The continuously variable transmission is called CVT transmission for short. The CVT transmission, which can provide stepless speed regulation, is especially preferred by Japanese automobile manufacturers. For this reason, it is also called the Japanese gearbox. The working principle of the CVT Gearbox is briefly that it works with the movement of two pulleys whose diameter is constantly changing. These two pulleys are connected to each other with a steel braided belt. One of the pulleys is the input pulley and the other is the output pulley. The speed of the car is adjusted by changing the diameters with the help of hydraulic pressure. There is no gear shifting as in other transmissions. The answer to the question of how the CVT transmission works will be explained in detail in the rest of the page.
*For detailed information about other transmission types and to see all transmission types together, you can check the What is a Gearbox and what are its types page.
CVT transmission started to be used in the 1950s, but due to the backwardness of the technology, it was used in low-power engines. In the early 2000s, with the development of technology, steel braided belts were produced and CVT transmission started to be used in high power engines. Today, it draws attention as a gearbox type that can be preferred with its smoothness.
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How Does a CVT Transmission Work? Working Principle
As mentioned above, the CVT gearbox, which adjusts the speed by changing the diameter of the two pulleys, has a stepless worm gear ratio. It provides stepless speed regulation. It does not have gear shifts as usual. When the speed of the vehicle is wanted to be increased, the hydraulic pressure and the pulley diameter change, so the speed of the vehicle increases as the input and output pulley ratios change.
In manual or automatic transmissions, engine speed and vehicle speed are dependent on each other. But the CVT transmission is also not dependent. The speed of the vehicle can be increased even though the engine speed remains constant. For example, when the engine speed is 3000 rpm, the speed of the car may be 70 km / h or 130 km / h. As we mentioned above, this change can be explained by the ratio of input and output pulley diameter.
Although torque converter is mostly used for clutch, multi-plate hydraulic clutch is also used. CVT transmissions do not have gears and synchromesh. It has a planetary gear group and is used for reverse gear movement.
Although CVT transmissions do not have gear ranges, virtual gear stages have been created by software so that drivers can manually select. The driver can upshift or downshift by moving the gear lever or the paddle shift behind the steering wheel in the + – direction. The change made here will only be to change the pulley diameters. These diameters will be determined by the values determined by the software.
CVT Transmission Usage
The control of the CVT transmission is the same as with other automatic transmissions. The vehicle has two pedals, brake and accelerator. As in other automatic transmissions, there are P, R, N, D gear shift positions. Some models also have an S position. It has D position for normal and economical driving and S sport position for more aggressive driving. During use in the D position, gear ratios are changed before the engine speed rises too much, thus increasing the speed, thus fuel economy is provided as a result of low engine speed and high speed. The vehicle moves more fluently, the engine braking is less. When the gear is shifted to sport mode, the engine speed is increased even more so that the vehicle can reach the desired speed more quickly, even if the engine speed is reduced when the constant speed is reached, it is kept higher than in the D position and tries to react more quickly to the sudden acceleration demand. Likewise, even if the foot is taken off the accelerator pedal, the gear ratio is not changed and remains constant, so that it can respond better in case of acceleration again, and also causes more engine braking.
In the D position, the car is more fluid, in the S position it responds more sharply. The operating characteristics of the CVT transmission vary depending on the manufacturer, the technology used and the software. The response of the transmission differs according to the driving style of the vehicle. For example, in aggressive sports driving, it can change gears at certain gear ratios (Nissan x-tronic), as if there is a cvt transmission gear range.
What are the CVT Transmission Advantages and Disadvantages?
CVT Gearbox working principle is a type of transmission that is curious. Since it is not very common, many questions come to mind. We hope that we will answer these questions with the advantages and disadvantages section that we have explained under this title.
I – What are the Advantages of CVT Transmission?
Thanks to the infinite gear range, there is no gear range and thus gear shifts are not felt.
Since there is no need for gear shifts, the engine always runs in the ideal rev range.
Another advantage is that the fuel consumption is less than other automatic transmission types. It provides this by working in the ideal rev range.
Especially at high speeds (constant speeds or highway driving) on flat roads, it provides a very low gear ratio and ensures that the engine speed is very low. Low engine speed brings low fuel consumption. The more gears a transmission has (i.e. the greater the gear ratio change range), the less fuel consumption of that vehicle will be.
Since there is no gear shifting, the power from the engine will not be interrupted.
It is long-lasting in terms of its working principle and not giving much opportunity to user error. Therefore, maintenance costs will be less.
It provides a good engine braking opportunity on hill descents.
By enabling the engine to operate in the most appropriate rpm range, better performance and fuel economy are provided. As you know, the engine can give its maximum torque and power at certain rev ranges, and the rev range where it can achieve maximum fuel economy is also certain. The CVT transmission ensures that the engine runs in these rev ranges, ensuring the most economical driving. In excess power demand, it allows the engine speed to increase and power to increase, in this case, fuel economy is compromised.
*You can get detailed information about car engines by going to the engine working principle page.
What are the Disadvantages of CVT Gearbox?
Throttle response is slower than other transmission variants.
Although the engine speed will increase when the accelerator pedal is pressed for rapid acceleration, the acceleration of the car will be a little slower and later. To eliminate this feature, the gear can be shifted to S, that is, sport mode.
The use of an extra hydraulic pump causes power loss in the engine. Hydraulic pressure is produced with the help of ATF pump. With this pressure, the pulley diameters are changed.
Which Vehicles Have CVT Gearbox? What Are Vehicles Using CVT Transmissions?
*Honda: Jazz, City, Civic (2017’den önce tam otomatik, 2017’den sonra CVT şanzıman ‘a geçti).
*Nissan (x-tronic): Micra, Juke (benzinli), Pulsar (benzinli), Qashqai, X-Trail
*Subaru (Lineartronic): Forester, Legacy, XV, Outback, Exiga, Impreza,
*Toyota (Multidrive s): Yaris, Corolla, Auris, C-HR, Verso, Avensis
*Renault (x-tronic): Koleos
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