润滑油环境粘度对非稳态热弹流润滑的影响

分析了不同的环境粘度对非稳态热弹流润滑的影响。指出了摩擦因数不是单调地随环境粘度的变化而变化,在一定工况下,会存在一个最优的环境粘度。粘度的变化对膜厚的影响大于对压力的影响,使用粘度系数高的润滑油,会形成较高的第二压力峰和较大的表面摩擦力,对接触疲劳寿命有不利影响。     

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     

光干涉法测定润滑油压粘系数的研究

作者在点接触弹流润滑试验装置上,采用光干涉技术测定不同润滑油的弹流膜厚。并以英国Imperial College提供的标准油作为基准,标定出国产润滑油的压粘系数。文中讨论了测量原理和分析计算,以及提高测量精度的措施。本文还对几种不同系列及同一系列不同粘度的润滑油的压粘系数与温度影响进行了研究。     

润滑油粘度对齿轮接触疲劳寿命影响的研究

通过热弹流润滑数值计算,分析了润滑油粘度对齿轮接触疲劳寿命的影响。研究结果表明：就齿轮润滑而言,并非润滑油粘度越高齿轮疲劳寿命就越长;当粘度超过某一临界值时,疲劳寿命随粘度增加反而降低。同时还指出齿面压力分布中的第二压力峰是个相当重要的参数,它对轮齿接触区次表面应力分布影响较大。     

齿轮润滑性能的多重网格技术应用研究

对齿轮的弹流润滑问题应用多重网格技术进行了数值计算与分析,并用于分析齿轮的弹流润滑性能。计算结果表明,多重网格技术应用于齿轮弹流数值计算具有收敛速度快、数值稳定性好等优点。增大齿轮的模数、传动比和压力角等参数,以及提高转速、增大润滑油粘度可以提高齿面间的润滑油膜厚度。     

高速单圆弧齿轮等温弹性流体动力润滑数值解

本文对高速单圆弧齿轮的等温弹流理论作了研究,成功地获得了可在IBM—PC/XT上执行的圆弧齿轮弹流数值解计算程序。由一系列的数值计算结果所绘制的线图,既可在微型机屏幕上显示,又可同时在小型绘图机上输出。在此基础上,计算和分析了轮齿表面平均速度、螺旋角和润滑剂粘度对承载能力及最小膜厚的影响;并将本文数值解结果与用Dowson—Higginson线接触理论拟合公式所得最小膜厚值进行了比较,表明用拟合公式计算单圆弧齿轮弹流膜厚与较为精确的数值解结果有较大的差别。     

双渐开线齿轮分阶参数对弹流润滑特性的影响研究

针对双渐开线齿轮分阶参数对弹流润滑特性影响的问题,根据双渐开线齿轮齿廓啮合特点及弹流润滑理论,推导出了双渐开线齿轮接触线长度及当量曲率半径计算公式。建立了双渐开线齿轮弹流润滑模型,研究了双渐开线齿轮分阶参数对弹流润滑特性的影响;通过数值计算,得出了最小油膜厚度及摩擦系数在啮合周期内的分布情况。研究结果表明:采用该模型得出的最小油膜厚度与已有算例及经验公式得出的数值结果偏差较小;与双渐开线齿轮齿腰高度系数相比,齿腰切向变位系数对最小油膜厚度的影响较小,最小油膜厚度随高度系数的增大而减小;摩擦系数随齿腰高度系数的增大而增大,随齿腰切向变位系数的增大而减小。     

线接触弹流润滑综合数值分析

应用多重网格法和多重网格积分法数值求解rNewton流体和Ree-Eyring流体线接触等温和热弹流润滑问题,分析了滑滚比对摩擦因数的影响,指出了润滑油的流变性和热效应对线接触弹流润滑油膜粘度的影响,以及不同滑滚比时压力、膜厚和温度的分布规律。结果表明：等温润滑时的摩擦因数随着滑滚比的增加而增加,热弹流润滑时的摩擦因数随着滑滚比的增加先增加后减小,热效应和非牛顿流体的剪稀作用均会使润滑油的等效粘度降低,从而影响摩擦因数;热效应的存在使油膜变薄,且在所讨论的工况条件下Newton流体的膜厚比Ree-Eyring流体的稍薄,热效应使第二压力峰变矮,且Ree-Eyring流体的第二压力峰矮于Newton流体的第二压力峰;纯滚动时,Ree-Eyring流体的温度比Newton流体的温度高,有滑滚比时,Newton流体的温度比Ree-Eyring流体的温度高,且油膜的温度随滑滚比的增加而增加。     

考虑温度影响的钢丝绳橡胶输送带粘弹性模型建立及压陷阻力分析

为了研究带式输送机运行过程中,输送带覆盖层与托辊的压陷阻力变化规律,以三元件固体模型为基础,考虑温度对输送带粘弹性能的影响,提出并建立一种考虑温度的三元件四变量热粘弹动力学参数模型。再利用变温动态压缩实验,得到不同温度下的动态加载力与时间的曲线,通过一阶傅里叶级数拟合和推导获得了输送带橡胶覆盖层的热粘弹动力学参数模型公式,并对公式的准确性进行了验证,最后建立了包含温度、带速等参数的输送带压陷阻力系数计算方程,分析了各因素对压陷阻力系数的影响,并通过实验验证了压陷阻力系数计算方程,研究结果为指导带式输送机的节能运行控制提供了依据。     

不同工况条件对直齿轮副弹流润滑特性的影响研究

根据弹流润滑理论与渐开线直齿轮齿廓啮合特点,建立非牛顿流体直齿轮副弹流润滑模型,采用数值方法求解不同工况条件对油膜压力、油膜厚度分布及啮合周期内摩擦因数的影响。研究表明,转速、输入转矩及润滑油粘度产生变化,均会影响油膜压力及膜厚分布,最终导致啮合周期内摩擦因数发生变化,且摩擦因数在靠近节点处达到最小值。     

Thermoelastohydrodynamic Analysis of Spur Gears with Consideration of Surface Roughness

Thermoelastohydrodynamic lubrication (TEHL) analysis for spur gears with consideration of surface roughness is presented. The model is based on Johnson’s load sharing concept where a portion of load is carried by fluid film and the rest by asperities. The solution algorithm consists of two parts. In the first part, the scaling factors and film thickness with consideration of thermal effect are determined. Then, simplified energy equation is solved to predict the surfaces and film temperature. Once the film temperature is known, the viscosity of the lubricant and therefore friction coefficient are calculated. The predicted results for the friction coefficient based on this algorithm are in agreement with published experimental data as well as those of EHL simulations for rough line contact. First point of contact is the point where the asperities carry a large portion of load and the lubricant has the highest temperature and the lowest thickness. Also, according to experimental investigations, the largest amount of wear in spur gears happens in the first point of contact. Effect of speed on film temperature and friction coefficient has been studied. As speed increases, more heat is generated and therefore film temperature will rise. Film temperature rise will result in reduction of lubricant viscosity and consequently decrease in friction coefficient. Surface roughness effect on friction coefficient is also studied. An increase in surface roughness will increase the asperities interaction and therefore friction coefficient will rise.     

Tribological characterization of environmentally adapted ester based fluids

Fundamental properties of six synthetic ester base fluids, suitable for the formulation of environmentally adapted lubricants, have been investigated. High pressure viscosity data for the test fluids were obtained through experimental measurements with a high pressure Couette rheometer. The temperature, pressure and viscosity data η(p, T) were parameterized against the Roelands pressure–viscosity equation. Thermal conductivity and specific heat capacity data were obtained using a transient hotwire method, and the EHD friction coefficient, γ, was obtained experimentally as well. The results from these measurements are reported, and the correlation between thermal properties, molecular structure, and the fluid rheology parameters, of the test fluids are discussed.     

Effects of the Lubricant Piezo-Viscous Properties on EHL Line and Point Contact Problems

This paper presents the application of the free-volume viscosity model in a Newtonian elastohydrodynamic line and point contact simulation using a more effective multigrid approach. According to recent experimental studies using high pressure viscometers, the free volume-based pressure–viscosity relationship closely represents the realistic piezo-viscous behavior for the high pressure typically encountered in elastohydrodynamic applications [1]. The effects of different pressure–viscosity relationships, including the exponential model, the Roelands model, and the free-volume model are investigated through an example with poly-alpha-olefin lubricant. It is found that the real pressure–viscosity behavior predicted by the free-volume model yields a higher viscosity at the low-pressure area, which results in a larger central film thickness. The fact that film thickness is formed mainly by the entraining action at the inlet area significantly weighs the importance of viscosity variation from different models in this area. The inlet area is a low-pressure area, and accordingly, the real viscosity of the lubricant predicted by Doolittle model undergoes a rapid increase in a convex function, being apparently larger than the Roelands one. Furthermore, the Doolittle model leads to higher pressure spike amplitude than that observed using the Roelands model. To solve the problem, a full multigrid approach has been used upon the assumptions of isothermal condition. Multigrid is more effective because it uses coarser grid levels to remove errors of different frequencies, which could be more quickly smoothed away than those on simply the fine grid alone. The developed coarse grid correction cycle proves to be an efficient tool to solve the EHL problem for a wide range of load conditions.     

Generalized reynolds equation with slip at bearing surfaces: Multiple-layer lubrication theory

A generalized form of Reynolds equation for fluid lubrication has been derived considering the effects of viscosity variation in the film and slip at the bearing surfaces. Various specific cases have been deduced and the concept of multiple-layer lubrication introduced. The higher lubricant viscosity near the bearing surface is beneficial in reducing the coefficient of friction but the effect of slip is unfavourable.     

基于不同黏压模型的空间液体润滑剂弹流油膜厚度的研究

基于牛顿流变模型针对空间液体润滑剂进行等温线接触弹流润滑数值分析。在相同工况下,采用Barus模型、Roelands模型和Yasutomi自由体积黏度模型分别计算空间液体润滑剂的弹流油膜厚度,并与实验结果进行比较。结果表明:Yasutomi自由体积黏度模型更能真实地反应空间液体润滑剂的黏压关系;与其他黏压方程相比,由于Yasutomi自由体积黏度模型在低压区域产生较高的黏度,因而得到较高的油膜厚度。     

Piezoviscous Effects in Nonconformal Contacts Lubricated Hydrodynamically

The analysis in this Paper is concerned with the piezoviscous-rigid regime of lubrication for the general case of elliptical contacts. In this regime, several, formulas of the lubricant film thickness have been proposed. However, either the load parameter W is not included, which has a strong effect on film thickness, or the film thickness is overestimated by using the Barus formula for pressure viscosity characteristics. In the current study, the Roelands formula has been used for the pressure-viscosity relationship. The effects of the dimensionless load, speed, and materials parameters, the radius ratio, and the lubricant entrainment direction have been investigated. Forty-one cases were used in obtaining the minimum film thickness formula: H₀ = 178G^0.386U^1.266W^?0.880 (1 ? e^?0.0387α Contour Plots indicate in detail the pressure developed between the contacting solids.     

Combined effects of surface roughness and viscosity variation due to additives on long journal bearing

Abstract

The combined effects of surface roughness and viscosity variation due to additives on long journal bearing are analytically studied. The variation in viscosity along the film thickness is considered. The presence of solid particles in the lubricant is an increased effective viscosity, which increases the load carrying capacity and decreases the frictional coefficient, whereas the viscosity variation tends to decrease both the load carrying capacity and coefficient of friction for non-micropolar fluid case. The modified Reynolds type equation for surface roughness has been derived on the basis of Eringen’s micropolar fluid theory. The generalised stochastic random variable with non-zero mean, variance and skewness is assumed to mathematically model the surface roughness on the bearing surface. Numerical results were obtained for the fluid film pressure, load carrying capacity and the coefficient of friction. It is observed that the combined effect is to increase the load carrying capacity and to decrease the coefficient of friction, which improves the performance of the bearing.     

Lubrication theory for couple stress fluids and its application to short bearings

Couple stresses may have a significant effect on the behaviour of bearings and a generalized Reynolds equation is derived to include these effects. The problem of the short journal bearing is analysed. An increase in the effective viscosity increases the load-carrying capacity and frictional drag and decreases the coefficient of friction. The longer the chain length of the lubricant or of the additive molecule is, the greater are the effects due to couple stresses.     

Lubricant additives effects on the hydrodynamic lubrication of misaligned conical–cylindrical bearings

Conical–cylindrical bearings are used in electrohydraulic servo systems to improve the control accuracy, eliminate the static friction and increase the normal load‐carrying capacity. A non‐Newtonian rheological model to investigate theoretically the effects of lubricant additives on the performance of misaligned conical–cylindrical bearings is proposed in this study. In this model, the non‐Newtonian behaviour resulting from blending the lubricant with polymer additives is simulated by Stokes couple stress fluid model. The formed boundary layer at the bearing surface is described through the use of a hypothetical porous medium layer that adheres to the bearing surface. The Brinkman‐extended Darcy equations are utilised to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. The misalignment of the cylinder rod is also considered. A modified form of the Reynolds equation is derived and solved numerically using a finite difference scheme. The effects of bearing geometry and non‐Newtonian behaviour of the lubricant on the steady‐state performance characteristics such as pressure distribution, load‐carrying capacity and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load‐carrying capacity and reduce the coefficient of friction as compared to the Newtonian lubricants. Furthermore, the misalignment of the piston rod has significant effects on the performance of conical–cylindrical bearings. Copyright © 2007 John Wiley & Sons, Ltd.     

Computational fluid dynamics and full elasticity model for sliding line thermal elastohydrodynamic contacts

Classically, the EHD problem is solved using the Reynolds assumptions to model the fluid behaviour, and the Boussinesq elastic deformation equation to model the solid response, both being coupled with the load balance equation. The development of an alternative approach is presented here in order to solve at once the Navier-Stokes equations (mass conservation and momentum equilibrium), the full elasticity and energy equations for the line EHD problem in a fluid-structure interaction approach.The Finite Element Method is used to solve the mathematical formulation in a fully coupled way, inspired from Habchi et al. (2008) [1]. After linearisation with the Newton procedure, all the physical quantities (pressure, velocity field, deformations and temperature) are solved together in a unique system. An important benefit of this approach is the possibility to implement in a simple manner the non-Newtonian and thermal effects; in fact all the quantities can vary through the film thickness. The extension to non-Newtonian rheology and the pressure and temperature dependencies for the viscosity and density are taken into account in a direct way to allow an acceptable prediction of the friction coefficient. Gradients across the film thickness and temperature fields in both the fluid and the two solids are naturally computed and analysed. As a case study, we focus first on the pure sliding cylinder-on-plane contact. It is shown that thermal effects due to friction in the central zone of the contact play a role in heating the lubricant at the inlet zone, via heat conduction in the solids. By increasing the Slide-to-Roll Ratio (SRR), the occurrence of dimples and the subsequent effects in different parts of the contact under zero entrainment velocity conditions are then studied.