Continuously variable transmission
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.
CVTs are used in cars, tractors, side-by-sides, motor scooters, snowmobiles, bicycles, and earthmoving equipment.
Each element of the chain must have conical sides that fit the pulley when the belt is running on the outermost radius.
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.
This is achieved by having a stack of many small rectangular plates in each chain link that can slide independently from side-to-side.
Due to the interlocking surfaces, this type of drive can transmit significant torque and so has been widely used in industrial applications.
[10][11] Toroidal CVTs, as used on the Nissan Cedric (Y34) ,[12][13] and those built by CVTCORP,[14] consist of a series of discs and rollers.
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).
Efficiency is generally high because most of the dynamic friction is caused by very slight transitional clutch speed changes.
[21] 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).
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."
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.
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.
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.
A cone CVT varies the drive ratio by moving a wheel or belt along the axis of one or more conical rollers.
Friction-disk transmissions were used in several vehicles and small locomotives built in the early 20th century, including the Lambert and Metz automobiles.
The transmission on early Plymouth locomotives worked this way, while on tractors using friction disks, the range of reverse speeds was typically limited.
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.
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] 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.
[46] Marketing terms for CVTs include "Lineartronic" (Subaru), "Xtronic" (Jatco, Nissan, Renault), INVECS-III (Mitsubishi), Multitronic (Volkswagen, Audi), "Autotronic" (Mercedes-Benz) and "IVT" (Hyundai, Kia).
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.
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.
Many small tractors and self-propelled mowers for home and garden use simple rubber belt CVTs.
The design used a variable-displacement swash-plate pump and fixed-displacement gear-type hydraulic motor combined into a single compact package.
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.
Some drill presses and milling machines contain a simple belt-drive CVT system to control the speed of the chuck, including the Jet models J-A5816 and J-A5818.
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.
[53][54] The handsfree and continuously stepless operation combined with low maintenance make the CVT an appealing solution for the use on city eBikes and by commuters.
