油润滑渐开线斜齿轮摩擦动力学特性及疲劳寿命预估

发布时间：2018-05-17 21:10

本文选题：渐开线齿轮 + 混合弹流润滑　；参考：《北京理工大学》2014年博士论文

【摘要】：渐开线斜齿轮因传动平稳、承载能力强被广泛应用于高速重载传动。随着传动系统对转速和转矩的大幅度提高，斜齿轮传动的啮合平稳性、效率特性及疲劳寿命等问题成为高速重载齿轮研究的重点和热点。在高速大功率运行工况下，齿轮传动表现出强非线性动力学特征。齿面在大范围变滑滚比状态下作高速剪切运动并产生瞬时高温，导致润滑油粘度大幅度降低，油膜厚度显著减小，润滑状态复杂多变。本文全面考虑了渐开线斜齿轮在混合润滑状态下的弹流润滑特性、热效应以及摩擦学特性与动力学行为的耦合关系，建立了齿轮的摩擦动力学模型；考虑残余应力和硬度梯度的影响以及裂纹在不同阶段的生长机制建立了齿轮接触疲劳寿命的全过程预估模型。本文首先建立了啮合接触区二维有限长线接触混合弹流润滑模型，基于最小弹性势能原理确定了低速稳态工况的载荷分布规律，并对弹流润滑模型进行数值求解，获得了接触区的稳态润滑特性。在求解过程中，采用Reynolds方程的统一差分格式解决了混合弹流润滑中粗糙峰接触区的判定问题，应用多重网格积分法加速了表面弹性变形的计算，并对多重网格法和Gauss-Seidel松弛迭代法联立求解，获得了接触区的润滑特性，揭示了齿面粗糙峰的峰值、方向相关特征和分布密度等因素对润滑特性的影响规律。当齿轮在高速大转矩工况下工作时，由于润滑油膜内部的高剪切作用以及混合润滑状态下粗糙峰间的摩擦剪切作用，接触区将产生大量的热。在弹流润滑状态下，入口区的剪切热将降低润滑剂的粘度，并导致由卷吸速度带入接触区的油量减少，从而使油膜厚度减薄。为了对齿面进行热分析，将能量方程、移动点热源法和热流分配系数相结合，建立了齿面温升模型，并与弹流润滑方程相耦合，通过求解获得了油膜中层温升和两齿面的温升分布特征，进而揭示了热流在齿面不同位置的传导规律。在实际运转中，尤其在高速工况下，由于齿形和装配误差的存在，以及油膜的瞬态挤压效应，齿轮啮合副在运动过程中将不可避免地产生动态传递误差，进而引起载荷冲击和振动。为了深入剖析润滑特性与动力学行为的耦合关系，综合考虑啮合刚度的时变特性、油膜瞬态挤压效应，齿面形貌特征以及摩擦转矩对动力学行为的影响，建立了渐开线斜齿轮的摩擦动力学模型。在数值求解过程中，建立了油膜变形量的解析模型，实现了动力学方程与弹流润滑方程的解耦，以相对线位移满足啮合周期性的假设为依据，确定了动力学方程的边界约束条件。对摩擦动力学模型进行迭代求解，获得了啮合过程中动态啮合力的变化特征以及接触区油膜压力和温升分布的动态变化过程，揭示了动态工况下斜齿轮接触区的润滑规律。从齿轮失效形式来看，点蚀、剥落等接触疲劳失效是最常见的失效形式，其失效机理较为复杂，与基体材料的晶体组织结构、材料缺陷以及局部应力分布有关。本文针对渗碳淬火齿轮的表面材料属性，考虑残余应力和硬度梯度的影响，以次表面最大剪切应力为评价参数，基于风险疲劳累积理论建立了裂纹萌生寿命模型，用以预测沿齿面深度方向微裂纹的萌生位置和形核寿命。在裂纹扩展寿命模型中，，考虑裂纹在晶粒内部的非线性扩展规律以及相邻晶粒间的非连续扩展特征，建立了短裂纹扩展模型。综合考虑疲劳裂纹扩展速率的不同阶段，建立了长裂纹扩展的统一方程，进而完成了对齿轮接触疲劳寿命的预估。
[Abstract]:The involute helical gear is widely used in high speed heavy load transmission because of its smooth transmission and strong bearing capacity. With the great improvement of the speed and torque of the transmission system, the meshing stability, efficiency characteristics and fatigue life of the helical gear transmission have become the focus and hot spot in the research of high speed heavy load gear. The wheel transmission shows strong nonlinear dynamic characteristics. The tooth surface performs high speed shear movement and produces instantaneous high temperature under the state of large range slip ratio. The viscosity of lubricating oil is greatly reduced, the thickness of oil film decreases significantly, and the lubrication state is complex and changeable. The elastohydrodynamic lubrication characteristics of involute helical gear in mixed lubrication state are fully considered in this paper. The thermal effect, the coupling relationship between the tribological characteristics and the dynamic behavior, the friction dynamic model of the gear is established, and the full process prediction model of the gear contact fatigue life is established by considering the influence of the residual stress and the hardness gradient and the growth mechanism of the crack in different stages.
In this paper, a two dimensional finite long line contact hybrid elastohydrodynamic lubrication model is established. Based on the principle of minimum elastic potential energy, the load distribution law of the low speed steady state is determined. The elastohydrodynamic lubrication model is solved numerically to obtain the steady state lubrication characteristics of the contact area. The unified difference of Reynolds equation is adopted in the solution process. The determination of the contact area of the rough peak in mixed elastohydrodynamic lubrication is solved by the fractional format. The multi grid integration method is applied to accelerate the calculation of the elastic deformation of the surface. The lubrication characteristics of the contact area are obtained by the simultaneous solution of the multigrid method and the Gauss-Seidel relaxation iteration method. The peak of the rough peak, the direction correlation feature and the distribution density are revealed. The influence of degree and other factors on the lubrication characteristics.
When the gear is working at high speed and high torque, the contact zone will produce a lot of heat due to the high shear inside the lubricating oil film and the friction shear between the rough peaks in the mixed lubrication state. In the elastohydrodynamic lubrication state, the shear heat of the entrance area will reduce the viscosity of the lubricant and lead to the oil from the entrainment velocity into the contact area. In order to make the thickness of the oil film thinner, the temperature rise model of the tooth surface is established by combining the energy equation, the moving point heat source method and the heat flow distribution coefficient, and the temperature rise of the middle layer of the oil film and the temperature rise distribution of the two tooth surface are obtained by solving the equation of the energy equation, the moving point heat source method and the heat flow distribution coefficient, and the heat flow is revealed in the tooth surface. The law of conduction in different positions.
In the actual operation, especially in high speed conditions, due to the existence of tooth shape and assembly error and the transient extrusion effect of oil film, the gear meshing pair will inevitably produce dynamic transfer error in the process of motion, and then cause the load impact and vibration. Considering the time-varying characteristics of the meshing stiffness, the transient extrusion effect of the oil film, the profile of the tooth surface and the influence of the friction torque on the dynamic behavior, the dynamic model of the involute helical gear is established. In the numerical solution, the analytical model of the deformation of the oil film is established, and the decoupling of the dynamic equation and the elastohydrodynamic lubrication equation is realized. On the basis of the assumption that the line displacement satisfies the meshing periodicity, the boundary constraint conditions of the dynamic equation are determined. The dynamic variation of the dynamic meshing force in the meshing process, the dynamic changing process of the oil film pressure and the temperature rise distribution in the contact area are obtained by iterative solution of the friction dynamic model, and the contact gear contact under dynamic conditions is revealed. The law of lubrication in the area.
From the form of gear failure, contact fatigue failure, such as pitting and peeling, is the most common failure form. Its failure mechanism is more complex, which is related to the crystal structure, material defects and local stress distribution of the matrix material. In this paper, the effects of the surface material properties of carburized quench gear and the influence of residual stress and hardness gradient are taken into consideration. The maximum shear stress is the evaluation parameter. Based on the risk fatigue accumulation theory, the crack initiation life model is established to predict the initiation position and the nucleation life of the micro cracks in the depth of the tooth surface. In the crack propagation life model, the nonlinear propagation law of the crack in the grain and the discontinuous expansion between the adjacent grains are considered. Characteristics, a short crack propagation model is established. Considering the different stages of fatigue crack growth rate, a unified equation for long crack propagation is established, and then the fatigue life of gear contact is estimated.
【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH132.413

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