Transmission CVT

Transmission CVT

A continuously variable transmission (CVT) is a transmission that can change seamlessly through an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios. The flexibility of a CVT allows the input shaft to maintain a constant angular velocity.

A CVT usually has a low efficiency of 88%, but it can provide a cheap automatic gear solution by enabling the engine to run at its most efficient revolutions per minute (RPM) for a range of vehicle speeds, allowing a small car (CVT can't handle high torques[need quotation to verify]) to have an acceptable fuel efficiency at low cost.

Alternatively, it can be used to maximize the performance of a vehicle by allowing the engine to turn at the RPM at which it produces peak power. This is typically higher than the RPM that achieves peak efficiency. Finally, a CVT does not strictly require the presence of a clutch. Nevertheless, in some vehicles (e.g. motorcycles) a centrifugal clutch is added, to facilitate a "neutral" stance, which is useful when idling or manually reversing into a parking space.

Uses

A Chain-driven CVT

Many small tractors for home and garden use have simple rubber belt CVTs. For example, the John Deere Gator line of small utility vehicles uses a belt with a conical pulley system.CVTs should be distinguished from Power Sharing Transmissions (PSTs), as used in newer hybrid cars, such as the Toyota Prius, Highlander and Camry, the Nissan Altima, and newer-model Ford Escape Hybrid SUVs. CVT technology uses only one input from a prime mover, and delivers variable output speeds and torque; whereas PST technology uses two prime mover inputs, and varies the ratio of their contributions to output speed and power. These transmissions are fundamentally different.

The Ford C-MAX hybrid, Ford C-MAX Energi hybrid, Mitsubishi Lancer, Proton Inspira, Honda Insight, Honda Fit, and Honda CR-Z hybrids, the Nissan Tiida/Versa SL and SV models), Nissan Versa Note (S Plus and higher), Nissan Cube, Juke, Sentra, Altima, Maxima, 2013 1.2 Note, Rogue, X-Trail, Murano, Sunny, Micra, Honda Capa, Honda Civic GX (CNG), Honda Civic Hybrid, Honda Accord, Jeep Patriot and Compass, and Subaru Forester Impreza, Legacy and Outback, Dodge Caliber, and Toyota Corolla offer CVT.

Types

Variable-diameter pulley (VDP) or Reeves drive

In this most common CVT system, there are two V-belt pulleys that are split perpendicular to their axes of rotation, with a V-belt running between them. The gear ratio is changed by moving the two sheaves of one pulley closer together and the two sheaves of the other pulley farther apart. Due to the V-shaped cross section of the belt, this causes the belt to ride higher on one pulley and lower on the other.

Toroidal or roller-based CVT (Extroid CVT)

Toroidal CVTs are made up of discs and rollers that transmit power between the discs. The discs can be pictured as two almost conical parts, point to point, with the sides dished such that the two parts could fill 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 which transfer power from one side to the other.

A cvt transmission assembly

By Aaron Hernandez Villalpando