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What is the continuously variable transmission CVT?

1. The continuously variable transmission CVT

Overview

CVT, usually refers to an automotive transmission, also known as a continuously variable transmission, it has been a hundred years History. CVT distinction stepped transmission is that it is not the speed ratio intermittent dots, but a series of continuous values, thereby achieving a good economy, power and driving comfort, but also reduces costs and emissions.

CVT technology has once again become one of the new technologies of attention, here to do a presentation on the principle of CVT in simple terms, so that we understand exactly CVT technical and manual and automatic transmissions are now large-scale use of any different.

The continuously variable transmission (CVT: ContinuouslyVariableTrans-mission) and in that a stepped difference, it is not the speed ratio intermittent dots, but a series of continuous variation of, for example, may have varied from 3.455 to 0.85. CVT structure is simpler than conventional transmissions, smaller, both manual transmission gear pair not numerous, there is no complex planetary gearset of the automatic transmission, which mainly depends on the driving and driven wheels and bring the metal to achieve infinitely variable speed ratio.

The principle is the same as an ordinary transmission gear sizes in the control groups have watched together, to form different gear ratios, as the size of the bicycle pedal by the chain wheel driven wheels at different the speed of rotation. Due to different velocities of the thrust generated by each group of gears of different sizes, so that the rotational speed of the transmission output also changes, in order to achieve rotation, regardless of the grade of bradycardia.

CVT Ratchet variable groove width and a belt for power transmission, i.e. when the ratchet groove width changes elbow, to change the contact radius corresponding driving wheel and the driven wheel of the variable speed belt, the belt generally with a rubber band, metallic tape and metal chain. Stepless CVT is truly of, and it has the advantage of heavyLight weight, small size, fewer parts, and has a high AT comparison operating efficiency, low fuel consumption. But the disadvantage is also obvious CVT, the belt is easily damaged, can not bear a greater load, can only be restricted to about 1 liter automotive low power and low torque, and therefore the automatic transmission in the percentage share of about 4 or less . In recent years, after a major car company’s strong research, the situation has improved. CVT will be the development direction of the automatic transmission.

There are three CVT domestic product, namely, Audi, Fit, Siena (Pa Polyols), fourth paragraph CVT is listed Cowin. Four products, only Audi and Cowin with Cruise.

CVT development history:

CVT technology development, has been a hundred years of history. Benz originator CVT is employed in the automotive art, as early as 1886 will be V-shaped rubber belt CVT attached to the car company’s gasoline. In 1958, the Dutch company DAF, Dr. H.Van Doorne successfully developed double V-shaped rubber belt CVT, called Variomatic and equipment on the DAF Daffodil sedan manufactured, which sold more than 1 million. However, due to a series of defects in the rubber belt type CVT: power limited (limited torque 135Nm less), unstable energy clutch, a hydraulic pump, the belt and the clamping means greater losses, and therefore is not generally accepted automotive industry.

However, studies to improve the performance and belt CVT transmission power limit has been engaged, the torque converter integrated into the CVT system, the main clamping force of the driven wheels to achieve electronic control employed in the CVT efficient pumps, with a belt with a metal instead of the traditional rubber band. New advances in technology to overcome the technical defects of the original CVT system, results in a larger transfer torque capacity, better performance of second-generation CVT is available.

into the 1990s, the automobile industry for research and development of CVT technology growing importance, especially in the mini-car, CVT is considered a key technology. The rapid development of global science and technology, making the new electronic technology and automatic control technology has been used to a CVT. The

1997Six months, Nissan has developed for use on the car 2.0L CVT. On this basis, in 1998, Nissan has developed includes a manual shift mode CVT Design for mid-size sedan. New CVT using a newly developed high strength and a high width strip hydraulic control system. To obtain greater torque capacity through the use of these advanced technologies, Nissan CVT research and development of electronic control technology, changing the transmission ratio of the full implementation of electronic control gear, the car may have been in the downhill engine braking control according to vehicle speed, but also in It can increase the speed ratio smoothly on slippery surfaces to prevent slipping. Nissan plans to use its CVT range from 1.0 L to expand the car’s 3.0L.

Mitsubishi CVT has selected the smooth power transfer without loss of energy of the direct injection engine to drive the car. V-belt / gear transmission mechanism may ensure that the engine power is transmitted smoothly without interruption at all rates. Fight tooth CVT eradication of the phenomenon by a conventional automatic transmission gear shift, so as to obtain more satisfactory response and control. Preparation Mitsubishi direct injection engine (1.5 L of or less) in combination with a CVT.

Japan’s Fuji Heavy Industries also has 15 years of experience in the development of the CVT. In May 1997, it is Vistro FHI miniature car equipped with computer-controlled all-E-CVT (containing six-speed manual shift mode CVT). The driver can be performed without operating the clutch six-speed transmission. FHI uses a torque converter with a lock-type electronically controlled CVT in Pleo miniature car, the slide can be kept to a minimum torque converter, a planetary gear for switching the lockup forward by small / reverse gear. Ratio ranging from 1: 10-5.5: 1.

in the first half of 1999, Ford’s US and German ZF companies as Ford cars and light truck production CVT. In 2001 production of Ford’s design in Batavia, Ohio, and the new joint venture will, CFT23 type CVT with electronic management functions. ZF designed for a torque converter type transmission is a CVT, the use of steel for automobile production laterally mounted engine front-drive. ZF companies can drive vehicles and rear wheel drive automobile production CVT series of wheels that are mounted in the longitudinal direction of the engine. ZF company said: Compared with the four-speed automatic transmission, CVT systemIt can be increased by 10 percentage acceleration performance, fuel economy improved by 10 percentage -15 percentage. Compared with A locking torque converter, CVT system more efficient without leakage. Ford is designing a light-duty trucks and all within the company? With traction drive CVT, including rear-wheel drive and all-wheel drive trucks. In the synovial fluid using the special traction drive a movable slide instead of the belt and the drive wheel. The relative position of the sliding portion of the gear ratio determined, power is transmitted between the very thin layer of liquid oil components.

German ZF company from mid-1999 to provide steel for CVT VT1 drive for Rover 216 cars. Such transmission CVT includes a helical gear or a suitable hydraulic system, wet clutch. The integrated ECU in the system may allow the mechanical, hydraulic and electronic systems further combinations, which make better use of the unique advantages of the various systems.

Bosch type CVT electronic control system is based on the sensor and actuator control electronics unit / module on the basis of the torque. Bosch has an independent member, actuators, sensors and ECU transmission shift comprise a single module, the transmission manufacturer simply add an integrated control unit.

Different types:

The automatic transmission is easy to operate, and reduce driver fatigue born, according to the gear shift control system, which can be divided into hydraulic pilot electronically controlled hydraulic automatic transmission and the automatic transmission; transmission ratio-change mode can be divided into a stepped automatic transmission and a continuously variable automatic transmission. Therefore, the continuously variable transmission is actually an automatic transmission, but it is more than common automatic transmission is much more complex, technically more advanced.

The continuously variable transmission and a common hydraulic automatic transmissions biggest difference is in the structure, which is composed of a gear shift hydraulic control system, there are gear, it can be realized in two block between the continuously variable transmission, and a continuously variable transmission is a transmission wheel and a two belt composed of simpler structure than the conventional automatic transmission, smaller. Further, it can freely change the gear ratio to achieve full CVT, vehicle speed change is more stable, the shift is not the kind of conventional transmission ldquo; Dayton rdquo; feeling.

Transmission Category:

In order to achieve a continuously variable transmission, the transmission may be employed by the liquid transmission mode, the power transmission and mechanical transmission in three ways.

Liquid transmission:

transmission fluid divided into two categories: one is hydraulic, and the motor is mainly composed of a pump or a variable transmission composed of valves and pumps for medium power transmission. Another class of hydraulic type, using a fluid coupling or torque variable speed fluid drive, for high-power (hundreds to thousands kW). The main features of transmission fluid are: speed range, can absorb shock and prevent overload, high transmission efficiency, long life, easy to automate: high manufacturing precision, expensive, constant torque output characteristics, compared with the slip ratio large, prone to oil spills during the operation.

Power transmission:

Power transmission is basically divided into three categories: one is an electromagnetic sliding type, which is installed an electromagnetic clutch slip in the induction motor, by changing the excitation current governor, this is a kind of lagging behind the speed control mode. It features simple structure, low cost, easy operation and maintenance: the biggest slide, low efficiency, severe fever, are not suitable for long-term load operation, it is generally used only for small power transmission. Type II is a DC motor type, to achieve speed change by changing the flux or armature voltage. Which is characterized by a wide range of speed, higher precision, but complex equipment, costly, difficult to maintain, generally used for medium power range (tens to hundreds of kW), the formula has been gradually replace AC motor. Type AC motor is three, pole carried by the speed, pressure and frequency. Most practical applications by frequency control, i.e., using a horn to obtain the power amplitude, and the drive motor speed change. Which is characterized by good performance speed, large-scale, high efficiency, automatic control, small size, suitable for a wide power range: mechanical properties at deceleration Dan constant torque, low-speed operation is not enough stable and low efficiency, high price, maintenance professionals need. In recent years, as an advanced drive, the transmission apparatus excellent in the rapid development of mechanical CVT produces a certain impact.

Mechanical Transmission:

The main characteristics of the mechanical transmission are: speed stability, and slip ratio, reliable, constant power having mechanical properties, high transmission efficiency, simple structure, convenient maintenance, relatively cheap; but higher machining parts and lubrication requirements, low carrying capacity, resistance to overload and impact resistancePoor, it is generally suitable for the medium and small power transmission.

CVT transmission applications:

In 1987, the Japanese Subaru CVT transmission equipped cars on the market, to be successful. European Ford and Fiat will VDT-CVT equipped cars in the displacement of 1.1L to 1.6L. As technology advances, the energy crisis and increasing global energy-saving awareness of environmental protection, the basis of summing up the experience of the first generation CVT, developed a better performance, greater torque capacity CVT. Currently, the world’s major car manufacturers in order to improve the competitiveness of their products, are vigorously CVT research and development. Now NISSAN, TOYOTA, FORD, GM, AUDI and other famous car brands, are equipped with CVT transmission car sales, the annual output of CVT cars worldwide has reached nearly 500,000. It is worth noting that, equipped with the CVT auto market, from the original Japanese, European, have infiltrated the North American market, so the CVT auto is the main trend of car development.

Our country has a huge auto market, auto industry is one of China’s national industry. However, the automatic transmission (AT) needed for China’s auto industry all rely on imports, which makes domestic cars equipped with the AT, costs a lot, and equipment development and production of its own CVT transmission, which costs less, indicating that the market outlook is very CVT optimism.

At present, China is considering the development of car automatic transmission problems. Since ldquo; nine middot; five rdquo;? Car during the research and development of metal belt continuously variable automatic transmission has been included in major national research programs to track the world’s technology development and the development of China’s national conditions of the car.

in the last ten years, CVT technology has approached a major step forward, making the CVT has more than 100-year-old mechanical transmission MT and has more than 50 years of automatic transmission AT is more competitive force. CVT technology is at the beginning of the life cycle, CVT features will further increase.

the CVT characteristics:

1, the economy

can be fairly wide range of the CVT inStepless inner circle, to obtain the best match with the drive train of the engine operating conditions, improved fuel economy of the vehicle. Germany’s Volkswagen Golf VR6 in their cars were installed 4-AT and CVT carry out urban cycle and ECE ECE test cycle suburbs, proved CVT can effectively conserve fuel.

2, power

determines the back-up power car cars climbing ability and acceleration. The greater the power back-up car, the car’s dynamics better. Since the characteristics of the continuously variable transmission CVT, it is possible to obtain the maximum power reserve ratio, the CVT dynamic performance was superior mechanical transmission (MT) and an automatic transmission (AT).

3, emission

wide operating range of the CVT speed ratio, the engine can work in optimum operating conditions, thus improving the combustion process and reduce exhaust emissions. ZF will own production of CVT loading test, its exhaust emissions of cars installed 4-AT reduced by approximately 10 percentage.

4, Cost

the CVT system is simple, the number of parts is less than the AT (about 500) (about 300), once the car manufacturers began mass production, the cost of the CVT It will be smaller than AT. As a result the system can save fuel, as well as large-scale production systems, materials innovation, the CVT components (such as belt or chain driving wheel, a driven wheel and a hydraulic pump) production costs, reduced by 20 -30 Percentage Percentage .

Needless to say, the technical content and manufacturing difficulties to be higher than the CVT transmission MT, similar to the AT transmission, because the metal belt CVT simple structure, the number of parts contained less than 40 percentage transmission AT about the quality of the vehicle and therefore has also been reduced.

5, driving smoothness

Because the CVT ratio change is continuous, so the car’s acceleration or deceleration process is very gentle, and driving is very simple and safe. Thereby allowing users access to a full range of ldquo; rdquo ;. driving fun

Disadvantages:

The extensive use of hydraulic automatic transmission (AT) shift without a clutch, gear position change less large, flat connectionStable, it is easy to operate, convenient to both bring to motorists, but also to bring comfort to the car people. But also many shortcomings, one of the slow response to changes in speed, no manual transmission is sensitive, so many people like to play car manual transmission open car; the second is cost oil uneconomical, low torque converter transmission efficiency is limited scope in recent years, the introduction of electronic control technology improve this problem; third is the institution complex and difficult to repair. In the torque converter hydraulic oil circulating high speed produces a high temperature, hydraulic oil temperature specified use. In addition, if the car can not be started due to battery power shortage, we can not start with a cart or trailer method. If the fault haulage vehicle, pay attention to the drive wheels off the ground, to protect the automatic transmission gear from damage.

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