Optimal control of clamping force in EMB system based on nonlinear disturbance observer

Abstract

This paper investigates the optimization control of clamping force in electronic-mechanical braking (EMB) systems, which are characterized by significant nonlinearities. To address the impact of factors such as gaps, wear, friction, and disturbances on the clamping force output accuracy within the brake actuator, an improved sliding mode control strategy (ISMC) embedded with a nonlinear disturbance observer (NDO) is proposed. The control strategy targets the clamping force and comprehensively accounts for the nonlinear aspects of the EMB system by modeling them as composite disturbances. A cascaded NDO is used to predict and compensate for the total disturbances in real-time, thereby improving control precision. Furthermore, the sliding mode control rate is enhanced by replacing the traditional switching function with a saturation function to mitigate chattering effects. Simulation and experimental results demonstrate that the proposed EMB controller can rapidly and accurately align the output clamping force with the target value, without compromising system stability. It significantly suppresses chattering, adapts to road surfaces with varying friction coefficients, and improves response speed by 44.2%, while reducing overshoot by an average of 79.67% across various braking conditions. Additionally, the controller is capable of rapidly and accurately adjusting the target value in response to sudden wheel load changes, ensuring stability and reliability during the braking process and reducing the vehicle’s braking distance by an average of 7.61%. In long-duration braking tests, the disturbance compensation mechanism allows the controller to estimate and compensate for output errors in real-time, minimizing the risk of performance degradation due to prolonged braking. In conclusion, the EMB controller designed in this study significantly enhances the braking system’s response speed, stability, and safety under dynamic and complex conditions.