In the continuous evolution of the world, transmission technology has always been one of the focus of attention. From the early 6AT to today's 9AT, 10AT, to CVT's continuously variable transmission, as well as the challenges and breakthroughs of dual-clutch transmissions, every step is the product of engineers in the pursuit of better performance and higher efficiency.
Automatic transmissions (ATs) have always been known for their combination of planetary gears and torque converters. This miraculous device achieves an increase in gears through a clever combination of planetary gear sets, such as Aisin's 6AT that achieves 6 gears using only 3 sets of planetary gears. Subsequently, it was upgraded to 8AT, and the three sets of planetary gears were still used, and eight gears were achieved through different combinations. Some manufacturers even add a set of planetary gears to the 10AT to achieve more gear options.
The ingenuity of this design lies in the large degree of freedom, and the combination of different planetary gears allows for multiple gears, making the shifting more flexible and smooth. That's why it's relatively easy to upgrade the number of gears with an AT gearbox.
As a continuously variable gearbox, the CVT can theoretically have an infinite number of gear ratios, so there are theoretically an infinite number of gears. However, in practice, in order to achieve the manual automatic mode, OEMs usually simulate multiple gears. This is not because of technical necessity, but more to provide a more comfortable operating feeling that is more in line with the driver's Xi.
The CVT is characterized by the use of a lever mechanical or electronic control unit to simulate discrete gears, so that the driver can better feel the sense of gear switching in a conventional transmission while driving. This does not affect the CVT's actual continuously variable speed capability.
Compared to the AT and CVT, the dual-clutch transmission is more difficult to upgrade. Upgrading from the original 6th to 7th gear is relatively straightforward, requiring only the addition of a shift fork. However, to break through the 7 gears, there were a number of technical challenges to face.
Dual-clutch transmissions rely on gear meshing to create gears, and one gear requires two sets of gears to match. Unlike AT gearboxes, which can use planetary gears to combine multiple gears, the addition of gear sets leads to an increase in the size and weight of the gearbox, which is a major obstacle to upgrading.
The bearing capacity of the input shaft also became a limiting factor. Dual-clutch transmissions typically have two input shafts, with the hollow shaft having a relatively low capacity. If a gear set is added in order to increase gears, the length of the hollow shaft needs to be increased, which necessitates re-optimization of the size and strength of the hollow shaft, and may require a redesign of the entire gearbox.
Honda's 8-speed dual-clutch transmission is a prime example. In order to solve the problem of shift shock, Honda introduced a torque converter, although it succeeded in reducing the impact feeling when shifting. This also brings a series of new problems, such as an increase in cost, an increase in fuel consumption, a decrease in shift efficiency, and an increase in the volume of the gearbox. This series of problems makes this technology not suitable for all vehicle models, but only for some vehicles with specific needs.
Although the rise of new energy vehicles, especially electric vehicles, has made many manufacturers focus on battery technology and electric drive systems, fuel vehicles still dominate the market. Under the impact of new energy, traditional technologies such as gearboxes face some technical problems, which hinder their further technological progress.
The evolution of automotive transmission technology is a continuous process. Despite the challenges, engineers are struggling to overcome technical challenges to deliver more efficient and intelligent variable speed solutions. Whether it is the ingenious design of the AT, the continuously variable transmission of the CVT, or the breakthrough of the dual-clutch transmission, it reflects the pursuit of innovation and excellent performance.