Adaptive Dual-loop Pressure Control for an Integrated Electro-hydraulic Brake System Considering Uncertain Nonlinear Characteristics

Integrated electro-hydraulic brake system (IEHB) has become one of the fundamental chassis subsystems of intelligent electric vehicles (IEVs), whose active braking performance has a direct and important impact on the performance and safety of IEVs. To improve the accuracy and robustness of active braking, this study proposes an adaptive dual-loop control strategy, which comprehensively and systematically solves the IEHB uncertain nonlinear characteristics including parameter uncertainties of the mechanism friction and the nonlinear variation of hydraulic characteristics. First, a pressure-based continuous friction model is formulated for characterizing mechanism friction. An equivalent linear model for the IEHB hydraulic characteristics is constructed in the I/O sense by analyzing the nonlinear hydraulic dynamics using a dynamic linearization (DL) method. Next, a pressure-loop adaptive control method called DL-based non-smooth disturbance resistance control (DL-NSDRC) is proposed, which flexibly adapts to nonlinearly varying hydraulics while dealing with unexpected disturbances. For the servo loop, an adaptive control method called immersion and invariance-based backstepping adaptive control (I&I-BAC) is proposed, which is robust to parameter uncertainties. Finally, hardware-in-the-loop experiments are conducted. The results show that the proposed method provides at least 50% active braking control improvement compared to the baseline. This will further enhance the performance and safety of IEVs.