Effect of friction material properties on thermoelastic instability of clutches

During the synchronizing process, inhomogeneous temperature field of vehicular shift clutches is investigated with thermoelastic instability (TEI) theory. A two dimensional theoretical model is built and a perturbation method is selected for determining the critical condition of TEI. The TEI theory and the critical speed are testified by experiments. The result shows that the instability, which is caused by coupling effects of frictional heat, thermal stress and elastic stress, leads to a strong perturbation in the temperature field, on condition that the engaging speed exceeds the critical speed. When hot spots number is less than 5, the copper-based material is more unstable; when it is more than 5, the paper-based material is more unstable. The stability of clutches can be improved by reducing the elastic modulus, increasing the thermal conductivity of the friction material and reducing the thermal expansion coefficient of the mating material.