An automatic transmission is a device that selects the gear ratio according to the conditions of the road surface, terrain and speed without the direct participation of the driver. In a car equipped with automatic transmission, the accelerator (gas pedal) sets the speed at which the car is moving, and does not determine the engine speed - this is the principle of the automatic transmission.
History shows that automatic transmission was invented somewhere in the thirties of the twentieth century. Since the advent of such a transmission, the principle of operation of an automatic transmission has not changed much, but depending on the time and certain technical requirements, it has been constantly supplemented. Thanks to such additions, automatic transmissions appeared, differing in their options and models. Different manufacturers have different specifications.
With distinctive characteristics, all automatic transmissions have one principle of operation. This is due to the fact that they have almost the same device, if you do not take into account some small nuances.
Automatic transmission device
Automatic transmission device
- The main one is a torque converter, which is also called a fluid coupling - this is a mechanism located between the engine of the machine and the gearbox housing. The functional task of the fluid coupling is the transmission and redistribution of torque during the start of the car;
- Torque is transmitted indirectly via planetary gears;
- Friction clutches are responsible for choosing one or another gear, they are often called a “package”;
- One of the mechanisms is the overrunning clutch, which mainly performs the function of reducing shocks in "packets" during gear changes. In some cases, during automatic transmission operation, the overrunning clutch disables engine braking;
- The box device also includes drums and connecting shafts;
The principle by which automatic transmission works
To control the automatic transmission, there is a special set of so-called spools that direct oil under a certain pressure to the pistons located in the friction clutches and brake bands. It is possible to set the position of the spools in automatic or manual mode, using the gear shift knob.
You also need to know that the automation that controls the automatic transmission can be hydraulic and electronic. Hydraulic is called automation, using oil pressure obtained from a centrifugal regulator. In turn, the centrifugal governor is connected to the automatic transmission shaft, which is located at the outlet. The hydraulic system is designed to use oil pressure in accordance with the position of the accelerator. The machine is given information about the position in which the gas pedal is located - this is a command for the spools to switch.
Automatic transmission scheme
The electronic control system contains solenoids responsible for moving the spools. The solenoids are connected to the automatic transmission control unit by cables; it is also possible to connect them to the control of the ignition system and fuel injection. In this case, the movement of the solenoids is controlled by an electronic control unit. The unit controls the solenoids also depending on the position of the gear lever, the speed at which the car is moving and the position of the accelerator.
Features of using automatic transmission
In order to avoid various breakdowns and troubles, you need to know how the automatic transmission works and how to use it. Cars equipped with an automatic are very practical and convenient vehicles. Even despite the fact that many motorists are skeptical about such transmissions, they are very popular. Usually it all depends on what the person is used to. If the driver loves dynamics, speed, then automatic transmission is not an option for him. Having considered the device, technical characteristics and how the automatic transmission works, it becomes clear that it is intended for people who prefer a more relaxed driving style.
The torque converter performs the function of smoothly connecting the box to the engine
In any case, before you start mastering a car with a gun, you need to study all the nuances and rules for using such a transmission. It is important to understand that neglecting some features, you can disable the automatic transmission in a fairly short time. You also need to know that repairing or replacing the entire automatic transmission will cost a round sum.
Rules for operating the machine
Even if the entire transmission is electronically controlled, the driver is required to follow certain rules for controlling it using the gear selector knob:
The appearance of the car gave rise to an ongoing race to improve all the systems and mechanisms of this vehicle. From methods and materials for the body to high-tech control methods. Karl Benz came up with the first device that allows in several modes to transfer engine forces to the running system.
The progressive thought of several generations of designers and inventors brought this device to the gearbox known to us today. But car manufacturers were not going to stop there, and already at the beginning of the last century, attempts began to automate this process. By the 30s of the XX century, manufacturers came close to solving the problem. But neither technologically nor economically it was impossible to establish mass production, although successful prototypes were created.
The first mass-produced car with an automatic transmission is considered to be the Buick Roadmaster, released in 1947.. The first model had only two gears, but a few years later a three-speed automatic transmission was launched into the series, which has not fundamentally changed to this day, although the modern transmission has become several orders of magnitude more accurate and more complex.
How automatic transmission works and its types
There is no clutch pedal on machines with an automatic, except for those models where it is possible to switch to manual control. This critical role is played by the automatic transmission.. The energy of the engine through a complex mechanism, which will be discussed below, is transferred to the transmission. The device of the system is designed in such a way that the switching of modes is regulated by automation. How this happens can be understood by understanding the operation algorithm and the main components of the automatic transmission:
- torque converter. Represents the evolution of a clutch developed back in 1903. The place where torque is transferred from the engine to the output shaft. The principle is simple. A pumping turbine connected to the engine accelerates the oil inside the housing, which transfers energy to the blades of the gearbox mechanism. Thus, there is no rigid mechanical connection between the input and output shafts. In this case, the transformation of the torque does not occur. Provides it with an additional element called the rotor. It is located between the turbines and the special design of the blades gives additional torque to the power plant. The force is transferred to the mechanism directly responsible for changing the gear ratio;
- planetary reductor. The main part of the automatic transmission. A complex mechanism assembled from a central or sun gear, a crown or a large central gear and a set of satellites mounted on a part called a carrier. By changing the position of individual elements of the automatic transmission along the axis, several combinations are formed that output several rotation speeds of the central shaft. The number of options is commonly referred to as transmissions.. A direct analogue with a manual transmission, but the circuit does not need a clutch, the function of which is performed by a fluid coupling. Such a system requires precise and complex control. It is impossible to ensure efficient switching of such a complex mechanism in manual mode;
- control system. Two types of devices are possible. The first is hydraulic mechanisms. Today, this type is used mainly in budget cars. Cars of the middle class and above are equipped with electronically controlled automatic transmission. In the first case, the sensors, reacting to a change in oil pressure in the system, actuate hydraulic pushers. They actuate a complex combination of clutches and brakes by mechanically shifting gears. The system is set up in such a way that it is impossible to “jump over” the transmission. Switching is possible only sequential. The electronic control system is more efficient. Sensors collect more complete information about the operation of the automatic transmission. This is the temperature of the liquid, and the speed of rotation of each axis. The control unit gives a signal to the actuators. The triggering algorithm for a whole group of parts at once is under the control of electronics. Clutches, brakes and solenoid valves, often referred to as solenoids, are almost constantly in motion while riding;
- selector lever. This is the "handle" located in the cabin. All over the world, the marking of the selector positions common to all automatic transmissions has been adopted. R - reverse. N - neutral gear. D - the main position of the selector when driving, from start to stop. P - Parking. S - sport mode. Some manufacturers of elite and executive cars supply the switch block with additional provisions. For example, Tiptronic has the ability to switch from automatic mode to mechanical control of the gearbox.
The scheme discussed above refers to the classical version. The principle of operation of variators and robots is different. The difference in price is also significant.
Well-established technologies, large volumes of production of a classic automatic transmission make it more affordable than both a variator and a robotic gearbox, which, however, have some advantages.
For example, the variator does not have switching stages at all, and the gear ratio changes are carried out by a mechanism resembling two conical pulleys. The moving belt simultaneously changes the input and output shaft diameters, which changes the output speed without power loss and jerks. The robot is essentially a high-quality manual transmission with efficient electronic control. Fans of mechanics can always switch to their favorite mode.
Advantages and disadvantages
The advantages of automatic transmission are many. Managing mechanics requires a lot of learning and constant attention while driving. This problem does not apply to owners of cars with automatic equipment. Most of the time when driving, the box is in one position - D, which means movement or drive. But these are not all bonuses. The advantages are as follows:
- Comfort and focus on the road environment, not on the devices.
- Saving engine life. The machine does not allow mechanics to work in critical modes, which prevents wear of the main parts and consumables.
- Safe driving in difficult climatic conditions. Together with other systems, the machine does not allow the driver to make critical mistakes in control.
However, not only the advantages are noted by specialists and ordinary car owners. There are also disadvantages:
- Higher than manual transmission fuel consumption. The efficiency of the machine can be up to 12% lower than that of mechanics. However, this does not apply to the latest generation of automatic transmissions. Improving production technologies today reduces this difference to a minimum.
- Dynamics. Automatic mode does not allow the car's systems to work in extreme conditions, which deprives the driver to fully feel the full power and capabilities of the car. But for most city dwellers, this is not the case. In everyday life, where progress is complicated by traffic jams, crossings and traffic lights, the automatic machine is more of a blessing than a disadvantage.
- Car cost. Models with automatic transmission are much more expensive than their counterparts with manual transmission.
- Impossibility of towing. If the transmission breaks down, you have to call a tow truck. The ability to move a turned off car is limited to a short distance at minimum speed, and then with experience and knowledge of how to do it safely for the mechanics of the car.
- Repair. The complexity of the design and the high price of spare parts and maintenance, which includes more consumables, makes owners of cars with automatic transmission shell out.
How to drive a car with an automatic transmission
There are no difficulties in training and subsequent operation. Unlike mechanics, you do not need to look at the tachometer needle or determine the moment of switching by sound. The positions of the handle of the machine are as follows:
- Parking. Indicated by the letter P. In this position, the blocked output shaft prevents the vehicle from moving. On level ground, this is enough to maintain stability, but on an inclined surface, it is recommended to use the hand brake;
- The position of the handle N corresponds to the neutral gear on the manual transmission. With the control system turned off, the machine can be moved;
- Reverse is indicated by the letter R, which means reverse. In this position, it is impossible to start the engine, and when moving forward, a sharp shift of the selector to reverse will certainly disable the gearbox;
- The main position is marked on the selector with the letter D. Switching all gears forward, from the lowest to the highest, occur in this mode.
- Additional Provisions. These include the Sport mode, marked as S. This mode makes the most of the engine power. Acceleration dynamics is noticeably higher for cars with the additional Kickdown option. For even and economical driving, the Overdrive function is available. Some models have a separate switch for winter mode. If the automatic transmission breaks down, the automation can block the mechanism in the current gear and go into emergency mode.
Features of operating a car with automatic transmission
The order of operations required to start moving on most machines with a machine gun is the same:
- Insert the key and turn it to ignition mode.
- Press the brake pedal.
- Move the selector lever to the desired position. Either forward or backward.
- Release the brake pedal.
The car will begin to move smoothly in the selected direction, without even pressing the pedal, using which you can accelerate the dynamics. The machine first of all reacts precisely to the operation of the accelerator. Drive mode is not switched during short stops, for example, at a traffic light. Only brakes are used. The "Parking" position is turned on for a longer stop.
- Off-road and uneven surfaces should be avoided. Slippage should ideally be avoided in general;
- You need to let the system warm up. Automatic transmission will reach the declared level only at a certain oil temperature. Therefore, even in the summer, it is better to avoid sudden accelerations and high speeds for the first few minutes of movement;
- Do not overload. The machine has a more sensitive mechanics, which is designed for certain loads. It is strongly not recommended to overload the interior or pull a heavy trailer;
- You also need to pay attention to the documentation. Is towing allowed for this type of automatic transmission. Some models are not subject to forced movement at all. Some species have strict speed and distance limits.
The global trend today is, of course, cars with automatic transmission. Characteristics in many ways approached highly skilled driving on mechanics. Conveniences are undeniable and do not need additional advertising.
You have purchased a car with an automatic transmission and do not know how to deal with your new type of transmission. Our simple tips will help you understand how to drive a car with automatic transmission and avoid the most common mistakes made by motorists.
What is the difference between automatic transmission and manual transmission
Unfortunately, not everyone knows how to properly use an automatic transmission on a car, mistakenly believing that the operation of such a car is practically no different from using a manual transmission. But this approach leads to a decrease in the potential of the transmission and even its breakdown.
A manual transmission has its advantages, but most modern motorists choose automatic transmission. It is easier to drive such cars, since they do not have a clutch pedal. There are only two pedals - brake and gas. Learning to drive a car with an automatic transmission is easier, but those who have been driving a car with mechanics for a long time cannot get used to the peculiarities of using an automatic transmission.
Its main advantage is the ability to automatically select the gear ratio in accordance with road conditions. This is a handy feature, as shifting gears does not require movements such as depressing the clutch pedal during gear changes, stops and starts.
However, it should be understood that the use of automatic transmission requires certain knowledge and skills. And first you need to figure out what modes it has.
Automatic transmission modes
To understand how to use automatic transmission correctly. you need to understand the intricacies of its modes. Letters with corresponding meanings are indicated on the box:
P - parking mode. This position helps to start the unit. It can only be turned on after the car has completely stopped and the driver has put the handbrake in active mode.
D - driving mode. It helps to activate the driving mode of the car, while the transmission is automatically transferred to the desired modes. It is in this mode that the transmission stays the longest.
R - reverse. It can only be activated when the car is completely stopped and the brakes are applied.
N - neutral mode, puts the engine to idle, torque is not transmitted to the wheels at this time. It is not recommended to turn it on while the car is moving. As a rule, it is used to warm up the engine during a cold period of time.
D3 - engine speed reduction position. In this mode, braking is more effective, it is used on small uphill and downhill.
D2 - used in extreme driving conditions, for example, when driving on a mountain serpentine or ice.
Switching the lever from mode D to position D2 and D3 can be carried out directly while the vehicle is moving.
Driving a car with an automatic transmission in general is not much different from driving a mechanic. However, it requires compliance with certain rules and knowledge of some points that will help you make the most of the transmission's capabilities.
How to drive automatic transmission
In order to start the engine, you need to depress the brake pedal, and without releasing it, move the gear lever from position P, N or R to position D. Many drivers in the learning process may forget that the brake pedal must be depressed when doing this. .
In order to increase the speed of the car, it is enough just to press the gas pedal harder, and the engine will automatically begin to gain the desired number of revolutions. Unlike the operation of a manual transmission, no effort is required on the part of the driver, so the reaction to the traffic situation is greatly accelerated. In order to slow down, just release the accelerator pedal, that is, the gas. The less force applied to it, the slower the car will move.
For a complete stop or a quick decrease in speed, just use the brake pedal. To then start moving again, you only need to move your foot from the brake to the gas. At the same time, the gear lever can always remain in the driving mode, that is, in position D. It makes sense to switch to another gear only during long stops with the engine completely turned off.
When driving in the city, the driver simply needs to switch the selector lever to the “driving” position, after which he will need to work with the gas and brake pedals to reduce and increase speeds. Everything is extremely simple here, which is why most city cars are equipped with automatic transmissions.
Using winter mode
Most new cars are equipped with an additional mode for driving in winter. It is indicated by the icons "*", "W", "SNOW", "HOLD", "WINTER". This mode is very useful when driving on snowy or icy roads. Its purpose is to eliminate slips and skids. It completely disables first gear.
Important! You should not turn on the winter mode when driving in the warm season on a dry road, as the load on the transmission in this case increases greatly, which can lead to its overheating.
The purpose of using the winter mode is to limit the acceleration of the engine speed above the individual gears.
Disadvantages of automatic transmission
Some owners of cars with automatic transmission reinstall gearboxes to continue using a manual transmission. This is due to the presence of some shortcomings of the automatic transmission.
These include:
Important! Despite the fact that many drivers practically do not use the handbrake when parking cars with automatic transmission, you should still use the handbrake, as this is provided for by the Rules of the Road.
Automatic transmission. How to use the automatic transmission is shown in the video:
An article on how to use the automatic transmission correctly - symbols on the automatic transmission panel, starting the engine, moving and stopping, possible errors. At the end of the article - a video about using an automatic box.
At the moment, there are three types of automatic transmissions: "classic", with "stepless variator", with "robotic mechanics". Depending on the modification and manufacturer, these types of transmissions may differ slightly (a different number of gears, a slightly different lever stroke - straight or zigzag, symbols, etc.), but the main functions will be the same for everyone.
The growing popularity of automatic transmission is understandable - it is more convenient to operate (than "mechanics" - manual transmission), especially for beginners, reliable and protects the engine from overload. Everything seems to be simple! However, drivers still make mistakes, and even the most reliable mechanism can fail if it is not properly operated. Next, we will consider how to properly use the automatic transmission and how to properly operate it.
To learn how to use the "machine" correctly, you first need to figure out what the alphabetic characters (English letters) and numbers on the automatic transmission panel with the gear shift knob mean. Just note that depending on the brand of the car, the numbers and letters may vary.
- "P"- "parking". Turns on when the car is parked. A kind of analogue of the parking brake, only with the blocking of the shaft, and not with the pressing of the brake pads.
- "R"- "reverse". Turns on for reverse. It is commonly referred to as "reverse speed".
- "N"- "neutral". Neutral gear. Often referred to as "neutral". Unlike in P park mode, in neutral N mode, the wheels are unlocked so the car can coast. Accordingly, the machine can also spontaneously roll down a slope in a parking lot if the wheels are not fixed with a handbrake.
- "D"- "drive". Forward mode.
- "A"- "automatic". Automatic mode (practically, the same as the "D" mode).
- "L"- "low" (low). Downshift mode.
- "B"– Same mode as "L".
- "2"– the driving mode is not higher than the second gear.
- "3"– the driving mode is not higher than the third gear.
- "M"- "manual". Manual control mode with up / down transfer through the signs "+" and "-". This mode imitates a mechanical shift mode with a manual transmission, only in a simpler version.
- "S"- "sport". Sports driving mode.
- "OD"- Overdrive. Upshift (fast mode).
- W- "winter". Driving mode for the winter period, in which starting off starts from second gear.
- "E"- "economy". Driving in economy mode.
- HOLD- "retention". Used in conjunction with "D", "L", "S", as a rule, on Mazda cars. (Read the manual).
For example, in the manual of some cars, the letter "B" means "Block" (blocking) - a differential lock mode that cannot be engaged while driving.
And if the designations “1” and “L” are present in an all-wheel drive car, then the letter "L" may not mean "Low" (decrease), but "Lock"(lock) - which also means differential lock.
Starting an engine with an automatic transmission has the following features:
- In a car with automatic transmission, there are only two pedals: "brake" and "gas". Therefore, the left leg of the driver is practically not used. When starting the engine, the “gas” pedal is not pressed, but in some brands of cars it is necessary to press the brake pedal, otherwise the engine will not start (read the instruction manual).
However, driving instructors advise making it a rule to always press the brake pedal before starting the engine with automatic transmission. This will prevent the machine from moving unintentionally in neutral "N" mode, and will also allow you to quickly switch to "D" or "R" driving modes. (Without pressing the brake pedal, you will not be able to switch to the indicated modes and move off).
- In cars with automatic transmission, protection is provided - automatic blocking of engine start in case of incorrect position of the gear lever. This means that the engine with automatic transmission can only be started if the gear lever is in one of two positions: either “P” (parking) or “N” (neutral). If the PP lever is in any other position intended for movement, the blocking protection against incorrect start will be activated.
This protective function is very useful, especially for beginners, and especially in cities with a large “car density”, where cars are packed tightly together in parking lots and in traffic. After all, even experienced drivers sometimes forget to “take the car off the speed” before starting the engine, as a result of which, when starting, the car immediately starts driving and crashes into the nearest car or obstacle.
It is possible to start the engine with automatic transmission both in the “P” (parking) mode and in the “N” (neutral) mode, however, manufacturers recommend using only the “P” mode. Therefore, it is better to set one more rule for yourself - park and start the engine only in the “parking” mode.
- After turning the key in the ignition it is recommended to wait a few seconds before starting the starter to give the fuel pump time to turn on and pump up compression.
Most drivers who switch from "mechanics" to "automatic" at first automatically perform the actions that they are accustomed to doing repeatedly when driving a car with a manual transmission. Therefore, such drivers, before starting to drive with automatic transmission on the road in the general traffic flow, are recommended to pre-train alone.
So, the standard procedure for starting off on a car with automatic transmission is as follows:
- Insert the key into the ignition switch.
- Depress the brake pedal with your right foot (the left foot is not used when driving with automatic transmission).
- Check the position of the gear lever - it should be in the "P" - "parking" position.
- Start the engine (with the brake pedal depressed).
- Also, with the brake pedal depressed, switch the PP lever to the “D” - “drive” position (forward movement).
- Fully release the brake pedal, after which the car will move off and start moving forward at a low speed - about 5 km / h.
- To increase the speed of movement, you need to press the "gas" pedal. The harder you press the gas pedal, the higher the gears and speed will be.
- To stop the car, you need to remove your right foot from the "gas" pedal and squeeze (her) the brake pedal. The car will stop.
- If you plan to leave the car after stopping, then with the brake pedal depressed, move the gear lever to the "P" - "parking" mode. If a stop was required in a traffic jam, at a traffic light or a pedestrian crossing, then, naturally, the PP lever does not need to be switched to “parking”. After you decide to continue driving again, release the brake pedal and press the "gas" pedal to increase speed.
To prevent damage to the engine when switching to manual mode "M" on the go, all automatic transmissions have special protection. Switching to manual control "M" is relevant in the following situations:
- When driving off-road in low gear to avoid slipping.
- When coasting down a hill, with engine braking. It is not recommended to use the neutral mode "N" for coasting, as it is harmful to the automatic transmission. And the coast in the "D" mode is not very convenient, as there is a gradual decrease in speed.
- For comfortable cornering and other manoeuvres, including for quick acceleration when overtaking.
- The most common mistake leading to automatic transmission failure is switching on the "D" - "drive" mode (forward movement) without a complete stop when reversing. And, the same thing, just the opposite - the inclusion of the "R" (reverse) mode without a complete stop when moving forward.
- The second common mistake (rather delusion) is related to the “N” (neutral) mode. The fact is that this mode is an emergency mode to unlock the wheels for short-term towing or rearrangement of the car in case of any malfunction. And just for this!
But many inexperienced drivers use the neutral mode "N" in traffic jams during short stops, which leads to water hammer and premature wear of the automatic transmission. In traffic jams with frequent stops, you need to use the "D" mode along with the brake pedal. If you need to stop - the brake pedal is pressed, if you need to slowly move forward - the brake pedal is simply released, and the car slowly rolls forward. And you can drive like that all day long.
- The third mistake transition to the neutral mode "N" from the mode "D" on the go, on the highway. This is dangerous (especially at high speed), as it can stall the engine, as a result of which the power steering and brake boost will turn off, and the car will become almost uncontrollable.
- Another mistake - towing a car with automatic transmission for a distance of more than 40 km and at a speed of more than 50 km/h. In the “automatic” box, unlike the manual transmission, the oil supply system works under pressure, but it does not work when towing. Accordingly, the parts of the “machine” rotate “dry”, without lubrication, as a result of which they wear out very quickly.
- A common mistake is attempt to start a car with automatic transmission "from the pusher". And although such attempts often lead to the desired result (the engine starts), it still has a destructive effect on the automatic transmission mechanism, and with such frequent operation, the “machine” may not work out even half of the pledged resource.
Conclusion
It is quite possible that for someone the automatic transmission will seem like a complex and finicky mechanism, despite the simplicity and ease of use. But this is only at first glance. In fact, "automatic machines" have proven themselves to be quite reliable units, but, of course, subject to their correct and competent operation. It is especially convenient to use automatic transmission in big cities, where you often have to stand in traffic jams.
Video on how to use the "machine":
The automatic transmission does not have a clutch. In an automatic transmission, you do not need to shift gears yourself. According to many experts, the journey that energy takes from the engine to the chassis in an automatic transmission car is absolutely amazing!
In this article, we will pave our way through the automatic transmission. We will start with the key unit in the automatic transmission - the planetary gear set. At the same time, since our site is trying to characterize any unit of the car as simply and understandably as possible even for a novice motorist, we will try to simplify as much as possible this, probably most often the most complex unit in the entire car, and thus consider it only superficially - for the concept the general principle of operation of the machine. So, how does an automatic transmission (or simply "automatic box") work?
Just like a manual transmission, the main job of an automatic transmission is to allow the engine to operate over a narrow range of speeds while allowing the vehicle to operate over a wide range of output speeds.
Without a gearbox, the car will be limited to one gear ratio, and that ratio must be chosen to allow the car to drive at the right speed. If, for example, you want a top speed of 80 km/h, then the gear ratio will be similar to third or fourth gear in most manual transmissions. You have probably never tried to drive a manual car using only third gear. If you did, you would quickly find that the car hardly accelerates from a stop, and at high speed the engine would growl quite strongly, keeping the tachometer needle on the red line. And the car will wear out very quickly from this. Thus, the use of gears makes it possible to make more efficient use of engine torque.
The main difference between manual and automatic transmissions is that a manual transmission locks and unlocks different sets of fixed gears on the output shaft to achieve different gear ratios, while an automatic transmission has the same set of gears for almost all possible gear ratios. This becomes possible in automatic transmission thanks to the planetary gear set.
Let's see how the planetary gear set works in an automatic transmission.
If you try to take apart and look inside an automatic transmission, you will find a huge assortment of parts in a fairly small space. Among other things, you will see:
- planetary gear
- Knot group set for gear locking
- A set of three clutches for blocking other parts of the automatic transmission
- hydraulic system
- Large gear pump to move liquid around the box
The focus is on the planetary gear set. The size of a rather big melon (depending on the car) it creates all the different gear ratios. And everything else in the automatic transmission is actually designed to help the planetary gear do its job.
Almost any planetary gear set of an automatic transmission consists of three main components (see the figure below):
- Sun gear (yellow)
- Satellites and satellite carriers (red)
- Toothed shaft (epicycle) (blue circle around satellites)
Each of these three components can be removed and replaced in case of severe wear.
Now let's take a look at how the planetary gear set works in action: the table below shows the various gear ratios and how they are obtained - to see, click on the button on the left of the table.
So we see that this set of gears can produce all the different gear ratios without having to engage or disengage any other gear. But that's not all - with two of these planets in a row, we can get four forward gears and one reverse gear.
In fact, most automatic transmissions do not have such a simple planetary gear set operation scheme - in modern cars, while there is only one epicycle, 2 or more solar shafts with satellites move inside it, and a description of such a scheme goes far beyond the scope of this article.
Hydraulic system, pumps and regulators in automatic transmission
Hydraulic system of the machine- this is a very complex assembly of channels through which oil flows and which perform a number of important automatic transmission functions. For example, here are some of the features of an automatic transmission:
- When the vehicle is in Drive (D), the transmission automatically selects a gear based on vehicle speed and accelerator position.
- If you accelerate relatively gently, changes will occur at lower speeds than if you were accelerating at full throttle (called "Eco", "Overdrive", etc. depending on the car model).
- If you release the gas pedal, the gears will shift to the next lower gear.
- If you move the shift lever to a lower gear (for example, from mode D to mode L), and the car is going too fast, the automatic transmission will wait until the car slows down, and only then will it shift into a lower gear.
- If you set the gearbox lever to second gear (available in almost all car models), then the car will never switch to other gears on its own, even if it comes to a complete stop, until you move the gear lever.
This is what the hydraulic system of the automatic transmission looks like
You've probably seen what it looks like before. It really is the "brain" of an automatic transmission. In the picture below you can see a huge number of channels to provide all the different components in the box. Passages are molded into metal and are an efficient way to route fluid.
Pump
Typical gear pump
Automatic transmissions have a very precise and neatly placed pump called a gear pump. The pump is usually located in the gearbox cover. It draws fluid from the sump at the bottom of the automatic transmission and supplies it to the hydraulic system. It also feeds the torque converter.
Regulator
The regulator in the car is a smart valve that tells the system how fast the car is going to accelerate. Thus, the faster the car moves, the faster and more the regulator supplies oil to the system. Inside the regulator is a spring-loaded valve that opens as the regulator itself spins quickly and thus regulates the amount of oil supplied to the system.
Electronic automatic transmission control system
Electronic transmission control, which is becoming more common in new cars, still uses hydraulics to actuate the clutch and other groups of mechanisms, but each hydraulic circuit is controlled by an electrical impulse. This simplifies gear control and allows for more advanced control schemes.
Above we have seen some of the control strategies driven by mechanical action. Electronically controlled automatic transmissions have more complex control schemes. In addition to monitoring vehicle speed and throttle position, the controller can monitor engine speed if the brake pedal is depressed, and even the anti-lock brake system. Using this information and advanced control strategies based on an intelligent automatic transmission system, an electronically controlled transmission can do things such as:
- Reduce speed automatically when descending a hill to control speed and reduce brake wear.
- Upshift when braking on slippery surfaces to increase braking torque from the engine.
- Prohibit upshifting if the vehicle is entering a curve or driving on a winding road.
