Research On FlexRay Bus Technology Based On Four-wheel Steer-by-wire System

With the rapid development of automotive electronic technology,automotive electronic control and intelligent level is constantly improved,wire control technology began to be used in the automotive steering system.The wire controlled four-wheel steering system,which is formed by the combination of wire control technology and four-wheel steering system,can use intelligent control strategy to control the front and rear wheel rotation,improve the steering performance index,and bring great prospects for the development of four-wheel steering vehicles.In order to realize the signal transmission between nodes,the communication network design in the system is the key.In this paper,the FlexRay bus with fast transmission speed,high security and reliability is used as the node communication network of the four-wheel steer-by-wire system.According to the structure and control requirements of the steering system,under the FlexRay bus protocol,this paper studies the FlexRay bus technology based on the four-wheel steer-by-wire system,and designs the FlexRay bus network which can realize the node communication of the four-wheel steer-by-wire system.The main contents of this paper include:1.By referring to the relevant literature,this paper summarizes the theoretical research and practical application of FlexRay bus technology,which prov:ides a reference for the design of the FlexRay bus network of the four-wheel steer-by-wire system.2.This paper studies an optimization method of static segment message encapsulation and scheduling in FlexRay bus,which is used to improve the utilization of static segment bandwidth.Through the establishment of bandwidth utilization model,the paper analyzes the factors affecting the bandwidth utilization,then uses message encapsulation method to determine the optimal length of static slot,and uses message scheduling method to reduce the number of static slot,so as to reduce the waste of unused bandwidth and achieve the goal of improving bandwidth utilization.3.According to the working principle and node function of the wire controlled four-wheel steering system,a suitable FlexRay bus network architecture is proposed,and the types of signals transmitted on the bus are analyzed.Using the static segment message encapsulation and scheduling optimization method proposed in this paper,the frame encapsulation and scheduling mode of static segment signal and the message encapsulation mode of dynamic segment signal are designed,so as to further design the communication global parameters of FlexRay bus network.Based on the communication simulation software CANoe,the node communication database and virtual simulation model of the four-wheel steer-by-wire system are established,which verifies the correctness of the design of the relevant parameters of the FlexRay bus network based on the four-wheel steer-by-wire system.4.When using canoe software for communication simulation,the nodes can not describe the active steering control algorithm completely and accurately in the programming,so this paper designs the joint simulation of CANoe/Matlab based on the four-wheel steer-by-wire system.In Matlab/Simulink software,the controller algorithm model is established,and the actual signal value obtained by the algorithm is sent to canoe software through the software interface for joint simulation,which restores the real node communication process.The joint simulation verifies the correctness of the steering control strategy and the FlexRay bus network parameter design.5.T he hardware and software of the FlexRay bus network of the four-wheel steer-by-wire system are designed,including the selection of chips and the design of software programs.On the experimental bench of the four-wheel steer-by-wire system,the correctness and feasibility of the FlexRay bus network design of the four-wheel steer-by-wire system are verified by the physical node communication test experiment.