Research On Stability Control For In-wheel Motor Electric Vehicle

The increasingly prominent energy crisis and environmental pollution determine that electric vehicles are the future development direction of the automotive industry.Compared with centralized drive EV,hub motor EV has the advantages of higher transmission efficiency and better dynamic controllability,and is an ideal platform for developing high-performance automobiles.However,due to the elimination of traditional mechanical differential in hub motor electric vehicles,the safety and controllability of turning become the key factors affecting its application,so it is necessary to conduct electronic differential control research on hub motor electric vehicles.For a long time,the safety of automobile has been an important topic with the development of automobile.In particular,the hub motor electric vehicle has the advantage of independently adjustable driving torque of the wheel,which can provide more implementation schemes for direct yaw moment control,and is an ideal platform to study direct yaw moment control.Therefore,it is necessary to study the direct yaw torque control of hub motors and electric vehicles.The main research contents of this paper are as follows:(1)In the MATLAB/Simulink built eight degrees of freedom vehicle model,in order to ensure the model precision,based on the Carsim and MATLAB/Simulink to build electric car wheel motor model,and in a variety of working conditions of eight degrees of freedom vehicle model verification,validation results show that the established eight degrees of freedom vehicle model has high accuracy,can be used in the wheel hub motor in electric vehicle stability control system.(2)Based on the ackerman steering model,the target speed of each driving wheel when the hub motor vehicle turns is calculated,the motor model in the d-q coordinate system is established,and the speed ring is designed based on the sliding mode control,so that the actual speed of the hub motor can follow the target speed calculated by the ackerman steering model.It is verified under low speed large turn and medium speed sinusoidal turn.The simulation results show that the electronic differential control designed in this paper can meet the differential requirements of the inner and outer wheels when driving around the corner,effectively inhibit the tire sliding,and improve the vehicle maneuverability.(3)The stability criterion is designed based on the center of mass lateral deflection Angle-center of mass lateral deflection Angle velocity(d?-?)phase plane,the stability domain and the instability domain of d?-? phase plane are divided by two boundary linearequations,and the influence of vehicle speed and road adhesion coefficient on the stability domain of d?-? phase plane is analyzed.A map of the slope and intercept of the line on the boundary of the stability domain is established,and the parameters of the stability domain are obtained by looking up the two-dimensional table.The simulation results show that the stability criterion is reasonable and effective.Freedom model of the vehicle,and the influence of vehicle speed and road adhesion coefficient on the stability domain of d?-?phase plane is analyzed.A map of the slope and intercept of the boundary line in the stability domain is established through a large number of simulations.The parameters of the stability domain are determined by the two-dimensional table lookup method.The homocentric side deflection Angle and the velocity of the homocentric side deflection Angle are brought into the stability domain inequality to judge whether the automobile is in the stability domain,that is,whether the automobile is unstable.The simulation results show that the stability criterion is reasonable and effective.(4)To solve the problem that it is difficult to measure the center of mass sideway Angle directly,an algorithm for estimating the center of mass sideway Angle based on extended kalman filter is designed.The simulation results show that: when the vehicle is stable and unstable,the estimation of the side deflection Angle of the center of mass based on the extended kalman filter algorithm designed in this paper can follow the output value of Carsim and meet the requirements of the stability control system.(5)Take advantage of the hierarchical structure of wheel hub motor electric cars direct yawing moment control research,based on the linear quadratic optimal control theory to design the upper controller used for decision making to cars drive stable required additional yawing moment,and objective function is minimum sum of squares to the wheel load rate of the lower level controller based on quadratic programming design,the specific assigned to each additional yawing moment wheels.Move in double line compared to the average torque distribution under the condition of the stability of the control effect,the simulation results show that the torque distribution method based on linear quadratic programming control effect is better than that of the average torque distribution way,with the current yawing moment control for each wheel load rate minimum sum of squares,to leave more space adjustable and tire force is advantageous to the vehicle stability.