Research On Stability Control Of Four Wheel Hub Motor Drive Vehicle

The history of traditional fuel vehicles has been over 120 years.With the explosive growth of number of vehicles in recent decades,the automobile industry is facing three urgent problems to be solved: firstly,over-consumption of non-renewable fossil fuels;then,emissions of automobile exhaust the contribution rate to air pollution is increasing.Lastly,the number of casualties caused by traffic accidents is quite huge.The development of electric vehicle technology provides a solution to the above problems.Due to the diversity of sources of electric energy,the development of electric vehicles has become the main solution to fuel shortage and air pollution of vehicle.Therefore,the development of electric vehicle stability control technology very necessary and urgent.The driving modes of electric vehicles are divided into two types: centralized driving and distributed driving.In this paper,the distributed driving vehicle stability control is selected as the research direction.The wheel drive motor is used as the power source in the distributed drive vehicle and the performance of the motor has an impact on the dynamic characteristics of the vehicle.The motor is taken as the research object of this paper.The BLDC model is derived and modeled based on Simulink,Based on the motor model and Carsim software to build Carsim-Simulink co-simulation platform.After reading a great deal of literature about vehicle stability control both at home and abroad,the vehicle dynamics modeling,tire model derivation,the building of vehicle state observer and the establishment of vehicle stability controller and other related work are carried out.The subject of specific work to be done as follows:1.The advantages and disadvantages of several common motors are analyzed and choose the BLDC motor as the research object.The theoretical model of the motor is deduced.The modular motor control model is established by Simulink and the motor simulation is carried out.Finally,based on the motor model,build Carsim-Simulink electric vehicle dynamics co-simulation platform.2.Vehicle dynamics and tire dynamics research.Seven degrees of freedom vehicle model and two degrees of freedom vehicle model are set up respectively.The simulation data of the two models are represent the actual and ideal state of the vehicle.The pure longitudinal slip and the purely lateral brush model are deduced under the uniform vertical load,and the simulation accuracy of the above model is verified.3.Vehicle speed estimation.Several common observer methods are analyzed and the sliding model observer is chosen to observe the state of the vehicle.The observer,variable structure and sliding mode observation theory are expatiated systematically.Finally,the vehicle state observer is established based on the sliding model variable structure theory to estimate the longitudinal and lateral speed of the vehicle.4.Ground maximum friction coefficient identification and tire stiffness identification.Based on the pure longitudinal sliding brush model,the formula for identifying the maximum friction coefficient of the road under different tire slip conditions is deduced,and the slip rate threshold method is introduced to complete the road friction coefficient identification module.Based on the known data,the longitudinal and lateral distribution stiffness of the tire is identified to improve the accuracy of the model.5 vehicle stability control strategy development.According to the vehicle stability control target design vehicle stability controller,the controller is divided into two layers.The upper controller based on the demand of vehicle center of mass and yaw rate design sliding mode control to achieve the actual state of the vehicle to follow the ideal state,and eventually the target difference into the vehicle yaw moment;lower controller Taking the yawing moment of the vehicle as the input,the control strategy was developed considering the attachment limit of the tire and the working efficiency of the vehicle to realize the differential control of the four vehicles and to distribute the required yaw moment to each wheel.