An automatic transmission , also called automatic , automatic transition switching , n automatic speed (where n is the number of front gear ratios), or AT , is a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, frees the driver to move gear manually. Like other vehicle transmission systems, it enables internal combustion engines, most suitable for running at relatively high rotational speeds, to provide the range of torque speeds and output required for vehicle travel. The number of advanced gear ratios are often expressed for manual transmissions as well (eg, 6-speed manual).
The most popular form found in cars is the hydraulic automatic transmission. Similar but larger devices are also used for heavy commercial and industrial vehicles and equipment. The system uses fluid coupling in place of friction clutches, and completes gear changes with hydraulic locking and unlocks planet gear systems. The system has a defined set of gear ranges, often with a parking pawl that locks the transmission output shaft to keep the vehicle from rolling forward or backward. Some machines with a limited speed range or fixed engine speed, such as some forklifts and lawn mowers, use only torque converters to provide variable propulsion of the engine to the wheels.
In addition to the traditional hydraulic automatic transmission, there are also other types of automatic transmissions, such as continuously variable transmission (CVT) and semi-automatic transmission, which relieves the driver of having to manually move the gear, using a transmission computer to replace the gear if, for example, the driver is repairing the machine. Despite the superficial similarities with other transmissions, traditional automatic transmissions differ significantly in internal operation and the driver's nuance of semi-automatic and CVT. Unlike conventional automatic transmissions, the CVT uses a belt or other torque transmission scheme to allow "unlimited" gear ratios rather than fixed tooth ratio. Semi-auto retains the clutch like a manual transmission, but controls the coupling through electrohydraulic means. The ability to move gears manually, often via a paddle shifter, can also be found in certain automatic transmissions (manumi like Tiptronic), semi-automatic (BMW SMG, VW Group DSG), and CVT (like Lineartronic).
The real advantage of automatic transmission to the driver is the lack of clutch pedals and manual shifting patterns in normal driving. This allows the driver to operate the car with as few as two limbs (possibly using a tool to control positions within range of limbs that can be used), which allows the disabled to drive. The lack of manual shifting also reduces the attention and workload required in the cabin, such as monitoring the tachometer and taking the hand from the wheel to move the shifter, allowing the driver to ideally keep both hands on the wheel at all times and to focus more on the road. Controlling the car at low speeds is often easier with automatic than manual, due to the side effects of clutch fluid coupling design called "creep" which causes the car to move while driving the teeth, even when idle. The main disadvantage of most popular hydraulic designs is to reduce the mechanical efficiency of power transfer between the engine and the drivetrain, due to the fluid coupling that connects the engine to the gearbox. This can result in lower power/torque ratings for automated machines compared to manuals with the same engine specifications, as well as reducing fuel efficiency in riders in the city because the engine must maintain a standby against fluid coupling resistance. Advances in transmission and coupling design have narrowed this gap significantly, but clutch-based transmission (manual or semi-automatic) is still preferred in the trim-sport trim levels of various production cars, as well as in many league racing cars.
Automatic transmission was invented in 1921 by Alfred Horner Munro of Regina, Saskatchewan, Canada, and patented under Canadian patent CA 235757 in 1923. (Munro obtained British patent GB215669 215.669 for his invention in 1924 and US patent 1,613,525 on January 4 1927). Being a steam engineer, Munro designed his device to use compressed air rather than hydraulic fluid, thus lacking power and never finding commercial applications. The first automatic transmission using hydraulic fluid may have been developed in 1932 by two Brazilian engineers, JosÃÆ'Ã… © Braz Araripe and Fernando Lehly Lemos; subsequent prototypes and plans were sold to General Motors who introduced it in 1940 Oldsmobile as a "Hydra-Matic" transmission. They were put into tanks built by GM during World War II and, after the war, GM marketed them as "war-tested." However, a Wall Street Journal article credits ZF Friedrichshafen with discovery, occurring shortly after World War I. ZF's origins in dental manufacturing for aircraft engines began in 1915; the company was founded by Ferdinand von Zeppelin.
Video Automatic transmission
History
Modern automatic transmission can trace its origins to the early gearbox "horse-drawn carriages" developed in 1904 by the Sturtevant brethren from Boston, Massachusetts. This unit has two forward speeds, a change of ratio brought by a machine-driven flyweight. At higher engine speeds, high gears are activated. When the vehicle slows down and the engine RPM decreases, the gearbox will shift back to low. Unfortunately, metallurgy at that time did not suit the task, and due to sudden gear changes, the transmission would often fail without warning.
One of the key developments in arriving at an automatic transmission is the use of planetary transmission in the vehicle gearbox. Perhaps the first use of Wilson-Pilcher was made between 1900 and 1907. Wilson-Pilcher used two epicyclic gearboxes that allowed 4 front teeth to be selected by moving a single gear change lever. In the shape of this gearbox the planet's gear is in a constant net, and all it takes is to use a mechanism to repair or release an outer ring rotation. The action of the tooth change lever is mechanically locked or frees the outer circle of each episeptic tooth by the internal brake/clutch. The vehicle also has a separate clutch cone operated by a foot pedal that can stick in a position to run the engine when stationary, eg. to start. Like the more modern automatic transmission, the gears are helical to reduce noise, and are sealed in oil-filled gearboxes. There are no reports from manufacturers that want to automate gear replacements, although the design eliminates the requirement to use clutch legs except when starting or stopping.
A better known car that also uses planetary transmission is the Model T Henry Ford 1908. The Model T, in addition to being cheap and reliable by today's standards, features a simple two-planet, two-speed transmission and instead uses straight-toothed operations The manual is controlled by the driver using a pedal. The pedal moves the transmission friction elements (band and clutch) to select the desired gear. In some cases, this type of transmission requires less driver skill than a contemporary manual transmission that is not synchronized, but it is still necessary for the driver to know when to make the switch, and how to start the car smoothly.
The first automatic transmission using hydraulic fluid was developed in 1932 by two Brazilian engineers, JosÃÆ'Ã… © Braz Araripe and Fernando Lehly Lemos; Later, the prototype and the project were sold to General Motors, which introduced technology in the 1940s Oldsmobile model as a "Hydra-Matic" transmission. However, an article published by the Wall Street Journal crediting German auto parts company ZF Friedrichshafen for discovery, which will occur shortly after World War I.
In 1934, both REO and General Motors developed a semi-automatic transmission that was more difficult to operate than a fully manual unit. This design, however, continues to use the clutch to engage the engine with the transmission. The General Motors unit, dubbed "Automatic Safety Transmission," is famous for using a planetary gearbox that acts as hydraulically controlled power and is sensitive to road speed, anticipating future developments.
In line with developments in the 1930s the auto gearbox shifted Chrysler's work on adapting fluid couplings for automotive use. Created in the early 20th century, fluid coupling is the answer to the question of how to avoid stalling the engine when the vehicle is stopped with transmission in the tooth. Chrysler itself never uses a liquid clutch with its automatic transmission, but uses it in conjunction with a hybrid manual transmission called "Fluid Drive" (the same Hy-Drive uses a torque converter). The developments in automatic gearbox technology and fluid coupling eventually culminated in the introduction in 1939 from General Motors Hydra-Matic, the world's first mass-production automatic transmission.
Available as an option in 1940 Oldsmobiles and then Cadillac, Hydra-Matic combines liquid coupling with three hydraulically controlled planetary gearsets to produce four forward and reverse speeds. The transmission is sensitive to throttle engine position and road speed, resulting in automatic up and down transitions that vary according to operating conditions.
Hydra-Matic was later adopted by Cadillac and Pontiac, and sold to various other car makers, including Bentley, Hudson, Kaiser, Nash, and Rolls-Royce. It was also found used during World War II in several military vehicles. From 1950 to 1954, Lincoln's car was also available with Hydra-Matic. Mercedes-Benz then designed a four-speed fluid-clutch transmission which in principle is similar to Hydra-Matic, but from a different design.
Interestingly, the original Hydra-Matic incorporates two features that many emulate in today's transmissions. The Hydra-Matic ratio scattered through four gears produces excellent "steps" and acceleration within the first good gear spacing, good gear spacing, and the effect of overdrive on the fourth, based on the ratio of the lower numerical axle rods used in vehicles. time. In addition, in third and fourth gear, the fluid coupling only handles a portion of the engine torque, resulting in a high degree of efficiency. In this case, the transmission behavior is similar to that of a modern unit that incorporates a locking torque converter.
In 1956, GM introduced the "Jetaway" Hydra-Matic, which was different in design from older models. Overcoming the shift quality problem, which is a continuing problem with the original Hydra-Matic, the new transmission uses two fluid clutches, the main one that connects the transmission to the engine, and the secondary that replaces the clutch assemblies that control the forward gearset in the original language. The result is a smoother displacement, especially from first to second gear, but with losses in efficiency and increased complexity. Another innovation for Hydra-Matic's new style is Park's position on voters. The original Hydra-Matic, which continued in production until the mid-1960s, still uses an inverse position for parking pawl engagement.
The first automatic torque converter, Buick's Dynaflow, was introduced for the 1948 model. This was followed by Packard's Ultramatic in mid-1949 and Chevrolet's Powerglide for the 1950 model. Each of these transmissions has only two forward speeds, relying on converters for additional torque multiplication. In the early 1950s, BorgWarner developed a series of three-speed automatic torque converters for American Motors, Ford Motor Company, Studebaker, and several other manufacturers in the US and other countries. Chrysler was late in developing its true self, introducing the PowerFlite two-speed powered converter in 1953, and the three-speed TorqueFlite in 1956. The latter was the first to use the Simpson Composite planetary coupler.
General Motors produced a double turbine torque converter from 1954 to 1961. These include Twin-Turbine Dynaflow and three-turboglide transmission turbines. The shift takes place in the torque converter, not through the pressure valves and changes in the planetary gear connections. Each turbine is connected to the drive shaft via different toothbrush. This is phased from one ratio to another according to demand, rather than changing. Turboglide actually has two speed ratios in reverse, with one turbine spinning backwards.
In the late 1960s, most four-speed transmissions and fluid-speed transmissions have disappeared for the sake of a three-speed unit with a torque converter. Also around this time, whale oil has been removed from the automatic transmission fluid. In the early 1980s, this was being augmented and eventually replaced by a transmission equipped with overdrive providing four or more speeds ahead. Many transmissions also adopt locking torque converters (mechanical couplings lock the torque converter and turbine converter pumps to eliminate slip at cruising speed) to improve fuel economy.
Since the computerized control unit (ECU) becomes more capable, most of the logic built into the transmission valve body is lowered to the ECU. Some manufacturers use a separate computer dedicated to a transmission called transmission control unit (TCU), also known as a transmission control module (TCM), which shares information with computer management machines. In this case, the solenoid is turned on and off by the computer's control shift pattern and tooth ratio, not the valve spring in the valve body. This allows more precise control of the shift points, shift quality, lower shift times, and (in some newer cars) semi-automatic controls, where drivers tell the computer when to shift. The result is an impressive combination of efficiency and fluency. Some computers even identify driver styles and adapt to the best.
ZF Friedrichshafen and BMW are responsible for introducing the first six speeds (ZF 6HP26 in the BMW 7 Series 2002 (E65)). The Mercedes-Benz 7G-Tronic was the first of seven speeds in 2003, with Toyota introducing eight speeds in 2007 on the Lexus LS 460. Derived from the 7G-Tronic, Mercedes-Benz launched a semi-automatic transmission with torque converters replaced with wet wet clutch called AMG SPEEDSHIFT MCT. The Jeep Cherokee 2014 has the world's first nine speed automatic transmission for passenger vehicles to market.
Maps Automatic transmission
Parts and operations
Hydraulic automatic transmission
The dominant form of automatic transmission is operated hydraulically; using fluid couplings or torque converters, and a set of planetary gearsets to provide various gear ratios.
Hydraulic automatic transmission consists of three main components:
Torque converter
Type of fluid coupling, hydraulically connect the engine to the transmission. It replaces clutch friction in manual transmission. It transmits and separates engine power to planetary gears, allowing the vehicle to stop with the engine still running without stalling.
A torque converter differs from a fluid coupling, in which case it provides a variable amount of torque multiplication at a low engine speed, increasing the acceleration of the breakaway. The fluid clutch works well when both the impeller and the turbine rotate at the same speed, but are very inefficient at the initial acceleration, where the rotation speed is very different. The multiplication of torque is performed by a third member in a coupling assembly known as the stator, which acts to modify the fluid flow depending on the relative rotational speed of the impeller and turbine. The stator itself is not rotating, but the vane is so shaped that when the impeller (driven by the engine) rotates at high speed and the turbine (which receives transmitted power) rotates at low speed, the flow fluid touches the turbine blades in a multiplying manner torque applied. This causes the turbine to start spinning faster when the vehicle accelerates (ideally), and when the relative rotational speed equates, the torque multiplication is reduced. Once the impeller and turbine spins within 10% of their respective speeds, the stator stops functioning and the torque converter acts as a simple fluid clutch.
Gears planetary wheel
It consists of a set of planetary gear and clutches and bands. It is a mechanical system that provides various gear ratios, changing the rotational speed of the output shaft depending on which planet's gear is locked.
For the effects of tooth change, one of two types of couplings or bands is used to hold certain members of the gearset of the immobile planet while allowing other members to rotate, thus transmitting torque and resulting in a reduction in gear or overdrive ratio. The clutch is driven by a valve body (see below), the sequence is controlled by the internal transmission programming. In principle, this type of device known as sprag or roller clutch is used for upshifts/downshifts routine. Operating a lot as a ratchet, it transmits torque in only one direction, free wheel or "occupy" in the other. The advantage of this type of coupling is that it eliminates the sensitivity of the simultaneous release time of the clutch/apply on two planetary, simply "taking" the load of the drivetrain when it is moved, and releasing automatically when the next sprag gear clutch assumes torque transfer. These bands come into play for manually selected gears, such as low or reverse distance, and operate on the planet's drum rim. Bands are not applied when the drive/overdrive range is selected, the torque sent by the sprag grip instead. Band is used for braking; GM Turbo-Hydramatics combines this..
Hydraulic control
Using a special transmission fluid that is sent under pressure by the oil pump to control the various couplings and bands that modify the output velocity depending on vehicle running conditions.
Not to be confused with the propellers inside the torque converter, pumps are usually gear pumps installed between the torque converter and planetary gears. It pulls the transmission fluid from the sump and presses it, which is necessary for the transmission components to operate. The input for the pump is connected to the home of the torque converter, which in turn is tripled to the flexplate engine, so the pump puts pressure every time the engine runs and there is enough fluid transmission, but the disadvantage is that when the engine is not running, no oil pressure is available to operate the main components transmission, and as such it is not possible to start a vehicle equipped with an automatic transmission. Early automatic transmission also has a rear pump for the purpose of towing, ensuring the lubrication of the rear components.
The governor is connected to the output shaft and adjusts the hydraulic pressure depending on the speed of the vehicle. Modern designs have replaced mechanical governors with electronic speed sensors and computer software. Engine loads are monitored either by throttle cable or vacuum modulator . Modern designs have replaced these mechanical devices with electronic signals transmitted via the CAN bus. The valve body is the hydraulic control center that receives the pressurized fluid from the main pump operated by the fluid coupling/torque converter. Pressure from the pump is regulated and used to run the spring valve network, check the ball and the servo piston. The valve uses the pump pressure and pressure of the centrifugal governor on the output side (as well as the hydraulic signal from the range selector and the throttle valve or modulator ) to which ratio control is selected on gearset; as the vehicle and engine speed changes, the difference between the pressure changes, causing different valve sets to open and close. This valve-controlled hydraulic pressure drives various clutch actuators and brake bands, thus controlling the operation of the planet's gearset to select the optimal gear ratio for current operating conditions. However, in many modern automatic transmissions, the valves are controlled by electro-mechanical servos controlled by an electronic machine control unit (ECU) or a separate transmission control unit (TCU, also known as transmission control module (TCM).
Hydraulics & amp; lubricating oil, called automatic transmission fluid (ATF), provides lubrication, corrosion prevention, and hydraulic media to deliver mechanical power (for transmission operations). Primarily manufactured from processed oils, and processed to provide properties that promote smooth power transmission and improve life, ATF is one of the few automatic transmission parts that require routine service as the vehicle ages.
The number of parts, together with the complex design of the valve body, initially makes the hydraulic automatic transmission much more complicated (and expensive) to be made and improved than a manual transmission. In most cars (except for US families, luxury cars, sport utility vehicles and minivan models), they usually have an extra-fee option for this reason. Mass manufacturing and improvements over decades have reduced this cost gap.
In some modern cars, computers use sensors on the engine to detect throttle position, vehicle speed, engine speed, engine load, etc. to control the right shift point. The computer transmits information through a solenoid that directs the correct clutch or servo fluid to control the shift.
Continuous variable transmission
Different types of automatic transmissions are basically a continuously variable transmission , or CVT , which can smoothly and stepless change the gear ratio by varying the diameters of a pair of belts or chains. - Pulley, wheel or cone connected. Some continuous variable transmissions use a hydrostatic drive - which consists of a variable displacement pump and a hydraulic motor - to transmit power without a gear. Some early forms, such as the Hall system (which dates back to 1896), use fixed displacement pumps and variable displacement motors, and are designed to provide robust variable transmission for early commercial heavy motor vehicles. The CVT design is usually fuel-efficient as a manual transmission in city driving, but the initial design loses efficiency as engine speed increases.
A slightly different approach to CVT is the concept of toroidal CVT or unlimited variable transmission (IVT). These concepts give the ratios of zero and backward teeth.
E-CVT
Some hybrid vehicles, especially Toyota, Lexus and Ford Motor Company, have an electronically controlled CVT (E-CVT). In this system, the transmission has a fixed gear, but the ratio of wheel speed to engine speed can continue to vary by controlling the third input speed to the differential using a generator motor.
Double clutch transmission
A dual-clutch transmission , or DCT (sometimes referred to as a twin-clutch transmission or dual clutch transmission), is a type of semi-automatic transmission and a modern electrohydraulic manual transmission. It uses two separate grips for odd and even devices. Basically it can be described as two separate manual transmissions (with each clutch) contained in a single housing, and work as a unit. They are usually operated in full automatic mode, and many also have the ability to allow the driver to manually move gears in semi-automatic mode, though still using transmission electrodes.
Automatic Manual Transmission
Also known as semi-automatic transmission (SAT) and several other names, this type of automatic transmission uses ordinary coupling and gear settings but automates the action using sensors, actuators, processors, and pneumatics. The AMTs were born out of the need to make affordable and fuel-efficient auto cars. It's very simple and affordable. They are also not too expensive to fix. Fuel efficiency is their top priority and rivals manual transmission. AMT is based on an electronic control unit and a hydraulic system that controls the use of clutch and gearshift, enabling the driver to change gears without using clutches, either sequentially or completely automatically.
Automatic transmission mode
Conventionally, to select the mode of transmission operation, the driver moves the selected lever located either on the steering column or on the floor (as with the manual on the floor, except that the automatic selector on the floor does not move in the same type of pattern as the manual lever does). To select a mode, or to manually select a certain gear ratio, the driver must press the button (called the shift-lock key) or draw the handle (only on the shifter mounted column). Some buttons select the vehicle position selector for each mode in the cockpit instead, freeing up space in the center console.
Vehicles that comply with US Government standards must have a P-R-N-D-L ordered mode (left to right, top to bottom, or clockwise). Previously, the automatic transmission of the selected quadrant often used the P-N-D-L-R layout, or similar. Such patterns lead to the number of deaths and injuries caused by driver mistakes that lead to accidental tooth selection, and the danger of having a selector (when worn) jumps back from low gears during engine braking maneuvers.
Most automatic transmissions include several ways to force the tooth decay (Throttle kickdown) to the lowest possible gear ratio if the throttle pedal is completely depressed. In many older designs, kickdown is done by mechanically moving the valve in the transmission. Most modern designs use solenoid-operated valves triggered by switches on throttle connections or by machine control units (ECUs) in response to a sudden increase in engine power.
The mode selection allows the driver to choose between a predefined shift program. For example, Fuel saving mode by raising gear at lower engine speeds, while Sport mode (aka "Power" or "Performance") delayed upshifting for maximum acceleration. Some transmission units also have Winter mode, where a higher gear ratio is selected to keep the rotation as low as possible while on a slippery surface. This mode also changes the way the computer responds to throttle input.
Conventionally, the automatic transmission has a selector position that allows the driver to limit the maximum possible transmission ratio. In older transmissions, this is achieved by a mechanical lockout on the body of the transmission valve preventing the increase until locking is released; on computer-controlled transmissions, the same effect is performed by the firmware. Transmission can still raise the teeth and lower the gear automatically between the remaining ratios: for example, in the range 3 , the transmission can switch from one to two to three, but not to a fourth or higher ratio. Some transmissions will still rise automatically to a higher ratio if the machine reaches the maximum allowed speed in the selected range.
- Third (3)
- This mode limits transmission to the first three gear ratios, or sometimes locks the transmission in third gear. It can be used for climbing or downhill. Some vehicles will automatically shift up from third gear in this mode if a certain round per minute (RPM) range is reached to prevent engine damage. This equipment is also recommended when pulling the trailer.
- Second (2 or S)
- This mode limits transmission to the first two gear ratios, or locks transmission in second gear on Ford, Kia, and Honda models. It can be used to drive in bad conditions like snow and ice, as well as climbing or descending the hills in winter. It is usually advisable to use a second gear to start on snow and ice, and the use of this position allows this with an automatic transmission. Some vehicles will automatically move up from second gear in this mode if a certain RPM range is reached to prevent engine damage.
- Although traditionally considered second gear, there is another name used. Chrysler's three-speed automatic model since the late 1980s has called this gear 3 when using traditional names for Drive and Low . Oldsmobile has referred to the second gear as the 'Super' range - which was first used on their 4-speed Hydramatic transmission, although the use of the term continued into the early 1980s when GM's Turbo Hydramatic automatic transmission was standardized by all their divisions years after 4-speed Hydramatic discontinued.
Some automatic pistols, especially those installed in larger capacity or high torque engines, either when "2" is selected manually, or by enabling winter mode, will start in the second gear instead of the first, and then not shift to the tooth higher until back to "D." Also note that like most American automatic transmissions, selecting "2" using the selection lever will not tell the transmission is only in gear 2; Instead, it will only limit transmission to gear 2 after extending the duration of gear 1 through higher speed than normal operation. The 2000-2002 Lincoln LS V8 (automatic five-speed without manumatic capability, as opposed to the optional sports package w/5-speed manu-matic) starts in 2nd gear during most starts in both winter and season the other by choosing the notch "D5" transmission in shiftgate (for fuel savings), while "D4" will always start on first gear. This is done to reduce the torque multiples when moving forward from a stop in conditions where traction is limited - on snow-covered roads or ice, for example.
- First (1 or L [Low])
- This mode locks transmission only in first gear. In older vehicles, it will not change to any other gear range. Some vehicles will automatically shift out of first gear in this mode if a certain RPM range is reached to prevent engine damage. This, like the second, can be used during winter, for towing, or for driving downhill to improve the engine braking effect. The "Austin Mini" auto transmission differs in this case - This mode locks the transmission in first gear, but the gearbox has a freewheel overrun. Closing the throttle after acceleration produces a vehicle that keeps going at the same speed and only slows down due to friction and wind resistance. During this time, the machine's RPM will drop back to idle until the throttle is pressed again. What this means is that in "First", engine braking is unavailable and "2" is the lowest gear that should be used when downhill. 4-speed Automatic Transmission from Mini (and 1100/1300) is unusual as it allows manual selection of all advanced gears, allowing the driver to "take off" from a stationary position in one of the four ratios. It also does not give the position of "Park".
Manual control
Some transmissions have modes in which the driver has full control over the change of ratio (either by moving the selector, or through the use of a button or paddle), completely override the automatic function of the hydraulic controller. Such control is particularly useful in cornering, to avoid undesirable gear rise or decline that can damage the balance or attractiveness of the vehicle. The "manumatic" shifter, which was first popularized by Porsche in the 1990s under the trade name Tiptronic, has become a popular choice in sports cars and other performance vehicles. With the prevalence of electronically controlled transmissions almost universal, they are relatively simple and inexpensive, requiring only software changes, and provision of actual manual controls for the driver. The number of correct manual controls provided varies greatly: some systems will override driver options under certain conditions, generally to prevent engine damage. Because this gearbox also has a throttle kickdown switch, it is not possible to fully utilize engine power at low to medium engine speeds.
Manufacturer-specific mode
As well as the above mode there are other modes, depending on the manufacturer and model. Some examples include:
- D5
- In Hondas and Acuras equipped with a five-speed automatic transmission, this mode is commonly used for toll road use (as stated in the manual), and uses the five front gear ratios.
- D4
- This mode is also found in Honda and Acura four or five automatic speeds, and only uses the first four gear ratios. According to the manual, it is used for stop-and-go traffic, such as driving in the city.
- D3 or 3
- This mode is found in Honda, Acura, Volkswagen and Pontiac four-speed automatic and uses only the first three gear ratios. According to the manual, it is used for stop-and-go traffic, such as driving in the city.
- D2 and D1
- This mode is found in older Ford transmissions (C6, etc.). In D1, all three gears are used, while in D2 the car starts in second gear and upshifts to third.
- S or Sport
- This is generally described as Sport mode. It operates in a manner identical to the "D" mode, except that the change of ride changes much higher in the engine spin range. It has an effect on maximizing all available engine output, and therefore improves vehicle performance, especially during acceleration. This mode will also lower the higher rotation range compared to "D" mode, maximizing the engine braking effect. This mode will have an adverse effect on fuel economy. Hyundai has a Norm/Power switch next to gearshift for this purpose at Tiburon .
Some early GMs were equipped with the HYDRA-MATIC transmission used (S) to show the Second gear, which is equal to position 2 on Chrysler, shifting between only first and second gears. It will be recommended for use on steep levels, or slippery roads like dirt, or ice, and limited to speeds below 40 mph. (L) is used in some early GMs to show the (L) ow gear, which equals position 2 on Chrysler, locking transmission into first gear. It will be recommended for use on steep levels, or slippery roads such as dirt, or ice, and limited to speeds below 15 mph.
- -, and M
- This is for the selection of manual gear modes in certain automatic pistols, such as Porsche and Tiptronic Honda and BMW and Steptronic Kia. M features can also be found in vehicles such as the Dodge Magnum and Journey; Pontiac G6; Mazda3, Mazda6, and CX-7; Toyota Camry, Corolla, Fortuner, Previa and Innova; Kia Forte (K3/Cerato), Optima (K5), Cadenza (K7) and K9 (Quoris). Mitsubishi montero sport/pajero sport and some Audi (Audi TT) models have no M, and instead have and -, separated from the rest of the shift mode; the same goes for some Peugeot products like the Peugeot 206. Meanwhile, the driver can shoot up and down at will by diverting the shift lever (console attached) similar to the semi-automatic transmission. This mode can be involved either through the selector/position or by actually changing the gear (for example, overturning the gear wheel mounted near the driver's finger on the steering wheel).
- Winter (W)
- In some models of Volvo, Mercedes-Benz, BMW and General Motors, winter mode can be involved so that the second gear is chosen instead of the first when pulling away from the stationary, reducing the possibility of traction loss due to the wheel spinning over snow or ice. In GM cars, this is the D2 in the 1950s, the Second Gear Started after 1990, and the Snow/Ice mode in the 2010s. At Ford, Kia, and Honda automatics, this feature can be accessed by moving the 2nd gear selector to start, then removing the foot from the accelerator while selecting D after the vehicle moves.
- Rem (B)
- Selectable modes on some Toyota models, as well as electric cars from some manufacturers. This can be used to reduce speed, or maintain a decreased speed, without the use of conventional brakes. In a non-hybrid car, mode B chooses a lower gear to improve engine braking. GM called this "HR" ("hill retarder") and "GR" ("grade retarder") in the 1950s. In hybrids such as the Toyota Prius, which has a fixed gear ratio, B mode slows the car partly by increasing engine air intake, which increases engine braking. In electric cars such as the Nissan Leaf and Mitsubishi i-MiEV, B mode increases regenerative braking levels when the accelerator pedal is released.
Some automatic transmissions modified or designed specifically for drag racing can also incorporate transbrake as part of the body of the manual valve. Powered by an electric solenoid control, the transbrake simultaneously involves first and reverse gear, locking the transmission and preventing the spinning input shaft. This allows the driver of the car to raise the engine's RPM against the resistance of the torque converter, then launch the car just by releasing the transbrake switch.
Comparison with manual transmission
Most cars sold in North America since the 1950s have been available with automatic transmissions, based on the fact that three major American automakers have started using automatic pistols. In contrast, in Europe manual gearboxes are standard, with only 20% of drivers choosing an automatic gearbox compared to the United States. In some Asian markets and in Australia, automatic transmissions have become very popular since the 1980s.
Vehicles equipped with automatic transmissions are not as complicated to drive. Consequently, in some jurisdictions, drivers who have passed their driving tests in vehicles with automatic transmissions will not have the license to drive a manual transmission vehicle. Instead, the manual license will allow the driver to drive the vehicle with automatic or manual transmissions. The countries where the license restrictions apply include several states in Australia, Austria, Botswana, Belgium, Belize, China, Croatia, Denmark, Dominican Republic, Estonia, Finland, France, Germany, Hong Kong, Hungary, India, Indonesia Ireland, Philippines, Poland, Portugal, Qatar, Romania, Russia (as of April 2014), Saudi Arabia (as of March 2012), Singapore, Slovenia, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Trinidad and Tobago, United Arab Emirates, and the United Kingdom.
Conventional manual transmission is often a basic piece of equipment in a car, with options as automatic transmission such as conventional automatic, semi-automatic, or CVT.
Effects on vehicle control
Cornering
Unexpected tooth changes may affect the vehicle's attitude in marginal conditions.
Maintaining a constant velocity
Torque and CVT transmission converters make changes in vehicle speeds less clear by the sound of the engine, as they separate the engine speed from the speed of the vehicle.
A locking torque converter that works and breaks off at a certain speed can make this speed unstable - the transmission wastes less power above the speed at which the torque converter is locked, typically causing more power to the wheels for the same throttle input.
Controlling wheelpin
The torque converter responds quickly to the loss of traction (torque) by increasing the speed of the drive wheel for the same engine rotation. Thus, in most conditions, where static friction is higher than kinetic friction, engine speed must be lowered to ward off the cart when it occurs, requiring faster or faster throttle reduction by the driver than with manual transmission, making wheelpin more difficult to be controlled. This is most evident in driving conditions with much higher static friction than kinetic, such as heavy snow (which turns into ice due to friction), or snow on ice.
Ascending slippery slopes
In situations where the driver with a manual transmission can not buy gearshift, for fear of losing too much speed to reach the top of the hill, the automatic transmission is at a big advantage - while driving a manual car depends on finding a not too low gear to enter the bottom of the hill at the speed required, but not too high to stop the engine on a hill, sometimes an impossible task, this is not a problem with automatic transmissions, not just because of rapid gearshift, but they usually retain some power on the driving wheels during tooth replacements.
Energy efficiency
The previous hydraulic automatic transmission is almost always more energy efficient than manual transmission due mainly to viscous losses and pumping (parasitic losses), both in torque converters and hydraulic actuators. 21% is a loss on Chrysler Torqueflite 3 speed compared to the modern GM 6L80 automatic. A relatively small amount of energy is required to suppress the hydraulic control system, which uses fluid pressure to determine the correct shift pattern and operates various automatic coupling mechanisms. However, with technological developments some modern continuous variable transmissions are more fuel efficient than their manual counterparts and modern 8-speed automatics are within 5% as efficiently as manual gearboxes.
Manual transmission uses mechanical coupling to transmit torque instead of torque converter, thus avoiding the main source of loss in automatic transmission. Manual transmission also avoids the hydraulic control system power requirements, relying on the human muscle power of the vehicle operator to release the clutch and drive the gear lever, and the operator's mental strength to make the right gear ratio choice. Thus the manual transmission requires very little engine power to function, with main power consumption due to drag of the gear truck buried in gearbox lubricating oil.
The on-road acceleration of an automatic transmission can sometimes exceed that of an identical vehicle equipped with a manual transmission in a turbocharged diesel application. Turbo-boosts are usually lost between the gear changes in the manual while the accelerator pedal automatically can remain completely depressed. However, this still largely depends on the number and optimal range of gear ratios for each unit, and whether the removal of the spooldown/accelerator off represents a significant advantage to counter the slightly higher power consumption of the automatic transmission itself.
Automatic transmission model
Some of the most recognizable automatic transmission families include: General Motors: Dynaflow, Powerglide, Turboglide, Hydra-Matic, Dual Range Hydra-Matic, Jetaway Hydra-Matic, Whirlaway Hydra-Matic, Roto Hydra Matic, "Turbo-Hydramatic" TH350, TH400 and 700R4, 4L60-E, 4L80-E. Holden: Powerglide, Trimatic.
- Cummins: 68 RFE (plugged into Ram's diesel segment)
- Chrysler: PowerFlite, TorqueFlite LoadFlyte (for Trucks), TorqueCommand (when used in AMC cars starting in 1972) 727 and 904, A500, A518, 45RFE, 545RFE
- BorgWarner: Flight-O-Matic, Flash-O-Matic, (later Aisin AW)
- Automatic ZF Friedrichshafen transmission
- Mercedes-Benz Transmission: The name of the automatic transmission is G-Tronic with a number before g which means the number of gears owned by the transmission.
- Allison Transmission
- Voith Voith Turbo
- Aisin AW: Aisin AW is a Japanese auto parts supplier, known for its automatic transmission and navigation system
- Honda
- Nissan/Jatco
- Volkswagen Group: 01M
- Drivetrain Systems International (DSI): M93, M97 and M74 4-speed, M78, and M79 6-speed
- Hyundai Hyundai Powertech: 4F12, 4F16, 4F23 4-Speed, 5F25, 5F16, 5F23 5-Speed, 6F17, 6F26, 6F40 6-Speed, 8R40, 8R50 8-Speed, Mini Cooper - Automatic or manual transmission model
Automatic transmission families are usually based on Ravigneaux, Lepelletier, or Simpson planet gimlet. Each uses the setting of one or two central solar wheels, and ring gears, with different planet gear arrangements that surround the sun and blend into the ring. The exception to this is Honda's Hondamatic line, which uses a sliding gear on a parallel axis like a manual transmission without planetary gearsets. Although Honda is very different from all other automatics, it is also very different from the automatic manual transmission (AMT).
Many of the above AMTs exist in the modified country, created by their racing fans and mechanics by systematically reengineering the transmission to achieve higher performance levels. This is known as "performance transmission". Examples of high-performance transmission manufacturers are General Motors and Ford.
See also
References
Further reading
- Thomas W Birch (2012). Automatic transmission and transaxles . Upper Saddle River, N.J.: Pearson Education. ISBN: 9780132622271.
External links
- Original Canada Patent Munro
- How Automatic Transmission Works on HowStuffWorks
- How to Drive a Car with Automatic Transmission
- Automatic transmission death
- US5370589 The concept of Lepelletier is shown in this patent
- "What Makes Auto Automatic Transmission." Popular Mechanics , February 1955, p. 169-173, simple basics with pictures.
Source of the article : Wikipedia
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