Research and/or Engineering Questions/Objective The rising popularity of EVs has led to a resurgence of interest in drum brakes. With a larger share of the braking load being taken up by the motor, the drawbacks of the drums having less braking power is negated. Drum brakes also benefit from less complex mechanical design, have no residual brake drag, and the enclosed design is less susceptible to corrosion and debris emission. For the commercial EVs, the elimination of engine noise makes brake noise a major contributor to vehicle noise. Although considerable effort has been directed at determining disc brake friction material engineering properties used for NVH simulations, much less data is available for drum brakes. Methodology With the renewed interest in drum brakes, there is an increased need for property data for NVH simulations to optimize noise performance. Similar to disc brakes, the modeling of drum brake performance requires a complete set of friction material engineering properties determined over the preloads and temperatures encountered in brake applications. Ultrasonic methods have been successfully used to measure both the uniformity and mechanical properties of disc brake friction materials (SAEJ2725). The method is based on the precise measurement of speed of both longitudinal and shear waves propagating in various pad directions. The curvature of drum brakes gives rise to several challenges which need to be addressed to ensure the accuracy and precision of the measurements. This is particularly an issue for the measurement of preload sensitivity and the out-of-plane Young’s and shear modulus. The curvature of the pad requires additional sample preparation sets and acquisition methods to mitigate the influence of the curvature on the test results. Results Results are presented for three different drum brake formulations and platforms. The measurement approach and data analysis parallels that used for the elastic property measurements of disc pad friction materials, SAEJ2725. A complete set of elastic properties and engineer properties are measured on all formulations over the temperature range from 20°C to 320°C and preloads from 5 bar to 30 bar. This drum brake friction material elastic properties will be compared with that typically encountered in the analysis of friction material taken from disc pads. The sample preparation techniques, data collection methods, and analysis procedures used to mitigate the influence of curvature will be discussed. Several mitigation methods are evaluated and compared including curvature matching, sensor aperture reduction, and enhanced sample preparation. Results will be presented quantifying the errors introduced by component curvature. Limitations of this study In this work, measurements are made using test parts cut from drum segments prior to attachment to the metal shoe. For bonded segments additional sample preparation would be needed. The method described in this work is a destructive test. More work is needed to determine which engineering properties can be determined non-destructively. Novelty and Innovation This work is the first paper to demonstrate the use of ultrasonic methods to determine the complete set of elastic properties on drum brake friction materials. Conclusions: In this work, test methods suitable for measuring mechanical properties of drum brake segments are demonstrated. The influence of curvature on the measurement variability is assessed and optimal methods are formulated to mitigate the influence of curvature.
Dr. Donald Yuhas, President, Industrial Measurement Systems Inc.; Ms. Carol Vorres, Applications Engineer, Industrial Measurement Sysyems Inc.; Ms. Loretta Oleksak, Product Engineer, Industrial Measurement Systems Inc.; Mr. Vijay Subramanian, Product Engineer, Alroko GmbH & Co KG; Mr. Saikiran Divakaruni, Senior Product Engineer, ZF Friedrichshafen AG