Experimental Investigation of Self-Excited Squeal

The squeal noise generated during the dry friction between a friction pad and a rotating disc, changes its inherent form (i.e. its sound pressure level and its frequency) with the normal load and sliding speed. The present study is based on the establishement of squeal regime for a relatively long time period (from ½ to 5 hours in a continuous manner) and then to accomplish the analysis of generated signals. The different properties existing in such signals are thoroughly investigated using an experimental setup simulating the disc brake assembly. The results indicate that sound pressure level of squeal noise is greatly reduced by increasing the system rigidity in normal direction of contact. Moreover, inaudible squeal is investigated at great values of system rigidity. The effect of contact stiffness on the establishement of squeal regime at a particular frequency, is observed. A simple technic is proposed to estimate the dynamic contact stiffness value. It is also found that normal load has a significant effect on the sound pressure level of the peaks in the sound spectrum and the frequencies of these peaks.