An Investigation Of The Fault Tolerant Control Of Vehicle Steer-By-Wire System

Along with the progress of the scientific technology, and the improvement of people's living standard, consumers are concerning more and more to the vehicle's driving performance and the manipulating. The issuses that how to improve the stability of vehicle steering control system and the traveling safety, how to improve the working conditions of the driver, how to reduce traffic accidents and how to protect the personal safety and so on, are becoming very prominent.In this trend, Steering-By-Wire System (SBW) have emerged to meet this objective needs. It is a new developing generation of steering systems after EPS which is better than EPS in the manipulation characteristics. Because it cancels the mechanical connection between the steering wheel and the road wheel, it completely gets rid of the inherent limitations from the traditional system, and brings the convenience to the drivers, at the same time it improves the safety of vehicles. It is a new great innovation of steering system.Otherwise, the greatest hidden danger of SBW system is the security and reliability, the fault-tolerant control is a new approach to issue that question. At present, the major European enterprises are in company with fault-tolerant control to solve the security performance of SBW system.Against this background, this paper study on the fault-tolerant control of SBW system. The specific contents are as follows:In Chapter one, it is the introduction. The development trends and research background of SBW system and the fault-tolerant control are detaily introduced, and the important significance and the development status of fault-tolerant control of SBW system are stated. In this chapter, the main research work of this paper is described.Chapter Two is the theory base of this paper. Firstly, it states several common ways of the fault-tolerant control. At present, the fault-tolerant control has two major categories: hardware redundancy and software redundancy. The software redundancy is mainly using analytical redundancy. Hardware redundancy provides the backup to the important parts or the vulnerable parts to improve the performance of fault-tolerant systems. Hardware redundancy includes static redundancy and dynamic redundancy; Analytical redundancy mainly improves the redundancy of the entire control system through the design of the controller, so as to improve the fault-tolerant performance of the system. Analytical redundancy usually includes: Reconstruction controller; Integrity design; Fault-tolerant controller design based on the application of self-control; Fault-Tolerant control based on artificial intelligence. According to the characteristics of SBW system, this paper adopts the method of combining software redundancy and hardware redundancy。And software redundancy selects the method of integrity control. In the last, it states the way solving.In Chapter Three, the SBW system fault-tolerant control Test-bed is set up. According to the characters of SBW systems, two mathematic modules (steering wheel modules and steering actor module) are established separately. SBW system's main faults are the faults of sensors and actuators. And it puts the point on the Integrity Control of those two modules. And the way is proved by the mathematical methods.Chapter Four clarifies the advantage of the xPC real-time simulation system. During the development of SBW system, the actual vehicle test always require a lot of time, manpower and material resources, and a long cycle of time and so on which make it hard to meet the needs of the market. The application of Hardware-In-The-Loop can quickly solve these issues. This chapter set up the model of SBW fault-tolerant strategy, and the model is simulated through the software of Matlab/Simulink for several faults of sensors. Then put the model is put in the xPC target machine. The point of this capter is the Hardware-In-The-Loop based on the xPC target thechnology of the faults of the steering wheel angle sensor, the moment sensor, and the feedback motor current. The Hardware-In-The-Loop test testifies that the intergery controller can offset the sign which has faults, and it still can insure the right function.Chapter Fifth conclusions and draw up the whole paper.In this paper, some innovations are as follows:1. For the Steer-By-Wire system, this paper uses the way of combining the software redundancy and hardware redundancy insteading of hardware redundancy purely. This way can not only ensure the system's security and reliability, but also can resolve the cost problem.2. It is the first time to apply the ideological of integrity control to SBW system. Integrity Control mainly resolves the problem such as the card death, the saturated fault, and the saturated fault of actuators or sensors, particularly when that circuit is in the opening circumstance, or simultaneously with the fault of sensors'and actors'failure, the closed-loop system is still stable. The main fault of SBW system is about the sensor and actuator, so it plays a positive role to combine the integrity ideas and SBW system.3. The Matlab / Simulink model of fault-tolerant control of SBW system which is based on xPC Target machine haves the Hardware-In-The-Loop testing, verificating the integrity of the controller meeting the fault-tolerant requirements of SBW system.The following is the vision for the future:Due to the constraints of the time and conditions, SBW fault-tolerant control of this paper is only aimed at several sensor failures, through the Hardware-In-The-loop test based on the xPC target technology. A number of other uncommon sudden failures are not taken into account. And for the reasons of the equipments, the failure of steer actors are not tested on the xPC Target, only simulated through the software of Matlab/Simulink. In the future work, we need gradually research this work.The author think the future work schould be the focus of on the actual vecihle test, considerating the outside factors to SBW system.Then the fault-tolerant control will be improved.SBW system is currently limited to the concept car. And it is not applied to the production. Otherwise, the research of the fault-tolerant technology of SBW system is still in the early stage of the world. Now there is no consummate technology. Therefore, there is still a long difficult journey to go for studying the fault tolerant control of SBW system.