Abstract
V-belt type Continuously Variable Transmissions (CVT) are applied in an increasing number of vehicles as a result of their unparalleled shift comfort. Large ratio coverage allows for reduced engine speed, improved highway driving comfort and reduced fuel consumption. With the advent of the competing automatic transmissions with 6 or even 7 steps, it becomes increasingly important to further improve the performance in terms of efficiency, robustness and torque capacity of the CVT. Improvements on the efficiency of the push-belt CVT by reducing variator clamping forces to minimum values are well established. By reducing clamping such that the variator operates in its most efficient point, the mechanical load on this variator is minimized and hydraulic actuation losses are reduced. The control technique allows for best possible transmission efficiency, combined with improved robustness for slip damage.
In earlier studies, the relation between variator slip and functional transmission properties has been described. Conditions for optimum performance regarding efficiency and robustness were identified and validated for steady state conditions. However, stability robustness during ratio changes proved to be insufficient during tests in an experimental vehicle.
To deal with CVT slip dynamics during transient behaviour, a theoretical model is necessary. In this paper, a novel CVT shifting model, recently proposed by Carbone, is tested experimentally and compared to the model of Ide. The relationship between the clamping forces acting on the moving pulley sheave, the rate of change of speed ratio, the loading conditions and the belt velocity, are investigated both from a theoretical and an experimental point of view.
Keywords: CVT, Slip Dynamics, Shift Dynamics, Slip Control, LQG Control.