Complex eigenvalues analysis predicts the unstable modes with growth of oscillations (eigenvalues simplify the analysis here by separating out the friction forces into each of three dimensions). The Figure shows a simplified model of the tribometer used in a previous study of brake squeal. The determinant shows the kinetic friction force K in the three dimensions when a normal load F is applied to the rotor turning at speed N in rpm. The pair of pads have a friction coefficient μ and friction force Kn, whereas the friction force of the caliper is denoted by Kcaliper (where y is the friction coefficient of the caliper). The pads exert a pressure E and have a density ρ and volume ν.
The analysis plots the non-uniform contact pressure distribution, which has a maximum at the leading edge of the pad. The complex eigenvalues analysis determines the unstable modes.
Figure: Simplified disc, pad and caliper model of the tribometer used in previous studies of brake squeal.
The tests did find that Lapinus’ RB210 fibres virtually eliminated brake noise. These fibres offer high temperature reinforcement to NAO/non-steel disc pad applications. The (extreme) low shot fibres have especially stabilized the friction levels over various driving conditions, and have reduced both pad and rotor wear over a broad temperature range. The latest rubber-coated RB210 fibres reduce high frequency squeal and low frequency moan/groan of NAO/non-steel disc pads. This was hardly changed by material formulation, friction level or material properties.
Figure 2 shows a Scanning Electron Microscope view of the pad-rubbing surface of silent (left) and noisy (right) brakes. The pad condition is clearly critical.