Abstract

The occurrence, growth, limit cycle amplitude and mitigation of brake squeal noise are investigated using a predictive analytical coupled modal model. The model is developed to analytically determine the effect of the combined mechanisms of falling friction, spragging and mode coupling in brake squeal for the first time. In addition, the handling of the brake pad mechanics and sliding friction is newly contributed. The modelling leads to closed form analytical criteria for brake squeal that suggests that spragging is required for mode coupled squeal, in contrast with the falling friction mechanism. In particular, spragging is shown to be an important necessary condition for two types of mode coupled squeal; stiffness and viscous, determined by negative damping from the complex stiffness and coupled modal damping, respectively. The efficient analytical predictions are then verified using previous numerical and experimental investigations of brake squeal including the effect of damping. The results concur and quantify practical observations and show that squeal amplitude is primarily dependent upon sliding velocity and independent of growth rate with a minimal difference in squeal amplitudes due to the different mechanisms. The efficient closed form solution is then used to predict the amplitude of the limit cycle brake squeal noise and to investigate a wide range of parameters to mitigate its occurrence. The closed form modelling and solutions provide important insight; into the occurrence and mitigation of the underlying mechanisms of brake squeal (including falling friction, spragging, stiffness and viscous mode coupling), and on the brake pressure dependent modes and the brake pad angle of attack.

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