| When the vehicle is in long-term continuous braking,high-strength braking or frequent braking,the temperature of friction brake disc or brake drum will increase greatly,which will reduce the friction coefficient between friction pairs and aggravate their wear,resulting in the dangerous heat recession phenomenon with partial or total loss of braking efficiency.Permanent magnet retarder is a kind of auxiliary braking device,which can effectively shunt the load of friction brake,improve the service life of friction brake and the safety performance of vehicle braking,and has the advantages of non-contact,small volume,light weight,low temperature rise of magnet,saving energy and environment protection.Therefore,it is particularly important to carry out structural innovation and design theory research on permanent magnet and friction integrated braking device.Permanent magnet and friction integrated braking device integrates permanent magnet braking function and friction braking function.It is expected to give full play to their respective advantages in the braking process.However,there are great differences in the structure principle and working characteristics between the permanent magnet brake and the friction brake,so it is necessary to carry out dynamic coordinated control between the permanent magnet brake and the friction brake.At the same time,the analysis of braking intention is one of the key problems in the integrated braking technology of permanent magnet and friction.Correctly and timely identifying the driver's braking intention and braking strength can optimize the braking force distribution strategy,shorten the brake action time,give full play to the advantages of permanent magnet braking,and improve the braking sense consistency and the braking performance of vehicle.Based on the above background,this paper focuses on the design theory and system coordination control of permanent magnet and friction integrated braking device.The main research contents of this paper are as follows:First,a novel design scheme of permanent magnet and friction integrated braking device was proposed.Based on the passenger car,a structure design scheme of permanent magnet and friction integrated braking device which can be mounted next to the wheel was proposed.The structure and working principle of permanent magnet and friction integrated braking device were described.According to the selected vehicle data,the braking torque and structural parameters of permanent magnet and friction integrated braking device were designed and calculated.The optimal design model of permanent magnet brake was constructed,and the structure parameters of permanent magnet brake were optimized based on particle swarm optimization algorithm.Through the closed magnetic circuit analysis and the three-dimensional magnetic field finite element analysis,the magnetic flux leakage coefficients of permanent magnet brake were calculated in the maximum braking torque state and the non-braking state,then the design parameters of prototype for permanent magnet and friction integrated braking device were determined.Second,the multi field coupling numerical simulation method of permanent magnet and friction integrated braking device was explored.The multi physical coupling mechanism of permanent magnet and friction integrated braking device was analyzed in detail.Aiming at the coupling problem of electric field,magnetic field and temperature field,the mathematical model of multi field coupling,the mathematical model of electromagnetic field and the mathematical model of temperature field for the permanent magnet and friction integrated braking device were established.The multi field coupling numerical simulation of permanent magnet brake was carried out by using indirect coupling analysis method and direct coupling analysis method,and the results were compared with the test results.Based on the direct coupling analysis method,the temperature changes of permanent magnet and friction integrated braking device were analyzed by numerical simulation under two working conditions of medium intensity braking and constant speed downhill braking.The results show that the permanent magnet brake can effectively improve the anti-heat decay performance of friction brake.Third,a method of brake intention recognition was explored based on the support vector machine(SVM).Based on the VBOX ? performance test system for vehicle,a vehicle test platform was built for the brake intention identification.A certain number of sample data were obtained through the braking test.Based on the basic theory of SVM,the SVM model of brake intention recognition was constructed with the characteristic parameters of braking pedal displacement,braking pedal force and braking deceleration.The RBF kernel function was selected as the kernel function of SVM,and the penalty factor C and the kernel function parameter ? were optimized based on the k-fold cross validation method and the grid search method.Based on the actual test data of vehicle,three typical braking conditions,namely gentle braking,conventional braking and emergency braking,were selected to test the SVM model via off-line,which verified the accuracy and effectiveness of SVM model.Fourth,the vehicle co-simulation model of permanent magnet and friction integrated braking device was constructed.From the perspective of dynamic collaborative work process and braking mode switching process,the collaborative mechanism of permanent magnet and friction integrated braking system was analyzed.The vehicle co-simulation model of permanent magnet and friction integrated braking system was built based on Car Sim and Simulink.The mathematical model of permanent magnet brake was established,and the control strategy of permanent magnet braking torque based on forward look-up table,reverse look-up table and stepper motor closed-loop control was designed.The mathematical model of EHB system was constructed,and a double closed-loop control strategy of wheel cylinder pressure based on the Smith predictive compensation control algorithm was proposed.The simulation results show the effectiveness of the proposed models and control strategies.Fifth,a dynamic coordinated control strategy of permanent magnet and friction integrated braking device was proposed.The anti-saturation PID closed-loop control was adopted to solve the problem of brake strength reverse deviation response hysteresis.Three typical brake force distribution curves of integrated braking system were defined,and the braking force distribution strategies of the front and rear axles of vehicle and the braking force distribution strategies of permanent magnet brake and friction brake were formulated on the basis of considering the constraints of ECE regulations.Aiming at the problem of brake mode switching smoothness,a joint coordinated control strategy of U-shaped transition coordinated control and dynamic compensation coordinated control was designed.Two quantitative evaluation indexes of permanent magnet braking proportion coefficient and braking impact degree were adopted,and the proposed braking force distribution strategy and dynamic coordinated control strategy were verified and analyzed by simulation.Finally,the related experimental research on the permanent magnet and friction integrated braking device was carried out.The braking characteristic test platform and coordination control test platform of permanent magnet and friction integrated braking system were built.The experimental research on braking characteristics and coordinated control of permanent magnet and friction integrated braking device was carried out,which verified the practical effectiveness of the proposed coordination control strategy for permanent magnet and friction integrated braking device. |
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