Research On Steering Stability Control For 8×8 In-wheel Motor Drive Vehicle

Steering performance plays core role in vehicle safety.In the four-wheeled passenger car,electronic stability control systems are capable of ensuring the vehicle’s steering stability.However,for 8×8 in-wheel motor drive vehicles,the corresponding control system is not yet mature due to changes in the driving form as well as vehicle chassis structure.Thus,this article mainly studies steering stability control strategies and optimization methods for this type of vehicles.In this paper,the dynamics of each sub-system related to vehicle steering performance is analyzed,and a twenty-three degrees of freedom dynamic model of the vehicle is established.It contains six degrees of freedom for vehicle space motion,and vertical displacement and rotation of each wheel,and steering input.By analyzing the steering stability perforrmance of the vehicle,the longitudinal vehicle speed,yaw rate,and slip angle are selected as the reference state variables for vehicle steering stability.Through the analysis of the driver input,the reference state of the vehicle is obtained by combining the two-degreeof-freedom linearization model of the vehicle.On this basis,the vehicle’s steering stability controller is designed with a modular hierarchical control structure.The stability control of the vehicle during steering is achieved by optimizing the distribution of the longitudinal force and the lateral force of the tire.At a deeper level,the control system includes the movement state tracking controller and torque distribution controller.For the characteristics of overdrive,non-linear,and increased failure probability of actuators in 8×8 in-wheel motor drive vehicle,Sliding Mode Control is used to construct a vehicle motion state tracking controller.According to the difference between the current motion state of the vehicle and the reference state,the desired forces for the vehicle are solved.Torque distribution controller is constructed based on friction circle constraints and energysaving optimization conditions,and the generalized torques are distributed to in-wheel motors and other actuators.For the failure of the actuator,the function of the control system is reconstructed by constraining the range of its output during torque distribution.Aiming at the coupling characteristics of tire longitudinal force and lateral force,this paper proposes a decoupling method based on the “friction circle guide angle”,which can quickly and accurately determine the value range of the tire longitudinal force and lateral force.Aiming at the energy loss caused by tire and road wear during vehicle steering,this paper proposes an energy-saving optimization method based on “tire slip energy loss rate”,which can effectively reduce the wear energy loss between vehicles on the road surface.Finally,a simulation model is built by using Matlab/Simulink(?) platform.The steering stability control strategy proposed in this paper is verified by simulation with different adhesion coefficients.The result shows that the control system can effectively improve the steering stability of the vehicle under the extreme working conditions,and it has strong fault tolerance in the event of actuator failure.