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An automatic transmission that can switch smoothly between a continuous range of useful gear ratios is referred to as a continuously variable transmission (CVT), also known as a shiftless transmission. Single-speed transmission, stepless transmission, pulley transmission, or, on account of cruisers, a "turn and-go" transmission.
Other mechanical transmissions, in comparison, only provide a limited number of gear ratios. With the right control, a CVT's flexibility may enable the input shaft to keep its angular velocity constant even when the output speed changes.
While less efficient than a manual transmission, a belt-driven design achieves an average efficiency of around 88%, which can be justified by lower production costs and the ability to run the engine at its most effective speed over a range of output speeds.
Transmission types
Manual
Sequential manual
Non-synchronous
Preselector
Automatic
Manumatic
Semi-automatic
Electrohydraulic
Dual clutch
Continuously variable
Bicycle gearing
Derailleur gears
Hub gears
When power is more important than economy, the CVT ratio can be adjusted to allow the engine to turn at the RPM that produces the most power. This is usually higher than the RPM at which maximum efficiency is achieved. A belt-driven CVT also provides ease of use and mechanical simplicity in low-mass, low-torque applications (such as motor scooters).
A CVT does not necessitate the presence of a clutch. Nonetheless, a centrifugal clutch is added to some vehicles (e.g., motorcycles) to facilitate a "neutral" stance, which is useful when idling or manually reversing into a parking space.
USES
Vehicles with motors
CVTs with simple rubber belts (non-stretching fixed circumference manufactured using various highly durable and flexible materials) are commonly used in small, motorized vehicles, where their mechanical simplicity and ease of use outweigh their relative inefficiency. CVTs, typically of the rubber belt or variable pulley variety, are used in nearly all snowmobiles, utility vehicles, golf carts, and motor scooters.
CVTs, along with several other electronic systems and driver aids, were banned from Formula One in 1994 due to concerns about rising R&D costs and maintaining a certain level of driver involvement with the vehicles.
CVT systems for go-karts have recently[when?] been developed and have proven to improve performance and engine life expectancy. The CVT system is also used in the Tom car off-road vehicle line.
A few vehicles that offer CVT are the Chrysler Pacifica mixture, the Passage C-MAX half and half, the Mitsubishi Lancer, the Evade Type, the Toyota Corolla, the Scion level of intelligence, the Honda Understanding, Fit, CR-Z half and half, CR-V, Capa, Honda Urban, Honda Accord, the Nissan Tiida/Versa (SL, SV, and Note S In addition to or higher models), Block, Juke, Sentra, Altima, Maxima, 2013 1.2 Note, Rebel, X-Trail, Murano, Pathfinder, Radiant and the non-Mexican Micra, the Jeep Loyalist and Compass, the Suzuki SX4 S-Cross, and the Subaru Forester, Impreza, Heritage, Outback and Crosstrek, Suzuki Kizashi, Toyota Allion 2009 onwards, Toyota Premio 2009 onwards, Toyota Avalon, Toyota Imprint X, and so on.
CVTs should be separated from power-sharing transmissions (PSTs), which are found in contemporary hybrid vehicles such as the Toyota Prius, Highlander, and Camry, as well as the Nissan Altima and Ford Escape Hybrid SUVs. PST technology employs two prime mover inputs and alters the ratio of their contributions to output speed and power, whereas CVT technology uses only one prime mover input and produces variable output speeds and torque. These broadcasts are diametrically opposed.
Variable belt drives were utilized in farm equipment, including harvester combines, as early as the 1950s. Many small tractors and self-propelled lawn mowers for the home and garden employ a simple rubber belt CVT as well. Hydrostatic devices are more popular on bigger machines; sliding belts are used on walk-behind self-propelled mowers.
When the oscillating movement is timed with that of the pistons, ratcheting CVTs that convert rotary motion to oscillating motion and back to rotary motion utilizing roller clutches are well fitted to reciprocating engines. This method has a promising future because ratcheting CVTs are also IVT (they provide the clutch function) and have a great energy efficiency. They might assist manufacturers in meeting future pollution limits while also boosting the performance of reciprocating engines.
Electric engines are being downsized.
Instead of being dimensioned based on the maximum torque (e.g., that necessary for starting or in the event of sudden mechanical overload), motors utilizing this type of CVT may be dimensioned by matching the maximum power with the maximum intended speed (that of a vehicle by example). Such a CVT is only utilized during starting or in the event of mechanical overload, and it may be unplugged the majority of the time, with the engine sending torque straight to the output. To make these adjustments automated, new concepts such as changing the gearbox ratio to the resistive torque and centrifugal clutches may be implemented.
For bicycles
A ratchet CVT has been proposed. The crankset swings a lever, which produces the reciprocating action of a double rack, which turns the wheel as it advances backward and toward the wheel. Since 2007, the NuVinci Continuously Variable Transmission has been offered.
Transfers of medium and high power
In small to medium-sized agricultural and earthmoving equipment, hydrostatic CVTs are widespread. Because these machines' engines are often run at constant power levels to supply hydraulic power or to power machinery, mechanical efficiency losses are countered by improved operational efficiency, such as shorter forward-reverse shuttle times in earthmoving activities. The transmission output is changed to regulate both the speed and direction of motion.
This is especially useful in equipment designed to pivot or skid steer using differential power, as the required differential steering action can easily be supplied by independent CVTs, allowing steering to be accomplished without braking losses or tractive effort loss and allowing the machine to pivot in place. A CVT allows the forward speed of a tractor or combine harvester to be controlled independently of engine speed during mowing or harvesting activities. This enables the operator to slow or speed as needed to accommodate differences in crop thickness.
Systems for producing electricity
Since the 1950s, CVTs have been utilized in aircraft electrical power generation systems, and since the early 1970s, in Sports Car Club of America (SCCA) Formula 500 race vehicles.
Some drill presses and milling machines include a pulley based CVT system with a pair of manually adjustable conical pulley halves on the output shaft through which a broad drive belt from the motor loops. The pulley on the motor, on the other hand, is generally fixed in diameter or has a number of given-diameter steps to allow for a variety of speed ranges.
On the drill press, a handwheel marked with a scale matching to the chosen machine speed is connected to a reduction gearing system, allowing the operator to accurately manage the spacing between the pulley halves. This gap width so modifies the speed ratio between the fixed pulley of the motor and the variable pulley of the output shaft, adjusting the speed of the chuck. In a belt transmission, a tensioner pulley is used to take up or release slack in the belt as the speed is changed. Most of the time, the speed must be altered while the motor is operating.
To improve rotational speed, doubly fed induction generators are typically paired with multi-stage gearboxes. These gearboxes may be replaced by completely CVTs in the future, but only fully geared ones since they provide adequate mechanical efficiency.
A CVT and flywheel can be installed between an energy source (such as a wind turbine) and the generator. When the energy supply is sufficient, the generator is directly connected to the CVT, which regulates its rotational speed. When it falls below a certain level, the generator is turned off and the energy held in the flywheel is released. Only when the flywheel's speed is sufficient is kinetic energy transformed into electricity, sporadically but always at the ideal pace.
In 2016, FCA US LLC unveiled the 2017 Chrysler Pacifica Hybrid minivan, which has a CVT rather than the 9-speed automatic seen in gasoline vehicles.
Toyota developed an entirely new CVT for the 2019 Toyota Corolla Hatchback, complete with a "launch gear," or a physical first gear from a conventional automatic transmission beside the CVT pulley. From 0 to 25 mph, the gearbox would remain in this launch gear to help with acceleration from a stop and to increase CVT durability. The gearbox would shift to the CVT pulley after 25 mph.
Marketing names
Lineartronic: Subaru
Xtronic Jatco: Nissan, Renault
K CVT, CVTi, eCVT: Toyota, Honda
INVECS-III: Mitsubishi
Multitronic: Volkswagen, Audi
Autotronic: Mercedes
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