WORKING OF CVT
C.V.T. (Continuously Variable Transmission) is a system that makes it possible to vary progressively the transmission ratio. So it allows selection of an infinite number of ratios, (between a minimum and a maximum value).
In the vehicle, the input of the CVT system is connected to the engine flywheel and the output of the system is connected to the road wheels. The system consists mainly of two pulleys. The CVT pulley has two conical drums. The distance between the two drums is controlled by the engine speed. In the starting stage the distance between the drums is least. At this time the belt will be at the outer part of the conical pulley and this will give maximum gear ratio.
When the engine speed increases, the clutch of the CVT fly out’s and the liner’s on the clutch come in contact with the drum. The shaft connected to the drum drives the spur gears in the gear system. This results in the rotation of the output shaft. This is shown in the fig.1.a.
When the engine speed increases the conical pulley gets departed. This results in the motion of the belt downwards due to the decrease in diameter of the conical pulley and thus increases the speed of the output shaft. This is shown in the fig.1.b
When the engine speed is decreased, the conical pulley contract, this results in the motion of the belt upward due to the increase in diameter of the conical pulley and thus increases the speed of the output shaft. Because the diameter of the conical pulley is larger than the input pulley.
DEVELOPMENT OF CVT
Leonardo da Vinci, in 1490, conceptualized a stepless continuously variable transmission.   The first patent for a toroidal CVT was filed in 1886. 
From the 1950s, CVTs, have been applied to aircraft electrical power generating systems.
A CVT, called Variomatic, was designed and built by the Dutchman Huub van Doorne, co-founder of Van Doorne’s Automobile Fabriek (DAF), in the late 1950s, specifically to produce an automatic transmission for a small, affordable car. The first DAF car using van Doorne’s CVT, the DAF 600, was produced in 1958. Van Doorne’s patents were later sold to Volvo along with DAF’s car business and CVT was used in Volvo 340.
The Ford Fiesta and Fiat Uno were the first mainstream European cars to be equipped with steel-belted CVT (as opposed to the less robust rubber-belted DAF design), in 1987.
In the 1980s and 1990s, the Subaru Justy was offered with a CVT. While the Justy saw only limited success, Subaru continues to use CVT in its keicars to this day, while also supplying it to other manufacturers.
Nissan first introduced CVT in the 1992 Nissan March with a unit sourced from Subaru. In the late 1990s. Nissan designed its own CVT that allowed for higher torque,, and includes a torque converter. This gearbox was used in a number of Japanese market modles.
Nissan is also the only car maker to bring roller-based CVT to the market in recent years. Their toroidal CVT, named the Extroid, was available in the Japanese market Y34 Nissan Gloria and V35 skyline GT-8. However, the gear box was not carried over when the Cedric/Gloria was replaced by the Nissan Fuga in 2004.
After studying pulley-based CVT for years, Honda also introduced their own version on the 1995 Honda Civic VTi. Dubbed Honda Multi Matic, this CVT gearbox accepted higher torque than traditional pulley CVTs, and also includes a torque converter for “creep” action.
Toyota introduced the E-CVT in the 1997 Prius, and all subsequent Toyota and Lexus hybrids sold internationally continue to use the system. Although sold as a CVT it is in fact not such a device as the gear ratios are fixed and the transmission is actually a Power Split Transmission (PST), allowing either the electric motor or the ICE (internal combustion engine) or both to propel the vehicle. The response of the complete system (under computer control) is similar in feel to a CVT in that the ICE speed is relatively low and constant under low power or high and constant under high power.
BMW used a belt-drive CVT as an option for the low and middle range MINI in 2001, forsaking it only on the supercharged version of the car where the increased torque levels demanded a conventional automatic gear box. The CVT could also be manually “shifted” if desired with software simulated shift points.
General Motors designed a CVT for use in small cars, which was first offered in 2002. After just three years, however, this transmission will be phased out in favour of conventional planetary automatic transmissions.
Audi has, since 2000, offered a chain-type CVT as an option on some of its larger-engine models, for example the A4 3.0L V6.
The 2005 Ford Freestyle, Five Hundred and Mercury Montego use a chain driven CVT; known as the CFT30, allowing engine torque to go up to 300 N.m. The transmission was designed in co-operation with the German automotive supplier ZF Friedrichshafen and was produced in Batavia, Ohio at Batavia Transmissions LLC; (a subsidiary of Ford Motor Company) until 3/22/07. The Batavia plant also produced the belt driven CFT 23 CVT which went in the Ford Fous C-Max, and still produces 4 speed automatic (CD4E) for the Ford Escape and Mazda Tribute. The CVT is computer controlled and combines fuel efficiency and smooth riding. Ford also sold Escort (European version) and Orion models in Europe with CVTs in the 1980s and 1990s. ZF Friedrichshafen supplied is belt drive VT-1 CVT unit to BMW for use in some versions of the European Mini Cooper.
The 2007 Dodge Caliber  and the related Jeep Compass employ a CVT using a variable pulley system as their optional automatic transmission.
Contract agreements were established in 2006 between MTD and Torotrak for the first full toroidal system to be manufactured for outdoor power equipment such as jet skis, ski-mobiles and ride – on mowers.
Many small tractors for home and garden use have simple hydrostatic or rubber belt CVTs. For example, the John Deere Gator line of small utility vehicles (used by many parks, stadiums, colleges, and other places where miscellaneous items must be displaced by laborers) use a belt with a conical pulley system. They can deliver a lot of power but can also build up speed to 10-15 MPH, all without need for a clutch or gears shift. Most snowmobiles use CVTs. Most new motor scooters today are equipped with CVT. Virtually all snowmobile and motor scooter CVTs are rubber belt/variable pulley CVTs.
Some combine harvesters have CVTs. The machinery of a combine is adjusted to operate best at a particular engine speed. The CVT allows the forward speed of the combine to be adjusted independently of the engine speed. This allows the operator to slow down and speed up as needed to accommodate variations in thickness of the crop.
CVTs have been used in SCCA Formula 500 race cars since the early 1970s.
More recently, CVT systems have been developed for go-karts and have proved to increase performance and engine life expectancy. The Tomcar range of off-road vehicles also utilizes the CVT system.
Some older drill presses contain a pulley-based CVT where the output shaft (which the chuck is connected to) has a pair of manually-adjustable conical pulley halves to which a wide drive belt from the motor loops through. The pulley on the motor, however, is usually fixed in diameter, or may have a series of given-diameter steps to allow a selection of speed ranges. A handwheel on the drill press, marked with a scale corresponding to the desired machine speed, is mounted to a reduction gearing system for the operator to precisely control the width of the gap between the pulley halves. This gap width thus adjusts the gearing ratio between the motor’s fixed pulley and the output shaft’s variable pulley, changing speed of the chuck; a tensioner pulley is implemented in the belt transmission to take up or release the slack in the belt as the speed is altered. Almost always, the drill press’ speed cannot be changed without the motor running, though..
Chapter – 3
ADVANTAGES AND DRAWBACKS
Compared to hydraulic automatic transmissions:
● CVTs scan smoothly compensate for changing vehicle speeds, allowing the engine speed to remain at its level of peak efficiency. They might also avoid torque converter losses. This improves both fuel economy and exhaust emissions. However, some units (e.g., Jatco “Extroid”) also employ a torque converter. Fuel efficiency advantages as high as 20% over four-speed automatics can be obtained.
● CVTs have much smoother operation. This can give a perception of low power, because many drivers expect a jerk when they begin to move the vehicle. The satisfying jerk of a non-CVT can be emulated by CVT control software though, eliminating this marketing problem.
● Since the CVT keeps the engine turning at constant RPMs over a wide range of vehicle speeds, pressing on the accelerator pedal will make the car move faster but doesn’t change and sound coming from the engine as much as a conventional automatic transmission great-shift. This confuses some drivers and, again, leads to a mistaken impression of a lack of power.
● Most CVTs are simpler to build and repair.
● CVT torque handling capability is limited by the strength of their belt or chain, and by their ability to withstanding friction wear between torque source and transmission medium for friction-driven CVTs. CVTs in production prior to 2005 are predominantly belts or chain driven and therefore typically limited to low powered cars and other light duty applications. More advances IVT units using advanced lubricants, however, have been proven to support any amount of torque in production vehicles, including that used for buses, heavy trucks, and earth moving equipment.
TYPES OF CVT
4.1 Infinitely Variable Transmission (IVT)
A specific type of CVT is the infinitely variable transmission (IVT), which has an infinite range of input/output ratios in addition to its infinite number of possible ratios; this qualification for the IVT implies that its range of ratios includes a zero output/ input ratio that can be continuously approached from a defined “higher” ratio. A zero output implies an infinite input, which can be continuously approached from a given finite input value with an IVT. Low gears are a reference to low ratios of output/input which have high input/output ratios that are taken to the extreme with IVTs, resulting in a “neutral”, or non-driving “low” gear limit. Most continuously variable transmissions are not infinitely variable.
Most (if not all) IVTs result from the combination of a CVT with an epicyclic gear system (which is also known as a planetary gear system) that facilitates the subtraction of one speed from another speed within the set of input and planetary gear rotations. This subtraction only needs to result in a continuous range of values that includes a zero output; the maximum output/input ratio can be arbitrarily chosen from infinite practical possibilities through selection of extraneous input or output gear, pulley or sprocket sizes without affecting the zero output or the continuity of the whole system. Importantly, the IVT is distinguished as being “infinite” in its ratio of high gear to low gear within its range; high gear is infinite times higher than low gear. The IVT is always engaged, even during its zero output adjustment.
The term “Infinitely Variable Transmission” does not imply reverse direction, disengagement, automatic operation, or any other quality except ratio selectabilty within a continuous range of input/output ratios from a defined minimum to an undefined, “infinite” maximum. This means continuous range from a defined output/input to zero output/input ratio.
4.2 Ratcheting CVT
The Ratcheting CVT is a transmission that relies on static friction and is based on a set of elements that successively become engaged and then disengaged between the driving system and the driven system, often using oscillating or indexing motion in conjunction with one-way clutches or ratchets that rectify and sum only “forward” motion. The transmission ratio is adjusted by changing linkage geometry within the oscillating elements, so that the summed maximum linkage speed is adjusted, even when the average linkage speed remains constant. Power is transferred from input to output only when the clutch or ratchet is engaged, and therefore when it is locked into a static friction mode where the driving & driven rotating surfaces momentarily rotate together without slippage.
These CVTs can transfer substantial torque because their static friction actually increases relative to torque throughput, so slippage is impossible in properly designed systems. Efficiency is generally high because most of the dynamic friction is caused by very slight transitional clutch speed changes. The drawback to ratcheting CVTs is vibration caused by the successive transition in speed required to accelerate the element which must supplant the previously operating & decelerating, power transmitting element. An Infinitely Variable Transmission (IVT) that is based on a Ratcheting CVT and subtraction of one speed from another will greatly amplify the vibration as the IVT output/input ratio approaches zero.
Ratcheting CVTs are distinguished from Variable Diameter Pulleys (VDPs) and roller-based CVTs by being static friction-based devices, as opposed to being dynamic friction-based devices that waste significant energy through slippage of twisting surfaces.
4.3 Variable – diameter pulley (VDP)
In this system, there are two v-belt pulleys that are split perpendicular to their axes of rotation, with a v-belt running between them. The gear ratio is changed by moving the two sections of one pulley closer together and the two sections of the other pulley farther apart. Due to the v-shaped cross section of the belt, this causes the belt to ride higher on one pulley and lower on the other. Doing these changes the effective diameters of the pulleys, which changes the overall gear ratio. The distance between the pulleys does not change, and neither does the length of the belt, so changing the gear ratio means both pulleys must be adjusted (one bigger, the other smaller) simultaneously to maintain the proper amount of tension on the belt.
Variable diameter pulley
4.4. Roller-based CVT
Consider two almost-conical parts, point to point, with the sides dished such that the two parts could fill the central hole of a torus. One part is the input, and the other part is the output (they do not quite touch). Power is transferred from one side to the other by one or more rollers. When the roller’s axis is perpendicular to the axis of the almost-conical parts, it contacts the almost-conical parts at same-diameter locations and thus gives a 1:1 gear ratio. The roller can be moved along the axis of the almost-Conical parts changing angle as needed to maintain contact. This will cause the roller to contact the almost-conical parts at varying and distinct diameters, giving a gear ratio of something other than 1:1. Systems may be partial or full toroidal. Full toroidal systems are the most efficient design while partial toroidals may still require a torque converter (e.g., Jatco “Extroid”), and hence lose efficiency.
4.5 HYDROSTATIC CVTS
Hydrostatic transmissions use a variable displacement pump and a hydraulic motor. All power is transmitted by hydraulic fluid. These types can generally transmit more torque, but can be sensitive to contamination. Some designs are also very expensive. However, they have the advantage that the hydraulic motor can be mounted directly to the wheel hub, allowing a more flexible suspension system and eliminating efficiency losses from friction in the drive shaft and differential components. This type of transmission is relatively easy to use because all forward and reverse speeds can be accessed using a single lever.
This type of transmission has been effectively applied to a variety of inexpensive and expensive versions of ridden lawn mowers and garden tractors. Many versions of riding lawn mowers andgarden tractors propelled by a hydrostatic transmission are capable of pulling a reverse line tiller and even a single bladed plow.
One class of riding lawn mower that has recently gained in popularity with consumers is zero turning radius mowers. These mowers have traditionally been powered with wheel hub mounted hydraulic motors driven by continuously variable pumps, but this design is relatively expensive. A company call Hydro-Gear, a joint venture between Sauer-Danfoss and Agri-Fab, Inc., of Sullivan, Illinois, created the first cost-effective integrated hydrostatic transaxle suitable for propelling consumer zero turning radius mowers. An integrated hydrostatic transaxle (IHT) uses a single housing for both hydraulic elements and gear-reducing elements. As of May 9,2007, Hydro Gear remains the only company producing integrated hydrostatic transaxles for consumer zero turning radius mowers in North America.
Some heavy equipment may also be propelled by a hydrostatic transmission; e.g., agricultural machinery including foragers and combines, but not anything that works the ground because the transmission cannot transmit enough torque.
4.6. Hydristor IVT
The Hydristor torque converter is a true IVT in that the front unit connected to the engine can displace from zero to 27 cubic inches per revolution forward and zero to -10 cubic inches per revolution reverse. The rear unit is capable of zero to 75 cubic inches per revolution. The common “kidney port” plate between the two sections communicates the hydraulic fluid under pressure and suction return in a “serpentine-torodial” flow path between the two Hydristor internal units. The IVT ratio is determined by the ratio of input displacement to output displacement. Therefore, the theoretical range of Hydristor IVT ratios is I/infinity to +-infinity/1 but real-world ratios are constrained by physics.
4.7. Simkins’ Ratcheting Cvt
This transmission is an example of a Ratcheting CVT, prototyped as a bicycle transmission, protected under U.S. Patent # 5516132. The input is the crank with a round hub integrated with it, and an array of twelve arms that are pivotally mounted to pins in the hub circle. Each arm has a pinion gear mounted on a one way clutch that allows only clockwise rotation of the pinion relative to the arm. All of these pinions are engaged with a large ring gear that is integrated with the chain wheel as the output, and the ring gear/chain wheel assembly is mounted to a mechanism that enables it to be adjusted from a position of concentricity with the crank hub to various amounts of eccentricity with the crank hub. Adjustment of this eccentricity variably changes the output/input ratio from 1:1 to 2.6:1 as the ring gear/sprocket assembly is moved from a position concentric with the crank hub to an eccentric position.
The eccentricity control mechanism is connected to a spring that pushes the transmission into its eccentric high gear position. The largest spread of the arms is indicative of the gear ratio because the spreading arms are the only arms whose pinions (and one-way clutches) are locked and driving the ring gear/chainwheel assembly. Strong pedaling torque causes this mechanism to react against the spring, moving the ring gear/chainwheel assembly toward a concentric, lower gear position. When the pedaling torque relaxes to lower levels, the transmission self-adjusts toward higher gears, accompanied by an increase in transmission vibration. This transmission behaves according to the definition of a Ratcheting CVT.
Variomatic is the stepless, fully automatic transmission of the Dutch car manufacturer DAF, using a drive belt and two pulleys.It was the first continuously variable transmission (CVT) (as opposed to shifting between separate gears). In theory, this always produces the optimum torque. The variomatic was introduced by DAF in 1958, also putting an automatic gear box in the Netherlands for the first time. The variomatic was introduced on a lower priced version of the DAF 600. Because the system does not have separate gears, but one (continuously shifting) gear and a separate ‘reverse mode’(as opposed to a reverse gear), the gear works in reverse as well, giving it the interesting side-effect that one can drive backwards as fast as forwards. As a result, in the former Dutch annual backward driving world championship, the DAFs had to be put in a separate competition because no other car could keep up. Thus, these very cheap and simple cars were the ‘formula one’ in this competition.
The system lost popularity over the years and manual transmission remained dominant in Europe. Audi reintroduced an improved version of the variomatic in the early 21st century under the name Multitronic. This system uses a metal belt and lacks a limit to the number of gears available, switching between them without noticeable shocks. These metal drive belts are the most important part of CVT. The only factory still producing these belts, the Bosch factory in the Netherlands, produced the ten millionth belt on 9 May 2007. It is used in over 40 car models, these days even including expensive brands like Mercedes.
Variable diameter Pulley
The final drive has two pulleys with moveable conical drums. The distance between the drums is controlled by the engine vacuum in the inlet manifold and engine RPM, through centrifugal weights inside the drums. Between the two pulleys runs a drive belt. As a result of change in the distance of the conical drums in both pulleys, the diameters and so also the reduction ratio changes continuously.
With the DAF 600-55 each rear wheel was propelled individually by a pair of conical drums and drive belt with the effect of a limited slip differential: if a drive wheel on slippery road revs up, the other wheel can still transfer the full torque. This results in unusually good traction characteristics, which were also a reason for successes of the
DAFs in rallies. It was even used in a Formula 1 car, but it was only allowed to start in once race before it was banned since it gave an unfair advantage.
The Variomatic is also used in today’s motorscooters. It is a standard part of all common scooters since 1985, and several companies such as Malossi, Polini, Doppler and Stage6 are offering tuning clutches and variomatic for most common 50, 70 and 125 cc scooters.
A version of the Variomatic called Transmatic is still made by DAF’s Van Doorne’s Transmissie b.v. in Tilburg, The Netherlands and Nissan Primera is offered with this transmission.
Today the Continuously Variable Transmission (CVT) works according to the same principle. Rather than rubber drive belts, the modern transmission is made much more durable by the use of steel link belts. The CVT is available in cars such as Audi, Honda and the MINI ONE and MINI Cooper.
Chapter – 5
THE VEHICLES WITH CVT
5.1 NEW AUTOMOBILES EQUIPPED WITH CVT
● Audi A4 2.0/1.8T/2.4/3.0/2.0 TDI/2.5 TDI
● Audi A6 2.0/1.8T/2.4/3.0/2.5 TDI
● [Daihatsu Mira Custom] 0.661 3 cyl
● Dodge Caliber
● Fiat Punto 1.2L
● Ford Escape Hybrid 2.3 L 4 cyl
● Ford Five Hundred 3.0 L 6 cyl
● Ford Focus C-MAX 1.6 L TDCi 110 PS
● Ford Freestyle 3.0 L 6 cyl
● Honda Civic HX 1.7L 4 cyl
● Honda Civic Hybrid 1.3 L 4 cyl
● Honda City 1.5 L
● Honda HR-V 1.6 L
● Honda Insight 1.0 L 3 cyl
● Honda Jazz 1.4L / Honda Fit 1.3 L/1.5 L
● Jeep Compass 2.4 L
● Jeep Patriot 2.4 L
● Lexus GS 450h 3.5 L 6 cyl
● Lexus RX400h 3.3 L 6 cyl
● Mercedes-Benz A_Class
● Mercedes-Benz B-Class
● Mercury Montego 3.0 L 6 cyl
● Microcar MC1/MC2 505cc 2 cyl diesel or petrol
● Microcar Virgo 505cc 2 cyl diesel or petrol
● Mitsubishi Colt 1.5 L MIVEC 4 cyl with INVECS-III CVT(Asian-Oceanian version only, 72 kW)
● Mitsubishi Lancer 1.6 L/1.8 L MIVEC 4 cyl with INVECS-III CVT (Asian version only) the 2008 version also.
● MG F/MG TF 1.8L
● BMW MINI one and Cooper
● Nissan Altima (from 2007)
● Nissan Cube
● Nissan Maxima (from 2007)
● Nissan Micra 1.0 L/1.3 L
● Nissan Murano 3.5 L
● Nissan Primera 2.0L
● Nissan Qashqai 2.0L
● Nissan Sentra (from 2007)
● Nissan Serena 2.0L
● Nissan Skyline 350GT-8
● Nissan Tiida/Versa
● Open Vectra 1.8L
5.2 OLD AUTOMOBILES EQUIPPED WITH CVT
● DAF 600
● DAF 750
● DAF Daffodil
● DAF 33
● DAF 44
● DAF 46
● DAF 55
● DAF 66
● Fiat Uno
● Ford Fiesta
● Honda Civic ESi
● Honda Civic HX
● Nissan Micra
● Subaru Justy
● Volvo 66
● Volvo 300 series
● Volvo 440/460
● Daewoo Matiz II with E3CVT (currently GM Daewoo)
Chapter – 6
FABRICATION OF WORKING MODEL
The Continuously variable transmission (CVT) is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios.
A CVT need not be automatic, nor include zero or reverse output. Such features may be adapted to CVTs in certain specific applications.
Other mechanical transmission only allow a few different discrete gear ratios to be selected, but the continuously variable transmission essentially has an infinite number of ratios available within a finite range, so it enables the relationship between the speed of a vehicle engine and the driven speed of the wheels to be selected within a continuous range. This can provide better fuel economy than other transmissions by enabling the engine to run at its most efficient speeds within a narrow range.
CVTs have been refined over the years and are much improved from their origins
In this project we are making a working model of CVT system used in Kinetic Honda. By this model anyone can understand the working of a CVT.
To make this project we used a (1) C.V.T. system of Kinetic Honda and (2) a ½ hp Induction motor.
(1) C.V.T. system of Kinetic Honda
a. The main parts of the system are
b. Three spur gears
c. Output shaft
d. Input shaft
e. Conical Pulley
(2) ½ HP Induction motor.
The Experiment setup is as shown in the figure 3. Tthe Induction motor and CVT system setup are mounted on a stand made of mild steel. The size of the stand is 60*50. Four rails are connected on the stand to mount the induction motor and CVT system. The induction motor drives the CVT system with the help of a belt used in Kinetic Honda
Using Induction Motor we drive the input shaft of the C.V.T. with the help of a belt. When the supply is ON, the induction motor starts to drive the C.V.T system. During the starting stage the diameter of the C.V.T. pulley will be larger than the pulley diameter fitted to the induction motor. When the motor is switched on the C.V.T. pulley gets departed and one end of it connected to liner come into contact with drum of the C.V.T. system. This results in the rotation of the output shaft.
When the conical pulley departs, the speed of the output shaft increases this can be shown by taking three readings ie. belt at the outer end of conical pulley,belt about middle of the conical pulley and belt at the inner diameter of conical pulley. As in the table given below.
POSITION OF THE BELT
DISTANCE BETWEEN THE TWO SECTIONS OF CONICAL PULLEY(MM)
SPEED OF OUTPUT SHAFT (RPM)
In inner diameter
In medium diameter
In outer diameter
The project assigned to us CVT (continuously variable transmission) has been successfully completed with a working model. CVT is a transmission system which have been is use for decades in various operational condition. It is renowned for its cost effectiveness and simplicity.