Adaptive Dual-Loop Pressure Control for an Integrated Electro-Hydraulic Brake System Considering Uncertain Nonlinear Characteristics

Integrated electro-hydraulic brake (IEHB) system 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 ( $\text{I}\&\text{I}$ -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.

I. Introduction

Intelligent electric vehicles (IEVs) have become the future direction of automotive development by improving energy economy and driving safety [1], [2], [3], [4]. Many functions have been designed to enhance the performance of IEVs, such as brake energy recovery [5] and advanced driver assistance systems [6]. All of the above functions require a braking system with active braking capability that responds positively to non-driver braking requests [7]. Therefore, the accuracy and robustness of active braking have a direct and significant impact on the IEV driving experience and safety.