计入轴瓦弹性的应力偶流体润滑分析

推导了计入轴瓦弹性的应力偶流体润滑轴承的变形雷诺方程。数值分析表明,刚性轴瓦的最大油膜压力值比弹性轴瓦的最大油膜压力值大,且随着应力偶参数的增大,最大油膜压力提高明显;润滑油分别为牛顿流体和应力偶流体时,弹性系数越大轴承的承载力越小,应力偶参数越大轴承的承载力越大,且轴承的偏心率越大,应力偶参数对承载力的影响越明显,应力偶参数对刚性轴瓦材料的影响比对弹性轴瓦材料的影响大。     

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.     

The effects of surface irregularities on the performance characteristics of flexible finite journal bearings lubricated with couple stress fluids

A numerical solution for the elastohydrodynamic lubrication of finite journal bearings is presented. Couple stress effects resulting from blending the lubricant with various additives are considered. Elrod's cavitation algorithm, which automatically predicts film rupture and reformation in the bearings, is implemented in the solution scheme. A simple elastic model is used to describe the elastic deformation of the bearing liner. Furthermore, the effects of surface waviness on the performance of the bearing are incorporated into the analysis. A comprehensive study illustrates the effects of couple stress, liner flexibility, and surface waviness on the steady‐state performance of finite‐width journal bearings. The results show that these effects should be considered at higher values of the eccentricity ratio.     

轴颈倾斜对人字槽径向气体轴承性能影响的数值研究

由于制造误差、偏斜力矩及弹性变形等原因会导致轴颈在轴承中倾斜,使轴承气膜厚度和压力分布发生变化,会对轴承的工作性能产生影响。为研究轴颈偏斜对轴承性能的影响,通过有限元摄动法求解雷诺方程,研究轴颈偏斜角度和偏斜距离对人字槽气体轴承气膜厚度、压力场、静态和动态特性的影响,并分析轴颈倾斜对人字槽径向轴承临界质量等参数的影响规律。结果表明:轴颈偏斜距离变化对轴承静态和动态性能影响较大,偏斜角度对轴承性能影响较小;随着偏斜距离增大,量纲一承载力和临界质量均大幅减小、量纲一摩擦力矩呈现小幅下降趋势。     

A Study of Dynamically Loaded Journal Bearings Lubricated with Non-Newtonian Couple Stress Fluids

This paper is to theoretically investigate the behavior of dynamically loaded journal bearings lubricated with non-Newtonian couple stress fluids. To take into account the couple stress effects due to the lubricants blended with various additives, the modified Reynolds equation for dynamic loads governing the film pressure is derived. The film pressure is solved numerically with Reynolds boundary conditions and then various bearing characteristics are calculated. The effects of couple stresses on bearing performance characteristics are analyzed. The results conclude that couple stress fluids lubrication improves the bearing performance under dynamic loads.     

An inverse solution for finite journal bearings lubricated with couple stress fluids

This paper presents an inverse solution for finite journal bearings lubricated with couple stress fluids to estimate the eccentricity ratio and the couple stress parameter for a given experimentally measured pressure distribution. The least-squares optimization technique is used to solve the inverse problem. An efficient numerical scheme is developed to solve the direct lubrication problem, which consists of the modified Reynolds equation, the film thickness equation, and the boundary conditions for the pressure field. The flexibility of the bearing liner is considered in the film thickness equation by a simple elastic model. The proposed inverse algorithm was tested using numerically simulated pressure distribution. The results showed that as the percentage of random error added to the numerically calculated pressure data points increases, the number of iterations required for convergence increases slightly, and the accuracy of the predictions decreases especially in the case of elastic liner.     

套齿联轴器对航空发动机振动特性的影响

研究了航空发动机套齿联轴器的连接刚度,推导了套齿动态啮合力计算模型,分析了随扭矩、套齿不对中和动态相对位移变化的套齿啮合力和啮合刚度。依据航空发动机套齿连接结构,建立了含套齿联轴器的三支点转子动力学模型,分析了套齿连接刚度对系统频率响应特性的影响,在考虑转轴间角度不对中的情况下,分析了套齿连接刚度对系统不对中响应的影响规律。结果发现,动态啮合力模型能够更加真实地模拟套齿连接刚度的变化,但是,当其径向啮合刚度变化不大时,其计算结果与等效刚度模型的计算结果相同,套齿角向刚度对系统动力性能影响很大,在套齿设计、装配和使用中需要重视。     

Approximate closed‐form solution for the dynamical analysis of short bearings with couple stress fluid

The film forces in journal bearings may cause self‐exciting oscillations under particular operating conditions; if the amplitude of these oil‐whirl oscillations becomes too large, it may involve unsafe machinery dynamics. Thus, there is a need to understand the dynamic characteristics of the journal bearings evaluating the performances of the couple stress lubricants used to minimise the friction losses in steady operating conditions. The purpose of this paper was to illustrate a method to formulate with closed‐form solutions the non‐steady fluid film forces, and the stiffness and damping coefficients for ‘short’ liquid‐lubricated couple stress journal bearings, assuming the micro‐continuum Stokes' model. It is shown that the model allows the advantage of minimising the computational time required for the non‐linear dynamic analysis of couple stress journal bearings without any significant loss of accuracy, while the analytical form of the solution involves a better readability of the parameter effects on the system unsteady behaviour. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface roughness effect on finite journal bearings with flexible porous liners

The effects of surface roughness on the static characteristics of finite porous journal bearings under hydrodynamic lubrication conditions are investigated in this paper. The well‐established Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to incorporate the effects of surface roughness into the Reynolds equation. The analysis takes into account the flexibility of the porous liner by using a thin liner model. The effects of velocity slip at the surface of the porous medium are considered in the analysis by using the Beavers‐Joseph criterion. The mathematical model is then solved numerically by finite‐difference methods for mean hydrodynamic pressure, which in turn gives the hydrodynamic load. The effects of the surface roughness parameter, surface pattern, eccentricity ratio, length‐to‐diameter ratio, permeability parameter, and flexibility parameter on the hydrodynamic load‐carrying capacity, attitude angle, and friction factor are discussed.     

计入轴倾斜时轴-轴承系统跨学科耦合分析

采用动力学仿真软件ADAMS和有限元分析软件ANSYS,辅以手工编程的方法,研究了变载荷作用下轴-轴承系统动力学、摩擦学、刚度和强度耦合分析问题的建模和求解,着重讨论轴受载变形倾斜对轴-轴承系统动力学行为、轴承的摩擦学特性和轴颈表面动应力的影响。耦合分析计算结果表明：动应力在轴颈表面沿轴向和周向的分布与油膜压力沿轴向和周向的分布密切相关;动应力随时间的变化与轴-轴承系统的动力学响应密切相关。轴倾斜使得轴-轴承系统的动力学响应、润滑性能以及轴颈表面动应力发生改变。     

A Comparative Study of Static and Dynamic Characteristics of Parabolic and Plane Inclined Slider Bearings Lubricated with MHD Couple Stress Fluids

In this article the couple stress effects on the static and dynamic characteristics of parabolic and plane inclined slider bearings in the presence of an applied magnetic field with squeeze action is analyzed theoretically. The modified magnetohydrodynamic (MHD) couple stress Reynolds equation is derived. The closed-form solution for the film pressure of parabolic and inclined plane slider bearings is obtained and used to study the MHD couple stress static and dynamic characteristics of these bearings. The results predict a higher steady load-carrying capacity, dynamic stiffness, and damping coefficient for the bearings lubricated with MHD couple stress fluid than the corresponding Newtonian case. It is observed that the parabolic-shaped slider bearings provide greater steady load-carrying capacity, dynamic stiffness, and damping coefficients compared to the plane inclined slider bearings.     

Effect of surface roughness on static and dynamic characteristics of MHD couple stress lubrication of parabolic slider bearing

The effect of surface roughness on static and dynamic characteristics of parabolic slider bearing lubricated with couple stress fluid in the presence of magnetic field is theoretically analysed in this paper. The modified stochastic MHD couple stress Reynolds-type equation is derived on the basis of Christensen stochastic theory and considered two types of roughness pattern namely longitudinal and transverse. Expressions for steady pressure and load, dynamic stiffness and damping coefficients are obtained for both roughness patterns. Compared to smooth surface, transverse roughness pattern provides larger load-carrying capacity, dynamic stiffness and damping coefficients, whereas longitudinal roughness pattern has adverse effects. The presence of couple stress and applied magnetic field improves the bearing performance.     

The effect solid particle lubricant contamination on the dynamic behavior of compliant journal bearings

The proposed work concerns a theoretical and numerical investigation of the effect of solid particle contamination of lubricant oils on the static and dynamic characteristics of a finite length compliant journal bearing operating under isothermal conditions with laminar flow. In the present investigation, we use simple models based on the Einstein's mixture theory, which is characterized by the presence of suspended rigid particles in a fluid. Using the classical assumptions of lubrication, a Reynolds equation is derived and solved numerically by the finite difference method. The displacement field at the fluid film bearing liner interface due to pressure forces is determined using the elastic thin layer model. The results obtained show that the presence of suspended rigid particles in the lubricating oil (solid contamination) has significant effects on the hydrodynamic performance characteristics such as the pressure field, friction force, flow rate, elastic surface deformation as well as stability maps of the rotor‐bearing system (critical mass and whirl frequency) especially at high volumetric concentration.     

Lubrication of a narrow porous journal bearing with a couple stress fluid

This paper describes a theoretical investigation of the rheological effects of couple stress fluids on the performance of narrow porous journal bearings. A most general modified Reynolds equation is derived for narrow porous journal bearings using the Stokes constitutive equations for couple stress fluids. The fluid in the film region and in the porous region has been modelled as a couple stress fluid. The analysis takes into account velocity slip at the porous interface using the Beavers‐Joseph criterion. A closed‐form expression for field pressure is obtained for narrow journal bearings. Eigen‐type expressions for field variations are obtained. The dimensionless load‐carrying capacity, attitude angle, and coefficient of friction are presented for different operating parameters. It is observed that narrow porous journal bearings with couple stress fluids as lubricant show a significant increase in load‐carrying capacity with reduced coefficient of friction as compared to the Newtonian case. The present study predicts the effects of the percolation of polar additives (microstructures) into the porous matrix on the bearing performance.     

On the performance of dynamically loaded journal bearings lubricated with couple stress fluids

A numerical study of the performance for a dynamically loaded journal bearing lubricated with couple stress fluids is undertaken. First of all, on the basis of micro-continuum theory, the generalized Reynolds equation for dynamic loads is derived. Then it is simultaneously solved with the force balance equation of the journal, thus obtaining the transient oil film pressure, the transient position and velocity of the journal center. Results from this analysis are presented for a typical engine crankshaft bearing. It is shown, compared with Newtonian lubricants, that under a dynamic loading lubricants with couple stress yield an obvious increase in oil film pressure and oil film thickness, but a decrease in the side leakage flow. Moreover, the effects of couple stress on friction force and friction coefficient vary considerably with time.     

基于摩擦学特性和轴倾斜的轴-轴承系统动力学问题探讨

以弹性轴的多柔体动力学理论为基础,通过ADAMS软件进行动力学仿真,解决了考虑轴承摩擦学特性和轴受载变形倾斜时弹性轴-轴承系统在正弦激励力作用下的动力学求解问题。得到的主要结论是:考虑轴倾斜时一阶固有频率略有下降,二阶固有频率略有上升;二阶共振时振动幅度增大;最小油膜厚度减小,最大油膜压力上升。传统的避开共振频率的设计方法仍然是减小最大倾斜角发生的有效方法。     

Calculation of Journal Bearing Dynamic Characteristics Including Journal Misalignment and Bearing Structural Deformation©

A detailed journal bearing analysis for accurate evaluation of film dynamic characteristics is presented. The new formulation is based on a local perturbation of the oil film at each computational node that captures the important effects of journal misalignment and bearing structural deformation in rotor dynamics and engine NVH applications. The new algorithm is an extension to the classical approach of evaluating film dynamic characteristics based on journal eccentricity perturbation. The governing equations for the oil film pressure, stiffness, and damping are solved using a finite difference approach and their output is validated with numerical results from the literature.     

On the design and development of hybrid journal bearings: a review

This paper presents a comprehensive review of developments in the design and application of hydrostatic and hybrid journal bearing systems during the last few decades. Revolutionary changes have taken place in the applications of hydrostatic and hybrid journal bearings, from very low‐speed radar to very high‐speed turbo‐machinery and ultra‐precision machine tools requiring high stiffness to improve accuracy. Hydrostatic and hybrid bearings are of interest because of their potential at very high operating speed and heavy load‐carrying capacity. This paper also outlines the analyses done of these types of journal bearings in practical application, which has led to improved bearing design. This review critically discusses the parameters that significantly affect the static and dynamic performance of a journal bearing. This review includes coverage of recent publications in the literature pertaining to hydrostatic and hybrid journal bearings focusing on the influence of parameters such as bearing geometry, supply pressure, flow control devices, fluid compressibility, fluid inertia, journal misalignment, bearing flexibility, surface roughness, and thermal effects. Copyright © 2006 John Wiley & Sons, Ltd.     

Linear Stability Analysis of Hydrodynamic Journal Bearings with a Flexible Liner and Micropolar Lubrication

A linear stability analysis of hydrodynamic journal bearings is presented, including the effects of elastic distortion of the liner and micropolar lubrication. Hydrodynamic equations of the lubricant and equations of motion of the journal are solved simultaneously with the deformation equations for the bearing surface to predict the fluid film pressure distributions theoretically. The components of stiffness and damping coefficients, critical mass parameter, and whirl ratio, which reflect the dynamic characteristic of the journal bearing, are calculated for varying eccentricity ratio taking into account the flexibility of the liner and the micropolar properties of the lubricant. The results presented show that stability decreases with an increase in the value of the elasticity parameter of the bearing liner and micropolar fluids exhibit better stability in comparison to Newtonian fluids.     

Effect of laser textured dimples on the lubrication performance of cylinder liner in diesel engine

Laser surface texturing (LST) technique was utilised on a cylinder liner in a diesel engine. In order to analyse the effect of LST micro‐dimples on the lubrication and friction properties of cylinder liner–piston ring (CL–PR), we developed a new mixed lubrication model on the basis of the average Reynolds equation and asperity contacts equation. The model can consider the coupling effects between the surface roughness of non‐texturing regions and micro‐dimples and the synergistic effects of multi‐micro‐dimples. The results show that cylinder liner surface by LST can form effective hydrodynamic lubrication effect in most regions of the strokes, only near the dead points, the friction pair is in mixed lubrication state, asperity contact plays a major role in balancing the external load and the asperity friction force is obvious. The micro‐dimple parameters were optimised to obtain a better lubrication effect with the following optimised results: r_p = 30–60 µm, S_p = 0.2–0.4 and e = 0.03–0.1. Copyright © 2012 John Wiley & Sons, Ltd.