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Continuously variable transmission (CVT)

Kevin R. Lang
21W. 732
May 3, 2000

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Abstract
As the U.S. government enacts new regulations for automotive fuel economy and emissions, the
continuously variable transmission, or CVT, continues to emerge as a key technology for improving the
fuel efficiency of automobiles with internal combustion (IC) engines. CVTs use infinitely adjustable
drive ratios instead of discrete gears to attain optimal engine performance. Since the engine always runs
at the most efficient number of revolutions per minute for a given vehicle speed, CVT-equipped vehicles
attain better gas mileage and acceleration than cars with traditional transmissions.
CVTs are not new to the automotive world, but their torque capabilities and reliability have been
limited in the past. New developments in gear reduction and manufacturing have led to ever-more-robust
CVTs, which in turn allows them to be used in more diverse automotive applications. CVTs are also
being developed in conjunction with hybrid electric vehicles. As CVT development continues, costs will
be reduced further and performance will continue to increase, which in turn makes further development
and application of CVT technology desirable.
This paper evaluates the current state of CVTs and upcoming research and development, set in
the context of past development and problems traditionally associated with CVTs. The underlying
theories and mechanisms are also discussed.