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Continuously variable transmission
Continuously variable transmission
Continuously variable transmission
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Pulley-based CVT
Automotive transmissions
Manual
Automatic / Semi-automatic

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.[1] 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.[2][3]

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.

Types

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Pulley-based

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Belt-driven CVT for a motor scooter
A PIV chain drive
CVT in a Claas Mercator combine harvester. The pulley's effective diameter is changed by pushing the two conical discs either towards or away from each other.

The most common type of CVT uses a V-belt which runs between two variable-diameter pulleys.[4] 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.[5]

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.[5] 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,[6] 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.[7][8] 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).[9][10][11]

Positively Infinitely Variable (PIV) chain drives are distinct in that the chain positively interlocks with the conical pulleys. This is achieved by having a stack of many small rectangular plates in each chain link that can slide independently from side-to-side. The plates may be quite thin, around a millimeter thick. The conical pulleys have radial grooves. A groove on one side of the pulley is met with a ridge on the other side and so the sliding plates are pushed back and forth to conform to the pattern, effectively forming teeth of the correct pitch when squeezed between the pulleys. Due to the interlocking surfaces, this type of drive can transmit significant torque and so has been widely used in industrial applications. However, the maximum speed is significantly lower than other pulley-based CVTs. The sliding plates will slowly wear over years of usage. Therefore the plates are made longer than is needed, allowing for more wear before the chain must be refurbished or replaced. Constant lubrication is required and so the housing is usually partially filled with oil.[12][13]

Toroidal

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Toroidal CVT used in the Nissan Cedric (Y34)

Toroidal CVTs, as used on the Nissan Cedric (Y34),[14][15] and those built by CVTCORP,[16] consist of a series of discs and rollers. The discs can be pictured as two almost-conical parts arranged point-to-point, with the sides dished such that the two parts could fit into the central hole of a torus. One disc is the input, and the other is the output. Between the discs are rollers, which vary the ratio and transfer power from one side to the other. When the rollers' axes are perpendicular to the axis of the discs, the effective diameter is the same for the input discs and the output discs, resulting in a 1:1 drive ratio. For other ratios, the rollers are rotated along the surfaces of the discs so that they are in contact with the discs at points with different diameters, resulting in a drive ratio of something other than 1:1.[17]

An advantage of a toroidal CVT is the ability to withstand higher torque loads than a pulley-based CVT.[18] In some toroidal systems, the direction of thrust can be reversed within the CVT, removing the need for an external device to provide a reverse gear.[19]

Ratcheting

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A ratcheting CVT uses a series of one-way clutches or ratchets that rectify and sum only "forward" motion. The on-off characteristics of a typical ratchet means that many of these designs are not continuous in operation (i.e. technically not a CVT), but in practice, there are many similarities in operation, and a ratcheting CVT is able to produce a zero-output speed from any given input speed (as per an infinitely variable transmission). The drive ratio is adjusted by changing linkage geometry within the oscillating elements so that the summed maximum linkage speed is adjusted, even when the average linkage speed remains constant.

Ratcheting CVTs can transfer substantial torque because their static friction actually increases relative to torque throughput, so slippage is impossible in properly designed systems. Efficiency is generally high because most of the dynamic friction is caused by very slight transitional clutch speed changes. The drawback to ratcheting CVTs is the vibration caused by the successive transition in speed required to accelerate the element, which must supplant the previously operating and decelerating power-transmitting element.

The design principle dates back to before the 1930s, with the original design intended to convert rotary motion to oscillating motion and back to rotary motion using roller clutches.[20] This design remains in production as of 2017, for use with low-speed electric motors.[21] An example prototyped as a bicycle transmission was patented in 1994.[22] The operating principle for a ratcheting CVT design, using a Scotch yoke mechanism to convert rotary motion to oscillating motion and non-circular gears to achieve uniform input to output ratio, was patented in 2014.[23]

Hydrostatic/hydraulic

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A hydrostatic CVT uses an engine-driven, positive-displacement pump to deliver oil under pressure to one or more hydraulic motors, the latter creating the torque that is applied to the vehicle's driving wheel(s). The name "hydrostatic CVT", which misuses the term "hydrostatic", differentiates this type of transmission from one that incorporates a hydrodynamic torque multiplier ("torque converter") into its design.

In a hydrostatic CVT, the effective "gear ratio" between the engine and the driving wheel(s) is the result of a difference between the pump's displacement—expressed as cubic inches or cubic centimeters per revolution—and the motor's displacement. In a closed system, that is, a system in which all of the pump's output is delivered to the motor(s), this ratio is given by the equation GR = Dm ÷ Dp, where Dp is the pump's effective displacement, Dm is the motor's displacement, and GR is the "gear ratio".

In a hydrostatic CVT, the effective "gear ratio" is varied by varying effective displacement of the pump, which will vary the volume of oil delivered to the motor(s) at a given engine speed (RPM). There are several ways in which this may be accomplished, one being to divert some of the pump's output back to the reservoir through an adjustable valve. With such an arrangement, as more oil is diverted by opening the valve, the effective displacement of the pump is reduced and less oil is delivered to the motor, causing it to turn more slowly. Conversely, closing the valve will reduce the volume of oil being diverted, increasing the effective displacement of the pump and causing the motor to turn more rapidly.

Another method is to employ a variable displacement pump. When the pump is configured for low displacement, it produces a low volume of oil flow, causing the hydraulic motor(s) to turn more slowly. As the pump's displacement is increased, a greater volume of oil flow is produced for any given engine RPM, causing the motor(s) to turn faster.

Advantages of a hydrostatic CVT include:

  • Capacity scalability. A hydrostatic CVT's power-transmission capacity is readily adapted to the application by using a correctly-sized pump and matching hydraulic motor(s).
  • Flexibility. As power transfer from the engine-driven pump to the hydraulic motor(s) is through the medium of flowing oil, the motor(s) can be mounted in otherwise-inconvenient locations by using hoses to convey oil from the pump to the motor(s), thus simplifying the design of all-wheel drive articulated vehicles.
  • Smoothness. As the effective "gear ratio" of a hydrostatic CVT is infinitely-variable, there are no distinct transitions in torque multiplication, such as produced with conventional, geared transmissions.
  • Simplified control. Operation through the full range of forward and reverse speeds can be controlled using a single lever or a foot pedal to actuate a diversion valve or variable-displacement pump.
  • Arbitrarily slow crawl speeds. The potential for high torque multiplication at very low speeds allows for precise vehicle movement while under load.

Disadvantages of a hydrostatic CVT include:

  • Reduced efficiency. Gears are one of the most efficient methods of mechanical power transmission, with efficiencies as high as 90 percent in many cases. In contrast, few hydrostatic transmission systems achieve more than about 65 percent efficiency. This is due to a combination of internal losses in the pump and motor(s), and losses in the piping and valves.
  • Higher cost. For a given level of power-transmitting capacity, a hydrostatic CVT will be more expensive to produce than an equivalent geared transmission. In addition to the pump and motor(s), a hydrostatic system requires the use of an oil reservoir, piping and in many applications, an oil cooler, this last item being necessary to dissipate the waste heat that results from hydrostatic power transmission's relatively low efficiency.
  • Greater weight. Due to the high oil pressure at which a hydrostatic CVT operates, the pump and motor(s) are under considerable mechanical stress, especially when maximum power and loading is being applied. Hence these items must be very robust in construction, typically resulting in heavy components. Additional weight will be found in the oil reservoir and its oil load, as well as the piping and valving.

Uses of hydrostatic CVTs include forage harvesters, combine harvesters, small wheeled/tracked/skid-steer loaders, crawler tractors, and road rollers. One agricultural example, produced by AGCO, splits power between hydrostatic and mechanical transfer to the output shaft via a planetary gear in the forward direction of travel (in reverse, the power transfer is fully hydrostatic). This arrangement reduces the load on the hydrostatic portion of the transmission when in the forward direction by transmitting a significant portion of the torque through more efficient fixed gears.[24]

A variant called the Integrated Hydrostatic Transaxle (IHT) uses a single housing for both hydraulic elements and gear-reducing elements and is used in some mini-tractors and ride-on lawn mowers.

The 2008–2010 Honda DN-01 cruiser motorcycle used a hydrostatic CVT in the form of a variable-displacement axial piston pump with a variable-angle swashplate.

Cone

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Evans Variable Speed Countershaft

A cone CVT varies the drive ratio by moving a wheel or belt along the axis of one or more conical rollers. The simplest type of cone CVT, the single-cone version, uses a wheel that moves along the slope of the cone, creating variation between the narrow and wide diameters of the cone.

Some cone CVT designs use two rollers.[25][26] In 1903, William Evans and Paul Knauf applied for a patent on a continuously variable transmission using two parallel conical rollers pointing in opposite directions and connected by belts that could be slid along the cones to vary the transmission ratio.[27][28] The Evans Variable Speed Countershaft, produced in the 1920s, is simpler—the two rollers are arranged with a small constant-width gap between them, and the position of a leather cord that runs between the rollers determines the transmission ratio.[29]

Epicyclic

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In an epicyclic CVT (also called a planetary CVT), the gear ratio is shifted by tilting the axes of spherical rollers to provide different contact radii, which in turn drive input and output discs. This is similar in principle to toroidal CVTs. Production versions include the NuVinci CVT.[30]

Hybrid electric

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Several hybrid electric vehicles—such as the Toyota Prius, Mitsubishi Outlander PHEV, and Ford Escape Hybrid—use electric variable transmissions (EVTs, sometimes eCVT) to control the contribution of power from the electric motor and the internal combustion engine. These differ from standard CVTs in that they are powered by an electric motor in addition to the engine, often using planetary gears to combine their outputs instead of a belt used in traditional CVTs. A notable example is the Toyota Hybrid Synergy Drive.

The design is known for its durability with engineers reporting that internal parts "looked perfect, and would have been good for many more miles" after a complete teardown of the HF45 eCVT in a hybrid Ford Escape which operated as a New York City taxi for 450,000 miles (720,000 km).[31]

Other types

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Friction-disk transmissions were used in several vehicles and small locomotives built in the early 20th century, including the Lambert and Metz automobiles. Used today in snow blowers, these transmissions consist of an output disk that is moved across the surface of the input disk upon which it rolls. When the output disk is adjusted to a position equal to its own radius, the resulting drive ratio is 1:1. The drive ratio can be set to infinity (i.e. a stationary output disk) by moving the output disk to the center of the input disk. The output direction can also be reversed by moving the output disk past the center of the input disk. The transmission on early Plymouth locomotives worked this way, while on tractors using friction disks, the range of reverse speeds was typically limited.[32]

Still in development, the magnetic CVT transmits torque using a non-contact magnetic coupling.[33] The design uses two rings of permanent magnets with a ring of steel pole pieces between them to create a planetary gearset using magnets.[34] It is claimed to produce a 3 to 5 percent reduction in fuel consumption compared to a mechanical system.[34]

Infinitely variable transmissions

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Diagram of an IVT

Some CVTs can also function as an infinitely variable transmission (IVT) which offers an infinite range of low gears (e.g. moving a vehicle forward at an infinitely slow speed). Some IVTs prevent back driving (where the output shaft can freely rotate, like an automotive transmission in neutral) due to providing high back-driving torque. Other IVTs, such as ratcheting types, allow the output shaft to freely rotate. The types of CVTs which are able to function as IVTs include epicyclic, friction-disk, and ratcheting CVTs.

History

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The idea for a continuously variable transmission originated with Leonardo da Vinci in 1490. While he didn't patent it or mass-produce it, his design was a concept for a step-less variable speed transmission.[35]

Later, in 1879, Milton Reeves invented a CVT (then called a variable-speed transmission) for use in sawmilling. In 1896, Reeves began fitting this transmission to his cars,[36] and the Reeves CVT was also used by several other manufacturers.

The 1911 Zenith Gradua 6HP motorcycle used a pulley-based Gradua CVT.[37][38] A year later, the Rudge-Whitworth Multigear was released with a similar but improved CVT. Other early cars to use a CVT were the 1913–1923 David small three-wheeled cyclecars built in Spain,[39] the 1923 Clyno built in the U.K., and the 1926 Constantinesco Saloon built in the U.K.

Applications

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Passenger vehicles

[edit]
See also: List of automobiles with continuously variable transmissions
2000–present Toyota K CVT

In 1958, the Dutch DAF 600 became the first mass-production car to use a CVT.[40] Its Variomatic transmission was used in several vehicles built by DAF and Volvo until the 1980s.[41]

In 1987, the ECVT, the first electronically controlled steel-belted CVT, was introduced as an optional transmission on the Subaru Justy,[42][43] Production was limited to 500 units per month due to Van Doorne's limited production output. In June of that year, supplies increased to 3,000 per month, leading Subaru to make the CVT available in the Rex kei car.[44] Subaru has also supplied its CVTs to other manufacturers (e.g., the 1992 Nissan Micra and Fiat Uno and Panda).[45] Also in 1987, second-generation Ford Fiesta and first-generation Fiat Uno were introduced with steel-belted CVTs, which are called CTX and Unomatic in Ford and Fiat, respectively.

The 1996 sixth-generation Honda Civic introduced a pulley-based Honda Multi Matic (HMM) CVT which included a multi-plate clutch, not a torque converter, to prevent idle creep.[46]

Use of CVTs then spread in the following years to models including the 1998 Nissan Cube, 1999 Rover 25 and 1999 Audi A6.[47]

The 1999 Nissan Cedric (Y34) used a toroidal CVT—unlike the pulley-based designs used by other manufacturers—marketed as the Nissan Extroid, which incorporated a torque converter. Nissan then switched from toroidal to pulley-based CVTs in 2003 marketed as the Nissan Xtronic.[48] The version of the CVT used with the VQ35DE engine in the fourth-generation Nissan Altima is claimed to be capable of transmitting higher torque loads than other belt CVTs.[49]

The 2019 Toyota Corolla (E210) is available with a CVT assisted by a physical "launch gear" alongside the CVT pulley. At speeds of up to 40 km/h (25 mph), the launch gear is used to increase acceleration and reduce stress on the CVT. Above this speed, the transmission switches over to the CVT.[50]

Marketing terms for CVTs include "Lineartronic" (Subaru), "Xtronic" (Jatco, Nissan, Renault), INVECS-III (Mitsubishi), Multitronic (Volkswagen, Audi), "Autotronic" (Mercedes-Benz) and "Intelligent Variable Transmission (IVT)" (Hyundai, Kia).

Racing cars

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In the United States, Formula 500 open-wheel racing cars have used CVTs since the early 1970s. CVTs were prohibited from Formula One in 1994 (along with several other electronic systems and driving aids) due to concerns over escalating research and development costs and maintaining a specific level of driver involvement with the vehicles.[51]

Small vehicles

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Many small vehicles—such as snowmobiles, golf carts, and motor scooters—use CVTs, typically of the pulley variety. CVTs in these vehicles often use a rubber belt with a non-stretching fixed circumference manufactured using various highly durable and flexible materials, due to the mechanical simplicity and ease of use outweighing their comparative inefficiency. Some motor scooters include a centrifugal clutch, to assist when idling or manually reversing the scooter.[52]

The 1974 Rokon RT340 TCR Automatic off-road motorcycle was fitted with a snowmobile CVT. The first ATV equipped with a CVT was the Polaris Trail Boss in 1985.[citation needed]

Farm and earthmoving equipment

[edit]

Combine harvesters used variable belt drives as early as the 1950s. Many small tractors and self-propelled mowers for home and garden use simple rubber belt CVTs. Hydrostatic CVTs are more common on the larger units.[example needed] In mowing or harvesting operations, the CVT allows the forward speed of the equipment to be adjusted independently of the engine speed; this allows the operator to slow or accelerate as needed to accommodate variations in the thickness of the crop.

Hydrostatic CVTs are used in small- to medium-sized agricultural and earthmoving equipment. Since the engines in these machines are typically run at constant power output (to provide hydraulic power or to power machinery), losses in mechanical efficiency are offset by enhanced operational efficiency. For example, in earthmoving equipment, the forward-reverse shuttle times are reduced. The speed and power output of the CVT is used to control the travel speed and sometimes steering of the equipment. In the latter case, the required speed differential to steer the equipment can be supplied by independent CVTs, allowing the steering to be accomplished without several drawbacks associated with other skid steer methods (such as braking losses or loss of tractive effort).

The 1965 Wheel Horse 875 and 1075 garden tractors were the first such vehicles to be fitted with a hydrostatic CVT. The design used a variable-displacement swash-plate pump and fixed-displacement gear-type hydraulic motor combined into a single compact package. Reverse ratios were achieved by reversing the flow of the pump through over-centering of the swashplate. Acceleration was limited and smoothed through the use of pressure accumulator and relief valves located between the pump and motor, to prevent the sudden changes in speed possible with direct hydraulic coupling. Subsequent versions included fixed swash plate motors and ball pumps.[citation needed]

The 1996 Fendt Vario 926 was the first heavy-duty tractor to be equipped with a IVT transmission. It is not the same thing as a hydrostatic CVT. Over 100,000 tractors have been produced with this transmission.[53]

Power generation systems

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CVTs have been used in aircraft electrical power generation systems since the 1950s.[citation needed]

CVTs with flywheels are used[citation needed] as a speed governor between an engine (e.g. a wind turbine) and the electric generator. When the engine is producing sufficient power, the generator is connected directly to the CVT which serves to regulate the engine's speed. When the power output is too low, the generator is disconnected, and the energy is stored in the flywheel. It is only when the speed of the flywheel is sufficient that the kinetic energy is converted into electricity, intermittently, at the speed required by the generator.

Other uses

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Some drill presses and milling machines contain a simple belt-drive CVT system to control the speed of the spindle, including the Jet models J-A5816 and J-A5818.[54] In this system, the effective diameter of only the output shaft pulleys is continuously variable. The input pulley connected to the motor is usually fixed in diameter (or sometimes with discrete steps to allow a selection of speed ranges). The operator adjusts the speed of the drill by using a hand wheel that controls the width of the gap between the pulley halves. A tensioner pulley is implemented in the belt transmission to take up or release the slack in the belt as the speed is altered.

Winches and hoists are also an application of CVTs, especially for those adapting the transmission ratio to the resistant torque.

Bicycles with CVT gearing have had limited commercial success, with one example providing a range of gearing equivalent to an eight-speed shifter.[55] The bicycle's short gearing assisted when cycling uphill, but the CVT was noted to significantly increase the weight of the bicycle.[56]

The rise of the electric bicycle has brought a reappraisal of the CVT as a better solution for an optimal drive train set up in comparison to gearing systems historically applied on human powered bicycles.[57][58] The handsfree and continuously stepless operation combined with low maintenance make the CVT an appealing solution for use on city eBikes and by commuters.[59]

See also

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References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Continuously variable transmission

View on Grokipedia
from Grokipedia
A continuously variable transmission (CVT) is an system used in vehicles that provides an infinite number of gear s within a finite range, enabling seamless variation of the drive without discrete gear shifts. Unlike conventional stepped transmissions, a CVT adjusts the continuously to keep the operating at its most efficient speed for any given load or speed demand. The concept of the CVT dates back to the late , when sketched early designs for a stepless transmission mechanism. Practical development began in the , with Milton Reeves inventing a friction-based CVT in 1879 initially for use in sawmills to provide variable speed control. The first automotive application appeared in 1958 with the DAF 600's Variomatic, a belt-driven CVT introduced by the Dutch automaker , which allowed smoother acceleration in small cars. By the 1980s and , CVTs gained traction in production vehicles, with Subaru launching the ECVT in the Justy model in 1987 and introducing its version in the Civic in 1996, marking wider adoption for improved fuel economy. CVTs operate using various mechanisms, with the most common being pulley-based systems featuring two variable-diameter connected by a metal belt or , where the pulley widths adjust to alter the effective . Other types include hydrostatic drives, which use pumps and motors for variation; traction drives, relying on rolling contact between surfaces for transfer; and toroidal designs, employing spherical rollers between concave disks. These configurations enable applications beyond passenger cars, including tractors, all-terrain vehicles, snowmobiles, and hybrid electric systems where precise power splitting is beneficial. Key advantages of CVTs include enhanced by maintaining optimal engine RPMs, smoother acceleration without shift interruptions, and simpler with fewer moving parts compared to traditional automatics. However, they can exhibit a "rubber-band" driving feel due to the lack of fixed ratios, and belt or wear may lead to higher long-term maintenance needs in high-torque scenarios. As of 2025, major manufacturers like , , and Subaru integrate advanced CVTs with simulated shift modes to balance efficiency and driver engagement in a growing share of compact and midsize vehicles.

Fundamentals

Definition and principles

A continuously variable transmission (CVT) is a type of that can vary its gear ratio continuously over a range, rather than in discrete steps, allowing the to operate at optimal speeds matched to the vehicle's speed or load requirements. This stepless variability enables smoother power delivery by eliminating the need for fixed gear shifts, providing an infinite number of ratios within predefined limits. The basic principles of CVTs involve achieving variable input-to-output speed ratios through mechanical, hydraulic, or electrical mechanisms, all of which transmit power without relying on fixed gears. In mechanical approaches, such as traction drives, between contacting elements adjusts the effective diameter to alter the ; hydraulic systems use fluid pressure to vary displacement in pumps and motors; and electrical variants convert to electrical form via generators and motors for control. These methods ensure seamless adjustment of the transmission , optimizing and speed transmission across operating conditions. CVTs typically offer ratio coverage ranging from about 4:1 to 7:1, meaning the maximum reduction ratio to the minimum (often an overdrive) spans this spread, though specific designs vary. The "stepless" shifting inherent to CVTs allows for continuous, smooth acceleration without the interruptions of gear changes, maintaining by holding RPM steady during speed increases. Fundamentally, CVTs leverage the physics of multiplication and speed variation through changes, where power conservation dictates that output increases as output speed decreases. For instance, the output speed ωout\omega_{\text{out}} relates to the input speed ωin\omega_{\text{in}} by the equation: ωout=ωinr\omega_{\text{out}} = \frac{\omega_{\text{in}}}{r} where rr is the transmission (r>1r > 1 for speed reduction). This variation enables amplification at the output, Tout≈Tin⋅rT_{\text{out}} \approx T_{\text{in}} \cdot r (neglecting losses), facilitating adaptation to load demands.

Key components and operation

In the most common belt-driven continuously variable transmissions (CVTs), the core components include primary and secondary , also known as sheaves, which are variable- elements that form the basis of the mechanism. These consist of two conical halves each, allowing the effective to adjust by changing the spacing between the halves. A flexible belt or connects the primary (input) to the secondary (output) , transmitting while accommodating the varying diameters. Hydraulic actuators, powered by pressurized oil, control the movement of the halves, while electronic control units integrate sensors to manage the system. In operation, torque flows from the engine crankshaft to the primary pulley, where rotational input drives the belt or chain. The actuators then adjust the spacing of the primary pulley's halves to widen or narrow the gap, increasing or decreasing its effective and causing the belt to ride higher or lower in the pulley grooves. This action inversely adjusts the secondary pulley's to maintain belt tension, altering the overall continuously without discrete steps—the is determined by the pitch radii of the pulleys. The belt transfers the adjusted torque to the secondary pulley, which connects to the output driveshaft, delivering power to the wheels. Lubrication systems play a critical role in CVTs by circulating specialized transmission fluid to reduce in the and actuators, while also providing cooling to dissipate heat generated from belt- contact and hydraulic operation. This fluid minimizes wear and maintains efficiency, as excessive heat can degrade the belt or . Control mechanisms rely on electronic sensors monitoring parameters such as throttle position, vehicle speed, and load to automatically modulate the ratio via the actuators. The processes this data to optimize the positions, ensuring the operates at efficient RPMs during acceleration or cruising.

Types

Belt-driven pulley CVTs

Belt-driven pulley CVTs employ two pairs of conical pulleys—one driving pair connected to the input shaft and one driven pair on the output shaft—linked by a flexible belt that transmits torque through friction. The pulleys feature adjustable widths achieved by axially sliding the conical halves closer together or farther apart, which alters the effective radius at which the belt rides and thereby continuously varies the transmission ratio without discrete steps. This design allows for seamless ratio changes from underdrive to overdrive, optimizing engine performance across a wide speed range. In operation, hydraulic or electromechanical actuators control the axial movement of the halves to compress or extend them, maintaining belt tension and adjusting the based on demands such as or cruising. The actuators apply clamping force to the , ensuring the belt does not slip under load; hydraulic systems use pressurized for precise control, while electromechanical variants employ and spindles for improved by reducing hydraulic losses. These systems are typically limited to capacities up to around 400 Nm in automotive applications, constrained by the belt's strength and characteristics. Modern implementations, like Nissan's Xtronic CVT as of 2025, incorporate simulated shift logic to mimic traditional gear changes, enhancing driver engagement. Variants of belt-driven CVTs differ primarily in belt construction: traditional rubber V-belts, suitable for lower-power uses like scooters due to their flexibility and high , contrast with modern push-belts composed of layered metal bands and rigid elements that "push" rather than pull, enabling higher durability and load handling. Push-belt designs, often featuring a series of interlocking links, have become dominant in passenger vehicles for their superior transmission and longevity under repeated stress. The DAF Variomatic, introduced in the 1958 DAF 600, marked the first commercial application of a belt-driven pulley CVT, using a rubber V-belt between variable pulleys to provide automatic ratio adjustment.

Toroidal CVTs

Toroidal continuously variable transmissions (CVTs) utilize pairs of doughnut-shaped toroidal discs and power rollers to achieve friction-based power transmission without belts or chains. The design features input and output discs that are concave and form a toroidal cavity, with rollers positioned between them to contact both surfaces. By tilting or oscillating the rollers on their trunnions, the points of contact shift along the disc radii, allowing the effective gear ratio to vary continuously from underdrive to overdrive. Torque is transmitted through shear forces in the thin film of traction fluid between the rolling elements, which temporarily solidifies under pressure to prevent direct metal-to-metal contact and enable efficient power transfer. Two primary configurations exist: double-toroidal and half-toroidal. In the double-toroidal setup, two toroidal cavities operate in parallel, each with multiple rollers, often incorporating regenerative gearing to extend the range and balance loads axially. This arrangement enhances capacity and smoothness but increases complexity. The half-toroidal configuration employs a single cavity with discs shaped as halves of a , clamped over two or three rollers; it simplifies the structure by using thrust bearings on trunnions and is more compact for automotive applications. Operation in both relies on hydraulic actuators to adjust roller tilt and apply clamping forces proportional to , ensuring stable contact and shifts in approximately 2 seconds. These systems offer advantages in compactness and , particularly for high- scenarios, with overall efficiencies reaching up to 95% under optimized conditions due to low slippage in the traction film. Their robust roller-disc interface supports higher loads compared to belt-based designs, with limits around 450 Nm in prototypical automotive units, making them suitable for passenger vehicles and electric drives. However, capacity is constrained by Hertzian contact stresses, typically kept below 2.24 × 10^9 N/m² to ensure over 2,600 hours of operation. A notable example is the Extroid CVT, a half-toroidal design introduced in 1999 for front-wheel-drive vehicles like the and Gloria. It employs two pairs of power rollers between input and output discs, with hydraulic control tilting the rollers to achieve a ratio spread of 4.4:1, transmitting up to 430 Nm of . This configuration provides smooth acceleration and improved in mid-size sedans, demonstrating practical viability in production.

Ratcheting CVTs

Ratcheting CVTs approximate continuous ratio variation through mechanisms that convert rotary input into oscillatory motion, which is then rectified into unidirectional output using one-way clutches or , allowing incremental adjustments to the effective gear ratio. The design typically involves helical gears, cams, or linkages with multiple engaging elements positioned out of phase to minimize , providing near-infinite ratios via fine-tuned stroke lengths or pivot positions. A classic example is the Zero-Max adjustable speed drive, which employs an eccentric connected to one-way clutches on the output shaft, enabling manual adjustment of the ratio from zero to maximum input speed. In operation, the input shaft drives reciprocating elements—such as pushrods or followers—that engage and disengage progressively, with allowing slipping or locking to tune the output speed finely without discrete steps. For instance, in cam-based variants, the cam profile dictates the , which is adjusted by shifting the follower's position along the cam axis, while one-way bearings ensure only forward motion contributes to output rotation. This progressive engagement rectifies the intermittent power flow, though it inherently introduces some variation in output due to the on-off nature of the clutches. Compared to true friction or traction CVTs, ratcheting designs exhibit limitations in smoothness, often producing noticeable from backlash in the engaging elements, which can lead to vibrations in high-precision applications. They are predominantly used in low-power scenarios, such as bicycles, small industrial tools, and auxiliary drives in machinery, where simplicity and cost-effectiveness outweigh the need for seamless operation. in these systems typically reaches 90-93% within optimal and speed ranges, benefiting from direct mechanical engagement that avoids slippage losses common in belt-driven types.

Hydrostatic CVTs

Hydrostatic CVTs employ a driven by the input shaft and a —either fixed or —connected via a closed-loop hydraulic circuit to transmit power through pressurized fluid flow. The and are typically designs featuring adjustable swashplates for displacement control, with high-pressure lines operating at up to 5000 psi (approximately 345 bar) to handle substantial power levels. A supplements the system to replenish losses, cool the circuit, and maintain low-pressure relief, ensuring reliable operation in a compact configuration such as in-line or U-shaped arrangements. In operation, the swashplate angle on the (and motor, if variable) is adjusted via servo mechanisms to vary the volumetric displacement, which directly controls the flow rate and achieves seamless changes without discrete steps. This adjustment enables an infinite range of speed , with the output speed determined by the of displacement to motor displacement (i=DpDmi = \frac{D_p}{D_m}), allowing reversal by shifting the to negative angles for bidirectional . multiplication occurs as builds across the motor, providing high output at low speeds, while overall typically ranges from 80% to 85%, influenced by volumetric and mechanical losses in the and motor (approximated as the product of their individual efficiencies). These transmissions excel in heavy machinery applications, such as agricultural , skid-steer loaders, and excavators, where they deliver precise speed control and high starting —up to 48 kNm in low-speed, high- designs—ideal for tasks requiring and zero-speed holding without clutches. Mineral-based hydraulic oils, such as ISO VG grades, are commonly used for their compatibility with system pressures and temperatures. Variants include hydro-mechanical configurations that integrate the hydrostatic unit with mechanical elements, such as planetary gear sets, to extend the overall range beyond the fluid circuit's limits and improve across broader operating conditions, as seen in power-split designs like the Sundstrand Responder.

Cone CVTs

Cone CVTs, also known as conical traction drives, employ conical surfaces in direct mechanical contact to achieve variable speed through friction-based . The fundamental design features two opposing cones—one connected to the input shaft and the other to the output shaft—rotating in opposite directions, with one or more intermediate rollers or balls positioned between them to facilitate transfer. These rollers are typically arranged in a planetary configuration, such as two rows of five stepped planet rollers each, allowing for coplanar axes where the rolling radii determine the speed . Axial sliding of the cones or rollers adjusts the contact points, varying the effective diameters and thus the transmission continuously from high to low speeds. In operation, the input cone is driven by the power source, and is transmitted to the output cone via shear forces in the elastohydrodynamic (EHD) contact patches between the rollers and cones, relying on adhesive rather than positive . Traction fluids, with coefficients around 0.1, are used to enhance grip and minimize slip, while high normal loads—often applied hydraulically or via ramps (e.g., 41° )—prevent gross slippage and ensure equal load distribution across multiple rollers through controlled creep. The change occurs smoothly as the roller position shifts axially, altering the contact on the cones; for instance, designs like the Nasvytis drive achieve ratios up to 250:1 in a single stage with three rows of planets. Efficiency reaches 94-96% in optimized systems, though heat generation from necessitates advanced , such as cone-rib designs with holes reducing temperatures by up to 34 K. Historically, CVTs found early applications due to their high and compact size, particularly in demanding environments. During and subsequent decades, traction drive variants powered naval guns, aircraft , and gas-turbine engines, with post-war developments like the (75 kW, 582 kg) and Fafnir CVT (up to 37 kW, 85% efficiency) proposed or used in auxiliary transmissions and experimental designs. They were also employed in propulsion, exemplified by the Nasvytrac Drive (373 kW, 48.2:1 ratio, 53,000 rpm) for high-speed rocket-engine pumps in cryogenic conditions. Despite these uses, modern adoption remains rare in mainstream applications owing to challenges like roller wear, fatigue under high loads (e.g., life limited to 3000-50,000 hours at 70% load), and sensitivity to precise control, favoring other CVT types for broader commercial viability.

Epicyclic CVTs

Epicyclic continuously variable transmissions (CVTs) incorporate planetary gear sets, also known as epicyclic s, where the rotational speeds of the sun gear, planet carrier, or ring gear are modulated continuously to achieve seamless ratio changes. In this design, power is typically split between a direct mechanical path and a variable path, with the planetary gears combining the outputs to produce an infinitely variable overall ratio. Unlike traditional belt or CVTs, epicyclic variants leverage the inherent compactness and torque-handling capability of planetary systems, often integrating hydrodynamic or geared elements to vary the speed of one component without discrete shifts. The operation relies on selectively controlling the motion of planetary elements through variable braking, clutches, or mechanisms. For instance, a variable brake or adjustable hydrodynamic device can impose a continuously tunable resistance or speed on the ring gear or carrier, allowing the overall gear ratio to sweep smoothly from underdrive to overdrive. This modulation enables the transmission to maintain optimal input speeds across a wide output range, with the planetary set superimposing the variable and fixed paths. In geared configurations, such as those using oscillating or tilting gears, the contact radii or phasing between elements provide the continuous variation, eliminating slippage common in friction-based CVTs. A representative example is the Vorecon, a fully mechanical epicyclic CVT that employs a hydrodynamic integrated with a planetary gear set. Here, input power from a prime mover drives both the output shaft directly and a secondary path through the torque converter, whose guide vanes or scoop tube position is adjusted to control slip and thus the speed contribution from the variable path. The planetary gears then combine these flows, achieving ratios from 1:1 to as low as 1:6, suitable for high-power applications up to 50 MW. This design has been deployed in over 600 installations for gas turbines and compressors in oil and gas sectors, demonstrating reliability with mean times between failures exceeding 48 years. Another geared example is the Epilogics IVT developed by and Pires, which uses a series of planetary stages with phased planet gears to enable continuous ratio adjustment without belts or fluids. The system varies the relative phasing of planet carriers via a control mechanism, blending power paths for ratios spanning underdrive to overdrive, with experimental prototypes handling automotive levels. Epicyclic CVTs offer potential for hybrid integration by replacing the variable brake or hydrodynamic element with modulation on one planetary component, enhancing control and regenerative capabilities while retaining in gear phases up to 95%. This contrasts with fixed-ratio epicyclic transmissions, where elements are either locked or braked discretely to select predefined ratios, limiting adaptability; in CVTs, the continuous modulation of at least one element ensures infinite ratios within the design range, prioritizing and smoothness over stepped changes.

Hybrid and electric CVTs

Hybrid and electric CVTs integrate electric motors and generators with mechanical elements to enable seamless power delivery and ratio variation in hybrid and fully electric vehicles. A common design pairs a planetary gearset as the power split device with two electric machines: one functioning primarily as a generator (MG1) and the other as a traction motor (MG2). This configuration simulates continuous gear ratios without traditional belts or pulleys, allowing the internal combustion engine to run at efficient speeds while electric components handle variability. In operation, power is divided between a mechanical path directly from the engine through the planetary gearset and an electric path managed by the motors, optimizing overall efficiency. The Toyota Hybrid Synergy Drive exemplifies this approach, where virtual transmission ratios are achieved through the speed differential between the motors and the engine, enabling smooth transitions across driving conditions. The total output power is the sum of engine and electric contributions, expressed as Pout=Pengine+PelectricP_{out} = P_{engine} + P_{electric}, with the effective ratio given by r=ωMG2−ωMG1ωenginer = \frac{\omega_{MG2} - \omega_{MG1}}{\omega_{engine}}, where ω\omega denotes angular speeds. This power-split mechanism supports modes like electric-only propulsion and , where is recovered via the motors to recharge the battery. By 2025, advancements in hybrid and electric CVTs emphasize enhanced efficiency through refined electric control systems and better integration with regenerative braking, particularly in electric vehicle applications where multi-speed simulation improves range and performance. These systems now offer greater torque capacity compared to earlier designs, supporting applications in larger vehicles while maintaining compact footprints and high reliability.

Other variants

Magnetic continuously variable transmissions (CVTs) utilize electromagnetic fields to achieve transfer without physical contact between components, enabling smooth ratio changes and reduced wear. These systems typically employ permanent magnets or electromagnets arranged in configurations such as rotors or planetary setups, where varying the strength or alignment modulates the effective gear ratio. For instance, a proposed by Atallah et al. features a with pole pieces and an inner for delivery to a differential, demonstrating potential in automotive applications with efficiencies up to 90% in prototypes. Another variant, the electromagnetic CVT (EMCVT), integrates cone-and-belt mechanisms with electromagnetic actuators for precise control, offering advantages in collaborative through efficient delivery and energy performance. Infinitely variable transmissions (IVTs), a of CVT concepts, include hydraulic-mechanical hybrids that combine hydrostatic units with planetary gears to provide an infinite range of ratios, including a neutral state at zero output speed. These systems split power between a hydraulic path for variable ratio and a mechanical path for efficiency, allowing seamless transitions without discrete steps. John Deere's IVT in the 7000 TEN Series tractors exemplifies this, using an electro-hydraulic hydrostatic system integrated with a mechanical power train for agricultural applications, achieving broad speed ranges while maintaining high capacity. Research on IVT power flows highlights their ability to optimize efficiency across operating conditions, with ratios analyzed for neutral gear configurations to minimize losses. Emerging technologies in CVT design include ball-based variators, which use tilting spherical elements to vary contact diameters between input and output rings, providing high and . The NuVinci CVT, developed by Fallbrook Technologies, employs six to eight balls in a planetary arrangement for bicycles and light vehicles, offering a coverage of up to 3.5:1 with minimal losses compared to chain drives. Adaptive systems enhance CVT performance by dynamically adjusting frictional interfaces, such as through electro-rheological fluids or variable clamping forces, to optimize traction under varying loads. A passively adaptive rotary-to-linear CVT, for example, tunes gear ratios based on axial forces, suitable for robotic actuators with up to 20% gains in variable-speed operations. Niche applications include CVT-like variators for pitch control, where mechanical variators adjust blade angles continuously to optimize aerodynamic efficiency across wind speeds. These systems employ traction drives or hydraulic variators to enable precise, real-time pitch adjustments, reducing loads and improving capture in variable conditions, as explored in NREL studies on variable-speed turbines. Despite these innovations, many prototype variants, such as magnetic and adaptive friction CVTs, face commercialization challenges due to high development costs and complexity in scaling for , often limiting them to specialized or experimental uses.

Comparisons

With stepped transmissions

Stepped transmissions, such as conventional automatic transmissions (ATs) with 6 to 10 fixed gear or manual transmissions, operate by shifting between discrete gear ratios, leading to fluctuations in RPM as the accelerates or decelerates. In contrast, continuously variable transmissions (CVTs) provide seamless ratio changes across an infinite range, enabling the to operate at a more constant RPM near its peak point, which minimizes fuel consumption and emissions. This continuous operation in CVTs results in smoother acceleration without the interruptions of gear shifts, but it can produce a characteristic "rubber-band" , where the engine RPM rises disproportionately to vehicle speed, creating a less direct throttle response compared to the stepped shifts in traditional transmissions. Despite this, CVTs offer fuel economy advantages, particularly in urban driving cycles with frequent stops and starts, where studies indicate potential savings of 3 to 5% over stepped ATs by optimizing speed. Control strategies differ markedly: stepped transmissions typically employ a for smooth launches and hydraulic or electronic systems to manage discrete shifts between gears, ensuring power delivery during transitions. CVTs, however, rely on electronic modulation of the ratio—such as adjusting diameters in belt-driven designs—to maintain optimal engine loading without physical shifts, though this requires precise feedback control to manage slip and clamping forces.
AspectCVTStepped Transmission (e.g., 6-10 speed AT)
Efficiency85-90% overall, with advantages in variable load due to optimal RPM holding86-94%, higher in steady-state but losses from shifts and (up to 20% slip)
ComplexityFewer components (e.g., no multi-clutch packs for shifts), but specialized belt/ mechanicsMore , clutches, and valves; higher assembly complexity
CostComparable or higher costs compared to multi-speed ATs due to specialized components, but simpler with fewer parts; higher repair costs for beltsHigher initial production from intricate gear sets in advanced designs, but proven reduces long-term ownership costs

Infinitely variable transmission concepts

An infinitely variable transmission (IVT) is defined as a system capable of providing an infinite number of gear ratios within a continuous range that includes a zero output speed , allowing neutral operation without additional clutches or discrete gears. This distinguishes IVTs from standard CVTs without zero-ratio capability and represents a specific of continuously variable transmissions focused on full range including standstill. Continuously variable transmissions (CVTs), which achieve variation through mechanical elements like belts or traction drives, encompass IVTs as a category when designed with the zero-ratio feature. IVTs achieve infinite variability through various means, including mechanical, fluid, or electrical systems. Pure hydrostatic IVTs, for instance, employ a variable-displacement and motor to modulate fluid flow, yielding ratios from zero (stationary output) to a maximum determined by component sizing, without relying on elements. Similarly, electric IVTs utilize a generator-motor pair or direct electric drive, where electronic control decouples input and output speeds, providing infinite ratios via and speed modulation independent of mechanical gearing. These configurations offer bidirectional power flow and high flexibility. Theoretically, IVTs enable optimal operation by continuously matching speed to the most efficient RPM for any given speed or load, minimizing consumption and emissions compared to stepped transmissions. This ideal matching is facilitated by the transmission's infinite range, expressed as: i∈[0,∞)i \in [0, \infty) where ii is the speed ratio (output/input), allowing the system to span from standstill to unlimited overdrive without discrete shifts. While most practical automotive IVTs are implemented within CVT designs for their compactness and cost-effectiveness, forms like hydrostatic or full electric drives highlight the scope of IVT concepts, particularly in hybrid or off-road applications where hydraulic or electrical control predominates.

History

Early inventions

The concept of a continuously variable transmission (CVT) can be traced back to the late , when sketched early ideas for a stepless gear system in his notebooks around the . These conceptual drawings depicted a mechanism using conical pulleys and a belt to achieve variable ratios without discrete steps, serving as a precursor to modern CVT designs, though da Vinci never built or ed a working model. The first for a friction-based belt CVT was filed in by Daimler and Benz in . In the , practical inventions emerged with Milton Reeves developing the first functional CVT in 1879 for use in sawmilling operations. Reeves' leather belt system featured adjustable pulleys that allowed continuous speed variation to control the rate at which saws cut wood, addressing inefficiencies in fixed-speed machinery for agricultural and industrial applications. This variable-speed transmission marked an early application of CVT principles outside conceptual sketches, and Reeves later adapted it for automotive use starting in 1896. Early 20th-century advancements included toroidal CVT designs, with the first patent granted to in 1935 for a friction-based system using rolling elements between curved discs to vary ratios smoothly. A significant breakthrough occurred in the with the development of the belt CVT by Hub van Doorne at (Van Doorne's Automobiel Fabriek). in 1955, the Variomatic employed expandable pulleys and a belt to provide seamless ratio changes, enabling efficient power transfer without traditional gears. It debuted in road use with the 1958 (also known as the Daftrant), a small powered by a 590 cc two-cylinder engine producing 20 horsepower, marking the first production automotive CVT and demonstrating viability for vehicles.

Commercial adoption

The commercialization of continuously variable transmissions (CVTs) accelerated in the late , transitioning from niche applications to broader market integration, particularly in passenger vehicles and two-wheelers. In 1980, introduced the V-Matic belt drive system in its TACT 50cc scooter, marking the first widespread commercial adoption of CVT technology in motorcycles and establishing a standard for seamless, user-friendly shifting that simplified operation and improved ride quality. This innovation quickly expanded across 's scooter lineup in the , capitalizing on growing demand for automatic transmissions in urban mobility. The 1987 launch of the in the United States represented a pivotal moment, as it became the first production passenger car available with a CVT in the U.S. market, featuring an electronically controlled ECVT paired with a 1.2-liter engine and optional all-wheel drive. Building on early prototypes from prior decades, this model addressed consumer needs for fuel-efficient, compact vehicles amid economic shifts like the 1987 downturn. By the late 1990s, European manufacturers entered the fray, with introducing the CVT in late 1999 on the A6 sedan, equipped with a 2.8-liter producing 200 horsepower; this chain-driven system offered both automatic and sequential modes, targeting premium-segment efficiency and performance. Entering the 2000s, CVT adoption surged in , propelled by stringent fuel economy mandates such as Japan's Top Runner program (updated in the late ) and China's inaugural Fuel Economy Standards for passenger vehicles in 2004, which emphasized technologies like CVTs to reduce oil imports and emissions. exemplified this trend with the 2003 crossover, the first North American model to feature the Xtronic CVT, which utilized an advanced belt-and-pulley design for smooth acceleration and a claimed 12% fuel economy improvement over conventional automatics. These regional policies fostered rapid growth, with CVTs becoming integral to meeting corporate average fuel consumption targets across Asian automakers. A key barrier to earlier widespread use—belt slippage and limited durability—was overcome through material and design advancements in the and , enabling CVTs to handle higher in 2-liter-class engines by the late 1990s and up to 3.5-liter applications by 2002, resulting in reliable lifespans exceeding 100,000 miles under normal conditions. By 2010, these enhancements contributed to CVTs comprising approximately 10% of new vehicles in , reflecting their established role in fuel-efficient mass-market production.

Recent advancements

In the 2010s, introduced enhancements to its Xtronic CVT, including a new generation model in 2011 that achieved up to 10% improvement in fuel economy compared to previous versions through optimized design and control systems. During the same period, Subaru addressed reliability concerns in its Lineartronic CVT by implementing fixes such as improved and component durability, leading to extended warranties up to 10 years or 100,000 miles for affected 2010-2015 models and enhanced performance in subsequent iterations. By 2025, integrated a CVT into the front-wheel-drive , delivering smoother acceleration and responsive shifting for urban driving. The EV-CVT segment is experiencing rapid growth, with the e-CVT market projected to reach USD 10.8 billion by 2033 at a CAGR of 12.4% from 2025, driven by demand in hybrid and electric powertrains. These systems now support capacities exceeding 500 Nm through advanced maraging steels in push-belts and enhanced cooling mechanisms to manage heat buildup. Technological progress includes the adoption of electromechanical actuators in CVTs, which replace traditional hydraulic systems to lower energy consumption and improve overall efficiency by operating at reduced power levels. Additionally, data-driven predictive control strategies, leveraging AI for ratio optimization, enhance energy efficiency in CVT systems for autonomous vehicles, contributing to fuel economy gains of up to 10% in optimized setups. Emerging applications feature full electric CVTs in drones and , where compact designs like ball-based or novel geared mechanisms provide variable ratios from constant-speed , enabling precise adjustment in actuators.

Applications

Passenger and light vehicles

Continuously variable transmissions (CVTs) have become a dominant choice in compact cars and light SUVs, particularly among Asian manufacturers, due to their emphasis on and smooth operation in urban environments. For instance, the 2025 Nissan , equipped with Nissan's Xtronic CVT, achieves EPA-estimated fuel economy of 30 and 40 in its base S and SV trims, making it a popular option for budget-conscious commuters. Similarly, the 2025 Nissan utilizes the same Xtronic CVT paired with a 1.5-liter turbocharged , delivering up to 30 and 37 in front-wheel-drive models, which enhances its appeal for family-oriented light-duty transport. In stop-and-go traffic, CVTs provide seamless ratio adjustments without discrete gear shifts, resulting in smoother acceleration and reduced mechanical stress compared to traditional automatics. This minimizes "shift shock," allowing the to maintain optimal RPMs and potentially lowering wear on both and transmission components during frequent starts and stops. The exemplifies this benefit, with its CVT offering refined power delivery that eliminates abrupt changes, contributing to a more comfortable drive in congested city conditions while supporting up to 36 mpg combined efficiency. CVTs hold a significant in new passenger vehicles from Asian brands, with the region accounting for approximately 48% of the global CVT market in recent years, driven by adoption in models from , , and Subaru. This penetration is bolstered by seamless integration with turbocharged engines, as seen in the Rogue's 201-horsepower 1.5-liter turbo setup, which leverages the CVT's infinite ratio range to optimize delivery and fuel economy without compromising drivability. Consumer perceptions of CVTs have evolved, with early complaints about the "rubber band" effect—where engine RPM rises without proportional speed increase—being addressed through simulated step shifts that mimic traditional gear changes. These programmed shifts reduce the droning noise during , providing a more engaging and familiar driving feel, as implemented in the Civic's G-Design Shift logic for natural response.

Racing and high-performance vehicles

In the 1990s, continuously variable transmissions (CVTs) were trialed in Formula 1 racing, where the Williams team developed a for their FW15C in , partnering with Van Doorne's Transmissie to create a metal belt system that delivered seamless ratio adjustments for superior traction and acceleration. This innovation allowed the car to maintain optimal engine RPM during corners and straights, potentially revolutionizing lap times, but the FIA banned CVTs ahead of the 1994 season, mandating four to seven fixed gears to preserve competitive balance and prevent cost escalation among teams. In modern motorsports, CVTs have seen limited but notable adoption in hybrid rally applications, such as the Hybrid Rally Team's modified and Civic Hybrid vehicles, which utilize Bosch GS-CT CVTs to optimize torque delivery from the hybrid powertrain, , and ; testing showed these setups completing a 6 km rally 20 seconds faster than manual equivalents. High-performance road vehicles have also incorporated CVT-like systems for enhanced dynamics, exemplified by the e-tron electric , which employs dual rear electric motors delivering 919 Nm of with electronic that variably distributes power to individual wheels for precise handling, mimicking the seamless modulation of a CVT while achieving 0-60 mph in approximately 3.9 seconds. Similarly, the integrates a Lineartronic CVT with Symmetrical All-Wheel Drive, enabling active distribution for improved cornering response in performance driving. These setups prioritize quick power deployment over traditional stepped shifts, allowing the engine or motors to operate at peak efficiency without interruption. A key advantage in and high-performance contexts is the CVT's ability to perform instant ratio changes, keeping the power source in its optimal RPM band for maximum and responsiveness without the lag of gear . Recent 2025 developments include reinforced belts using advanced cords and high-temperature compounds, enabling CVTs to handle loads exceeding 600 Nm, as seen in upgraded systems like Subaru's TR690 variant, which supports sustained high-output demands in tuned applications. However, limitations persist in heat management during prolonged high-RPM operation, where belt slippage and fluid degradation can occur under loads, necessitating enhanced cooling to prevent power or failure.

Small engines and recreational vehicles

Continuously variable transmissions (CVTs) have become dominant in scooters, particularly through Honda's V-Matic system, which was introduced in 1980 on the TACT 50cc model and integrates belt drive with automatic gear ratio adjustments for smooth operation. The V-Matic employs centrifugal weights in the drive pulley that expand with increasing engine speed, widening the pulley's diameter to automatically vary the transmission ratio without rider input, enhancing ease of use in urban commuting. This design has set a standard for scooter CVTs, enabling seamless acceleration and widespread adoption in low-displacement engines up to 250cc. In all-terrain vehicles (ATVs) and snowmobiles, has pioneered CVT designs optimized for variable terrain, using a V-belt system with drive and driven clutches that automatically adjust ratios to maintain optimal engine RPM during acceleration, climbing, or load changes. These transmissions handle diverse conditions like , , or trails by providing precise power delivery without manual shifting, supporting outputs up to approximately 142 Nm in models like the ProStar-equipped vehicles. For bicycles, the NuVinci (now Enviolo) hub CVT offers seamless pedaling by using a planetary ball system that continuously varies gear ratios under load or at standstill, eliminating discrete shifts for consistent across terrains. Recent Enviolo CVP hubs, such as the Urban model, weigh around 2.18 kg and support up to 55 Nm of , making them suitable for urban and trekking bikes while requiring minimal maintenance. CVTs in these small-engine and recreational applications provide 10-15% better or energy utilization in variable-speed scenarios compared to fixed-gear systems, as they maintain the or pedaling effort at peak points without the losses from mismatched ratios.

Industrial and agricultural equipment

Continuously variable transmissions (CVTs), particularly hydrostatic variants, are integral to modern tractors, enabling precise speed control and seamless power adjustment to match varying field loads such as plowing or tilling. John Deere's Infinitely Variable Transmission (IVT) systems, employed in models like the 8R series, utilize hydrostatic principles to deliver infinitely variable ratios, allowing operators to maintain optimal across speeds from as low as 0.05 km/h in creeper mode to 50 km/h in , with the hydrostatic providing effective ratio ranges up to approximately 10:1 for enhanced traction and fuel savings. In earthmoving equipment, integrates CVTs into wheel loaders like the next-generation 966 XE series to provide variable output tailored to demanding digging and tasks, ensuring consistent power without losses. These systems facilitate smooth acceleration and load adaptation, with 2025 model updates incorporating refined dynamics for up to 35% improved over traditional powershift designs. Factory machinery benefits from CVTs in applications requiring adjustable conveyor speeds, such as assembly lines, where they enable fine-tuned synchronization with production processes to minimize jams and optimize throughput. Industrial-grade CVTs, often hydrostatic or belt-driven, demonstrate high , routinely achieving over 10,000 operating hours before major servicing under continuous duty cycles. A key advantage in these heavy-duty contexts is the smooth power delivery of CVTs, which reduces operator fatigue by eliminating the need for frequent gear shifts and providing consistent response during prolonged operations.

Power generation systems

In wind turbines, continuously variable transmissions (CVTs) enable the maintenance of constant generator rotational speed despite fluctuations in wind velocity by dynamically adjusting the gear ratio between the rotor and generator. This decoupling allows the turbine to operate at optimal tip-speed ratios across a broader range of wind conditions, maximizing power extraction without relying on complex . For instance, mechanical CVTs like the NuVinci rolling traction design facilitate variable-speed operation starting at lower wind thresholds (e.g., 5.0 m/s compared to 6.5 m/s in fixed-ratio systems), thereby enhancing overall energy capture. Studies demonstrate significant gains in yield from CVT integration; one of horizontal-axis turbines using a CVT to optimize turbine-generator reported an approximate 50% increase in annual production relative to direct-drive configurations, achieved by delaying pitch control activation to higher speeds. Hydrostatic CVTs, in particular, have been explored for offshore and utility-scale applications, providing lightweight, reliable speed regulation to sustain generator output under variable loads. In backup generators, hydrostatic CVTs facilitate load balancing by allowing to vary speed in response to , ensuring stable electrical output without abrupt shifts. This configuration integrates a and variable-displacement motor to transmit power efficiently, reducing mechanical stress and enabling seamless transitions during outages. An example is the integrated hydrostatic-driven , which combines axial components for compact, high-efficiency operation in emergency power scenarios. Emerging applications in 2025 include CVT-enhanced hybrid power setups for (EV) grid integrations, where variable-speed generators support bidirectional flow to stabilize grid loads during peak charging. These systems leverage CVTs to optimize or turbine speeds, aiding (V2G) protocols by providing reliable without fixed-ratio limitations. Hybrid CVTs in microgrids combine solar photovoltaic arrays with -driven generators to deliver stable power output, using the transmission's ratio control to synchronize intermittent renewables with baseload needs. This setup ensures frequency and by adjusting speeds to match fluctuating solar input, minimizing curtailment and blackouts in isolated networks. For example, variable-speed diesel generators employing CVTs integrate with solar storage to maintain consistent AC output for remote communities. Overall, CVTs in power generation systems enhance efficiency by precisely matching prime mover speeds to electrical loads, which reduces consumption compared to fixed-speed alternatives. In one , a 50 kW variable-speed generator with a mechanical CVT achieved annual savings of approximately 12,000 liters over six months of operation, primarily through low-speed idling at partial loads that cuts parasitic losses.

Other specialized uses

In systems, continuously variable transmissions (CVTs) enable variable speeds by decoupling operation from rotation, allowing engines to run at optimal points across varying loads and speeds. This approach is particularly beneficial in thrusters, where 360-degree steerable pods require precise control for maneuvering in dynamic maritime environments. Studies have demonstrated savings of up to 13% in marine plants equipped with CVTs, achieved through reduced specific fuel consumption during partial load operations common in shipping routes. Early applications of CVTs in focused on drive systems to optimize rotor speeds for varying flight conditions, addressing limitations of fixed-ratio transmissions that constrained and envelopes. A notable early invention from introduced a two-gear planetary gearbox as a precursor to variable systems, enabling rotor speed adjustments to improve handling qualities and reduce power demands. In modern unmanned aerial vehicles (UAVs) or drones, CVTs integrated into hybrid electric systems (HEPS) facilitate adjustment by maintaining ideal operating lines for power delivery, allowing seamless adaptation to weight variations during missions such as or delivery. This enhances endurance and stability, with control strategies optimizing engine and synergy for up to 20% gains in variable-load scenarios. In , miniature CVTs serve as key components in arm joint s, providing continuously adjustable transmission ratios for precise and speed control in dynamic tasks. These systems combine CVTs with variable actuators, such as those based on actively variable four-bar linkages, to enable robots to handle unpredictable loads while minimizing energy loss and vibrations. For instance, a CVT-enhanced actuator can dynamically shift ratios to deliver high for heavy lifting or high speed for rapid positioning, improving overall adaptability in collaborative human-robot environments. Such designs draw briefly on cone traction principles for compact, friction-based ratio changes without discrete steps. CVT concepts for space rover drives have been studied by since 1981 for managing terrain variability on extraterrestrial surfaces and electric propulsion in harsh environments.

Advantages and limitations

Operational benefits

Continuously variable transmissions (CVTs) enhance fuel economy by maintaining the engine at its optimal (RPM) for a given load, minimizing inefficient operation across varying speeds and conditions. This capability allows for seamless ratio adjustments that keep the engine in its most efficient range, resulting in fuel savings of approximately 10% compared to previous-generation CVTs in mid-size vehicles. In hybrid applications, such as parallel hybrid systems, CVTs contribute to overall fuel economy improvements of 20-30% over conventional vehicles by optimizing power distribution between the engine and . The absence of discrete gear shifts in CVTs eliminates shift shocks, providing smoother and deceleration that enhances driving comfort. This stepless operation reduces (NVH) levels, as there are no abrupt torque interruptions associated with traditional transmissions. Manufacturers like incorporate features such as G-Design Shift to align engine sound with vehicle speed, further improving the perceived smoothness and overall NVH performance during linear . CVTs offer superior through instant adjustments, enabling quicker power delivery without the delays of gear in stepped transmissions. This allows the transmission to match output precisely to demands, resulting in more immediate and better control in dynamic scenarios. For instance, advanced CVT controls can rapidly build G-forces in response to accelerator input, enhancing agility without compromising efficiency. By promoting efficient engine operation, CVTs contribute to lower environmental impact through reduced emissions. Optimized RPM holding minimizes fuel consumption, directly lowering tailpipe CO2 output; for example, Honda's advanced CVT belt technology achieves CO2 emissions below 100 g/km in compact cars, a reduction from previous levels of 120 g/km. Recent 2025 implementations demonstrate these gains, with improved power transmission efficiency supporting broader regulatory goals for emissions cuts in passenger vehicles.

Technical drawbacks

One significant technical drawback of continuously variable transmissions (CVTs), particularly belt-driven designs, is their limited capacity. In standard belt configurations without reinforcement, belts tend to slip when exceeds approximately 400-500 Nm, as the frictional grip between the belt and becomes insufficient to transmit higher loads without deformation or loss of contact. This constraint restricts CVT applications to engines producing moderate , often necessitating reinforcements like metal push-belts or chains for higher-power vehicles, though even these have practical limits based on pulley clamping forces and belt material strength. Friction in CVT variators, arising from the sliding contact between belts or chains and adjustable pulleys, generates substantial heat, particularly under high-load conditions. This overheating can degrade lubrication and accelerate wear unless mitigated by advanced cooling systems, such as external oil coolers or enhanced fluid circulation. Consequently, overall transmission efficiency often drops to around 85-90% under load due to these frictional losses, compared to 86-94% for conventional stepped transmissions, as energy is dissipated as heat rather than mechanical output. CVTs exhibit greater mechanical complexity than traditional stepped transmissions, incorporating more components such as variable s, hydraulic actuators, and sophisticated control valves to achieve ratio changes. This increased part count—often 20-30% more moving elements—elevates the potential for points, including bearing or valve malfunctions, complicating design and assembly. A perceptual drawback during operation is the "rubber-band effect," where the revs rise disproportionately to , creating a sensation of disconnection akin to a slipping . This occurs because the CVT holds the at high RPM for optimal power while the ratio adjusts gradually, lacking the discrete shifts of geared transmissions that synchronize revs and speed more intuitively.

Reliability and maintenance considerations

Continuously variable transmissions (CVTs) can achieve a lifespan exceeding 150,000 miles under normal driving conditions when subjected to regular , such as changes every 30,000 to 60,000 miles, though some models like Honda's have been reported to last over 300,000 miles with diligent upkeep. Nissan CVTs, for instance, often surpass 200,000 miles with proper servicing, while neglect can lead to failure as early as 60,000 miles. The drive belt or in belt-driven CVTs typically endures for 100,000 to 150,000 miles before requiring replacement, depending on factors like load and heat exposure, which accelerate wear if not managed. Common failure modes in CVTs include wear from prolonged and degradation, which reduces and cooling efficiency, leading to slipping, shuddering, or overheating. These issues are exacerbated by contaminated or inadequate servicing, causing inconsistent belt grip and accelerated component breakdown. By 2025, advancements in synthetic CVT s, such as AMSOIL's 100% synthetic formulation and Valvoline's full synthetic options, have improved thermal stability and frictional properties, helping to extend transmission life through better resistance to degradation and reduced . In 2025, new developments include enhanced metal push-belts with improved for higher torque applications in compact vehicles. Diagnostics for CVT issues often rely on electronic monitoring systems that detect ratio errors, slippage, or anomalies via onboard sensors, triggering warning lights or diagnostic trouble codes for early intervention. Repair costs for common CVT problems, such as fluid system overhauls or partial rebuilds, typically range from $2,000 to $5,000, depending on the model and extent of damage, though full replacements can exceed this. Best practices for longevity include avoiding aggressive acceleration and heavy towing, which generate excess heat and stress, alongside adhering to manufacturer-recommended fluid changes using OEM or compatible synthetics. Manufacturers like Subaru and have responded to reliability concerns with extensions in 2025; Subaru extended CVT coverage to 10 years or 100,000 miles for select 2019-2020 models, while extended it to 84 months or 84,000 miles for affected vehicles (such as 2015-2018 and 2016-2018 Maxima) under class action settlements.

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