Continuously variable transmission

Transmission types
Manual Sequential manual Non-synchronous Preselector
Automatic Manumatic
Semi-automatic Electrohydraulic Dual clutch Saxomat
Continuously variable
Bicycle gearing Derailleur gears Hub gears
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A continuously variable transmission (CVT) is a transmission that can change steplessly through an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios. The flexibility of a CVT allows the driving shaft to maintain a constant angular velocity over a range of output velocities. This can provide better fuel economy than other transmissions by enabling the engine to run at its most efficient revolutions per minute (RPM) for a range of vehicle speeds. Alternatively it can be used to maximize the performance of a vehicle by allowing the engine to turn at the RPM at which it produces peak power. This is typically higher than the RPM that achieves peak efficiency. Finally, a CVT does not strictly require the presence of a clutch, allowing the dismissal thereof. In some vehicles though (i.e. motorcycles), a centrifugal clutch is nevertheless added,^[1] however this is only to provide a "neutral" stance on a motorcycle (useful when idling).

Uses

A Chain-driven CVT

Principle of Variator

Many small tractors for home and garden use have simple rubber belt CVTs. For example, the John Deere Gator line of small utility vehicles use a belt with a conical pulley system. They can deliver an abundance of power and can reach speeds of 10–15 mph (16–24 km/h), all without need for a clutch or shifting gears. Nearly all snowmobiles, old and new, and motorscooters use CVTs, typically the rubber belt/variable pulley variety.

Some combine harvesters have CVTs. The CVT allows the forward speed of the combine to be adjusted independently of the engine speed. This allows the operator to slow or accelerate as needed to accommodate variations in thickness of the crop.

CVTs have been used in aircraft electrical power generating systems since the 1950s and in Sports Car Club of America (SCCA) Formula 500 race cars since the early 1970s. CVTs were banned from Formula 1 in 1994 due to concerns that the best-funded teams would dominate if they managed to create a viable F1 CVT transmission.^[2] More recently, CVT systems have been developed for go-karts and have proven to increase performance and engine life expectancy. The Tomcar range of off-road vehicles also utilizes the CVT system.

Some drill presses and milling machines contain a pulley-based CVT where the output shaft has a pair of manually-adjustable conical pulley halves through which a wide drive belt from the motor loops. 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. In most cases the speed must be changed with the motor running.

CVTs should be distinguished from Power Sharing Transmissions (PSTs), as used in newer hybrid cars, such as the Toyota Prius, Highlander and Camry, the Nissan Altima, and newer-model Ford Escape Hybrid SUVs. CVT technology uses only one input from a prime mover, and delivers variable output speeds and torque; whereas PST technology uses two prime mover inputs, and varies the ratio of their contributions to output speed and power. These transmissions are fundamentally different. However the Mitsubishi Lancer, Proton Inspira, Honda Insight, Honda Fit, and Honda CR-Z hybrids, the Nissan Tiida/Versa (only the SL model), Nissan Cube, Juke, Sentra, Altima, Maxima, Rogue, Murano, Honda Capa, Honda Civic HX, Jeep Patriot and Compass use CVT.

Types

Toyota Super CVT - i

Variable-diameter pulley (VDP) or Reeves drive

In this most common CVT system,^[3] 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 sheaves of one pulley closer together and the two sheaves 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 this changes the effective diameters of the pulleys, which in turn 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 in order to maintain the proper amount of tension on the belt.

The V-belt needs to be very stiff in the pulley's axial direction in order to make only short radial movements while sliding in and out of the pulleys. This can be achieved by a chain and not by homogeneous rubber. To dive out of the pulleys one side of the belt must push. This again can be done only with a chain. Each element of the chain has conical sides, which perfectly fit to the pulley if the belt is running on the outermost radius. As the belt moves into the pulleys the contact area gets smaller. The contact area is proportional to the number of elements, thus the chain has lots of very small elements. The shape of the elements is governed by the static of a column. The pulley-radial thickness of the belt is a compromise between maximum gear ratio and torque. For the same reason the axis between the pulleys is as thin as possible. A film of lubricant is applied to the pulleys. It needs to be thick enough so that the pulley and the belt never touch and it must be thin in order not to waste power when each element dives into the lubrication film. Additionally, the chain elements stabilize about 12 steel bands. Each band is thin enough so that it bends easily. If bending, it has a perfect conical surface on its side. In the stack of bands each band corresponds to a slightly different gear ratio, and thus they slide over each other and need oil between them. Also the outer bands slide through the stabilizing chain, while the center band can be used as the chain linkage.^{[note 1]}

• CVT "Japanese umbrella" presented by Artamonoff Technologies

Nissan Motors Extroid CVT

Toroidal or roller-based CVT (Extroid CVT )

Toroidal CVTs are made up of discs and rollers that transmit power between the discs. The discs can be pictured as 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 disc is the input, and the other is the output (they do not quite touch). Power is transferred from one side to the other by rollers. When the roller's axis is perpendicular to the axis of the near-conical parts, it contacts the near-conical parts at same-diameter locations and thus gives a 1:1 gear ratio. The roller can be moved along the axis of the near-conical parts, changing angle as needed to maintain contact. This will cause the roller to contact the near-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, and hence lose efficiency.

Diagrams:

• Animated image of a toroidal CVT on HowStuffWorks

Magnetic CVT

A magnetic continuous variable transmission system has been developed at the University of Sheffield in 2006 and is now (2011) commercially available.^[4] Two rotating transmission disks, each with magnets attached, synchronously revolve. A change in the radius of the magnets on each of the disks causes a change in the transmission ratio.

Infinitely variable transmission (IVT)

A specific type of CVT is the infinitely variable transmission (IVT), in which the range of ratios of output shaft speed to input shaft speed includes a zero ratio that can be continuously approached from a defined "higher" ratio. A zero output speed (low gear) with a finite input speed implies an infinite input-to-output speed ratio, which can be continuously approached from a given finite input value with an IVT. Low gears are a reference to low ratios of output speed to input speed. This low ratio is taken to the extreme with IVTs, resulting in a "neutral", or non-driving "low" gear limit, in which the output speed is zero. Unlike neutral in a normal automotive transmission, IVT output rotation may be prevented because the backdriving (reverse IVT operation) ratio may be infinite, resulting in impossibly high backdriving torque; ratcheting IVT output may freely rotate forward, though.

The IVT dates back to before the 1930s; the original design converts rotary motion to oscillating motion and back to rotary motion using roller clutches.^[5] The stroke of the intermediate oscillations is adjustable, varying the output speed of the shaft. This original design is still manufactured today, and an example and animation of this IVT can be found here.^[6] Paul B. Pires created a more compact (radially symmetric) variation that employs a ratchet mechanism instead of roller clutches, so it doesn't have to rely on friction to drive the output. An article and sketch of this variation can be found here ^[7]

Most IVTs result from the combination of a CVT with a planetary gear system (which is also known as an epicyclic gear system) which enforces an IVT output shaft rotation speed which is equal to the difference between two other speeds within the IVT. This IVT configuration uses its CVT as a continuously variable regulator (CVR) of the rotation speed of any one of the three rotators of the planetary gear system (PGS). If two of the PGS rotator speeds are the input and output of the CVR, there is a setting of the CVR that results in the IVT output speed of zero. The maximum output/input ratio can be chosen from infinite practical possibilities through selection of additional input or output gear, pulley or sprocket sizes without affecting the zero output or the continuity of the whole system. The IVT is always engaged, even during its zero output adjustment.

IVTs can in some implementations offer better efficiency when compared to other CVTs as in the preferred range of operation because most of the power flows through the planetary gear system and not the controlling CVR. Torque transmission capability can also be increased. There's also possibility to stage power splits for further increase in efficiency, torque transmission capability and better maintenance of efficiency over a wide gear ratio range.

An example of a true IVT is the SIMKINETICS SIVAT that uses a ratcheting CVR. Its CVR ratcheting mechanism contributes minimal IVT output ripple across its range of ratios.

Another example of a true IVT is the Hydristor because 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.

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 and decelerating, power transmitting element.

Ratcheting CVTs are distinguished from 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. An example of a ratcheting CVT is one prototyped as a bicycle transmission protected under U.S. Patent 5,516,132 in which strong pedalling 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.

A running prototype and animation of a functioning two stage ratcheting CVT can be found below:

• Naudic rotorCVT, presented by Varibox CVT Technologies

Hydrostatic CVTs

Honda DN-01 motorcycle: Swashplate animation.

The Japanese Type 10 tank uses Hydraulic Mechanical Transmission (HMT).

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.

An integrated hydrostatic transaxle (IHT) uses a single housing for both hydraulic elements and gear-reducing elements. This type of transmission, most commonly manufactured by Hydro-Gear^{[citation needed]}, 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 and garden tractors propelled by a hydrostatic transmission are capable of pulling a reverse tine 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. Hydro-Gear, created the first cost-effective integrated hydrostatic transaxle suitable for propelling consumer zero turning radius mowers.

Some heavy equipment may also be propelled by a hydrostatic transmission; e.g. agricultural machinery including foragers, combines, and some tractors. A variety of heavy earth-moving equipment manufactured by Caterpillar Inc., e.g. compact and small wheel loaders, track type loaders and tractors, skid-steered loaders and asphalt compactors use hydrostatic transmission. Hydrostatic CVTs are usually not used for extended duration high torque applications due to the heat that is generated by the flowing oil.

The Honda DN-01 motorcycle is the first road-going consumer vehicle with hydrostatic drive that employs a variable displacement axial piston pump with a variable-angle swashplate.

Variable toothed wheel transmission

A variable toothed wheel transmission is not a true CVT that can alter its ratio in infinitessimal increments, but rather approaches CVT capability by having a large number of ratios, typically 49. This transmission relies on a toothed wheel positively engaged with a chain where the toothed wheel has the ability to add or subtract a tooth at a time in order to alter its ratio relative to the chain it is driving. The "toothed wheel" can take on many configurations including ladder chains, drive bars and sprocket teeth. The huge advantage of this type of CVT is that it is a positive mechanical drive and thus does not have the frictional losses and limitations of the roller-based or VDP CVT’s. The challenge in this type of CVT is to add or subtract a tooth from the toothed wheel in a very precise and controlled way in order to maintain synchronized engagement with the chain. This type of transmission has the potential to change ratios under load because of the large number of ratios, resulting in the order of 3% ratio change differences between ratios, thus a clutch or torque converter is necessary only for pull-away. No CVTs of this type are in commercial use, probably because of above mentioned development challenge.

Naudic Incremental CVT (iCVT)

This is a chain-driven system which is advertised at *[2] Although an iCVT works, it has the following weakness:

High Frictional Losses

The variator pulley of an iCVT is choked using two small choking pulleys. Here one choking pulley is positioned on the tense side of the chain of the iCVT. Hence there is a considerable load on that choking pulley, the magnitude of which is proportional to the tension in its chain. Each choking pulley is pulled up by two chain segments, one chain segment to the left and one to the right of the choking pulley; here if the two chain segments are parallel to each other than the load on the choking pulley is twice the tension in the chain. But since the two chain segments are most likely not parallel to each other during operations of an iCVT, it is estimated that the load on a choking pulley is between 1 to 1.8 times of the tension of its chain.

Also, a choking pulley is very small so that its moment arm is very small. A larger moment arm reduces the force needed to rotate a pulley. For example, using a long wrench, which has a large moment arm, to open a nut requires less force than using a short wrench, which has a small moment arm. Assuming that the diameter of a choking pulley is twice the diameter of its shaft, which is a generous estimate, then the frictional resistance force at the outer diameter of a choking pulley is half the frictional resistance force at the shaft of a choking pulley.

Shock and Durability

The transmission ratio of an iCVT has to be changed one increment within less than one full rotation of its variator pulley. Has to be changed one increment means that the transmission diameter of the variator pulley has to be changed from a diameter that has a circumferential length that is equal to an integer number of teeth to another diameter that has a circumferential length that is equal to an integer number of teeth; such as changing the transmission diameter of the variator pulley from a diameter that has a circumferential length of 7 teeth to a diameter that has a circumferential length of 8 teeth for example. This is because if the transmission diameter of the variator pulley does not have a circumferential length that is equal to an integer number of teeth, such as a circumferential length of 7½ teeth for example, improper engagement between the teeth of the variator pulley and its chain will occur. For example, imagine having a bicycle pulley with 7½ teeth; here improper engagement between the bicycle pulley and its chain will occur when the tooth behind the ½ tooth space is about to engage with its chain, since it is positioned a distance of ½ tooth too late relative to its chain.

Regarding the previous paragraph, the chain of an iCVT forms an open loop on its variator pulley that partially covers its variator pulley such that an open section, which is not covered by the chain, exist. This is similar to a sprocket of a bicycle where there is a section of the sprocket that is covered by its chain, and a section of the sprocket that is not covered by its chain. During one complete rotation, the toothed section of the variator pulley of an iCVT passes by the open section and re-engages with the chain. Here if the transmission diameter of the variator pulley does not represent an integer number of teeth, improper re-engagement between the teeth of the variator pulley and its chain will occur. Also, the transmission diameter of the variator pulley cannot be changed while the toothed section of the variator pulley is covering the entire open section of its chain loop. Since this is similar to where a plate is glued across the open section of a chain loop, which does not allow expansion or contraction of the chain loop as required for transmission diameter change of the variator pulley. Therefore the transmission diameter of the variator pulley has to be changed one increment during an interval where the variator pulley rotates from an initial position where a portion of the toothed section of the variator pulley is positioned at the open section of the chain loop but not covering the entire open section, to the final position where the toothed section of the variator pulley passes by the open section of the chain loop and is about to re-engage with the chain. Since it takes less than one full rotation to rotate the variator pulley from its initial position to its final position mentioned in the previous sentence, the transmission diameter of the variator pulley has to be changed one increment within less than one full rotation.

In addition, as the transmission diameter is increased, the chain has to be pushed up the inclined surfaces of the pulley halves of the variator pulley, while the tension in the chain tends to pull the chain towards the opposite direction. Hence a large force, which is larger than the tension in the chain, is required to change the transmission diameter. Since the transmission ratio has to be changed within less than one full rotation of the variator pulley, a large force has to be applied on the pulley halves within a very short duration. If for example the variator pulley rotates at 3600 rpm, which is equivalent to 60 revolutions per second, then the force required to change the transmission ratio has to be applied within 1/60 seconds. This would be similar to hitting something with a hammer. Therefore, here significant shock loads are applied to the variator pulley during transmission ratio change that increases the transmission diameter. These shock loads my cause comfort problem for the driver of the vehicle using an iCVT. Also an iCVT has to be designed as to be able to resist these shock loads which would most likely increases the cost and weight of an iCVT.

Torque Transfer Ability & Reliability

The teeth of the variator pulley of an iCVT are formed by pins that extend from one pulley half to the other pulley half and slide in the grooves of the pulley halves of the variator pulley. Here torque from the chain is transferred to the pins and then from the pins to the pulley halves. Since the pins are round and the grooves are curved, line contact between the pins and the grooves are used to transfer force from the pins to the grooves. The amount of force that can be transmitted between two parts depend on the contact area of the two parts. Since the contact areas between the pins and their grooves are very small, the amount of force that can be transmitted between them, and hence also the torque capacity of an iCVT, is limited.

Another possible problem with an iCVT is that the pins of the variator pulley can fall-out when they are not engaged with their chain. And wear of the pins and the grooves of the pulley halves can cause some serious performance and reliability problems.

Diagram and video clip:

• iCVT

Cone CVTs

The Evans friction cone, a type of cone CV

A cone CVT varies the effective gear ratio using one or more conical rollers. The simplest type of cone CVT, the single-cone version, uses a wheel that moves along the slope of the cone, creating the variation between the narrow and wide diameters of the cone.

The more sophisticated twin cone mesh system is also a type of cone CVT.^[8][9]

In a CVT with oscillating cones, the torque is transmitted via friction from a variable number of cones (according to the torque to be transmitted) to a central, barrel-shaped hub. The side surface of the hub is convex with a specific radius of curvature which is smaller than the concavity radius of the cones. In this way, there will be only one (theoretical) contact point between each cone and the hub at any time.

A new CVT using this technology, the Warko, was presented in Berlin during the 6th International CTI Symposium of Innovative Automotive Transmissions, on December 3–7, 2007.

A particular characteristic of the Warko is the absence of a clutch: the engine is always connected to the wheels, and the rear drive is obtained by means of an epicyclic system in output.^[10] This system, named “power split”,^[11] allows the engine to have a "neutral gear":^[12] when the engine turns (connected to the sun gear of the epicyclic system), the variator (i.e., the planetary gears) will compensate for the engine rotation, so the outer ring gear (which provides output) remains stationary.

Diagrams:

• Warko CVT

Radial roller CVT

The working principle of this CVT is similar to that of conventional oil compression engines, but, instead of compressing oil, common steel rollers are compressed.

For more details see EP1688645A1

Prototype applications for wind farms Video 1

Inside mechanical parts Video 2

The motion transmission between rollers and rotors is assisted by an adapted traction fluid, which ensures the proper friction between the surfaces and slows down wearing thereof. Unlike other systems, the radial rollers do not show a tangential speed variation (delta) along the contact lines on the rotors. From this, a greater mechanical efficiency and working life are obtained. The main advantages of this CVT are the manufacturing inexpensiveness and the high power efficiency.

• Girotto Brevetti CVT

History

Leonardo da Vinci, in 1490, conceptualized a stepless continuously variable transmission.^[13] The first patent for a friction-based belt CVT was filed in Europe^{[clarification needed]} by Daimler and Benz in 1886, and a US Patent for a toroidal CVT was granted in 1935.^{[14] [15]}

In 1910 Zenith Motorcycles built a V2-Motorcycle with the Gradua-Gear which was a CVT. This Zenith-Gradua was so successful in hillclimb events, that it was eventually barred, so that other manufacturers had a chance to win.^{[citation needed]}

1912 the British motorcycle manufacturer Rudge-Whitworth built the Rudge Multigear. The Multi was a much improved version of Zenith’s Gradua-Gear. The Rudge Multi was so successful that CVT-gears were eventually barred at the famous Tourist Trophy race (which was the world's most important motorcycle race before World War I) from 1913 on.^{[citation needed]}

In 1922 Browne offered a motorcycle with variable-stroke ratchet drive using a face ratchet.^[16]

An early application of CVT was in the British Clyno car, introduced in 1923.

A CVT, called Variomatic, was designed and built by Hub van Doorne, co-founder of Van Doorne's Automobiel 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.^[17] Van Doorne's patents were later transferred to a company called VDT (Van Doorne Transmissie B.V.) when the passenger car division was sold to Volvo; its CVT was used in the Volvo 340.

Many snowmobiles use a rubber belt CVT. In 1974, Rokon offered a motorcycle with a rubber belt CVT.

CVTs are used in some ATVs. The first ATV equipped with CVT was Suzuki's LT80 mini in 1987.

In early 1987, Subaru launched the Justy in Tokyo with an electronically controlled continuously variable transmission (ECVT) developed by Fuji Heavy Industries, which owns Subaru. In 1989 the Justy became the first production car in the U.S. to offer CVT technology. While the Justy saw only limited success, Subaru continues to use CVT in its kei cars to this day, while also supplying it to other manufacturers.^[18]

In the summer of 1987 the Ford Fiesta and Fiat Uno became the first mainstream European cars to be equipped with steel-belted CVT (as opposed to the less robust rubber-belted DAF design). This CVT, the Ford CTX was developed by Ford, Van Doorne, and Fiat, with work on the transmission starting in 1976.^[18]

The 1992 Nissan March contained Nissan's N-CVT based on the Fuji Heavy Industries ECVT.^[18] In the late 1990s, Nissan designed its own CVT that allowed for higher torque and included a torque converter. This gearbox was used in a number of Japanese-market models. Nissan is also the only car maker to bring a 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 gearbox was not carried over when the Cedric/Gloria was replaced by the Nissan Fuga in 2004. The Nissan Murano, introduced in 2003, and the Nissan Rogue, introduced in 2007, also use CVT in their automatic transmission models. In a Nissan Press Release, July 12, 2006, Nissan announced a huge shift to CVT transmissions when they selected their XTronic CVT technology ^[19] for all automatic versions of the Nissan Versa, Cube, Sentra, Altima and Maxima vehicles in North America, making the CVT a mainstream transmission system. One major motivator for Nissan to make a switch to CVTs was as a part of their 'Green Program 2010' aimed at reducing CO2 emissions by 2010. To date Nissan has had the most success with producing their CVTs in high volume and on a wide range of vehicles. The CVT found in Nissan’s Maxima, Murano and the V6 version of Altima is considered to be the worlds first "3.5L class" belt CVT and can hold much higher torque loads than other belt CVTs.^[20]

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. The CVT is also currently employed in the Honda City ZX that is manufactured in India and Honda City Vario manufactured in Pakistan.

Toyota used a Power Split Transmission (PST) in the 1997 Prius, and all subsequent Toyota and Lexus hybrids sold internationally continue to use the system (marketed under the Hybrid Synergy Drive name). The HSD is also referred to as an Electronically-controlled Continuously-variable Transmission. The PST allows either the electric motor or the internal combustion engine (ICE) or both to propel the vehicle. In ICE-only mode, part of the engine's power is mechanically coupled to the drivetrain, with the other part going through a generator and a motor. The amount of power being channeled through the electrical path determine the effective gear ratio. Toyota also offers a non-hybrid CVT called Multidrive for models such as Avensis.

Audi has, since 2000, offered a chain-type CVT (Multitronic) as an option on some of its larger-engine models, for example the A4 3.0 L V6.

Fiat in 2000 offered a Cone-type CVT as an option on its hit model Fiat Punto (16v 80 PS ELX,Sporting) and Lancia Y (1.2 16V).

BMW used a belt-drive CVT (manufactured by ZF Friedrichshafen) 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 gearbox. The CVT could also be manually "shifted" if desired with software-simulated shift points.

MG-Rover used an identical ZF CVT transmission on its Rover 45 and MG ZS models.

GM introduced its version of CVT known as VTi in 2002. It was used in the Saturn Vue and Saturn Ion models. This transmission was quickly withdrawn in 2005 models due to high failure rates.^{[citation needed]}

Ford introduced a chain-driven CVT known as the CFT30 in their 2005 Ford Freestyle, Ford Five Hundred and Mercury Montego. The transmission was designed in cooperation with German automotive supplier ZF Friedrichshafen and was produced in Batavia, Ohio at Batavia Transmissions LLC (a subsidiary of Ford Motor Company) until March 22, 2007. The Batavia plant also produced the belt-driven CFT23 CVT which went in the Ford Focus C-MAX. Ford also sold Escort and Orion models in Europe with CVTs in the 1980s and 1990s.

Contract agreements were established in 2006 between MTD Products 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.^[21]

The 2007 Dodge Caliber and the related Jeep Compass and Jeep Patriot employ a CVT using a variable pulley system as their optional automatic transmission.^[22]

The 2008 Mitsubishi Lancer model is available with CVT transmission as the automatic transmission. DE and ES models receive a standard CVT with Drive and Low gears; the GTS model is equipped with a standard Drive and also a Sportronic mode that allows the driver to use 6 different preset gear ratios (either with the shifter or steering wheel-mounted paddle shifters).

The 2009 SEAT Exeo is available with a CVT automatic transmission (multitronic) as an option for the 2.0 TSI 200 hp (149 kW) petrol engine, with selectable 'six-speeds'.^[23]

Subaru offers CVT on the 2010 Legacy and 2010 Outback (Lineartronic).

The US Patent Office issued patent number 7,647,768 B1 for a Torque Converter Transmission that offers a continuously variable tranmission that does not use belts or friction. This transmission can be used in any application where any automatic is currently used.

See also

• Kinetic energy recovery system (in motorsport)
• List of automobiles with continuously variable transmissions
• Planetary gear
• Power band

Notes

1. ^ Harris, William. "Diagram of Pulley-based CVTs". Auto.howstuffworks.com. http://auto.howstuffworks.com/cvt2.htm. Retrieved 2011-06-17. 

References

1. ^ use of clutch with CVT
2. ^ Keith Collantine (2007-05-03). "Banned! Continuously Variable Transmission". F1fanatic.co.uk. http://www.f1fanatic.co.uk/2007/05/03/banned-continuously-variable-transmission-cvt/. Retrieved 2011-06-17. 
3. ^ Fischetti, Mark (January 2006). "No More Gears". Scientific American 294: 92. 
4. ^ "Magnomatics CVT magnetic gear". Magnomatics.com. http://www.magnomatics.com/technology/Magnetic-CVT.aspx. Retrieved 2011-06-17. 
5. ^ Jones, Franklin D., et al. (1930). Ingenious Mechanisms for Designers and Inventors. Industrial Press. ISBN 0831110848. pp. 343–345, Volume I.
6. ^ "drives". Zero-max.com. http://www.zero-max.com/products/drives/drivesmain.asp. Retrieved 19 September 2009. 
7. ^ "FEVj Infinitely Variable Transmission". Fuel-efficient-vehicles.org. 2 August 1994. http://www.fuel-efficient-vehicles.org/FEV-IVTransmission.php. Retrieved 19 September 2009. 
8. ^ "CVT Explained". http://www.youtube.com/watch?v=MhFK5gfAGpM. Retrieved 2011-08-27. 
9. ^ "CVT transmission". http://www.youtube.com/watch?v=pyYNvwKPAKA. Retrieved 2011-08-27. 
10. ^ "Toyota Prius - Power Split Device". Eahart.com. http://eahart.com/prius/psd/. Retrieved 2010-12-14. 
11. ^ "John's Stuff - Toyota Prius Education - Power Split Device". John1701a.com. 2006-01-31. http://john1701a.com/prius/prius-psd.htm. Retrieved 2010-12-14. 
12. ^ [1]^{[dead link]}
13. ^ Birch, Stuart. "Audi takes CVT from 15th century to 21st century". SAE International. http://www.sae.org/automag/techbriefs_01-00/03.htm. Retrieved 30 November 2007. 
14. ^ Harris, William. "How CVTs Work". HowStuffWorks, Inc.. http://auto.howstuffworks.com/cvt.htm. Retrieved 3 December 2007. 
15. ^ McGarry, Ben. "A Proposed Durnin IVT Transmission - A Review by Dr. Ben McGarry, Principal Engineer at e3k Think". Infinitely Variable Transmission. http://infinitelyvariabletransmission.com.au/wp-content/uploads/2010/05/dDrive-Transmission-Report.pdf. Retrieved 11 August 2010. 
16. ^ Cycle, April 1974, page 52.
17. ^ Hilton Holloway, Martin Buckley (2002). 20th Century Cars. Carlton. ISBN 1-84222-835-8. 
18. ^ ^{a b c} Poulton, M.L. (1997). Fuel Efficient Car Technology. Computational Mechanics Publications. p. 69. ISBN 1853124478. 
19. ^ "Nissan Technological Development Activities Overview: Xtronic Cvt". Nissan-global.com. http://www.nissan-global.com/EN/TECHNOLOGY/INTRODUCTION/DETAILS/CVT/. Retrieved 19 September 2009. 
20. ^ CVT. Jatco. http://www.jatco.co.jp/ENGLISH/CVT/JF010E.html 
21. ^ "Torotrak announces agreement to form Joint Venture for high-volume manufacture of IVT technology". Torotrak. http://www.torotrak.com/Investor/Information/RNS/031105.htm. Retrieved 4 December 2007. ^{[dead link]}
22. ^ "Dodge Caliber, Jeep Compass, & Jeep Patriot". The Ecology Center. Archived from the original on 10 March 2008. http://web.archive.org/web/20080310012253/http://www.greenmachinestour.org/actcaliber.shtml. Retrieved 4 December 2007. 
23. ^ "SEAT Exeo 2.0 TSI technical information". http://www.seat.com/static/su/com/SEAT/site/2009/exeo/Techtables/2_0_TSI_147_Multitronic.html. Retrieved 14 September 2009. 

External links

• Nissan CVT
• Nissan Global CVT
• The Simplest Automatic Transfer Box