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The efficiency of belt-type continuously variable transmission (CVT) -apart from the power consumption of auxiliary systems such as hydraulics -predominantly depends on the energy dissipated during sliding at the belt-disc contacts. These sliding motions are a consequence of elastic deformations and misalignments because of clearances, resulting in a socalled spiral path of the belt elements on the discs and hence tangential and radial sliding motions.The performance of such systems can be predicted through an iterative computation by numerically solving a set of differential equations for the forces and motions coupled with a finite-element computation of the deformations.A comparison with elaborate measurements of deflections, belt motions, and losses shows that a relatively simple modified Coulomb type friction model with a steep gradient through the origin delivers sufficiently accurate results. The computations reveal the existence of 'locked' zones with extremely low 'creeping' motions.Thus, the mechanisms of power transmission in belt-type CVT are better understood and designers have a validated tool to optimize shaft and disc geometry concerning maximum efficiency.

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