To date, cars are equipped with various types of gearboxes. And if previously the majority was mechanics, now more and more drivers prefer the machine. This is not surprising, because such a transmission is more convenient in operation, especially when it comes to trips in the city. Until recently, such boxes were characterized by low efficiency. Old torque converters slowly shifted gears and with them the car was spending much more fuel. But today, the design, device and principle of operation of the automatic transmission are slightly different. These boxes are ways to switch quickly and with them the car uses less fuel. But first things first.
Types
At the moment there are several varieties of automatic gearboxes. This is a classic automatic machine with a torque converter, a variator and a DSG robot. The latter was developed specifically by Volkswagen-Audi. The device and the principle of operation of the automatic transmission of these types is significantly different. But what unites them is the switching of speeds in automatic mode. Next, we consider in detail the features of each of these transmissions.
Ordinary machine
It is a hydromechanical gearbox. Despite the fact that the design appeared more than half a century ago, it is still very relevant. Of course, its device has been substantially modified to this day. Now these boxes have six gears. If we talk about cars from the 80s and 90s, they had a four-speed automatic transmission.
The design of this gearbox includes:
- Manual Transmission.
- Torque converter or bagel.
- Control system.
If a front-wheel drive vehicle is equipped with such a transmission, then the main gear and differential are also included. One of the most basic parts in an automatic gearbox is a torque converter. It consists of several parts. This is a pump, turbine and reactor wheel. Thanks to them, a smooth transmission of torque from the internal combustion engine to a manual transmission is carried out.
Also, the clutch (freewheel and interlock) is included in the automatic transmission device. These elements, together with the turbine wheels, are closed in a round metal case, shaped like a donut. Inside the torque converter there is a working ATP-liquid. A pump wheel is connected to the crankshaft. And from the checkpoint there is a turbine. A reactor wheel is also located between these two elements.
How it works?
What is the principle of operation of an automatic transmission of this type? A classic closed loop automaton operates. As we said earlier, there is ATP fluid inside. It is a kind of gear oil. But, unlike a mechanical box, it not only performs a lubricating function, but also transmits torque. What is the automatic transmission fluid coupling principle of operation? Under pressure, this fluid enters the turbine wheel (from the pump wheel), and then enters the reactor. Since it has blades of a special shape, the speed of the fluid flow during rotation of the element begins to gradually increase. Thus, ATP oil drives a turbine wheel.
Peak torque in the transmission is generated when the vehicle pulls away. As the speed of the machine increases, an interlocking clutch is put into operation. The latter serves to tightly block the “donut” automatic transmission in certain modes of engine operation. This usually happens when the shaft rotation speed is the same. So, the torque is transmitted to the box directly, without “grinding” and gear ratio changes. By the way, on modern automatic gearboxes, a slip clutch is used. It is able to exclude the complete torque converter lock in certain modes. This contributes to a smooth set of speed and fuel economy.
Manual gearbox in automatic transmission
As such, the mechanics familiar to all motorists are not in this transmission. The role of a mechanical box is performed by a planetary gearbox. It can be designed for a different number of steps - from four to eight. But still, the most common options are six-speed automatic transmissions. In rare cases, you can meet a nine-speed automatic (for example, on the "Range Rover Evog").
How is automatic transmission arranged? This node in the transmission is a set of several sequential speeds. All of them are united in a planetary series. The planetary gear includes the following components:
- Sun and ring gear.
- Drove.
- Satellites.
If you delve deeper into the device and the principle of operation of the automatic transmission torque converter, you can notice that the change in torque is carried out precisely with the help of a carrier, as well as a crown and sun gear. When the second mechanism is blocked, the gear ratio increases. The lock itself is performed by the operation of the clutches. They hold the details of the planetary gear by connecting them to the box body. Depending on the car brand, the design uses a multi-disc or belt friction brake. Both types of systems are controlled by hydraulic cylinders. The signal to the clutches comes from the distribution module. And to exclude the rotation of the carrier in the opposite direction, the automatic transmission device has an overrunning clutch.
Control system
Now it is impossible to imagine an automatic transmission, the principle of operation of which would not be dependent on electronics. So, this system includes various sensors, a distribution module and a control unit. During automatic transmission operation, the system reads information from various elements. This is a temperature sensor for ATP fluid, the shaft speed at the outlet and inlet, and the position of the accelerator. All these signals are processed in real time. Then, the control unit generates control pulses that arrive at the actuators. We also note that the principle of operation of the automatic transmission valve body is based not only on reading data from sensors, but also on matching signals that are available in the electronic engine control unit.
The distribution module is responsible for controlling the flow of the working fluid and for the action of the friction clutches, which consists of:
- Solenoid valves (they have a mechanical drive).
- Spool valves.
- The aluminum case in which the above details are enclosed.
Considering the principle of operation of the Toyota automatic transmission, it is important to note such a thing as solenoids. These parts are also called solenoid valves. What are solenoids for? Thanks to these elements, the pressure of the ATP fluid in the box is regulated. Where does the oil pressure come from? This task is performed by a special automatic gear pump. The principle of its operation is simple. This element acts from the hub of the "donut". I rotate with a certain frequency, it grabs the impellers with a certain amount of oil and pumps it. And so that the working fluid does not overheat and the principle of the automatic transmission of the car is not violated, the design of some boxes has a radiator. It can be taken separately to the front (hidden under the bumper) or connected to the main cooling radiator. The latter pattern is often practiced on Mercedes cars.
Selector
The principle of operation of the automatic transmission selector is extremely simple. This mechanism is structurally connected to the spool, which performs a certain automatic transmission operation mode. There are several of them:
- Parking.
- Reverse.
- Neutral.
- Drive.
But that is not all. If we consider the principle of operation of the automatic transmission "Honda", you will notice that the selector has a sports mode. To turn it on, just move the handle to the appropriate position. Considering the principle of operation of the Nissan automatic transmission, it is worth saying that on some models there is the possibility of manual gear shifting.
DSG Robot
This type of automatic transmission has appeared relatively recently. The first models began to be used only in the middle of the 2000s. Initially, such boxes were installed on Skoda cars. But they can also be found on the Volkswagen and Audi.
Among the features it is worth noting a completely different principle of automatic transmission. The torque converter as such is absent here in principle. Instead, a dual-disc clutch and a dual-mass flywheel are used. This design can significantly reduce the time interval between gear changes.
If we talk about the device, the design of this box includes:
- Manual gearbox with two rows of gears.
- Electronic control system.
- Differential.
- Main gear.
- Double grip.
All of the above items are enclosed in a single metal case. Why is the design used double clutch and two rows of gears? If we consider the principle of operation of an automatic transmission of a car with DSG, it should be noted that while one transmission is in operation, the second is already being prepared for subsequent inclusion. This happens during acceleration and at lower speeds. Friction clutches are also present in such a gearbox. They are connected through the main hub to the rows of gears in the transmission.
There are several types of DSG boxes:
The principle of operation of an automatic transmission of the first type is based on the action of “wet” clutch. So, in the box there is a special oil that provides not only lubrication, but also cooling of the friction clutches. Pressure fluid circulates in the system and transmits torque.
As for the second type of DSG, dry clutch has already been applied here. The principle of operation is similar to the manual transmission - the disk is pressed against the flywheel and already transmits torque through the force of friction. According to experts, such a design scheme is less reliable. The disk resource is about 50 thousand kilometers, and the replacement cost reaches $ 700 along with consumables.
Gear ranges include reverse gear, as well as odd and even speeds. Each row is a set of shafts (consisting of primary and secondary), as well as a specific set of gears. To carry out the movement backward, an intermediate shaft with a reverse gear is used in the design.
As in the classic machine, there is electronics that controls gear changes. This includes the control unit, sensors and actuators. So, first the sensors read data about the speed of the shafts and the position of the gearshift fork, and then the unit analyzes this information and applies a certain control algorithm.
The hydraulic circuit of the DSG consists of:
- Spool valves that work from the selector.
- Solenoid valves (the same solenoids). They serve to change gears in automatic mode.
- Pressure control valves, which contribute to the smooth operation of the friction clutch.
How does DSG work?
The principle of operation of the hydraulic system of the automatic transmission of the robot consists in sequential switching of a number of gears. When the car starts to move, the system turns on the first speed. In this case, the second is already engaged. As soon as the car has gained a higher speed (about 20 kilometers per hour), the electronics switches the speed to a higher one. The third gear is already engaged. This happens right up to the highest. If the machine slows down, the electronics engages an already reduced gear. Switching is carried out instantly, since two rows of gears are involved in the design.
Application
It is worth noting that such a transmission is not used on every car. As we said earlier, the bulk are cars from the VAG concern. But commercial vehicles (for example, Volkswagen Crafter) are not equipped with them. And all because the box is designed for a certain threshold of torque. It should not exceed 350 Nm.
This applies to six-speed transmissions. DSG at seven speeds and does not withstand more than 250 Nm. Therefore, you can meet such a box maximum on the Tuareg and weaker cars such as the Passat or Octavia.
Variable speed drive
This gearbox also works in automatic mode. It appeared half a century ago, but only the last 10-15 years have been actively applied. What is a variator? This is a continuously variable automatic transmission, which smoothly changes the gear ratio by means of a belt or chain transmission. The gear ratio changes as the vehicle speeds up. At the moment, such a box is widely used by the following automakers:
- Nissan.
- Mercedes.
- Honda.
- Audi.
- "Subaru."
- "Toyota".
- Ford.
What are the advantages of this box? Thanks to a smooth change in gear ratio, the car picks up speed quickly and without jerking. The driver and passengers do not feel jolts during acceleration, no matter how much the accelerator pedal is pressed. However, there are pitfalls. This box also has torque limits, as does the DSG. Therefore, it is mainly used in passenger cars.
Varieties of CVTs
There are several types of transmission data:
- Toroidal.
- V-belt variator.
In this case, both types of boxes have almost the same device and principle of operation. The variator design includes:
- Control system.
- A pulley that provides torque transmission.
- Chain or belt drive.
- Box release mechanism (used to engage reverse gear).
In order for the transmission to absorb torque, clutch is used in the design. It can be of several types:
- Centrifugal automatic.
- Electronic.
- Multi-disc.
There are also such variators, where a torque converter is used as a clutch (as on classic automatic machines). Usually such a scheme is practiced on the boxes of "Multimatic" from "Honda". Experts believe that this type of clutch is the most reliable and resourceful.
Drive unit
As we have already said, a different drive can be used in the variator - a chain drive or a belt drive. The latter is more popular. The belt comes on two pulleys that form conical disks. These pulleys are able to move and move apart depending on the need. To approach the discs, special springs are provided in the design. The pulleys themselves have a small angle. Its value is approximately 20 degrees. This is done so that the belt moves with minimal resistance during operation of the box.
Now about the chain drive. The chain on an automatic variable gearbox consists of several metal plates that are connected by axles. According to experts, such a drive and design is more flexible. The chain is able to bend at an angle of up to 25 degrees without loss of resource. But unlike the belt one, this drive has a different principle of operation. The automatic transmission transmits torque during point contact with the pulleys. High voltage (friction force) is generated in certain areas. This achieves high efficiency. And so that the pulleys do not wear out from such stress, they are made of high-strength bearing steel.
Reverse gear in the variator
Since the variator drive can only rotate in one direction, to implement the reverse gear, the engineers had to develop a separate planetary gearbox. It is arranged and works similarly to a reducer in a classic machine.
Control system
Similar to the previous automatic transmissions, the variator uses an electronic control system. However, its principle of operation is somewhat different. So, the system provides adjustment of the diameter of the variator disks.
As the speed changes, one pulley diameter increases, and the second decreases. The modes are controlled through the selector thanks to the automatic transmission sensor. The principle of operation of the variator with a chain drive and a belt drive is to change the diameter of the pulleys.
About problems
Due to the complex design and low prevalence, many services refuse to work with such transmissions. Therefore, the CVTs did not take root in our country. As shown by operating experience, the resource of this box, even with proper maintenance, is no more than 150 thousand kilometers. In view of this, it is reasonable to buy such cars only in new condition, which are under warranty. It’s dangerous to take a car on the variator from hand - you can get into expensive repairs, which not every service will take.
To summarize
So, we found out the device and the principle of operation of the hydromechanical automatic transmission, robotic and CVT. As you can see, all these boxes are arranged differently and have their own algorithm of action. Which transmission is better to choose? Experts say that the most reasonable choice would be a classic machine. As shown by operating experience, car owners with DSG and CVT often turned to services and these boxes are expensive to maintain. , . , . , 300 400 . , , 250. , -, 60 .