【作者】 田杰；

【导师】 高翔；

【作者基本信息】 江苏大学 ， 车辆工程， 2011， 博士

【摘要】 线控转向系统(Steering By Wire, SBW)是未来具有无人驾驶功能的智能汽车必不可少的重要组成部分。它取消了转向盘和转向轮之间的机械连接,可以任意设计转向系统的角传动比和力传动比,因此从根本上解决传统转向系统的固定传动比造成的汽车转向特性随车速而变化的缺陷。更重要的是线控转向系统能够在驾驶员转向角的基础上叠加一个附加转向角,优化车辆对驾驶员输入的响应或提高车辆在紧急情况下的稳定性,所以近年来成为国内外研究的焦点之一。本文首先针对前轮转向模块的控制目标和控制要求,将控制系统分成前轮转角控制(上层控制)系统和转向执行电机控制(下层控制)系统两个部分。针对下层控制系统,对前轮转向模块进行了动力学分析及建模,设计了一种基于分数阶微积分理论的新型分数阶PIλDμ控制器,仿真结果表明：该控制器在实现前轮正常转向和回正功能的同时,对提高转向系统性能的鲁棒性也是有效的。针对上层控制系统,设计了基于模糊控制的前轮转角控制算法,仿真结果表明：基于模糊控制设计的理想传动比能满足设计要求。并将上层和下层控制系统结合在一起,选取典型工况,对所建立的模型及控制算法控制系统进行了仿真分析,验证了所提出的分层控制系统是有效的,可行的。其次,为了防止车辆在行驶的过程中出现诸如严重的过多转向或不足转向,本文提出了一种基于主动前轮转向(Active Front Steering, AFS)和横摆力矩(Direct Yaw Moment Control, DYC)协调控制的非线性控制策略,并设计了基于滑模变结构控制的AFS控制器、DYC控制器和统一协调AFS和DYC工作的协调控制器。仿真结果表明采用协调控制策略的车辆具有更好的响应特性。控制系统中存在着不适当的时滞,对于高速行驶的汽车、性能有着不利的影响。本文在车辆稳定性研究的基础上引入控制时滞,对线性时滞系统的稳定性、时滞对车辆系统动态特性的影响以及系统的时滞补偿问题等方面进行了具体的研究。并对时滞对车辆稳定性控制系统的影响以及系统的时滞补偿进行了仿真分析。结果表明,控制系统的稳定性得以提高。最后本文还从硬件和软件两个方面入手开发了线控转向系统的台架试验装置,并利用此试验装置对前轮转向模块的基于分层结构的控制系统进行了验证。试验研究与理论模型研究结果基本相符。本论文的创新点在于：首先对分数阶控制理论进行了研究,通过优化方法实现了分数阶PIλDμ控制器中五个参数的整定。构造了分数阶PIλDμ控制器的仿真模型,解决了分数阶系统不能直接在MATLAB仿真环境中直接进行仿真的问题。并将分数阶控制理论应用在了前轮转向模块的转向和回正控制中。其次将分数阶PIλDμ控制器和模糊控制器有机地结合在一起,实现了该模块的分层结构控制。提出了基于AFS和DYC协调控制的车辆稳定性控制策略,克服了各系统单独工作时的缺陷。并对装备线控转向系统的车辆进了车辆稳定性的时滞影响和补偿研究。本文的研究为线控转向系统的研究和开发提供了新的思路和方法。更多还原

【Abstract】 Steering by wire system (SBW), which has no mechanical linkage between the steering wheel and the front wheels, is one of the indispensable components in the future intelligent automaobile which has the fuction of driving without driver. The transmission ratio of SBW system can be randomly designed, so its steering characteristics can remain the same while the speed changes. Furthermore, it can add an additional steering angle to the driver’s input, which can optimize the vehicle’s response on the driver’s input or improve the stability in case of emergency. So recently it becomes the research focal.Firstly, the control aims and demands of the front wheel steering module were presented in this paper. And the control system based on hierarchical structure, which included the control system of front steering angle(the upper control) system and the control system of steering actuator motor(the lower control) system, was proposed. For the lower control system, the dynamics equations of the front wheel steering module were established and a new PIλDμcontrol method based on fractional calculus was designed. The simulation results showed that the normal steering function and the aligning function could be realized by the PIλDμcontroller and the robust of the steering-by-wire system could be improved. For the upper control system, a front-wheel steering angle control strategy based on fuzzy control was designed to overcome the pitfalls of the traditional steering system. And the simulation results showed that the ideal transmission ratio based on fuzzy control could meet the demands. The control system based on hierarchical structure is simulated for the model and the control algorithm with typical operating conditions. And the simulation results showed that the hierarchical control svstem was effective.Then a coordinated control strategy for active front steering (AFS) and direct yaw moment (DYC) was proposed to avoid serious over-steering and under-steering. And AFS controller and DYC controller based on variable structure control were designed. A coordinated controller was also designed to adjust the controllers—AFS and DYC according to the control logic. Simulation results show that the vehicle with coordinated control of AFS and DYC achieve better the stability when steering.Improper time-delay which exists in the control systems, will has unfavorable effect on the characteristics of the control system. So control time-delay was introduced to the study of vehicle atability which had been discussed in the paper. Some researches on the stability of linear time-delay system, the effects of time-delay on vehicle dynamic characteristics and the time-delay compensation of the controlled system were carried out. The simulation and analysis of the time-delay effects and compensation were performed. The simulation results show the controlled system with time-delay compensation can achieve better stability.At last, this paper developed SBW bench test devices from two aspects of hardware and software. With this test device, the control system based on hierarchical structure of the front wheel steering module was verified. The results of test and simulation were basically agreed.The innovation of this paper is as the following. Firstly, the fractional order control theory has been studied, the five parameters of fractional PIλDμcontroller were achieved through the optimization method. To solve the issue that fractional order system can not be directly in the MATLAB simulation environment, simulation model of fractional PIλDμcontroller was constructed. And the fractional order control method was successfully appied to the normal steering and the aligning control of the front wheel steering module. Secondly, the fractional PIλDμcontroller and the fuzzy controller were combined organically to achieve the hierarchical control. Vehicle stability control strategy based on AFS and DYC coordinated control was proposed to overcome the defects when AFS and DYC control worked alone. The time-delay effects and compensation were performed for the vehicle with the steering by wire system. This study provides new ideas and methods for the research and development of the steering by wire system.更多还原