【作者】 王虎；

【导师】 桂长林；

【作者基本信息】 合肥工业大学 ， 机械设计及理论， 2010， 博士

【摘要】 缸套失圆现象在内燃机中普遍存在,它严重影响整机的动力性、经济性、环保性和可靠性。然而由于内燃机结构复杂,零部件之间无论静态配合关系还是动态的力学、热流传递关系均具有复杂性、多样性,缸套失圆问题分析难度大,以致研究人员很难在众多的影响因素中给出定量分析结果,只能在设计中更多的依据经验处理此问题,这也严重阻碍了人们对内燃机缸套失圆形成机理的了解。长久以来,如何有效减轻内燃机缸套失圆及其带来的负面影响一直是困扰内燃机工作者的重要课题。本研究以某企业正在生产的某款采用干式缸套的四缸内燃机为研究对象,分别计算了机械负荷和耦合冷却流场的热负荷作用下的缸体变形和缸套失圆;在试验验证缸套热负荷计算结果的基础上,对综合多因素下的缸套失圆问题进行了研究,并对失圆缸套下的活塞环适应性、活塞环与缸套之间油膜厚度的不均匀周向分布以及其对机油耗的影响给出定量计算和分析。首先,本文在阐述现有的螺栓预紧力计算和分配模型、曲轴连杆动力学计算模型的基础上,结合试验测得的示功图数据,以额定工况和最大扭矩工况为计算工况,运用缸体-等刚度缸盖有限元模型,对螺栓预紧力、活塞侧推力、气缸压力这些机械负荷共同作用下的内燃机缸套失圆问题进行了仿真计算。同时,在对冷态、热态下的缸套变形和失圆数据进行分析讨论的基础上,对机械负荷中对缸套失圆产生主要影响的各影响因素进行了综合评价。其次,运用传统的内燃机热负荷分析方法,在综合论述缸内传热计算模型、缸壁传热分配模型、活塞环-缸套摩擦计算分配模型及冷却水腔传热边界计算模型的基础上,结合4105柴油机的具体特征,合理运用热负荷边界条件的计算模型,针对缸体-等刚度缸盖模型,计算了额定工况和最大扭矩工况下的温度场、热变形、缸套失圆。在对热负荷作用下的温度场、缸套变形和失圆数据进行分析讨论的基础上,对运用传统热负荷分析方法计算的缸套失圆进行了评价,并对热负荷对缸套失圆的影响进行了定量讨论。第三,运用CFD方法,对内燃机机体内冷却流场进行了仿真计算,分析并讨论了冷却流场的流速分布特征及其带来的非均匀冷却效果。以整体冷却流场的计算结果为基础,针对缸体与冷却水的流固耦合模型,应用共轭传热方法,计算并分析了缸体内的冷却水流速场以及在其影响下缸体与冷却水耦合模型的温度场、热变形及缸套失圆问题,计算表明,由于冷却流场流速分布的影响,缸体的温度分布、热变形存在着显著的周向、轴向的变化,流固耦合共轭传热方法是研究热负荷影响下缸套变形失圆问题的较为精确有效的方法,为内燃机的优化设计提供了有效的方法。第四,通过对复杂干缸套机体的加工和传感器的固定安装,选用热电偶作为测温传感器,配合多功能巡检测温装置,实现了对四缸柴油机的多缸多点多工况的动态温度测量,通过对各缸套之间及缸套自身周向和轴向温度的对比分析,研究探讨了多缸柴油机额定工况下缸套温度分布的规律和特点。同时,对其它工况条件恒定下的变转速和变负荷的缸套温度变化规律和分布特点进行了探讨,并通过与前面两章不同仿真方法计算结果的比较,评价了这两种仿真方法的有效性和准确性。第五,综合考虑真实工况下的各种影响因素,探讨了多因素影响下缸套热变形和失圆的计算方法。对螺栓预紧力、活塞侧推力、气缸气体压力、热负荷及冷却流场共同作用下的缸套变形失圆进行了计算,并对真实工况下的缸套失圆问题进行了讨论和评价。第六,通过傅里叶展开分析方法近似模拟变形后的缸套径向变形,结合自由状态及安装状态下的活塞环变形曲率,建立了活塞环适应性分析的数学计算模型,对活塞环与各变形缸套内壁面的接触压力进行了定量计算和分析,结合接触压力的分布图,对活塞环与四个缸体缸套的第一道密封面进行了评价。第七,针对缸套失圆对润滑油膜厚度周向分布的影响问题,运用数值计算方法,建立了变形缸套下活塞环变形及润滑油膜周向分布的数学模型,计算了在弹性张紧力、气体压力、油膜支反力等共同作用下的活塞环变形,并通过失圆缸套与变形活塞环之间的位置关系,求得失圆缸套下的不同截面润滑油膜的周向分布。第八,运用上章活塞环与失圆缸套之间的油膜周向分布数据,对失圆缸套下,通过刮油、惯性甩油、通过开口间隙上窜这三种途径的活塞环—缸套摩擦副的润滑油消耗进行了定量计算,并通过与理想圆形缸套下的机油消耗量的比较,具体讨论和分析了缸套变形对机油消耗的定量影响。最后,总结了本文所作的主要工作及主要创新点,对今后的进一步研究提出了作者的一些看法。更多还原

【Abstract】 It is common that the cylinder liner is non-circular when engine is firing or not, and this has great influence on engine’s performance including power, economy, environmental protection and durability. Because of the analytic difficulty coming from the complexity of engine body structure, variety of the static and dynamic relationship between components、forces and heats, the researchers can only use some experimental formulas in engine design, and this block our understanding of its forming theory and process. It is an important work for the researcher to reduce the negative effects from the non-circular of the cylinder liner. The main tasks of this paper are not only to comprehensive assess each factor according to numerical simulating results, but also to calculating deformation and non-circular of the cylinder liner caused by multiple factors. We also study the piston ring conformability, oil film thickness between piston ring and cylinder liner along circumferential direction and oil consumption considering non-circular of cylinder liner.At the beginning of this dissertation, the present status of the joint bolts preloading model, dynamical calculation of crankshaft are reviewed. Using pressure-time data from engine test , the deformation and non-circular of the cylinder liner are numerical calculated in rated and maximum torque condition considering influence of all mechanical factors including joint blot preloading, piston thrust force and gas pressure on engine block-equal stiff head model. Each mechanical factor is comprehensive assessed after discussion of the deformation results.Secondly, using traditional thermal boundary conditions, the temperature distribution, thermal deformation of the block-equal stiff head simulating mode and distortion of the cylinder liner are calculated and analyzed. The influence of each traditional thermal factor to distortion of cylinder liner is discussed.Thirdly, based on conjugate heat transfer theory, considering influence of coolant flow, the temperature distribution of cylinder block-cooling water coupling model and thermal deformation of the cylinder liners was calculated with the help from the calculating results of CFD analysis for the whole cooling water system. The flow and pressure field of the whole cooling system, the temperature distribution of the coupling model and thermal deformation of the cylinder liners were demonstrated, which showed that the temperature and thermal deformation had remarkable changes along axial and circumferential direction, and these also provided theoretical evidence for failure simulation and optimization design of diesel engine.Fourthly, the temperature of multiple key dots in the cylinder inner surface of machined dry liner engine under different working conditions are measured using thermocouple sensors and thermal tour detector in order to verify simulation models that are used in traditional thermal analysis and fluid-solid couple analysis. The characteristics of temperature distribution and the changing relation between working temperature of cylinder liner and working condition—speed and torque—are studied. By comparison to the test results, it shows that the fluid-solid coupled analysis method is reasonable and efficient.Fifthly, considering multiple causing factors including mechanical and thermal load, the more reasonable distortion of the cylinder liner is examined in real condition, thus provided a kind of more accurate and high efficiency means to evaluate the performance of the piston-piston ring-cylinder liner set.Sixthly, a computational model for examining the conformability of piston ring to deformed cylinder is developed. This computational model incorporates Fourier Fat Transfer that is used to fit and analysis the deformed cylinder bore data and algorithm method that is used to calculating the curvature change of the ring between free state and mounted state. The contact pressure between ring and bore through an engine cycle is calculated, and the seal of the ring is also assessed.Seventhly, in order to predict the effect of cylinder deformed on oil consumption, a simple and easy technique to calculate the film thickness in deformed cylinder is developed. The model takes into account of the ring tension, gas pressure and film support pressure and their interactions to calculate the deformation of the ring in the cylinder using the theorem of the three moments. The film thickness along both circumferential and axial direction through whole engine cycle is calculated and evaluated in the end.Eighthly, a model that used the oil film thickness obtained from the above chapter to calculate the amount of oil transported to combustion chamber by passing between ring and cylinder is proposed. The model takes into account of three major part of oil passing to the chamber, including the amount of oil scraped by ring through whole engine cycle, the amount of oil thrown by inertial force, the amount of oil pushed by reversed gas pressure during certain crank angels. The amount of oil transportation in the deformed cylinder is calculated and is compared with the one in the round cylinder.Finally, essential work and some certain innovative points of this dissertation are summarized. Some suggestions for the future research on this field are presented by the author.更多还原