【作者】 覃刚；

【导师】 周济； 陈立平；

【作者基本信息】 华中科技大学 ， 机械设计及理论， 2011， 博士

【摘要】 本文从分形理论的基本思想出发,探索性地提出了一种针对复杂机械系统的模型分解方法——分形解构法——该方法的核心思想是将一个复杂模型的复杂性尽量均衡地分解到各层次的局部优化模型中,使得各局部优化模型的复杂程度较低,便于设计与优化,同时各局部优化模型需要通过“过渡性性能指标参数”发生紧密联系,从而能保证模型的整体性不被破坏。进而,本文将此方法应用到多轴车辆底盘这一工程实例中,完善了多轴车辆底盘相关的整车动力学理论及双横臂油气悬架的悬架动力学理论,构造了针对多轴车辆底盘的分形解构法优化模型架构和优化流程,并实现了某型8轴底盘的优化算例。本文的创新性主要表现在以下几个方面：本文基于分形理论的思想,提出了针对复杂机械系统的模型分解方法——分形解构法。该方法是一种基于层次分解思想的建模方法,可以在一定程度上解决传统建模方法在面对复杂机械系统时所遇到的单个模型规模大、求解效率低、模型整体性能随参数变化的规律性差、模型优化困难、模型划分与工业研发体系不协调等问题。在具体的优化策略方面,提出了非完全独立的局部优化模型间的轮换优化方法,数值计算表明,该优化策略可以提高优化设计的计算效率。针对多轴车辆底盘,完善了整车动力学的相关理论,将其扩展为适合于任意轴距布置的多轴汽车的理论,提出了多轴车辆转向时各车轮侧偏角的最佳分布条件,并推导了相关公式：推导了多轴车辆不足转向度的解析表达式及相关的操稳判据；提出了多轴车辆直线制动稳定性条件；提出了多轴车辆制动工况下各轴附着系数利用率均衡分布时所需的各悬架的性能要求和各悬架的制动力要求,并推导了相关公式。采用旋量方法重新推导了悬架动力学的相关理论,指出了经典悬架力学中侧倾中心、纵倾中心等概念的不足之处,将其重新定义为侧向力诱导系数和纵向力诱导系数,使其从静态性能指标参数改变为动态性能指标参数,从而增强了悬架动力学对整车动力学的直接的、动态的理论支持。推导了双横臂独立悬架侧向力诱导系数和纵向力诱导系数的解析表达式。按照本文提出的分形解构法思想,构建了多轴车辆底盘的优化模型架构,成功地对8轴双横臂油气悬架底盘进行了优化设计。更多还原

【Abstract】 Based on the fractal theory, the fractal decomposition method is proposed to decompose the complex mechanical system by the author through the exploratory way. The main idea of fractal decomposition method is to decompose the complexity of the model to the local optimization model in each level uniformly, which makes the model designed and optimized easily through reducing the complexity of each local optimization model. At the same time, the integrity of original model will not be violated, because all the local optimization models are related through the transition index parameters.The proposed method is used in the design of multi-axis chassis. The vehicle dynamic theory of the multi-axis chassis and double-wishbone oil suspension are complemented. The framework and flow of optimization model of multi-axis chassis based on the fractal decomposition method are constructed, and the numerical optimization example of an 8-axis chassis is presented.The original research of this work can be summarized as follows:Firstly, the fractal decomposition method is proposed to decompose the complex mechanical system based on the fractal theory in this thesis. From both the science and technology theory and the practical engineering, a new modeling and optimization framework is proposed, where this framework can solve some problems which are large size, low-solving efficiency, irregular, difficult to optimization, and model decomposed inconsistent with industrial manufacture system when traditional modeling methods are used in complex mechanical systems. In specific optimization, a rotational optimization method among the independent local optimization models is proposed, and the numerical example shows that this method is more efficient than traditional method.Secondly, the vehicle dynamic theory is complemented. The vehicle dynamic theory is extended to the multi-axis vehicle with any wheelbase layout, which provides the theory for multi-axis chassis modeling and simulation. In detail, the optimum distributed condition of each wheel slip angle for multi-axis vehicle is proposed, and some related formulas are introduced; the analysis expression of understeer and correlative handling criteria of multi-axis vehicle are induced; the stabilization condition of straight brake is proposed; to obtain high brake efficiency of each axle, the conditions of each suspension performance and brake force on each axle are proposed, and some related formulas are introduced.Thirdly, the suspension dynamic theory is introduced by screw theory method. The shortcoming of some concepts such as roll center, trim center and so on are indicated, and they are re-defined as lateral force inducing factor and longitude force inducing factor, which transforms the original static performance index to dynamic performance index, so the suspension dynamic theory supports the vehicle dynamic more directly and dynamically. The analysis expressions of lateral force inducing factor and longitude force inducing factor of double wishbone suspension are introduced in this thesis.Lastly, based on the proposed fractal decomposition theory, multi-axis chassis optimization model framework is constructed, and an 8-axis double wishbone hydro-pneumatic suspension chassis is optimized.更多还原