SAE International On Tangential Friction Induced Vibrations in Brake Systems 2008-01-2580

The basis for the analysis of friction in brake systems is the brake pad's tribological interface. An investigation of this interface reveals friction intensive surface structures, so-called 'patches'. Their development is determined by an equilibrium of flow, which depends on the loading of the brake pad and which allows extensive insights into friction dynamics, wear behavior and heat generation. All of these aspects are mostly influenced by the varying size of the patches over time. This paper deals with a detailed analysis of the lateral vibrational dynamics of these patches on a very fast timescale. This timescale is so small that processes of patch growth and destruction are negligible. Beyond that, the vibration frequencies of the patches, as well as the actual local friction power on each of these surface structures, vary over a wide range of values, which is the result of a great variety of patch sizes and heights in the interface. Generally, one would expect a smoothing of these local and stochastically distributed vibration effects. It can however be shown, that the oscillations of the patches are subject to synchronization processes, with the result being in-phase patch vibrations on macroscopic areas of the brake pad of significant size. Thereby, self-excited vibrations of the patches can lead to lateral oscillations of the pad's friction force on a macroscopic scale. These are able to excite the whole system of brake pad and disk.