Compared with automatic gearbox and dual clutch, CVT has an advantage that all gearboxes can't match: ride comfort. It should be said that the history of CVT gearbox is longer than that of automatic gearbox. 1899, the belt continuously variable transmission has been invented successfully. This is the prototype of CVT principle.
After experiencing the dishes such as adhesive tape and belt, the transmission mode of CVT is divided into chain type or steel belt type, which is driven by two pulleys. The diameter of the pulley is variable to adjust the speed of the chain or steel belt. Although CVT is better in ride comfort and fuel economy, its manufacturing cost is higher than AT and DCT, and its later maintenance cost is also higher. Moreover, compared with the latter two, CVT is not suitable for sports cars because it can bear lower torque and is limited by the life of steel belts.
For Audi, the dual-clutch technology with lower cost and more mature technology has achieved fuel performance no less than CVT. Although ride comfort is not comparable, from the product point of view, CVT is no longer necessary. At present, Audi has stopped the research and development of CVT gearbox, and all its cars will adopt 7-speed dual clutch or 8AT gearbox in the future.
But Japanese brands, especially Nissan, still prefer to use CVT. In the field of CVT, Nissan has a number of exclusive patents and is the most in-depth research manufacturer of CVT among automobile manufacturers. This is in line with the concept that Japanese cars pursue comfort.
Manufacturers such as Toyota and Ford have also developed eCVT gearboxes for hybrid power systems, also known as PSD (Power Splitter) technology. The reason why eCVT technology is specifically mentioned is that although it is called CVT, it is actually completely different from the real CVT.
Its principle is very simple, with the help of a group of planetary gears to achieve the "integration" of engine power and motor power. Therefore, eCVT is actually just a power combination scheme, not a gearbox in the traditional sense. Why do you say that? Because the vehicle engine equipped with eCVT will not directly drive the vehicle in most cases.
In fact, the motor in the hybrid power system directly drives the vehicle. The engine will directly drive the vehicle only when cruising at high speed, which is equivalent to ordinary cars driving at the highest grade. In most cases, including acceleration and deceleration, eCVT vehicles are directly driven by motors.
Therefore, in eCVT technology, the engine speed has nothing to do with the vehicle speed, and it is used to drive the generator under most working conditions. Since it is directly driven by the motor, it means that there is only one transmission ratio. In this case, eCVT not only has excellent ride comfort, but also can achieve the lowest energy consumption. When slowing down, the kinetic energy of the vehicle can be recovered into the battery pack.
Technically, in fact, eCVT is the ultimate pursuit of automobile gearbox. However, because the hybrid power system includes engine, generator, motor and battery pack, the manufacturing and maintenance cost of powertrain is much higher than that of ordinary cars. Nevertheless, eCVT has only 22 moving parts (automatic gearbox has more than 100), so the failure rate will be very low in theory.
At present, all hybrid models of Toyota, Lexus and Ford use eCVT gearboxes, and some hybrid models of Nissan and Honda use eCVT.