[YesAuto Transmission Technology] Can you think of it? Only a steel belt binds the world together. The concept of continuously variable transmission has even gone through nearly four centuries before being used by the world. Seeing today’s cars equipped with CVT continuously variable transmissions, it must be an Italian painter of the 15th century. Leonardo would certainly smile in relief, perhaps just like the Mona Lisa under his brush. what? CVT is still related to Da Vinci? In today's article, we will talk about the past and present and technical characteristics of CVT.
● The birth of CVT gearbox: Who is the “child”?
Recently, what Da Vinci did has sparked a discussion in our editorial department. I remember the elementary school Chinese teacher told us that Leonardo was a famous painter. However, when looking through the history of the CVT continuously variable transmission on the wiki, I accidentally discovered the name of Da Vinci. Da Vinci is also related to CVT?
To understand the life experience of CVT continuously variable transmission, it must be traced back to the end of the fifteenth century. Leonardo Da Vinci is not only a famous painter who painted the Mona Lisa, he also proposed the concept of CVT continuously variable transmission. . In addition to these, the all-rounder Leonardo was also a sculptor, architect, musician, mathematician, engineer, inventor, anatomist, geologist, botanist and writer. But it was not until 1958 that the Dutch Hub van Doorne designed a modern CVT continuously variable transmission.
Although the Dutch invention was very creative, it did not cause much trouble in Europe. Instead, it gradually became popular in Japan. Japanese companies in the 1980s and 1990s began to develop CVT technology, such as Jatco. , Aisin, Honda, etc.
In contrast, the German auto parts giant Bosch (BOSCH) is more foresighted. In 1995, it acquired DAF's CVT transmission pressure steel belt patent, and focused on the development and production of this core component of CVT transmission, becoming a global Most car companies purchase CVT gearbox steel belt suppliers. So why is the CVT gearbox so fascinating for car companies? Please continue to look down.
● What is going on with CVT?
◆ Why is the CVT gearbox called a continuously variable gearbox?
As we all know, manual, dual-clutch or ordinary AT automatic gearboxes use different sizes of gears to achieve different gears. How does the CVT continuously variable gearbox achieve countless gears? Is there a more complicated structure?
◆ secret behind a strip?
Why is Bosch visionary? Why did it acquire this seemingly simple pressure steel belt patent? What is the “big world” behind it? Let us take this steel belt out and study it separately.
It is this pressure steel belt that transmits power between the cone and disc groups. What kind of structure does it have to ensure that it does not slip during work?
◆ Besides Bosch, are there other manufacturers capable of producing steel belts?
Although we mentioned earlier that Bosch holds the patent of CVT pressure steel belt, there are always some manufacturers who are unwilling to be restrained by Bosch. In order to break Bosch's blockade of CVT core technology, they can only find another way. For example, Audi and Schaeffler have thought of using chain-type steel belts as the transmission between the cones and discs.
◆ Why do you say that CVT models have good fuel economy?
For CVT gearboxes, it can adjust the transmission ratio steplessly and linearly within its transmission ratio range. That is to say, the engine speed is controlled within the optimal speed range, and the CVT control unit can match the most suitable gear ratio value to output torque. This is the advantage that manual gearboxes, AT automatic gearboxes, and dual-clutch automatic gearboxes do not possess and improve fuel economy.
In addition, compared with other gearboxes, models equipped with CVT gearboxes will not be interrupted in power when shifting gears and can continuously output torque. So from this point of view, CVT gearboxes are also more fuel-efficient.
◆ How does the CVT gearbox achieve a wider transmission ratio ?
Although the larger the transmission ratio range, the more beneficial it is to improve fuel economy, but any gearbox cannot blindly broaden the transmission ratio range due to restrictions on size and weight. At present, the largest transmission ratio among the mass-produced CVT gearboxes is the chain-type continuously variable transmission developed by Schaeffler and Audi. Its maximum transmission ratio is 7.7.
◆ Hydraulic torque converter in CVT gearbox
Like ordinary AT automatic transmissions, models equipped with CVT continuously variable transmissions do not have the clutch mechanism between the engine and the gearbox as in traditional manual transmission models, but are generally connected by a hydraulic torque converter. The torque converter can not only transmit torque, but also form a flexible connection between the engine and the automatic transmission. In addition, the internal lock-up clutch can also be used for rigid coupling when necessary.
Since the torque converter internally transmits torque through oil, it can alleviate the fluctuation of engine torque, and the liquid transmission torque is allowed to have a certain speed difference, so it can undertake the work similar to the semi-linkage of the clutch in a manual transmission (MT) . But its disadvantages are power delay and low transmission efficiency, so a lock-up clutch is generally added to the torque converter.
Of course, the coupling time of the lock-up clutch must also be appropriate. Premature coupling will cause vibration and affect ride comfort; too late coupling will affect transmission efficiency and slow acceleration response. In addition, a torsion damper is integrated in the lock-up clutch. When the clutch is engaged, the torsion damper can absorb part of the vibration to improve ride comfort.
◆ Do not like peace and smoothness?
However, the smoothness is sometimes not what people want. Therefore, in order to increase people's driving pleasure when driving CVT models, some manufacturers have set up simulated gears for CVT gearboxes to simulate a certain sense of frustration. For example, the CVT gearbox mounted on Toyota Corolla can simulate 8 gears. In fact, in theory, CVT can simulate countless gears.
The manual shift function means that the driver can control the speed of the shift by himself, which provides better driving pleasure on the one hand, and makes driving more convenient on the other hand. For example, in a downhill section, manually control the vehicle in a low gear, use the engine itself to control the speed of the vehicle, reduce the load of the brake system, and maintain a low safe speed. In addition, using the second gear with lower output torque to start in manual mode, to a certain extent, avoids the phenomenon of starting slipping when driving on snow.
● Which brands can see CVT gearboxes?
At present, the global car companies using CVT gearboxes are roughly divided into the following factions:
Jatco can be said to be the largest CVT transmission company in the world. In 1999, Nissan separated its automatic transmission department. The independent department acquired a Jatco company that started automatic transmissions in 1970. The new company is still known as Jatco. JATCO currently supplies car manufacturers such as Nissan, Mitsubishi, Mazda, Suzuki, Renault, Chrysler, BMW, Volkswagen, Ford, Subaru and so on.
Nissan, which insists on CVT gearboxes, is undoubtedly the biggest customer of JATCO. Since the initial pressure steel belt could not withstand excessive torque, the early CVT gearboxes were only used on Nissan's small displacement models. The current Nissan 3.5L displacement model can also be equipped with a CVT continuously variable transmission.
Established in 1969, Japan’s Aisin Seiki is a company that specializes in the production of gearboxes, while Toyota is the majority shareholder behind Aisin. Therefore, the current CVT gearboxes in Toyota’s models are all from Aisin, with three generations of CVT technology Innovative, the latest S-CVT gearbox capable of simulating 8-speed has been installed on Ralink and Corolla models.
Unlike other manufacturers, Honda has always been obsessed with the independent development of CVT continuously variable transmission technology. It began researching CVT technology in the 1980s. In 1995, it used its self-developed CVT transmission for the first time. Six generations of Honda Civic.
Among the CVT models of the Chinese brand, the Belgian Punch Powertrain company is the supplier behind the CVT continuously variable transmission technology. In the early days, Bunche was just a factory of the Dutch DAF Group. Later, after the transmission giant ZF ZF reversed, it acquired DAF's CVT business and began independent production of CVT gearboxes. The CVT models produced by Geely, Great Wall, JAC, BYD, Dongfeng Liuqi, etc. are all from Nanjing Bangqi Automatic Transmission Co., Ltd.
In addition, Chery's early CVT gearboxes also used Punch's products, but later Chery independently developed CVT continuously variable transmission technology and successfully got rid of its dependence on Punch.
● New Audi cars are no longer equipped with CVT
It is worth mentioning that in the latest Audi models, we no longer see the configuration of the Multitronic CVT gearbox. For example, the new generation of Audi A4 eliminates the CVT and uses a 7-speed S-tronic dual-clutch gearbox. But this is not to say that the CVT gearbox is not good, but for Audi, on the technical level, no matter how good the CVT gearbox is, it does not meet its positioning for the pursuit of operability, and consumers also have more of Audi. Sports requirements. In addition, Audi was unable to match the CVT with its quattro four-wheel drive system. From the perspective of business operations, although the cost of CVT gearboxes is low, it does not have an advantage in cost compared with other gearboxes with large-scale common parts, and reducing the variety of purchased gearboxes can reduce its cost. The overall cost. Therefore, it can only be said that CVT is not suitable for Audi's models at this stage. On the contrary, Japanese brands that pay more attention to economy and practicality prefer this.
There will still be room for improvement in future CVT gearbox technology, such as the optimized design of pressure steel belts and chains. On the one hand, the friction loss power is reduced. On the other hand, the steel belts and chains can be miniaturized to achieve a wider transmission ratio; Use the torque sensor to further optimize the hydraulic control system of the conical disc pressing mechanism and so on.
At present, the global car companies that use the most CVT continuously variable gearboxes belong to Japanese brands, and the pressure steel belts of Japanese brand CVT gearboxes are almost all from Bosch, so it can be said that Bosch is the big one behind the global CVT gearboxes. guy. In addition, although the chain-type CVT gearbox jointly developed by Schaeffler and Audi also has a certain market share, even Audi itself has abandoned CVT gearboxes. As for Schaeffler's CVT business, everything is unknown. At home, Chinese brands have introduced CVT technology from the Belgian Punch Company, and CVT models have also appeared. However, the momentum of the country's support for the development of DCT dual-clutch transmissions has overwhelmed the company's attention to other automatic transmissions. Perhaps, it is the final destination of CVT in Japan, which pays more attention to practicality and smoothness.