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Hybrid vehicles are becoming an increasingly popular choice for both consumers and manufacturers due to their potential for superior fuel economy and low emissions compared with conventional vehicle power trains. Traditionally there have been two types of hybrid vehicle configurations; the parallel hybrid configuration takes advantage of power regeneration for short periods of zero emissions operation, whilst the series hybrid configuration acts as a continually variable transmission (CVT) so that increased engine efficiency can be obtained. The recent interest in hybrid vehicles has led to a number of non-traditional configurations, most notably the power-splitting hybrid electric vehicle, which uses an epicyclic gear as the power-splitting device, and can operate as either a series or a parallel hybrid. A further improvement to this configuration is proposed with the use of a Milner CVT (MCVT) to replace the epicyclic gear set.

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.