Cvt transmission

CVT (Continuously Variable Transmission) technology is a stepless speed change technology. By using the cooperation of the drive belt and the driving and driven wheels with variable working diameters to transmit power, the transmission ratio can be continuously changed, so as to obtain the best matching between the transmission system and the engine working conditions. Common CVT includes hydro-mechanical CVT and metal belt CVT.

variable drive

At present, there are more and more CVT models in the domestic market. 1987, Subaru of Japan put the car equipped with CVT transmission on the market and achieved success. Ford and Fiat in Europe are also equipped with VDT-CVT on cars with displacement from 1. 1L to1.6L. With the development of technology, the global awareness of energy conservation and environmental protection has been enhanced by the energy crisis. Based on the experience of the first generation CVT, a CVT with better performance and greater torque capacity is developed. At present, in order to improve the competitiveness of products, the world's major automobile manufacturers are vigorously developing CVT. Now Nissan, Toyota, Ford, GM, Audi and other famous automobile brands are selling cars equipped with CVT transmissions, and the annual output of CVT cars worldwide has reached nearly 500,000. It is worth noting that the automobile market equipped with CVT first penetrated into the North American market from Japan and Europe, so CVT is the main trend of automobile development today.

China has a huge automobile sales market, and the automobile industry is one of our national industries. The automatic transmission (AT) needed by China's automobile industry is imported, which greatly increases the cost of domestic cars equipped with AT, while the cost of CVT transmission developed and produced by the equipment itself does not increase much, indicating that the market prospect of CVT is promising.

At present, China is considering the development of automobile automatic transmission. Since the "Ninth Five-Year Plan", the research and development of metal V-belt CVT for automobiles has been included in the national major scientific and technological research plan, in order to track the technological development of the world and develop automobiles suitable for China's national conditions.

In the last decade, CVT technology has taken a big step forward, making CVT more competitive than mechanical transmission MT with a history of more than 100 years and automatic transmission AT with a history of more than 50 years. CVT technology is at the beginning of its life cycle, and the characteristics of CVT will be further improved.

The development of CVT technology has a history of more than one hundred years. German Mercedes-Benz Company is the originator of adopting CVT technology in automobiles. As early as 1886, the V-type rubber belt CVT was installed on the gasoline engine produced by the company. 1958, Dr. H.VanDoorne of Dutch DAF company successfully developed a double V-shaped rubber belt CVT named Variomatic, which was installed on Narcissus cars manufactured by DAF company, and the sales exceeded 1 10,000 vehicles. However, the rubber belt CVT has a series of defects, such as limited power (torque is limited below 135Nm), unstable clutch operation, large energy loss of hydraulic pump, transmission belt and clamping mechanism, so it has not been generally accepted by the automobile industry.

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 1.0 L to 3.0L cars.

Japan's Mitsubishi company chose CVT to transmit the power of direct injection engine smoothly, and there was no 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 Rover 2 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.

type

Automatic transmission is born for simple operation and reducing driving fatigue. According to the control mode of gear transmission system, it can be divided into hydraulic automatic transmission and electro-hydraulic automatic transmission. According to the change of transmission ratio, it can be divided into step automatic transmission and stepless automatic transmission. Therefore, CVT is actually a kind of automatic transmission, but it is much more complicated and high-tech than the common automatic transmission.

The biggest difference between CVT and ordinary hydraulic automatic transmission lies in its structure. The latter is composed of hydraulically controlled gear transmission system or gear, which can realize step-by-step speed change between different gears, while CVT is composed of two sets of speed change wheels and a transmission belt, which is simpler in structure and smaller in size than the traditional automatic transmission. In addition, the transmission ratio can be changed freely, and the whole stepless speed change can be realized, which makes the speed change more stable and will not have the "stuck" feeling when the traditional transmission shifts gears.

In order to realize stepless speed change, hydraulic transmission, electrical transmission and mechanical transmission can be used.

hydraulic drive

There are two kinds of hydraulic transmission: one is hydraulic transmission, which is mainly composed of pump and motor or valve and pump, and is suitable for medium and small power transmission. The other is hydraulic type, which adopts hydraulic coupler or hydraulic torque for variable speed transmission and is suitable for high power (hundreds to thousands of kilowatts). The main characteristics of liquid transmission are: wide speed range, shock absorption and overload prevention, high transmission efficiency, long service life, easy automation, high manufacturing accuracy, high price, constant torque output, large slip rate and easy oil leakage during operation.

power transmission

Electric drive is basically divided into three categories: one is electromagnetic sliding type, which is to install an electromagnetic sliding clutch in asynchronous motor to change the reverse speed regulation mode of its excitation current. Its characteristics are simple structure, low cost, convenient operation and maintenance: maximum sliding, low efficiency, serious heat, not suitable for long-term load operation, so it is generally only used for low-power transmission. The second type is DC motor type, which realizes speed regulation by changing magnetic flux or armature voltage. Its characteristics are wide speed range and high precision, but the equipment is complex, the cost is high and the maintenance is difficult.

variable drive

Generally used in the middle power range (tens to hundreds of kilowatts), it has been gradually replaced by AC motors. The third type is the AC model, which adjusts the speed by changing poles, regulating voltage and frequency. The most practical application is variable frequency speed regulation, that is, the variable amplitude power supply is obtained by using the horn, and then the motor is driven to change speed. It is characterized by good speed regulation performance, wide range, high efficiency, automatic control, small size and wide applicable power range. Mechanical characteristics are constant torque in deceleration section, low efficiency, unstable low-speed operation, high price and professional maintenance. In recent years, frequency converter, as an advanced and excellent transmission device, has developed rapidly, which has had a certain impact on mechanical continuously variable transmission.

mechanical drive

The main characteristics of mechanical transmission are: stable rotating speed, small sliding rate, reliable operation, constant power mechanical characteristics, high transmission efficiency, simple structure, convenient maintenance and relatively cheap price; However, parts have high requirements for machining and lubrication, low bearing capacity and poor overload and impact resistance, and are generally suitable for medium and small power transmission.

4 Brand Profile Editor Audi Multitronic CVT/ Manual Integrated Transmission

Audi's Multitronic transmission is based on the original continuously variable transmission, and a transmission component called multi-piece chain belt is added. This component greatly expands the application range of continuously variable transmission, which can transmit and control the power output with a peak value of 400N·m, and its transmission ratio exceeds the limit value of the previous automatic transmission. The obvious advantages of this kind of transmission are less energy consumption and fast response. From the overall performance of the vehicle, the 0 ~ 100 km/h acceleration time of Audi A6 2.8 car equipped with Multitronic transmission is 1.3 s faster than that of ordinary automatic transmission models of the same class, and the fuel consumption per 100 kilometers is reduced by 0.9 L.

Multitronic also adopted a brand-new electronic control system to overcome the shortcomings of the original CVT. For example, when going uphill or downhill, the system can automatically detect the slope, increase the power output or increase the braking torque of the engine by adjusting the speed ratio, and assist the vehicle to run.

Compared with the traditional automatic transmission, Multitronic has higher flexibility. When adding or deleting transmission modes, the transmission ratio and radius of gears can be changed only by changing the computer program, so it can be used with many different types of engines with different output characteristics.

Yun Qi continuously variable transmission

Yun Qi CVT adopts VT 1F CVT produced by German ZF company. Coupled with its excellent engine, this whole set of power and transmission system comes from BMW MINICOOPER. CVT has four driving modes: stepless speed change, automatic cruise, sport mode and 6-speed manual, and it is closer to intelligent control with electronic throttle. The fuel consumption of Yun Qi equipped with CVT gearbox is only 0.3 L higher than that of the original factory (manufacturer's figure).

Palio (Siena, windy on weekends) Speedgear

PALIO Speedgear is a manual/automatic electronic continuously variable transmission (ECVT), which was first applied to small cars by Nanjing Fiat. It provides two shift modes: electronic stepless automatic shift mode and 6-speed sequential manual shift mode. Drivers can choose different shift modes according to their own preferences. Speedgear consists of hydraulic torque converter, two variable diameter steel belt wheels and a transmission metal belt (a certain number of steel plates and two 9-layer steel belts), which has a wider transmission ratio and has the characteristics of simple structure and compact volume of continuously variable transmission.

Installing CVT

Fit CVT is specially designed for small cars, belonging to a new generation of steel belt CVT, which allows high torque transmission between two pulleys, runs smoothly and has high transmission efficiency, and performs better in small cars. Fit CVT transmission also has S gear (sports mode), which not only pursues fluency, low fuel consumption, but also enjoys driving pleasure.

5 working principle editing start clutch driving pulley metal belt power input shaft half shaft power output

driven gear

Differential machine

planetary gear

Power output of differential half-shaft gear

driving gear

Intermediate rotation

driven gear

The driven pulley of the driven shaft has no specific gear, which is similar to an automatic gearbox in operation, but the change of speed ratio is different from the jumping and stopping process of the automatic gearbox, but continuous, so the power transmission is continuous and stable.

CVT (Continuously Variable Transmission) technology is a stepless speed change technology. By using the cooperation of the drive belt and the driving and driven wheels with variable working diameters to transmit power, the transmission ratio can be continuously changed, so as to obtain the best matching between the transmission system and the engine working conditions. Common CVT includes hydro-mechanical CVT and metal belt CVT.

There are many structures such as V-shaped rubber belt, metal belt, multi-disc, steel ball, roller turntable, etc. Most of them use metal belt and variable radius roller to transmit power. By changing the radius of driving roller and driven roller, the transmission ratio can be changed. Theoretically, this transmission mode is very efficient, but it must be based on the ability to carry transmission power. Because the friction between the steel belt and the drum is used to transmit power, the working conditions of the steel belt and the drum are very bad. In order to effectively transmit power, it is not allowed to slip between the steel belt and the drum, and a lot of heat energy has already been generated. If it slips again, it is likely to cause internal parts to burn or be seriously consumed. In order to increase the static friction, the most direct method is to increase the pressure between the steel strip and the roller. However, with the increase of friction, the loss of power transmission will also increase, which invisibly increases fuel consumption. The strength of steel strip is also an important factor. Therefore, CVT gearbox has the advantages of comfort, high efficiency and energy saving. The disadvantage is that the current general CVT gearbox cannot bear large torque. Otherwise, it will be compensated by higher fuel consumption.

The difference between CVT and CVT is that its speed ratio is not a discontinuous point, but a series of continuous values, for example, it can change from 3.455 to 0.85. CVT is simpler in structure and smaller in size than traditional transmission. It has neither numerous gear pairs of manual transmission nor complex planetary gear sets of automatic transmission. It mainly depends on the driving wheel, driven wheel and metal belt to realize the stepless change of speed ratio.

Its principle is that several groups of gears with different sizes, like a common gearbox, are divided and combined under control to form different speed ratios, like a bicycle pedal driving wheels to rotate at different speeds through large and small wheels and chains. Because different forces have different thrust on each group of gears, the output speed of the gearbox changes accordingly, thus realizing slow rotation regardless of grades.

CVT adopts variable groove width drive belt and ratchet wheel to transmit power, that is, when the ratchet wheel changes the groove width elbow, the contact radius between the driving wheel and the driven wheel also changes to change the speed. The drive belt generally adopts rubber belt, metal belt and metal chain. CVT is truly stepless speed change. Its advantages are light weight, small volume and few parts. Compared with AT, CVT has higher working efficiency and lower fuel consumption. However, the disadvantage of CVT is also obvious, that is, the transmission belt is easy to be damaged and cannot bear a large load. It can only be used in low-power and low-torque vehicles with a displacement of about 1 liter, so the automatic gear occupancy rate is below 4%. In recent years, the situation has improved after vigorous research by major automobile companies. CVT will be the development direction of automatic gearbox.

In CVT transmission system, the traditional gear is replaced by a pair of pulleys and a steel belt. Each pulley is actually a V-shaped structure consisting of two conical disks. The engine shaft is connected with a small pulley, and the big pulley is driven by a steel belt. The mystery lies in this special pulley: the transmission pulley of CVT has a strange structure and is divided into two movable halves, which can be relatively close or separated. The conical disk can be tightened or opened under the hydraulic thrust, and the width of the V-shaped groove can be adjusted by extruding the steel chain. When the conical disk moves inward and tightens, the steel chain moves in the direction outside the center of the circle (centrifugal direction) under the extrusion of the conical disk, otherwise it will be electrically driven to the center of the circle.

6 Disadvantages Editor The hydraulic automatic transmission (AT), which is widely used now, does not need clutch shifting, and the gear changes little and greatly, with stable connection and simple operation, which brings convenience to drivers and comfort to passengers. However, there are also many shortcomings. First, it is slow to respond to speed changes and insensitive to manual gears, so many riders like to drive manual gears; Second, the fuel consumption is uneconomical, the transmission efficiency is low and the torque range is limited. In recent years, the introduction of electronic control technology has improved this problem; Third, the mechanism is complex and it is difficult to repair. The high-speed circulating hydraulic oil in the torque converter will produce high temperature, so the specified high-temperature resistant hydraulic oil should be used. In addition, if the car cannot be started due to insufficient battery power, it cannot be started by a cart or trailer. If the faulty vehicle is towed away, the driving wheel must be off the ground to protect the automatic wave gear from damage.

7 feature editing CVT technology has only been used in automobiles for ten years, but its advantages over traditional manual and automatic transmissions are obvious:

1. Simple structure, small volume and few parts. The cost after mass production is definitely lower than the current ordinary automatic transmission;

2. Its working speed ratio range is wide, and it is easy to form an ideal match with the engine, thus improving the combustion process and further reducing fuel consumption and emissions;

3. High transmission efficiency, low power loss and good economy.

Of course, CVT technology also has its weaknesses, for example, the transmission belt is easy to be damaged and cannot bear a large load. These technical difficulties make it always used in small-displacement and low-power cars.

At present, CVT technology is developing rapidly, and major automobile manufacturers are strengthening research and development in this area. Especially in the bright future of hybrid electric vehicles, the position and function of CVT are irreplaceable and will be the general trend of transmission development in the future.

Characteristics of continuously variable transmission

8 feature editing 1, high speed regulation accuracy, up to 0.5- 1 rpm.

2. The speed range is wide, and the speed ratio can be adjusted at will between11.4-1/7.

3, high strength, long service life, fully sealed design and strong environmental adaptability.

4, convenient adjustment, stable operation, continuous operation, positive and negative rotation.

5, good adaptability, can be directly connected and combined with other motor deceleration devices to realize low-speed stepless speed change.

6, small size, compact structure, using high-quality aluminum alloy die-casting once molding, beautiful appearance, never rust.

economy

CVT can realize stepless speed change in a wide range, so as to obtain the best matching between the transmission system and the engine working conditions and improve the fuel economy of the whole vehicle. German Volkswagen installed 4-AT and CVT on its golf VR6 car, and conducted ECE urban cycle and ECE suburban cycle tests respectively, which proved that CVT can effectively save fuel (see table 1).

Fuel consumption comparison of Volkswagen Golf VR6 with 4-AT and CVT.

Test fuel consumption 4- in CVT

ECE urban cycle, L/ 100 km 14.4 13.2

ECE suburb/remote area, L/ 100km 10.8 9.8.

variable drive

90 km/h uniform, L/ 100 km 8.3 7.0

120km/h, l/100km 10.3 9.2

dynamic characteristics

The reserve power of the car determines the climbing ability and acceleration ability of the car. The greater the reserve power of the car, the better the power of the car. Because of CVT's stepless speed change characteristics, the transmission ratio of maximum reserve power can be obtained, so the dynamic performance of CVT is obviously superior to that of mechanical transmission (MT) and automatic transmission (at).

avoid

CVT has a wide working range of speed ratio, which can make the engine work in the best working condition, thus improving the combustion process and reducing exhaust emissions. ZF Company has tested its own CVT, and the exhaust emission is about 10% lower than that of the vehicle equipped with 4-AT.

expense

CVT system has a simple structure, and the number of parts is less than AT (about 500) (about 300). Once automobile manufacturers start mass production, the cost of CVT will be lower than that of AT. Because the system can save fuel, with the mass production and the innovation of system and materials, the production cost of CVT parts (such as transmission belt or chain, driving wheel, driven wheel, hydraulic pump, etc.) will be reduced by 20%-30%.

There is no doubt that the technical content and manufacturing difficulty of CVT transmission is higher than that of MT transmission, and it is similar to at transmission. Because of its simple structure, metal belt CVT contains about 40% less parts than at transmission, and the quality of the whole vehicle is also reduced.

Driving comfort

Because the speed ratio of CVT changes continuously, the acceleration or deceleration process of the car is very gentle, and it is very simple and safe to drive. Let users get all-round "driving pleasure".

model

ZH series cone-disk ring-disk CVT MB series planetary friction mechanical CVT.

Precise speed regulation, expanding power XP type and expanding speed regulation range PX type stepless speed change

UDL series planetary cone-disk CVT P-type toothed chain CVT (JB/T 6952- 1993)

W series cone-ring CVT v-type broadband CVT

MT type four-phase parallel connecting rod pulsating CVT URX series ring cone planetary CVT

UD series planetary cone-disk CVT

TXF planetary cone-disk CVT

RX series planetary cone CVT U series three-phase parallel connecting rod pulsating CVT

WMB type three-phase parallel pulsating stepless transmission BWJ series variable speed worm reducer

XZW Series Planetary Bevel Gear CVT Swing Pin Chain CVT

U34 Series Three-phase Parallel Connecting Rod Pulsating CVT 93 JWB Planetary Cone Disk CVT

WMBLF series CVT for vertical kettle GMW series belt CVT

D-type planetary cone-disk CVT MWB series belt CVT

PU series tension automatic adjustment CVT HZ series ring cone planetary CVT

PSR roller CVT PS series tooth chain CVT

DMB series large speed ratio mechanical continuously variable transmission GPZH series steel-to-steel conical disk ring disk mechanical continuously variable transmission p

XB series steel ball continuously variable transmission