点接触润滑状态转化的实验观察

利用球-盘接触润滑油膜厚度的光干涉测量法，通过卷吸速度或载荷的改变实验研究了弹性流体动力润滑与流体动力润滑转化过程中油膜厚度的变化规律。实验结果显示这2种润滑状态之间存在明显的过渡区。与已有的理论一致，在弹性流体动力润滑区和流体动力润滑区，油膜厚度与卷吸速度或载荷在对数坐标中呈直线关系。在两者的过渡区，固体表面的弹性变形量随卷吸速度或载荷的变化发生明显的变化，油膜厚度与速度或载荷的关系不再为对数坐标中简单的线性关系。使用已有的润滑状态区理论不能得到实验观测到的润滑状态的转化过渡区。     

离心脱开型超越离合器弹流润滑分析

离心脱开型超越离合器是航空传动系统中的重要部件,具有低速楔合传动、高速离心脱开的特性,使离合器在不同工作模式下接触载荷与转速呈不同的关系,因此需针对不同工况下离心脱开型超越离合器弹流润滑性能进行分析.建立离心脱开型超越离合器弹流润滑模型,采用多重网格分析方法进行数值求解,分析进油温度与速度对超越离合器弹流润滑性能的影响...     

海水润滑塑料轴承的微观热弹流润滑分析

考虑轴承表面海水润滑膜温度场和轴承表面横向粗糙度等因素,对塑料轴承的弹流润滑问题进行了研究。利用压力求解的多重网格法和弹性变形求解的多重网格积分法以及温度求解的逐列扫描技术,得到塑料轴承微观热弹流润滑问题的完全数值解,讨论了连续波状粗糙度、载荷、轴承转速对海水润滑膜压力及膜厚的影响。数值计算结果表明：轴承表面粗糙度对润滑膜压力和膜厚分布都有一定影响,连续波状粗糙度使润滑膜压力和膜厚分布产生振荡;转速和载荷对压力分布影响较小,随转速的增大、载荷的减小,膜厚都有明显的增大。     

指数率流体热弹流润滑分析

应用多重网格技术,求得了指数率非牛顿流体线接触热弹流润滑的数值解,分析了油膜压力、厚度和温度等随流变指数、速度参数、滑滚比及载荷参数的变化关系,并与相同工况下的等温解进行了比较。结果表明,随着流变指数的增加,油膜厚度和温度、入口处的当量粘度、最小膜厚、中心膜厚和最大温升均增大,而油膜压力和摩擦因数的变化较小。指数率流体弹流润滑问题的热效应不可忽略;与压缩功项相比,油膜能量方程中的热耗散项对温度的影响最大。同时,无量纲速度参数、滑滚比和载荷参数等均影响热弹流润滑特性。     

急停问题的椭圆接触弹流润滑分析

将机械急停时滚动轴承、齿轮等的弹流润滑油膜的渐变过程简化为从稳恒状态突然转化为恒载荷纯挤压状态,然后随时间的推移挤压效应逐渐消失的过程,建立了椭圆接触瞬态弹流润滑模型。假设润滑油为牛顿流体,在等温条件下用多重网格技术进行了动态数值求解,讨论了急停前卷吸速度分别沿椭圆接触区的长轴和短轴方向时,不同参数条件下的残留弹流润滑膜的压力和膜厚随时间的变化规律。数值计算结果表明,急停后润滑油会逐渐被挤出接触区,因此残留油膜只能保持很短的时间;较高的Hertz接触压力会通过增加润滑油粘度而延长残余油膜的维持时间,但不能根本上改变上述变化趋势,卷吸速度的方向也不能改变上述变化趋势。     

Film Forming Behavior of Greases Under Starved and Fully Flooded EHL Conditions

Improving knowledge on the film forming behavior of greases is essential to be able to develop efficient greases. This article examines how operating conditions (e.g., temperature, lubrication condition [fully flooded/starved]) and base oil viscosity influence the film forming properties of greases by comparing the behavior of two lithium-based greases and their respective base oils in rolling point contact. It is found that the onset and degree of starvation is controlled by speed (u) × viscosity (ν)/load (W) factor (uν/W) and temperature and that low uν/W values promote entrainment of thickener into contact. Thus, grease with low base oil viscosity shows significant thickener entrainment in the low speed region compared to the one with high base oil viscosity, which leads to the formation of thickener-rich viscous material during extended running with the low base oil viscosity grease. The results suggest that the shape of the film thickness versus speed curve is viscosity and uν/W range dependent. Furthermore, for the test conditions used in this study, grease-lubricated contacts appear to shift from the initial fully flooded condition to starved condition over a prolonged running of 2 h. The results from this study concur with those reported in the literature that fully flooded oil elastohydrodynamic lubrication (EHL) theory or film thickness cannot be directly applied or taken as a guideline in grease-lubricated contacts.     

基于Carreau流变模型的圆柱滚子轴承热混合润滑分析*

为了研究圆柱滚子轴承接触区的混合润滑性能,建立基于Carreau非牛顿流体的热混合润滑模型,求解非牛顿流体线接触热混合润滑数值解。研究滑滚比、卷吸速度及载荷对线接触混合润滑特性的影响,并与相同工况下牛顿流体热混合润滑的结果进行对比。结果表明：随着滑滚比、卷吸速度及载荷的增大,油膜温度都会升高,Carreau非牛顿流体的温度要低于牛顿流体的温度;油膜厚度随着滑滚比、载荷的增大而减小,随着卷吸速度的增大而增大,Carreau非牛顿流体与牛顿流体膜厚相差不大;随着滑滚比的增大,2种流体的平均摩擦因数均增大,随着卷吸速度和载荷的增大,2种流体的载荷比均减小。     

纳米级润滑膜的粘度修正与薄膜润滑计算

根据纳米级润滑膜的试验测试结果提出薄膜润滑状态的粘度修正公式 ,并在此基础上建立了润滑膜厚度计算的数值计算方程。将该数值计算结果与弹流理论计算值和试验值进行对比表明 ,在薄膜润滑条件下 ,膜厚与速度和润滑油粘度的关系与弹流润滑计算结果相差较大 ,可明显看出弹流润滑向薄膜润滑的过渡 ,所提出的粘度修正式与试验结果则有较好的一致性     

海水润滑赛龙陶瓷轴承的摩擦学性能研究

分析海水润滑轴承的主要磨损形式,建立海水润滑赛龙陶瓷轴承的弹流润滑模型,通过数值计算发现在赛龙陶瓷/钢摩擦副间可以形成海水弹流润滑膜,轴承间水膜厚度分布有明显颈缩现象,但压力分布图中第二压力峰不明显;随着转速的增加,海水润滑膜膜厚及最小膜厚都变薄;相同条件下,赛龙陶瓷轴承用海水润滑比用纯水和油润滑时更不容易形成弹流润滑薄膜。     

N次谐波凸轮-挺柱副的润滑特性分析

将线接触弹流润滑理论应用于发动机配气机构，计算了某N次谐波凸轮-挺柱副润滑的稳态最小膜厚、膜厚比等参数，分析了凸轮．挺柱副稳态润滑在设计转速下随凸轮转角的变化特征，比较和讨论了发动机转速变化对润滑性能的影响。结果表明，凸轮桃尖区多为部分弹流润滑状态和边界润滑，工作段其它部分多为部分弹流、完全弹流和动力润滑状态。曲轴转速提高一般情况下对增加稳态最小膜厚有利，但由此导致的载荷波动量增加对最小膜厚的稳定性不利，从而使表面摩擦和磨损的可能性增加。     

水润滑塑料合金轴承的弹流润滑分析

建立水润滑塑料合金轴承的数学模型,对水润滑条件下塑料合金轴承的弹流润滑问题进行数值模拟,讨论转速和载荷对水润滑膜压力和膜厚的影响。结果表明:在水润滑条件下,转速对水润滑膜的压力影响不明显,而膜厚及最小膜厚随转速的增大而明显增大;随载荷的增大,压力峰值有明显增大,而在入口区压力随载荷增大而减小,膜厚及最小膜厚随载荷增大而减小。     

椭圆接触纯自旋问题的弹流润滑数值分析

研究了椭圆接触纯自旋问题的等温弹流润滑,用多重网格法求得了完全数值解,研究了速度、载荷、椭圆比和计算区域对压力和膜厚的影响。结果表明,在轻载、高速、大椭圆比条件下,椭圆接触的纯自旋运动可产生润滑膜,油膜的形状和压力分布都和经典弹流润滑截然不同;椭球的自旋速度、载荷、椭圆比以及承载域的大小都对压力和膜厚有很大的影响。     

变速点、线接触副弹流润滑油膜的观测

应用光干涉方法,在自制的光弹流试验机上分别对纯滚动条件下点接触和线接触形成的弹流油膜进行变卷吸速度实验,并进行油膜测量。结果表明,在卷吸速度为零时都有封油现象的出现。随着卷吸速度的增加,油膜厚度增加,点接触形成的弹流油膜具有典型的马蹄形特征,线接触形成的弹流油膜在接触区端部有类似点接触的马蹄形收缩。要达到同样的最大赫兹接触压力,施加在线接触实验上的载荷要比施加在点接触实验上的载荷大40倍左右。     

偏心凸轮副时变乏油润滑数值分析

为研究乏油条件下偏心凸轮副的润滑状态,基于凸轮-挺杆机构建立时变乏油润滑模型,探究一个周期内6个典型瞬时(60°、120°、180°、240°、300°、360°)的压力和油膜厚度变化规律,并分析不同凸轮旋转角度下转速、初始载荷和润滑油黏度等参数对接触区润滑状态的影响。结果表明：当凸轮转至180°时,膜厚最小,压力最大,乏油状况最严重;限量供油下最小膜厚出现在凸轮转角为180°时,但是凸轮转角为0°时乏油速度最快,乏油程度更深;增大凸轮旋转速度时乏油速度更快,乏油程度更深;相同供油条件下,润滑油黏度越高使得接触区乏油情况越严重,乏油速度更快,乏油程度更深;载荷对接触区的润滑状态的影响较小,只在凸轮转角为0°接触区卷吸速度最大时,能够体现出载荷对接触区润滑状态的影响。     

Interferometry Measurement of Spin Effect on Sliding EHL

This paper describes interferometry measurement of the film profiles of sliding elastohydrodynamic lubrication (EHL) contacts with spin. In the custom-made EHL test rig, spin motion is introduced through adjusting the center offset of the ball-on-disc contact with respect to the disc rotation axis. A parameter, spin ratio S _sp, is employed to represent the spin level, which is defined as the ratio of the Hertzian contact radius to the center offset. Experimental results show that with spin the film shape is obviously skewed, and the film thicknesses at the two side lobes are no longer the same; therefore, the symmetry of the classical horseshoe film shape is lost. The film thickness dependences on entrainment speeds are significantly influenced by the spin ratio S _sp, and high spin ratios induce high speed indices. At a fixed spin ratio S _sp, with increasing sliding speeds the film thickness difference between the two side lobes becomes large, and the horseshoe film shape is more distorted. When applied loads are raised, more spin is introduced, film thickness decreases, and film shape is obviously twisted.     

渐开线直齿轮瞬态微观热弹流润滑分析

考虑了瞬态效应、轮齿表面油膜温度场和轮齿表面纵向粗糙度等因素,对渐开线直齿圆柱齿轮的弹流润滑问题进行研究。载荷由双齿或单齿承担,根据实际载荷谱简化的轮齿载荷曲线,利用压力求解的多重网格法和弹性变形求解的多重网格积分法以及温度求解的逐列扫描技术,得到渐开线直齿轮瞬态微观热弹流润滑问题的完全数值解,讨论了轮齿间油膜的厚度、压力、温度沿啮合线的变化规律。数值计算结果表明,齿轮表面纵向粗糙度对轮齿间油膜的压力、膜厚、温升都有较大影响。考虑轮齿表面粗糙度后,油膜压力和温升明显增大,并随压力的增加而影响越来越显著,粗糙峰使油膜压力分布和温度分布产生振荡,轮齿表面的粗糙峰对摩擦因数影响较小,摩擦因数和最高温升在节点两侧最大。     

薄膜润滑与润滑状态图

讨论了速度、固体表面能、滑动比、润滑剂粘度和化学性能对薄膜润滑状态下油膜厚度的影响,以及弹流润滑向薄膜润滑转化条件和液体膜失效条件。进而提出了新的润滑状态划分准则以及不同润滑机理下膜厚的变化情况。     

Effect of Surface Velocity Directions on Elastohydrodynamic Film Shape

This article is focused on the effects of the angle between lubricant entrainment velocity and sliding velocity on elastohydrodynamic film thickness distribution. Thin-film colorimetric interferometry was used to evaluate the film thickness distribution in smooth glass–steel contacts to provide basic data on the effects of the slide–roll ratio and the direction of sliding with respect to entrainment velocity. It was observed that as the sliding perpendicular to the entrainment velocity increased, the overall film thickness was reduced and asymmetry of the film profile with respect to the direction of the entrainment velocity increased. The asymmetry of the film profile with respect to the direction of the entrainment velocity increased with the entrainment speed or the overall film thickness. When the speed of the glass disk was larger than that of the steel ball, a dimple was formed even if there was a difference in direction between the entrainment and sliding velocities. A part of the dimple was exhausted from the elastohydrodynamic lubrication (EHL) conjunction as the angle between the entrainment and sliding velocities approached 90°.     

Occurrence of Wall Slip in Elastohydrodynamic Lubrication Contacts

Preliminary experimental work has been carried out to identify some of the boundary slip phenomena of highly pressurised polybutenes in an elastohydrodynamic lubrication (EHL) conjunction. The movement of the oil is signified using an entrapment that can be readily formed by the impact of a steel ball against a layer of oil on a glass block in an optical EHL test apparatus. The post-impact lateral movement of the entrapment was investigated under the conditions: (i) pure rolling, (ii) pure glass block sliding (steel ball stationary) and (iii) pure ball sliding (glass block stationary). It was observed that under pure rolling the entrapped oil travels within the contact region at the entrainment speed, which is correlated with EHL theory. Under pure glass block sliding conditions, the speed of the entrapped oil core is less than the entrainment speed, and in the extreme cases, this core can be nearly stationary. Under pure ball sliding conditions, the oil core moves at a speed greater than the entrainment speed. The observation indicates that the oil/steel ball interface can sustain higher shear stress than the oil/glass (chromium coated) interface and there is a boundary slip in terms of relative sliding at the latter interface under the experimental conditions. Furthermore, the amount of slip increases with an increase in the pressure. These experiments provide evidence of the existence of wall slippage, which leads to the abnormal EHL film profile characterised with an inlet dimple as reported earlier.     

高黏度油润滑弹塑性接触问题数值仿真*

针对高黏度润滑油工况下,已有弹塑性润滑模型计算结果失真的问题,采用半解析法建立弹塑性润滑接触模型,通过逐步增加润滑油初始黏度的方式来进行仿真计算,消除了接触区压力曲线的波动,从而克服先前计算失真的问题;基于各向同性强化准则下的J2流动理论,采用径向返回算法求解塑性应变,并且将塑性应变引起的残余变形考虑至润滑油膜厚度方程中。研究结果表明：弹塑性润滑压力主峰相比于弹流润滑结果明显降低,二次压力峰相对变化较小;弹流润滑的中心膜厚与弹塑性润滑中心膜厚接近,但最小膜厚稍大;对于较高的速度和黏度工况,塑性应变区域会向表面及接触区出口处移动。