安全、稳定、可靠的线控系统是自动驾驶系统实现的关键技术之一，这包括线控驱动、线控制动以及线控转向系统的设计和实现。其中，线控驱动系统已成为车辆标配，线控制动系统也日趋成熟，而线控转向系统仍停留在传统助力转向的基础之上，有着较大的局限性。由于取消了机械连接，线控转向系统带来诸多好处，然而，其最大的缺陷是当系统发生故障时将无法通过机械冗余的方式来保证系统安全。因此，如何保证系统的安全性就成为其能否得到广泛应用的关键问题。 在此背景下，本课题主要围绕乘用车线控转向系统展开研究，核心问题是如何从设计和控制层面提高其安全性和可靠性。具体地，本文主要进行了三个方面的研究：线控转向系统冗余设计，线控转向系统控制策略以及控制权切换策略研究。 首先，针对线控转向系统冗余设计，基于ISO 26262:2018，详细分析和总结了线控转向系统可能出现的失效形式和潜在故障，对转向系统的机械和控制器部分分别进行了设计，并进行了详细分析，以使其满足功能安全的需求，为线控转向系统的设计提供参考。 其次，针对线控转向系统控制策略，进行了两个方面的研究。其一,基于当前使用最为广泛的PID控制器，设计了两种具有不同类型控制回路的控制系统，并应用于线控转向系统的轨迹跟踪控制问题。通过理论分析和实车验证，以探索在库伦摩擦力存在的情形下，两种控制回路之间的本质区别。其二，考虑到线控转向系统的结构，提出了一种针对带有内反馈线性级联系统的解耦控制算法，并给出了该控制器渐进稳定的充要条件以及应用于线控转向系统的仿真结果。 再次，对于装备线控转向系统自动驾驶车辆的控制权切换问题，提出了一种针对L3/L4级别自动驾驶的状态安全切换架构，为软件架构设计提供参考。然后，针对该架构中极为关键的问题之一——驾驶员介入识别问题，通过理论分析和实验验证，提出了一种基于鲁棒观测器的驾驶员介入识别算法，可有效对驾驶员介入进行识别，以保证自动驾驶系统到驾驶员安全、及时、平滑地切换。 最后，针对本文提出的线控转向系统架构，进行了硬件在环测试台架的设计及综合测试用例框架的搭建和实现，提供了线控转向系统的软硬件设计及验证平台，为后续研究奠定了基础。
Secure, stable, and reliable execution system is one of the key technologies in realizing automated driving systems, including drive-by-wire, brake-by-wire, and steer-by-wire systems. Among which, drive-by-wire system has already become an essential part of the vehicle, and the brake-by-wire system is also becoming more mature everyday, while the steer-by-wire is still counting on the traditional electric power steering systems, with great limitations. Because of the cancellation of the mechanical connection, the steer-by-wire system brings a couple of benefits. However, at the same time, the greatest limitation of the system is that it will be impossible to ensure the safety of the system through mechanical redundancy when the system fails. Therefore, how to ensure safety of the system becomes the key issue for its commercialization. In view of this, the main focus of this paper is the passenger car steer-by-wire system, and the core issue is, how to improve the safety and reliability of the system from the point of design and control. Specifically, this thesis mainly focuses on three aspects around the system: redundant design of the steer-by-wire system, control strategies of the steer-by-wire system, and takeover control strategies for automated vehicles equipped with the system. Firstly, on redundant design of the steer-by-wire system, based on ISO 26262:2018, the possible failure modes and potential faults regarding the system has been analyzed and summarized in great detail. Based on which, the mechanical and electrical parts of the system have also been analyzed and designed separately in detail, with detailed theoretical analysis, trying to satisfy functional safety requirements as required by ISO 26262. The aim is to provide some references for designing of the steer-by-wire system. Secondly, on control strategies of the steer-by-wire system, two researches have been conducted. For one, based on the most widely used PID controller, two control systems with different types of control loops have been designed and applied to the tracking problem of the steer-by-wire system. Through theoretical analysis as well as experiment on a real vehicle, the purpose is to explore the essential differences between the two control loops in the presence of Coulomb friction. For another, considering the structure of the steer-by-wire system, a decoupling control algorithm for a linear cascade system with internal feedback loops has been proposed, with necessary and sufficient conditions for guaranteeing the asymptotic stability of the controller and simulation results in applying to the steer-by-wire system. Thirdly, for takeover control problems of automated vehicles equipped with the steer-by-wire system, a safety-oriented state transition architecture has been proposed for automated vehicles aiming at level 3/level 4 automated driving, which aims to provide a reference for software architecture design of automated driving systems. In addition, aiming at one of the most critical problems in the proposed architecture--driver intervention identification, a driver intervention identification algorithm based on robust observer has been proposed after theoretical analysis and experimental verification, which intends to ensure safe, timely, and smooth switching of control authority over the vehicle from the automated driving system to the driver. Finally, based on the proposed architecture of the steer-by-wire system, the hardware-in-the-loop test bench has been designed and built. At the same time, the framework of the test case for testing the performance of the system has been established and realized, which lays the foundation for subsequent researches.
