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. project he is working on the modelling and control of an electromechanically actuated metal V-belt CVT.Rob Pulles received his MSc degree in Mechanical Engineering from Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands, in October 2004. During his MSc project he designed and implemented a slip control strategy for a Continuously Variable Transmission. After that he worked as a visiting scientist at Eindhoven University of Technology in order to implement this slip control strategy in a production car (Nissan Primera). He now works for the company Drive Train Innovations (DTI) on the identification and control of an Automatic Manual Transmission.Sjoerd Simons is currently carrying out his MSc project in the Mechanical Engineering Department of the Eindhoven University of Technology (TU/ e), Eindhoven, The Netherlands. In his MSc project he has implemented a slip control strategy in a production car (Nissan Primera) and furthermore he is optimising the slip control strategy for transient operating modes of the Continuously Variable Transmission. Maarten Steinbuch received the MSc and PhD degrees in Mechanical Engineering from Delft University of Technology in 1984 and 1989 respectively. From 1987±1999 he was with Philips Electronics. Since 1999 he has been full professor and head of the Control Systems Technology group within the Mechanical Engineering Department, Eindhoven University of Technology. His research interests are modelling and control of automotive power trains and motion systems. He was an associate editor of the IEEE Transactions on Control Systems Technology, IFAC Control Engineering Practice and IEEE Control Systems Magazine. He is currently editor-at-large of The European Journal of Control. Bram Veenhuizen received his MSc degree in Experimental Physics from the Free University of Amsterdam in 1984 and his PhD from the University of Amsterdam in 1988. After employment by SKF (1988±1995) and van Doorne's Transmissie (1995±2002) he joined the Eindhoven ...

Abstract-Continuously Variable Transmissions (CVT)can be used to operate a combustion engine in a more optimal working point. Unfortunately, due to the relatively low efficiency of modern production CVT's the total efficiency of the driveline is not increased significantly. This low efficiency is mainly caused by losses in the hydraulic actuation system and the variator. Decreasing the clamping forces in the variator greatly improves the efficiency of the CVT. However, lower clamping forces increase the risk of excessive belt slip, which can damage the system. In this paper a method is presented to measure and control slip in a CVT in order to minimize the clamping forces while preventing destructive belt slip. To ensure robustness of the system against torque peaks, a controller is designed with optimal load disturbance response. A synthesis method for robust PI(D)-controller design is used to maximize the integral gain while making sure that the closed loop system remains stable. Experimental results prove the validity of the approach.

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