Surface modification of brake discs to reduce squeal problems

Abstract

Noise and squeal from brakes is a problem in the automotive industry and large efforts are made to reduce the squeal tendencies. The approach taken is mainly to improve the design of the caliper, to fine-tune the brake pad material and finally to trim by introducing shims on the backside of the pads. Despite these efforts still no general solutions exist. To advance the situation, a deeper understanding of the actual source of excitation of the sound in the friction interface is needed. Earlier investigations by the present authors have made it clear that grit blasting of a disc lowers the coefficient of friction between disc and pad and may have a strong influence on the squeal propensity. Depending on the pattern of the grit blasted area the noise can be either promoted or reduced. In the present investigation, a spiral shaped modification of the brake disc surface topography has been tested with respect to the noise reduction properties. All tests have been made in a brake test equipment consisting of a complete front wheel corner of a car. The treatment has resulted in a significant reduction of the generation of noise. Unfortunately, due to wear the silencing effect has a limited life-time, here around 3000 long brakings.