Determination of Variator Robustness Under Macro Slip Conditions for a Push Belt CVT

Developments in clamping force control for the push belt Continuously Variable Transmission (CVT) aim at increased efficiency in combination with improved robustness. Current control strategies attempt to prevent macro slip between elements and pulleys at all times for maximum robustness. In order to search for the limiting factors in developing a new control strategy, situations where macro slip occurs have been investigated. New tribological insights show that macro slip is acceptable to a certain extent. An important failure mechanism proves to be the occurrence of adhesive wear in the contact leading to a loss in torque transfer. As a combination of normal load and slip speed, respectively clamping force and slip rate in a variator, a transition can be found from a safe wear region to an excessive/adhesive wear region. The occurrence of this transition has been verified with experiments on CVT variator level. New applications based on current understanding are found in the field of new control strategies.