Improving Push Belt CVT Efficiency by Control Strategies Based on New Variator Wear Insight 2004-40-0039

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. 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. It turns out that macro slip is acceptable to a certain extent.

The new wear insight allows fundamental different control strategies. In particular strategies based on CVT slip measurement and control are of interest. These control strategies enable lower clamping forces while retaining robustness. Consequently, CVT efficiency increases which will lead to an improvement in fuel consumption of approximately 5%.