New insights into the tribology of brake systems

Abstract

In spite of remarkable efforts the perfect brake pad in terms of friction performance, wear, noise, and costs has not been found to date. This is mostly because the development is still based on the extensive ‘trial-and-error’ method, as a reliable reproduction or even prediction of those issues is still not possible. A theory regarding the interaction of friction and wear in the interface shows that the tribological behaviour of the system is determined by the growth and destruction of characteristic hard structures (‘patches’) on a mesoscopic length scale. A respective equilibrium of flow taking into account that the main part of the friction power is transmitted by the patches leads to a physically derived dynamic friction law. This paper shows the results that can be gained using this sophisticated law and how it explains several measured phenomena on different timescales. Based on this assumption a cellular automaton model is introduced where the choice of its inner variables and its boundary conditions allows a description of the processes in the interface, as a matter of principle. The paper deals with the formulation of the rules considering the interactions between the patches, friction, wear, and temperature and the resulting dynamic effects. The rules are derived from physical laws and measurements. The occurring timescales according to this model are pointed out and a method towards the problem's simplification with the help of specific algorithms is presented.