Comprehensive wheel cylinder pressure estimation based on systematic hydraulic control unit model

Wheel cylinder pressure (WCP) is a crucial state for vehicles, directly influencing safety, comfort, and fuel economy. Serving as the foundation for sensor-less control and sensor redundancy, WCP estimation is a promising work for brake-by-wire systems (BBW). Nevertheless, WCP estimation is a challenging problem due to the nonlinear characteristics and intricate coupling within the hydraulic control unit (HCU). To enhance the performance of BBW, this paper proposes a comprehensive WCP estimation scheme based on the systematic HCU model. Component models including direct current (DC) motor pump and normally open valve (NOV) are established first. Considering the pulsation of the plunger pump, a modified nonlinear observer (MNO) is used to observe the angular speed of the DC motor. Inspired by the critical state, the linear pressure-drop relationship of NOV is analyzed and the NOV is simplified as a relief valve model expressed by algebraic equations. Dividing the HCU into the pump front part, pump rear part, and cylinder part, the systematic HCU model is then established, based on which, the comprehensive cause-based WCP estimation scheme is proposed. Next, simulations utilizing Amesim validate the angular speed estimator, while bench experiments prove the NOV model. Finally, vehicle tests under active and passive pressure regulating conditions are conducted. The results indicate the proposed scheme exhibits satisfactory performance while preserving computational efficiency.