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This paper gives an overview of the development of a number of loss models for the pushing metal V-belt CVT. These were validated using a range of experimental data collected from two test rigs. There are several contributions to the torque losses and new models have been developed that are based upon relative motion between belt components and pulley deflections. Belt slip models will be proposed based upon published theory, expanded to take account of new findings from this work. The paper introduces a number of proposals to improve the efficiency of the transmission based on redesign of the belt geometry and other techniques to reduce frictional losses between components. These proposed efficiency improvements have been modelled and substituted into a complete vehicle simulation to show improvements in vehicle fuel economy over a standard European drive cycle.

The Milner CVT is a patented [1] rolling traction transmission offering advantages of high power density and simplicity of construction and operation. A 90 mm diameter prototype variator is described which was sized for a maximum rated input power of 12 kW. Experimental data are presented demonstrating high efficiency and low shift forces. Resistance to overload torque is shown to be exceptional and preliminary durability trials indicate a highly viable concept for series production. Based upon the measured data, characteristics of larger variators are predicted and prospects for automotive applications discussed.

This paper introduces the work ongoing at the University of Bath in a series of projects aimed at characterising the driveability of CVT equipped vehicles and using the findings to help develop a strategy for a prototype powertrain controller during transient driving situations. Results of the driveability investigation of a first project in this series have already been published [1], where the driveability of three CVT vehicles was appraised. A follow-up project extends this work appraising more CVT vehicles and also comparing driveability aspects of CVT transmissions to conventional AT. The paper relates the common experimental part of the two projects showing linked results and describing how a simulation program can be used to predict and improve the driveability of the powertrain controller.