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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.

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.

A supercharger system which boosts the engine via a direct drive from the engine crankshaft has been identified as a possible solution to improve low-end torque and transient response for a conventional turbocharged SI engine. However, the engine equipped with a fixed-ratio supercharger is not as fuel-efficient especially at high load and low speed due to the fact that a large portion of the intake mass air flow has to recirculate through a bypass valve causing inevitable mechanical and flow losses. In addition, the fixed drive ratio of the supercharger which is mainly determined by the full-load requirements might not be able to provide sufficient over-boost during a transient. The fact that a clutch may be necessary for high engine speed operation on the fixed-ratio supercharger system is another issue from the perspective of cost and NVH performance.

The Milner continuously variable transmission (MCVT) is a traction drive transmission based on rolling contacts analogous to those found in angular contact roller bearings. The MCVT is applicable to very high power density applications or those with demanding packaging constraints, due primarily to the existence of multiple traction contacts on each of the rolling elements. The transmission has been modelled analytically and then Design of Experiments (DoE) techniques have been applied to create response surface model sets describing performance criteria over a wide range of design input factors. The response surface models have then been interrogated to find optimal solutions. The results show that it is possible to create a transmission with a significantly higher ratio range (10:1), compared with 5:1 that is typical for existing designs [1].