Pressure Estimation Algorithms in Decoupled Electro-Hydraulic Brake System
Considering the Friction and Pressure-Position Relationship 2019-01-0438
The electro-hydraulic brake (EHB) system is based on a hydraulic system, which is directly derived and exploited from the most spread vehicle brake architecture. The motor-type EHB adopts electric motor and reduction gear instead of piston pump, high-pressure accumulator and several valves. The motor-type EHB has started the mass production. Most of the pressure control solutions are based on standard pressure-based feedback control, requiring a pressure signal. Although the pressure sensor can produce the pressure feedback signal, it will increase cost and enlarge installation space. The rotation angle of electric motor is available by the built-in sensor, so the pressure can be estimated by using the rotation angle. The pressure control is influenced intensely by the typical nonlinearities (i.e. friction, pressure-position relationship) and uncertainties (i.e. brake pads wear, temperature effect). Faced with the issues, this work investigates several pressure estimation approaches of motor-type EHB. The critical characteristics of the motor-type EHB are tested and analyzed through the experimental platform. The mathematical model of the motor-type EHB is built. The Gauss exponential model is selected to describe the friction phenomenon, and the friction force calculated by the Gauss model can match the real friction force with an accuracy of approximate 90%. The pressure-position relationship is fitted by a quadratic polynomial, which includes several time-varying parameters. The afore-mentioned mathematical model is combined into a control-oriented model. Based on the control-oriented model, the nonlinear interconnected observation approach and the recursive least squares approach with forgetting factor (RFF) are utilized to design the pressure estimator, respectively. The comparison and analysis of the proposed estimators have been conducted via simulations. Most importantly, this study realized a pressure estimation without add-in sensors, which makes EHB realizable to become the actuator for automobile active safety systems, giving a promising way to achieve far better performance.