Equipping cars with an automatic transmission made it possible to reduce the amount of load placed on the driver while driving. Let's talk about the device automatic transmission automatic transmission.
Benefits of using
Application automatic transmission eliminates the need for constant use of the shift lever. The speed change is performed automatically, depending on the engine load, the speed of the car and the desires of the driver. Compared with manual box gears, automatic transmission has the following advantages:- increases the comfort of driving a car due to the release of the driver;
- automatically and smoothly performs switching, coordinating the engine load, speed, degree of pressing the gas pedal;
- protects the engine and undercarriage car from overloads;
- allows manual and automatic switching speeds.
There are some differences in the layout and design of the automatic transmission of front-wheel drive and rear wheel drive car. Automatic transmission for front wheel drive vehicles more compact and has a compartment inside its body main gear- differential.
The principle of operation of all machines is the same. To ensure the movement and performance of its functions, an automatic transmission must be equipped with the following components: a drive mode selection mechanism, a torque converter, a control and monitoring unit.
What is the automatic transmission made of?
- Torque converter (1)- corresponds to the clutch in a manual box, but does not require direct control by the driver.
- Planetary gear (2)- corresponds to the gear block in a manual transmission and serves to change the gear ratio in an automatic transmission when shifting gears.
- Brake Band, Front Clutch, Rear Clutch (3)– components by means of which gear shifting is carried out.
- Control device (4). This assembly consists of an oil sump (transmission pan), a gear pump and a valve box.
It not only transmits torque, absorbs and smoothes engine vibrations, but also drives the oil pump located in the gearbox housing. Oil pump fills the torque converter with transmission fluid and creates operating pressure in the management and control system.
Therefore, the opinion is incorrect that a car with an “automatic” box can be started forcibly without using a starter, but by dispersing it. The automatic transmission pump receives energy only from the engine, and if it does not work, then pressure is not created in the control and monitoring system, no matter what position the drive mode selector lever is in. Therefore, forced rotation cardan shaft does not oblige the gearbox to work, and the engine to rotate.
planetary gear- unlike a mechanical transmission, which uses parallel shafts and interlocking gears, automatic transmissions overwhelmingly use planetary gears.
The gearbox housing contains several planetary gears, they provide the necessary gear ratios. And the transmission of torque from the engine through planetary mechanisms to the wheels occurs with the help of friction discs, differentials and other devices. All these devices are controlled by transmission fluid through the command and control system.
Brake band- a device used to block the elements of the planetary gear set.
The valve box is a system of channels with located valves and plungers that perform the functions of control and management. This device converts vehicle speed, engine load, and gas pedal pressure into hydraulic signals. On the basis of these signals, due to the sequential inclusion and exit from the operating state of the friction blocks, the gear ratios in the gearbox are automatically changed.
automatic box gears is a device that provides the choice of gear ratio in accordance with the conditions pavement, 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 time and certain technical requirements constantly supplemented. Thanks to such additions, automatic transmissions appeared, differing in their options and models. At different manufacturers they have different specifications.
At 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 through 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
For automatic transmission control special set so-called spools, directing oil under a certain pressure to those in friction clutches oh and brake bands pistons. It is possible to set the position of the spools in automatic or manual mode, using the shift lever.
You also need to know that automation, automatic transmission manager, can be hydraulic and electronic. Hydraulic is called automation, using oil pressure obtained from 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
IN electronic system controls, there are 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. Automatic cars 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 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 general principle machine operation. 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 this ratio must be chosen to allow the car to drive desired speed. If you, for example, want top speed at 80 km / h, then the gear ratio will be similar to the third or fourth gear in most mechanical 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 standstill, but 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 mechanical box gear locks and unlocks various sets fixed gears on the output shaft to achieve different gear ratios, while in an automatic transmission the same set of gears is almost all possible options gear numbers. 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 disassemble and look inside the automatic transmission, you will find huge assortment details 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 gear reversing.
In fact, most automatic transmissions do not have such a simple circuit planetary gear work - in modern cars while there is only one epicycle, 2 or more solar shafts with satellites move inside it, and the description of such a scheme is 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 whole line important functions of the automatic transmission. 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, the changes will take more low speeds than if you accelerated by full throttle(the so-called "Eco", "Overdrive" mode, 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. The passages are molded in metal and are effective way fluid routing.
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 delivers it to 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 given mechanical action. automatic transmission with electronic control have more complex schemes management. In addition to monitoring vehicle speed and position throttle valve, the controller can control the engine speed if the brake pedal is pressed, and even anti-lock braking system. Using this information and advanced management strategies based on intelligent system An automatic transmission with electronic transmission control can do things like:
- 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.
- Prevent switching to overdrive when the vehicle is entering a curve or driving on a winding road.
An automatic transmission (abbreviated as automatic transmission) is one type of vehicle transmission. The automatic gearbox independently (eliminates the direct intervention of the driver in the process) sets the desired ratio of gear ratios, based on driving conditions and various factors.
Engineering terminology recognizes as "automatic" only the planetary element of the assembly, which is directly related to gear shifting and, together with the torque converter, creates a single automatic stage. Important point: automatic transmission always works in conjunction with a torque converter - it guarantees correct work unit. The role of the torque converter is to transmit a certain amount of torque input shaft, as well as in preventing jerks when changing gears.
Options
The automatic transmission is, nevertheless, a conditional concept, because there are its subspecies. But the ancestor of the class is a hydromechanical planetary gearbox. It is the hydraulic machine that is associated with automatic transmission, for the most part. Although currently there are alternatives:
- robotic box ("robot"). This is a variant of "mechanics", but switching between steps is automated. This is possible due to the presence in the design of the “robot” of electromechanical (electropneumatic) actuators, which are driven by electronics;
- variable speed drive. Subspecies continuously variable transmission. It is not directly related to gearboxes, but implements the power of the power unit. The process of changing the gear ratio occurs gradually. The V-chain variator has no steps. In general, the principle of its operation can be compared with a bicycle speed sprocket, which, as it unwinds, gives the bicycle acceleration through the chain. Automakers, in order to bring the operation of this transmission closer to traditional ones (with steps) and to get rid of the mournful hum during acceleration, create virtual gears.
Device
Hydromechanical box - "automatic" consists of a torque converter and an automatic planetary box gears.
The design of the torque converter includes three impellers:
Each element of the gas turbine engine (torque converter) requires a strict approach in production, synchronous integration, balancing. Based on this, the gas turbine engine is manufactured as a non-separable and non-repairable unit.
The structural location of the torque converter: between the transmission housing and power plant- which is similar to the installation niche for the clutch on the "mechanics".
Purpose of gas turbine engine
The torque converter (relative to a conventional fluid coupling) converts the engine torque. In other words, there is a short increase in traction, which is received by the box - "automatic" when accelerating the vehicle.
The organic drawback of the gas turbine engine, following from its principle of operation - cranking turbine wheel when interacting with the pump. This is reflected in energy losses (GDT efficiency at the moment uniform motion auto - no more than 85 percent), and leads to an increase in heat emissions (some modes of the torque converter provoke a greater heat emission than the power unit), increased consumption fuel. Now automakers on their cars integrate a friction clutch into the transmission, which blocks the gas turbine engine at the moment of uniform movement at high speed and higher stages - this reduces friction losses of the torque converter oil and reduces fuel consumption.
What is a friction clutch for?
The task of the clutch package is to switch between gears by communicating / disengaging parts of the automatic transmission (input / output shafts; elements of planetary gearboxes and deceleration in relation to the automatic transmission case).
Coupling design:
- drum. Equipped with the necessary slots inside;
- hub Has outstanding external teeth of a rectangular shape;
- set of friction discs (ring-shaped). It is located between the hub and the drum. One part of the pack consists of metal outer lugs that fit into the drum splines. The other is plastic with internal cutouts for the teeth of the hub.
The friction clutch communicates by compression by an annular piston (integrated into the drum) of the disk set. Oil supply to the cylinder is carried out using drum, shaft and body (automatic transmission) grooves.
The overrunning clutch has free slip in a certain direction, and in the opposite direction it is wedged and transmits torque.
Overrunning clutch includes:
- outer ring;
- separator with rollers;
- inner ring.
Node task:
Automatic transmission control unit: device
The block consists of a set of spools. They control the oil flow towards the pistons (brake bands)/friction clutches. The spools are arranged in a sequence that depends on the movement of the gearbox/automatic selector (hydraulic/electronic).
hydraulic. Applies: oil pressure centrifugal governor, which interacts with the output shaft of the box / oil pressure, which is formed during pressing the accelerator pedal. These processes convey electronic unit control data on the angle of inclination of the gas pedal / speed of the car, followed by switching the spools.
Electronic. Solenoids are used to move the spools. The wire channels of the solenoids are located outside the automatic transmission housing, and go to the control unit (in some cases - to the combined control unit for the fuel injection and ignition system). The received information about the speed of the car / angle of inclination of the gas determines the further movement of the solenoids through the electronic system / the handle of the automatic transmission selector.
Sometimes the automatic transmission works even with a faulty electronic automation system. True, provided that the third gear (or all stages) is on in the manual mode of controlling the box. 
Selector control
Varieties of the position of the selectors (automatic transmission lever):
- floor. The traditional location in most cars is on the central tunnel;
- stalk. This arrangement is often found in american cars(Chrysler, Dodge), as well as Mercedes. Activation desired mode transmission occurs through pulling the lever towards you;
- on the center console. Applies to minivans and some ordinary cars(eg: Honda Civic VII, CR-V III), which frees up space between the front seats;
- button. Layout received wide application on sports cars (Ferrari, Chevrolet Corvette, Lamborghini, Jaguar and others). Although it is now being integrated into civil vehicles(premium class).
Slots of floor selectors are:
Box operation
How to use the box - "automatic" correctly? Two pedals and many transmission modes can plunge an inexperienced driver into a stupor. At first glance, everything is simple, but there are nuances. Below are explanations of how to use the automatic transmission correctly.
Modes
Basically, the “automatic” box has the following positions on the selector:
- P is the implementation of the parking lock: blocking the drive wheels (integrated inside the gearbox and does not interact with parking brake). An analogue of setting the car into gear ("mechanics") when it is parked;
- R - reverse gear (it is forbidden to activate while the car is moving, although blocking is now applied);
- N-mode neutral gear(activation is possible with a short parking / towing);
- D- forward stroke(the entire transmission range of the box is involved, sometimes two higher gears are cut off);
- L - mode activation low gear(slow speed) for the purpose of moving off-road or on such, but with difficult conditions.
Auxiliary (advanced) modes
Present on boxes with extensive operating ranges (the main modes may also be labeled differently):
- (D) (or O / D) - overdrive. Economy mode and measured movement (whenever possible, the box switches to the top);
- D3 (O / D OFF) - deactivation of the highest stage for active driving. It is activated by braking by the power unit;
- S - gears spin up to maximum speed. There may be the possibility of manual control of the box.
Take into account:
"automatic" regarding manual transmission it brakes with the engine only in certain modes, in the rest, the transmission has free slip through overrunning clutches, and the car coasts.
Example - manual transmission mode (S) provides for motor deceleration, but automatic D does not.
While driving
How to use the "automatic" box correctly in the direction of travel? Modern transmissions allow the transition from one mode to another without pressing the button on the selector lever (except R). And in order not to prevent the arbitrary start of the movement of the machine during a stop, you must press the brake pedal when switching modes.
You also need to know how to properly tow a car with automatic transmission. You must adhere to the following recommendations:
- check the level oily liquid in a box for compliance with factory standards;
- turn the ignition key, remove the lock from the steering column;
- switch the selector to N mode;
- towing is recommended no more than 50 kilometers, at a speed of 50 kilometers per hour, and less. When stopping, it is desirable to cool the box;
- it is forbidden to start the engine while towing.
And in real life, and in the virtual space there is an eternal dispute between the owners of cars with automatic weapons and manual gearboxes. This dispute is also endless, like the one that is primary: an egg or a chicken. Without entering into it, we will simply try to fill in certain gaps in the knowledge of those novice car owners who have an automatic transmission installed.
What is it, automatic transmission?
We hear such types of automatic transmissions as tiptronic and steptronic. A few words about these common names.
Tiptronic- this is an automatic transmission with the ability manual switching gears. In manual control mode, the driver manual selection transmission by pushing the selector lever in the "+" or "-" direction.
Steptronic- Automatic transmission used in BMW. It also has the ability to manually shift gears, but the shift speed is increased, and is comparable to a manual transmission. In steptronics, the lever moves in positions P, R, N, and D. In addition, there is an “M / S” (Manual / Sport) position, which in the “sport” mode holds the gear until it reaches maximum number rpm, then upshift occurs.
How does an automatic transmission work?
Automatic hydromechanical box gears in the classic version consists of planetary gearboxes, a torque converter, overrunning and friction clutches, connecting drums and shafts.
Without going into the wilds, especially with your own hands, it is strongly not recommended to do it, the principle of operation automatic transmission differs in that gear shifting occurs due to the interaction of planetary mechanisms and a hydromechanical drive using electronic actuators.
Features of the operation of the automatic transmission have already been covered on the pages of the site. But we will repeat.
- A box - an automatic machine before starting to move requires careful warming up, especially in winter.
- It is not recommended to move the selector lever to the P and R positions while driving.
- There is no need to turn on neutral when descending a mountain, there will be no fuel economy (as it is believed), but braking problems may arise.
- Engine braking is not available in all modes. Learn more about operation in various modes the manufacturer gives instructions in the manual. For all our carelessness, it is advisable to adhere to these instructions. First of all - this, and secondly, not the last - this is the cost of repairs or complete replacement gentle and sensitive unit - automatic transmission
Well, actually, you can start, warm up and start moving.
Good luck to you car lovers.
