CVT-Continuously variable transmission
#1

A continuously variable transmission (CVT) is a transmission that can change continuously with an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a set number of gear ratios. The flexibility of a CVT allows the shaft to maintain a constant angular velocity in the range of output speeds. This can provide better fuel economy than other transmissions, allowing the engine to its most efficient revolutions per minute (RPM) for a range of vehicle speeds. Alternatively, you can use to optimize the performance of a vehicle, allowing the engine to the speed at which peak power occurs. This is usually higher than the RPM that carries a maximum of efficiency. Finally, a CVT is not strictly required the presence of a clutch, which allows dismissal of it.

In some vehicles themselves (ie motorcycles), is a centrifugal clutch, however added, but only to provide a "neutral" position on a bike (useful when idle).


2 Types
2.1 Variable-diameter pulley (VDP) or Reeves drive
2.2 Toroidal or roller-based CVT (Extroid CVT )
2.3 Magnetic CVT
2.4 Infinitely Variable Transmission (IVT)
2.5 Ratcheting CVT
2.6 Hydrostatic CVTs
2.7 Variable toothed wheel transmission
2.8 Naudic Incremental CVT (iCVT)
2.8.1 High Frictional Losses
2.8.2 Shock and Durability
2.8.3 Torque Transfer Ability & Reliability
2.9 Single Tooth Cone CVT
2.10 Cone CVTs
2.11 Radial roller CVT





The principle of the drive


Many small tractors for home and garden use have simple CVTS rubber band. For example, use John Deere Gator line of small utility vehicles with a belt with a conical pulley system. They can provide high power and can reach speeds of 10-15 km / h (16 to 24 km / h), all without the need for a clutch and gearshift. Nearly all the snowmobiles, old and new, and use CVTS scooters, rubber bands typical / variable pulley black.

Some of the harvesters have CVTS. CVT allows the combination of speed, engine speed to adjust independently. It allows the driver to slow down or accelerate the need to adapt to variations in the thickness of the harvest.

Continues and has been used in aircraft systems generating electricity since 1950, and the Automobile Club of Sports of America (SCCA) Formula 500 cars since the early 1970s. CVTS were banned from Formula 1 in 1994 because of fears that the better funded teams would dominate, if they have succeeded in creating a viable F1 CVT. [2] Recently, CVT systems are designed for go-kart and has proven to increase performance and engine life. The range of Tomcar off-road vehicles also uses the CVT.

Some drills and milling machines contain a CVT pulley base where the output shaft has a pair of hand-adjustable conical pulley halves, through a wide belt loop of the motor. The dial on the engine is usually fixed in diameter, or may have a number of steps given diameter to allow a variety of speed ranges. A steering wheel on the drill press, marked with a scale that matches the desired engine speed, is mounted on a reducing system for the operator to precisely control the width of the gap between the two halves of pulley. The width of the slot then adjusts the speed between the motor pulley shaft output pulley fixed and variable, changing from Chuck. A pulley is implemented in the drive belt to absorb or release slack in the belt when the speed is changed. In most cases, the speed must be changed with the engine running.
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#2
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to get information about the topic"CVT-Continuously variable transmission" refer the page link bellow
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CVT-Continuously variable transmission

[attachment=18005]
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 (ie motorcycles), a centrifugal clutch is nevertheless added[1] , however this is only to provide a "neutral" stance on a motorcycle (useful when idling).




USES ׃
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.



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.



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.


Magnetic CVT
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.
4) 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.

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