Most CVTs are of the "belt and cone" type, with friction between the belt and the variable-diameter "cone" pulleys being the mode of power transmission. These belts can slip and wear out eventually. The Toyota Hybrid Synergy Drive's CVT uses an epicyclic planetary gear set (the "power split device") in conjunction with MG1 (motor-generator #1) to achieve an effectively infinitely variable gear ratio with no belts or friction drives at all. There's no comparable slip or wear mechanism here. Much more elegant!

Stan