【作者】 张立香；

【导师】 刘守荣；

【作者基本信息】 中国农业大学 ， 机械制造及其自动化， 2014， 博士

【摘要】 现代农业装备在由小型向大型、由简单向复杂转化的过程中,其可靠性日益受到重视。可靠性技术在农机产品中的应用在国内尚处于起步阶段,目前对农机产品的研发大多采用传统设计方式,不考虑设计变量的随机性,因此导致农机产品的可靠性普遍偏低,无法满足用户需求。本文以提高农机产品可靠性和延长其使用寿命为目的,展开从零部件可靠性分析到系统可靠性分析、从单指标可靠性评价到多指标可靠性综合评价的研究工作。具体内容如下：(1)针对极限状态方程未知的情况,对结构可靠性分析方法进行研究。从正可靠性分析的角度出发,提出一种基于样本点全插值的响应面法,并对样本点是否有效的问题进行了分析,提高了计算效率。从逆可靠性分析的角度出发,提出一种基于逆可靠性原理抽样的响应面法,并与Kriging近似方法相结合,提高了分析的计算效率和求解精度。分别针对这两种方法进行了数值算例验证,并采用这两种不同的方法对联合收割机的驱动半轴进行可靠性分析。(2)对驱动桥壳的疲劳载荷获取方式和寿命进行分析。建立了驱动桥壳关于离散路面不平度的垂向动载荷数学模型,以此获取驱动桥壳的垂向载荷时间历程；对驱动桥壳在恒幅载荷、随机载荷和混合载荷下的疲劳寿命进行分析；并在混合载荷下,分析了驱动桥壳疲劳寿命和最危险部位相对于设计变量的变化规律。通过试验法获得联合收割机前桥壳危险点的应变时间历程,根据应力与应变的关系获得其应力时间历程,通过雨流计数法编制载荷谱；利用名义应力法和Miner疲劳累积损伤法则,计算各危险点的疲劳寿命值,得出最危险部位为前桥壳支撑车体的位置。(3)对联合收割机变速箱传动系统的可靠性进行分析。根据不同零部件对变速箱系统可靠性的影响程度,对联合收割机变速箱系统的零部件进行分类；根据变速箱传动原理,分别对变速箱Ⅰ档失效、Ⅱ档失效、Ⅲ档失效和倒档失效做了详细的分析,最终得出联合收割机变速箱系统传动失效的故障树模型和系统失效的数学模型;通过重要度分析,得出各零部件对联合收割机变速箱系统传动失效的结构重要度、概率重要度和相对概率重要度求解模型。(4)对多指标可靠性综合评价方法进行研究,提出了一种基于区间抽样和可拓理论的神经网络可靠性评价方法。根据可靠性评价指标和评价结果的等级区间的对应关系,通过区间抽样和排列组合的方式生成可靠性指标样本,利用可拓原理和主观修正法判断各指标组合样本的评价等级,最终生成用以网络训练的可靠性数据样本；利用熵误差函数建立BP神经网络的学习过程,并通过在输出层增加判断层的方式对网络结构进行调整,以此提高神经网络的收敛速度,并用该方法构建了联合收割机底盘的可靠性评价模型。更多还原

【Abstract】 In the process of small to large size and simple to complex model, the reliability of Modern Agricultural Equipment gradually becomes the focus of attention. However, in the domestic, the application of reliability technology in agricultural machinery products is still in a fledging period, and traditional design method is most adopted when agricultural machinery products is studied. In consequence, the reliability of agricultural machinery products is generally low in our country, and unable to meet the demands of users. In this paper, with the purpose of improving the reliability and prolonging the service life of agricultural machinery products, research is carried out from components reliability analysis to systems reliability analysis and from single index reliability evaluation to multi-index comprehensive evaluation. The main researches in this paper are presented as follows:(1) Aiming at the condition of limit state equation unknown, research on the structural reliability analysis method is carried out. From the perspective of forward reliability analysis, a response surface method based on all sample point interpolation is proposed, and the effectiveness of the sample points is analyzed. From the aspect of inverse reliability analysis, a response surface method based on inverse reliability principle sampling is proposed, and the proposed method is combined with Kriging approximate. These two proposed methods both can accelerate calculation efficiency and improve the precision of solution. Numerical examples are used to verify these two methods, respectively. The reliability of driving axle shaft of combine harvester is studied respectively adopting these two proposed methods.(2) The way of obtaining load of drive axle housing and the fatigue life of drive axle housing are analyzed. The vertical dynamic load mathematical model about discrete road roughness is constructed for the drive axle housing, and vertical load time history is obtained using the measured discrete road roughness. Fatigue life of drive axle housing is predicted under constant load, random load and hybrid load. Besides, under the hybrid load the change rule of fatigue life and dangerous part relative to design variable is studied. Strain time history of dangerous points of front axle housing of combine harvester is obtained by the experiment, and stress time history is acquired according to the stress-strain relationship. Then, load spectrum is formulated by appling rainflow counting method. The fatigue life of each dangerous point is calculated by using the nominal stress method and Miner damage rule. The most dangerous part is the location of the front axle housing supporting the body of combine harvester.(3) Reliability analysis of gearbox transmission system of combine harvester is conducted. Firstly, the components are classified on the basis of their importance to the reliability of gearbox transmission system. Secondly, according to the transmission principle, the failure of first gear, second gear, third gear and reverse gear are made detailed analysis, respectively. Finally, the fault tree model and the mathematical model of system failure are established. Based on the importance analysis, the solution models of structural importance, probability importance and relative probability importance are built for the gearbox transmission system of combine harvester.(4) A neural network reliability evaluation method based on interval sampling and extension theory is put forward to establish the reliability evaluation model of combine harvester chassis. Based on corresponded relationship between reliability evaluation index and evaluation result’s graded interval, reliability index sample is generated by means of interval sampling and permutation-combination, and the evaluation order of each combination sample is determined by applying extension theory and subjective correction, finally the reliability data sample used for network practice is created. The learning algorithm of BP neural network is established using entropy error function, and network structure is adjusted by increasing judge layer in output layer. The proposed method can improve the convergence rate of the neural network and the accuracy of reliability evaluation.更多还原