1. Introduction
CVT technology has once again become one of the new technologies of attention, do it here introduce the principle of CVT’s easy to understand, so that we understand what the manual transmission and CVT technology is now widely used and have automatic transmission What is the difference.
CVT now on the market car equipped with a manual transmission main gearbox (MT), automatic transmission (AT), a continuously variable transmission (CVT).
2,1, MT:
a manual transmission (MT: Manual Transmission), the gear set, since the gear teeth of each gear set is fixed, so that each a gear speed ratio value (i.e., so-called “level”). For example, a transmission gear ratio is 3.455, 2.056 is the second gear, fifth gear and then to 0.85, then multiply these figures is the total reduction gear ratio of the main transmission ratio, a total of only five values (i.e. 5), so that it It is a stepped transmission.
The most common is the manual transmission, transmission, its basic configuration with one sentence, that is a two-axis axis, referring to the input shaft, the shaft and the intermediate shaft, which constitute the main body of the transmission, of course, a reverse shaft. Known as manual transmission manual gear type transmission, comprising a gear can slide axially, by the engagement of the different gears of the transmission torque reaches purposes.
3,2, AT:
The automatic transmission (AT: Automatic Transmission) using a vehicle speed and the load (accelerator pedal stroke) of two-parameter control gear according to automatically lift the two parameters above. AT the same point of the MT, it is both are step-variable transmission, but AT can be automatically increased or decreased in accordance with the gear speed of the vehicleYou can eliminate my hand car “frustrated” the gear change feeling. Structure
(1) AT is:
Compared with the manual transmission, the hydraulic automatic transmission (AT) are very different in structure and use. Manually waves mainly composed of gears and shafts, the transmission torque variation produced by the different gear combinations thereof; and AT is a torque converter, a planetary gear and the hydraulic control system components, through a combination of hydraulic transmission and a variable speed gear to achieve moment. Wherein the torque converter is the most characteristic component AT, which consists of a pump wheel, a turbine, and a stator composed of other components, engine power is transmitted directly to the input torque and the clutch action.
(2) AT advantages and disadvantages:
AT clutch without shift gear change less, smooth connection, it is easy to operate, easy to bring both the motorist, who also bring comfort to ride. 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.
(3) AMT
AMT transformation in (manual transmission) on the basis of the original mechanical transmission, mainly the manual shift control portion. I.e. robotic system in the case of a constant overall transmission structure controlled by the microprocessor to automate the installation shift. Thus AMT is actually done by a robotic system for operating the clutch and the selected gear of two actions. Since the AMT can be modified in the manual transmission is the production base on the good production inheritance, with responsibility for investment is also low, likely to be accepted production plant. AMT’s core technology is computer-controlled, electronic technology and quality will directly determine the quality of the performance and operation of the AMT.
4,3, CVT:
The continuously variable transmission (CVT: ContinuouslyVariableTrans-mission) with a stepped difference is that it is not the speed ratio intermittent dots, but a series of continuous values, 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 with ordinary sizes gearbox under the control gear sets have watched together, to form different gear ratios, as the size of the bicycle pedal by the drive wheel and the chain wheels to rotate at different speeds . 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 using a variable groove width and a belt ratchet 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, metal band, and metal chain. CVT is true of the stepless, it has the advantage of light 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.
5, CVT development history
CVT technology development, it 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 H.Van Doorne BoGuests successful development of the 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 of the CVT in the energy-saving pump, belt with 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.
first half of 1997, Japan’s 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.
Japanese company Mitsubishi has selected CVT 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 development CVT experience. 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.
first half of 1999, Ford’s US and German ZF production companies CVT for Ford’s cars and light trucks. 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 system 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 company-matched 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.
6, the application of CVT transmission
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. From research and development of metal belt type car during the “Ninth Five-Year” 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. CVT technology is at the beginning of the life cycle, CVT features will further increase.
What is CVT? Base member
The main structure and working principle of the CVT As shown, the system mainly comprises a driving wheel set, driven wheel set, and a hydraulic pump 1 with a metal.
CVTTransmission (CVT) electronic control system architecture diagram
the metal strip is made of metal rings and two beams hundreds of sheet metal. Driving wheel and the driven wheel set set by the movable and stationary discs, and the elements close to the cylinder side of the pulley the shaft can slide, the other side is fixed. The movable plate and the fixed plate are tapered structure, the tapered surface thereof to form a V-groove engaged with V-belt metal. Output power of the engine output shaft is transmitted to the first drive wheel of the CVT, and then transmitted through the V-belt to the driven wheels, the final reduction gear, a differential transmitted to the wheel to drive the car. Work driving wheel and the driven wheel disc movable axially movable to change the working radius of the driving wheel, the driven wheel tapered surface engaged with the V-belt, thus changing the transmission ratio through. Amount of axial movement of the movable plate is adjusted to achieve the driving wheel, the driven wheel cylinder pressure of the hydraulic pump by the control system as required by the driver. Since the radius of the driving wheel and the driven working wheel can be implemented continuously adjusted to achieve a continuously variable transmission.
In the hydraulic system of the metal belt type continuously variable transmission, the role of the slave cylinder is to control the tension of the metal strip, power from the engine to ensure efficient, reliable delivery. Active cylinder control bevel wheel axially movable position, with movement along the V-groove in the driving wheel set of metal, unchanged since the length of the metal strip, the driven wheel set along with the change of the metal V-groove in the opposite direction. Radius of gyration metal strip on the driving wheel set and a driven wheel set changes, continuous change in speed ratio.
when the car started, the working radius of the driving wheel is small, the transmission can obtain a large gear ratio, which then drives the axle to have sufficient torque to ensure that cars have great acceleration. As vehicle speed increases, the working radius of the driving wheel is gradually reduced, the working radius of the driven wheel increases correspondingly, the CVT transmission ratio decreased, so that the car can travel at a higher speed.
7, CVT characteristics
1, the economy
the CVT continuously variable transmission may be implemented in a fairly wide range, so as to obtain the drive train and engine operating best match conditions, to improve the fuel economy of the vehicle. Germany’s Volkswagen Golf VR6 in their cars were installed 4-AT and CVComparative fuel consumption ECE urban cycle T of suburban and ECE test cycle, fuel economy can be effectively demonstrated CVT (Table 1)
4-AT is mounted and a CVT VW Golf VR6 vehicle
Test fuel 4- AT CVT
ECE urban cycle, L / 100km 14.4 13.2
ECE suburban / remote loop, L / 100km 10.8 9.8
90km / h uniform, L / 100km 8.3 7.0
120km / h, L / 100km 10.3 9.2
2, backup power dynamics
car determines the car’s 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
CVT system configuration is simple, the number of parts is less than the AT (about 500) (about 300), once the car manufacturers began mass production, CVT will cost less than the 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% transmission AT, the whole thus the quality of the car 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 “driving pleasure.”
8, References
http://baike.baidu.com/view/86470.htm