| In this thesis,the physical and mathematical model of the braking system is established,the fuzzy PID control method is determined,the fuzzy PID controller is designed and the simulation model of the braking system is established.The simulation is used to verify whether the fuzzy PID brake control system meets the requirements of accurate pressure building and fast braking,as well as the effectiveness of ABS.The research contents of this thesis are:(1)Physical and mathematical model of the hydraulic braking system.According to the structural characteristics and working principle of the actuator of the linear hydraulic brake system,the mathematical and physical models of each component of the actuator are established.This includes the accumulator model,the inlet valve model,the brake wheel cylinder model,the outlet valve model and the eight-degree-of-freedom model of the whole vehicle.(2)Determination of fuzzy PID control method.The principles and applications of PID control and fuzzy control were studied,and by comparing the advantages and disadvantages of both,fuzzy PID was determined to carry out the control.The deviation and deviation rate of the input braking force and the increment of the three parameters of the output PID of the controller were fuzzified,the affiliation function of the linguistic variables,the thesis domain and the triangular distribution method were determined,and the Mamdani algorithm was used for fuzzy reasoning.The fuzzy rules were also established based on the influence of the three PID parameters on the control system,and finally the output was determined to be anti-fuzzy using the center of gravity method.(3)Fuzzy PID controller design and joint simulation modeling.AMESim and MATLAB software are briefly introduced.Using fuzzy toolbox to edit membership function,universe and fuzzy rules,the designed fuzzy controller is introduced into the workspace,and the fuzzy controller is combined with the PID controller in Simulink.A fuzzy PID controller is established to control the duty cycle of the solenoid valve.The models of wheel cylinders and inlet and outlet valves built in AMESim are integrated with the control part to form a joint simulation model of boosting,depressurization and pressure retention.(4)Simulation verification of the braking system.Run the simulation and let the vehicle perform braking tests at different speeds on high,medium and low adhesion roads respectively.By comparing the vehicle speed,braking distance and braking force curves of the fuzzy PID and PID-controlled brakes,it was found that the fuzzy PID-controlled brakes had better braking effect and more accurate control of the braking force.The modeling and simulation of the anti-lock system,the control method with the target of slip rate is developed,and Stateflow is used to make the logic judgment,and send the increment,decrement and pressure-holding signals to the braking system in AMESim to execute,and control the braking force output to the single-wheel vehicle model to perform the real-time adjustment of slip rate.Running the joint anti-lock simulation model,the vehicle is tested at 25m/s on high,medium and low adhesion roads.From the simulation results,it can be seen that the wheel slip rate can be maintained at the optimal slip rate,and it can play a good role in anti-lock.After simulation analysis and comparison,it is found that the fuzzy PID-controlled brake of this thesis has better braking effect and can achieve precise control of braking pressure and fast braking.The anti-lock system also plays the role of anti-lock well and can keep the slip rate working at the optimal slip rate. |
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