The Effect of Environmental Humidity and Temperature on Friction Level and Squeal Noise Propensity for Disc Brake Friction Materials

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. All experiments were performed with two different class friction materials, NAO and SEMI-MET. The final results show that friction level of NAO and SEMI-MET materials can be influenced by cooling air temperature and/or humidity in more than 10%, and that squeal noise propensity can be changed by different setups of cooling air temperature and humidity.