Clutches are devices for disengaging the connection between the driveshafts and power units, and hence transferring rotational energy. Two inertias travelling with different angular velocities are brought to the same speed by engaging the clutch. The dissipation of energy during the operation results in a rise in temperature. When considering the parameters which contribute to the effectiveness of clutches, the properties of carbon fibre reinforced carbon (known as carbon-carbon) composites are considered to be superior to any other candidate materials available. The cost of devices made from such materials has precluded their use in “everyday” applications and limited them to “high end” motor sport use such as Formula 1. This work considers the frictional properties of carbon-carbon composites in race clutch applications when combined with launch control systems, and how by improving the modelling of the co-efficient of friction of the material would lead to improved race starts. The work investigates the causes of frictional instability and how to promote more consistent coefficient of friction values through both bedding analysis and mathematical modelling. Physical testing was undertaken using a clutch dynamometer to explore the effects of temperature, input speed and clamp loads upon the friction coefficient. Using infra-red sensors, a novel method was developed for the direct measurement of surface temperature of the plates. Banding of the clutches was also investigated. Materials testing was undertaken on the carbon-carbon clutch material to characterise its properties for thermal expansion, emissivity, specific heat and thermal conduction and this was novel in its contribution to the access of this data to the wider research community. The influence of carbon structure, physical, thermal, mechanical and chemical properties, as well as friction films, on the performance of carbon-carbon friction materials were modelled using MATLAB®. This was novel in the incorporation of surface behaviours into the full model. This model was then used to replicate clutch dynamometer data and predict coefficient of friction values. Results gave good predictions, with small errors in comparison with experimental data.
Lawrence, G
Department of Mechanical Engineering and Mathematical SciencesFaculty of Technology, Design and Environment
Year: 2008
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