Performance optimisation of the push-belt CVT by variator slip control

Continuously variable transmissions (CVTs) are applied in an increasing number of vehicles. Large ratio coverage allows for reduced engine speeds, which adds to both highway driving comfort and reduced fuel consumption. It becomes increasingly important to further improve the performance in terms of efficiency, robustness and torque capacity of the CVT. This paper describes the possibilities of improving the CVT by minimising variator clamping forces. This is accomplished by using slip control technology. This technique allows for the best possible transmission efficiency, combined with improved robustness for slip damage. This paper first describes the relation between variator slip and functional transmission properties. The conditions for optimum performance regarding efficiency and robustness are identified. This leads to the development of a variator slip controller. The remaining sections describe experimental results on two test rigs and in a production vehicle. The paper concludes with an outlook into further developments.