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Continuously variable transmission
A continuously variable transmission (CVT) is an automated transmission that can change through a continuous range of gear ratios, typically resulting in better fuel economy in gasoline applications. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant angular velocity while the vehicle moves at varying speeds. Thus, CVT has a simpler structure, longer internal component lifespan, and greater durability. Compared to traditional automatic transmissions, it offers lower fuel consumption and is more environmentally friendly.
CVTs are used in cars, tractors, side-by-sides, motor scooters, snowmobiles, bicycles, and earthmoving equipment. The most common type of CVT uses two pulleys connected by a belt or chain; however, several other designs have also been used at times.
The most common type of CVT uses a V-belt which runs between two variable-diameter pulleys. The pulleys consist of two cone-shaped halves that move together and apart. The V-belt runs between these two halves, so the effective diameter of the pulley is dependent on the distance between the two halves of the pulley. The V-shaped cross-section of the belt causes it to ride higher on one pulley and lower on the other; therefore, the gear ratio is adjusted by moving the two sheaves of one pulley closer together and the two sheaves of the other pulley farther apart.
As the distance between the pulleys and the length of the belt does not change, both pulleys must be adjusted (one bigger, the other smaller) simultaneously to maintain the proper amount of tension on the belt. Simple CVTs combining a centrifugal drive pulley with a spring-loaded driven pulley often use belt tension to effect the conforming adjustments in the driven pulley. The V-belt needs to be very stiff in the pulley's axial direction to make only short radial movements while sliding in and out of the pulleys.
The radial thickness of the belt is a compromise between the maximum gear ratio and torque. Steel-reinforced V-belts are sufficient for low-mass, low-torque applications like utility vehicles and snowmobiles, but higher-mass and -torque applications such as automobiles require a chain. Each element of the chain must have conical sides that fit the pulley when the belt is running on the outermost radius. As the chain moves into the pulleys the contact area gets smaller. As the contact area is proportional to the number of elements, chain belts require many very small elements.
A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by enabling the engine to run at its most efficient RPM regardless of the vehicle's speed. When power is more important than economy, the ratio of the CVT can be changed to allow the engine to turn at the RPM at which it produces the greatest power.
In a chain-based CVT, numerous chain elements are arranged along multiple steel bands layered over one another, each of which is thin enough to easily bend. When part of the belt is wrapped around a pulley, the sides of the elements form a conical surface. In the stack of bands, each band corresponds to a slightly different drive ratio, and thus the bands slide over each other and need sufficient lubrication. An additional film of lubricant is applied to the pulleys. The film needs to be thick enough to prevent direct contact between the pulley and the chain, but thin enough to not waste power as each chain element enters it.[citation needed]
Some CVTs transfer power to the output pulley via tension in the belt (a "pulling" force), while others use compression of the chain elements (where the input pulley "pushes" the belt, which in turn pushes the output pulley).
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Continuously variable transmission AI simulator
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Continuously variable transmission
A continuously variable transmission (CVT) is an automated transmission that can change through a continuous range of gear ratios, typically resulting in better fuel economy in gasoline applications. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant angular velocity while the vehicle moves at varying speeds. Thus, CVT has a simpler structure, longer internal component lifespan, and greater durability. Compared to traditional automatic transmissions, it offers lower fuel consumption and is more environmentally friendly.
CVTs are used in cars, tractors, side-by-sides, motor scooters, snowmobiles, bicycles, and earthmoving equipment. The most common type of CVT uses two pulleys connected by a belt or chain; however, several other designs have also been used at times.
The most common type of CVT uses a V-belt which runs between two variable-diameter pulleys. The pulleys consist of two cone-shaped halves that move together and apart. The V-belt runs between these two halves, so the effective diameter of the pulley is dependent on the distance between the two halves of the pulley. The V-shaped cross-section of the belt causes it to ride higher on one pulley and lower on the other; therefore, the gear ratio is adjusted by moving the two sheaves of one pulley closer together and the two sheaves of the other pulley farther apart.
As the distance between the pulleys and the length of the belt does not change, both pulleys must be adjusted (one bigger, the other smaller) simultaneously to maintain the proper amount of tension on the belt. Simple CVTs combining a centrifugal drive pulley with a spring-loaded driven pulley often use belt tension to effect the conforming adjustments in the driven pulley. The V-belt needs to be very stiff in the pulley's axial direction to make only short radial movements while sliding in and out of the pulleys.
The radial thickness of the belt is a compromise between the maximum gear ratio and torque. Steel-reinforced V-belts are sufficient for low-mass, low-torque applications like utility vehicles and snowmobiles, but higher-mass and -torque applications such as automobiles require a chain. Each element of the chain must have conical sides that fit the pulley when the belt is running on the outermost radius. As the chain moves into the pulleys the contact area gets smaller. As the contact area is proportional to the number of elements, chain belts require many very small elements.
A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by enabling the engine to run at its most efficient RPM regardless of the vehicle's speed. When power is more important than economy, the ratio of the CVT can be changed to allow the engine to turn at the RPM at which it produces the greatest power.
In a chain-based CVT, numerous chain elements are arranged along multiple steel bands layered over one another, each of which is thin enough to easily bend. When part of the belt is wrapped around a pulley, the sides of the elements form a conical surface. In the stack of bands, each band corresponds to a slightly different drive ratio, and thus the bands slide over each other and need sufficient lubrication. An additional film of lubricant is applied to the pulleys. The film needs to be thick enough to prevent direct contact between the pulley and the chain, but thin enough to not waste power as each chain element enters it.[citation needed]
Some CVTs transfer power to the output pulley via tension in the belt (a "pulling" force), while others use compression of the chain elements (where the input pulley "pushes" the belt, which in turn pushes the output pulley).