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.
CVT 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. It can also be used to build kinetic energy recovery system.
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 (e.g. motorcycles), a centrifugal clutch is nevertheless added, however this is only to provide a "neutral" stance on a motorcycle (useful when idling, or manually reversing into a parking space).
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. 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, Hinda Fit, and Honda CR-Z hybrids, the Nissan Tiida/Versa (only the SL model), Nissan Cube, Juke, Sentra, Altima, Maxima, Rogue, Murano, Micra, Honda Capa, Honda Civic HX, Jeep Patriot and Compass, and Subaru Impreza, Legacy and Outback offer CVT.
http://en.wikipedia.org/wiki/Continuously_variable_transmission
CVT 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. It can also be used to build kinetic energy recovery system.
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 (e.g. motorcycles), a centrifugal clutch is nevertheless added, however this is only to provide a "neutral" stance on a motorcycle (useful when idling, or manually reversing into a parking space).
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. 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, Hinda Fit, and Honda CR-Z hybrids, the Nissan Tiida/Versa (only the SL model), Nissan Cube, Juke, Sentra, Altima, Maxima, Rogue, Murano, Micra, Honda Capa, Honda Civic HX, Jeep Patriot and Compass, and Subaru Impreza, Legacy and Outback offer CVT.
http://en.wikipedia.org/wiki/Continuously_variable_transmission
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