Characteristic Test And Nonlinear Control Of Vehicle Electro-Hydraulic Braking System

Environmental pollution and energy problems forced traditional vehicles to transform to new energy vehicles,which put forward higher requirements for brake system:(1)new energy vehicles cannot provide enough power because of the cancelling of the usage of the engine,which may be solved by providing a new power equipment or finding a new way;(2)new energy vehicles should have braking energy recovery function;(3)new energy vehicles use a variety of composite braking mode,whose decoupling problem between master cylinder and wheel cylinder need to be solved.Electro-hydraulic braking system adapts to the development of new energy vehicles: it uses electricity as the brake power source,which solves the power problem as well as the decoupling problem.Meanwhile the energy recovery device could be easily integrated into the system.However,electro-hydraulic braking system is a mechanical,electric and hydraulic hybrid system.In order to accurately control wheel cylinder pressure of the system,it is necessary to consider the nonlinear characteristics of the system.In the existing control methods,the sliding mode control and the nonlinear backstepping method are model based control method,which can solve nonlinear problems well.Therefore,in this paper,the characteristics of the electro-hydraulic braking system are studied,and the mathematical model of the electro-hydraulic braking system is established,and then the nonlinear control algorithm is designed.The main contents of this paper include:(1)The hardware-in-loop test of the characteristics of the electro-hydraulic braking system.First of all,an electronic hydraulic brake system hardware-in-loop test bench need to be built,which includes three parts: electro-hydraulic braking system,dSPACE real-time simulation platform and hydraulic test module.Then the characteristics of electro-hydraulic braking system is tested.(2)Modeling of electro-hydraulic braking system.The brake-wheel integrated model is built using power bond graph method.This integrated model contains brake pipes,pressure regulating valves,brake and wheel model,and it takes the volumetric compliance,resistance,inductance effect of the brake pipes and the resistance effect of the solenoid valve as well as compressible characteristics of brake fluid into account.(3)Design and analysis of the nonlinear control strategy.Two methods have been taken in the design of nonlinear control strategy: the sliding mode control and the nonlinear backstepping control.Sliding mode control strategy is based on the purpose of the integrated control of the chassis system,it regards the braking system and the wheel as a whole,and its feasibility is verified by the co-simulation of MATLAB/Simulink and AMESim.The nonlinear backstepping control strategy is based on real-time purpose,it regards the braking system and the wheel as two independent parts and design corresponding control strategy for them respectively.Finally,the off-line simulation and hardware-in-loop experiment are implemented to verify the effectiveness of controller.The results of off-line simulation and hardware-in-loop experiment prove that the designed sliding mode control strategy and nonlinear backstepping control strategy can precisely control the slip ratio of the wheel and the brake wheel cylinder pressure,ensure the safety of the vehicle.