Continuously variable transmission

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Continuously variable transmission

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The variable transmission ( CVT ) is a transmission in the ratio of the rotational speeds of two as the input shaft and output of a vehicle or other machine, can be continuously within a given providing an infinite number of ratios.

The continuously variable should not be confused with the split transmission (PST), as in the Toyota Prius and other vehicles that use two or more with one output, despite similarities in their function.

A CVT not be automatic, nor include zero or output. Such features may be to CVTs in certain specific

Other mechanical transmissions allow a few different discrete ratios to be selected, but the continuously transmission essentially has an infinite of ratios available within a range, so it enables the relationship the speed of a vehicle, engine, and the speed of the wheels to be selected a continuous range. This can better fuel economy other transmissions by enabling the to run at its most efficient speeds a narrow range.

CVTs been refined over the and are much improved from origins.


Infinitely Transmission (IVT)

A specific of CVT is the infinitely variable transmission ( IVT ), has an infinite range of input/output in addition to its infinite number of ratios; this qualification for the IVT that its range of ratios a zero output/input ratio can be continuously approached from a higher ratio. A zero implies an infinite input, can be continuously approached from a finite input value an IVT. Low gears are a reference to low of output/input which have input/output ratios that are to the extreme with IVTs, in a neutral, or non-driving low gear

Most continuously variable are not infinitely variable.

Most (if not IVTs result from the of a CVT with an epicyclic gear (which is also known as a gear system) termed split device that the subtraction of one speed from speed within the set of input and gear rotations. This only needs to result in a range of values that a zero output; the maximum ratio can be arbitrarily chosen infinite practical possibilities selection of extraneous input or gear, pulley or sprocket without affecting the zero or the continuity of the whole system. the IVT is distinguished as being infinite in its of high gear to low gear its range; high gear is times higher than low

The IVT is always engaged, even its zero output adjustment.

The Infinitely Variable Transmission not imply reverse direction, automatic operation, or any other except ratio selectability a continuous range of input/output from a defined minimum to an infinite maximum. This continuous range from a output/input to zero output/input

Additionally, IVT offers better when compared to other as most of the power flows planetary gear and not the controlling and torque transmission capability is There’s also possibility to power splits for further in efficiency, torque transmission and expanded gear ratios

Ratcheting CVT

The Ratcheting CVT is a transmission relies on static friction and is on a set of elements that successively engaged and then disengaged the driving system and the driven often using oscillating or motion in conjunction with clutches or ratchets that and sum only forward motion. The ratio is adjusted by changing geometry within the oscillating so that the summed maximum speed is adjusted, even the average linkage speed constant. Power is transferred input to output only the clutch or ratchet is engaged, and when it is locked into a friction mode where the driven rotating surfaces rotate together without

These CVTs can transfer torque because their friction actually increases to torque throughput, so slippage is in properly designed systems. is generally high because of the dynamic friction is caused by slight transitional clutch changes. The drawback to ratcheting is vibration caused by the successive in speed required to accelerate the which must supplant the operating decelerating, power element.

An Infinitely Variable (IVT) that is based on a CVT and subtraction of one speed from will greatly amplify the as the IVT output/input ratio approaches

Ratcheting CVTs are distinguished Variable Diameter Pulleys and Roller-based CVTs by being friction-based devices, as opposed to dynamic friction-based devices waste significant energy slippage of twisting surfaces.

pulley (VDP) or Reeves

In this system, there are two pulleys that are split to their axes of rotation, a V-belt running between The gear ratio is changed by the two sections of one pulley closer and the two sections of the other pulley apart. Due to the V-shaped cross of the belt, this causes the to ride higher on one pulley and on the other. Doing this the effective diameters of the pulleys, changes the overall gear

The distance between the pulleys not change, and neither does the of the belt, so changing the gear means both pulleys be adjusted (one bigger, the smaller) simultaneously to maintain the amount of tension on the belt.


(marketed as the Traction CVT, CVT, Nuvinci CVP, or

Consider two almost-conical parts, to point, with the sides such that the two parts fill the central hole of a One part is the input, and the other is the output (they do not quite Power is transferred from one to the other by one or more rollers. the roller’s axis is perpendicular to the of the almost-conical parts, it contacts the parts at same-diameter locations and gives a 1:1 gear ratio.

The can be moved along the axis of the parts, changing angle as to maintain contact. This cause the roller to contact the parts at varying and distinct giving a gear ratio of other than 1:1. may be partial or full toroidal.

toroidal systems are the most design while partial may still require a torque (e.g. Jatco Extroid), and lose efficiency.


Hydrostatic transmissions use a variable pump and a hydraulic motor. All is transmitted by hydraulic fluid. types can generally transmit torque, but can be sensitive to contamination. designs are also very However, they have the that the hydraulic motor can be directly to the wheel hub, a more flexible suspension and eliminating efficiency losses friction in the drive shaft and components.

This type of is relatively easy to use because all and reverse speeds can be accessed a single lever.

This of transmission has been effectively to a variety of inexpensive and expensive of ridden lawn mowers and tractors. Many versions of lawn mowers and garden propelled by a hydrostatic transmission are of pulling a reverse tine and even a single bladed

One class of riding lawn that has recently gained in with consumers is zero radius mowers. These have traditionally been with wheel hub mounted motors driven by continuously pumps, but this design is expensive. A company called a joint venture between and Agri-Fab, Inc. of Sullivan, created the first cost-effective hydrostatic transaxle suitable for consumer zero turning mowers. An integrated hydrostatic (IHT) uses a single for both hydraulic elements and elements.

As of May 9, 2007, Hydro-Gear the only company producing hydrostatic transaxles for consumer turning radius mowers in America.

Some heavy equipment may be propelled by a hydrostatic transmission; agricultural machinery including and combines, but not anything that the ground because the transmission transmit enough torque.


The Hydristor torque converter is a IVT in that the front unit to the engine can displace from to 27 cubic inches per revolution and zero to -10 cubic inches per reverse. The rear unit is of zero to 75 cubic inches per The common kidney port between the two sections communicates the fluid under pressure and return in a serpentine-torodial flow between the two Hydristor internal

The IVT ratio is determined by the ratio of displacement to output displacement. the theoretical range of Hydristor IVT is 1/infinity to +-infinity/1 but real-world are constrained by physics.

Simkins’ CVT

This transmission is an example of a CVT, prototyped as a bicycle protected under U.S. #5516132. The input is the crank a round hub integrated with it, and an of twelve arms that are mounted to pins in the hub circle. arm has a pinion gear mounted on a one way that allows only rotation of the pinion relative to the

All of these pinions are engaged a large ring gear is integrated with the chainwheel as the and the ring gear/chainwheel assembly is to a mechanism that enables it to be from a position of concentricity the crank hub to various amounts of with the crank hub. of this eccentricity variably the output/input ratio from 1:1 to as the ring gear/sprocket assembly is from a position concentric the crank hub to an eccentric position.

The control mechanism is connected to a that pushes the transmission its eccentric high gear The largest spread of the arms is of the gear ratio because the arms are the only arms pinions (and one-way are locked and driving the ring assembly. Strong pedaling causes this mechanism to against the spring, moving the gear/chainwheel assembly toward a lower gear position. the pedaling torque relaxes to levels, the transmission self-adjusts higher gears, accompanied by an in transmission vibration.

This behaves according to the definition of a CVT.

Variable toothed CVT

Variable toothed wheel relies on a toothed wheel engaged with a chain the toothed wheel has the ability to add or a tooth at a time in order to its ratio with relation to the it is driving. The toothed wheel can on many configurations as is listed in the patent specifications and include chains, drive bars and teeth. This type of CVT is not a CVT that can alter its ratio in increments but rather approaches CVT by having a large number of typical 49, as is described in the VW owned patent application DE10010741A1. The advantage of this type of CVT is it is a positive mechanical drive and does not have the frictional and limitations of the Roller based or VDP CVT s. The in this type of CVT is to add or subtract a from the toothed wheel in a precise and controlled way in order to synchronized engagement with the

This type of transmission has the to change ratios under because of the large number of resulting in the order of 3% ratio differences between ratios, a clutch or torque converter is necessary for pull away. of this type of CVT is in commercial use because of above mentioned challenges. Other examples of type of CVT can be found in the following specifications: US5406863, WO9404411, and WO2005036028.

Diagram and video

Girotto iCVT

The Girotto is a mechanical transmission with a transmission ratio between an rotor and an output rotor together by means of a coupling for transmission of the rotary movement, in that it comprises between the rotor and the output rotor one or free wheels arranged in with the coupling free and able to transmit to one of the two rotors the movement supplied by the coupling wheel. Rotor is understood as clearly any rotating mechanical able to transmit, receive or rotary movement. Publication EP1688645

Advantages and drawbacks

Compared to automatic transmissions.

CVTs can compensate for changing vehicle allowing the engine speed to at its level of peak efficiency. might also avoid converter losses. This both fuel economy and emission s. However, some (e.g.

Jatco Extroid) employ a torque converter. efficiency advantages as high as 20% four-speed automatics can be obtained.

have much smoother This can give a perception of low because many drivers a jerk when they to move the vehicle. The expected of a non-CVT can be emulated by CVT control though, eliminating this problem.

Since the CVT keeps the turning at constant RPMs a wide range of vehicle pressing on the accelerator pedal make the car move faster but change the sound coming the engine as much as a conventional transmission gear-shift. This some drivers and, leads to a mistaken impression of a of power.

Most CVTs are to build and repair.

CVT torque capability is limited by the strength of belt or chain, and by their to withstand friction wear torque source and transmission for friction-driven CVTs. CVTs in prior to 2005 are predominantly or chain driven and therefore limited to low power ed car s and other duty applications. More IVT units using advanced however, have been to support any amount of torque in vehicles, including that for buses, heavy trucks, and moving equipment.


da Vinci. in 1490, conceptualized a continuously variable transmission. 1 The patent for a toroidal CVT was filed in 2

From the 1950s. CVTs been applied to aircraft power generating systems.

A called Variomatic. was designed and by the Dutchman Hub van Doorne, co-founder of Van Automobiel Fabriek (DAF), in the 1950s, specifically to produce an transmission for a small, affordable The first DAF car using van Doorne’s the DAF 600. [1] was produced in 1958. Van patents were later to a company called VDT (Van Transmissie B.V.) when the car division was sold to Volvo ; CVT was used in Volvo 340.

The Fiesta and Fiat Uno were the mainstream European cars to be with steel-belted CVT (as opposed to the robust rubber-belted DAF design), in

In the 1980s and 1990s, the Subaru was offered with a CVT. the Justy saw only limited Subaru continues to use CVT in its keicars to day, while also it to other manufacturers.

Nissan introduced CVT in the 1992 Nissan with a unit sourced Subaru. In the late 1990s, designed its own CVT that allowed for torque, and includes a torque This gearbox was used in a of Japanese market models. is also the only car maker to roller-based CVT to the market in recent

Their toroidal CVT, the Extroid, was available in the Japanese Y34 Nissan Gloria and V35 Skyline However, the gearbox was not carried when the Cedric/Gloria was replaced by the Fuga in 2004.

After pulley-based CVT for years, Honda introduced their own version on the Honda Civic VTi. Honda Multi Matic, CVT gearbox accepted higher than traditional pulley and also includes a torque for creep action. The CVT is also employed in the Honda City ZX is manufactured in India.

Toyota introduced the E-CVT in the Prius. and all subsequent Toyota and hybrids sold internationally to use the system (marketed under the Synergy Drive name). sold as a CVT it is in fact not such a as the gear ratios are fixed and the is actually a Power Split (PST), allowing either the motor or the ICE (internal combustion ) or both to propel the vehicle. The of the complete system (under control) is similar in feel to a CVT in the ICE speed is relatively low and constant low power or high and constant high power.

BMW used a CVT as an option for the low and middle range in 2001, forsaking it only on the version of the car where the increased levels demanded a conventional gearbox. The CVT could also be shifted if desired with simulated shift points.

Motors designed a CVT for use in small which was first offered in After just three however, this transmission be phased out in favor of conventional automatic transmissions.

Audi since 2000, offered a -type CVT as an option on some of its models, for example the A4 3.0 L V6.

Ford a chain-driven CVT known as the CFT30 a maximum torque capacity of 221 (300 Nm) in their 2005 Freestyle. Ford Five and Mercury Montego. The transmission was in cooperation with German supplier ZF Friedrichshafen and was produced in Ohio at Batavia Transmissions LLC (a of Ford Motor Company) 3/22/07.

The Batavia plant produced the belt-driven CFT23 CVT went in the Ford Focus and Escape Hybrid and still the 4-speed automatic (CD4E) for the Escape and Mazda Tribute. also sold Escort version) and Orion models in with CVTs in the 1980s and

ZF Friedrichshafen supplied its belt VT-1 CVT unit to BMW for use in some of the European Mini Cooper.

The Dodge Caliber 3 and the related Compass employ a CVT using a pulley system as their automatic transmission.

Contract were established in 2006 MTD and Torotrak for the first full system to be manufactured for outdoor equipment such as jet skis, and ride-on mowers.


small tractors for home and use have simple hydrostatic or belt CVTs. For example, the Deere Gator line of utility vehicles (used by parks, stadiums, colleges, and places where miscellaneous must be displaced by laborers) use a with a conical pulley They can deliver a lot of power but can build up speed to 10-15 all without need for a clutch or

Most snowmobiles use CVTs. new motorscooters today are equipped CVT. Virtually all snowmobile and scooter CVTs are rubber pulley CVTs.

Some harvesters have CVTs. The of a combine is adjusted to operate at a particular engine speed. The CVT the forward speed of the combine to be independently of the engine speed.

allows the operator to slow and speed up as needed to accommodate in thickness of the crop.

CVTs been used in SCCA 500 race cars since the 1970s.

More recently, CVT have been developed for and have proved to increase and engine life expectancy. The range of off-road vehicles utilizes the CVT system.

Some drill presses contain a CVT where the output shaft the chuck is connected to) has a pair of conical pulley halves to a wide drive belt the motor loops through. The on the motor, however, is usually in diameter, or may have a series of steps to allow a selection of ranges. A handwheel on the drill marked with a scale to the desired machine speed, is to a reduction gearing system for the to precisely control the width of the gap the pulley halves. This gap thus adjusts the gearing between the motor’s fixed and the output shaft’s variable changing speed of the chuck; a pulley is implemented in the belt to take up or release the slack in the as the speed is altered.

However, the drill press’ almost always cannot be without the motor running.

New equipped with CVT

Old automobiles with CVT


1. ^ Hilton Martin Buckley (2002). Century Cars . Carlton. 1-84222-835-8.

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of input/output ratios in addition to its number of possible ratios; qualification for the IVT implies that its of ratios includes a zero ratio that can be continuously from a defined ‘higher’

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A sequential manual (or sequential manual gearbox ) is a of manual transmission used on and high-performance cars or auto where gears are selected in and random access to specific is not possible.

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automatic transmission abbreviated as AT) is an automobile gearbox can change gear ratios as the vehicle moves, thus the driver from having to gears manually (similar but devices are also used for locomotives).

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Tiptronic is a type of automatic transmission developed by and used in its vehicles and those of its A Tiptronic transmission can operate as the common type of automatic but it also allows the driver to the automatic mode by

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A semi-automatic (also known as clutchless transmission . dual-clutch transmission . manual transmission . e-gear . or shift gearbox

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A twin-clutch or dual clutch transmission is a semi-automatic transmission with clutches for odd and even gears. The clutch drives the odd numbered and reverse, while the inner drives the even numbered

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Saxomat was a type of automatic available as an option on Fiat Saab 93, Volkswagen Beetle, Goliath, DKW, BMW, NSU, Glas, Trabant and Opel sold it as Olymat; and Wartburg named the system

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A non-synchronous transmission is a form of based on gears that do not use mechanisms. They are found in various types of agricultural, and military vehicles.

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Variomatic is the fully automatic transmission of the car manufacturer DAF, using a belt and two pulleys. It was the first variable transmission (CVT) (as to shifting between separate

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In 2000 Audi launched a new transmission called Multitronic . on the principles of continuously variable (CVT) popularised by DAF, offers a stepless automatic in which the ratio between the shaft and output shaft can be

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on a bicycle is the selection of appropriate ratios for optimum efficiency or Different gears and ranges of are appropriate for different people and of cycling. Multi-speed bicycles gear selection to suit the e.g.

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Derailleur gears are a variable transmission system commonly on bicycles, consisting of a chain, sprockets and a mechanism to move the from one sprocket to another.

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Hub or internal-gear hubs are a type of system used on bicycles. Hub are used mostly on utility and various types of small bicycle, such as folding

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Toyota Hybrid System

305 (225 ft·lbf) @ 0 rpm

For other of Hybrid Transportation, see .

A hybrid (HV) is a vehicle that two or more distinct power to propel the vehicle such as:

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The ratio is the relationship between the of teeth on two gears that are or two sprockets connected with a roller chain, or the circumferences of two connected with a drive

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Fuel economy in automobiles is the of fuel required to move the over a given distance. the fuel efficiency of petroleum has improved markedly in recent this does not necessarily into fuel economy

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An is something that produces an effect from a given The origin of engineering however, from the design, building and of (military engines) because such devices came to be in battles there were few mechanical devices used.

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In a continuous function is a function for intuitively, small changes in the result in small changes in the Otherwise, a function is said to be .

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Epicyclic gearing or planetary is a gear system that of one or more outer gears, or gears, rotating about a or sun gear.

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In geometry, a torus tori ) is a surface of revolution by revolving a circle in three space about an axis with the circle, which not touch the circle. Examples of include the surfaces of doughnuts and tubes.

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A variable displacement is a device that converts energy to hydraulic (fluid) Some of these devices can be reversible, meaning that can act as a hydraulic motor and generate energy from fluid

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Hydraulic fluids are a large of mineral oil, water or fluids used as the medium in systems. These fluids are in machinery and equipment ranging brakes, power steering, and to backhoes, excavators, garbage and industrial

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differential is a device, consisting of gears, that each of the driving wheels to at different speeds, while equal torque to each of


A vehicle’s wheels at different speeds, especially turning corners.

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A lawn or lawnmower is a piece of equipment has one or more revolving blades to cut or other plants of a lawn at an length.

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