Automatic transmission circuit diagram and work. Automatic transmission principle of operation

20.09.2019

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The first torque converter appeared more than a hundred years ago. Having undergone many modifications and improvements, this effective method of smooth transmission of torque is now used in many areas of mechanical engineering, and the automotive industry is no exception. Driving a car has become much easier and more comfortable, since now there is no need to use the clutch pedal. The device and principle of operation of the torque converter, like everything ingenious, are very simple.

History of appearance

The world's first mass-produced passenger car without a clutch pedal

The principle of transmitting torque by means of fluid recirculation between two impellers without a rigid connection was first patented by the German engineer Hermann Fettinger in 1905. Devices operating on the basis of this principle are called a fluid coupling. At that time, the development of shipbuilding required designers to find a way to gradually transfer torque from a steam engine to huge ship propellers in the water. With a rigid connection, the water retarded the sharp stroke of the blades at start-up, creating an excessive reverse load on the engine, shafts and their connections.

Subsequently, modernized fluid couplings were used on London buses and the first diesel locomotives in order to ensure their smooth starting. And even later, fluid couplings made life easier for car drivers. The first production car with a torque converter, the Oldsmobile Custom 8 Cruiser, rolled off the General Motors factory in 1939.

Device and principle of operation

Torque converter device

The torque converter is a closed chamber of a toroidal shape, inside which pump, reactor and turbine impellers are placed close to each other coaxially. The internal volume of the torque converter is filled with automatic transmission fluid circulating in a circle, from one wheel to another. The pump wheel is made in the torque converter housing and is rigidly connected to the crankshaft, i.e. rotates with engine speed. The turbine wheel is rigidly connected to the input shaft of the automatic transmission.

Between them is the reactor wheel, or stator. The reactor is mounted on a freewheel that allows it to rotate in one direction only. The blades of the reactor have a special geometry, due to which the fluid flow returned from the turbine wheel to the pump wheel changes its direction, thereby increasing the torque on the pump wheel. This is the difference between a torque converter and a hydraulic clutch. In the latter, there is no reactor, and, accordingly, the torque does not increase.

Torque converter - principle of operation

Principle of operation The torque converter is based on the transfer of torque from the engine to the transmission through a recirculating fluid flow, without a rigid connection.

The driving pump wheel, connected to the rotating crankshaft of the engine, creates a fluid flow that falls on the blades of the turbine wheel located opposite. Under the influence of fluid, it sets in motion and transmits torque to the input shaft of the transmission.

With an increase in engine speed, the speed of rotation of the pump wheel increases, which leads to an increase in the force of the fluid flow, entraining the turbine wheel. In addition, the liquid, returning through the reactor blades, receives additional acceleration.

The fluid flow is transformed depending on the rotation speed of the impeller. At the moment of alignment of the speeds of the turbine and pump wheels, the reactor prevents the free circulation of the liquid and begins to rotate due to the installed freewheel. All three wheels rotate together, and the system begins to work in fluid coupling mode, without increasing torque. With an increase in the load on the output shaft, the speed of the turbine wheel slows down relative to the pump wheel, the reactor is blocked and again begins to transform the fluid flow.

Advantages

Smoothness of movement and starting off.
Reducing vibrations and loads on the transmission from uneven engine operation.
Ability to increase engine torque.
No need for maintenance (replacement of elements, etc.).

Flaws

Low efficiency (due to the absence of hydraulic losses and rigid connection with the engine).
Poor vehicle dynamics associated with the cost of power and time to spin up the fluid flow.
High price.

Lock mode

Lock-up torque converter device

In order to cope with the main shortcomings of the torque converter (low efficiency and poor vehicle dynamics), a locking mechanism was developed. The principle of its operation is similar to the classic clutch. The mechanism consists of a blocking plate, which is connected to the turbine wheel (and therefore to the gearbox input shaft) through the torsional vibration damper springs. The plate on its surface has a friction lining. At the command of the transmission control unit, the plate is pressed against the inner surface of the torque converter housing by means of fluid pressure. Torque begins to be transmitted directly from the engine to the gearbox without the participation of fluid. In this way, loss reduction and higher efficiency are achieved. The lock can be engaged in any gear.

Slip mode

Torque converter lockup may also be incomplete and operate in what is known as "slip mode". The blocking plate is not completely pressed against the working surface, thereby ensuring partial slippage of the friction lining. The torque is transmitted simultaneously through the blocking plate and the circulating fluid. Thanks to the use of this mode, the car's dynamic qualities are significantly increased, but at the same time, smoothness of movement is maintained. The electronics ensures that the lock-up clutch is engaged as early as possible during acceleration, and disengaged as late as possible when decelerating.

However, the controlled slip mode has a significant drawback associated with abrasion of friction surfaces, which are also subjected to strong temperature effects. Wear products get into the oil, worsening its working properties. The slip mode allows you to make the torque converter as efficient as possible, but at the same time significantly reduces its service life.

There are more and more vehicles with automatic transmission every year. And, if here - in Russia and the CIS - "mechanics" still continues to prevail over "automatic", then in the West, cars with automatic transmission are now in the vast majority. This is not surprising if we take into account the undeniable advantages of automatic transmissions: simplification of driving, consistently smooth transitions from one gear to another, protection of the engine from overloads, etc. adverse operating conditions, increasing driver comfort while driving. As for the shortcomings of this transmission option, modern automatic transmissions, as they improve, gradually get rid of them, make them insignificant. In this publication - about the device of the "automatic" box and all its pluses / minuses in work.

An automatic transmission is a type of transmission that provides automatic, without direct driver intervention, the choice of gear ratio that best suits the current driving conditions of the vehicle. The variator does not apply to automatic transmission and is allocated to a separate (stepless) class of transmissions. Because the variator makes changes in gear ratios smoothly, without any fixed gear stages at all.

The idea of automating gear shifting, saving the driver from having to frequently depress the clutch pedal and “work” with the gear lever, is not new. It began to be introduced and perfected at the dawn of the automotive era: at the beginning of the twentieth century. Moreover, it is impossible to name any particular person or company as the sole creator of an automatic transmission: three initially independent lines of development led to the emergence of the classic, now widely used hydromechanical automatic transmission, which eventually merged into a single design.

One of the main mechanisms of the automatic gearbox is the planetary gear set. The first mass-produced car equipped with a planetary gearbox was produced back in 1908, and it was the Ford T. Although in general that gearbox was not yet fully automatic (the driver of the Ford T was required to press two foot pedals, the first of which shifted from lower to higher gear, and the second included reverse), it already made it possible to significantly simplify control, according to compared to conventional gearboxes of those years, without synchronizers.

The second important point in the development of the technology of future automatic transmissions is the transfer of clutch control from the driver to a servo drive, embodied in the 30s of the twentieth century by General Motors. These gearboxes were called semi-automatic. The first fully automatic gearbox was the Kotal planetary electromechanical gearbox introduced into production in the 1930s. It was installed on French cars of the now forgotten Delage and Delaye brands (they existed until 1953 and 1954, respectively).

The car "Deljazh D8" is a premium class of the pre-war era.

Other auto manufacturers in Europe also developed similar clutch and band systems. Soon, similar automatic transmissions were implemented in cars of several more German and British brands, the famous and now living of which is the Maybach.

Specialists from another well-known company, the American Chrysler, have gone further than other automakers by introducing hydraulic elements into the design of the gearbox, which replaced servo drives and electromechanical controls. Chrysler engineers developed the first ever torque converter and fluid clutch, which are now included in every automatic transmission. And the first ever hydromechanical automatic transmission, similar in design to the modern one, was introduced on production cars by the General Motors Corporation.

Automatic transmissions of those years were very expensive and technically complex mechanisms. In addition, not always distinguished by reliable and durable work. They could look advantageous only in the era of non-synchronized manual transmissions, driving a car with which was quite hard work, requiring a well-developed skill from the driver. When mechanical gearboxes with synchronizers became widespread, automatic transmissions of that level were not much better than them in terms of convenience and comfort. While manual transmissions with synchronizers had much less complexity and high cost.

In the late 1980s/1990s, all major automakers were computerizing their engine management systems. Systems similar to them began to be used to control the switching of speeds. Whereas previous solutions used only hydraulics and mechanical valves, now computer-controlled solenoids began to control fluid flows. This made shifting smoother and more comfortable, improved economy and increased transmission efficiency.

In addition, some cars were introduced "sports" and other additional modes of operation, the ability to manually control the gearbox ("Tiptronic", etc. systems). The first five- and more-speed automatic transmissions appeared. The improvement of consumables made it possible on many automatic transmissions to cancel the oil change procedure during the operation of the car, since the resource of the oil poured into its crankcase at the factory became comparable to the resource of the gearbox itself.

The design of the automatic transmission

A modern automatic transmission, or "hydromechanical transmission", consists of:

torque converter (aka “hydrodynamic transformer, gas turbine engine”);
planetary mechanism for automatic gear shifting; brake band, rear and front clutches - devices that directly change gears;
control device (assembly consisting of a pump, valve box and oil collector).

A torque converter is needed to transmit torque from the power unit to the elements of an automatic transmission. It is located between the gearbox and the motor, and thus performs the function of a clutch. The torque converter is filled with a working fluid that captures and transfers engine energy to the oil pump, located directly in the box.

The torque converter consists of large wheels with blades immersed in a special oil. The transmission of torque is not carried out by a mechanical device, but by means of oil flows and their pressure. Inside the torque converter there are a pair of vane machines - a centripetal turbine and a centrifugal pump, and between them - a reactor, which is responsible for smooth and stable changes in torque on the drives to the wheels of the vehicle. So, the torque converter does not come into contact with either the driver or the clutch (it “is” the clutch itself).

The pump wheel is connected to the engine crankshaft, and the turbine wheel is connected to the transmission. When the pump wheel rotates, the oil flows thrown off by it spin the turbine wheel. So that the torque can be changed over a wide range, a reactor wheel is provided between the pump and turbine wheels. Which, depending on the mode of movement of the car, can be either stationary or rotate. When the reactor is stationary, it increases the flow rate of the working fluid circulating between the wheels. The higher the speed of the oil, the greater the effect it has on the turbine wheel. Thus, the moment on the turbine wheel increases, i.e. the device "transforms" it.

But the torque converter cannot convert the speed of rotation and the transmitted torque within all required limits. Yes, and to provide movement in reverse, he is also not in force. To expand these capabilities, a set of separate planetary gears with different gear ratios is attached to it. Like several single-stage gearboxes assembled in one case.

The planetary gear is a mechanical system consisting of several satellite gears that rotate around a central gear. The satellites are fixed together with the help of a carrier circle. The outer ring gear is internally meshed with the planetary gears. The satellites fixed on the carrier rotate around the central gear, like the planets around the Sun (hence the name of the mechanism - “planetary gear”), the outer gear rotates around the satellites. Different gear ratios are achieved by fixing different parts relative to each other.

Brake band, rear and front clutch - directly change gears from one to another. The brake is a mechanism that blocks the elements of the planetary gear set on the fixed body of the automatic transmission. The friction clutch blocks the moving elements of the planetary gear set among themselves.

Automatic transmission control systems are of 2 types: hydraulic and electronic. Hydraulic systems are used on obsolete or budget models, and are gradually being phased out. And all modern automatic boxes are electronically controlled.

The life support device for any control system can be called an oil pump. Its drive is carried out directly from the crankshaft of the engine. The oil pump creates and maintains a constant pressure in the hydraulic system, regardless of the engine speed and engine loads. If the pressure deviates from the nominal value, the operation of the automatic transmission is disrupted due to the fact that the gear shift actuators are controlled by pressure.

The shift point is determined by vehicle speed and engine load. To do this, a pair of sensors is provided in the hydraulic control system: a high-speed regulator and a throttle valve, or modulator. A high-speed pressure regulator or hydraulic speed sensor is installed on the output shaft of the automatic transmission.

The faster the vehicle travels, the more the valve opens, and the greater the pressure of the transmission fluid passing through this valve becomes. Designed to determine the load on the engine, the throttle valve is connected by a cable either to the throttle valve (if we are talking about a gasoline engine) or to the high pressure fuel pump lever (in a diesel engine).

In some cars, not a cable is used to supply pressure to the throttle valve, but a vacuum modulator, which is activated by a vacuum in the intake manifold (the vacuum decreases as the load on the engine increases). Thus, these valves create such pressures that will be proportional to the speed of the vehicle and the workload of its engine. The ratio of these pressures and allows you to determine the moments of gear shifting and blocking of the torque converter.

In the "catching the moment" of the gear shift, the range selection valve is also involved, which is connected to the automatic transmission selector lever and, depending on its position, allows or prohibits the inclusion of certain gears. The resulting pressure created by the throttle valve and the speed regulator causes the corresponding switching valve to actuate. Moreover, if the car accelerates quickly, then the control system will turn on the higher gear later than when accelerating calmly and evenly.

How it's done? The changeover valve is under oil pressure from the high-speed pressure regulator on one side, and from the throttle valve on the other. If the machine is accelerating slowly, then the pressure from the hydraulic speed valve builds up, which causes the shift valve to open. Since the accelerator pedal is not fully depressed, the throttle valve does not create much pressure on the shift valve. If the car accelerates quickly, then the throttle valve creates more pressure on the shift valve, and prevents it from opening. To overcome this opposition, the pressure from the high-speed pressure regulator must exceed the pressure from the throttle valve. But this will happen when the car reaches a higher speed than it does when accelerating slowly.

Each shift valve corresponds to a certain level of pressure: the faster the car moves, the higher the gear will be engaged. The valve block is a system of channels with valves and plungers located in them. The switching valves supply hydraulic pressure to the actuators: clutches and brake bands, through which the various elements of the planetary gear are blocked and, consequently, the switching on (off) of various gears.

Electronic control system just like hydraulic, it uses 2 main parameters for operation. This is the speed of the car and the load on its engine. But to determine these parameters, not mechanical, but electronic sensors are used. The main ones are working sensors: speed at the input of the gearbox; speed at the output of the gearbox; working fluid temperature; selector lever position; accelerator pedal position. In addition, the control unit of the "automatic" box receives additional information from the engine control unit, and from other electronic systems of the car (in particular, from ABS - anti-lock braking system).

This allows you to more accurately determine the moments of need for switching or locking the torque converter than in a conventional automatic transmission. Based on the nature of the change in speed for a given engine load, an electronic gearshift program can easily and instantly calculate the force of resistance to vehicle movement and, if necessary, adjust: introduce appropriate amendments into the shifting algorithm. For example, later include higher gears on a fully loaded vehicle.

In other respects, automatic transmissions with electronic control, just like conventional, "not burdened with electronics" hydromechanical gearboxes, use hydraulics to engage clutches and brake bands. However, with them, each hydraulic circuit is controlled by a solenoid valve, not a hydraulic valve.

Before the start of the movement, the pump wheel rotates, the reactor and turbine wheels remain stationary. The reactor wheel is fixed on the shaft by means of an overrunning clutch, and therefore it can only rotate in one direction. When the driver turns on the gear, presses the gas pedal, the engine speed increases, the pump wheel picks up speed and the turbine wheel spins with oil flows.

The oil thrown back by the turbine wheel falls on the fixed blades of the reactor, which additionally “twist” the flow of this liquid, increasing its kinetic energy, and direct it to the blades of the pump wheel. Thus, with the help of the reactor, the torque increases, which is what is required for the vehicle gaining acceleration. When the car accelerates and begins to move at a constant speed, the pump and turbine wheels rotate at approximately the same speed. Moreover, the oil flow from the turbine wheel enters the reactor blades from the other side, due to which the reactor begins to rotate. There is no increase in torque, and the torque converter goes into a uniform fluid coupling mode. If the resistance to the movement of the car began to increase (for example, the car began to go uphill), then the speed of rotation of the driving wheels, and, accordingly, the turbine wheel, falls. In this case, the oil flows again slow down the reactor - and the torque increases. Thus, automatic torque control is performed, depending on changes in the driving mode of the vehicle.

The absence of a rigid connection in the torque converter has both advantages and disadvantages. The advantages are that the torque changes smoothly and steplessly, torsional vibrations and jerks transmitted from the engine to the transmission are damped. The disadvantages are, first of all, in the low efficiency, since part of the useful energy is simply lost when the oil liquid is “shoveled” and is spent on driving the automatic transmission pump, which ultimately leads to an increase in fuel consumption.

But to smooth this shortcoming in the torque converters of modern automatic transmissions, a blocking mode is used. In the steady state of motion in higher gears, the mechanical blocking of the torque converter wheels is automatically activated, that is, it begins to perform the function of a conventional classic clutch mechanism. This ensures a rigid direct connection of the engine with the drive wheels, as in a mechanical transmission. On some automatic transmissions, the inclusion of the lock mode is also provided for in lower gears too. The movement with blocking is the most economical mode of operation of the “automatic” box. And when the load on the drive wheels increases, the lock is automatically turned off.

During the operation of the torque converter, a significant heating of the working fluid occurs, which is why the design of automatic transmissions provides for a cooling system with a radiator, which is either built into the engine radiator or installed separately.

Any modern “automatic” box has the following mandatory provisions on the cab selector lever:

P - parking, or parking lock: blocking the drive wheels (does not interact with the parking brake). Similarly, as in the "mechanics" the car is left "at speed" when parked;
R - reverse, reverse gear (it was always forbidden to activate it at the moment the car was moving, and then a corresponding lock was provided in the design);
N - neutral, neutral gear mode (activated during a short stop or when towing);

D - drive, forward movement (in this mode, the entire gear ratio of the box will be involved, sometimes two higher gears are cut off).

And it may also have some additional, auxiliary or advanced modes. In particular:

L - “downshift”, activation of the low gear mode (slow speed) for the purpose of moving in difficult road or off-road conditions;
O/D - overdrive. Mode of economy and measured movement (whenever possible, the “automatic” 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.
The automatic transmission may also have a special button that prohibits shifting to a higher gear when overtaking.

Advantages and disadvantages automatic boxes

As already noted, the significant advantages of automatic transmissions, compared with mechanical ones, are: the simplicity and comfort of driving a vehicle for the driver: you do not need to squeeze the clutch, you also need to “work” with the gear lever. This is especially true when traveling around the city, which, in the end, make up the lion's share of the car's mileage.

Gear shifts on the "automatic" are smoother and more uniform, which helps protect the engine and the leading components of the car from overloads. There are no consumable parts (for example, a clutch disc or a cable), and therefore it is more difficult to disable the automatic transmission, in this sense. In general, the resource of many modern automatic transmissions exceeds the resource of manual transmissions.

The disadvantages of automatic transmissions include a more expensive and complex design than manual transmissions; the complexity of repair and its high cost, lower efficiency, worse dynamics and increased fuel consumption compared to manual transmission. Although, the improved electronics of the 21st century automatic gearboxes cope with the right choice of torque no worse than an experienced driver. Modern automatic transmissions are often equipped with additional modes that allow you to adapt to a specific driving style - from calm to "frisky".

A serious disadvantage of automatic gearboxes is the impossibility of the most accurate and safe gear shifting in extreme conditions - for example, in difficult overtaking; at the exit from a snowdrift or serious mud, by quickly shifting reverse and first gear (“in buildup”), if necessary, start the engine “with a pusher”. It must be admitted that automatic transmissions are ideal, mainly for ordinary trips without emergency situations. First of all - on city roads. “Automatic” boxes are not very suitable for “sports driving” either (acceleration dynamics lag behind “mechanics” in conjunction with an “advanced” driver) and for off-road rallying (it can’t always perfectly adapt to changing driving conditions).

As for fuel consumption, in any case, an automatic transmission will have more than a mechanical one. However, if earlier this figure was 10-15%, then in modern cars it has dropped to insignificant levels.

In general, the use of electronics has significantly expanded the capabilities of automatic transmissions. They received various additional modes of operation: such as economical, sports, winter.

The sharp increase in the prevalence of “automatic” boxes was caused by the appearance of the “Autostick” mode, which allows the driver, if desired, to independently select the desired gear. Each manufacturer gave this type of automatic transmission its own name: "Audi" - "Tiptronic", "BMW" - "Steptronic", etc.

Thanks to advanced electronics in modern automatic transmissions, the possibility of their “self-improvement” has also become available. That is, changes in the switching algorithm depending on the specific driving style of the "owner". Electronics has provided advanced features for automatic transmission self-diagnosis as well. And it's not just about remembering fault codes. The control program, controlling the wear of the friction discs, the oil temperature, promptly makes the necessary adjustments to the operation of the automatic transmission.

gear.

Read in this article

Hydraulic pump: device and principle of operation

GDT includes the following parts:

Pump wheel;
Reactor (stator);
Turbine wheel;
Locking mechanism;

These parts are in a single strong and sealed case, which is usually mounted on the ICE flywheel. Also, the torque converter is filled with ATF transmission fluid, and during operation, the oil noticeably heats up and mixes inside the gas turbine engine.

A pump wheel is rigidly attached to the torque converter housing, which rotates from the engine shaft and creates transmission fluid flows inside the converter. These flows, in turn, rotate the reactor as well as the turbine wheel. At the same time, a gas turbine engine differs from a conventional fluid coupling precisely in the presence of a reactor.

The reactor (aka stator) is connected to the pump wheel using a freewheel. Such a connection makes it possible to ensure that if the speed of the pump and the turbine differ greatly, then the reactor is blocked in automatic mode.

The stator lock allows more transmission fluid to be transferred to the impeller. The presence of a reactor in the GDT device allows you to increase the torque by 3 times during the acceleration of a car with automatic transmission. The turbine is connected to the gearbox shaft, the connection is rigid.

It is important to understand that the transmission of torque inside the torque converter occurs without a direct connection of the individual components, that is, the torque is actually transmitted through the fluid.

This means that shock loads are minimized, the machine with a torque converter accelerates smoothly from the start, there are no jerks, then while driving, gear changes are smooth.

However, this solution also has certain disadvantages. Increased heating often occurs inside the gas turbine engine. Such an increase in temperature occurs due to the fact that the turbine wheel slips relative to the pump wheel, since in most operating modes the torque of the turbine and pump wheels is not equal.

The result of slippage is significant heat generation, reduced transmission efficiency and increased fuel consumption. At the same time, in order to reduce fuel consumption, a torque converter lock-up is used, which is implemented using the GDT lock-up mechanism.

GDT blocking mechanism

The specified locking mechanism provides the possibility of a rigid connection between the pump and the turbine. If the torque converter is blocked, the automatic transmission operates in such a mode when the engine and transmission are rigidly connected to each other, the transmission of torque from the internal combustion engine to the automatic transmission occurs without loss.

GDT lock in the Box - an electronically controlled automatic machine works in such a way that the signal to turn on the locking mechanism comes from the gearbox, the lock itself is turned on according to a given algorithm prescribed in the program.

At the initial stage, many "machines" initiated the blocking of the torque converter only when the car accelerated to a certain speed (above 60-70 km / h). More modern automatic transmissions block the torque converter at low speeds (from 20 km / h).

As a result, fuel economy is achieved not only when driving on the highway, but also in the city, where the speed is usually low. A still locked torque converter allows you to achieve an effect on the automatic transmission at a certain speed.

Simply put, the engine ECU stops the supply of fuel to the cylinders at the moment when the torque converter lockup is activated. At this time, the engine shaft continues to rotate due to the movement of the car "freewheeling", and not due to energy from the combustion of fuel in the cylinders.

It would seem that locking the torque converter allows you to improve the performance of this type of transmission, achieve fuel efficiency, increase efficiency, etc. On the one hand, this is true, but the rigid connection between the internal combustion engine and the gearbox by blocking the gas turbine also means that shock loads begin to be transmitted to the motto and transmission.

As a result, the resource of the automatic gearbox decreases, since the inclusion of the locking mechanism increases the load and wears out faster. There is also a rapid contamination of the transmission oil, gears with a locked torque converter do not turn on so smoothly.

What is the result

As you can see, the torque converter is actually a separate unit, placed outside the body of the automatic transmission itself. At the same time, the normal operation of a hydromechanical gearbox without a torque converter (torque converter) is impossible. For this reason, the automatic transmission and gas turbine assembly are usually called "automatic transmission", that is, without separation of these units.

Finally, we note that even taking into account the strength of the housing, high loads on the torque converter (including temperature) can disable this element. As a result, the torque converter begins to flow, and malfunctions occur in the operation of the internal components of the device.

Given that the cost of torque converters for different models of automatic transmissions is quite high, many qualified automatic transmission repair shops repair torque converters. During the repair, the gas turbine engine is disassembled, worn elements are replaced, after which the body is welded in order to restore tightness.

Characteristic

In addition to this element, the design includes many other systems and mechanisms. But the main function (this is the transmission of torque) is performed by the automatic transmission torque converter. In common parlance, it is called a "donut" due to the characteristic shape of the structure.

It is worth noting that for front-wheel drive cars, the automatic transmission torque converter includes a differential and final drive. In addition to the function of transmitting torque, the "donut" takes on all the vibrations and shocks from the engine flywheel, thereby smoothing them to a minimum.

Design

Let's look at how the automatic transmission torque converter works. This element consists of several nodes:

Turbine wheel.
Lockup clutch.
pump.
Reactor wheel.
Freewheel clutches.

All these mechanisms are placed in a single case. The pump is directly connected to the engine crankshaft. The turbine mates with the gears of the gearbox. The reactor wheel is placed between the pump and the turbine. Also in the design of the “donut” wheel there are blades of a special shape. The operation of an automatic transmission torque converter is based on the movement of a special fluid inside (transmission oil). Therefore, the automatic transmission also includes oil channels. In addition, it has its own radiator. What it is for, we will consider a little later.

As for the clutches, the locking one is designed to fix the position of the torque converter in a certain mode (for example, "parking"). The freewheel clutch serves to rotate the reactor wheel in the opposite direction.

The principle of operation of the automatic transmission torque converter

How does this element work in the box? All actions of the "donut" are carried out in a closed cycle. So, the main working fluid here is the "transmission". It is worth noting that it differs in viscosity and composition from those used in mechanical boxes. During the operation of the torque converter, the lubricant flows from the pump to the turbine wheel, and then to the reactor wheel.

Thanks to the blades, the liquid begins to rotate faster inside the "donut", thereby increasing the torque. When the crankshaft speed increases, the angular velocity of the turbine and impeller equalize. The fluid flow changes its direction. When the car has already gained sufficient speed, the “donut” will only work in fluid coupling mode, that is, it will only transmit torque. When the speed of movement increases, the GTF is blocked. In this case, the clutch is closed, and the transmission of torque from the flywheel to the box is carried out directly, with the same frequency. The element disengages again when shifting to the next gear. This is how the smoothing of the angular velocities occurs again until the moment when the speed of rotation of the turbines becomes equal.

Radiator

Now about the radiator. Why is it separately displayed in automatic transmissions, because such a system is not used on the “mechanics”? Everything is very simple. On a mechanical box, oil performs only a lubricating function.

At the same time, it is only half filled. The fluid is contained in the transmission pan and the gears are wetted in it. In an automatic transmission, the oil performs the function of transmitting torque (hence the name "wet clutch"). There are no friction discs here - all energy goes through turbines and oil. The latter is constantly moving in channels under high pressure. Accordingly, the oil needs to be cooled. For this, such a transmission has its own heat exchanger.

Faults

The following transmission failures are distinguished:

GTF malfunction.
Breakage and
Malfunction of the oil pump and monitoring sensors.

How to determine a breakdown?

It is rather difficult to find out which element has failed without dismantling the box and disassembling it. However, it is possible to predict a serious repair by several signs. So, if there are malfunctions of the automatic transmission torque converter or brake band, the box will “kick” when switching modes. The car starts to twitch if you put the handle from one mode to another (and when the foot is on the brake pedal). Also, the box itself enters emergency mode. The car only moves in three gears. This suggests that the box needs serious diagnostics.

As for the replacement of the torque converter, it is carried out with the complete dismantling of the box (the drive shafts, the “bell” and other parts are disconnected). This element is the most expensive component of any automatic transmission. The price of a new gas turbine engine starts at $ 600 for budget car models. Therefore, it is important to know how to properly use the box in order to delay repairs as much as possible.

How to save checkpoint?

It is believed that the resource of this transmission is an order of magnitude lower than that of mechanics. However, experts note that with proper maintenance of the unit, you will not need to repair or replace the automatic transmission torque converter. So, the first recommendation is a timely oil change. Regulation - 60 thousand kilometers. And if at the manual transmission the oil is filled for the entire period of operation, then in the “machine” it is the working fluid. If the grease is black or has a burning smell, it needs to be replaced immediately.

The second recommendation concerns compliance with temperature regimes. Do not start driving too early - the temperature of the box oil should be at least 40 degrees. To do this, move the lever through all modes with a delay of 5-10 seconds. So you warm up the box and prepare it for operation. It is undesirable to drive in cold oil, as well as in very hot. In the latter case, the liquid will literally burn (when replacing, you will hear the smell of burning). The automatic transmission is not suitable for drifting and hard use. Also, do not turn on the neutral gear on the go, and then turn on the "drive" again. So you will break the brake band and a number of other important elements in the box.

Conclusion

So, we found out what an automatic transmission torque converter is. As you can see, this is a very important node in the box. It is through it that torque is transmitted to the box, and then to the wheels. And since the oil is the working fluid here, you must follow the regulations for its replacement. So the box will delight you with a long resource and smooth switching.

Now most cars are produced with automatic transmissions or CVTs, since these types of transmissions are more convenient to use compared to a manual transmission.

What role does the torque converter play?

To ensure smooth shifting and ensure continuous transmission of torque (for the CVT), a completely different type of clutch is used.

In cars with a CVT and automatic transmission, a torque converter acts as a clutch - an element that transmits torque from the power plant to the gearbox.

The peculiarity of this element, which is part of the transmission design, is that the transmission of force occurs through a fluid, that is, there is no rigid connection between the motor and the gearbox (although this is not entirely true).

The torque converter allows for stepless transmission of force, and with the possibility of changing the torque and speed of rotation.

Also, at the moment of changing the stage (in automatic transmission), the torque converter allows you to disconnect the engine and transmission from each other, and then smoothly resume the transfer of force.

In fact, the device acts as a clutch, but with some additional functions.

Device, principle of operation, modes

The design of the torque converter includes only a few elements:

Pump wheel;
Turbine wheel;
Stator, aka reactor;
Frame;
Locking mechanism;

The torque converter is mounted on the engine flywheel, but one of its components has a rigid connection with the gearbox shaft.

If we draw an analogy of this type of transmission with a conventional friction-type clutch, then the pump wheel acts as a drive disk (rigidly connected to the engine crankshaft), and the turbine wheel acts as a driven disk (attached to the gearbox shaft). But there is no physical contact between these wheels.

It is noteworthy that even the location of these wheels is identical to the friction clutch - the turbine wheel is located between the flywheel and the pump wheel.

All components of the torque converter are enclosed in a sealed housing filled with a special working fluid - ATF oil. Due to its shape, this transmission element received the popular name "donut".

The essence of the torque converter is very simple. On the wheels of the device there are blades that redirect the liquid in a certain direction.

Rotating together with the flywheel, the pump wheel creates a fluid flow and directs it to the turbine blades, thereby ensuring the transfer of force.

If the design included only these two wheels, then the torque converter would not differ from the fluid coupling, in which the torque on both components is almost the same.

But the task of the torque converter is not only the transmission of force, but also its change.

So, at the start, it is necessary to ensure an increase in the torque on the driven wheel (at the start of movement), and during uniform movement, to exclude the so-called “slippage”.

To perform these functions, a reactor and a blocking mechanism are provided in the design.

The reactor is another paddle wheel, but of a much smaller diameter, and it is located between the turbine and the pump, the reactor is connected to the latter by means of an overrunning clutch.

The task of this element is to increase the fluid flow rate, which leads to an increase in torque.

The reactor works like this: if there is a big difference between the main wheels of the torque converter, the overrunning clutch blocks the reactor, preventing it from rotating (because of this, another name for the component is the stator).

At the same time, its blades, which have a special shape, increase the speed of the fluid flow that enters it after passing through the turbine wheel, and direct it back to the pump.

Thus, the reactor significantly increases the torque required to generate sufficient force at the start of movement.

With uniform movement, the torque converter is blocked, that is, a rigid connection appears in it, and this is done by the locking mechanism used in the design.

Previously, in automatic transmissions, this component worked only at higher speeds. Now, the electronic gearbox control systems used block the torque converter in almost all stages.

That is, as soon as the torque for a certain gear approaches the required parameters, the mechanism works.

When changing gear, it turns off to ensure smooth shifting and turns on again. This eliminates the possibility of "slippage" of the torque converter, which increases its resource, reduces loss of effort and reduces fuel consumption.

It is noteworthy that the locking mechanism is, in fact, a friction clutch, and it works on the same principle. That is, the design has a friction disc, which is fixed on the turbine.

In the disengaged state of the locking mechanism, this disk is in the depressed state. When the lock is turned on, the clutches are pressed against the torque converter housing, thereby achieving a rigid transmission of torque from the motor to the gearbox.

In general, if we consider the functioning of the torque converter, then there are three modes of its operation:

Transformation (turns on when an increase in torque is required to create more effort. The reactor operates in this mode, providing an increase in the flow rate);
Fluid clutch (in this mode, the reactor is not involved and the torque on the driving and driven wheels is almost the same);
Blocking (the turbine is rigidly connected to the body to reduce slippage losses).

The electronic system used to control the operation of the torque converter provides a very quick change in its operating mode, adjusting the functioning of this element to the emerging conditions.

Features of torque converters of different cars

Despite the fact that many automakers are trying to introduce their own design features into the arrangement of transmission elements, the torque converter is almost identical for everyone.

If there is a difference, then it usually comes down to some small details, as well as materials for the manufacture of component parts.

For example, in Subaru cars, the "weak point" of the torque converter is the friction lining of the locking mechanism. Especially such a malfunction manifests itself on cars equipped with the latest generation automatic transmission.

On BMWs equipped with ZF gearboxes, many car owners had problems with the electronic control system, which led to vibrations at certain speeds, bumps when switching, etc.

That is, all problems with the torque converter arose due to its improper control.

It is worth noting that because of this, the checkpoint itself worked problematic, so it is very difficult to identify the cause.

On Mazda vehicles with automatic transmissions, the most common torque converter problem is the rapid wear of the reactor overrunning clutch.

And so with almost every brand of car - there is sure to be some specific component of the device that fails most often.

Node malfunctions

Although the torque converter itself has a not particularly complex design, with not so many components, there are a lot of malfunctions that can occur with it. Some of them have already been mentioned above.

Since this element is the link between the power unit and the gearbox, problems in its operation immediately affect the functioning of the transmission.

The main breakdowns of the torque converter are:

Wear of bearings - support or intermediate (between the turbine and the pump). This malfunction manifests itself in the form of a soft rustling sound when the transmission is operating without load. As the speed increases, this sound disappears, but gradually the range of automatic transmission modes in which the sound is present will expand. This problem is eliminated by disassembly, troubleshooting and replacement of worn elements;
Severe clogging of the oil filter. This problem is accompanied by the appearance of vibration - first at high speeds, then in almost all modes, and the vibration itself will increase. The malfunction is eliminated by replacing the filter element and working fluid;
Overrunning clutch worn or damaged. Because of this, the reactor does not work, so the increase in torque does not occur. As a result, the car's acceleration dynamics decreases. The problem is “treated” by replacing the clutch;
Breakage of the splined connection of the turbine wheel with the gearbox shaft. The result of such a breakdown is the cessation of movement, since rotation is simply not transmitted to the box. The malfunction is eliminated by restoring the spline connection (in some cases, by replacing the torque converter);
Destruction of the wheel blades or the reactor. A malfunction is accompanied by the appearance of a loud metal rattle and knock. Repair in this case consists of replacing damaged components or the entire assembly;
"Oil Starvation" Lack of oil leads to overheating, melting of plastic elements. The consequences of a lack of lubricant can be the most serious, therefore, it will not be possible to restore the transmission to work together with the torque converter by restoring the ATP level, it will be necessary to disassemble the nodes, assess the condition of the element and replace the damaged components;
Overheat. Occurs either due to "oil starvation", or due to clogging of the gearbox cooling system. In the second case, cleaning of the radiator, filters, replacement of the working fluid is required;
Control system malfunction. The problem manifests itself by unauthorized stopping of the power plant when switching automatic transmission stages. The malfunction is eliminated by diagnostics and replacement of elements of the electronic component of the transmission.

It is worth noting that the indicated signs of certain malfunctions can be considered indirect, and it is impossible to accurately determine the problem with the components of the torque converter, especially since many of the signs are also inherent in breakdowns of automatic transmissions.