Oscillatory Instabilities Generated in a Double-Pin and Disc Undamped System: A Mechanism of Disc-cbrake Squeal

Abstract
A dynamic analysis is presented of a double-pin and disc system, which is undamped and has linear characteristics. A self-induced oscillatory motion is generated which can become unstable for certain combinations of the system's parameters. Unstable motion requires a set of inequality equations to be satisfied, and a necessary, but not sufficient condition is that one or both of the pins shall have a negative (digging-in) angle of orientation to the disc surface within the range 0 < θ < tan−1 μ. Sufficient conditions for unstable motion are dependent on the magnitudes of the system parameters and may be obtained by giving unequal values to corresponding parameters on the two-pin systems. Distinct changes from a ‘quiet’ to a ‘noisy’ state are observed on an experimental system; the ‘noisy’ state regions having a good correlation with the instability regions shown theoretically. It is concluded that a ‘kinematic constraint’ or ‘geometrically induced’ class of instability exists theoretically which essentially describes the mechanism of squeal noise generation in disc-brakes.

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