automatic box gears - automatic transmission, a mechanism for changing the gear ratio of the transmission, which works without the direct participation of the driver. A car equipped with an automatic transmission has a reduced number of control devices, instead of three pedals (“gas”, brake and clutch) it has two pedals (“gas” and brake, there is no clutch release pedal). At the same time, the “gas” pedal does not serve to increase or decrease engine speed, as in a car with a manual gearbox, but to change the speed of the car. Unlike a manual gearbox, an automatic transmission is not equipped with a shift lever, but with an operating mode selector.
According to the device, automatic transmissions are divided into ordinary two and three-shaft manual gearboxes, supplemented by a torque converter (instead of a dry clutch) and an automatic shift system (with electronic, electromechanical or electropneumatic control), and on planetary, in which the planetary gearbox is paired with a torque converter. The most typical are planetary automatic transmissions with a torque converter.
Device
A planetary automatic transmission consists of a torque converter, a planetary gearbox (planetary gearboxes), drums, friction and overrunning clutches, connecting shafts. Automatic transmission drums are equipped with belt brakes to stop them and engage the desired gear of the planetary gearbox.
torque converter in automatic transmission performs the functions of a clutch and is installed between the crankshaft of the engine and the gearbox. The torque converter consists of driving and driven turbines and a stator fixed relative to the engine (sometimes the stator is rotating, in which case it is equipped with a band brake - the use of a movable stator adds flexibility to the torque converter at low engine speeds and improves its performance). The drive turbine rotates, as does the clutch drive, at the same frequency as crankshaft engine. The driven turbine rotates due to hydrodynamic forces arising from the viscosity of the liquid filling the internal cavity of the torque converter. The main purpose of the torque converter is to transfer the rotation of the crankshaft to the gears of the planetary gearbox with slip, which ensures smooth switching gears and start moving the car. At high engine speeds, the driven turbine is blocked and the torque converter is turned off, transferring torque from the crankshaft to the gears of the automatic transmission directly (respectively, losses).
Planetary gearbox or planetary gearbox - a complex of a large ring gear (epicycle), a small sun gear and satellite gears connecting them, mounted on the carrier. IN different modes During the operation of the gearbox, different gears rotate, and one of the blocks (epicycle, sun gear or planet carrier) is fixed motionless.
Automatic transmission scheme: 1 - turbine wheel;
2 - pump wheel;
3 - reactor wheel;
4 - reactor shaft;
5 - input shaft planetary gearbox;
6 - main oil pump;
7 - clutch II and III gears:
8 - brake I and II gears;
9 - clutch III gear and reverse gear;
10 - clutch freewheel I transfer;
11 - reverse brake;
12 - the first intermediate shaft;
13 - the second intermediate shaft;
14 - a drum with a gear rim;
15- centrifugal regulator;
16 - secondary shaft;
17 - gear shift mechanism;
18 - throttle valve;
19 - cam
Friction clutches are designed to shift gears by engaging (or, conversely, disengaging) the gears of the automatic transmission planetary gearbox. The coupling consists of a hub (hub) and a drum. On the outer surface of the hub and the inner drum there are rectangular teeth (on the hub) and the same splines (inside the drum), which correspond in shape to each other, but are not engaged. Between the hub and the drum is a set (package) of annular friction discs. Half of the disks are made of metal and equipped with protrusions included in the slots of the inner surface of the drum. The second half of the disks is made of plastic and has cutouts into which the teeth of the hub enter. Thus, the mechanical coupling of the hub and the drum occurs through the friction of the metal and plastic disks of the friction clutch package.
The communication and disengagement of the hub and the friction clutch drum occurs after the disk pack is compressed by an annular piston installed inside the hub. The piston is hydraulically driven. Fluid is supplied to the drive cylinder under pressure through annular grooves in the drum, shafts and crankcase of the automatic transmission.
The overrunning clutch is used to reduce shock loads on friction clutches when shifting gears and to turn off the engine when the vehicle is coasting (in some modes AKP work). The overrunning clutch is designed in such a way that it slips freely when rotating in one direction and jams when rotating in the opposite direction (transferring torque to the parts of the automatic transmission). It consists of two rings - outer and inner - and a set of rollers located between them, separated by a separator. After an increase in engine speed and an automatic transmission gear change, one of the planetary gear blocks tends to rotate in the opposite direction - the overrunning clutch jams this block, preventing reverse rotation.
The principle of operation of the automatic transmission
Consider the operation of a four-speed automatic transmission equipped with two planetary gears.
First gear. The sun gear of the first planetary gear set is not connected to the engine, the first row is not involved in the transmission of torque. The sun gear of the second row is connected to the engine crankshaft (let's add - through a torque converter). Carrier with satellites of the second planetary gear set is connected to the gearbox output shaft. The epicycle (the largest ring gear) of the second row at low engine speeds scrolls through the overrunning clutch, torque is not transmitted to the transmission mechanisms. As soon as the engine speed increases, the overrunning clutch blocks the ring gear - the transmission of torque through the satellites and carrier begins. The car pulls away and starts moving.
Second gear. The first row sun gear is locked and stationary. The carrier with satellites of the first row engages with the epicycle of the second row through a freewheel. The epicycle of the first row engages with the carrier of the second row, which is connected to the gearbox output shaft. Torque from the engine is transmitted through the second row sun gear. Both planetary gear sets of the gearbox operate in this mode.
third gear. The gears of the first row do not take part in the transmission of torque. The second row sun gear and the second row epicycle are connected to the input shaft, the torque is transmitted by the planet carrier to the output shaft. There is no torque conversion - the automatic transmission operates in direct transmission mode.
In 1st, 2nd and 3rd gears, the driver cannot brake with the engine. To ensure the possibility of engine braking, the overrunning clutch is blocked by a friction clutch. Then, when the “gas” pedal is released, the gears of the box will not separate the transmission mechanisms from the engine.
fourth gear. This is an overdrive mode when the transmission ratio is greater than one. The first row sun gear is stopped. The torque is transmitted to the carrier with satellites of the first planetary gear set. The epicycle of the first row engages with the carrier of the second row, which, in turn, transmits torque to the transmission mechanisms. The sun gear and the epicycle of the second row are not involved in the transmission of torque.
Reverse. The first row sun gear is connected to the engine crankshaft. The carrier of the second row is blocked by a friction clutch. The epicycle of the first row engages with the carrier of the second row, which, in turn, is connected to the output shaft. The output shaft rotates in the opposite direction.
Automatic transmission control systems
The automatic transmission operating modes control system is made in the form of hydraulic drives that transfer oil pressure from the hydraulic pump to the pistons of the actuators friction clutches and brake bands of drums. The oil flow in the oil lines is redistributed by spools, which are controlled either manually by the position of the automatic transmission selector, or automatically. Block automatic control Automatic transmission can be hydraulic or electronic.
The "classic" automatic transmission is controlled by a hydraulic mechanism, which consists of centrifugal regulator fluid pressure mounted on the output shaft of the motor and pressure sensor hydraulic drive gas pedals. The spools move under the pressure of both hydraulic circuits, which allows the automatic transmission to shift gears in accordance with the engine speed and the position of the gas pedal.
In the electronic automatic control system, instead of the hydraulic drive of the spools, an electromechanical one is used - the spools are moved by solenoids. The commands to move the spools are given by the electronic control unit, in modern cars - by the central on-board computer of the car. The same computer usually controls both the ignition system and fuel injection. The electronic control unit receives commands to move the spools from the speed sensor of the engine output shaft and the position of the "gas" pedal. You can also change gears in manual mode by moving the selector to the desired position.
Most modern automatic transmissions provide manual control of the box even after a complete failure of the electronic control system. In this case, in any case, you can manually turn on the direct (third according to the four-stage scheme described above) transmission, and if the electrical mechanical part control systems - all transmissions by manual transfer of the selector.
AKP selector
In the 50s of the last century, the “PRNDL” selector became the generally accepted standard for the automatic transmission control system - by listing the order in which automatic gearbox modes are switched on. It was this sequence that was recognized as the safest and most rational from the point of view of the automatic transmission design.
Automatic transmission operating modes - switch selector positions.
P - parking mode. The engine is disconnected from the transmission. The automatic transmission is blocked by an internal mechanism and is connected to the transmission, which ensures that all transmission mechanisms are blocked. At the same time, the AKP is in no way connected with parking brake and does not eliminate the need for its use in parking lots.
R - reverse mode. In all modern automatic transmissions, the selector in this position is supplemented with a locking mechanism that prevents accidental engagement of reverse gear when the vehicle is moving forward.
N - neutral mode AKP. It is activated during stops, coasting, towing.
D - main mode work of the automatic transmission ("Drive"). All stages of the automatic transmission are engaged (usually also an overdrive, which otherwise can be switched on by an additional position of the selector lever marked "2" or "D2").
L - low gear mode, which is used for off-road driving and on steep slopes.
This procedure for switching the automatic transmission selector was enshrined in the United States by law in 1964. Deviation from this standard is considered unacceptable from the point of view of vehicle safety.
Section of a six-speed preselective Volkswagen automatic transmission Direct Shift Gearbox.
Automatic transmission(Also automatic transmission, automatic transmission) - a type of car gearbox that provides automatic (without the direct participation of the driver) selection of the gear ratio corresponding to the current driving conditions, depending on many factors.
In recent decades, along with classic hydromechanical automatic transmissions, various options for automated manual transmissions (“robotics”) are also offered. electronic control and electromechanical or electropneumatic actuators.
Story
Three initially independent lines of development led to the emergence of the classic hydromechanical transmission, which were subsequently combined into its design.
The earliest of these can be considered used on some early car designs, including the Ford T - planetary mechanical transmissions. Although still requiring a certain skill from the driver for the timely and smooth engagement of the corresponding gear (for example, on a two-stage planetary Ford transmissions T this was done with the help of two foot pedals, one shifted the lower and higher gears, the second turned on the reverse), they already made it possible to significantly simplify his work, especially in comparison with the traditional type gearboxes used in those years without synchronizers.
Chronologically, the second direction of development, which subsequently led to the emergence of an automatic transmission, can be called work on the creation of semi-automatic transmissions, in which part of the gear shifting was automated. For example, in the mid-1930s, the American firms Reo and General Motors almost simultaneously introduced semi-automatic transmissions of their own design. Most interesting was the GM-designed transmission: like the later fully automatic transmissions, it used a planetary gear that was hydraulically controlled depending on the speed of the car. However, these early designs were not reliable enough, and most importantly, they still used the clutch to temporarily decouple the engine and transmission when shifting gears.
The third line of development was the introduction of a hydraulic element into the transmission. Chrysler Corporation was the clear leader here. The first developments date back to the 1930s, but such a transmission received mass distribution on cars of this company already in the last pre-war and post-war years. In addition to the introduction of a hydraulic clutch (later replaced by a torque converter), it differed in that, in parallel with a two-stage conventional manual gearbox, an automatically engaged overdrive (overdrive with a gear ratio of less than one) worked in it. Thus, although from a technical point of view it was a manual transmission with hydraulic element and overdrive, the manufacturer declared it as a semi-automatic.
She carried the designation M4 (on pre-war models, commercial designations - Vacamatic or Simplimatic) and M6 (since 1946, commercial designations - Presto-Matic, Fluidmatic, Tip-Toe Shift, Gyro-Matic and Gyro-Torque) and was originally a combination three units - hydraulic clutch, traditional manual gearbox with two steps forward, and automatically (on M4 vacuum, on M6 electric drive) of the overdrive being turned on.
Each block of this transmission had its own purpose:
- the hydraulic clutch made the car start smoother, allowed you to “throw the clutch” and stop without disengaging the gear or clutch. It was later replaced by a torque converter, which increased torque and significantly improved the dynamics of the car compared to a fluid clutch (which slightly worsened acceleration dynamics);
- a manual transmission served to select the operating range of the transmission as a whole. There were three operating ranges - lower (Low), upper (High) and reverse (Reverse). There were two gears in each range;
- the overdrive was automatically activated when the car exceeded a certain speed, thus shifting gears within the current range.
Switching the operating ranges was carried out by a conventional lever located on the steering column. Later versions of the derailleur mimicked automatic transmissions and had a range indicator quadrant above the lever, like an automatic transmission - although the gear selection process itself was not changed. A clutch pedal was present but used only for range selection and was painted red.
Get under way in ordinary road conditions It was recommended in the "High" range, that is, in the second gear of the two-speed manual gearbox and the third gear of the transmission as a whole, since the high torque of the multi-liter six- and eight-cylinder Chrysler engines allowed this. On the rise and when driving through the mud, it was necessary to start moving from the “Low” range, that is, from the first gear. After exceeding a certain speed (varied depending on specific model transmission) there was a switch to the second gear due to the automatic overdrive switching on (the manual transmission itself remained in the first gear). If necessary, the driver switched to the upper range, while in most cases the fourth gear was switched on immediately (since the overdrive was already on to receive the second gear) - it had a total gear ratio of 1: 1. Go through all available four gears with practical driving was almost impossible, although the transmission was formally considered a four-speed. The reverse gear range also included two gears and engaged as usual after the car came to a complete stop.
Thus, for the driver, driving a car with such a transmission was very similar to driving a car with a two-speed automatic transmission, with the difference that switching between the ranges occurred with the clutch pressed.
This transmission was installed from the factory or was available as an option on cars of all divisions of the Chrysler Corporation in the 1940s and early 1950s. After the introduction of the true two-speed PowerFlite automatic transmission, later the three-speed TorqueFlite, semi-automatic transmissions of the Fluid-Drive family were discontinued, as they interfered with the sales of fully automatic transmissions. The last year they were installed was 1954, this year they were available on the cheapest brand of the corporation - Plymouth. In fact, such a transmission became a transitional link from manual gearboxes to hydrodynamic automatic transmissions and served for “running in” technical solutions later used on them.
Also in the early 1940s, there was a three-speed transmission, designated Slushomatic, in which the first gear was conventional, and the second was combined into a single range with an automatically engaged third.
However, the world's first fully automatic transmission was created by another American company - General Motors. In the 1940 model year, this became available as an option on Oldsmobile cars, then Cadillac, and later Pontiac. She carried the commercial designation Hydra-Matic and was a combination of a fluid coupling and a three-speed planetary gearbox with automatic hydraulic control. In total, there were four forward steps in the transmission as a whole (plus reverse). The transmission control system took into account factors such as vehicle speed and position throttle valve. The Hydra-Matic transmission has been used not only in vehicles from all divisions of GM, but also on vehicles from brands such as Bentley, Hudson, Kaiser, Nash and Rolls-Royce, as well as some models military equipment. From 1950 to 1954, Lincoln cars were also equipped with the Hydra-Matic transmission. Subsequently, the German manufacturer Mercedes-Benz developed on its basis a four-speed transmission that is very similar in principle of operation, although it has significant design differences.
In 1956, GM introduced an improved Jetaway automatic transmission that featured the use of two fluid clutches instead of the Hydra-Matic's one. This made gear changes much smoother, but resulted in a large reduction in efficiency. In addition, a parking mode appeared on it (selector position “P”), in which the transmission was blocked by a special stopper. On the Hydra-Matic, the lockup included reverse mode "R".
since 1948 model year On Buick cars (a brand owned by GM), a two-speed Dynaflow automatic transmission became available, distinguished by the use of a torque converter instead of a fluid coupling. Subsequently, similar transmissions appeared on Packard (1949) and Chevrolet (1950) cars. As conceived by their creators, the presence of a torque converter, which has the ability to increase torque, compensated for the lack of a third gear.
Already in the early 1950s, three-speed automatic transmissions with a torque converter developed by Borg-Warner appeared. They and their derivatives have been used on vehicles from American Motors, Ford, Studebaker and others, both in the US and abroad, such as International Harvester, Studebaker, Volvo and Jaguar. In the USSR, many of the ideas incorporated in its design were used in the design of automatic transmissions. Gorky Automobile Plant installed on the Volga and Chaika cars.
In 1953, Chrysler also introduced its two-speed PowerFlite automatic transmission. Since 1956, a three-stage TorqueFlite became available in addition to it. Of all the early developments of automatic transmissions, Chrysler models are often called the most successful and perfect.
In the mid-1960s, the modern automatic transmission switching scheme, P-R-N-D-L, was finally approved and (in the USA) legally fixed. Gone are push-button range shifters and older non-parking lock transmissions.
By the mid-1960s, early examples of two- and four-speed automatic transmissions in the United States had almost universally fallen into disuse, giving way to three-speed with a torque converter. Fluid for automatic transmissions was also improved - for example, since the late 1960s, scarce whale blubber was excluded from its composition, replaced by synthetic materials.
In the 1980s, increasing demands on the economy of cars led to the emergence (more precisely, the return) of four-speed transmissions, in which the fourth gear had a gear ratio of less than one (“overdrive”). In addition, blocking on high speed torque converters, which make it possible to significantly increase the efficiency of the transmission by reducing the losses that occur in its hydraulic element.
In the late 1980s-1990s, computerization of engine control systems took place. The same systems, or similar ones, began to be used to control automatic transmissions. Whereas earlier control systems used only hydraulics and mechanical valves, now computer-controlled solenoids control fluid flows. This made it possible both to make shifts smoother and more comfortable, and to improve efficiency by increasing the efficiency of the transmission. In addition, on some cars there are “sports” transmission modes, or the ability to manually control the gearbox (“Tiptronic” and similar systems). The first five-speed automatic transmissions appear. Perfection Supplies allows many automatic transmissions to eliminate the oil change procedure, since the resource of the oil poured into its crankcase at the factory has become comparable to the resource of the gearbox itself.
In 2002, a six-speed automatic transmission developed by ZF (ZF 6HP26) appears on the BMW seventh series. In 2003 Mercedes-Benz creates the first seven-speed 7G-Tronic transmission. IN 2007 year Toyota introduced the Lexus LS460 with an eight-speed automatic transmission.
Design
Traditional automatic transmissions consist of a torque converter, planetary gears, friction and overrunning clutches, connecting shafts and drums. Also, sometimes a brake band is used, which slows down one of the drums relative to the automatic transmission case when a particular gear is engaged. The exception is the Honda automatic transmission, where the planetary gearbox is replaced with shafts with gears (as on a manual gearbox).
The torque converter is structurally installed in the same way as the clutch on a transmission with a manual gearbox - between the engine and the automatic transmission itself. The torque converter housing with the drive turbine is attached to the engine flywheel, as is the clutch basket. The main role of the torque converter is to transmit torque with slippage when starting off. On high revs engine (and usually in 3-4 gears), the torque converter is usually blocked by a friction clutch inside it, which makes slippage impossible and eliminates the energy (and fuel consumption) spent on viscous oil friction in the turbines.
The torque converter consists of three turbines - input (made integral with the housing), output and stator. The stator is usually silently braked to the automatic transmission case, but in some versions, the stator braking is switched on by a friction clutch in order to maximize the use of the torque converter in the entire speed range.
Various automated "robotic gearboxes" also exist. There are currently two generations of robotic boxes. The first generation is a compromise between a manual and automatic transmission in which there are units traditional for manual gearboxes (not controls) - a clutch and a gearbox with a mechanical drive, but they are controlled by electronics. They do not provide the proper smoothness of gear changes due to a sharp interruption of torque and insufficiently perfect automation. Their reliability is also not very high yet. These are boxes made by Aisin Seiki: Toyota Multimode and Magneti Marelli: Opel Easytronic, Fiat Dualogic, Citroën Sensodrive, as well as Ricardo, mounted on sports cars- Lamborgini, Ferrari, Maserati, etc.
On this moment robotic boxes with one clutch (for compact cars) are almost universally discontinued. They are still on some Opel models and Fiat and probably, with a restyling of models, will be replaced by high-speed 6-speed planetary, Aisin type Seiki AWTF-80SC. This box is already used in Alfa Romeo, Citroën, Fiat, Ford, Lancia, Land Rover/Range Rover, Lincoln, Mazda, Opel/Vauxhall, Peugeot, Renault, Saab and Volvo vehicles. This box is for front wheel drive vehicles with torque up to 400 N/m (6500 rpm), making it suitable for turbocharged and diesel engines.
The second generation of robotic gearboxes is called the preselective gearbox. The most famous representative of this type is Volkswagen DSG (developed by Borg-Warner), it is also on the Audi S-tronic, as well as Getrag Porsche PDK, Mitsubishi SST, DCG, PSG, Ford Dualshift. A feature of this gearbox is that there are two separate shafts for even and odd gears, each of which is controlled by its own clutch. This allows you to pre-switch the gears next transfer, and then almost instantly shift the clutch, while breaking the torque does not occur. This type automatic transmission is currently the most advanced in terms of economy and shifting speed.
Tiptronic
TipTronic is a semi-automatic automatic transmission mode pioneered by Porsche. In Russia, the word "tiptronic" is often used to name all similar designs from other manufacturers, although it is a Porsche trademark (other manufacturers call similar designs differently).
In this mode, gear selection is carried out by the driver manually by pushing the selector lever in the “+” and “–” directions - switching to next broadcasts up and down. In the canonical design, only downshifting is automatically performed when the engine speed drops to idle. Transmissions from a number of manufacturers, in addition, automatically upshift when the maximum engine speed is reached. Mechanically, the gearbox is the same as a conventional automatic transmission, only the selector lever and control automation have been changed. A sign of TipTronic-like automatic transmissions is an H-shaped cutout for moving the selector lever, as well as + and - symbols.
Automatic transmission selector positions
Kinds of selectors
The selector determines the mode of operation of the automatic transmission. The location of the selector lever may vary.
American car with paddle shifter automatic transmission.
On American-made cars until the 1990s, for the most part, the selector was located on the steering column, which made it possible to seat three people on a solid front sofa. To switch the transmission operating modes, it was necessary to pull it towards you and move it to the desired position, which was indicated by an arrow on a special indicator - a quadrant. Initially, the quadrant was placed on the casing of the steering column, later it was transferred to the instrument panel on most models.
Selectors located on the instrument panel next to the steering column and instrument panel can also be attributed to a close type, such as some Chrysler models of the 1950s or the previous generation Honda CR-V.
A typical modern automatic transmission selector
On European cars, the floor arrangement has traditionally been the most common.
On Japanese cars both options were met, depending on the target market - on cars for the domestic Japanese and American markets, and in our time, automatic transmission paddle selectors are found, while for other markets, floor selectors are almost exclusively used.
Currently, a floor selector is commonly used.
On minivans and commercial vehicles of wagon and half-bonnet layout, as well as some SUVs and crossovers with a high driving position, the selector on the instrument panel in the center (or high on the console) is quite common.
A mid-1950s Plymouth with a push-button automatic transmission selector (left side of instrument panel).
There are systems for selecting automatic transmission operating modes without a lever, in which buttons are used to switch - for example, on Chrysler cars of the late 1950s and early 1960s, Edsel, domestic "Seagull" GAZ-13, many modern buses(of the well-known in Russia, one can name urban models LiAZ, MAZ with Allison automatic transmission, which has a push-button selector).
If the system has a selector lever, the desired mode is selected by moving it to one of the possible positions.
To prevent accidental mode switching, special protection mechanisms are used. So, on cars with a steering column selector, to switch the transmission range, you need to pull the lever towards you, only after that it can be moved to the desired position. In the case of a floor lever, usually a lock button is used, located on the side under the driver's thumb (most models), on top (for example, on the Hyundai Sonata V) or in front (examples - Mitsubishi Lancer X, Chrysler Sebring, Volga Siber, Ford Focus II ) on the lever. Or to move it, you need to drown the lever a little. In other cases, the slot for the lever is stepped (many Mercedes-Benz models, Hyundai Elantra i30 platform or Chevrolet Lacetti, on the latter the slot is stepped, and the lever must be drowned to switch between driving modes (after D and P-R). Also, many modern models have a device that prevents the automatic transmission selector lever from being moved if the brake pedal is not depressed, which also increases the safety of handling the transmission.
Basic operating modes
As for operating modes, almost any automatic transmission has the following modes, which have become standard since the late 1950s:
- "R" (English) park) - parking lock (the drive wheels are locked, the lock is located inside the automatic transmission itself and is not connected with the usual parking brake);
- "R" (English) "Reverse"; on domestic models- "Зх") - reverse gear (it is unacceptable to turn on until the car stops completely, on modern transmissions there is often a blockage);
- "N" (English) "Neutral"; on domestic - "N") - neutral mode (turns on for a short stop and when towing a short distance);
- "D" (English) Drive; on domestic ones - “D”) - forward movement (as a rule, all stages are involved, or all, except for overdrive);
- "L" (English) "Low"; on domestic - "PP" (forcibly lowering), or "Tx") - downshift, “quiet running” (for driving in difficult road conditions).
Since the late 1950s, these regimes have been arranged in this sequence. In 1964, in the United States, it was enshrined as mandatory for use by the American Society of Automotive Engineers (SAE).
Previously tried to use other options, but it turned out to be inconvenient, even unsafe. For example, consumers accustomed to mechanical transmissions of those years with a paddle lever, in which it was necessary to pull the lever towards you and lower it down to engage first gear, accidentally turned on reverse and got into
The history of the creation of automatic transmission
The idea of creating a transmission with an automatic transmission arose at the beginning of the last century. Some cars had gearboxes very similar to those used on modern cars.
In Europe, Mercedes produced in 1914 a small batch of cars with a gearbox that can be called automatic.
In the late 1930s of the 20th century, firms such as Chrysler, Ford and GMC came close to mass production of cars with automatic transmission, and the first of these was GMC, which began installing automatic transmission in 1940.
Hydramatic for Oldsmobile and Cadillac vehicles. This transmission included a three-speed gearbox with a hydraulic shift control system.
Further development of automatic transmissions, up to the beginning of the 80s of the twentieth century, followed the path of improving production technology and improving the quality and reliability of the mechanical part of the automatic transmission. No fundamentally new solutions were used here.
In the same time hydraulic system automatic transmission control is constantly modernized. They sought to bring it to full perfection in order to ensure maximum comfort of a trip by car. An example is Mercedes, which for its automatic transmissions 722.3, 722.4, 722.5 has developed an original and unique in complexity hydraulic control unit circuit.
Starting in the 1980s, car manufacturers began to use an electronic automatic transmission control system. This was first done in 1983 by Toyota. Then in 1987, Ford also began using an electronic unit in A4LD transmissions to control the overdrive and torque converter lock-up clutch. In 1984, Chrysler introduced the ultra-modern transmissions A604 and A606 (41TE and 42LE) for front-wheel drive vehicles with a fully electronic and very progressive control system for that time. By 1991, GMC had developed the 4L60-E and 4T60-E transmissions, also with a fully electronic control system.
To date, two trends in the development of transmissions with automatic transmission can be distinguished.
One of them is characterized by a constant increase in the number of gears. In the early 80s of the twentieth century, the fourth (overdrive) gear appeared in automatic transmissions, which was caused by the need to significantly improve the fuel and economic performance of cars. At the same time, torque converter lockup was used to achieve the same goal. Then, in the early 90s of the same century, in order to improve dynamic characteristics cars, five-speed automatic transmissions were developed (another downshift appeared). In early 2001, the German company BMW began to install a six-speed automatic transmission from the company ZF-6HP26 on their cars. Here, unlike the five-speed automatic transmission, a second overdrive appeared. And finally, in recent years, companies such as Honda, Audi, Nissan, etc. have begun to actively use transmissions with continuously variable gear ratio (CVT).
In accordance with the second trend in the development of transmissions with automatic transmission, there is an improvement electronic block management and software. At first, these were simple systems, the task of which was to determine the moments of gear shifting and ensure the required quality of these shifts. Then there were programs that analyzed the driver's driving style and independently made a decision on the choice of a gearshift algorithm (sporty or economical). Later, a manual control function was added, which allowed the driver to independently determine the moments of gear shifting, as is the case with manual transmission. In addition, in parallel with the expansion of automatic transmission control capabilities, the self-diagnosis program was improved.
The idea of \u200b\u200bcreating an automatic transmission appeared almost simultaneously with the advent of a car equipped with. At the same time, automakers, inventors and enthusiasts from different countries started working on the unit.
As a result, already at the very beginning of the 20th century, prototypes began to appear that had a transmission similar to a modern automatic machine. In this article, we will talk about how the first automatic transmission was created and when it appeared, get acquainted with the history of automatic transmission, and also answer the question of who invented the automatic transmission.
Read in this article
Who invented the automatic transmission and when did the first automatic transmission appear
As you know, the transmission is the second most important unit after. At the same time, the appearance of an automatic transmission was a real breakthrough, since thanks to such a gearbox, not only comfort, but also safety when driving is significantly increased.
Such a gearbox is a system consisting of a torque converter () and a planetary box. The principles and foundations of the planetary gear were known in the Middle Ages, and the German Hermann Fettinger created the torque converter at the beginning of the 20th century.
The first to combine the box and the gas turbine engine American inventor Azatur Sarafyan, better known as Oscar Banker. It was he who patented the automatic transmission in 1935, although to obtain a patent for more than 7 years he defended his right in the fight against large automakers.
Sarafyan was born in 1895. His family ended up in the United States as a result of the infamous Armenian Genocide, which took place in Ottoman Empire. After settling in Chicago, Asatur Sarafyan changed his name to become Oscar Banker.
A talented inventor created various useful devices, among which there are several solutions that are indispensable today (for example, a grease gun), but its main achievement is the invention of the first automatic hydromechanical gearbox. In turn, General Motors (GM), which previously installed semi-automatic box gears on their models, the first to switch to automatic transmission.
The history of the creation of an automatic transmission
So, the most important element, thanks to which the emergence of a full-fledged automatic transmission became possible, is a torque converter.
Initially, the gas turbine engine appeared in shipbuilding. Reason - instead of low-speed steam engines towards the end of the 19th century, more powerful steam turbines. Such turbines were connected directly to the propeller, which inevitably led to a number of technical problems.
The solution was the invention of G. Fettinger, who proposed a hydraulic machine, where the impellers of the hydrodynamic transmission, the pump, the turbine and the reactor were combined in one housing.
Such a torque converter was patented in 1902 and had a large number of advantages over other mechanisms and devices that could convert torque from the engine.
GDT Fettinger minimized the loss of useful energy, Device efficiency turned out to be high. In practice, the specified hydrodynamic transformer, on average, provided on ships an efficiency of about 90% and even more.
Let's get back to the gearboxes on cars. At the very beginning of the 20th century (1904), the inventors, the Startevent brothers from Boston, USA, introduced an early version of the automatic transmission.
This two-speed gearbox was actually an improved manual transmission, where the shifts could be automatic. In other words, it was a prototype boxes - robot. However, in those years, for a number of reasons mass production proved impossible, the project was abandoned.
The next automatic transmission began to be installed at Ford. Legendary Model Model-T was equipped with a planetary gearbox, which received two speeds for forward movement, as well as a reverse gear. Gearbox control was implemented using pedals.
Next came a box from Reo on General Motors models. Such a transmission may well be considered the first manual transmission, as it was a manual with an automated clutch. A little later, a planetary gear system began to be used, further bringing the moment of the appearance of full-fledged hydromechanical automatic machines.
The planetary mechanism (planetary gear) is best suited for automatic transmissions. In order to control the gear ratio as well as the direction of rotation of the output shaft, individual parts of the planetary gear are braked. In this case, relatively small and constant efforts can be used to solve the problem.
In other words, we are talking about automatic transmission actuators (, band brake). Also in those years, it was not difficult to implement the effective management of these mechanisms. Another need to equalize the speed individual elements There was no automatic transmission, since all the gears of the planetary gear are in constant mesh.
If we compare such a scheme with attempts to automate the work of a mechanical box, at that time it was an extremely difficult task. The main problem was that in those years there were no efficient, fast and reliable servo mechanisms (servo drives).
These mechanisms are necessary in order to move the gears or clutches for engagement. The servos also need to provide a lot of power and travel, especially when compared to compressing a clutch pack or tightening an automatic transmission band brake.
A qualitative solution was found only closer to the middle of the 20th century, and robotic mechanics became mass-produced only in the last 10-15 years (for example, or).
Further development of the automatic transmission: the evolution of the hydromechanical automatic transmission
Before moving on to the automatic transmission, we need to mention the Wilson gearbox. The driver selected the gear using the steering column switch, and the inclusion was made by pressing a separate pedal.
Such a transmission was a prototype of a preselective gearbox, since the driver pre-selected a gear, while its inclusion was carried out only after pressing the pedal, which stood in place of the manual transmission clutch pedal.
This decision facilitated the process of driving the vehicle, gear changes required a minimum of time compared to manual transmissions, which did not have in those years. At the same time, the significant role of the Wilson box lies in the fact that this is the first gearbox with a mode switch, which resembles modern counterparts ().
Let's get back to the automatic transmission. So, the Hydra-Matic fully automatic hydromechanical transmission was introduced by General Motors in 1940. This gearbox was installed on Cadillac, Pontiac, etc. models.
Such a transmission was a torque converter (fluid coupling) and a planetary gearbox with automatic hydraulic control. The control was implemented taking into account the speed of the car, as well as the position of the throttle.
The Hydra-Matic box was installed both on GM models and on Bentley, Rolls-Royce, Lincoln, etc. In the early 50s, Mercedes-Benz specialists took this box as a basis and developed their own analogue, which worked on a similar principle, but had a number of differences in terms of design.
Closer to the mid-60s automatic hydro mechanical boxes programs have reached the peak of their popularity. Also appearance synthetic lubricants on the fuel and lubricants market made it possible to reduce the cost of their production and maintenance, to increase the reliability of the unit. Already in those years, automatic transmissions did not differ much from modern versions.
In the 1980s, there was a trend towards a constant increase in the number of transmissions. In automatic boxes, fourth gear first appeared, that is, increased. At the same time, the torque converter lock-up function was also used.
Also, four-speed automatics began to be controlled using, which made it possible to get rid of many mechanical controls, replacing them.
For example, Toyota was the first to introduce an electronic automatic transmission control system in 1983. Then in 1987, Ford also switched to using electronics to control the overdrive and the GDT lockup clutch.
By the way, today automatic transmission continues to evolve. Given the hard environmental standards and rising fuel prices, manufacturers are striving to increase transmission efficiency and achieve fuel efficiency.
To do this, the total number of gears increases, the switching speed has become very high. Today you can find automatic transmissions that have 5, 6 or more “speeds”. The main task is to successfully compete with preselective robotic boxes of the DSG type.
In parallel, there is a constant improvement of automatic transmission control units, as well as software. Initially, these were systems that only determined the moment of gear shifting and were responsible for the quality of the inclusions.
Later, programs began to be “sewn up” into the blocks that are able to adapt to the driving style, dynamically changing gearshift algorithms (for example, adaptive automatic transmissions with economy, sport modes).
Later, the possibility of manual control of automatic transmission (for example, Tiptronic) appeared, when the driver can independently determine the moments of gear shifting like a manual box. Additionally, the automatic transmission received advanced features in terms of temperature control transmission fluid etc.
Read also
Driving a car with automatic transmission: how to use the box - automatic, automatic transmission modes, rules for using this transmission, tips.
Definition
Automatic transmission(automatic transmission, automatic transmission) - one of the varieties of gearboxes, the main difference from manual gearbox is that in automatic transmission gear shifting is provided automatically (i.e., direct participation of the operator (driver) is not required). The choice of gear ratio corresponds to the current driving conditions, and also depends on many other factors. Also, if traditional checkpoints use mechanical drive, then in an automatic gearbox a different principle of movement of the mechanical part, namely, a hydromechanical drive or a planetary mechanism is involved. There are designs in which a two-shaft or three-shaft gearbox works together with a torque converter. This combination was used on LiAZ-677 buses and in ZF Friedrichshafen AG products.
IN last years, automated mechanical gearboxes with electronic control and electro-pneumatic or electro-mechanical actuators came into use.
background
No wonder they say that laziness is the engine of progress, so the desire for comfort and a simpler, more convenient life has given rise to many interesting things and inventions. In the automotive industry, such an invention can be considered an automatic gearbox.
Although the design of the automatic transmission is quite complex and became popular only at the end of the 20th century, it was first installed in the Swedish bus of the Lysholm-Smith company in 1928. In mass production, automatic transmission came only after 20 years, namely, in 1947 in Buick car roadmaster. The basis of this transmission was the invention of the German professor Fettinger, who patented the first torque converter in 1903.
In the photographs, the same Buick Roadmaster is the first stock car having an automatic transmission.
In an automatic transmission, the role of the clutch is performed by a torque converter, which transmits torque to the gearbox from the engine. The torque converter itself consists of a centripetal turbine and a centrifugal pump, between which a guide vane (reactor) is located. All of them are located on the same axis and in the same housing, together with the hydraulic working fluid.
Closer to modernity
The middle of the 1960s was marked by final consolidation and US approval - modern scheme automatic transmission shifting - P-R-N-D-L. Where:
"P" (Parking)- Included neutral mode, in which the output shaft of the box is mechanically blocked, so that the car does not move.
"R" (Reverse) - "Reverse"– Engaging reverse gear (reverse gear).
"N" (Neutral) - "Neutral"- There is no connection between the gearbox output shafts and the input shafts. But at the same time, the output shaft is not blocked, and the car can move.
"D" (Drive) - "Main mode" - Automatic switching in full circle.
"L" (Low) - Driving in 1st gear only. Only 1st gear is used. The torque converter is blocked.
Increasing demands for fuel economy led to the return in the 1980s of four-speed transmissions in which fourth gear had a gear ratio of less than one ("overdrive"). Torque converters locking up at high speed also became widespread, which made it possible to increase the efficiency of the transmission by reducing the losses that occur in the hydraulic element.
In the period from 1980-1990, computerization of engine control systems took place. Similar control systems were used in the automatic transmission. Now control over the flows hydraulic fluid controlled by solenoids linked to a computer. As a result, gear shifting has become smoother and more comfortable, and the economy and work efficiency have increased again. In the same years, it becomes possible to manually control the gearbox ("Tiptronic" or similar). Invented the first five-speed gearbox. There is no need to change the oil in the gearbox, since the resource already filled into it is comparable to the resource of the gearbox.
Design
Traditionally, automatic transmissions consist of planetary gears, torque converters, friction and overrunning clutches, connecting drums and shafts. Sometimes a brake band is used, which slows down one of the drums relative to the automatic transmission case when one of the gears is engaged.
The role of the torque converter consists in the transmission of torque with slippage when starting off. At high engine speeds (3-4 gears), the torque converter is blocked by a friction clutch, which prevents it from slipping. Structurally, it is installed in the same way as the clutch on a transmission with a manual transmission - between the automatic transmission and the engine itself. The torque converter housing and the drive turbine are mounted on the engine flywheel, as is the clutch basket.
The torque converter itself consists of three turbines - the stator, the input (component of the housing) and the output. Usually, the stator is silently braked on the automatic transmission case, however, in some variants, the stator braking is activated by a friction clutch to maximize the use of the torque converter throughout the entire rev range.
Friction clutches("package") connecting and disconnecting the elements of the automatic transmission - output and input shafts and elements of planetary gearboxes, and braking them on the automatic transmission case, they change gears. The coupling consists of a drum and a hub. The drum has large rectangular grooves on the inside, and the hub has large rectangular teeth on the outside. The space between the drum and the hub is filled with annular friction discs, some of which are plastic with internal cutouts, where the teeth of the hub enter, and the other part is made of metal and has protrusions on the outside that enter the grooves of the drum.
By hydraulically compressing the disk pack with an annular piston, the friction clutch is communicated. Oil is supplied to the cylinder through grooves in the shafts, the automatic transmission housing and the drum.
Preview - Click to enlarge.
On the first, left, photo - a section of a torque converter eight-speed automatic transmission Lexus car, and on the second - a section of a six-speed preselective automatic transmission Volkswagen
The freewheel slides freely in one direction and jams with torque transmission in the other. Traditionally, it consists of an inner and outer ring and a separator with rollers located between them. Serves to reduce shocks in friction clutches when shifting gears, as well as to disable engine braking in some automatic transmission modes.
As an automatic transmission control device, a set of spools was used, which controlled the flow of oil to the pistons of the friction clutches and brake bands. The position of the spools is set both manually mechanically by the selector handle, and automatically. Automation can be electronic or hydraulic.
Hydraulic automation uses oil pressure from a centrifugal governor, which is connected to the automatic transmission output shaft, as well as oil pressure from the gas pedal pressed by the driver. As a result, the automation receives information about the speed of the car and the position of the gas pedal, depending on which the spools are switched.
The electronics use solenoids to move spools. Cables from the solenoids are located outside the automatic transmission and lead to the control unit, which is sometimes combined with the fuel injection and ignition control unit. Depending on the position of the selector lever, the gas pedal and the speed of the car, the electronics decide on the movement of the solenoids.
Sometimes, the automatic transmission is provided for without electronic automation, but only with the third forward gear, or with all forward gears, but with the obligatory switching of the selector handle. You will be advised on the breakdown and repair of the checkpoint.
