What is the working principle of CVT gearbox?

The history of 1.CVT began at 1899, and V-belt CVT with adjustable taper width and axial direction appeared. 1959 Van Dunne's continuously variable transmission was successfully installed on DAF cars with a total output of 825,000 vehicles. 1969, Van Doone developed an axially adjustable metal belt CVT, which was loaded in 1975. After 1990, it began to be promoted to Nissan, Mitsubishi and Ford in Japan. 1988, NSK of Japan began to develop semi-ring roller CVT. 1992, ZF and LUK companies in Germany developed the swing pin chain CVT. 1994 was successfully put into Audi A4 and A6 cars and mass production began. 1995, Torotrak, NSK and Mercedes-Benz successfully developed full-ring, disc and roller CVT. In 2006, the total output of vehicles equipped with CVT has reached 2.5 million. Edit paragraph 2. Nissan has long been committed to the research and development of CVT. 1992 successfully developed "N-CVT" on "K 1 1 March" (using electromagnetic clutch) and started mass production. 1997 Hyper-CVT (with hydraulic torque converter) was successfully developed for the first time, which can match 2.0L front-wheel drive vehicles. In 2000, the "EXTROID-CVT" matched with the 3.0L class rear-drive vehicle was successfully developed. Nissan also developed XTRONIC-CVT with hydraulic torque converter, which was successfully applied to 3.5L large displacement vehicles. XTRONIC- CVT is a combination of "hydraulic torque converter" and "steel belt and pulley" CVT. Teana car adopts REOFO9A continuously variable transmission, and Sylphy adopts REOFO 10A automatic transmission. Edit paragraph 3. Advantages of CVT (1) Good fuel economy CVT can realize stepless speed change in a fairly wide range and obtain the best matching between transmission system and engine working conditions. Depending on the stepless speed change of the transmission to adapt to the various speeds of the car, the engine can work in the best working condition for a long time, thus improving the combustion efficiency of the engine and improving the fuel economy accordingly. (2) The CVT with good power can realize closed-loop control with the engine, fully mobilize the maximum torque of the engine, and its performance of deceleration and torsion increase is obviously better than that of MT and at, so the acceleration performance of CVT car (0~ 100km/h) is 7.5% ~1.5% higher than that of AT car, at high speed. The characteristics of CVT make the power performance obviously superior to manual transmission (MT) and automatic transmission (AT). (3) Comfortable CVT can improve driving comfort. CVT has no gear, and the shifting process is continuous and linear, and there is no shift impact when accelerating, and there is no retreat of AT when accelerating rapidly. The transmission ratio of CVT system is relatively wide, generally 2.400-0.395. When driving at high speed, the engine speed is low and the noise is low, so that drivers and passengers can enjoy quiet and relaxed comfort during the journey. (4) The CVT transmission with good maneuverability and hydraulic torque converter can amplify the engine torque, so it starts quickly and accelerates more smoothly. When the driver overtakes, stepping on the accelerator deeply will not make him feel at-shift, but change the speed ratio to amplify the torque. When cornering AT high speed, there is no upshift phenomenon of AT when the throttle is released, and the torque can be kept outside the corner at high speed. CVT has better engine braking effect than AT. CVT can automatically detect the slope when going uphill and downhill, and automatically adjust the speed ratio to increase the torque output when going uphill. When going downhill, the engine braking torque can be increased to reduce the sliding speed when going downhill for a long time and improve the safety and maneuverability. (5) The reliability and service life of life-long maintenance-free CVT mainly depend on the materials of metal belt transmission parts. According to the technical data of VDT company in the Netherlands, the new design and technology have solved the problems existing in CVT in the past. The trial results of 800,000 sets of CVT in the world show that only 200 sets fail, and the failure rate is 0.25%. It can be seen that the system is of high quality and reliable in use. Using high-strength and high-quality materials and precision manufacturing technology, CVT can achieve the same life as the engine and be maintenance-free for life. (6) Less harmful gas emissions Because CVT can realize closed-loop control with the engine, the engine can often run in the economic speed range, which improves the combustion process, thus reducing harmful gas emissions and prolonging the service life of the three-way catalyst and oxygen sensor. German ZF Company tested its own CVT, and its harmful gas emission was reduced by about 10% compared with that of a car equipped with a 4-speed automatic transmission, which greatly reduced environmental pollution. (7) The structure of low-cost CVT system is simple, and the number of parts is much less than that of at. Once mass production begins, the cost of CVT will be lower than that of at. With the mass production and the innovation of systems and materials, the production cost of CVT will be further reduced. The assembly and maintenance costs are reduced, and CVT has a very broad prospect because of its simple structure, low cost and excellent performance. Edit paragraph 4. Structure and working principle of CVT The structure of CVT is mainly composed of two groups of pulleys (driving pulley and driven pulley) and transmission belt (steel belt) oil pump, hydraulic torque converter, actuator (valve body, oil circuit), sensor and computer. 1. The function of the hydraulic torque converter is to transfer the torque of the engine to the CVT, so that the car can start forward and backward smoothly. Hydraulic torque converter can amplify the torque of the engine and make it start faster. When the vehicle speed reaches the set speed, the pump wheel (wheel connected to the engine) and turbine wheel (wheel connected to CVT) of the hydraulic torque converter are locked, and the transmission efficiency at this time reaches 100%. Another function of hydraulic torque converter is to reduce the impact force from engine and road surface and prolong the service life of transmission parts. 2. Variable diameter pulley CVT has two groups of pulleys (driving pulley and driven pulley), and each group of pulleys is divided into two halves. One side of the pulley is fixed, and the other side of the pulley can slide on the shaft. The inner sides of the two pulleys are conical surfaces with inclined angles, and the two sides are opposite to each other to form a V-shaped groove, which is in contact with the side surface (meshing point) of the transmission belt. By controlling the clamping and loosening of the driving wheel and the driven wheel by oil pressure, the working diameter of the meshing point between the pulley cone and the transmission belt is changed (that is, the diameter of one wheel increases and the diameter of the other wheel decreases), thus changing the transmission ratio. (When the diameter of the driving wheel is small and the diameter of the driven wheel is large, it is in a deceleration state to improve the torque. When the diameter of the driving wheel is large and the diameter of the driven wheel is small, increase the speed. 3. The high-strength steel belt transmission belt consists of two bundles of annular steel belts and a pusher, each group has two bundles of annular steel belts, and each bundle of steel belts is formed by overlapping 12 layers (sheets) of high-strength steel sheets. The steel belt is made of T702 high-strength steel (the tensile strength of each piece reaches 2000mpa), and the pusher is composed of more than 400 high-strength pressure steel plates. The function of the annular steel belt is to press the push piece on the V-shaped groove of the pulley, so that sufficient friction force can be generated between the push piece and the pulley, and the push piece can slide longitudinally in the straight section of the steel belt, and the function of the push piece is to transmit torque through extrusion thrust. The biggest feature of Dongfeng Nissan steel belt CVT is "push transmission". 4.ASC intelligent logic control system Based on the second generation CVT, the third generation CVT was imported with a more advanced ASC control unit. The number of variable speed conversion modes has increased from 20 to more than 700. Through the information provided by sensors such as accelerator pedal, engine speed, vehicle speed and shift lever position, the computer can calculate and judge the driver's intention at any time, and then send control instructions to the execution system to provide actions that meet the driver's wishes at any time, and command to complete the execution actions such as forward and reverse gear switching, rapid acceleration, manual mode, economy mode and engine braking. High response execution system (including oil pump, solenoid valve, etc.). Gear switching device) can quickly and accurately execute various instructions issued by ASC control unit. Edit paragraph 5. Differences and advantages between Dongfeng Nissan CVT and other transmissions 1. Automatic transmission (AT) Compared with AT, Dongfeng Nissan CVT has the advantages of stepless speed change, wide speed change range, fast start, low engine speed at high speed, and reduced fuel consumption by more than 10%. 2. Dual-clutch automatic transmission (DSG) Compared with DSG, Dongfeng Nissan's CVT has a simple structure, a wider speed range and lower fuel consumption at high speeds. CVT started with a hydraulic torque converter, driven by transmission fluid, and without friction of parts, so it can achieve the same life as a car and be maintenance-free for life. 3. Dongfeng Nissan's chain drive CVT adopts steel belt drive, which is just the opposite of chain drive. For push transmission (the driving wheel pushes the driven wheel through the push plate of steel belt), the lower half of the push plate side contacts with the pulley, and the friction area is large. Push-and-pull transmission can transmit more torque, so Dongfeng Nissan's CVT can match the 3.5L large displacement engine. 4. Clutch CVT Dongfeng Nissan CVT adopts hydraulic torque converter, which can increase torque and greatly improve the starting acceleration performance. The ultra-low speed of hydraulic torque converter can ensure the accurate operation when starting on the slope and reversing into the warehouse. CVT with hydraulic torque converter can be installed on off-road vehicles that need super torque. This combination improves the climbing ability of the car and greatly improves the ability of the car to drive on rough roads. In addition, the hydraulic torque converter uses transmission fluid to transmit power without friction, which prolongs the service life of CVT and can realize lifelong maintenance-free.