Technology of a traction drive CVT: Past, present and future

In November 1999, traction drive half-toroidal CVT units were installed in mass-production vehicles for the first time in the world. Looking back in history, Charles W. Hunt of Richmond, New York, U.S.A., was the first to conceive the principle of a toroidal type CVT. But, his invention had not been commercialized for 120 years mainly because of poor endurance performance. Finally, after more than 21 and a half years of developments and advancements in basic lubrication and material technologies, technical problems of the traction drive CVT were successfully resolved. Today's technology aided in the achievement of a safe and comfortable traction drive CVT, which demands a well thought-out design, advanced materials, precise machining, and superior field simulation techniques. This paper describes detailed deliberations regarding rolling fatigue, bending fatigue, and white structure flaking for assuring endurance and performance of the traction drive CVT. A traction drive unit was examined after 118,500 km of running in the field for verification of CVT technology. Therefore, the half-toroidal CVT unit can play a role as an automotive transmission with appealing function and adequate durability.