Automatic Gearbox (automatic transmission) - a type of transmission in a car in which gear shifting is carried out electronically, without requiring the attention of the driver.
The first development that can be attributed to the automatic transmission class appeared in 1908 at the Ford plant in America. Model T, was equipped with a planetary, yet manual transmission. This device was not automatic, and required a certain set of skills and actions from drivers to drive, but was much easier to use than the non-synchronized manual transmissions that were common at that time.
Second milestone in the emergence of modern automatic transmissions was the transfer of clutch control from the driver to the servo drive in the 30s of the 20th century by General Motors. Such automatic transmissions were called semi-automatic.
The first truly automatic planetary gearbox "Kotal" was installed in Europe in 1930. At this time, various firms in Europe were developing clutch and brake band systems.
The first automatic transmissions were very expensive and unreliable, until experiments began in the late 30s to introduce hydraulic elements into their design to replace servos and electromechanical controls. Chrysler went this way of development, which developed the first torque converter and fluid coupling.
Modern automatic transmission designs were invented in the 40–50s of the 20th century by American designers.
In the 80s of the 20th century, automatic transmissions began to be equipped with computer control, for fuel economy, 4 and 5-speed automatic transmissions appeared.
Automatic transmission device and principles of operation
The main structural elements of the automatic transmission are always the same:
A torque converter that acts as a clutch. Through it, the rotational movement is transmitted to the wheels of the car. Its main task is to ensure uniform rotation without shocks. The torque converter consists of large wheels with blades immersed in torque converter oil. The transmission of torque is not carried out at the expense of mechanical device, but with the help of oil flows and pressure. The torque converter also houses a reactor responsible for smooth and high-quality changes in torque on the wheels of the car.
planetary gear, which contains a set of speeds. It locks some gears and unlocks others, determining the choice of gear ratio.
A set of clutches and brake mechanisms, responsible for the transition between gears and gear selection. These mechanisms block and stop the elements of the planetary gear.
Control devices (hydroblock) - controls the device. It consists of an electronic unit in which the box is controlled, taking into account all factors and sensors that collect information (speed, mode selection).
How does an automatic transmission work?
When the engine is started, oil is supplied to the torque converter, the pressure begins to increase. The pump wheel begins to move, the reactor and the turbine are stationary. When you turn on the speed and supply gasoline using the accelerator, the pump wheel starts to rotate faster. Flows of oil start spinning turbine wheel. These streams are either thrown to the stationary reactor wheel, then returned back to the turbine wheel, increasing its efficiency. The moment from the rotation is transmitted to the wheels and the car moves off. Upon reaching desired speed the pump and turbine wheels move alone quickly, while the oil flow enters the reactor from the other side (the movement occurs only in one direction) and it begins to rotate. The system goes into fluid coupling mode. If the resistance on the wheels increases (uphill), the reactor stops rotating again and enriches the pump wheel with torque. During the achievement of the required speed and torque, a gear change occurs. The electronic control unit gives a command, after which the brake band and clutches slow down the downshift, and the increasing oil pressure through the valve accelerates the upshift, due to this, switching occurs without loss of power. When the engine is stopped or the speed is reduced, the pressure in the system decreases and the reverse switching occurs. When the engine is off, the torque converter is not under pressure, so starting the engine from the “pusher” is not possible.
Advantages and disadvantages
Compared to manual transmissions, automatic transmissions have significant advantages:
- it is easier and more comfortable to drive a car with automatic transmission, the driver does not need additional skills and reflexes, gear changes are smoother, which is especially important for moving around the city;
- the engine and leading parts of the car are protected from overloads and their resource increases;
- the resource of many automatic transmissions significantly exceeds the similar resource of manual transmissions. With timely maintenance, the need for repairs occurs less frequently.
There are no consumable parts, such as, for example, a clutch disc or a cable, and it is much more difficult to disable an automatic transmission. The resource of the automatic transmission of the American and Japanese made, with modern maintenance can reach a million kilometers.
There is an opinion that cars with automatic transmission have slightly higher fuel consumption. Cars until the end of the 20th century often had incorrectly chosen moments and a limited number of speeds (2–3). On modern automatic transmissions, the number of gears is at least 4–5 (up to 19 on trucks). Modern computer automation copes with the choice of torque and speed in no way worse driver. In addition, fuel consumption on cars with manual transmission is highly dependent on the driving style and professional skills of the driver. Modern automatic transmissions have many modes, they are adapted to the driving style of the car owner.
A serious disadvantage of automatic transmission is the impossibility of accurate and safe gear shifting in extreme conditions- when overtaking, leaving a snowdrift by quickly shifting reverse and first gear (buildup), starting the engine "from the pusher". However, most city dwellers will choose comfortable traffic jams instead of the capabilities of a “smart” driver.
The second misconception of motorists is that automatic transmissions are not designed for driving a car in racing and off-road conditions. Civilian automatic transmissions are really not designed for sports driving and skid control - they do not have adequate cooling for such loads, and shift points are chosen for calm driving in urban conditions. However, automatic transmission equipped additional cooling and reconfigured for fast gear shifting will show best results than manual transmission. Formula 1 cars are equipped with automatic transmission and cope with very fast movement better than racing cars with manual transmission. long, controlled skids are also possible. off-road vehicles For a long time they have been equipped with machine guns, which do not affect patency in any way. Most drivers simply don't understand how an automatic transmission works.
Features and capabilities
Automatic transmission allows you to better control the car, reducing the demands on the driver's action - clutch and shift knob control, makes driving less tiring. The automatic transmission has a neutral position, a parking position (the rotation of the box is additionally blocked with the help of units), a reverse gear and several speeds for movement. Switching is carried out based on the speed and conditions (for example, when driving on an incline, a reduced speed may automatically turn on). The shift time of a serviceable transmission for city cars is around 150 ms, which is much faster than the reaction of an ordinary driver.
The main control of the automatic transmission is the gear shift knob, it can be located in the steering wheel area (old American and Japanese sedans or modern minivans) or at the traditional location of the automatic transmission lever. On older luxury models, the box could be controlled using a keypad.
To avoid accidental switching or dangerous situations, in the automatic transmission, various types of protection are used. In cars with automatic transmission, the engine cannot be started if the selector is in the speed position. Switching modes is carried out using the button for floor lever layouts, or pulling the lever when located on the steering wheel. The car can be removed from the parking lot only when the brake is pressed. In some cases, the slot is made in the form of steps.
Common modes of automatic transmission:
P - parking, automatic transmission is mechanically blocked, when you are in horizontal surfaces, the use of the parking brake is optional.
N - neutral. You can tow your car.
L (D1, D2, S) - driving in low gear (1st gear or 2nd gear).
D - automatic switching mode from first to last speed.
R - mode reversing. In addition, an overdrive button may be present on the automatic transmission, which prohibits the transition to more high gear when overtaking.
Neutral is usually located between D and R, or R is at the opposite end of the selector lever. This requirement was introduced to avoid accidents on the road and parking.
Also in the automatic transmission may be present various modes and work protocols. Eco - economical mode, implemented differently for different companies.
*Snow(Winter) - starting from second or third gear for slippery pavement or moving in snow or mud.
*Sport(Power) - shifts gears at higher engine speeds.
* ShiftLock (button or key) - unlocking the selector when the engine is off, used to transport the car if the engine or battery is out of order.
Some automatic transmissions have a mode manual switching gears. The most successful and common version of such an automatic transmission was Tiptronic, created by Porsche. hallmark is a control body, it is made in the form of the letter H and has the symbols "+" and "-".
In addition to Tiptronic, automatic transmissions include a variator and a robotic gearbox.
Features of a car with an automatic
Device automatic box transmission is more complex than manual transmission. Automatic transmission repair is much more difficult - it consists of where more spare parts. Usually, automatic transmission malfunctions are indicated by kicks and pauses when shifting gears, reverse gear or one of the speeds may disappear altogether. Otherwise, the vehicle may stop moving.
Automatic transmission diagnostics is usually carried out in several stages:
Visual oil control. If the oil is black or contains metal fragments in its composition, this indicates internal damage or wear of the automatic transmission. It is necessary to change the oil in the automatic transmission, which can solve most of the problems.
Diagnosis of errors using the diagnostic connector. The electronic controls of the box (sensors, computer) could fail, after which the box cannot function normally.
Test drive of the automatic transmission, for this they study the behavior of the box while driving.
Pressure measurements in each mode of automatic transmission.
Inspection of the internal state of the automatic transmission.
Do-it-yourself automatic transmission repair can only mean items 1 to 3 of this list. For other operations, you need warm box, special equipment and experienced professional. The last operation will require a lift, a crane and a whole set of tools. Removing, installing and replacing an automatic transmission is one of the most difficult and time-consuming car repairs. Repairing the internals of an automatic transmission can be comparable in cost to installing a new or contract box. It will be better if automatic transmission diagnostics and repairs are carried out by specialists.
To avoid such troubles, it is necessary to monitor the level and color of the oil in the box and change it in a timely manner (when it is written in the regulations). For different automatic transmissions apply various oils described in vehicle literature. Honda cars use their own special oil, if you fill in another box, it may fail.
It is necessary to operate the machine as carefully as possible, avoiding slippage, constant sudden braking and acceleration.
In the cold season, the machine must be given time to saturate with thickened oil. To do this, you need to warm up the car, turn on the gear and stand on the brakes for at least a minute, after which you can move off.
For most people, following this kind of simple operation will not cause problems. In their case, the automatic transmission will serve them for a very long time. Modern automatic transmissions are very reliable in design, they are not much more expensive than their mechanical counterparts, they give a feeling of comfort behind the wheel and make the life of any driver much easier.
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 to optimal speed engine depending on the selected driving mode.
Automatic transmission was invented in America, from where it became widespread. Currently in the US, and many European countries The popularity of manual transmissions is not very high; they are used by about 5% of drivers. However, the demand for cars with automatic transmission in Russia is constantly growing and today they are equipped with automatic transmission.
All automatic transmissions can be divided into several main types:
- Variators;
- Hydraulic automatic transmissions;
Hydraulic automatic transmission
The automatic transmission, based on the operation of a torque converter, has been seriously modified at the request of the Europeans and at the moment has received several operating modes (winter, sports, economical) corresponding to each.
also in classic slot machines the number of transmissions also increases. 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 bladed machines: a centripetal turbine, centrifugal pump. Among other things, the torque converter contains a reactor wheel, a clutch freewheel(overrunning clutch), blocking clutch. The impeller provides connection to crankshaft engine, and the turbine wheel - with a 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 (sprag clutch) provides rotation in reverse side reactor wheel.
Design mechanical box gears much easier allows 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;
- drove
Rotation is transmitted under the condition that one or two elements are blocked planetary gear. 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 we compare the variator with other automatic transmissions, then its advantage lies in the efficient use of engine power, because the speed crankshaft optimally coordinated with the load on your car, thanks to this, quite high fuel economy is ensured. 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 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 mechanism makes it rotate output shaft 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 the 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
General device robotic box gears:
- 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. Robotic automatic transmission may have either an electric drive of the clutch and gears, or a hydraulic one. Let's look at the advantages and disadvantages, as well as how each works. Electric motor and mechanical transmission 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 hydraulic drive performed by hydraulic cylinders controlled by solenoid valves, using high energy costs and having more fast speed gear changes (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. Having double clutch, you can select the next gear when the gear is on, and in right moment time to turn it on 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 executive mechanisms. 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.
You can also slow down other elements, as well as swap the 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, short video about 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 cross-sections are selected in such a way that at speeds idle move 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 angular velocities of the impeller and turbine are aligned, the blocking connects them into a single whole, 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 hydraulic system of the gearbox is automatic - ATF oil, provides lubrication, cooling, shifting and connection of the transmission to 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 probe.
As pressure source in automatic transmission internal gear pumps are used. The advantage of internal gear pumps is high power pump, especially at low speeds.
The benefit of the scientific and technological revolution primarily lies in the fact that all high tech and novelties from inventors make our life not only easier, but also more comfortable. The auto industry also does not stand still, and every year motorists receive such “sweets” as navigators, electronic systems monitoring the operation of vehicle components, correctors octane number and even autopilots, which in the future will help cars maneuver independently in close traffic. But when it comes to comfort, an automatic transmission immediately comes to mind - it was the automatic transmission that made life easier for motorists who do not want to enter into a “marriage contract” with capricious mechanics.
Automatic transmission has made life easier for drivers
Photo
In textbook terms, an automatic transmission, or automatic transmission, is a type of transmission that provides automatic (in other words, without driver intervention) selection of a gear ratio that corresponds to the prevailing driving conditions. The main difference between an “automatic” and a manual transmission is that the driver can make life much easier for his right hand. From the point of view of the design of the automatic transmission, it also differs in the action of its mechanical part - this means the use of a hydromechanical drive and planetary mechanisms. That is why professionals always say "automatic transmission", this term more accurately conveys its essence than the definition of "automatic transmission".
"Automatic" digression into history
For the fact that today we can enjoy a classic example of a hydromechanical transmission, we have to thank several independent lines of development, united together.
In order to get to the bottom of the truth in this whole story with automatic transmission, you should delve into the Ford T, which was used in the design of the planetary mechanical transmission. No, in the early days of the automotive industry, the driver still had to have certain skills, but this was already a significant simplification of the game called “car taming”. And if you consider that at that time the bulk of the cars were equipped with traditional boxes, devoid of synchronizers, then this was a real breakthrough.
The first automatic transmissions were installed on such beauties
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The second important invention that gave us the automatic transmission was the development of the American companies General Motors and Reo, which in the 30s of the last century brought semi-automatic transmissions to the market. But the reliability of these systems was still very far from ideal, and the clutch was still used to shift gears.
And, finally, in the same 1930s, the transmission was first introduced hydraulic element. Such transmissions began to be massively installed on Chrysler cars already in the post-war years. Later, the fluid coupling was replaced by a torque converter. But if you want to know who has the upper hand in installing a fully automatic transmission in their cars, then this was Company General Motors, which in the 40s of the twentieth century equipped their Oldsmobiles, Cadillacs and Pontiacs with them.
Lexuc LS 460 - happy owner of an eight-speed "automatic"
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And when in 2007 Toyota introduced the Lexus LS460, the design of which provided for an eight-speed automatic transmission, everyone understood that perfection has no limit. At least the one we could see today.
Device "machine": comfortable subtleties
The main parts of a traditional automatic transmission are a torque converter, planetary gears, friction and overrunning clutches, as well as connecting shafts and drums. In addition, in some cases, a brake band is also used, the purpose of which is to slow down one of the drums. The only exceptions are "automatic" Honda, instead of a planetary gearbox, using shafts with gears, as is done in the case of a manual gearbox.
Automatic transmission is a rather complicated device.
Photo
The main function performed by the torque converter is that when starting the car, it transmits the moment with slippage. When the engine picks up high revs, friction clutch blocks the torque converter and makes it impossible to slip. As for the planetary gearbox, its main task is to transmit torque indirectly.
Friction clutches, which are often called a "package", serve to shift gears by disengaging and communicating the elements of the box.
Automatic transmission device
Photo
The main difference between the “automatic” and the “mechanics” is that the manual transmission turns on and off different gears to get different output shafts. gear ratios, and the automatic transmission always uses the same set of gears. This is exactly what the planetary gear allows for automatic transmission.
Auto repair is best left to the professionals.
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Modes of operation of the "machine"
Since the late 50s of the last century, almost every automatic transmission has standard set operating modes, which are indicated in Latin letters on the shift lever:
▪ « N"(from the English. "neutral") - mode neutral gear, which, as a rule, is used during towing or when parking for a short time (in the domestic version - “H”);
▪ « D"(from the English" drive ") - the mode of movement forward, when all steps are involved, or all except those that increase gears (in the domestic version - "D");
▪ « R"(from the English. "reverse") - reverse mode, which under no circumstances should be turned on until the car has completely stopped (in the domestic version - "Zx");
▪ « L"(from the English. "low") - a low gear mode used for "quiet running" (in the domestic version - "PP" or "Tx");
▪ « R”(from the English“ park ”) - parking lock mode for the drive wheels (this locking system is not connected with the parking brake and is located directly inside the automatic transmission).
Since the middle of the twentieth century, automakers have begun to use a strict sequence of operating modes of the "machine" - P-R-N-D-L.
Standard layout of "automatic" modes
Photo
In addition to the main modes, there are often additional ones:
▪ « O/D"(from the English. "overdrive") - a driving mode that provides for the possibility of switching to an overdrive in automatic mode (this mode is very convenient to ensure that the movement on the highway is uniform);
▪ « D3"- a mode that uses only first, second or third gears, or disables overdrives (convenient for city driving);
▪ « S” (the number “2” is also used) - mode low gears or " winter mode»;
▪ « L"(The number "1" is also used) - a low gear mode, when turned on, only the first gear works.
You must always remember that the "automatic", unlike the "mechanics", can not slow down the engine in all modes. The automatic transmission knows when engine braking is inhibited, and so the freewheel transmission slips, allowing the car to coast. The same principle is used in bicycles.
This article continues a series of publications on electrical protection apparatus- circuit breakers, RCDs, difautomats, in which we will analyze in detail the purpose, design and principle of their operation, as well as consider their main characteristics and analyze in detail the calculation and selection of electrical protection devices. This cycle of articles will be completed by a step-by-step algorithm, in which the complete algorithm for calculating and selecting circuit breakers and RCDs will be briefly, schematically and in a logical sequence considered.
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Well, in this article we will understand what a circuit breaker is, what it is intended for, how it works and consider how it works.
Circuit breaker(or usually just "automatic") is a contact switching device that is designed to turn on and off (i.e. for switching) electrical circuit, protection of cables, wires and consumers (electrical appliances) from overload currents and from currents short circuit.
Those. The circuit breaker performs three main functions:
1) circuit switching (allows you to turn on and off a specific section of the electrical circuit);
2) provides protection against overload currents by turning off the protected circuit when a current exceeding the allowable current flows in it (for example, when a powerful device or devices are connected to the line);
3) disconnects the protected circuit from the supply network when large short-circuit currents occur in it.
Thus, the automata simultaneously perform the functions protection and features management.
According to the design, three main types of circuit breakers are produced:
— air circuit breakers (used in industry in circuits with high currents of thousands of amperes);
— molded case circuit breakers (designed for a wide range of operating currents from 16 to 1000 Amperes);
— modular circuit breakers , the most known to us, to which we are accustomed. They are widely used in everyday life, in our houses and apartments.
They are called modular because their width is standardized and, depending on the number of poles, is a multiple of 17.5 mm, this issue will be discussed in more detail in a separate article.
We, on the pages of the site, will consider exactly modular circuit breakers and residual current devices.
The device and principle of operation of the circuit breaker.
The thermal release does not operate immediately, but after some time, allowing the overload current to return to its normal value. If during this time the current does not decrease, the thermal release trips, protecting the consumer circuit from overheating, melting of the insulation and possible ignition of the wiring.
An overload can be caused by connecting powerful devices to the line that exceed the rated power of the protected circuit. For example, when a very powerful heater or electric stove with an oven is connected to the line (with a power exceeding the rated power of the line), or several powerful consumers at the same time (electric stove, air conditioner, washing machine, boiler, electric kettle, etc.), or a large number of simultaneously switched on appliances.
Short circuit the current in the circuit instantly increases, the magnetic field induced in the coil according to the law of electromagnetic induction moves the solenoid core, which activates the release mechanism and opens the power contacts of the circuit breaker (i.e. moving and fixed contacts). The line opens, allowing you to remove from emergency circuit power supply and protect the machine itself, the electrical wiring and the shorted electrical appliance from fire and destruction.
The electromagnetic release trips almost instantly (about 0.02 s), unlike the thermal one, but at much higher current values (from 3 or more rated current values), so the wiring does not have time to heat up to the melting temperature of the insulation.
When the contacts of the circuit are opened, when it passes through electricity, an electric arc occurs, and the greater the current in the circuit, the more powerful the arc. The electric arc causes erosion and destruction of the contacts. To protect the contacts of the circuit breaker from its destructive action, the arc that occurs at the moment of opening the contacts is directed to arc chute (consisting of parallel plates), where it is crushed, damped, cooled and disappears. When the arc burns, gases are formed, they are discharged outward from the body of the machine through a special hole.
The machine is not recommended to be used as a conventional circuit breaker, especially if it is turned off when a powerful load is connected (i.e. when high currents in the circuit), as this will accelerate the destruction and erosion of the contacts.
So let's recap:
- the circuit breaker allows you to switch the circuit (by moving the control lever up - the machine is connected to the circuit; moving the lever down - the machine disconnects the supply line from the load circuit);
- has a built-in thermal release that protects the load line from overload currents, it is inertial and works after a while;
- has a built-in electromagnetic release that protects the load line from high short-circuit currents and works almost instantly;
- contains an arc quenching chamber, which protects the power contacts from the damaging effects of an electromagnetic arc.
We have analyzed the design, purpose and principle of operation.
In the next article, we will look at the main characteristics of the circuit breaker that you need to know when choosing it.
See The design and principle of operation of the circuit breaker in video format:
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