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A continuously variable transmission (CVT) (also known as a single-speed transmission, stepless transmission, variable pulley transmission, or, in case of motorcycles, a twist-and-go) is an automatic transmission that can change seamlessly through an indefinite 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 belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by lower production cost and by enabling the engine to run at its most efficient revolutions per minute (RPM) for a range of vehicle speeds. Thus a small car can strike a balance between fuel efficiency and cost of manufacture. 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 greatest 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〔(【引用サイトリンク】title=use of clutch with CVT )〕 to facilitate a "neutral" stance, which is useful when idling or manually reversing into a parking space. == Uses == 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. They can deliver an abundance of power and can reach speeds of , all without need for a clutch or shifting gears. Nearly all snowmobiles, utility vehicles, golf carts and motor scooters use CVTs, typically the rubber belt or variable pulley variety. Some combine harvesters have CVTs. The CVT allows the forward speed of the combine to be adjusted independently of the engine speed. This allows the operator to slow or accelerate as needed to accommodate variations in thickness of the crop. CVTs have been used in aircraft electrical power generating systems since the 1950s and in Sports Car Club of America (SCCA) Formula 500 race cars since the early 1970s. CVTs were banned from Formula 1 in 1994 due to concerns that the best-funded teams would dominate if they managed to create a viable F1 CVT. More recently, CVT systems have been developed for go-karts and have proven to increase performance and engine life expectancy. The Tomcar range of off-road vehicles also utilizes the CVT system. Some drill presses and milling machines contain a pulley-based CVT where the output shaft has a pair of manually adjustable conical pulley halves through which a wide drive belt from the motor loops. The pulley on the motor, however, is usually fixed in diameter, or may have a series of given-diameter steps to allow a selection of speed ranges. A handwheel on the drill press, marked with a scale corresponding to the desired machine speed, is mounted to a reduction gearing system for the operator to precisely control the width of the gap between the pulley halves. This gap width thus adjusts the gearing ratio between the motor's fixed pulley and the output shaft's variable pulley, changing speed of the chuck. A tensioner pulley is implemented in the belt transmission to take up or release the slack in the belt as the speed is altered. In most cases, the speed must be changed with the motor running. 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. Some vehicles that offer CVT are the Ford C-MAX hybrid, the Mitsubishi Lancer, the Proton Inspira, the Proton Iriz, the Proton Saga FLX, the Proton Prevé, the Dodge Caliber, the Toyota Corolla, the Toyota iQ, the Honda Insight, Fit, CR-Z hybrid, CR-V, Capa, Civic GX (CNG), Civic Hybrid, City, HR-V and Accord, the Nissan Tiida/Versa (SL, SV, and Note S Plus or higher models), Cube, Juke, Sentra, Altima, Maxima, 2013 1.2 Note, Rogue, X-Trail, Murano, Sunny and Micra, the Jeep Patriot and Compass, the Suzuki SX4 S-Cross, and the Subaru Forester, Impreza, Legacy, and Outback. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「continuously variable transmission」の詳細全文を読む スポンサード リンク
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