Effect of Friction Torque on Electromechanical Brake System Dynamics

Actuator and roller screw mechanism are key components of electromechanical brake (EMB) system in automotive and aerospace industry. The inverted planetary roller screw mechanism (IPRSM) is particularly competitive due to its high load-carrying capacity and small assembly size. For such systems, friction characteristic and friction torque generated from rolling/sliding contacts can be an important factor that affects the dynamic performance as well as vibration behavior. This paper investigates the modeling and simulation of the EMB system in early design stage with special attention to friction torque modelling of IPRSM. Firstly, a step-by-step system model development is established, which includes the controller, servo motor, planetary gear train and roller screw mechanism to describe the dynamic behavior of the EMB system. Secondly, detailed analytical formulations are established to calculate the friction torque in the time domain for evaluating its influence on the EMB displacement dynamic response. Finally, the dynamic performance for the EMB system is simulated under various driving conditions. Simulation results show that the friction torque has a significant influence on system brake performance. Larger friction torque tends to increase the vibration level. A force control strategy is proposed to decrease the oscillatory movement caused by the friction.