【作者】 徐玉梁；

【导师】 付光琦；

【作者基本信息】 天津大学 ， 动力机械及工程， 2009， 博士

【摘要】 本课题紧密联系工程实际,以目前市场上应用范围广泛的493车用柴油机为研究对象,对车用柴油机正向工程开发中的重要环节——缸孔变形问题的机理、评价方法及优化设计思路进行全面深入的研究。目的是解决国内企业在车用柴油机整机开发及老机型改进过程中普遍遇到的机体缸孔变形过大从而影响机油消耗和颗粒物排放量进一步降低的难题,突破了正向工程设计中的技术难点,为由点及面的全面提高自主创新能力奠定基础。本文提出了整体接触多场分步耦合的研究方法,通过建立包含完整机体、缸盖、缸套、缸盖垫与缸盖螺栓的接触关系模型,避免了以往机体局部模型和单件研究的不足;通过对冷却水侧流场的CFD模拟获得缸体冷却水侧温度场的分布,减少了采用简单经验公式给出边界条件造成的误差;通过分步求解机体温度场的分布与热应力场下的变形,降低计算规模,实现了机体缸孔在机械负荷和热负荷下的耦合计算。根据缸盖垫各部分的不同力学特性,并结合缸盖垫载荷试验,本文提出了缸盖垫的非线性组合模型,最大限度简化模型的同时反映了零件的真实力学关系。通过在缸盖螺栓预紧力下机体缸孔变形的模拟计算与试验测量,对整体接触模型和边界条件的准确性进行了验证,在此基础上分步进行机械应力场、热应力场和耦合场下缸孔变形的模拟计算。根据耦合场模拟确定的综合优化方案,有效降低了493国Ⅲ样机的配缸间隙。性能与排放试验表明,此样机与原机相比最大扭矩增加10%,机油消耗率降低35%,ESC试验颗粒物排放量为0.09 g/kW?h,大大低于该机型国Ⅲ阶段0.13 g/kW?h的限值水平。不论是缸孔变形的模拟计算,还是缸孔变形的试验测量获得的都是缸孔的总变形。通过研究发现,机体缸孔的总变形可以分为位移变形和失圆变形两类,而位移变形和部分失圆变形可以被连杆侧隙或活塞环的弹力所弥补,不会造成活塞环密封环带的失效。在对缸孔各个横截面的变形应用快速傅立叶变换(FFT)的基础上,本文提出了缸孔变形的评价参数——最大有效变形?r e ffect?max,应用此参数可以更加准确的预测缸孔变形对机油消耗率和颗粒物排放的影响,为正向工程中机体缸孔变形的研究建立了行之有效的方法,具有重要的工程应用价值。更多还原

【Abstract】 Closely linked with engineering practices, this paper uses the widely-used 493 automotive diesel engine as the research object and analyzes comprehensively an important issue in the forward engineering development of automotive diesel engines—the mechanism, evaluation methods and optimization designing of cylinder bore deformation. The objective is to solve the difficult problem of how to further decrease oil consumption and particulates emission, a thorny problem that domestic enterprises often encounter due to excessive cylinder bore deformation in the development of new diesel engines or the optimization of existing models. The paper is a breakthrough in forward engineering designing, making it possible to gradually improve independent innovation capabilities.The integral contact multi-field indirect coupling method is put forward and an integral contact relation model including the complete cylinder block, cylinder head, cylinder liners, cylinder head gasket and cylinder head bolts is established to avoid the disadvantages of partial model and single component researches. The temperature field of coolant is obtained through the CFD simulation of flow field to reduce the errors arising from boundary conditions given by simple empirical formulas. The temperature field and deformation under thermal stress fields are solved respectively to decrease the computational complexity and the indirect coupling calculation of cylinder bore deformation in mechanical stress fields and thermal stress fields is implemented.Based on the mechanical properties of different parts of the cylinder head gasket and cylinder head gasket loading tests, a non-linear combined model of the cylinder head gasket is put forward to simplify the model as well as reflect the accurate mechanical relationship between the different parts. Through numerical simulation and static measurements of cylinder bore deformation under cylinder head bolt screw pre-moment, the integral contact relation model and boundary conditions are calibrated and verified. On this basis, the simulation of cylinder bore deformation in mechanical stress fields and thermal stress fields is conducted respectively. By utilizing the comprehensive optimization designing scheme devised according to the results of coupling simulation, the clearance between the cylinder liner and the piston of the new 493 prototype diesel engine is reduced effectively. The performance and emission tests show that the optimized prototype engine has a 10% increase in maximum torque and 35% decrease in oil consumption compared with the original engine. ESC test results show that the particulates emission is 0.09 g/kW?h, far below 0.13 g/kW?h, the required level of the third phase national emission regulation.Both the simulation and experimental measurement results are total cylinder bore deformation. This research shows that the total deformation can be divided into two kinds: displacement deformation and out-of-roundness deformation. Displacement deformation and part of out-of-roundness deformation can be made up by the clearance between the connecting rod and the piston or the elastic forces of the piston rings, thus unable to cause the failure of the sealing circular-bands of the piston ring . Based on the fast Fourier transformation of the cross-section deformation of the cylinder bore, an evaluation parameter of cylinder bore deformation, the maximum effective deformation ?r e ffect?max, is defined. Using this parameter, the effects of bore deformation on oil consumption and particulates emission can be predicted much more accurately, making it possible to establish an effective approach to cylinder bore deformation in forward engineering, an approach of great practical value in engineering.更多还原