【作者】 董红亮；

【导师】 邓兆祥；

【作者基本信息】 重庆大学 ， 车辆工程， 2009， 博士

【摘要】 随着人们对汽车操纵稳定性、安全性、乘坐舒适性等性能要求的提高,决定这些性能的两个主要的系统——转向系统和悬架系统也取得了很大的发展,如近几十年出现的四轮转向系统、主动悬架系统等。许多研究表明,汽车的转向系统与悬架系统之间存在强耦合,彼此互相影响。对汽车转向系统和悬架系统的单独控制在理论上忽视其它子系统的存在,也忽视对其它系统性能目标的影响,其效果并不是两个子系统单独控制效果的简单叠加,往往会出现控制效果的相互削弱,有必要进行两个子系统的综合控制。针对该领域研究存在的耦合机理不清晰、协调机制不健全等关键问题开展研究,发展出一种四轮转向和主动悬架的综合控制新方法,对提高车辆的综合性能具有重要意义。本文建立了包含四轮转向和主动悬架的整车统一动力学模型,模型包括了悬挂质量的侧向、横摆、垂直跳动、俯仰、侧倾和非悬挂质量的垂直跳动,共9个自由度。采用了能够反映轮胎非线性特性和侧向垂向耦合特性的侧向力半经验模型。对车辆动力学模型进行了试验验证。在整车9自由度模型的基础上进一步简化,分别建立了2自由度四轮转向模型和7自由度主动悬架模型,并分别设计了四轮转向和主动悬架最优控制器。建立了四轮转向系统的硬件在环仿真平台,采用步进电机作为后轮转向的执行机构,分别安装了两个角位移传感器检测前后轮转角。进行了四轮转向硬件在环仿真实验,结果表明,后轮转向的响应滞后时间小于30ms,对车辆转向系统响应的影响很小,在四轮转向的控制算法中可以不用考虑。通过灵敏度分析,研究了转向系统和悬架系统的耦合关系。由于簧上质量的耦合作用,车辆转向时簧上质量的离心力引起车身侧倾角和内外侧车轮垂直载荷的变化。一方面,由于悬架导向系的耦合作用,车身侧倾引起车轮侧倾转向和车轮外倾,影响车辆稳态转向特性;另一方面,由于轮胎侧向垂向耦合特性,内外侧车轮垂直载荷发生变化,导致前轴或后轴等效侧偏刚度减小,影响车辆转向特性。通过主动悬架的控制,转向时车身侧倾角明显减小,车轮侧倾转向和车轮外倾产生的侧向力也明显减小,车辆的稳态转向特性改变。考虑轮胎侧向垂向耦合特性,研究了四轮转向和主动悬架控制对车辆转向性能的影响。提出了一种基于车身姿态控制的四轮转向和主动悬架的协调控制策略。在引入主动悬架控制的同时,引入四轮转向的控制,并且对四轮转向的控制量进行调整。在此基础上,提出了一种基于前后悬架刚度匹配的协调控制策略,得到二者综合的协调控制策略。根据车辆横摆角速度响应与参考值的偏差,对主动悬架的控制量进行调整。通过方向盘角阶跃输入仿真,研究了采用不同控制系统时车辆的极限性能。结果表明,四轮转向系统对提高车辆极限性能几乎没有任何帮助;主动悬架系统能够有效控制轮胎垂直载荷,提高轮胎侧向力,从而显著提高车辆的极限性能;四轮转向和主动悬架的协调控制,能够提高内侧车轮垂直载荷,并合理分配前后轴轮胎侧向力,进一步提高了车辆的极限性能。更多还原

【Abstract】 With the increasing demand of handling and stability, safety, ride performance of vehicle, the steering and suspension systems which affect those performances have a great development, such as Four-Wheel Steering and Active Suspension systems introduced in the last decades. Many research papers indicate that vehicle steering and suspension systems have strong coupling effect and interact with each other. The independent control of steering and suspension systems ignore the existence of other system theoretically and the effect to other system performance, the result is not the simple overlap of the two separate control systems, but usually weakened by each other. So it is necessary to develop integrated control of the two systems. Aiming at the main problems of this research area such as coupling mechanism and coordination strategy, developing a new method for the integrated control of 4WS and Active Suspension shows great significance on vehicle performance.A full vehicle dynamic model including steering and suspension systems is constructed. There are 9 degrees of freedom, i.e., lateral, yaw, heave, pitch, roll of sprung mass and vertical displacement of four unsprung masses. A semi-empirical tire lateral force model is used to describe tire non-linear characteristic and lateral vertical coupling characteristic. Several experiments were carried out to validate the model. At the base of 9dof full vehicle model, a 2dof 4WS model and 7dof Active Suspension model are built separately. A hardware in-loop simulation platform of 4WS is constructed, the actuator of rear steering system is a step motor, the front and rear steering angle is measured by two angular displacement sensors. Hardware in-loop experiment is carried out. The response time of rear wheel steering system is less than 30 milliseconds, almost has no influence on steering system response, and could be left out in the 4WS control algorithm.The coupling mechanism is studied by means of sensitivity analysis. Vehicle body rolls and lateral weight transfers due to centrifugal force of sprung mass. On one side, due to guide mechanism of suspension, roll motion affects roll steering and wheel camber, thus affects steady state cornering characteristics. On the other side, due to tire lateral vertical coupling characteristic, lateral weight transfer affects tire effective cornering stiffness of front and rear axles, and affects steering characteristic.With active suspension control, body roll angle decreases greatly, so does lateral forces produced by roll steering and wheel camber, and steady state cornering characteristic changes. Considering tire lateral vertical coupling characteristic, effect of 4WS and active suspension control on cornering characteristic is also studied.An coordinated control strategy of 4WS and active suspension is proposed based on body roll control. Control quantity of 4WS is adjusted when active suspension is introduced. On the basis of previous control strategy, another coordinated control strategy based on front and rear suspension stiffness distribution is proposed. And the two control strategies are integrated. Control quantity of active suspension is adjusted accoording to the error between the actual yaw rate and the demand yaw rate.By simulating steering wheel step input, the limit performance of vehicle with different control system is researched. 4WS system almost has no effect on vehicle limit performance. Active suspension system has great improvement on vehicle limit performance due to tire load and lateral force improvement. Coordinated control of 4WS and active suspension has further enhancement on vehicle limit performance because of lateral load improvement and force distribution between front and rear active suspension.更多还原