A Nonlinear Wheel Cylinder Pressure Controller Based on CESO for Integrated Braking System

Brake-by-wire system (BBW) is quite important for the development of high-level autonomous vehicle which requires fully decoupled structure and superior braking performance. Integrated braking system (IBS) is a state-of-the-art technology of hydraulic BBW, consisting of mechanical, electrical, and hydraulic subsystems. However, the inherent nonlinear characteristics of hydraulic transmission dynamics cause delays and fluctuations in wheel cylinder pressure (WCP), which significantly impact brake performance and passenger comfort. Furthermore, the coupling of the subsystems within the IBS system amplifies the intricacies and challenges associated with controller design. This paper proposes a WCP control architecture to shorten the response time of WCP, suppress pressure fluctuation, and ensure stability. Further, a combined extended state observer (CESO) is designed to estimate unmeasurable states and total disturbance which includes model mismatch, uncertainties, and friction. Additionally, a WCP nonlinear controller (WNC) based on the backstepping method is designed and proved stable theoretically. The response time has been shortened 30$\mathbf{\%}$ approximately and the tracking precision has been improved 50$\mathbf{\%}$ approximately. Simulation results demonstrate that the proposed control architecture accurately estimates states, suppresses disturbances, meanwhile improves braking performance. The effectiveness and practical application of this control architecture are further validated through experiments on a test bench.