Thermoelastic contact problems in automotive brakes and clutches.

Abstract

This dissertation presents investigations on the phenomenon of frictionally excited thermoelastic instability (TEI) in an automotive disc brake and the transient behavior of thermoelastic contact problem in a loaded clutch. A parametric study is conducted to determine the effect of material properties and geometries on TEI problems in an automotive disc brake. The stiffness of caliper, which supports the pads, has great effect on TEI problems. To obtain more accurate solution, caliper is involved into TEI analysis by using substructure technique. A transient behavior of loaded clutch system is also investigated. Although TEI analysis can successfully predict the occurrence of instability, it cannot predict detailed evolution of the temperature and contact pressure fields. Therefore, transient analysis should be applied. Zagrodzki (2003) introduced a transient modal analysis (TMA) method to define a solution for the inhomogeneous (loaded) transient problem. In TMA, the temperature field appears as an integral of the applied loads convoluted with the eigenfunctions of the related homogeneous (unloaded) problem. Therefore, if sliding speed is variable, the eigenvalue solution should be repeated in each time step. In this dissertation, two alternative strategies for increasing computational efficiency are developed. They are referred as fast speed expansion (FSE) method and one-point fast speed expansion (OPFSE) method. Both of them can be applied to reduce the number of required eigenvalue solutions, and hence, lead to significantly reduction of computational time. These two methods are applied to a multidisc clutch system. The results show that the FSE and OPFSE methods can greatly reduce the computational complexity of the transient analysis, while maintain good accuracy. Contact area may change in size causing the thermoelastic problem to be non-linear. A transient solution of a three dimensional nonaxisymmetric thermoelastic contact problem is explored. This solution is applied to estimate the evolution of temperature field of a two-layer clutch system. The results show that, at a specific hydraulic pressure, maximum temperature reaches a peak value. In practice, maximum temperature could be reduced by increase of hydraulic pressure.