Continuously variable automatic transmissions (CVT) are popular especially in Japan. In Europe they have little appeal. But the increasing demands for emissions worldwide. Fuel consumption speak for the use of a CVT transmission.
Continuously variable transmissions (CVT) have not had a good reputation for a long time. Especially the acceleration with constant speed, mockingly described as rubber band effect, has found little acceptance. The CVT is now to get out of the niche. And the markets promise growth potential.
Largely unnoticed in Europe, worldwide CVT production has steadily increased to nearly seven million units per year today, automotive supplier Schaeffler states. This corresponds to 12.5 percent of all vehicles with automatic transmissions. The main focus, he said, is in the Asia-Pacific region, especially in Japan, where already 36 percent of all new passenger cars are equipped with CVT. Globally, the CVT has an overall market share of nine percent, he said. Supplier Bosch expects market share to grow worldwide and especially in regions such as China and North America. Currently, CVT transmissions are available in about 300 production models, he said. For example, the Subaru Outback features the third generation CVT transmission called Lineartronic, a joint development with Schaeffler's LuK brand.
How the further spread and development of the CVT continuously variable transmission will look also depends on local conditions and also preferences. Modular product strategies are advantageous here in order to respond tailor-made to the different requirements in the various markets of the world. "The CVT, for example, is a very convenient solution for high traffic densities with highly fluctuating driving speeds, as is already common in Japan today. The CVT can also score points in the NAFTA region, where smooth starting continues to be an important argument for customers", explains Dr. Hartmut Faust, Head of Development, Transmission Systems Division at Schaeffler. The automotive supplier is convinced that different transmission concepts will continue to exist in the future and that their characteristics will converge. The worldwide increasing requirements regarding emissions. Fuel consumption speak for the use of a CVT transmission. This is because the stepless adjustment of the transmission ratio without interrupting traction allows the engine to always be operated in the most fuel-efficient map range. "A CVT transmission shows its strengths particularly in stop-and-go traffic in the city. A CVT reduces fuel consumption by up to seven percent because the engine can always operate at the most efficient power point", says Stefan Seiberth, member of the Bosch board of management responsible for Gasoline Systems.
In addition, the CVT transmission is compact because it consists of only a small number of components. For example, the control unit can be integrated directly into the system. The dense design also lowers the manufacturing price. The transmission fits even in small city vehicles. This is one of the reasons why the continuously variable automatic system is so successful in Japan.
The operating principle of a CVT transmission is always the same. It most closely resembles a bicycle gearshift, explain the experts at Bosch: with a higher gear ratio, the diameter of the band is larger on the input shaft and smaller on the output shaft. With a lower gear ratio it is the other way round: then the diameter on the output shaft is larger and on the input shaft smaller. This stepless adjustment is possible because the connecting link belt rotates between two conical disks facing each other, each of which is located on the input and output shafts. These cone-like pairs of pulleys change their position depending on the engine speed. Torque the rotating diameter of the belt. This always enables an optimum ratio between the required torque and engine speed.
CVT transmissions are equally suitable for diesel, gasoline and hybrid drives. While the technology can save fuel in conventional combustion engines, it can also increase the electric range of hybrid drives, Bosch explains. This is possible because the CVT allows the combustion engine to run at a higher speed at the optimum operating point. This means that some of the energy released can be used for propulsion – the rest of the energy is then stored in the rechargeable battery.