In the past two decades of rapid development of the automobile industry, not only many high-tech technologies have been applied, but the power of engines has also been adjusted to higher and higher levels. Nowadays, a 2.0T engine can squeeze out more than 300 Horsepower and peak torque can reach 400 N·m, which is very powerful. As engine power increases, the transmission system must also keep pace. AT gearboxes have gradually developed from the earliest 4AT to 6AT, 8AT, and even to the current 9AT and 10AT. Of course, the higher the gear, the greater the torque it can withstand. However, more gears can indeed save fuel for the vehicle. At the same time, because the gear density is high, the gear shifting process is smoother, and the vehicle is more comfortable to drive.
Looking at the dual-clutch transmissions used by Volkswagen, starting from the 6-speed wet dual-clutch automatic transmission that was officially mass-produced and launched in 2002, to the launch of the first 7-speed dry dual-clutch transmission in 2008, in the past In the past 20 years, Volkswagen models have always adhered to the dual-clutch transmission camp, especially the 7-speed dual-clutch transmission, which is widely used in Volkswagen's best-selling models. So, what is the reason why Volkswagen has been "struggling" with dual-clutch transmissions? Is it just because the technical barriers cannot be broken?
1. Why does Volkswagen prefer dual-clutch instead of AT gearbox?
In fact, the reason why the Volkswagen brand uses dual-clutch transmissions is helpless because it does not have a controlling gearbox supplier, and the patented technology of AT gearboxes is used by Aisin, ZF, and Jetco Monopolized by transmission giants such as , Bosch and others, Volkswagen must first pay a high "protection fee" if it wants to develop AT transmissions. In fact, before dual-clutch technology was mature, Volkswagen Group's models were also using AT gearboxes. Nowadays, some imported high-end models are still using them, such as Touareg, A8L, etc., which have always used ZF's 8AT gearbox. .
In addition, compared with AT gearboxes, dual-clutch gearboxes have a lower threshold and production costs are also much lower. Therefore, compared to the AT gearbox, which is technically difficult and costly, why not use a dual-clutch gearbox. However, for the Volkswagen Group, it has not completely abandoned AT transmissions. Naturally aspirated engines matched with AT gearboxes, and turbocharged engines matched with dual-clutch gearboxes have always been standard configurations of Volkswagen models.
2. Why has Volkswagen always stuck with the 7-speed dual-clutch?
In fact, as early as the 2013 Vienna World Automobile Symposium, Volkswagen publicly stated that it would develop a 10-speed dual-clutch gearbox. However, after waiting for the release of Toyota and GM's 10AT gearbox in 2017, Volkswagen's 10-speed dual-clutch gearbox was not released. The main reason why this gearbox was not successfully born was due to cost and volume control. . Research and development is not difficult, but it is more difficult to reasonably control costs and mass-produce it. In addition, due to the unique structure of the dual-clutch gearbox, the volume will become larger after it is increased to 10 speeds, which places high requirements on the installation and placement of the gearbox.
First of all, the dual-clutch transmission relies on two sets of clutches to shift gears. One side is responsible for the odd-numbered gears 1, 3, 5, and 7, and the other side is responsible for the even-numbered gears 2, 4, and 6. Because it has two sets of clutches and gear sets, the size of the gearbox itself is already large. If the gears of the 7-speed gearbox are increased to 10 speeds, it can only be extended further back on the original basis. In this way, the volume will become larger, making the installation of the gearbox a primary problem. In order to achieve performance, the gearbox should first reduce the size of the gearbox as much as possible, and take small size as the first goal of gearbox development. Therefore, in general, it is not that Volkswagen cannot create a dual-clutch gearbox with more gears, but that the structure of the dual-clutch gearbox itself limits the development of dual-clutch gearboxes. The 7-speed dual-clutch is likely to be the current dual-clutch gearbox. The best choice for clutch gearbox.
Is there a big performance gap between the 3.7-speed dual-clutch and the 10-speed AT gearbox?
Although Volkswagen's 7-speed dual-clutch gearbox has not upgraded the number of gears from beginning to end, its performance has been continuously improved. From 2008, Volkswagen released the first 7-speed dual-clutch - DQ200 and DQ250 dry dual-clutch. Since it can only withstand 250 Nm of torque, this gearbox has been used in the mid-to-low end at first. Car models, such as: Lavida, Jetta, Bora, etc.
At the same time, because it was the first product, this dry dual-clutch gearbox also had many design flaws. It learned from the experience of the first-generation product. The following year, Volkswagen released the DQ500? 7-speed wet dual-clutch gearbox. It can withstand up to 600 Nm of torque, and due to the oil cooling method, the gearbox is not prone to overheating or causing gearbox failure. Later, Volkswagen launched a shrunken version of the DQ380 based on the DQ500. The DQ380 was lower in cost and more suitable for mid-range models. Later, this gearbox became one of the main gearboxes in the Volkswagen brand family car series. one.
In 2017, Volkswagen launched an upgraded version of DQ380 - DQ381. This gearbox was mainly optimized and modified in response to different emission regulations around the world at that time. Compared with the DQ380, the new-generation DQ381 gearbox has better transmission efficiency. At the same time, emissions have been reduced by 9g/km, and the economy is relatively better.
The AT gearbox transmits power through a planetary gear set. Each set of planetary gears has several power flows. Three sets of planetary gears can achieve 6-8 speeds, and four sets can achieve 6-8 speeds. It's 8-10 speed. Compared with a dual-clutch transmission that requires an additional gear for each additional gear, even a 10-speed AT transmission only requires 4 sets of planetary gears. Therefore, this is why the AT transmission can easily achieve 10 speeds. .
Although it does not have an advantage in gears, the dual-clutch gearbox also has its own advantages. Because there are two sets of clutches that control odd-numbered gears and even-numbered gears respectively, during the gear shifting process, the dual-clutch gearbox responds more quickly than the AT gearbox and can withstand higher torque.
In general, although the Volkswagen 7-speed dual-clutch gearbox has not improved the gears, the technology is constantly updated. However, since the dual-clutch gearbox only has 7 gears and no overdrive gears 8, 9, and 10, the AT gearbox must be more fuel-efficient under daily operating conditions. At the same time, the density between the multi-speed gears of the AT gearbox is greater and the shifting impact is smaller.
Summary:
In fact, Volkswagen has been stuck on the 7-speed dual-clutch gearbox and has been forced to do so. The technology of the AT gearbox is blocked, and the cost of using the AT gearbox will naturally not be too low. In addition, judging from the existing technology, it is basically unfeasible to achieve the purpose of saving fuel by increasing the gearbox gear. Due to the special structural design of the dual-clutch gearbox, there may be some shock during the shifting process, especially at low speeds. However, after years of improvements, Volkswagen's current 7-speed wet dual-clutch gearbox has a very low failure rate, and its smoothness is also higher. At the same time, dual-clutch gearboxes also have their own advantages, that is, they shift quickly, combine quickly, and can withstand a higher torque range. The gearboxes used by sports car brands such as Porsche and Ferrari that we know are also dual-clutch gearboxes. As for why domestic cars have followed suit and used dual-clutch gearboxes, I think it is almost the same as Volkswagen's situation. AT gearboxes can only be used through purchase, and the price is high, which increases the cost of the entire vehicle. The technical threshold for dual-clutch gearboxes is low and can be developed by oneself, thus saving costs.
This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.