摆动活齿传动的弹流润滑分析

在摆动活齿传动运动学分析的基础上,应用弹性流体动力理论对摆动活齿传动的弹流润滑问题进行了计算分析。结合实例,对其油膜厚度进行了计算,分析了摆动活齿传动的各啮合副所处的润滑状态,为摆动活齿传动的设计、制造提供了理论依据。     

A study of thermohydrodynamic lubrication in a circular journal bearing

An analytical method to determine the film temperature of circular journal bearings was developed, which considers the cavitation of the oil film and also recirculation and mixing of the lubricant. The results were verified experimentally. The theory is in good agreement with experiment over a wide range of operating conditions. The effects of journal speed, clearance ratio, lubricant viscosity and specific load on the bearing temperature were examined, and the following conclusions derived. (1) T_b,max, the maximum temperature on the bearing metal surface, increases considerably with the increase of speed and lubricant viscosity and with the decrease of clearance ratio. (2) With the increase of speed, the angular position of T_b,max varies considerably towards the direction of journal rotation from the upper stream side of the location of minimum film thickness, h_min, to the lower stream side of it. The change of angular position of T_b,max is greater than that of h_min. The contrary happens with decrease of the clearance ratio. (3) These characteristics of T_b,max correspond to those of the maximum temperature, T_f,max, in the oil film.     

Performance of finite journal bearings in non-laminar lubrication regime

Fluid dynamic lubrication of journal bearings in a superlaminar regime, ie a transition or turbulent regime, is the subject-matter of this study.Results obtained by solving an appropriately modified Reynolds bidimensional equation have been put in the form of operating diagrams which allow the correct design of journal bearings in real conditions of flow     

Feed pressure flow in plain journal bearings

The purpose of this short technical note is to update the literature on feed pressure flow in plain bearings and to give a summary of suitable equations for predicting such flows. The work is part of a detailed study of feed pressure flow¹.     

Load-carrying capability of water-lubricated ceramic journal bearings

The possibilities of using advanced ceramics in water-lubricated journal bearings were studied by performing tests on journal bearings lubricated with water. The materials studied were two aluminas (Al₂O₃), a zirconia-toughened alumina (ZTA), a partially stabilized zirconia (PSZ), a sintered silicon carbide (SiC), a reaction-bonded silicon carbide (SiSiC) and a β′-sialon. From the present study it can be concluded that water-lubricated journal bearings utilizing silicon carbide against itself offer good performance. Moderate performance can be achieved with an all-alumina sliding pair, provided that the loads remain low and that a high surface quality can be ensured.     

Linear stability analysis of hydrodynamic journal bearings under micropolar lubrication

The dynamic characteristics of hydrodynamic journal bearings lubricated with micropolar fluids are presented. The modified Reynolds equation is obtained using the micropolar lubrication theory. Applying the first order perturbation of the film thickness and steady state film pressure, the dynamic characteristics in terms of the components of stiffness and damping coefficients, critical mass parameter and whirl ratio are obtained with respect to the micropolar property for varying eccentricity ratios and slenderness ratios. The results show that micropolar fluid exhibits better stability in comparison with Newtonian fluid.     

Performance of three-lobe pressure-dam bearings

The use of multi-lobe bearings, considered to be more stable than ordinary circular bearings in industry is increasing daily. Studies have shown that performance can be further improved if pressure dams are incorporated into these bearings. Analysis of two-lobe pressure dam bearings has been reported in the literature. The present work was carried out to assess the performance of a three-lobe bearing with pressure dams. The results show that the performance of a three-lobe pressure-dam bearing is far superior to that of an ordinary three-lobe bearing.     

Numerical study of the thermo-hydrodynamic lubrication phenomena in porous journal bearings

In this work, a numerical simulation is presented for the thermo-hydrodynamic self-lubrication aspect analysis of porous circular journal bearing of finite length with sealed ends. It consists in analyzing the thermal effects on the behavior of circular porous journal bearings. The Reynolds equation of thin viscous films is used taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The presented results are in good agreement with those cited in the literature. The effects of dimensionless permeability parameter and eccentricity ratio on performance parameters are presented and discussed. The results showed that the temperature influence on the journal bearings performance is important in some operating cases, and that a progressive reduction in the pressure distribution, in the load capacity and attitude angle is a consequence of the increasing permeability.     

Numerical analysis of hydrodynamic bearings with significant journal lateral velocities

The previously reported¹ numerical analysis method for hydrodynamic journal bearings has been extended to take account of significant lateral velocities of the journal. Conditions encountered in bearings with substantial dynamic loading have therefore been covered. This paper is intended to be used in conjunction with reference 1, and it is essentially a refinement of the method described therein. Results obtained by means of the numerical analysis method presented here are given in reference 2. The application of these results to journal orbit prediction, and comparison with experimental orbits is covered by reference 5, and an example is presented herein.     

Analysis of hydrodynamic journal bearings lubricated with non-Newtonian fluids

A procedure for solving the Navier-Stokes equations for the steady, three-dimensional flow of a non-Newtonian fluid within a finite-breadth hydrodynamic journal bearing is described. The method uses a finite-difference approach, together with a technique known as SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) which has now become established in the field of computational fluid dynamics. The concept of ‘effective viscosity’ to describe the non-linear dependence of shear stress on shear rate is used to predict the performance of bearings having a single full-width axial inlet groove situated at the position of maximum film thickness. To illustrate the capabilities of the procedure, results are obtained for a range of non-linearity factors, and lead to the conclusion that the pressure distribution, attitude angle, end-leakage rate, shear force and load capacity can all be predicted for a variety of non-Newtonian lubricants using the SIMPLE numerical integration technique.     

Thermal characteristics of misaligned finite journal bearings

Adiabatic analysis of a journal bearing is presented for maximum allowable misalignment with a length: diameter ratio of one. The direction of journal misalignment is allowed to vary up to the axial plane containing the load vector. Reynolds and energy equations are solved simultaneously using finite differences, considering both axial and spiral oil inlet conditions. The results show that bearing behaviour is significantly affected by journal misalignment. It is also noted that thermal effects are more pronounced for bearings with axial rather than spiral oil inlet grooves.     

Active lubrication applied to radial gas journal bearings. Part 1: Modeling

Active bearings represent a mechatronic answer to the growing industrial need to high performance turbomachinery. The present contribution aims at demonstrate the feasibility of applying active lubrication to gas journal bearings. The principle of operation is to generate active forces by regulating radial injection of lubricant through the means of piezoelectric actuators mounted on the back of the bearing sleeves. A feedback law is used to couple the dynamic of a simplified rotor-bearing system with the pneumatic and dynamic characteristics of a piezoelectric actuated valve system. Selected examples show the considerable performance advantages of such new kind of bearing.     

Steady state analysis of noncircular worn journal bearings in nonlaminar lubrication regimes

the steady state behaviour of non-circular worn journal bearings is analysed for various wear depth parameters (δ₀), following Constantinescu's turbulent lubrication theory. Computed results are compared with published results. It is observed that geometric change caused by wear has a significant effect on the steady state characteristics of bearings.     

Ferrofluid lubrication of finite journal bearings using Jenkins model

The present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Jenkins model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analyzed using 2 control parameters: magnetic force coefficient and Jenkins viscosity. The obtained results are compared to those from Neurenger‐Rosensweig model. It is shown that pressure, load capacity, attitude angle, and side leakage increase and friction factor decreases when increasing the value of each control parameter at low and medium eccentricity ratios. However, the Jenkins viscosity parameter decreases the load capacity and increases the friction factor at high eccentricity ratios.     

Dynamic performance of plain gas journal bearings

This paper presents dynamic performance characteristics of plain gas journal bearings. The perturbation formulation suggested by Lund has been modified to obtain stiffness and damping properties. Since rotor bearing axes are never perfectly parallel, the effect of skew has also been considered. Stability studies have been carried out for selected compressibility parameters     

Grease lubrication of rolling element bearings — role of the grease thickener

The contribution of grease thickener to lubricant film formation was examined in this paper. Lubricant film thickness and friction were measured for different grease thickener types in a bearing simulation device. The results showed that the greases formed thick (20–80nm), low friction surface layers at low speeds, which were much greater than the corresponding base oil film. These films appeared to be formed by the physical deposition of thickener in the track during overrolling of the grease. This was confirmed by infrared reflection analysis, which showed the deposited films to have increased thickener content. The ability of grease to form renewable physically deposited solid films has significant implications for optimising lubricant formulation for certain applications, e.g. bearings operating at high temperatures and low speeds where a conventional elastohydrodynamic lubricating film would be inadequate. Copyright © 2007 John Wiley & Sons, Ltd.     

A numerical analysis method based on flow continuity for hydrodynamic journal bearings

A numerical method of hydrodynamic bearing analysis is presented which is simple in concept, yet capable of development to handle complex situations such as dynamic misalignment. It is similar to the finite difference solution of Reynolds equation, but incorporates a more realistic modelling of cavitation. The approach to a numerical solution is direct, and should facilitate a better ‘feel’ for the way in which the physical processes are modelled. Results produced with this analysis are compared with other published data for aligned crankshaft bearings and misaligned sterntube bearings.     

Squeeze film characteristics of long partial journal bearings lubricated with couple stress fluids

On the basis of microcontinuum theory, a theoretical analysis of hydrodynamic squeeze film behaviour for long partial journal bearings lubricated by fluids with couple stresses is presented. To take into account the couple stress effects due to the lubricant containing additives or suspended particles, the modified Reynolds equation governing the film pressure is derived by using the Stokes constitutive equations. Various bearing characteristics are then calculated. According to the results obtained, the influence of couple stress effects on the performance of the system is physically apparent and not negligible. Compared with the Newtonian lubricant case, the couple stress effects provide an enhancement in the load-carrying capacity and lengthen the response time of the squeeze film action. On the whole, the presence of couple stresses signifies an improvement in the squeeze film characteristics of the system.     

Linear stability performance analysis of finite hydrostatic porous journal bearings under the coupled stress lubrication with the additives effects into pores

A theoretical investigation into the stability performance characteristics of a finite externally pressurized porous journal bearing has been undertaken with the slip flow of coupled stress fluid. The analysis deals with the modified Darcy-type equation incorporating the additive effect in the porous bush. A modified form of Reynolds equation is obtained using Stokes micro-continuum theory of coupled stress fluids as lubricant. Applying the first-order perturbation of the film thickness and steady-state film pressure, the stability parameters are obtained under various parametric conditions. The results reveal that stability deteriorates with increase in coupled stress parameter for a value of percolation factor under full slip condition.     

Boundary Element Method for Elasto-hydrodynamic Lubricated Multi-body Contact

In this paper, a formulation for isothermal Elasto-Hydrodynamic Lubricated (EHL) contact problems, using the Boundary Element Method (BEM) is proposed. The BEM is used for modelling both bodies in contact. The proposed formulation evaluates directly the film thickness considering the elastic deformation of the bodies after treating the problem as a coupled system (solid–fluid–solid). The fluid is modelled using the Finite Difference Method (FDM). The forward iterative method is used as the solution algorithm of the elasto-hydrodynamic problem. The analysis demonstrate that the BEM is efficient for modelling both solids in contact and that the computational time remains low.