Research On Design And Testing Scheme For Redundant Security Of Steer-by-Wire System

Steer-by-wire system cancels the mechanical connection between the steering handwheel and the steering wheels,and replaces the traditional mechanical system with electronic and electrical equipment,so that the vehicle can be steered according to the driver’s input and driving conditions at the same time,improving the safety and comfort of the vehicle.However,since the reliability of electrical and electronic equipment is significantly lower than that of mechanical structures,the risks from system failure and random hardware failure also increase,so it is very important to realize the functional safety of the system through redundant and fault-tolerant safety mechanisms.In this paper,relying on the "Steer-by-Wire Integrated Controller Technology Development" project in cooperation with a carmakers,the reliability of the steer-by-wire controller is guaranteed at the level of electronic and electrical architecture by redundant design of the integrated controller of the steer-by-wire.,and on this basis,carry out research on redundant and fault-tolerant control strategies for steering actuators.First of all,according to the functional safety requirements in the concept development stage of ISO 26262,this paper analyzes the functions and structures of related items of the steer-by-wire system,and conducts hazard analysis and risk assessment in combination with usage scenarios and possible dangerous events.Control turns to the definition of Safety Integrity Level（ASIL）,and designs corresponding safety objectives for related hazardous events.On this basis,the relevant safety objectives are decomposed into relevant functional components,and a redundant design scheme of the integrated controller is proposed.On the basis of ensuring the safety of its own software and hardware structure,the integrated controller also needs to perform fault diagnosis and fault-tolerant control of key functional modules such as the main sensors,actuators,communication and power supply of the steerby-wire system.In order to meet the functional safety requirements of the integrated controller of the steer-by-wire system,based on the analysis of the functional safety requirements,this paper designs and develops the underlying software and hardware of the controller.In this paper,the cooperative working mode of the integrated controller is firstly designed to prevent the occurrence of conflict events caused by the misjudgment of the state between the master and slave controllers;secondly,the fault detection and processing mechanism of the controller is designed to ensure that the controller can Fast processing to ensure the failure of the integrated controller is available;then the Markov model of the dual-redundant integrated controller is established to analyze the reliability.It can be seen from the analysis that when the reliability of a single controller is high,the improvement of the reliability of the integrated controller is not obvious,but the purpose of the dual-redundancy design is to consider that the controller can still have a certain working ability after a single system failure,and can meet the functional safety requirements of failure availability.At the application software level of the integrated controller,the fault diagnosis and fault-tolerant control methods of steering execution system are mainly studied.Firstly,the steering actuator is managed by the state machine,and different fault processing modules are set up for different faults;secondly,the dynamic model of the vehicle and the steering system is established,and the front wheel rotation angle is estimated by the UKF algorithm.The estimated value is used as the test redundancy of the front wheel angle and the evaluation index of whether the related sensor fails.The application range and feasibility of the designed estimator are verified through the simulation experiment to prevent the danger caused by the error of the angle sensor during driving.By analyzing the structure of the motor of the steering actuator and its ECU,the safety and controllability of the actuator is judged;finally,the variable transmission ratio control and yaw with the vehicle speed are set according to the controllability of the actuator and the accuracy of the related sensors.The upper-level faulttolerant control method of angular velocity feedback control ensures the response performance of the steering execution system under normal conditions,and can also make the steering execution system enter a safe state when a fault occurs,ensuring driving safety.Finally,in order to verify the reliability of the designed redundancy scheme,the relevant functions and strategies are tested and verified.First,the reliability of the dual redundant integrated controller software module is verified by designing relevant test cases,and the reliability of the relevant software modules is proved by designing relevant test cases;Finally,the feasibility of the UKF method for corner estimation is tested through real vehicle experiments.