Research On Handling Stability Control Strategy Of Steer-by-Wire Vehicle Based On Variable Steering Ratio

With the arrival of the era of electrification,networking,intelligence and sharing of automobiles,the technology of automobile chassis-by-wire has ushered in a rapid development stage.As an important part of the vehicle chassis-by-wire system,steer-bywire system cancels the mechanical connection between the steering wheel and the steering actuation module,and realizes the mechanical decoupling between them.The drive-by-wire feature of the steering actuation module enable the vehicle to realize the variable steering ratio control and the active front wheel steering control function,thereby creating conditions for improving the handling stability of the vehicle.However,the steer-by-wire system cancels the mechanical connection,and the steerable wheel is driven by the steering actuator.Therefore,it is necessary to effectively design the angle tracking control algorithm of the steering actuator to ensure that the steering actuator can track the desired angle accurately.In view of the above problems,first of all,on the basis of the investigation of the research status at home and abroad,this paper relies on the national key research and development program "Multi-system Efficient Integration of In-wheel Motor Action Module and Vehicle Torque Vector Distribution Technology"(Project Number: 2021YFB2500703)and the Jilin Province Science and Technology Development Plan Projects "Research on decision-making and control of automatic lane change of electric vehicle with X-by-Wire chassis"(Project Number: 20230101121JC),the variable steering ratio of steer-by-wire system that varies with vehicle speed and steering wheel angle is designed,which improves the steering sensitivity of the vehicle at low speeds and the stability at medium and high speeds.Secondly,in order to ensure that the steering actuator of the steer-by-wire system can accurately track the desired steering angle under internal parameters and external torque disturbances,the angle tracking control algorithm based on linear active disturbance rejection control is designed.Finally,in order to reduce the influence of driving conditions such as side wind and split road on the vehicle’s handling stability,an active front wheel steering control algorithm considering the timing of intervention is designed.The specific research content of this paper is as follows:(1)Build a dynamical model of the steer-by-wire vehicle.In order to study the design method of variable steering ratio in steer-by-wire system,the angle tracking control algorithm of steering actuator and the active front wheel steering control algorithm.First of all,this paper uses MATLAB/Simulink software to build a dynamical model of the steer-bywire system.Secondly,using the interface setting and multi-software co-simulation function of CarSim software,the power steering model in the CarSim vehicle dynamical model is replaced by the built dynamical model of steer-by-wire system,thus forming a co-simulation dynamical model of the steer-by-wire vehicle.Finally,the dynamical model of the steer-bywire vehicle is tested and verified based on the double-lane shifting test,the steering effort test and the steering wheel angle sinusoidal input test.(2)Research on the design method of variable steering ratio in steer-by-wire system.First of all,the steering characteristics of the vehicle with traditional mechanical steering system are analyzed by using the CarSim vehicle dynamical model,and a method of designing the variable steering ratio based on the constant yaw rate gain is introduced.Secondly,according to the domestic and foreign research results of variable steering ratio and the analysis of the steering characteristics of traditional mechanical steering vehicles,a unified model of variable steering ratio that varies with vehicle speed and steering wheel angle is proposed.Thirdly,the vehicle speed is divided into five speed sections: low speed,medium speed,high speed,transition from low speed to medium speed and transition from medium speed to high speed,and the variable steering ratio of each speed section is designed based on the unified model of variable steering ratio.Finally,the particle swarm optimization algorithm is used to optimize the center ratio gradient coefficient value in the unified model of variable steering ratio at different speeds,and the control effect of the designed variable steering ratio is tested and verified by using the dynamical model of the steer-by-wire vehicle.(3)Research on the angle tracking control algorithm based on linear active disturbance rejection control.First of all,in order to improve the accuracy and robustness of the angle tracking control of the steering actuator in steer-by-wire system,thereby reducing the influence of internal parameters and external torque disturbances during the working process of the steer-by-wire system,the linear active disturbance rejection control is used to design the angle tracking control algorithm.Secondly,in order to verify the control effect of the designed angle tracking control algorithm,the other angle tracking control algorithm based on PID control is designed to compare the control effect.Finally,using the dynamical model of the steer-by-wire vehicle,and on the basis of the variable steering ratio control,the control performance of the designed angle tracking control algorithm is tested and verified.(4)Research on the active front wheel steering control algorithm of steer-by-wire system.First of all,based on the yaw rate deviation and the body side slip angle deviation,the active front wheel steering intervention timing is designed,and its rationality is verified by using the lateral velocity-yaw rate phase plane.Secondly,an active front wheel steering control algorithm based on yaw rate feedback is designed by using fuzzy adaptive PID control.Thirdly,in order to avoid the excessive impact of active front wheel steering on the driver’s normal driving,an active front wheel steering intervention threshold that varies with vehicle speed is designed.Finally,using the dynamical model of the steer-by-wire vehicle,the control performance of the designed active front wheel steering control algorithm considering the timing of intervention is tested and verified on the basis of the variable steering ratio control and the angle tracking control of the steering actuator.