A Unified Layer-by-Layer Progressive Framework for Sensorless Control of Brake-By-Wire Systems

Conventional control of Brake-by-Wire (BBW) systems, including electro-hydraulic brake(EHB) and electro-mechanical brake(EMB), relys on pressure sensors, the errors of which usually resulted inaccurate braking force tracking bringing a lot of safety hazards, e.g., wheel locking and slipping. To address challenges of accurate braking force control under the circumstance of the system nonliearities (such as friction) and uncertainties (such as stiffness characteristics) for a sensorless BBW system, this paper proposes a unified Layer-by-Layer Progressive (LLP) control framework to enable fast and precise brake control. The work has been conducted with three new contributions in the three cascaded stages within the control framework: in the coarse compensation stage, a load-adaptive LuGre friction model is proposed to handle modellable nonlinearities; in the fine compensation stage, an Adaptive Extended Disturbance Observer (AEDO) is developed to estimate and compensate for parameter uncertainties and external disturbances; and in the fine control stage, a cascaded nonlinear controller is designed to suppress unmodeled dynamics and residual disturbances. Through real-vehicle experiments, the proposed LLP method has been validated under both pulse and gradual braking conditions for BBW systems (include EHB and EMB systems). Under pulse braking conditions, the proposed method yields maximum response errors of 1.2bar for the EHB system and 6.3% for the EMB system. Under gradual braking conditions, the steady-state errors are 0.7bar for EHB and 1.74% for EMB. These results empirically confirm the effectiveness and robustness of the proposed method.