Recently, automatic transmissions are gaining more and more popularity. And there are reasons for that. Such a box is simpler to operate and does not require constant “play” with clutch in traffic jams. In large cities, such a checkpoint is far from rare. But the automatic transmission device is significantly different from classical mechanics. Many motorists are afraid to take cars with such a box. However, their fears are not justified. With proper operation, the automatic transmission will serve no less than mechanics. But in order to better understand it, you should study in detail the automatic transmission device of the car. We will talk about this in our article today.
Varieties
There are several types of data boxes. So, they distinguish:
- Hydromechanical automatic transmission.
- Robotic (DSG).
- CVT.
What are the features of each of them? Consider below.
Classic automatic
Hydromechanical transmission is the most common type of automatic transmission. The device of such a box assumes the presence of a torque converter, a mechanical gearbox and a control system. But this design is practiced on cars with rear-wheel drive. If this is a front-wheel drive car, then the differential is also included in the automatic transmission device, and the main gear.
The torque converter (the common name is “donut”) is the main unit in this transmission. It serves to change and transmit torque from the engine flywheel to the manual gearbox. Also, the bagel serves to damp vibrations and vibrations that occur during the transmission of rotational forces from the internal combustion engine.
The torque converter consists of several wheels. It:
- Turbine.
- Reactor.
- Pump wheel.
The design also includes two couplings - interlock and freewheel. All these details are enclosed in a separate toroidal casing, which looks like a donut (hence the specific name).
The pump wheel is connected to the crankshaft of the motor. Turbine interacts with a manual gearbox. A reactor wheel is located between these two elements. It, unlike all others, is motionless. Each wheel of the automatic transmission hydraulic transformer has blades, between which the working ATP-liquid passes.
The automatic transmission lock-up clutch is designed to block GTF (bagel) in specific ICE operation modes. A freewheel (also referred to as a freewheel) rotates the reactor wheel in the opposite direction.
GTF work
It is carried out in a closed cycle. So, ATP-liquid begins to flow from the pump to the turbine, and then to the reactor wheel due to the special shape of the blades, the oil flow rate begins to grow steadily. ATP-fluid makes the pump wheel rotate faster. Due to this, the power of torque increases. By the way, its maximum parameter is achieved at minimum speeds. This is necessary in order for the machine to move freely without hindrance even under load. When the car starts to pick up speed, the clutch is activated and the torque converter is blocked. In this situation, direct torque transmission is performed. It is worth noting that the lockup clutch is used in the automatic transmission in all gears, including the rear.
In modern cars, a slip clutch is used. This mode allows you to prevent a complete blockage of the mechanism, which has a positive effect on fuel consumption and ride smoothness.
Planetary reductor
This unit performs the function of a mechanical gearbox. The gearbox can be designed for four, six, seven or eight speeds. In rare cases, a nine-speed automatic transmission is used (for example, on Land Rover cars).
We continue to study the automatic transmission device. The planetary gear consists of several sequential gears. They form a planetary gear set. Each of the speeds includes several elements:
- Crown gear.
- Satellites.
- Sun gear.
- Drove.
How is the torque change made? Studying the automatic transmission torque converter device , it should be noted that this operation is performed using several elements of the planetary gear set. This drove, as well as two gears (solar and crown). Blocking the latter allows you to increase the gear ratio. The sun gear, on the contrary, reduces this ratio. And the carrier carries out a change in the direction of rotation of the elements.
Locking is carried out using clutches. This is a kind of brake that holds certain gear parts by connecting them to the gearbox housing. Depending on the brand of car (“Mazda” or “Ford”), the automatic transmission device assumes the presence of a tape or multi-disc brake. It closes with hydraulic cylinders. The latter are controlled from the distribution module. To prevent rotation of the carrier in the opposite direction, an overrunning clutch is used.
Electronic system
The device and automatic transmission operation of a modern car is impossible without an electronic control system. It includes:
- Control block.
- Input sensors.
- Automatic selector (we will consider the device later).
- Distribution module.
Note that the list of input elements is quite extensive. So, this includes sensors:
- The position of the gas pedal.
- ATP fluid temperatures.
- Shaft speeds at the inlet and outlet.
- Automatic gear selector positions.
The automatic transmission control unit continuously processes the signals that come from these elements and generates control pulses for the actuators. This unit interacts with the engine ECU.
The distribution module activates the friction clutches and controls the ATP fluid flows in the transmission. This module consists of spool valves, as well as solenoid valves with a mechanical actuator. These parts are enclosed in a separate aluminum housing and are interconnected by channels.
An important element in the Honda automatic transmission device is the solenoids. They are also called solenoid valves. They are needed to control the transmission oil pressure. And the spools perform the operation mode of the box. Elements are driven by an automatic transmission lever.
Since the main working fluid is ATP-oil, a gear pump is provided in the device of any automatic transmission. It works from the hub of the torque converter and is the basis of the gearbox hydraulic system. A special heat exchanger is provided in the Mercedes automatic transmission device for cooling the oil. This is a small radiator that is located in front of the car. On some models, it is enclosed with a main engine coolant radiator.
Automatic selector
It is this part that directly controls the automatic transmission. There are several automatic transmission modes:
- Parking.
- Reverse.
- Neutral.
- Drive (moving forward).
On some Nissan cars, the automatic transmission device requires a sport mode. To turn it on, it is necessary to put the gearbox selector in position S. The mode differs in that the gear change is carried out at higher engine speeds. Thereby, more torque and speed of the car are achieved. If we consider the "Qashqai Nissan", the automatic transmission device also implies the presence of a manual gearshift mode. Such a box is called Tiptronic.
DSG robotic transmission
This is the development of the concern Volkswagen Audi. This checkpoint appeared in the mid-2000s and is installed on most Skoda and Audi passenger cars, as well as on Volkswagen (including the Tuareg).
A key feature of the DSG automatic gearbox is a quick gear shift without breaking the power flow. This allows you to increase the performance and efficiency of the transmission. Cars with DSG are characterized by good acceleration dynamics. At the same time, they have lower fuel consumption compared to classic torque converters.
The device and operation of the automatic transmission of this type differs significantly from the previous gearbox. So, there is no familiar “donut”. Torque transmission through the use of two clutches. In addition, an anti-theft device can be installed on an automatic transmission of this type.
DSG transmission
It includes:
- Two-mass flywheel.
- Two rows of gears.
- Main gear and differential.
- Electronic control system.
- Double grip.
All this is enclosed in a metal case box. If we talk about dual clutch, it provides power transmission simultaneously to the second and first row of gears. If it is a six-speed DSG, there is a drive disk in the box (it is connected to a two-mass flywheel through the input hub) and friction clutches. The latter are connected with rows of gears through the main hub.
By the way, the type of clutch may differ on the DSG box. If it is a six-speed gearbox, the design uses a wet clutch. The oil provides not only lubrication, but also cooling of the friction discs. This significantly increases the resource units.
If we talk about a seven-speed transmission, a dry circuit is used here. This significantly reduces the amount of oil used. If in the first case, at least six and a half liters were required for the DSG to work, then in the second - no more than two. The pump that pumps the grease is electric. Such a design, according to experts, is less reliable and does not have a high resource.
As for the series of gears, the first is responsible for the operation of reverse and odd speeds. The second is used to control even gears. Each of the rows is a secondary and primary shaft with a specific set of gears. The primary element is complete and aligned, and the gears are rigidly connected to the shaft. At the same time, the secondary gears rotate freely. Also in the design there are synchronizers. They facilitate the inclusion of a particular speed in the checkpoint. In order for the car to move backward, an intermediate currency is provided in the DSG box; it is equipped with a reversing gear.
Gearshift control is provided by the electronics. It includes various sensors, a control unit and an electro-hydraulic unit with a mass of actuators. The control module is located in the crankcase of the automatic robotic gearbox. When operating the gearbox, the sensors analyze the speed of the shafts at the outlet and inlet, the oil pressure, the position of the forks for turning on the speeds, and also the temperature of the lubricant. Based on these signals, the ECU implements one or another control algorithm.
Thanks to the block, the hydraulic circuit of the gearbox is controlled. This system includes:
- Spool valves. They are driven by a gearshift lever.
- Solenoid valves These elements are used to switch speeds.
- Pressure control valves. Thanks to them, the friction clutch is operated.
The last two components relate to the executive control mechanisms of the robotic gearbox.
Also in the design of this box provides a multiplexer. It allows you to control hydraulic cylinders using electromagnetic valves. What is noteworthy, the number of the former is twice that of the latter. Thus, in the initial position of the element, some hydraulic cylinders are involved, and in the working position - others.
The algorithm of the robotic transmission consists in sequentially switching several rows of gears. So, when the car begins to move on the first, the second is already engaged with the second disk. After a set of certain revolutions, instant switching occurs. After all, the system does not need to choose one or another shaft - the gears are already included in the work.
Where is such a gearbox used? Basically, DSG is used on class B, C, and D cars. In many respects, everything depends on the technical characteristics of the motor itself. So, a six-speed gearbox is capable of withstanding a torque of 350 Nm. And the seven-band DSG is only 250. Therefore, such a box is not installed on powerful cars.
Variable speed drive
This is a relatively new type of automatic transmission, although the first copies began to be used in the 59th year. So, the first car with a variable gearbox was Daph. Further, such a scheme as manufacturers such as Ford and Fiat began to practice this scheme. However, this box was widely used only 10 years ago. Now this gearbox is used on cars:
- Mercedes.
- "Subaru."
- "Toyota".
- Nissan.
- Audi.
- Ford.
- Honda.
The key feature is that it does not have gears as such. The variator is a continuously variable transmission that provides a smooth change in gear ratios as the vehicle speeds up. The main plus of such a gearbox is the optimal coordination of the load on the car with the crankshaft speed. Thanks to this, high fuel efficiency and productivity are achieved. Smoothness is also noticeably improved, because twitching during dynamic acceleration is excluded here.
The car picks up speed quickly, while without jerking, as smoothly as possible. But due to certain restrictions on torque and power, variable automatic transmissions are used only on cars and some crossovers. Also, the cost of the machine on the variator increases significantly, since this transmission is quite high-tech.
Device and types
There are only two types of transmission data. It is a toroidal and V-belt variator. The latter received the greatest distribution. But regardless of type, they have the same device (automatic transmission "Toyota" is no exception). So, the design includes:
- CVT gear.
- A mechanism that provides torque transmission.
- Control system.
- Mechanism for disconnecting the gearbox and for engaging reverse gear.
In order for the box to receive and transmit torque, the following clutch mechanisms are used:
- Automatic centrifugal. It is applied on variators "Transmatik".
- Multi-disc wet. These are the Multimatic variators.
- Electronic (Hyper boxes used on some Japanese cars).
- Torque converter An example is Ecstroid, Multidrive, and Multimatic transmissions.
The last type of connection is the most popular and resource. Note that the variable gearbox drive itself can be belt or chain.
The first type consists of one or two belt drives. Also, the Toyota automatic transmission device includes two pulleys. The latter form some conical discs that can move apart and move together. Thus, a change in the diameter of the pulley. For convergence of the cones, special springs are provided in the Mazda automatic transmission device (sometimes centrifugal force is used). The conical disk has a 20-degree tilt angle. This allows you to provide movement of the drive belt with minimal resistance.
On variators "Multitronic" a metal chain is used. It is a few plates that are connected by axes. This design is characterized by good flexibility. The bending radius is up to 25 millimeters. Unlike the belt variator, the chain one provides torque transmission with the point contact of the plates with the disks. High stresses occur in these areas. Thanks to this design, a minimum loss in torque transmission and the best efficiency are ensured. Conical discs are made of high-strength bearing steel.
Due to the design features and the device, the automatic transmission valve body is not able to provide reverse movement. Therefore, the variator uses auxiliary mechanisms to engage reverse gear. This is a planetary gearbox. It has the same device and principle of operation as on classic torque converter automatic transmissions.
Also in the design of such a checkpoint there is an electronic control system. It provides synchronous adjustment of the diameter of the variator pulley depending on the current engine speed. This system provides the inclusion of reverse gear. The variator is controlled through a selector in the passenger compartment. The control modes are the same as on a conventional automatic transmission. The device and repair of these boxes are also similar. However, we note that many services are afraid to take these cars into operation, because they simply do not have the appropriate experience. Such a box appeared in Russia recently, and there are many myths surrounding it about the correctness of maintenance and repair. Experts say that for such a checkpoint it is enough just to change the oil in time and not to overheat the mechanism itself.
Conclusion
So, we found out what types of automatic gearbox are, how it is arranged and how it works. What to choose an ordinary motorist? Operating experience shows that the best option would be to buy a car with a classic torque converter automatic transmission. This box is familiar to many - it can be repaired and serviced at any service. In addition, modern machines of this type are distinguished by a good resource of 300-400 thousand kilometers. As for the DSG robot and stepless variator, such boxes take care of no more than 150 thousand on our roads. Further problems and serious investments begin. Therefore, you should refrain from buying them.