【作者】 刘志强；

【导师】 董惠娟；

【作者基本信息】 哈尔滨工业大学 ， 机械工程（专业学位）， 2018， 硕士

【摘要】 曲轴是发动机内部的重要零件,在发动机运行中曲轴长期处于高负荷运行状态。周期性变化气体压力、大质量零部件的惯性力以及对应的力矩作用于曲轴,使曲轴内产生快速变化的拉伸、压缩、扭转、弯曲等交变应力。为了保证相关设计功能的顺利实现,曲轴往往设计为非常复杂的形状,无论是曲柄销还是主轴颈,应力集中问题都是非常普遍的,而这一问题的客观存在,不仅容易导致曲轴疲劳裂纹的产生,同时所诱发的曲轴断裂问题也同样会影响发动机的正常工作。涡轮增压发动机由于爆发力大,其内部所承受的各种交变应力更加突出。因此,曲轴在涡轮增压条件下的强度可靠性及疲劳寿命的研究显得尤为重要。本文以某1.5-T直列四缸汽油机曲轴系作为分析对象,主要运用理论分析、计算机模拟和实验研究相结合的方法,采用当前的先进分析技术和工具,较全面分析了曲轴系的动态应力,来预测曲轴疲劳失效,旨在为发动机曲轴的设计开发提供参考。首先,理论分析曲轴及其附属零件运行状态和受力情况,针对待分析的曲轴系统为多体系统,引入多体动力学及子结构分析理论并建立起曲轴的多体动力学方程;针对本课题研究曲轴失效,探讨了疲劳分类及影响因素,确定曲轴属于何种疲劳,适合采用何种疲劳理论对其进行疲劳预测,以及适合采用哪种疲劳方法来预测曲轴疲劳。其次,使用CATIA软件对曲轴,机体等相关零件进行实体建模;运用Hyper Mesh有限元前处理软件,对必要的机体及相关零件进行网格划分,建立机体(轴承盖及配带轴瓦)的有限元模型;采用ABAQUS软件对建立的机体进行缩减,为建立多体动力学分析做好模型准备;应用多体动力学软件AVL—EXCITE POWER UNIT建立曲轴模型,软件可自动对曲轴进行有限元划分并缩减;在上述准备完成后基于动力学软件EXCITE POWER UNIT,建立了该机型曲轴系的多体动力学模型,而后基于动力学软件分析计算,得到15-T机型一个工作循环内曲轴的动态载荷谱。鉴于发动机曲轴上疲劳强度最薄弱处为曲拐圆角处,在分析曲柄强度的基础上利用圆角子模型完成曲轴疲劳强度研究——系统计算和分析力场数据、S-N曲线和曲轴圆角的动态载荷谱,运用FEMFAT疲劳分析软件对曲轴的疲劳寿命进行预测,分析得出该涡轮增压机型曲轴各个圆角处的疲劳安全系数。最后,计算曲轴在正常运转时不同工况下所受到的扭矩,选取不同工况下最大扭矩进行分析;得到扭矩后综合国内外现行实验方法,有针对性的选取曲轴弯曲疲劳试验试验方法;利用已有的曲轴疲劳弯曲试验机,对曲轴做弯曲疲劳实验以验证计算机仿真结果针对性和有效性。更多还原

【Abstract】 The crankshaft is a very important part of the engine,and is subjected to extremely highly mechanical loads during engine operation.In the actual work process,the crankshaft to withstand the cyclical changes in the gas pressure,inertia force of components with high quantity and corresponding torque,which easily leads to a rapid changes in the inner crankshaft including in the pull,pressure,bending,twisting stress.In order to complete the demanding design,crankshaft often is devised as complicated shape,whether in crank pin or in crank arm,and thus stress concentration is widely phenomena in the crankshaft design process.This problem existed in design not only gives arise to formation of fatigue crack,but also may lead to crankshaft breakdown and so make potential threats for the engine working.Especially,turbo supercharged engines will endure the more the above consequence than common ones due to their own explosive force.Therefore,it is more important to explore the strength and fatigue endurance of the crankshaft of turbo supercharged engines.In this research,we took a inline four-cylinder 1.5-T gasoline engine crankshaft system as the object of analysis,comprehensively analyzed the the dynamic stress of the crankshaft by theoretical analysis,computer simulation and experimental research methods,using the current advanced analytical techniques and tools,to predict the fatigue invalidation.It is designed to provide reference for the design and development of engine crankshaft.Firstly,we analyzed the operation state and force of crankshaft and its affiliated parts.In terms of multi-body system as crankshaft system,multibody dynamics theory and structural analysis theory were referenced to establish the multi-body dynamics equation;in term of fatigue invalidation,we detected the fatigue classification and factors influencing fatigue to identify which fatigue is involved,which theory is suitable to predict the fatigue and which method is used.Next,the CATIA software is used to model the crankshaft,body and other related parts.The indispensable body and the related components were meshed and established the finite element model using Hyper Mesh finite element preprocessing software.The model was established by ABAQUS software,which was prepared for the establishment of multi-body dynamics analysis.The crankshaft model was established by applying the multi-body dynamics software AVL-EXCITE POWER UNIT which automatically divided andreduced the crankshaft.After the completion of the above preparation,based on the dynamic software EXCITE POWER UNIT,a 15-T inline four-cylinder engine crankshaft multi-body dynamics analysis model was built.Based on the kinetic analysis,the dynamic load spectrum of the crankshaft in the working cycle of the engine was calculated.In view of the weakness of the crankshaft on the crankshaft of the engine,the crank angle fatigue strength analysis was carried out on the basis of the analysis of the crank strength:system calculation,analysis of force field data,the S-N curve of the material and the dynamic load spectrum of the crankshaft fillet.The fatigue life of the crankshaft was predicted by FEMFAT fatigue analysis software,and the safety factor at each fillet of the turbocharger crankshaft was analyzed.Finally,we calculated the crankshaft in the normal operation of the torque under different conditions,selected the maximum torque under different conditions for analysis and got the torque.And then we integrated currently domestic and interna tional experimental methods,specifically selected crankshaft bending fatigue test method,and did bending fatigue test to verify the accuracy of computer simulation and the rationality of prediction by the existing crankshaft fatigue bending test machine.更多还原