变卷吸速度的点接触热弹流润滑分析

非稳态热弹流润滑一直是研究的热点和难点,针对变卷吸速度的点接触热弹性流体动力润滑问题,利用多重网格积分法,得到变卷吸速度的点接触热弹性流体动力润滑完全数值解。结果表明:卷吸速度的变化会引起油膜压力、膜厚和温度的变化;当卷吸速度变化到一定值时,在接触区会产生油膜的凹陷;凹陷的产生可用“温度-粘度楔”机制解释。     

弹流润滑入口凹陷现象的数值模拟

入口凹陷(inlet-dimple)是近年来弹性流体动力润滑(EHL)研究中出现的一类新油膜形状特征。使用Circular流变模型,利用数值分析,研究了滑滚比、载荷及卷吸速度等对凹陷的影响,并与部分已有实验结果进行了比较。初步结果显示,当滑动较大时,入口区油/固体界面处表观粘度剧烈下降,产生伪滑移,从而诱发了较大的压力梯度而形成入口凹陷。     

滚子副润滑状态转变的光干涉试验研究

利用光干涉测量技术,测量了滚子-盘有限长线接触副的润滑油膜形状和厚度,研究了滚子副的润滑状态随载荷、速度转变的规律。结果表明,接触区卷吸速度增加或载荷减小,使得滚子-盘接触副润滑状态逐渐由弹流润滑转变为流体动力润滑,且在两种润滑状态转变过程中存在过渡状态;由载荷变化引起流体动力润滑状态转变为弹流润滑状态过程中,接触区表面发生了弹性变形,使得接触区的油膜厚度增加。速度变化使滚子-盘接触处于流体动力润滑状态时,油膜出口颈缩消失,最小膜厚位置由出口颈缩处移至接触区中心,油膜光干涉图关于滚子轴线对称。     

FB2型凸轮/平面挺柱的摩擦性能数值分析

通过运动学和动力学分析得到FB2型内燃机凸轮/平底挺柱摩擦副在一个周期内的综合曲率半径、卷吸速度和载荷变化情况,在内燃机凸轮/从动件的瞬态热弹性流体动力润滑数值仿真平台上研究FB2型凸轮与平底挺柱摩擦副的摩擦学性能.分析结果表明在凸轮的基圆段和缓冲段部分,摩擦因数在0.015～0.017之间,接触区中心的油膜厚度在0.9μm左右;在凸轮桃尖附近摩擦因数高达0.079;在卷吸速度为0的两个位置由于温度楔效应和挤压效应中心油膜厚度仍维持在0.313和0.270μm.     

脂润滑轮毂轴承弹流润滑数值分析

基于Ostwald模型建立脂润滑控制方程,运用多重网格法求得等温线接触脂润滑弹性流体动力润滑数值解,得到钢球-沟道的压力分布、油膜形状及最小油膜厚度。针对轿车轮毂轴承的典型应用工况条件,分析工况参数对油膜压力分布和油膜形状的影响。结果表明:脂润滑弹流膜具有与油润滑膜相同的二次压力峰和出口颈缩现象。在轿车轮毂轴承可能的承载条件下,随着载荷的减小,二次压力峰的高度降低,其位置向入口区移动;一定承载条件下,速度增加时,膜厚相应增加,油膜的平行部分缩短,二次压力峰的高度增加,其位置也向入口区移动;一定承载和卷吸速度下,润滑脂流变参数增大时,二次压力峰的高度升高,其位置向入口区移动,膜厚相应增加。     

径向柱塞泵定子与滚柱间最小油膜厚度研究

滚柱式径向柱塞泵定子与滚柱间润滑属于弹性流体动力润滑，文章推导了滚柱极径的变化所引起卷吸速度的相应变化，通过对压力、偏心和滚柱诸元素变化对油膜的影响，应用matlab对油膜进行了仿真，得出了最小油膜的变化规律。     

点线啮合齿轮冷胶合计算研究

根据弹性流体动力润滑理论,运用道森和希金森公式计算点线啮合齿轮各啮合点最小油膜厚度及膜厚比以估计齿面间的润滑状态,判别是否产生冷胶合.推导啮合点的综合曲率半径计算公式,确定啮合点单位齿宽法向载荷.根据点线啮合齿轮实际发生冷胶合的位置,确定了最小油膜厚度计算点,并根据大量实际计算提出修正后的最小油膜厚度计算公式.     

蜗杆传动的弹性流体动力润滑

从弹性流体动力润滑理论和蜗杆传动的特点出发，分析了有关文献对蜗杆传动弹性流体动力润滑条件分析中的不足，指出了滚动速度是建立润滑油膜和油压的重要条件，论证了滑动速度对润滑油膜和油压的形成也有较大影响。采用Dowson公式计算油膜厚度时，为了考虑滑动速度的影响可引入滑动速度系数Ks予以修正。     

高黏度齿轮油润滑状态转变的试验观察

利用双色光干涉润滑油膜测量技术,观察球-盘接触副内大黏度齿轮油润滑状态的转变过程,并对不同速度和载荷条件下润滑状态在不同区间内的转化进行定量分析。结果表明:在充分供油条件下,随卷吸速度增加,润滑油膜从弹流润滑状态向动压润滑状态转化,且2种润滑状态之间存在着明显过渡区间;而随着载荷的增加,润滑油膜从动压润滑向弹流润滑状态转化;在定量供油条件下,润滑油膜在弹流润滑区间内从富油润滑状态向乏油润滑状态转化。     

间歇运动条件下等温弹性流体动力润滑分析

以钢球与玻璃盘之间的纯滚动接触为例,研究间歇运动条件下的等温弹性流体动力润滑,采用多重网格法对钢球与玻璃盘之间的等温弹性流体动力润滑进行数值分析。研究发现,在卷吸速度变化的过程中,中心膜厚和最小膜厚随着卷吸速度的减小而降低,在卷吸速度降为0后,呈现纯挤压的凹陷油膜形状;重新加速以后,在速度为0时间段形成的油膜凹陷将随着运动逐渐移出接触区。与此对应的,中心膜厚值下降,最小膜厚也达到最低值。随后的运动过程中油膜厚度增加,第二压力峰先减小后增加。     

Experimental study on lubrication regime variation in point contacts

The change between elastohydrodynamic lubrication (EHL) and hydrodynamic lubrication (HL) under a wide range of entrainment speeds and applied loads was studied using an optical EHL apparatus. A log-log scale linear relationship was demonstrated in the two lubrication regions between the film thickness and the entrainment speed (or load). A transition region can be clearly discerned between these two regions in which the film thickness no longer bears a linear relationship with the entrainment speed (or load). It is shown that a piezoviscous effect can be distinguished in the HL region by the speed exponent or the load exponent, and that relative sliding has a significant influence on the transition region.     

界面滑移条件下点接触Stribeck曲线的实验研究

采用高黏度聚异丁烯润滑油,在光学弹流实验机上考察球-盘接触纯滑条件下的摩擦因数随卷吸速度和载荷的变化。结果表明,随着卷吸速度的增加,球-盘接触副进入弹流润滑并向流体动压润滑转变的过程中,摩擦因数并不像传统的Stribeck曲线一样,随着卷吸速度的增加而单调增加,而是呈现先上升、后下降、再上升的趋势,其中摩擦因数下降时的起始速度大致为凹陷出现的速度,摩擦因数再上升时的速度大致是润滑进入动压润滑的速度。初步论证界面滑移为产生上述波动的主要原因。     

界面滑移条件下弹流油膜的试验观察

在极低速纯滑动条件下完成高粘度聚丁烯弹流油膜的光干涉测量试验,观察到明显的油膜入口凹陷现象。试验结果表明,入口凹陷的深度随载荷的增加而增加,随卷吸速度的增加存在一个极大值。试验中润滑剂的粘度越高,入口凹陷越容易出现。纯滑动条件下,油膜厚度对速度和载荷的依赖关系明显偏离了经典的弹流理论。试验中观察到的入口凹陷证明了已有入口凹陷弹流数值分析的正确性。     

Study on Starved Lubrication Performance of a Cycloid Drive

The lubrication performance of cycloid drives affects the dynamic characteristics, mechanical efficiency, and contact fatigue behavior. Starved lubrication performance of a cycloid gear drive is studied using a numerical thermo-starved elastohydrodynamic lubrication model. The parameter of the inlet oil film thickness is chosen to represent the starvation degree. Effects of the inlet film thickness on the central film thickness, friction coefficient, frictional power loss, starting position of the effective film thickness, and lubrication efficiency are investigated. The optimum inlet film thickness is defined and is calculated under different rolling–sliding ratios, speeds, and loads. Finally, the optimum inlet film thickness during the meshing process of a cycloid drive is calculated.     

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...     

Energy Efficient Siloxane Lubricants Utilizing Temporary Shear-Thinning

This study investigates the rheologic properties, elastohydrodynamic film, and friction coefficients of several siloxane-based lubricants to assess their shear stability and their potential for energy efficient lubrication. Several siloxane-based polymers with alkyl, aryl, and alkyl-aryl branches were synthesized in order to examine the relationship between their molecular structures and tribological performance. Nuclear magnetic resonance spectroscopy and gel permeation chromatography were used to characterize the molecular structures and masses, respectively. Density, viscosity, elastohydrodynamic film thickness, and friction measurements were measured from 303 to 398 K. Film thickness and friction measurements were made at loads and speeds that cover the boundary, mixed, and full film lubrication regimes. These results illustrate that the shear characteristics of siloxane lubricants vary significantly with polymer length as well as branch structure and content. The findings provide quantitative insight into the features of siloxane molecular structure conducive to optimum film formation with minimum wear and elastohydrodynamic friction to enhance energy efficiency.     

Basics of mixed lubrication

This paper reviews recent research in mixed lubrication, focusing on the current understanding of lubricant entrainment, and thus film thickness, and of friction in thin‐film, rough‐surface lubricated contacts. By combining research using optical interferometry on the experimental side and numerical modelling on the theoretical side, we now have a reasonable understanding of micro‐elastohydrodynamic lubrication, although design rules are still lacking. The regime of true mixed lubrication, where there are both elastohydrodynamic and boundary lubricated regions within a single contact, remains quite poorly understood. New experimental techniques as well as new information about very thin‐film rheology under high‐strain and high‐pressure conditions are probably needed before much further progress can be made in this area.     

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.