柴油机缸套力学特性及变形研究

【作者】 毕玉华；

【导师】 叶燎原；

【作者基本信息】 昆明理工大学 ， 工程力学， 2012， 博士

【摘要】 随着节能减排政策的日益严格,柴油机缸内爆发压力提高到16Mpa以上,缸套-活塞组摩擦副的热负荷和机械负荷大幅度增加。受缸盖螺栓预紧力、活塞高速周期性往复运动、气缸体刚度不均匀以及冷却不均匀产生的影响,缸套与活塞环容易产生变形。当缸套变形失圆无法由活塞环的弹力进行补偿时,将产生不正常的间隙,从而产生油气泄漏,柴油机微粒(PM)排放量的50%是机油窜入燃烧室燃烧后产生的可溶有机物,因此控制缸套与活塞摩擦副变形与失圆,提高缸内密封性能,对降低机油耗,改善摩擦性能,以及减小排放,都具有重要的意义。以增压中冷柴油机为研究对象,针对缸套安装变形与工作变形的产生机理及影响因素进行了研究,提出了控制缸套变形的控制策略及解决方案,具体开展了以下研究工作：(1)预紧工况下缸套安装变形的特点与影响因素研究建立了机体-缸盖-缸套的装配耦合模型,在预紧工况下进行了装配体的静力分析,研究了缸套变形特点,并应用正交设计法,研究了结构因素与非结构因素对缸套变形的影响,优化了缸套结构。研究表明：预紧工况下各缸缸套整体呈现上部截面收缩变形,中下部截面扩张变形,最大变形处出现在缸套的上部；四个缸的缸套变形不均匀,其中一、四缸缸套变形较大,二、三缸变形较小；非结构因素中的螺栓预紧力、结构因素中的螺栓沉孔深度与缸套壁厚对缸套变形影响较大。(2)热负荷下缸套热态变形的特点与影响因素的研究在测试基础上,应用流固耦合传热方法,研究了缸盖、机体、缸套的热负荷以及冷却水套的流动均匀性,并研究了冷却水套结构对冷却均匀性以及缸套热变形的影响。研究表明：缸套上部热变形及变形梯度较大,中下部热变形及变形梯度相对较小,热负荷工况下的缸套平均热变形是预紧工况平均变形的16倍；相邻两缸间的缸套热变形相对较小,在第一缸和第四缸自由端出现较大的缸套热变形。由于各缸缸盖、机体、缸套温度场分布不均匀,冷却水套流动均匀性与冷却均匀性对应的最优方案是有差异的。(3)工作负荷下缸套热机耦合变形的特点与影响因素的研究考虑机械负荷与热负荷耦合作用,对机体与缸套的装配耦合模型进行了热机耦合分析,研究了不同负荷加载情况下缸套变形的特点。相比预紧工况与热负荷工况,工作负荷下的缸套最大主应力大幅度增加,缸套整体变形与热负荷工况相似,缸套变形幅度增加较小。综合分析,相比冷却均匀性的优化方案,预紧工况优化方案对于减小缸套的失圆度更有效；此外,受机体刚度影响,二缸与三缸、一缸与四缸的缸套变形对称,且变形呈豌豆形规律,机体结构刚度分布均匀性对于缸套变形起重要作用。(4)缸套动态变形的测试与分析采用应变测试方法,在外特性工况下对增压前后的缸套的动态应变进行了测试与分析,对比分析了增压中冷前后柴油机周向应变与径向变形的变化规律。随着转速的升高,柴油机缸套主推力面应变、次推力面应变、侧面应变随之增加；当发动机处于高转速时,自然吸气柴油机缸套的变形呈现明显无规则的振动特性,增压中冷柴油机缸套呈现有规则的、与最大爆发压力对应的振动特性,且最大转矩工况下的缸套主推力面变形大于其它工况变形。(5)缸套工作变形对活塞动力学特性以及密封性能及摩擦损失的影响研究在考虑缸套变形的基础上,研究了活塞组件结构、缸套变形均匀性以及对活塞二阶运动、机油耗、窜气量以及摩擦损失的影响关系。随着活塞头部间隙、配缸间隙、活塞销偏置量的增加,活塞平均摆角增大,活塞峰值敲击能量(KEP)增加；对于机油耗影响最大的是一环的切向弹力,对于窜气量影响最大的是二环切向弹力,对于摩擦磨损影响最大的是油环的切向弹力；随着各环切向弹力增大,机油耗、窜气量减小,摩擦损失增加。随着转速的增加,缸套变形不均匀性增加,机油耗、窜气量、环摩擦平均压力增加。通过对不同优化方案的活塞环组动力学特性分析,各方案对环组FMEP影响较小,对窜气量与机油耗的改善比较显著,其中预紧力优化方案对于机油耗的减小影响较大。更多还原

【Abstract】 With energy conservation and emission regulations being more strictly, the cylinder pressure of diesel increased to more than16Mpa. Thermal load and mechanical load in cylinder liner-piston group increased significantly. Cylinder liner and piston rings easily lead to deformation influenced by cylinder head bolt preload, piston high-speed periodic reciprocating, non-uniformity of cylinder block stiffness and thermal stress generated by non-uniform cooling. When the cylinder liner deformation and out-of-roundness can not be compensated by elastic force of piston rings, abnormal gap will emerge thus cause oil and gas leak. According to statistics,50%diesel particulate material (PM) emission is soluble organic matter produced by burning of lubrication oil fleeing into the combustion chamber. So it is significantly important for reducing oil consumption, emissions and improving friction properties that controlling cylinder and piston deformation and out-of-roundness, improving cylinder sealing performance. The engine used in this study was a turbocharged inter-cooled diesel, and the main purpose of the experiment was to get the principles and influencing factors about the cylinder liner installation distortion and deformation under working conditions. Some strategies and solutions in controlling the deformation of the cylinder liner were proposed. The following specific research works were carried out.(1) The study on characteristics of the cylinder liner installation deformation and influence factors under pre-tightening working conditionThe body cylinder head cylinder assembly coupling model was established. Static analysis was finished under preload condition. The experiment has researched the effects of structural and non-structural factors on the cylinder liner deformation with orthogonal design method, and cylinder structure was optimized. Studies have shown that for all cylinder liners, the shrinkage deformation was presented in cylinder upper section under preload conditions, and expansion deformation occurred in lower section. The maximum deformation was mainly occurred at the top of the cylinder liner. The deformation of four cylinder liners is non-uniform, cylinder liner1has larger deformation with cylinder liner4, and the deformation of cylinder liner2is smaller with cylinder liner3. The bolt preload in non-structural factors, the depth of countersunk and cylinder liner wall thickness have greater impact on cylinder liner deformation.2) The study on characteristics of the cylinder liner thermal deformation and influence factors under thermal load conditionBased on the engine bench test, the thermal load of cylinder head, cylinder block and liners, flow and cooling uniformity of the cooling jacket are studied by fluid-solid coupling heat transfer method. And the effect of cooling jacket structure on cooling uniformity and cylinder liner thermal deformation is studied. Studies have shown that the upper liners have larger thermal deformation value and gradient, the lower and central liners have relatively smaller thermal deformation value and gradient, the average thermal deformation of the cylinder liners under thermal load is16times of that under pre-tightening working condition. The regions between two cylinders have relatively smaller thermal deformation. At free areas of cylinder liner1and cylinder liner4have the largest thermal deformation. Due to each cylinder head, cylinder block and cylinder liner has non-uniformity distribution in temperature field, cooling water flow uniformity optimization scheme is different from cooling uniformity optimization scheme.(3) The study on characteristics of the engine cylinder liner thermal-mechanical coupling deformation and influence factors under working conditionWith considering the effect of mechanical load and heat load, the thermal-mechanical coupling analysis of cylinder block and liners assembly coupling model is made to research the different loading cases of the deformation features of the liners. Compared to pre-tightening working condition and thermal load working condition, the cylinder liner maximum main stress under working-load condition increases significantly, the cylinder liner deformation increases little and is similar to that under thermal load condition. In summary, the cylinder liner out-of-roundness of optimized case under pre-tightening working condition reduces more effectively than that of cooling uniformity optimized case. In addition, the deformation of cylinder liner2is symmetrical with that of cylinder liner3caused by the cylinder block stiffness, and the deformation law is pea-shaped, so is the deformation of cylinder liner1and the cylinder liner4. The cylinder block structure stiffness uniformity plays an important role in the liner deformation distribution.(4) The test and analysis of cylinder liner dynamic deformationThe cylinder liner dynamic deformation of TCI engine and naturally aspirated engine under full-load condition is tested by the strain test method, the liner circular and radial deformation of different engines is compared and analyzed. With the increase of engine speed, the deformation of cylinder liner thrust surface, anti-thrust surface and side surface increase. When the engine at a high speed, the cylinder liner deformation of the naturally aspirated diesel engine shows obviously random vibration characteristics, but the cylinder liner deformation of the TCI engine shows regular and maximum explosion pressure-related vibration characteristics, the deformation of cylinder liner thrust surface under maximum torque condition is larger than the deformation under any other condition.(5) The study on the effect of the cylinder liner deformation on piston dynamics characteristics, sealing performance and friction lossesOn the basis of the cylinder liner deformation, the effect of piston assembly structure and cylinder liner deformation uniformity on the piston secondary motion, oil consumption, blow-by and friction lose is studied. When the piston head gap, the gap between the piston and cylinder and piston pin offset increase, the piston average pendulum angle and peak striking power (KEP) increase. The top compression ring tangential elasticity has the greatest impact on the oil consumption, the second compression ring tangential elasticity has the greatest impact on the blow-by, and the oil ring tangential elasticity has the greatest impact on the friction lose. As each ring tangential elasticity increases, the oil consumption and blow-by decrease, the friction lose increases. As the engine speed increases, cylinder liner deformation non-uniformity, oil consumption, blow-by and friction ring average pressure increase.By studying the effect of pre-tightening working condition and cooling uniformity optimized case on the piston ring dynamics characteristics, each case has a little effect on the piston ring FMEP, and improves the oil consumption and blow-by greatly, the pre-tightening optimization scheme has great effect on reduction of the oil consumption.更多还原