Over the last decade or so the environmental pressures of the modern world have been dictating the work of the automotive engineer. Governments, under the pressure of the environmental lobby, have had to increase the constraints which modern motor vehicle must meet, in terms of emissions and fuel consumption. As the pressures of these constraints mount, the focus of the engineer has concentrated on improving the efficiency of the automobile. Most of the work has concentrated on the vehicle prime mover, the internal combustion engine. However, to date little of the work has concentrated on the transmission of the vehicle and improving its efficiency. This thesis details the work undertaken in a project to investigate and model the loss mechanism that exist in an automotive pushing metal V-belt continuously variable transmission (CVT). The aim of the project was to investigate the magnitude of inefficiency associated with each of the transmission components, particularly those associated with the belt itself, and develop an understanding of the effects of temperature on these loss mechanisms. The work entailed the development of a transmission test rig capable of measuring the losses through the transmission at very low power levels. The test rig developed is capable of testing the transmission at controlled low temperatures, with a high degree of accuracy and repeatability. The experimental work carried out on the transmission test rig is also supported with data from a further variator test rig, designed to measure belt slip, and with complete vehicle testing performed on a chassis dynamometer facility. The thesis introduces a number of new models for predicting both the torque losses and slip losses present in the transmission. Torque loss models are developed based upon the interactions of belt segments and bands and pulley deflections at belt entry and exit conditions. Slip is predicted due to the existence of gaps in the belt. A high degree of interaction between the slip and torque loss models is displayed, whilst both models are validated individually using the collected experimental data. Finally some proposals are made to improve the efficiency of the pushing metal V-belt CVT, based upon the findings of the modelling work.
|Date of Award||1 Jan 2001|
|Supervisor||Nicholas D Vaughan (Supervisor)|