Experimental investigation of friction-induced noise in disc brake systems

This paper presents experimental and analytical investigations examining th e influence of the interfacial forces between a rotating disc and a frictio n element on the generation of chatter and squeal. Due to inevitable misali gnment between the element and disc surface, a kinematic constraint instabi lity known as sprag-slip is created. The experimental measurements include time history records of normal and friction forces, time variation of the f riction coefficient, and acceleration of the friction element. The time his tory records of interfacial forces revealed short periods of high frequency component. It is found that the friction force is non-Gaussian and that it s power spectral density covers a wide frequency band. The dependence of th e root mean square of the friction coefficient on the relative velocity is found to have a negative slope at lower disc speeds. Depending on the direc tion of disc rotation, it is found that the friction velocity curve for clo ckwise disc speed is completely different from counter-clockwise rotation. The associated noise is also different in pitch and frequency content. The analytical modeling emulates the dynamics of the friction element. The tran sverse motion of the Friction element is described by a homogeneous partial differential equation with nonhomogeneous boundary conditions. The analysi s shows that the normal force appears as a coefficient of the stiffness ter m, while the friction force appears as a non-homogeneous term. Since the no rmal force varies randomly as observed experimentally, it acts as a paramet ric noise to the friction element, and results in parametric instability in the form of squeal or vibration.