Research On Steer-by-wire System Predictive Control Strategy For Active Safety Of Vehicle

Automotive active safety is an important research direction of vehicle safety design, the designation is to eliminate the possibility of accident, and prevent its occurrence prior to the accident. Steering system is a key component of the vehicle control by driver, it is related to the operation of the vehicle stability and the safety of the vehicle. A good operational stability has been required under normal driving conditions, which require vehicles driving in different conditions with different sensitivity, when encountered emergency, we need the driver to adjust the posture of the vehicle to avoid the danger by steering systems, braking systems and etc.It is hard for the traditional steering wheel to realize the active safety control and wheel steering stability control of vehicle, because of the fixed Transmission between steering wheel and wheels. Vehicle handling and active safety mostly rely on the experience and skills of the driver, in an emergency situation, the driver's instinctive react operation of the manipulation maybe error, which will make the vehicle lost control, and cause accidents.Steer-by-wire system divided the driver's control and the vehicle steering control into two relatively independent systems. The driver's controlling adds the judgment of the electronic control unit, instead of directly control the vehicle's steering. The transmission relationship between steering wheel and wheels can be changed according to the actual situation and the current vehicle posture by control system, so that the design of steering characteristics but to be addressed through the electronic control unit to determine control of the vehicle after the turn, steering wheel and the relationship between the wheels by the transmission control system according to the actual situation and the current drive to change the attitude, so that it bring the design of steering characteristics lots of free space for development.This paper combining the control:of steer-by-wire with the measurement and prediction of the vehicle attitude, researching the relationship between the safety of vehicle and the vehicle attitude, proposing the judgment method based on the vehicle safety attitude by fuzzy decision. And using AR prediction theory to predicted the safety of the vehicle, on the basis of the predicated dates to research the theory and methods, which to achieve the vehicle stability control and vehicle active safety control by adjusting the steering gear ratio. In this paper, the control system consists of three aspects:The first is the steering wheel control system, the key is the road sense and the control of aligning. Research on the force feedback of steering wheel model, and take the steering wheel angle and vehicle speed as a basis for calculation of aligning torque, then to establish the mathematical model of the steering wheel control system, using two-way feedback control methods which by current and motor speed. We should combine the PID control of expert fuzzy decision control strategy with the speed optimum control(BANG-BANG control), to achieve the unity of road sense and the control of aligning effectively, and to obtain more good results;Followed by the control of the front steering angle control system, its main purpose is to timely response to the operation of the driver on the steering wheel, thus requiring the control system with fast response, and not the same with the steering wheel control systems, the state of road is changing with the processing of vehicle, the control object model will continue to change in the control process. So we should be adopted control strategy is robust, sliding mode adaptive controller has a good performance of control, sliding mode variable structure control can be continuously adjusted the controller structure, and effective prevent the parameter variations and external disturbances, it is suitable for the uncertain control of front wheel angle, this paper use sliding mode control based on reaching law to realize fast track of the front steering angle;Finally is the decision-making system design which refer to the variable transmission ratio between the steering wheel and front wheel angle, the most prominent feature of steering by wire system which to be different from traditional system is variable gear ratio. The paper take the measurement and prediction of vehicle's body posture, predicted the vehicle's security status by fuzzy decision method, and introduced the risk assessment by the parameter of the roll angle and the roll angular velocity of vehicle's body. In the paper, proposed the simplified model of vehicle sideslip angle estimation, we estimated vehicle sideslip condition by the predicted of side slip angle. On the basis of the forecast evaluation of vehicle security status, we propose a method to achieve the stability steering control and active safety control in danger status by adjusting the transmission ratio.In this thesis, the research to the control strategy of wire steering system based on predicted of the parameters of vehicle attitude. We combine the expert fuzzy PID with the most rapidly decision-making optimal control to achieve the road sense and the aligning control, combined the predicament and the judgment of danger status with steering by wire control system innovatively, to achieve the active safety of vehicle control. And use sliding mode control based on the reaching law to achieve the fast follower control of front-wheel angle. This study search provides some new ideas and methods to the research of the by-wire steering system and vehicle active safety control.