However, the research on improving the performance of transmission belt and the power limit of CVT has been going on. Hydraulic torque converter is integrated into CVT system, the clamping force of driving wheel and driven wheel is electrically controlled, CVT uses energy-saving pump, and the traditional rubber belt is replaced by metal belt for transmission belt. The new technical progress overcomes the original technical defects of CVT system, which leads to the emergence of the second generation CVT with greater torque transmission capacity and better performance.
Since 1990s, the research and development of CVT technology has been paid more and more attention by the automobile industry, especially in mini-cars, CVT is considered as the key technology. With the rapid development of global science and technology, new electronic technology and automatic control technology are constantly being adopted in CVT.
1997 in the first half of the year, Nissan developed CVT for 2.0L cars. On this basis, Nissan developed 1998 CVT with manual shift mode for medium-sized vehicles. The new CVT adopts the newly developed high-strength wide steel belt and high hydraulic control system. By adopting these advanced technologies to obtain greater torque capacity, Nissan has researched and developed the electronic control technology of CVT. The change of transmission ratio is controlled by full-speed electronic control. When the car goes downhill, the engine braking can always be controlled according to the speed, and the speed ratio can be steadily increased on the wet road surface to prevent slipping. Nissan plans to expand the application scope of its CVT from 1.0L to 3.0L cars.
Japan's Mitsubishi Corporation chose CVT to transmit the power of the direct injection engine smoothly without energy loss to drive the car. V-belt/transmission wheel mechanism can ensure the smooth and uninterrupted transmission of engine power at various speeds. CVT eradicates the tooth-beating phenomenon of traditional automatic transmission when shifting gears, thus obtaining more satisfactory response and control. Mitsubishi is going to adopt the combination of direct injection engine (1.5L or less) and CVT.
Japan's Fuji Heavy Industries also has 15 years experience in developing CVT. 1In May, 1997, Fuji Heavy Industries assembled a fully computer-controlled E-CVT (CVT with six-speed manual shift mode) for its Vistro mini-car. The driver can make a six-speed shift without operating the clutch. Fuji Heavy Industries adopted an electronically controlled CVT with a locking torque converter on the Pleo mini-car. The slip of the torque converter can be kept to a minimum through a small range of locking, and the planetary gears are used to switch forward/reverse gears. The transmission ratio range is1:10-5.5:1.
1999 In the first half of the year, Ford Company of the United States cooperated with ZF Company of Germany to produce continuously variable transmissions for Ford's cars and light trucks. The new joint venture between Batavia and Ohio will start producing CFT23 CVT with electronic management function designed for Ford from 200 1. CVT designed by ZF Company is a kind of torque converter transmission, which uses steel belts produced for installing front-wheel drive cars with transverse engines. ZF can also produce CVT series longitudinal engines for front-wheel drive vehicles and rear-wheel drive vehicles. ZF said: Compared with four-speed automatic transmission, CVT system can improve acceleration performance 10% and fuel economy 10%- 15%. Compared with lock-up torque converter, CVT system is more efficient and will not leak oil. Ford is designing a traction drive CVT to match all the company's light trucks, including rear-wheel drive and all-wheel drive trucks. Traction drive uses a slider that moves along a special sliding fluid to replace the drive belt and drive wheel. The relative position of the sliding parts determines the transmission ratio, and the power is transmitted through a thin layer of liquid oil between parts.
German ZF Company started to provide steel belt drive VT 1 CVT for Rover2 16 in the middle of 199. The CVT includes spiral gear or transmission device, suitable hydraulic system and wet clutch. The ECU integrated in the system can further combine mechanical, hydraulic and electronic systems, so as to make better use of the unique advantages of various systems.
The electronic CVT control system of Bosch Company in Germany is based on the electronic/hydraulic module controlled by sensors and actuator units. Bosch integrates independent components, actuators, sensors and transmission shift ECU into a module, and transmission manufacturers only need to add an integrated control unit.