Simulations and Tests of Innovative Friction Laws in Brake Systems

Modeling of friction in mechanical systems is classically carried out by an incorporation of suitable algebraic functions. The general layout of these functions depends on the system under consideration [1]. For an analysis of brake systems, whose external parameters generally change rapidly, such steady state descriptions do not suffice. A detailed understanding of these systems and their dynamics requires innovative friction laws, which must be able to also capture transient effects in the contact zone. The tribological interface between brake lining material and brake disc is characterised by a closed-loop interaction between heat, wear and friction, which causes a continuous growth and destruction of smooth and hard surface structures [2]. This equilibrium of flow can be well reproduced by modern automata methods [3]. It is significantly influenced by external load parameters, such as normal force and sliding velocity, which modulate the life cycle and average size of the contact patches and by that the coefficient of friction over time. Based on this principal mechanism, a new mathematical description of friction has been derived, which uses a set of coupled differential equations. This layout gives insights into the third body dynamics during transient friction events. Therewith, predictions of the surface topography, heat distribution and friction characteristics of different brake lining compositions become possible. The performance of the developed model will be illustrated by a discussion of specific braking events, extracted from industrial testing procedures (AK-Master test). (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)