Continuously variable transmissions, commonly known as CVT's, have been shown to be feasible alternatives to the conventional multi-step gear transmissions (standard or automatic) typically used in automotive applications. Most CVT applications, however, rely on a shaft-to-shaft transmission arrangement, in which the belt-sheave action limits the load capacity of the transmission, particularly at the high power ranges (low speed, high torque).
In this paper, a system based on a combined planetary gear train and a continuously variable pulley system is presented. The uniqueness of this arrangement is that the variable pulleys provide a power/torque split and recirculation function, which, when combined with the planetary gear train function, produces a continuously variable power split transmission system. The CVT ratio (r) is used as the regulator of the overall transmission ratio (R), in such a way that at low speeds, the power circulating through the belt can be only a fraction (less than 50%) of the total input power. Then, as the continuous shift is made to the high speed range, the power circulation shifts towards the CVT unit, a much desired feature in automotive applications.