Shift dynamics modelling for optimization of variator slip control in a pushbelt CVT

Improvement of transmission efficiency of the pushbelt CVT by reducing variator clamping forces is well established. The increased risk of gross belt slip, resulting from reduced clamping forces, calls for novel variator control strategies, where direct control of belt slip plays a major role. First belt slip control attempts led to promising results in steady state and slow shifting conditions, but unacceptable slip occurred during fast shifting events. This was ascribed to the limitations in the underlying model, in which variator shift dynamics was neglected. In this paper theoretical variator shifting models are validated with experimental results. The results are used for model optimization of the variator shift dynamics. This results in an optimized CVT slip controller, as well as a controller for CVT ratio control. The controller is implemented and tested in a vehicle. Results of the experiments are presented. A comparison is made to the results obtained with the previous controller