The device and principle of operation of the automatic transmission of a car

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

Today, cars are equipped with various types of gearboxes. And if earlier the majority was mechanics, now more and more drivers prefer automatic. This is not surprising, because such a transmission is more convenient to use, especially when it comes to trips in the city. Until recently, such boxes were characterized by low efficiency. Old torque converters shifted gears slowly and with them the car spent much more fuel. But today the design, device and principle of operation of the automatic transmission are slightly different. These boxes are ways to quickly switch and with them the car consumes less fuel. But first things first.

Types

At the moment there are several varieties of automatic transmissions. This is a classic automatic with a torque converter, a variator and a DSG robot. The latter was developed specifically by the concern "Volkswagen-Audi". The device and principle of operation of automatic transmissions of these types is significantly different. But what unites them is the switching of speeds in automatic mode. Let's take a closer look at the features of each of these transmissions.

Regular machine gun

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 significantly improved 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.

This gearbox includes:

• Manual transmission.
• Torque converter or donut.
• Control system.

If a front-wheel drive car is equipped with such a transmission, then the main gear and differential are also included. One of the most basic parts in an automatic transmission is the torque converter. It consists of several parts. These are pumping, turbine and reactor wheels. Thanks to them, a smooth transmission of torque from the internal combustion engine to a manual transmission is carried out.

Another automatic transmission device includes a clutch (freewheel and blocking). 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 fluid. The pump wheel is connected to the crankshaft. And from the side of the checkpoint is the turbine. A reactor wheel is also placed between these two elements.

How does it work?

What is the principle of operation of this type of automatic transmission? A classic closed-loop machine operates. As we said earlier, there is ATP insideliquid. It is a kind of gear oil. But, unlike a mechanical gearbox, it not only performs a lubricating function, but also transmits torque. What is the principle of operation of an automatic transmission fluid coupling? Under pressure, this liquid enters the turbine wheel (from the pump wheel), and then enters the reactor wheel. Since it has blades of a special shape, the fluid flow rate begins to increase gradually during the rotation of the element. Thus, the ATP oil drives the turbine wheel.

Peak torque in the transmission is generated when the car starts off. As the speed of the machine increases, the lock-up clutch is activated. The latter serves to hard block the “donut” of the automatic transmission in certain operating modes of the internal combustion engine. This usually happens when the speed of rotation of the shafts is the same. So, the torque is transmitted directly to the box, without "lapping" and changing the gear ratio. By the way, a slipper clutch is used on modern automatic transmissions. It is able to eliminate the complete blocking of the torque converter in certain modes. This contributes to a smooth acceleration and fuel economy.

Manual transmission in automatic transmission

As such, there is no mechanics familiar to all motorists in this transmission. The role of the mechanical gearbox 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 find a nine-speed automatic (for example, on the Range Rover Evog).

How does an automatic transmission work? This node in the transmission is a set of several sequential speeds. All of them are united in a planetary gear set. The planetary gearbox includes the following components:

• Sun and ring gear.
• Carrier.
• Satellites.

If you delve into the device and principle of operation of the automatic transmission torque converter in detail, you will notice that the change in torque is performed precisely with the help of the carrier, as well as the ring and sun gears. When the second mechanism is blocked, the gear ratio increases. The blocking itself is performed by the operation of friction clutches. They hold the parts of the planetary gearbox by connecting them to the box body. Depending on the brand of the car, the design uses a multi-disc or band friction brake. Both types of systems are controlled by hydraulic cylinders. The signal to the clutches comes from the distribution module. And to prevent the carrier from rotating 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 which would not depend on electronics. So, this system includes various sensors, a distribution module and a control unit. During the operation of the automatic transmission, the system reads information from various elements. This is an ATP-liquid temperature sensor, shaft speed at the output and input, as well as the position of the accelerator. All these signals are processed in real time. Then the control unit generates controlimpulses that enter 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 the coordination of 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 operation of the friction clutches, which consists of:

• Solenoid valves (they are mechanically driven).
• Spool valves.
• Aluminum housing containing the above parts.

Considering the principle of operation of a 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 is the oil pressure coming from? This task is performed by a special automatic transmission gear pump. Its working principle is simple. This element operates from the “donut” hub. I rotate with a certain frequency, it captures a certain amount of oil with the impellers and pumps it. And so that the working fluid does not overheat and the principle of operation of the automatic transmission of the car is not violated, there is a radiator in the design of some boxes. It can be placed separately in the front (hidden under the bumper) or connected to the main cooling radiator. The latter scheme 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 modeautomatic transmission work. There are several of them:

• Parking.
• Reverse.
• Neutral.
• Drive.

But that's not all. If we consider the principle of operation of the Honda automatic transmission, you will notice that there is a sport mode on the selector. 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 mid-2000s. Initially, such boxes were installed on Skoda cars. But they can also be found on Volkswagens and Audis.

Among the features, it is worth noting a completely different principle of automatic transmission operation. The torque converter as such is absent here in principle. Instead, it uses a dual-plate clutch and a dual-mass flywheel. This design allows you to significantly reduce the time interval between gear changes.

In terms of device, this box includes:

• Manual transmission with two rows of gears.
• Electronic control system.
• Differential.
• Final gear.
• Double clutch.

All of the above elements are enclosed in a single metal case. Why does the design use a double clutch and two rows of gears? If we consider the principle of operation of an automatic transmission of a car with DSG, you neednote that while one gear is in operation, the second is already preparing for the next inclusion. This happens when accelerating and when decelerating. Friction clutches are also present in such a gearbox. They are linked through the main hub to the gear trains in the transmission.

There are several types of DSG boxes:

• Six-speed.
• Seven-speed.

The principle of operation of the first type of automatic transmission is based on the action of a "wet" clutch. So, in the box there is a special oil that provides not only lubrication, but also cooling of the clutches. Fluid under pressure circulates in the system and transmits torque.

As for the second type of DSG, a dry clutch has already been applied here. The principle of operation is similar to a manual transmission - the disc is pressed against the flywheel and, through friction, transmits torque. According to experts, such a design scheme is less reliable. The disk resource is about 50 thousand kilometers, and the replacement cost reaches $ 700, including consumables.

Gear ranges include reverse, even and odd speeds. Each row is a set of shafts (consisting of primary and secondary), as well as a certain set of gears. To carry out the movement back, the design uses an intermediate shaft with a reverse gear.

As in a classic machine, there is an electronics that controls the speed change. This includes the control unit, sensors and actuators. So, first, the sensors read data about the speed of the shafts andthe position of the gear fork, and then the unit analyzes this information and applies a specific control algorithm.

DSG hydraulic circuit consists of:

• Spool valves that operate from the selector.
• Solenoid valves (same solenoids). They serve to shift gears in automatic mode.
• Pressure control valves to keep the friction clutch running smoothly.

How does DSG work?

The principle of operation of the hydraulic system of the automatic transmission of the robot is to sequentially switch a number of gears. When the car starts to move from a place, the system includes 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 increased. The third gear is already engaged. This goes on up to the highest. If the car slows down, the electronics engage the already low gear. Shifting is instantaneous, as the design involves two rows of gears.

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 must not exceed 350 Nm.

This applies to six-speed transmissions. DSGat seven speeds and do not withstand more than 250 Nm at all. Therefore, you can meet such a box at most on the Tuareg and weaker cars like the Passat or Octavia.

Variator

This gearbox also works in automatic mode. It appeared half a century ago, but only the last 10-15 years have been actively used. What is a variator? This is a continuously variable automatic transmission that smoothly changes the gear ratio by means of a belt or chain drive. Gear ratios change as the vehicle picks up speed. 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 the smooth change in the gear ratio, the car picks up speed quickly and without jerking. The driver and passengers do not feel shocks during acceleration, no matter how hard the accelerator pedal is pressed. However, there are pitfalls here. Such a box also has torque limits, like DSG. Therefore, it is mainly used in passenger cars.

Varieties of variators

There are several types of transmission data:

• Toroid.
• V-belt variator.

At the same time, both types of boxes have almost the same device and principle of operation. The design of the variator includes:

• Systemcontrols.
• Pulley that provides torque transmission.
• Chain or belt drive.
• Box release mechanism (used to engage reverse gear).

In order for the transmission to perceive torque, a clutch is involved in the design. It can be of several types:

• Centrifugal automatic.
• Electronic.
• Multidisc.

There are also such variators where a torque converter is used as a clutch (as on classic automatic machines). Typically, such a scheme is practiced on Honda Multimatic boxes. Experts believe that this type of clutch is the most reliable and resourceful.

Drive

As we have already said, a different drive can be used in the variator - chain, dibo belt. The latter is more popular. The belt goes on two pulleys, which form conical disks. These pulleys are able to move and move apart depending on the need. To bring the discs closer together, special springs are provided in the design. The pulleys themselves have a slight angle of inclination. Its value is approximately 20 degrees. This is done so that the belt moves with minimal resistance during the operation of the box.

Now about the chain drive. The chain on an automatic variable gearbox is several metal plates that are connected by axles. According to experts, such a drive and design is more flexible. The chain is capable of bending at an angle of up to 25 degrees without loss of resource. But unlike a belt drive, this drive hasdifferent operating principle. The automatic transmission transmits torque through point contact with the pulleys. In certain areas, high stress (friction force) is formed. 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 CVT

Because the variator drive can only rotate in one direction, the engineers had to develop a separate planetary gearbox to implement the reverse gear. It is designed and works similarly to a gearbox in a classic machine.

Control system

Similar to previous automatic transmissions, the CVT uses an electronic control system. However, its principle of operation is somewhat different. So, the system provides adjustment of the diameter of the variator discs.

As the speed changes, one pulley diameter increases and the other 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 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, CVTs have not taken root well in our country. As experience has shown, 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 is dangerous to take a car on a variator from your hands - you can get onexpensive repairs, which not every service will undertake.

Summing up

So, we found out the device and principle of operation of a hydromechanical automatic transmission, a robotic one and a variator. 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 slot machine. As operating experience has shown, owners of cars with DSG and CVT often turned to services and these boxes are expensive to maintain. The classic slot machine has been on the market for a very long time, and its design is constantly being refined and improved. Therefore, such boxes are distinguished by a high resource, unpretentious in operation and can be repaired in any service. Practice has shown that the resource of an automatic transmission in a car is from 300 to 400 thousand kilometers. This is a serious period, given that some modern engines run only 250. But for such a transmission to last a long time, it is worth changing the ATP fluid in it regularly, namely every 60 thousand kilometers.