【作者】 杜峰；

【导师】 魏朗；

【作者基本信息】 长安大学 ， 载运工具运用工程， 2009， 博士

【摘要】 四轮转向(4WS)技术是改善汽车操纵稳定性及提高行驶安全性的最常用的、有效的主动底盘控制技术。为了充分发挥四轮转向系统对车辆侧向动力学的影响，基于近年来线控转向技术的发展，论文以前、后轮均可控的全主动四轮转向汽车为研究对象，以车辆侧向动力学特性及控制作为研究方向，全面考虑线性、不确定性及非线性因素对汽车操纵稳定性的影响，对四轮主动转向汽车控制策略进行了比较系统深入的研究。进行了4WS汽车非线性动力学模型分析以及基于多体动力学分析软件ADAMS的虚拟样机建模研究，并利用MATLAB/Simulink实现了4WS汽车非线性动力学模型的数值计算，为不同控制策略的研究和控制效果的验证提供了精度较高、运算较快的底盘控制系统实时仿真平台；此外，利用ADAMS/Controls模块实现了由MATLAB/Simulink设计的控制器与由ADAMS/View建立的4WS汽车虚拟样机进行“机械—控制系统”可视化联合仿真的思想。基于线控技术和最优控制原理，提出了四轮主动转向汽车的模型跟踪控制策略。在分析了车辆转向的理想状态后，进行了主动4WS汽车前、后轮转角最优跟随控制器设计和算法推导。开环仿真表明：在线性操纵区域内，基于最优控制的主动4WS汽车实现了零化汽车质心侧偏角与跟踪期望横摆率的控制目标；在引入“单点预瞄最优曲率”驾驶员模型后，通过闭环系统双移线仿真和评价指标分析得出：最优控制主动4WS汽车具有更好的路径跟踪精度和更优的主动安全性综合评价指标，对正常行驶情况下的驾驶员操作具有智能辅助作用，提高了汽车高速行驶时的转向性能。针对具有不确定性的4WS汽车，提出了非线性滑模变结构控制策略。将实际车辆的前、后轮侧偏刚度及外界干扰视为有界的不确定性参数，设计了四轮主动转向的滑模变结构控制器以克服车辆未知的参数摄动与外部扰动影响，并进行了控制效果的鲁棒性验证。闭环仿真表明：滑模控制的不确定性4WS汽车能够很好的跟踪确定性理想转向模型，控制系统对于一定范围内的车辆参数变化和外部干扰具有鲁棒性，对路面附着条件的变化具有一定的适应性。此外，论文基于扩展Kalman滤波理论，还研究了利用侧向加速度测量值对汽车质心侧偏角与横摆角速度进行状态估计的软测量技术。考虑到在轮胎侧偏力达到饱和情况下，4WS系统对车辆稳定性改善有限的局限，针对后轮具有主动转向功能的4WS汽车，提出了利用后轮主动转向和差动制动联合作用产生补偿横摆力矩的车辆稳定性控制策略(VSC)，进行了多变量输入输出的车辆稳定性控制系统模糊控制器的设计，并利用遗传算法对VSC模糊控制器参数及隶属函数分布进行了优化，改善了系统的瞬态响应性能。通过开环仿真及虚拟样机测试表明：所设计的VSC控制系统可以保障车辆在极限转向工况下的稳定性，有利于提高车辆在危险行驶中的主动安全性。针对4WS转向控制器与VSC稳定性控制器这两种主动控制子系统共存情况下的集成与协调策略进行了研究，利用状态变量相平面法进行了车辆失稳的量化判定，并依此确定这两种不同底盘控制子系统的有效作用域，采用模糊判决方法进行了控制任务分配，避免了二者之间控制目标的冲突与硬切换动作的发生，并通过数值仿真验证了所提出的协调控制策略的可行性。更多还原

【Abstract】 The four-wheel steering (4WS) system is an effective active control technology for improving maneuverability and safety of vehicle in common use. In order to take full advantage of 4WS vehicle, on the basis of the development of steer-by-wire (SBW) technology, the characteristics of vehicle lateral dynamics and its control strategies are regarded as the research direction by this thesis, and the influences of linearity, uncertainty and nonlinear on vehicle dynamics are also fully considered by this thesis, then, a systematic research on control strategies for active 4WS vehicle is carried out.In the beginning, the dynamics analysis of 4WS vehicle is carried out and its nonlinear differential equation is established, then the calculation method of this nonlinear model is studied and implemented by using the MATLAB/Simulink software. All above works provide a real-time simulation platform of chassis control system with higher accuracy and quicker runtime that can verify different control strategies and control effects for 4WS vehicle. Furthermore, a virtual prototype of 4WS vehicle is founded by using the ADAMS software, and the viewable simulation of this virtual prototype combined with the controllers designed by MATLAB/Simulink is also realized by using ADAMS/Controls block.By means of the SBW technology and optimum control theory, a control strategy which need follow an ideal model is proposed for active 4WS vehicle, and this ideal vehicle model followed is determined too. Subsequently, the optimum controller that is used to control the angles of front and rear wheels of 4WS vehicle is designed. The open loop simulation indicates that the optimum controller can decrease the sideslip angle, and can keep the desired yaw rate at the same time during a steering process. The close loop simulation after introducing driver model shows that the 4WS vehicle under optimum control has better accuracy in path deviation and better evaluation index of active safety, and has an intelligently assistant function for manipulate of driver. So, the maneuverability when vehicle is driving at higher speed is improved.A sliding mode variable structure control strategy (SMC) is studied when 4WS vehicles are disturbed by some uncertain elements. The SMC controller is designed for active 4WS vehicle by treating the cornering stiffness of the front and rear tires and outer disturbance as uncertain parameters, but their variance in a limited range, and by using a linearity model as an ideal target followed. This SMC controller can maintain the vehicle with near zero sideslip angles, and track desired yaw rate, the controlled vehicle system behaves favorable robustness: The simulation test of a closed-loop system indicates that the SMC controller can overcome the effect of parameters perturbations and outer disturbances on system stability, and can adapt variance of the road adhesion condition to a certain extent. Furthermore, a state estimate method for sideslip angle and yaw rate of vehicle is discussed by using the measurable lateral acceleration signal based on the Kalman filtering principle.Because the 4WS system has limited effect on stability of vehicle when the sum of all tyre side force arrive maximum, so, a vehicle stability control strategy (VSC) is proposed for 4WS vehicle, a fuzzy controller of VSC system with multi-input and multi-output variables is designed by combining active rear-wheel steering with differential braking technology. Furthermore, the distributing of membership function and scale parameters of fuzzy controller are optimized by using Genetic Algorithms and the optimized results indicate that the transient response of vehicle is improved. The open loop simulation shows that the VSC system can ensure effectively the stability, and increase the active safety during critical steering process of vehicle.A kind of coordination control project between the 4WS steering controller and VSC stability controller is researched. Firstly, whether or not the vehicle lost its stability is estimated by using phase plane of state variables. Secondly, the valid action ranges of different controller are determined, and the control signals of different controller are also assigned by using fuzzy method. With all of above works, the conflict of control goal between the two controllers and the hard switch action of rear wheels are avoided accordingly. At last, a simulation test shows that this coordination control strategy is feasible and effective.更多还原