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In order to reduce brake squeal noise shims are really common proposition, however, to define whether a shim is good or not to fix a specific problem, only two things are considered: damping and the noise results obtained in dynamometers tests. In this paper it is presented the importance of the contact stiffness between the baking plate and the piston or caliper on the squeal noise generation and how the shim contributes improve this factor. A method to measure this property is presented as well the results obtained using this method, correlating the contact stiffness of a non-painted, painted and shim applied backing plate. In the end, we are showing how the brake pressure may influence the shim contact stiffness and consequently the noise generation.

This paper addresses the effect of environmental humidity and temperature on friction level and squeal noise propensity of friction materials when measured in dynamometers at laboratory controlled test conditions. The present work investigates the influence of the environment conditions on the result of noise and friction evaluation of friction material for disc brakes. The relationship among environmental conditions and squeal noise propensity has been studied before by a few authors [1] and is still an open issue when concerns to standard evaluation performed at laboratory controlled conditions. The effect of two main environmental properties for dynamometer testing, cooling air temperature (between 10 and 30°C) and humidity (between 25 to 85%), on friction level and noise were evaluated using a front disc brake. A test matrix, based on SAE J2521, was developed to adequately evaluate these two variables separately into a NVH environmental chamber equipped dynamometer.

This work describes an approach to overcome squeal noise problems by increasing damping on brake pads using special designed underlayer materials. Experiments were conducted to characterize the damping properties of current and new underlayer materials and its effect on the total damping of the pads. Dynamometer tests were performed to verify the noise performance behavior of pads equipped with the different types of underlayers and physical tests were made to characterize its properties. By the end a discussion about the results is conducted to relate the physical properties of the designed materials and its results on dynamometer tests.