Research On Integrated Control Of Anti-Lock Braking System And Active Front Steering For Light Vehicle

For the sake of enhancing the integrated performance of vehicles, various control system for the chassis have been reaserched and exploited, such as longitudinal control for the brake and drive, transverse control for the turning and yaw moment and vertical control for the suspension. At present, Automobile chassis electronic control system, almost without exception, is developing around a particular function, and through the tire contact with the ground to have an impact. As in all directions, the move of cars is not independence, but interact with one another, therefore, which makes integrated chassis control has become the hot research and development, because to the traditional control it has a incomparable advantages: to eliminate the conflict of systems, to improve vehicle performance, reduce the sensor, reducing system complexity and get more functional.The research programme of the context is proposed Under this background..Anti-lock braking system (ABS) can effectively use the adhesion of tire and the road surface, and improve braking performance, shorten the braking distance. In the process of braking, vehicle can maintain the steering ability to prevent skidding occurred. However, sometimes, there was a contradiction between a short braking distance and braking stability. For example, when braking on the road of different adhesion for the left wheel and the right, the imbalance of braking force of the left wheel and the right will have a yaw torque, in an emergency situation general driver is impossible to make a timely response to this yaw moment. But for the front wheels, they are basically alone controled, so it will still have a great yaw torque. This requires drivers to take time to reverse the steering to the elimination the imbalance caused by yaw torque. Of course, this method can improve the stability, but will lead to longer braking distance.Vehicle Active front wheel steering system (AFS) according to the operational status of the vehicle and driver intent, could make appropriately amendments for the front-wheel steering angle to enhance the traffic stability of vehicles. However, if imposing large braking force to the steering wheel and leading to excessive wheel slip ratio, due to the lower of lateral adhesion coefficient, AFS basically loss of control.Clearly, these two vehicles chassis control system are very closely linked: if there is only ABS working in special vehicles braking conditions, it will produce conflicts between braking performance and horizontal stability; if there is only AFS working in the high-intensity brake circumstances, and still want to make appropriate amendments for the front wheel steering angle, it would be difficult to play its role. Therefore, the ABS and AFS integrated control could make them fully play their role, and enhance the integrated performance.Therefore, the study purpose and significance is obvious:Purpose: To improve the ABS braking efficiency, and ensure the working stability of AFS, to maintain the stability of the vehicle braking, at the same time shorten the braking distance. To some special conditions vehicles could be more easily manipulated, and make driving more flexibility.Significance: By the integrated control, related systems could effectively play the advantages and potential, so that make them" mutually complementary and beneficial", and further enhance traffic stability and safety of the vehicle.In this paper, the work of the specific study and its findings are as follows:1,Vehicle simulation model is the basis of the analysis for the integrated control system, but also has some significance for its theoretical analysis. This paper utilized MATLAB / Simulink software to study the entire vehicle system simulation modeling. Model use modular design, building seven degrees of freedom model of vehicle and hydraulic-braking systems model, they can simulate the driver intent, and simulate hydraulic braking system dynamic response characteristics in the braking conditions, and simulate vehicle movement, and can modify related vehicles parameters and adjust control parameter, and can change the road conditions and the control mode, and can demonstrate parameters curves of integrated control of the vehicle and the control system.2,In this paper, the control logic of Anti-lock Braking System (ABS) is based on the most practical and most popular methed: logic-threshold. We use MATLAB / Simulink modeling its controller, the control logic used Stateflow to achieve, these tools make the process of to control achieving the visualization, and can change the threshold easily accoeding to the dynamic display of the control process.3,In this paper, because of road adhesion coefficient, and vehicle speed changing in the process of traffic with the driving conditions change, in order to increase the robustness of the vehicle system parameter uncertainty, use sliding model control theory to design the AFS control strategy. Also considering the AFS controller control the front wheel steering angle almost in the linear range of tires and to improve vehicle handling and stability, therefore, establish a linear vehicle model of two degrees of freedom, the design of AFS controller is built on this reference model. Then establish model through MATLAB / Simulink.4,On the basis of studing related literature from both at home and abroad, this paper proposed threshold rules coordinated control strategy based on state recognition: before carring out the two subsystems-ABS and AFS-coordinated control, we should first determine their driving status on (Straight Driving or Steering Driving; When vehicle is steering driving, steady state response is Neutral-steer, Under-steer or Over-steer), and then according to specific driving conditions to determine the coordinated control strategy. Through determining whether one controlled parameter is more than the relevant threshold to achieve control strategy.5,Based on two special conditions: split ?μroad straight braking condition and the front wheel angle step input turning braking condition, this paper analyze the performance of the coordinated control system. Selection of these two conditions is because they can better reflect the performance of the two subsystems studied in this paper, and can understand of the relationship between them more clearly: complementarity and mutual benefit. This is also the objective coordinated control. In the process of simulation, use the method of comparative analysis, and it shows not only the advantages that coordinated control system compared to the each independent control subsystem, but also the coordinated control is better than of joint control in control effect.