A Review of Continuously Variable Transmissions: Classification and Performance Analysis

Abstract

Continuously variable transmissions (CVTs) have become an important element of modern powertrain systems due to their ability to provide smooth ratio variation and improve overall energy efficiency. However, the term “CVT” is often used in a narrow sense, typically referring only to belt or chain variators, while a broader range of transmission concepts remains insufficiently systematized. This lack of a unified classification complicates the comparison and selection of transmission systems for different applications.
The present paper aims to provide a comprehensive overview of continuously variable transmissions based on their operating principles and to develop a unified framework for their classification and comparison. The study considers friction-based mechanical CVTs, hydrostatic and hydromechanical transmissions, electromechanical power-split systems, as well as emerging technologies such as magnetic and traction-drive transmissions.
A set of key performance parameters is introduced, including transmission ratio range, torque and power capacity, efficiency, dynamic response, structural characteristics, and control complexity. Based on these parameters, a comparative analysis of the main CVT types is performed and summarized in a structured table.
The results show that each transmission type exhibits specific advantages and limitations depending on its physical operating principle. Friction-based systems offer compactness and relatively high efficiency, while hydrostatic and hydromechanical transmissions provide superior torque capacity and controllability. Electromechanical CVTs demonstrate high flexibility in hybrid systems, whereas emerging technologies show potential for further improvement.
It is concluded that no single CVT type can be considered universally optimal, and the selection of a transmission system must be based on specific application requirements. The proposed classification and comparative framework can be used as a basis for the design and selection of CVT systems in modern engineering applications.