Active Online Estimation of the Electromechanical Brake Coulomb Friction

Electro-mechanical braking (EMB) system has emerged as a potential candidate that serves the brake-by-wire technology. Several mechanisms are used to transmit the clamp force, where each has efficiency losses due to static friction and viscous damping. Compensating these losses is essential for accurate responses such that meeting the performance goal and improving the stopping distance of the EMB. Mathematical and empirical models are used to estimate these losses so that clamp force is accurately estimated and controlled. However, none of these models are capable of addressing the part-to-part variation or predicting the impact of other noise factors on these losses such as operating temperature and degradation. The purpose of this work is to online estimate the EMB coulomb friction by introducing an external torque command over a period of time while observing the system’s response. This approach continuously measures the coulomb friction while the system is in normal operation which allows for dynamic compensation for these losses leading to more accurate clamp force controls for EMB. In this EMB system, after each brake release, the inner pad is retracted to a pre-defined position, where an air gap is controlled to prevent drag. The algorithm considers safety aspects, hence, it is designed to operate right after the home position is achieved and only while system is in clearance state avoiding the possibility of drag. The simulation and experimental results showed relatively accurate estimation for the coulomb friction of different operating temperatures and parts conditions.