凸轮弹性流体动力润滑油膜厚度计算的新方法

本文先给出了全膜线接触弹流膜厚计算的统一公式，应用弹性流体动力润滑理论，探讨了凸轮油膜厚度的计算方法，利用MATLAB软件编制的程序可计算凸轮弹性流体润滑油膜厚度，凸轮膜厚比λ，从而能判断摩擦副之间的润滑状态，并对判断凸轮表面损伤坏形式，减少两接触表面的磨损，凸轮参数优化设计和使用寿命预测等具有重要意义。     

一种数值求解弹流润滑膜厚和压力的新方法

本文通过直接迭代法对弹流润滑中点,线接触的膜厚和压力进行数值求解。在接触区内,Ｇａｕｓｓ－Ｓｅｉｄｅｌ迭代法用于求解低压区压力,而Ｊａｃｏｂｉ双极子迭代法用同压区的求解。该方法有编程容易,计算速度快和收敛性好等优点。实际计算表明如何区分高压和低压区从而采用对应的迭代方法对收敛很重要。     

Elastohydrodynamic Film Thickness Mapping by Computer Differential Colorimetry

This paper describes a new experimental technique for the study of elastohydrodynamic (EHD) lubricant films. This technique, which is based on the computer processing of EHD chromatic interferograms, uses a combination of image analysis and differential colorimetry for film thickness evaluation. This approach overcomes some major limitations of conventional optical interferometry and allows the precise mapping of lubricant film thickness distribution in EHD contacts, including transient and quasistatic phenomena. The technique has been used for the evaluation of chromatic interference patterns obtained from a conventional optical test rig for rolling point contacts. Three-dimensional representations of lubricant film thickness and shape with high accuracy and spatial resolution have been obtained. The technique's accuracy has been checked and a comparison with conventional monochromatic interferometry has been done for validation. The technique's resolution has been confirmed through the observation of local film thickening just before the EHD exit constriction for both pure rolling and sliding conditions.     

A Limiting Solution for the Dependence of Film Thickness on Velocity in EHL Contacts with Very Thin Films

In recent years there have been substantial improvements in the capabilities of numerical modeling of elastohydrodynamic lubricant (EHL) films and it is now possible to analyze a very wide range of conditions rather than needing to rely on extrapolation using classical film thickness regression equations such as those of Dowson and Higginson. However, a new controversy has arisen concerning the film thickness-velocity dependence in EHL contacts at very low speeds and high loads, with some predictions showing a film thickness much less than that predicted by the classical equations. The present article applies the well-established limiting analysis, first presented by Grubin-Ertel, to the inlet of the EHL contact. It is shown that when the load is high and the speed is low (and the pressure gradient is very high in the inlet) an accurate resolution of the inlet pressure rise is critical for the determination of the film thickness. Discretization errors of this type might be responsible for discrepancies between the classical equations and some recently published numerical predictions.     

Elastohydrodynamic Film Thickness and Tractions for Oil-in-Water Emulsions

Emulsions, consisting of a small volume of oil dispersed in water in the form of small particles, are popular lubricants for metal rolling and some machine design applications. A number of mechanisms have been suggested for the lubricating behavior of emulsions, among which plate-out, starvation, and dynamic concentration are of particular interest here. At low speeds, the emulsion provides essentially the same lubricating ability as neat oil for a point contact, consistent with plate-out. At some critical speed, the emulsion behavior departs from the neat oil, associated with starvation of the inlet zone. At a second critical speed, dynamic concentration becomes the important mechanism. This article measures the film thickness and traction coefficients of oil-in-water emulsions in the different regimes of behavior and compares the results to existing theoretical understanding. The effect of droplet size is isolated as a causative element in fluid film formation.     

Elastohydrodynamic Lubrication in Extended Parameter Ranges — Part I: Speed Effect

Elastohydrodynamic Lubrication (EHL) has been given great attention in the last 40 years. Conventional theories by Dowson and Higginson for line contacts and Hamrock and Dowson for point contacts have been among the most important contributions and widely used in industries. However, commonly used film thickness formulae, developed more than 25–40 years ago when the computational power was very limited, were originally from curve-fitting based on limited numbers of numerical solutions obtained in relatively narrow parameter ranges. Actual operating conditions in typical engineering applications, such as gears, bearings, cams and traction drives, sometimes fall far outside those parameter ranges, and prediction through extrapolation is often difficult to give satisfactory results. As the computer technology and numerical simulation methods have been advancing greatly, one can now analyze cases in extended parameter ranges that cover various practical applications under severe conditions. This paper is Part I of a recent study, focusing on the speed effect on the EHL film thickness. In a relatively narrow speed range, the present results agree well with those from the conventional theory. In the extended speed and load ranges, however, the relationship between the film thickness and the rolling speed may no longer obey the simple power law described by the conventional theory. It appears to be a complicated function of speed, load and contact ellipticity. Commonly used formulae may often overestimate the film thickness especially when the load is heavy and the speed is not high.     

对角修形窄斜齿轮的弹流数值计算和膜厚测试

本文从弹流角度分析了修形前后线载荷分布及最大压力沿接触线的变化规律。本文应用Ｎｅｗｔｏｎ－Ｒａｐｈｓｏｎ方法与Ｎｅｗｔｏｎ下山法相组合的方法，在假定刚体中心膜厚相等的前提下，首先求出了修前斜齿轮某一时刻全接触线上的弹流润滑解，进而求解出修形后斜齿轮某时刻全部接触线各点的载荷分配，压力分布和油膜形状，在文献的基础上，研制了一套微机数据采和处理系统，测量了斜齿轮的中心油膜厚度，测量结果与计量结果基本一     

Elastohydrodynamic Lubrication in Extended Parameter Ranges—Part IV: Effect of Material Properties©

The present study extends the full numerical EHL solution to wide parameter ranges that cover practical and severe operating conditions commonly found in heavy-duty components. This article is the fourth part of the present study, and is focused on the effect of material properties on the film thickness, following three previous papers that investigated the effects of speed, load, and contact geometry, respectively. In this article, the pressure-viscosity coefficient is varied in a range from zero to 72.8 GPa^?1 and the elastic modulus from 80 to 400 GPa, sufficiently wide to cover different materials and lubricants commonly used in industries. More than 500 cases have been analyzed, and results show that in the extended parameter ranges the relationships between the material properties and the film thickness still primarily follow the simple power rules proposed by the conventional EHL theory. However, the exponents in the power-law functions no longer appear to be constants. They are indeed functions of speed and load. For the relationship between the pressure-viscosity coefficient and the central film thickness, the exponent appears to be quite close to 0.53 proposed by the Hamrock-Dowson formula if the speed and the load are moderate. When the speed is low and/or the load is heavy, this exponent may be considerably greater. The same trend is observed for the relationship between the elastic modulus and the film thickness. At moderate loads and speeds, the exponent is close to ?0.073, which is used in the Hamrock and Dowson formula. When the speed is decreased and/or the load increased, the exponent may become positive. It is found, in addition, that the exponents in these relationships are only weakly affected by contact ellipticity.     

Rolling Line Contact Problems in Elastohydrodynamic Lubrication: Modeling and Validation

A computer package has been developed and applied to solve line contact problems of elastohydrodynamic lubrication. The solutions computed by the package are maintained and are indexed by two dimensionless parameters, α and λ, within a database. Power law surfaces are fitted to the minimum film thickness and maximum pressure for each solution and are compared to interpolated surfaces of the same data, to film thickness measurements and to equations published previously in the literature.     

A Rough Shear-Thinning Correction for EHD Film Thickness

A film thickness correction for shear-thinning in elastohydrodynamic contacts has been available that requires parameters obtained from flow curves generated for the specific liquid. For instances for which reduced accuracy is acceptable, a new rough film thickness correction has been formulated for pure rolling and a moderate amount of sliding based on Van Krevelen's graphical technique of estimating shear-thinning from the molecular weight. It has been shown to be useful for high-molecular-weight base oils, when lubricant specific shear-thinning data is absent, although it should most often overestimate the film thinning.     

卷吸速度为任意方向的椭圆接触弹流润滑分析

以往的点接触弹流润滑研究往往局限于分析卷吸速度方向与接触椭圆短轴相重合的工况。但在实际工程问题中,有时卷吸速率方向与接触椭圆长轴相重合,有时卷吸速度方向与接触椭圆的对称轴成一夹角,针对这一问题,本文提出了一种独特的解决方法,压力和膜厚分析分别采用多重网格和多重网格积分法,无论卷吸速度的方向如何,总让Ｘ轴与速度方向一致,而Ｙ方向速度永远等于０。这样任意卷吸速度方向的工况和卷吸速度与接触椭圆短轴相重合     

用双圆盘试验测试润滑油的高压流变性能

本文介绍了作者研制的双圆盘试验机，并测试了两种国产润滑油的弹流润滑膜的弹性特征对载荷，滚动速度及滑差的依赖性。测定的润滑膜剪切弹性膜量值覆盖了其他学者试验结果的范围。     

滑动条件下弹流润滑的屈服膜厚与屈服边界

本文讨论了弹流润滑的屈服问题，从润滑剂的极限剪应力可以得到屈服膜厚的表达式。屈服膜厚是弹流润滑膜的下降 ，当利用拟合公式得到的膜厚小于屈服膜厚时，由于润滑已经处在非牛顿区，所拟全公式不再适用。本文还给出了用膜厚形式表示的屈服准则，并详细讨论了最大压力，平均速度和滑滚比对屈服膜厚的影响。     

Experimental Study of Lubricant Film Thickness Behavior in the Vicinity of Real Asperities Passing through Lubricated Contact

This article presents an experimental study of the influence of real surface micro-geometry on the film thickness in a circular elastohydrodynamic (EHD) contact formed between a real, random, rough surface of steel ball and smooth glass disk. Phase shifting interferometry was used to measure in situ initial undeformed rough surface profiles, whereas thin film colorimetric interferometry provided accurate information about micro-EHD film thickness behavior over a wide range of rolling speeds. Two real roughness features were studied in detail—a 56-nm-high ridge and a 90-nm-deep groove, both transversely oriented to the direction of surface motion. It was shown that the ridge is heavily deformed in a loaded contact and its height increases with increasing rolling speed. The asperity tip film thickness behavior is quite similar to the contact average film thickness when the film thickness is higher than the undeformed ridge height. However, below this limit the film is thicker than what the EHD theory predicts. For the groove, a local reduction in film thickness at the leading edge was observed. When the groove is passing through the EHD conjunction, it maintains its undeformed shape. The behavior of both roughness features studied shows good agreement with previous experimental observations conducted using an artificially produced ridge and groove.     

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°.     

Flow Characteristics of Hydraulic Fluids of Different Viscosities II. Flow in Pumps: Internal Leakage and Loss of Efficiency

A new type of hydraulic fluid, the high-water type, is being developed for use in industrial equipment which is currently using oil or oil-like fluids. In order to determine which factors affect the flow properties of high-water hydraulic fluids, a series of solutions ranging in viscosity from that of a water-glycol fluid (55 mPa·s or 250 SUS) to that of a high-water fluid (3 mPa·s or 35 SUS) was formulated by varying the amount of thickening agent. From flow rates of these fluids at known pressure and viscosity, the efficiency (percent loss of flow) was calculated. As would be expected, internal leakage from the high-pressure side of the pump to the low-pressure side was much greater with the 3 mPa·s fluids than with the 50 mPa·s fluids. Increasing the pump size increased pump efficiency at a given viscosity.

Equations relating pressure, viscosity and flow for two types of internal leakage were developed by mathematical or graphical analysis of the experimental data.     

弹性流体动力润滑发展的拐点研究

本文通过总结研究弹性流体动力润滑（以下简称弹流）自创立以来近半个世纪的发展历程,找出了对其发展起着重大作用的四个拐点,分析并揭示了其内在规律。     

粘塑性流体弹流润滑的研究进展

介绍了粘塑性流体弹流润滑产生的背景、国内外的研究现状,阐述了粘塑性流体弹流润滑未来亟待解决的问题。     

Viscosity-Pressure Correlation of Liquids

A single correlation was obtained to predict Newtonian viscosity-pressure coefficients of mineral oils, resin and polymer blends, pure hydrocarbons, and nonhydrocarbons. The correlation has been tested for a temperature range from 0°c (32 °F) to 135°C (275 °F). The empirical correlation makes use of atmospheric viscosity and density at the temperature of interest and viscosity-temperature property (m_o) of the fluids. When the correlation was compared with other leading correlations, it was shown to require less physical-property data, apply to n wider range of chemical compositions, cover a wider range in fluidity, and provide greater accuracy. The correlation is presented in the form of a polynominal equation.     

Starvation and Reflow in a Grease-Lubricated Elastohydrodynamic Contact

The lubrication mechanisms of a grease in a rolling-element bearing has been studied through the measurement of film thickness in a rolling point contact. To simulate bearing conditions the contact runs under fully starved conditions; there is no attempt to maintain bulk flow of the grease into the inlet using an external supply. In consequence the film thickness drops off rapidly as the contact progressively starves. After a few minutes rolling (at constant speed) an equilibrium film thickness is attained which has two components: a residual film (h_R) comprised of degraded grease thickener and a hydrodynamic component (h_EHD) due to the liquid phase from the grease. The hydrodynamic contribution represents a balance between lubricant lost from the contact and replenishment from the grease close to the track. The ability of the grease to replenish the rolling track has been inferred from measurements of lubricant reflow around the static contact. These results are discussed in light of current starvation and grease lubrication models.