【作者】 孙军；

【导师】 张建华；

【作者基本信息】 山东大学 ， 先进制造（专业学位）， 2022， 博士

【摘要】 为了满足日益严格的排放法规和油耗标准要求,内燃机将持续采用增压及燃油高压喷射等技术以改善燃烧的技术路线,内燃机气缸内的最大爆发压力将大幅提高,例如重卡用内燃机的气缸内最大爆发压力已经从国V排放标准期间的170-190bar提升至国Ⅵ排放标准的200-250bar。为了满足将于2022年12月1日开始实施的GB20891中关于560KW以下非道路用柴油机必须满足四阶段排放标准的要求,大型内燃机也是遵循上述技术路线降低排放和提高燃油经济性。为了满足在有限的空间内,以更轻的重量,更大的功率输出,实现“更高机动性、更大载重量、更大功率输出”的应用目标,对内燃机功率密度的期望越来越高,提升功率密度除了设计更紧凑的整体结构,更要求提高内燃机的升功率,相应地气缸内的爆发压力要继续提高到250～300bar,爆发压力的提高对曲轴的疲劳强度提出了更高的要求。单一工艺强化方式对曲轴的强度提升幅度有限,强化后的曲轴不能满足高爆压(≥220bar)、高功率密度内燃机的需求,需要进行复合强化。现代数值计算方法以及先进的试验测试技术为解决该类问题提供了很好的手段与条件。基于以上方法,本论文工作开展了基于曲轴圆角强化方法研究,其主要内容如下:现有应用的复合强化方式有氮化加圆角滚压或者圆角淬火加圆角滚压,两种复合强化都需要圆角滚压,但对非道路用大型内燃机曲轴的圆角滚压需要极大的滚压力,目前国内外研制的滚压机床都无法满足要求,滚压机床被德国Hegenscheidt公司垄断,进口一台轿车曲轴用的滚压机床需要一千万元,大型滚压机床价格更加昂贵。本文对内燃机曲轴圆角机械冲击强化机理进行研究,得出机械冲击可以使材料表面发生塑性变形,金属晶格发生畸变,产生残余压应力,抵消增强抗疲劳能力。搭建了机械冲击试验平台进行试样的冲击试验,验证了冲击强化技术的可行性。以有限元法数值计算为基础,本文工作建立了新的曲轴强化技术参数化模型,提出了不同工况下的计算方案。然后对曲轴圆角进行建模,通过对圆角冲击强化的仿真计算,计算并分析了不同参数下的响应结果,冲击角度、冲击速度和曲轴转角对冲击部位变形和应力分布的影响。根据计算结果,获得具有最佳冲击效果的各工艺参数,为后续开发冲击强化设备奠定了基础。根据试验与数值仿真获得参数,本论文研究对曲轴圆角机械冲击强化装置进行设计。基于有限元分析获得了对曲轴圆角冲击残余应力分布的影响规律,确定曲轴圆角冲击强化装置的结构和工艺参数,奠定了曲轴圆角机械冲击强化的理论基础,为制造能满足内燃机更高爆发压力和高功率密度要求的曲轴提供了设备保证。本论文研究设计并制造了曲轴圆角机械冲击强化装备,能够实现曲轴圆角的机械冲击强化,对不同处理状态的曲轴圆角进行冲击强化测试。对冲击强化处理后的曲轴圆角变形、表面硬度、表层及次表层残余应力分布、金相组织、曲轴疲劳强度等进行了试验研究,构建了冲击工艺、残余应力和疲劳强度之间的参数对应关系。试验结果表明,对于圆角半径为5.5±0.25mm的曲轴,经表面感应淬火和表面磨削加工后,采用材料为YG8整体硬质合金、半径为5.25mm的冲击锤头,按照冲击锤轴线与曲轴轴线成45°夹角、冲击锤冲击速度为3m/s、相临两次冲击之间曲轴转角为2°的工艺参数,对曲轴连杆颈圆角进行机械冲击,曲轴圆角的残余压应力能覆盖圆角区域并且衔接良好,曲轴圆角残余压应力较未进行机械冲击强化的曲轴提高60%,曲轴疲劳强度比未经机械冲击强化的提高31.7%,机械冲击强化效果明显。本文采用理论研究、仿真分析、试验验证等手段,系统研究了曲轴圆角机械冲击强化的关键技术,成功研制出可以进行自动加工的曲轴圆角机械冲击强化装备。研究确定了工艺路线并优化了工艺参数,实现了大型内燃机曲轴的圆角机械冲击强化,提高了曲轴的疲劳强度,解决了大型曲轴圆角强化的问题,对大型曲轴的强化工程应用提供了新思路、新方法和新装备,摆脱了对昂贵的进口设备的依赖。实践证明本论文研究内容的正确性及实用性。更多还原

【Abstract】 To meet the increasingly stringent requirements of emission regulations and fuel consumption standards,internal combustion engines will continue to adopt technologies such as supercharging and high-pressure fuel injecting to improve the efficient of combustion,thus the maximum explosive pressure will be increased dramatically accordingly.For heavy duty commercial vehicles,the maximum cylinder explosion pressure has increased from 170-190bar in the current national V standards to 200-250bar in next generation VI.To meet the requirements of GB20891,which stated that off road diesel engines below 560KW must meet the emission standard released in fourth stage,the medium and large capacity internal combustion engines will be required to improve emissions standard and decrease fuel consumption through new techniques subsequently.For the goal of "higher mobility,greater load capacity,and greater power output" within the limited space,the expectation of internal combustion engine power density is increased higher and higher.Not only the structure optimized,the explosive maximum pressure in the cylinder will be increased to 250-300bar.Thus,the requirement for the higher strength and more fatigue cycles of the crankshaft in proposed accordingly.For the limitation of separated measures available to improve the strength of crankshaft under higher explosive maximum pressure(≥220bar)and density of power performance,compound strengthening approaches are highly needed.Advanced numerical computations algorithms and newly invented experimental testing techniques provide good approaches and equipment for solving the urgent problems.Based on the above techniques,this work proposes the solution measures of crankshaft fillet strengthening.The main works are listed as follows:The main existing compound strengthening methods are classified into two categories,one is nitrogen hardening combined with fillet rolling,and the other is induction hardening with fillet rolling.Corner rolling is important and applied in both strategies of manufacturing processing for crankshaft.But for better results,extremely large rolling pressure is required to strengthen crankshafts mounted on off-road medium and large internal combustion engine.It is difficult that the current rolling equipment,no matter that manufactured at home or abroad,are capable to satisfy the requirements mentioned above.Deep rolling equipment is monopolized by Hegenscheidt,a German company.It needs 10 million Rmb to import a rolling equipment for automobile crankshaft,a larger one is more expensive.This work researched the mechanism of mechanical shock strengthening for crankshaft fillet on internal combustion engine,The conclusion could be stated as follows.The exterior surface material plastic deformation can be obtained through mechanical impacting,this processing result in the distortion of lattice.With the appearance of the distortion.compressive residual stress will be created.It can be expected to enhance the fatigue cycles of crankshaft through reducing the maximum tensional stress in working conditions.then a mechanical platform is established for shock testing,with which the feasibility of shock strengthening technology was validated.Using finite element method,this work established a new parameterized model of crankshaft to simulate strengthening procedure and proposed computational schemes under different working conditions.Through the simulation of the fillet impact strengthening,the response under different boundary conditions and loading parameters are solved,then resultant stress and displacement distribution analyzed.Different computational schemes,such as impacting angle,impacting speed,and crankshaft rotation angle,affect the deformation and stress distribution of the impact the local region.The optimal processing parameters holding best impact effect are obtained according to numerical results,which lays the foundation for the structure layout and parameters selections of subsequent impact strengthening equipment.According to the parameters obtained through experiment and numerical simulation,this work proposes the scheme of mechanical impact strengthening equipment for the crankshaft fillet.From numerical computation and analysis,the influence of crankshaft fillet impact on the residual stress distribution was obtained,which laid the theoretical foundation for the mechanical impact strengthening.Then the structure and processing parameters of the crankshaft fillet impact strengthening equipment can be determined.Using the equipment,the objective strength parameters can be satisfied for manufacturing crankshaft of heavy-duty internal combustion engine.Experiment was designed and conducted to get the parameters of impact strengthening,including the crankshaft fillet deformation,surface hardness,surface and subsurface residual stress distribution,metallography structure,crankshaft fatigue strength.The mathematical model was constructed between processing parameters and procedure,residue stress and fatigue cycles accordingly.Test results show that for the crankshaft with a fillet radius of 5.5±0.25mm,after surface induction quenching and surface grinding,the impact hammerhead with a radius of 5.25mm is applied according to the process parameters of 45° included angle between the impact hammer axis and the crankshaft axis,the impact speed of the impact hammer is 3m/s,and the crankshaft angle between two adjacent impacts is 2°.The crankshaft fillet is mechanically impacted,and the residual compressive stress of the crankshaft fillet can cover the circle.The residual compressive stress of the crankshaft fillet is 60%higher than that of the crankshaft without mechanical shock strengthening,and the fatigue strength of the crankshaft is 31.7%higher than that without mechanical shock strengthening.The resultant comparisons show general objective parameters are satisfied through the proposed mechanical shock strengthening.In conclusion,this work proposes compound measures,integrating theoretical development and simulation analysis,with experimental verification systematically.It proposes a solution to the key techniques of crankshaft fillet impact strengthening,and develops an automated crankshaft fillet mechanical impact strengthening equipment successfully.The impact strengthening of medium and large internal combustion engine crankshaft is implemented for specified type,in which the processing procedure is streamlined and the processing parameters are optimized.Results show that the fatigue strength of the crankshaft is increased.The equipment is manufactured for the strengthening of crankshaft in medium and large internal combustion engine,getting rid of the dependence on expensive imported equipment.The application and test of the compound measures has proved the effectiveness and reliability of the proposed solutions.更多还原