Dynamic Friction Laws and Their Impact on Friction Induced Vibrations 2010-01-1717

There are a few principal excitation mechanisms that brake system NVH simulations are based on, especially the high frequency squeal simulations. These mechanisms can be described by some simple mechanical models that exhibit excitation or self excitation effects induced by friction [ 1 ]. These models use very simple friction laws of Coulomb type, described by a friction coefficient that is either a constant or simple functions of some state variables, taking into account a Stribeck characteristic. Eigenvalues of the linearized models are computed in the frequency domain, and often used to judge the stabilities of the models. Industry applications typically use FEA programs in the modeling, which allows detailed descriptions of the geometry of the brake system, except the friction layer. In the friction layer between brake disk and pad, simple friction laws are used, which allows a modal analysis similar to that of the minimal models.

Measurements from the AK-Master or SAE J2521 , however, show that the friction coefficient is not a simple function of some state variables, describing a steady state behavior of friction. In the past several years, material dependent descriptions of the frictional brake interface have started attracting attention [ 2 ]. These aspects are greatly influenced by the tribological effects at the frictional interface, which can be characterized by typical wear patterns. Through investigation of dissipative self organizing processes at the frictional interface, brand new friction dynamics are discovered [ 3 ].

This paper gives an overview on the dynamic effects in the friction layer and their surprising impact on friction induced vibrations in brake systems.