1. Parking (P, Parking), is used while the car is in the parking lot, while the mode is not a parking brake. Switching on is carried out only after the machine has stopped. During the movement, the mode cannot be turned on, since the device of the switching mechanism has a special blocker. The parking mode allows you to start the power unit with a starter. The wheels are connected to the box shafts by a locking mechanism located in the box crankcase.
2. Reverse (R, Reverse), used for maneuvering in reverse. Turns on after a complete stop of the vehicle. The selector has a locking element that prevents accidental switching while driving.
3. Neutral position (N, Neutral), in which the gear is not engaged in the box. The difference from parking is the disabled wheel lock. The engine is allowed to start. Towing in neutral mode is prohibited, since there is no pressurized fluid supply in the box.
4. Driving mode (D, Drive), which is used to move the car. When the mode is turned on, the speeds are automatically switched up and down. Some transmissions use an additional L (Low) mode that limits upshifts and is used when driving in difficult road conditions.

Many manufacturers do not recommend leaving the car on slopes with only the box held, as this leads to deformation and seizing of the locking mechanism. When the car is stopped on a slope, the gearbox selector is first set to the neutral position, and then the handbrake lever is raised. When starting off, the car is held by the handbrake, then the box is moved to the driving position, and only then the parking brake is released.

About special modes

Special or additional modes are used to operate the car in off-road conditions or to change the nature of the transmission, taking into account the specifics of the movement. Additional modes are controlled by buttons or by moving the shift lever to a separate position.

Tiptronic mode

The mode name "Tiptronic" (Tiptronic) first appeared on Porsche cars in 1990. The mode allows you to switch the speed of the automatic transmission manually.

Developing the Tiptronic principle, the designers sought to combine the comfort of an automatic transmission and the advantages of a mechanical one in one unit. In manual shift mode, the driver can control the vehicle's dynamics in powertrain braking modes. It is also possible to force downshift before entering or during corner entry.

Manual mode is used to provide additional acceleration during acceleration. The disadvantage of using the Tiptronic mode is the complexity of the box design and delays when switching speeds, which can reach one second.

For manual shifting, the selector is moved to the left

Switching is performed either by the box selector switched to manual transmission control mode. When operating the lever, it is transferred to position D, and then to the side, into a separate row, indicated by the symbols "+" and "-". The “+” sign indicates the direction of movement of the lever to engage an upshift, the “-” sign indicates a downshift. The number of the selected gear is displayed on the display located on the instrument cluster.

Shift paddles

The designation of the paddle shifters is similar. One is used to shift speeds up, the second - down.

The manual mode for switching an automatic transmission can be called Steptronic - a brand name from the BMW concern. There are no cardinal differences in the operation and control algorithm from Tiptronic.

Sports modes

The inclusion of sports activates a special algorithm for switching speeds - at increased engine speeds. A number of vehicle manufacturers use the powertrain control unit in the operation algorithm, which provides a more intensive set of revolutions. When you take your foot off the gas pedal, the speed drops after a while, which allows you to provide acceleration dynamics when you press the pedal back. On some vehicles, when you turn on the sport mode, the suspension stiffness settings and the exhaust sound (using a special valve) can change.

Audi S5 selector, sport mode is activated by moving the lever all the way down

A special case of the sports mode can be called "kickdown", which turns on when you sharply press the gas pedal. This results in a downshift and faster acceleration of the vehicle even when the shift selector is in the normal position.

Other modes

Depending on the manufacturer of the car and box, there may be additional modes. Additional modes are controlled by moving the lever or by pressing individual buttons. The buttons are located on the lever or on the center console.

Overdrive, which is an additional overdrive. The function is used in some hydromechanical transmissions.

Overdrive mode is analogous to fifth or sixth gear in manual transmissions. When the mode is activated, it switches to an increased speed when the gas pedal is released, and when pressed back, the box goes down one or more speeds. When the overdrive is disabled, the shift is performed at increased speeds, while braking, the gear is held until the speed and speed drop to a certain value.

Overdrive is used when the car is moving along country roads without additional load (for example, a trailer). The mode is indicated on the selector by the letter D or O / D.

Overdrive button on Ford Fusion selector

The opposite of overdrive mode is the overdrive cut-off feature. It is indicated on the selector by the letters D3 or O / D Off. Can be used when driving in urban areas to ensure maximum dynamics. In fact, it is an early version of the sport mode.

D3 mode on the selector

Winter mode Manu (S or numbers 1 or 2) is activated by a button located next to the selector lever. When the mode is activated, gear shifting occurs at reduced engine speeds, which reduces wheel slip on snowy roads and ice. It is possible to further reduce slip by forcing the gearbox to shift from a standing start to second gear. After the start of the movement, the box is transferred to the standard mode D. When the winter mode is active, a kickdown is possible, but it is limited in engine speed.

The Manu button is clearly visible, located to the right of the lever

Instructions on how to use the automatic transmission

Brief instructions for operating automatic transmissions:

1. Start the engine.
2. Press and hold the brake pedal.
3. Move the selector to the drive or reverse position.
4. Release the parking brake.
5. Release the brake, as you release the car will begin to move smoothly.
6. After fully releasing the brake, press the gas to start moving. Releasing the throttle causes engine braking and speed reduction.
7. To stop, press the brake pedal.

Automatic transmission switching and control modes

When operating the transmission, the lever shifts in accordance with the recommendations outlined above. When switching, do not apply excessive force to the lever. Difficult shifting is a sign of a defective switch or cable drive.

Photo gallery

The photo shows the features of the control boxes on some cars. Control instructions are available in the instruction manual.

Features when driving a car with automatic transmission

There are no special differences in driving a car with an automatic transmission. When driving, it is recommended to avoid frequent and abrupt acceleration, as they lead to increased heat and wear of the box.

Does a car with an automatic transmission need a handbrake?

A car with an automatic transmission must have a working parking brake. Keeping the car in the parking lot only by the transmission leads to increased loads on the assembly, which can cause a breakdown.

How to use automatic transmission in traffic jams?

If you stay in traffic jams for a long time, especially at high air temperatures, it is recommended to periodically cool the unit. To do this, the selector is moved to the neutral position, the car is held by service brakes.

With a long stop in a traffic jam, you can move the box selector to the parking position. In addition to cooling the transmission, this will give the driver the opportunity to rest, since he does not need to keep the brake pedal depressed.

Paddle switches

Paddle switches are small plastic levers that are mounted on the steering wheel and connected via a flexible cable to the car's electronic system. When you press the petals, manual gear shifting occurs.

Ford steering wheel with paddles installed

Basic operating conditions for automatic transmission

During the operation of the box, the owner must follow a number of rules that extend the life of the unit. This is especially true for winter operation. In addition, the box imposes some restrictions on operation, which must also be remembered and observed.

Operation of the automatic transmission in winter

To warm up the box at a negative air temperature, you must:

1. Start the engine and let it run for 2-3 minutes.
2. Sit behind the wheel, holding the brake with your foot, start moving the selector in all positions. At each position, it is required to give a delay of 8-10 seconds. It is recommended to heat the box for another 5-6 minutes, periodically moving the selector in a circle.
3. Start moving smoothly, without pressing the gas pedal more than a third. Warm up the box in a smooth driving mode for several kilometers.

What should not be done with an automatic transmission?

To ensure the resource of the box, the owner should not perform the following manipulations:

1. The neutral position should not be included when coasting, since in this case lubrication and heat dissipation of the gearbox components are not provided. Excessive coasting can cause wear and burning of friction discs and plates in clutches.
2. It is forbidden to switch forward and reverse driving modes without completely stopping the car and rotating parts in the box. When switching, it is necessary to hold the car with a service brake. There are known cases of breakage of gears and the crankcase of the box. It is for this reason that it is not allowed to get out of the mud or snow drift by rocking the car.
3. Do not use the automatic transmission as a parking brake.
4. The car cannot be towed. Cars with automatic transmission are towed only with the drive wheels loaded onto the tractor.
5. It is forbidden to give an increased load on a cold transmission. It takes more time to warm up the box than to warm up the engine, so it is recommended to drive at low speed for the first 7-10 km without jerks and accelerations.
6. Avoid off-road driving with wheel spin.
7. It is not recommended to use cars with automatic transmissions for towing a heavy trailer.

Typical malfunctions of an automatic transmission

Some common faults:

1. Breakdowns of the switching scenes, which do not allow switching operating modes. Repair consists of replacing broken or worn parts. On some machines, access to the shift mechanism is difficult, so it may be necessary to dismantle the box or subframe along with the power unit and box.
2. Leakage of working fluid through seals or seals. The problem is solved by replacing worn parts and changing the fluid and filter.
3. Blocking the operation of the box due to failure of the control electronics. During the repair, blocks and wiring harnesses are changed.
4. The box does not allow you to move forward, but the reverse gear works. The reason is the wear of the couplings, jamming or clogging of the valves.
5. The reverse gear and part of the forward gears do not work. The cause of the breakdown is the wear of one of the working couplings or the breakdown of the hydraulic lines that ensure the operation of the unit.
6. When you try to switch the selector and start moving, there is a push, the mode switches, but the movement does not start. This is a symptom of a broken torque converter or low oil level. The filter may be clogged with wear products, which does not provide the necessary performance and pressure in the hydraulic system of the box.
7. It is possible to move forward only at one speed. The reason is wear of the couplings, breakage of the cuff of the clutch drive, jamming of the block valves.
8. Metallic noises while driving indicate worn bearings or gears. A rhythmic metallic knock at idle indicates wear on the discs in one of the clutches.
9. The problem with the movement of the car after warming up the box, while the box works fine on a cold one. The defect occurs as a result of wear or breakage of the blades on the impellers of the pump or turbine.

If problems arise with the automatic transmission, the owner must contact a specialized service. Attempts to repair it yourself can lead to irreversible consequences and the need to replace the box assembly.

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:

1. Variators;
2. 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 work 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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ARTICLE VIDEO How does automatic transmission work? What are all the pros and cons of driving a car with an automatic transmission, how reliable and durable is automation, what can and cannot be done if you have an automatic transmission, and is the automatic transmission really as “stupid” as they say about it or can it “do » car on the mechanics and leave it far behind? Read this article!

Automatic transmission device

The automatic gearbox consists of several main components:

Arrangement of elements in the automatic box:

planetary gear system

The heart of the automatic transmission is the planetary gear.

planetary gears have 3 degrees of freedom. This means that in order to transfer rotation, one of the 3 elements (satellites do not count) must be stopped.

If you do not stop any of the elements, then everyone will be able to make free movement, and in this case there will be no transfer of rotation.

It is possible to brake other elements as well, as well as to swap entry and exit points, getting different gear ratios and reverse directions of rotation.

In this case, the external dimensions of the structure will change slightly. Such properties determined the use of planetary mechanisms in the automatic gearbox.

Gearbox automatic, a short video on the device:

torque converter

A torque converter is used to transfer torque from the gearbox to the engine. In fact, it performs almost the same functions as the clutch in mechanics.

In addition, it can increase the torque by reducing the liquid flow rate by the reactor.

The principle of operation of the torque converter:

The torque converter consists of three main elements.

These are two blades, one on the side of the box, the other on the side of the engine. Between them is the so-called reactor. All these three parts are not mechanically interconnected, they are in a special liquid.

When the blades connected to the engine rotate, the torque is transferred with the help of liquid to the blades connected to the box, and the box starts to work.

The geometric characteristics of the torque converter blades and sections are selected in such a way that at idle speed the torque transmitted from the engine is very small and can be parried even by lightly pressing the brake pedal.

However, a slight pressure on the gas pedal, and a slight increase in speed, causes a significant increase in the transmitted torque.

This happens because with an increase in engine speed, the direction of the fluid flow changes in the direction of increasing pressure on the turbine blades.

The torque converters of modern automatic transmissions can increase the torque transmitted from the engine by two to three times. This effect only occurs when the crankshaft rotates significantly faster than the transmission input shaft.

As the car picks up speed, this difference decreases and the moment comes when the input shaft rotates, almost at the same speed as the crankshaft, but not exactly, since the transmission of torque from the engine to the automatic transmission is carried out through a liquid, i.e. with slippage.

This is part of the explanation why cars with automatic transmission are less economical and dynamic than exactly the same with manual transmission.

To minimize these losses, torque converters are equipped with locks. When the angular speeds of the impeller and turbine are aligned, the lock connects them into a single unit, eliminating slippage.

Couplings are used to connect the elements of the planetary mechanism to the input shaft of the gearbox, and brakes are used to stop relative to the housing. Both of them are most often multi-plate clutches.

Hydraulic system

The working fluid in the automatic transmission hydraulic system is ATF oil, which provides lubrication, cooling, gear shifting and transmission connection with the engine. As a rule, the oil in the box is in the crankcase.

Because the volume of oil during operation of the automatic transmission changes, it is connected to atmospheric air through the dipstick.

As pressure source in automatic transmission internal gear pumps are used. The advantage of internal gear pumps is the high pump power, especially at low speeds.

Due to the design feature, the automatic transmission provides automatic selection of the gear necessary for the movement of the car, without the participation of the driver in this process. At the same time, unlike a manual gearbox, the driver’s right hand is freed from gear shifting movements and there is no need to equip the car with a clutch pedal, which also excludes the driver’s foot movement to depress the clutch from the vehicle control process.

To start the movement of a car equipped with automatic transmission, the driver just needs to move the gearbox lever to the desired position and then all that remains is to adjust the speed with the gas and brake pedals. Driving a vehicle equipped with an automatic transmission is much easier, which gives the driver a greater opportunity to focus on the traffic situation.

Regardless of the type, any transmission - be it manual or automatic - performs the same function in a car - the efficient use of engine torque, but in different ways based on their design features.

Automatic transmission device

The functioning of an automatic transmission is based on the work of its planetary mechanisms and hydromechanical drive. In a small range of engine speeds, the automatic transmission allows the car to move in a wide range of speeds. Back to main elements automatic transmission devices include the following mechanisms:

• torque converter;
• planetary reductor;
• clutch packs;
• brake band;
• control device.

The main components and the principle of operation of the automatic transmission

The basis operating principle of automatic transmission the property of a fluid to transfer energy during rotation is assumed. This property made it possible to create a device (fluid coupling, torque converter), in which there is no rigid connection between the input and output shafts, and the mechanical energy between these shafts is transmitted using the flow of the working fluid.

The torque converter in an automatic transmission performs the function of automatically transferring torque from the power unit to the main components of the gearbox, which corresponds to the function of the clutch assembly in a manual gearbox. After reaching a certain engine speed, using the pressure of the working fluid on the torque converter units - the pump wheel, which is rigidly connected to the crankshaft of the power unit and the turbine wheel, interconnected with the main shaft of the gearbox, torque is transmitted. During a decrease in the speed of the power unit, the fluid pressure on the turbine wheel drops, and it stops. Accordingly, the clutch of the engine with the box is interrupted.

Due to the fact that the torque converter is limited in its ability to transmit mechanical energy in a wide range, it is connected to planetary multi-stage gears that provide gear shifting and reverse rotation.

According to its design, the planetary gearbox is a gear rotating around the central - "sun" gear. It functions by blocking and separating certain elements of the planetary series. A three-speed automatic transmission uses two planetary gears, and a four-speed automatic transmission uses three.

Clutch packs or a clutch system are mechanisms that lock the moving elements of a planetary gearbox together. According to its design, this is a set of several movable and fixed rings, which are blocked under the influence of a hydraulic pusher, which ensures the appropriate gear is switched.

The brake band also takes part in gear shifting, which temporarily blocks the necessary elements of the planetary gearbox. The principle of its operation is the self-clamping effect used to block these elements. Having a relatively small size, the brake band softens the impacts of the mechanisms at the time of their operation.

The control device is designed to regulate the functioning of the brake band and the operation of the clutches. It consists of a valve block with spools, springs, a system of channels and other elements. The control device performs the function of shifting gears based on the specific driving conditions of the vehicle - when accelerating, it engages a higher gear, and when braking, it lowers.

Automatic transmission operating modes

Automatic transmission can operate in several standard modes. All of them are denoted by symbols developed in the last century in Latin: P, D, N, R.

Parking mode "P" or parking– ensures that all gears are turned off. In this case, the drive wheels are blocked by the gearbox mechanisms, and it is disconnected from the engine. In this mode, the engine is started.

Video about warming up the automatic box:

Driving mode "D" or drive- provides automatic gear shifting when the car moves forward.

Mode "N" or neutral gear- provides disengagement of the driving wheels of the car from the gearbox. This mode is used during short stops or when the vehicle needs to be towed.

Reverse mode "R"- Provides reverse vehicle movement.

The driver's control of the automatic transmission must be carried out in the prescribed sequence: 1. Parking; 2. Reverse; 3. Neutral; 4. Movement.

In modern automatic transmissions, additional modes of operation are provided for a comfortable ride.

Mode low gear "L"- used during slow movement in difficult traffic conditions. In this mode, the gearbox operates only in the selected gear, regardless of changes in engine speed.

Modes "2" And "3"- are used when towing a load by a vehicle or in appropriate conditions. The numbers indicate the number of fixed gears in which the car is moving.

Overdrive mode "O/D" or "Overdrive"- used for frequent automatic upshifting. This mode provides a more economical and uniform movement of the car, mainly on highways.

Urban traffic mode "D3"- limits the automatic shifting of the box to third gear.

Balanced motion mode Norm- allows the box to shift to higher gears when the average values ​​\u200b\u200bof the rotation of the engine crankshaft are reached.

Winter driving mode "S" or Snow(may also be denoted by the symbol "W" or "Winter") - allows the car to start moving from second gear, thereby preventing slipping of the drive wheels. Also, while driving, the operation of the automatic transmission is performed more smoothly using low engine speeds.

Recently, more and more vehicles are equipped with automatic transmission. It is lighter and more comfortable to use and is ideal for beginners and traffic in the city with traffic jams and regular stops.

What is automatic transmission and its types

An automatic gearbox is one of the types of transmission in which the necessary gear ratio is set without driver intervention, 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 assembly, which is directly related to gear shifting, and together with the hydraulic transformer forms a single automatic unit.

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

Classic automatic transmission

The torque converter gearbox is a popular and classic transmission model found on most vehicles that roll off the assembly line today.

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

Robotic checkpoint

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

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

Variable speed drive

Variator - a device for smooth, stepless transmission of torque to the wheels.

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

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

The principle of operation of the automatic transmission

Several types of automatic transmissions 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 for the movement of vehicles.

When the engine is started, the 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 switching the selector lever and supplying fuel using the accelerator pedal, the pump blades increase speed. The increasing speed of the vortex flows begins to rotate the turbine blades. The oil whirlwinds are then transferred to the stationary reactor, then returned 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 pump wheel and the bladed central turbine move at the same speed, while the transmission fluid vortices hit the reactor wheel from the opposite side (movement is possible only in one direction) and it begins to rotate. The unit enters the hydraulic clutch state.

If the resistance to the wheels increases (uphill movement), the reactor wheel stops rotation and adds torque to the centrifugal pump. When the required speed and torque are reached, a gear change occurs in the planetary assembly.

The electronic control unit transmits a command, as a result of which the braking band and friction discs slow down the downshift, and the increased movement of fluid flows through the valve accelerates the upshift and ensures gear changes 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 off, there is no pressure in the torque converter, so starting the car with a push is not feasible.

Automatic box device

A classic slot machine consists of four main components:

• hydraulic transformer— replaces the clutch, converts and transmits torque to the wheels. It consists of a centrifugal pump, a vane turbine and a reactor that provides smooth and precise torque changes. The pump is connected to the crankshaft, and the turbine is connected to the box shaft. The transformation of energy is carried out due to the flow of liquid and the pressure formed by them. The torque converter changes the rotational speed and torque in a small interval, so a planetary assembly (box) is added to it.
• Planetary reductor consists of a central gear (sun), satellites, ring gear and planetary carrier. It shifts gears by locking some gears and unlocking others.
• Brake band, rear and front friction discs provide direct gear engagement.
• Control system consists of gear pump, oil sump, hydraulic unit and electronic control unit (ECU). The hydraulic unit consists of channels with solenoids (valves) and plungers that perform control and management functions. The ECU controls the information from sensors that collect various indicators.

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

IN variator the transformation of the gear ratio is performed by a mechanism that includes a driving and driven pulleys through which a 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

Depending on the type of automatic transmission, there are various automatic transmission modes. Each position of the selector lever or button on it is designed for different driving conditions with its own characteristics.

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

• R(parking) - blocking the drive wheels, the box shaft, is 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 a neutral gear in a manual transmission;
• D(drive) - movement in normal conditions with automatic selection of gears;
• L(D2)- reduced gear for driving in difficult conditions - off-road, steep descents and ascents, speed less than 40 km / h;
• D3- downshifting during small descents and ascents;
• R(reverse) - reversing, turns on at a complete stop and the brake pedal is pressed;
• O/D- the inclusion of fourth gear when driving at high speed;
• PWR- sports mode, to improve the dynamic qualities, the gear is upshifted at higher engine speeds;
• Normal- for smooth and economical movement;
• Manu- manual shift mode, recommended for use in winter.

How to start an automatic car

Features require competent launch. Degrees of protection have been developed to protect the box from mishandling and subsequent breakdowns.

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

To start, it is better to use the parking mode, as the drive wheels will be blocked on the vehicle and this will not allow it to roll. Neutral should only be used for emergency towing.

In addition to choosing the correct mode, in order 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 an anti-theft lock. If, with the correct execution of all the previous actions, the steering wheel does not spin and the key does not turn, the protection has turned on. To unlock it, 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 removed.

How to drive an automatic transmission and what not to do

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

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

For proper driving with automatic transmission, you should:

• move off after a push showing full gear engagement;
• in slipping conditions, you should turn on a lower gear and, while 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 of no more than 50 km / h in the selector position "neutral" and for a distance of no more than 50 km;
• it is not recommended to tow another vehicle, if necessary - the towed vehicle must 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 when the car is moving;
• driving in neutral downhill;
• push start;
• during a short stop (at a traffic light, in a traffic jam), select the parking mode or neutral, this reduces the life of the automatic transmission;
• during a long stop in urban mode, the selector must be put in the “parking” position;
• it is forbidden to turn on the reverse gear from the “drive” mode or to a complete stop;
• you can’t first set the parking mode on a slope, when parking the car on a slope, you must first put on the handbrake, and then put the “parking” selector in the position of the “parking” selector, to start moving from the slope, first the brake pedal, then removing the car from the handbrake, and only then select the mode for movement.

How to operate automatic transmission in winter

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

• proper 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 in turn with the brake pedal depressed to accelerate the heating of the transmission oil;
• the first 5-10 km after the start of movement, sharp acceleration and wheel slip should be avoided;
• to get out of the snow or ice, you need to turn on a lower gear and carefully drive out using the alternate operation of the brake and gas pedal;
• buildup is not recommended, as this method will adversely affect the torque converter;
• use low gears or semi-automatic mode for engine braking on more or less dry road surfaces, and use the brake pedal on slippery slopes;
• on icy slopes, wheel slip and sudden pressing of the accelerator pedal should be avoided;
• short-term, but clear and accurate, the transition to the “neutral” mode helps to stabilize the car by aligning the rotation of the wheels and exiting the skid.

Pros and cons of automatic transmission

There is a fan for every type of transmission. In connection with the increasing spread of automatic transmissions, their pros and cons should be identified for competent selection for the needs of the car owner.

The pros are:

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

The disadvantages include:

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

With proper 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 areas, will bring a lot of pleasant minutes.