Dynamic analysis of the Empact CVT

The dynamics of an electromechanically actuated metal V-belt (Empact) CVT is analyzed by studying a simplified linear model of the actuation system and a driveline model which includes the slip dynamics of the variator. The actuation system shows several CVT ratio depending modes. Linearization of the slip dynamics shows that the location and, moreover, the damping of the modes depends significantly on the amount of slip in the variator. Using pole-zero locations of the system it is shown that due to high overclamping a coupling between the primary and secondary side of the variator occurs with very large damping and due to underclamping the input and output sides of the variator are decoupled with low or even negative damping, resulting in an unstable system. Furthermore non-minimum phase behavior of the actuation is described. Using identification results from a non-linear model of the Empact CVT the interaction of the actuation and driveline dynamics is analyzed. Finally, measurements on a prototype of the Empact show similar behavior, however with very large damping of all of the modes.