Braking Pressure Tracking Control of a Pressure Sensor Unequipped Electro-Hydraulic Booster Based on a Nonlinear Observer

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Abstract
BBW (Brake-by-wire) can increase the vehicle safety performance due to high control accuracy and fast response speed. As one solution of BBW, the novel Integrated-electro-hydraulic brake system (I-EHB) is proposed, which consists of electro-hydraulic booster and hydraulic pressure control unit. The electro-hydraulic booster is activated by an electric motor that driving linear motion mechanism to directly produce the master cylinder pressure. With electro-hydraulic booster as an actuator, the hydraulic pressure control problem is a key issue. Most literatures deal with the pressure control issue based on the feedback pressure signal measured by pressure sensor. As far as the authors are aware, none of the proposed techniques takes into account the pressure sensor unequipped BBW. In this paper, there is no pressure feedback signal, but there is only position feedback signal measured by position sensor for control law design. This paper presents a cascade controller based on a nonlinear observer to track desired master cylinder pressure for a pressure sensor unequipped electro-hydraulic booster in the presence of both external disturbances and parameter uncertainties. The outer pressure tracking loop employs feedforward control law to increase the response speed with desired position of master cylinder piston rod as control output; the inner position control loop is designed using the sliding mode control algorithm. The stability of the overall closed-loop control system is proved on the basis upon Lyapunov theory and then the constraint zone of control parameter is calculated. Finally, the controller performance is verified through bench test. The results show that the proposed nonlinear cascade controller, together with the nonlinear observer, provides good tracking performance in the presence of parameter uncertainties and external disturbances.

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