| Safety, energy saving and environmental protection are the direction of the vehicledevelopment and eternal theme,which is particularly important for today’s world in whichthere are frequent traffic accidents,energy crisis and deteriorating environment.Especiallyin recent years, forced by the pressure of the energy saving and environmental protection,the various forms of electric vehicles are becoming the focus of research and developmentof the global automotive industry.The four-wheel independent drive electric vehicles basedon in-wheel motor is the more promising one.The state of motion of each wheel for thefour-wheel independent drive electric vehicle based on in-wheel motor are independentlyand there are no rigid mechanical connections between them which improve thetransmission efficiency greatly, simplify the car structure, reduce the weight and help toincrease the driving distance.So the in-wheel motor is called the final drive form of theelectric vehicles.The four-wheel drive torque is independently controllable for four-wheelindependent drive in-wheel motor electric vehicle and it is easy to make integrated controlwith steer-by-wire system and other X-by-wire systems using X-by-wire technology.Thereis more controllable degree of freedom compared with traditional internal combustionengine vehicles for the four-wheel independent drive electric vehicle.It is the ideal carrierfor studying the new generation of vehicle control technology and exploring the optimalvehicle dynamics performance.Summarize the domestic and foreign correlation research results, and make use of theadvantages of four-wheel independent drive and integrated control with the brake-by-wiresystem, steer-by-wire and other X-by-wire systems, a series of study work is done as forsimulation platform developed for the electric, acceleration slip regulation control based onfuzzy theory road identification, drive and steer integrated control algorithm, the energy saving control based on the motor efficiency map and the real vehicle experiments forintegrated control algorithm.The study is based on the National863Project(2012AA110904)“Electric vehicle chassis dynamics control system development” andNational Natural Science Fund Project (50775096)“Drive-by-wire chassis control methodsand key technology research”, the National Natural Science Fund Project Youth ScienceFund (51105165)“Research steer-by-wire system joystick and bidirectional controlmethod”.The main contents are as follows:(1)Simulation platform developed for electric vehicleFor the requirement of the control algorithm validation, establish the kinetic modelcontaining motor model by MATLAB/Simulink software with modular thinking.The modelcan basically reflect the four independent in-wheel motor electric vehicle dynamiccharacteristics.The model included15degrees of freedom: six degrees of freedom of thevehicle body, eight degrees of freedom of the rotation and the vertical jump of the fourwheels, one front wheel angle.The model was verified by commercial softwareCarSim.According to the study contents,determine the vehicle control architecture,whichwas easy to build the control algorithm module. The electric vehicle simulation platformcan achieve the study of simulation and control in a variety of operating conditions.(2)Study on acceleration slip regulation control based on fuzzy theory roadidentificationCombine with the characteristics of four-wheel drive torque independently andmeasuring speed and torque easily, the vehicle velocity estimation algorithm was designedbased on the Unscented Kalman Filter (UKF) theory and estimate electric vehiclelongitudinal speed, lateral speed and sideslip angle accurately. The road adhesioncoefficient was estimated proactively when the electric vehicle drive wheels drive in thesmall slip rate and the small adhesion coefficient region road and make the ASR system formore precise control.The methods were verified by the simulation in the docking road andsplit road.(3) Study on drive and steer integrated control Make use of the advantages of integrated control with the steer-by-wire system for theelectric vehicle with four-wheel independent drive in-wheel motors, the active frontsteering and the active drive yaw control integrated control algorithm that drive and steerintegrated control algorithm based on model predictive control theory wasstudied.Determine the hierarchical control structure, design the model predictive controlintegrated controller, study the rules driving force and the quadratic programming drivingforce distribution method which makes the the total tire load rate minimum.The integratedcontrol algorithm was verified by simulation experiments.The simulation results showedthat the integrated control algorithm enables electric vehicles track the expectationeffectively and enhance the vehicle stability and active safety in extreme conditions.(4) Study on the energy saving control based on the motor efficiency mapElectric vehicle mainly work in urban conditions. Because of the frequent accelerationand deceleration, the vehicle speed changes in a large range and the motors’driving/braking efficiency varies a lot.Combine with the character of the four-wheelindependent drive independently, energy saving control methods including drive energyconservation and regenerative braking were studied based on the efficiency map of themotor. Establish the energy saving target function and constraints, online real-timeoptimize the four-wheel drive torque, enhance the drive efficiency in drive energy saving.Based on the ideal braking force distribution theory and ECE regulations, parallelregenerative braking control method was studied to suit for four-wheel independent drivein-wheel motor electric vehicle. The braking intensity when the front axle separateregenerative braking was determined reasonably through simulation analysis of NEDC,UDDS and J1015typical urban cycle conditions and improve electric vehicle brakingenergy recovery rate in the low speed and low braking torque. Finally, the energy savingcontrol methods were verified in the NEDC, UDDS and J1015urban conditions’ simulationexperiments.The simulation results showed that energy-saving control methods improvethe energy efficiency and the energy saving effect was obvious.(5) Real vehicle experiment for drive and steer integrated control algorithm The straight line acceleration test, the steering function test and four-wheelindependent drive test were used to verify the functions and reliability of the electricvehicle. According to the conditions of the real vehicle, the step steering wheel angle inputand the sinusoidal steering wheel angle input experiments were used to validate theeffectiveness of the integrated control algorithm.Through the above study, the paper innovations are in the following aspects:(1)For the ASR control problem of the electric vehicle with the four-wheelindependent in-wheel motors, combine with the characteristics of four-wheel drive torqueindependently and measuring speed and torque easily, the acceleration slip regulationcontrol method based on fuzzy theory road identification was put forward. The roadadhesion coefficient was estimated proactively when the electric vehicle drive wheels drivein the small slip rate, the small adhesion coefficient region road,which makes the ASRsystem more precise control and make full use of the road adhesion coefficient to improvevehicle power performance and stability.(2)For the problem of four-wheel independent drive in-wheel motor electric vehicleintegrated with steer-by-wire system, the active drive yaw control and the active frontsteering integrated control algorithm that drive and steer integrated control algorithm basedon model predictive control theory was designed. Determine the hierarchical controlstructure, design the model predictive control integrated controller based on the modelpredictive control theory which doesn’t depend on the precise mathematics model and canrealize the closed loop correction feedback. The rules driving force method and quadraticprogramming driving force distribution method which makes the the total tire load rateminimum were studied.The integrated control algorithm can effectively improve thevehicle stability and active safety of the electric vehicle in extreme conditions.(3)For the problem energy saving control in urban conditions of t the electric vehiclewith the four-wheel independent in-wheel motors, the energy saving control method basedon the motor efficiency map driving/braking was put forward.Achieve drive energy savingcontrol by optimizing the driving moment of front and rear wheels and improve the drive efficiency.According to the ideal braking force distribution theory and ECE regulations,parallel regenerative braking control method was studied to suit for four-wheel independentdrive in-wheel motors electric vehicle based on the motor efficiency map.The brakingintensity when the front axle separate regenerative braking was determined reasonablythrough typical urban cycle conditions simulation and improve electric vehicle brakingenergy recovery rate in the low-speed low and low braking torque.The energy-savingcontrol method was simple and the energy saving effect was obvious. |
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