Pressure Control Strategy for Brake by Wire Systems Based on Hierarchical Structure
As the key actuator of an autonomous vehicle,the safety and response accuracy of the brake by wire(BBW)system directly affects the safety of the vehicle.To meet its safety requirements,the BBW system usually has two sets of independent pressure supply units to meet the pressure building capacity under single point of failure.The plunger pump type pressure supply unit has the characteristics of simple structure and low cost,so it is widely used BBW system.To ensure the stability and accuracy of pressure control under the influence of temperature disturbance in this kind of pressure supply unit,a hierarchical pressure control strategy is proposed with the consideration of the temperature estimation of the coil.Firstly,the thermal model and the hydraulic model of the pressure supply unit are developed.Secondly,a recursive least squares(RLS)method and an open-loop method are used to estimate the coil temperature when pressure states of system is observable and non-observable respectively.Finally,a hierarchical pressure control strategy based on a sliding mode controller(SMC)is designed.The bench test results show that the estimation error of the proposed temperature estimator is less than 8 ℃ under different test conditions,and the introduction of the temperature estimator under the same control strategy will effectively improve the pressure control accuracy,and the proposed hierarchical pressure control strategy can achieve pressure following at sinusoidal,pulsed and delta target pressures.
thermal modelhydraulic modelsliding mode controllerrecursive least squaresplunger pump
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