Easy-to-Use CVT-equipped Engines

The beluga is a white whale inhabiting the Arctic and its name was used for Yamaha’s BELUGA 50cc scooter released in 1981. It was Yamaha’s first mass-production scooter to feature an engine with a continuously variable transmission (CVT) for greater ease of use. After its appearance, the CVT was adopted on many 50cc scooters as well as those of other displacements as it underwent design improvements. Today, the CVT continues to make urban scooters and sport scooters user-friendly, easy-to-ride machines. 
The Passol 50cc scooter released in 1977 featured a flat footboard and a “step-through” design that enabled the rider to sit with the knees together. This won it popularity among housewives and other female users—a relatively untapped customer category—and it became a market hit. Sister models joined the Passol and helped further expand the market. However, with their development priority on lightness, the Passol line models had no transmission. So when you increased speed, engine rpm increased as well. The model that Yamaha developed in pursuit of even greater ease of use was the BELUGA and its CVT-equipped engine.
A CVT transmits drive force through the drivetrain while continuously changing the reduction ratio (gear equivalent) over a step-less continuum. It is comprised of a belt with a V-shaped cross-section running between fore and aft pulleys with valley-shaped grooves. The drive force is transmitted to the rear wheel via the friction between the belt and pulleys while the reduction ratio is varied. Because the pulleys move in accordance with changes in engine rpm, the way the “V-belt” contacts the pulleys also changes (technically, the diameter of the path run by the belt is altered). This means the reduction ratio changes over a step-less continuum (#1). Particularly in the case of the BELUGA’s CVT, a mechanism called a torque cam was adopted, drawing in part on the design of CVT units used on snowmobiles. That made it possible to provide optimum reduction ratios based on the drive load produced at times like when accelerating again after releasing the throttle or when going uphill.
This CVT unit was later adopted on all Yamaha scooters ranging from 50cc up to 250cc and 400cc displacements. Each model’s CVT unit was given settings optimized to fit the scooter’s particular purpose. The current Majesty YP250 model is fitted with an electronically controlled CVT called the Yamaha Chip Controlled Automatic Transmission (YCC-AT). It enables the user to choose from three different transmission modes to accommodate a variety of ride conditions. Shifting between modes is done at the push of a button and can be used to recreate the same feeling as with a motorcycle, like downshifting to get engine braking or to get a strong feeling of acceleration. By employing advanced control technology, CVT units can give the rider a completely new type of riding experience.