Clearance and friction-induced dynamics of chain CVT drives

A continuously variable transmission (CVT) is an emerging automotive transmission technology that offers a continuum of gear ratios between desired limits. A chain CVT is a friction-limited drive as its performance and torque capacity rely significantly on the friction characteristic of the contact patch between the chain and the pulley. Moreover, such a CVT is susceptible to clearance formation due to assembly defects or extensive continual operation of the system, which further degrades its performance and leads to early wear and failure of the system. The present research focuses on developing models to understand the influence of clearance and different friction characteristics on the dynamic performance of a chain CVT drive. A detailed planar multibody model of a chain CVT is developed in order to accurately capture the dynamics characterized by the discrete structure of the chain, which causes polygonal excitations in the system. A suitable model for clearance between the chain links is embedded into this multibody model of the chain CVT. Friction between the chain link and the pulley sheaves is modeled using different mathematical models which account for different loading scenarios. The mathematical models, the computational scheme, and the results corresponding to different loading scenarios are discussed. The results discuss the influence of friction characteristics and clearance parameters on the dynamic performance, the axial force requirements, and the torque transmitting capacity of a chain CVT drive.