Understanding the Contributions of Surface Morphology Transitions and the Phenomenon of Thermoelastic Instabilities on the Torque Output of a Carbon/Carbon Multi-Plate Clutch During Race-Start Conditions

The torque output of a carbon/carbon multi-plate Formula One clutch during race starts has proved to be both unstable and inconsistent. A one-dimensional heat transfer model utilising a Taguchi analysis suggested that a close interdependency exists between surface temperature, surface morphology and coefficient of friction (COF) thus affecting torque output stability. Friction surface examination showed that a non-uniform friction surface height may lead to thermoelastic instabilities (TEI) and effective friction radius (EFR) migration which directly affects torque output. A single clutch-plate interface dynamometer (SCID) confirmed the formation of narrow (~2 mm), high-temperature (1300-1650°C) hot bands during tests which replicated race start conditions, indicating the establishment of TEI. The hot bands did not move radially during single engagements but did migrate between successive engagements indicating that torque instability during single engagements is due to surface morphology effects alone whilst torque inconsistency between engagements is due to both surface morphology and EFR migration effects.