Study On Steer-by-wire System Of Passenger Car Modeling And Control Strategy

Steer-by-wire system as a new type of automotive steering system, has a biggestcharacteristic using bus technology to replace mechanical connection between the steeringwheel and the front steering wheel, and its transmission ratio can be set willfullyaccording to the running state of automotive. The early steering system has always existeda problem that it cannot combine steering portability and operational stability.Steer-by-wire system output instruction to control the angle of steering motor through theelectronic control unit, so as to control of the front wheel steering, then solve thecontradictory between steering portability and operational stability in the traditionalsteering system. In addition, the driver cannot perceive road information by mechanicalparts in the steer-by-wire system, it is necessary to simulate road feeling for drivers.In this paper, the structure, the principle, the key technical problems of thedevelopment and performance characteristics of steer-by-wire system are analyzed whichrefer to the previous studies. The structure is simplified reasonably using method ofreduction of order; the mathematical dynamic model and simulink simulation model areset up. The vehicle model is established using CarSim which is commercial simulationsoftware of the automobile, while the simulink simulation model is embedded inB-CLASS (NO ABS) of CarSim to replace the original steering system, then a unitedsimulation model about simulink and CarSim which is the basis and the plateau ofresearching control strategy of steer-by-wire system is established.In the control strategy of the front wheel angle, a control system based on yaw ratefeedback and combined with control of the variable gear ratio is designed. Thesteer-by-wire system is unable to establish its precise mathematical model. In order toimprove the control effect, a fuzzy PID controller is designed by combining fuzzy controlwith PID control, then applied to the control strategy of the front wheel angle for onlinefollowing control the parameters of the vehicle so as to obtain the offset angle of the frontwheel angle in real time. Results show that the portability and stability of the steer-by-wiresystem which adopt the fuzzy PID control is better than the steer-by-wire system whichadopt PID control and the steer-by-wire system without PID control. It is better to achievethe front wheel angle control.The simulation of road feel of steer-by-wire system is based on the road fee oftraditional mechanical steering system.The assembly model of steering wheel isestablished through analyzing aligning torque of passenger car to obtain the target torqueof road feel and join the variable transmission ratio control to improve the target torque. In order to control the road feeling motor to output applicable torque and deal withuncertainties in running process, the theory of artificial immune, fuzzy control and PIDcontrol are united to design a fuzzy immune PID controller adopted in the control strategyof road feel combination to simulate road feel. Results show that the effect following thetarget torque and anti-interference of the road feel which is generated by adopting thefuzzy immune PID controller is better than the road feel which is generated by adoptingthe PID controller.