Transient response of a journal supported on elastic bearings

By considering the inherent flexibility of the bearing liner, the non-linear dynamic response of a journal bearing system is determined in this study. The transient analysis is presented and the journal centre motion trajectories are plotted for rigid and flexible bearings. Effects of the different parameters such as the eccentricity ratio, and the deformation coefficient etc on non-linear trajectories are reported in this paper. The transient response of the system is also obtained for different values of the normalized journal mass which shows that a rotating system supported in a flexible bearing may have a better performance under dynamic conditions than one supported in rigid bearings.     

Comparison of power loss and pad temperature for leading edge groove tilting pad journal bearings and conventional tilting pad journal bearings

A study was undertaken to compare power loss and pad temperature characteristics between LEG (leading edge groove) tilting pad journal bearings and conventional tilting pad journal bearings with and without a seal tooth. All test bearings were double tilting type with six-pad LOP (Load On Pad), 300.6 mm inner diameter, and 120.0 mm effective length. Pad temperatures and power losses were compared and evaluated versus rotor rotational speed, oil flow rate, and static load. Four kinds of tilting pad journal bearings were evaluated, conventional tilting pad journal bearings with and without a seal tooth and LEG tilting pad journal bearings with and without a seal tooth.Test results indicate that tilting pad journal bearings without a seal tooth have lower power loss and pad temperature than tilting pad journal bearings with a seal tooth. Especially, conventional tilting pad journal bearing without a seal tooth has the lowest power loss and pad temperature among the test bearings.     

Developments in engine bearing design

Some of the important recent developments in engine bearing design techniques are highlighted. The availability of increased computing power has enabled more realistic assumptions about bearing conditions to be considered; these include oil feed features, oil film history, non-circular bearings, inertia effects due to journal centre movement, improved prediction of main bearing loads, flexible housings and special bearings. References to these advances are made, together with illustrations of how they affect predicted bearing performance. Experimental evidence is also being obtained, which helps to verify and give confidence in the analytical predictions     

Abrasive wear of bearing materials — a comparison of test methods

In a lubricated journal bearing, journal as well as bearing may suffer from wear if the lubricant contains hard abrasive particles. Wear may be particularly severe under conditions of boundary lubrication. Tests with 360° journal bearings show that, as far as friction and wear are concerned, the white metal SnSb8Cu4Cd and the bronze CuPb10Sn10 suffer equally from the addition of “air cleaner test dust” in the lubricant. In contrast, on addition of the abrasive, the composite process surface roughness of the bearing (which controls the ability of the bearing to re-establish thick film lubrication) remains virtually unaffected in the case of the white metal but increases considerably in the case of the bronze.The results of tests, performed with a block-on-ring method, do not agree well with those found with real journal bearings. Thus they are not suitable for qualifying materials for application in journal bearings lubricated with abrasive-containing lubricant.     

Novel approach to solve the dynamical porous journal bearing problem

Analytical pressure solutions are a simple and robust way to model plain journal bearings in rotordynamics, but cannot be extended to porous journal bearings. Using the method of weighted residuals—viz. Galerkin's method with global shape functions—a novel and fast approach to solve the dynamical porous journal bearing problem is proposed. This approach allows for the influence of rough surfaces on the hydrodynamic pressure implemented through flow-factors, journal misalignment and calculation of stiffness and damping coefficients for finite bearings. The proposed method will be verified using analytical expressions and new results will be shown for porous journal bearings including the influence of rough surfaces.     

Hydro-Roll: A Novel Bearing Design with Superior Thermal Characteristics

A novel journal bearing design, called hydro-roll, which combines a hydrodynamic journal bearing with a rolling-element bearing in series, is presented. The hydro-roll principally operates as a rolling-element bearing at low speeds and as a hydrodynamic bearing at high speed. When properly designed, the hydro-roll can offer superior performance over the conventional hydrodynamic bearing in terms of both wear and thermal characteristics. The hydro-roll prevents the severe wear which occurs during the start-up of hydrodynamic journal bearings since it operates as a rolling-element bearing whenever the sliding friction is too high. This characteristic has the important advantage of reducing the risk of catastrophic failure by bearing seizure.

At a steady high speed, the hydro-roll operates as a hydrodynamic journal bearing while the sleeve together with the inner race of the rolling-element bearing turn at a low speed. This study focuses on the thermal analysis of a journal bearing with a rotating sleeve in comparison to an identical stationary sleeve. The results indicate that the sleeve rotation reduces the risk of bearing failure due to local overheating of the sleeve. The minimum sleeve speed required for this effect is evaluated.     

Experimental Investigation into Friction Performance of Dimples Journal Bearing with Phyllotactic Pattern

In this paper, we discuss the developments of a novel dimples journal bearing and the experimental results on friction performance. Based on the phyllotaxis theory of biology, the lubricating dimples were positioned in the internal circle surface of the journal bearing. The effects of phyllotactic pattern parameters on the distribution of these dimples were discussed in detail and simulated. A series of experimental results was presented to examine the effect of phyllotactic coefficients and dimple diameters on the friction characteristics. It was shown that the friction performance of journal bearings can be evidently improved under the proper tested parameters. Meanwhile, the friction coefficients, which are obtained in the dimples journal bearings with phyllotactic pattern and linear pattern, were presented to reveal their differences, and lower values of friction coefficients were achieved for the proposed dimples journal bearing under the tested radial load and rotational speed.     

Load capacity and stiffness of misaligned hydrostatic recessed journal bearings

The effects of journal misalignment on the static properties of capillarycompensated hydrostatic journal bearings are investigated theoretically. It is demonstrated that misalignment reduces the stiffness as well as the load capacity and that the amounts of reduction are substantial when the value of the slope δ is greater than 0.2. The results of the analysis are applied to bearings with any number of recesses. Good agreement between theoretical and experimental results for the loci of the shaft centre and the stiffness is obtained.     

Combined effects of surface roughness and couple stresses on static and dynamic behaviour of squeeze film lubrication of porous journal bearings

Abstract

The combined effects of surface roughness and the couple stresses on the static and dynamic characteristics of squeeze film lubrication in porous journal bearings with no journal rotation are theoretically studied. The Stokes couple stress fluid model is considered to model the lubricants with additives. The surface roughness on the porous journal bearing is mathematically modelled by a random variable with non-zero mean, variance and skewness. The generalised stochastic Reynolds type equation is derived for the problem under consideration. The applied load is considered as a sinusoidal function of time to simulate the bearings operating under cyclic loads. The closed form expressions for the bearing characteristics are obtained for the short porous journal bearings. It is observed that the negatively skewed surface roughness and couple stresses improve the performance of the porous journal bearings as compared to the smooth journal bearings with Newtonian lubricants. However, the presence of positively skewed surface roughness on the bearing surface affects its performance.     

Numerical and Compact Model of Metal Mesh Foil Bearings

Metal mesh foil bearings (MMFBs) are novel gas foil bearings with lower manufacturing costs and higher inherent material energy dissipation ability than traditional bump-type foil bearings. To improve the design guidelines of MMFBs and predict bearing performance, a compact theoretical model is presented by considering the metal mesh substructure as assembled springs and dry friction joints. The proposed analytical model considers the effects of several factors such as relative density, wire diameter, geometrical size, and radial interference of the metal mesh substructure. The predicted stiffness coefficients, which take the dry friction effect into account, show strong nonlinear characteristics with the increasing displacement and have a significant difference between the loading and unloading process. A series of static load tests are conducted to verify the theoretical model of MMFBs. The hysteresis loops of static load versus bearing deflection with respect to the different relative densities predicted by this model are demonstrated by experimental data. The minimum film thickness, journal eccentricity, and attitude angle with respect to different relative densities, rotational speeds, and applied loads are presented and analyzed. The predicted results of the dynamic force coefficients show that the equivalent viscous damping coefficient and relative density have significant effects on bearing dynamic performance. Furthermore, the influence of radial thickness, wire diameter, and radial interference on bearing static and dynamic performance is discussed.     

A Porous Hydrostatic Gas Bearing for Use in Miniature Turbomachinery

An analytical program was conducted to establish recommended types of gas-lubricated journal bearings for use in miniature cryogenic turbomachinery. Very high rotative speeds, and the limiting damping properties of gas, indicated that fractional frequency whirl is prevalent, and the most difficult problem to overcome. Of the many journal bearing types investigated, the tilting pad hydro-dynamic and porous hydrostatic journal bearings were suited to the application.

A novel spring mounted, three shoe, porous hydrostatic bearing is discussed in terms of design and experimental results. A 1/2 inch diameter journal bearing is subjected to loading and speeds to 700 grams and 65,000 rpm, respectively. Excellent performance in terms of load capacity, power loss, and flow are indicated. Orbit motions of the floated bearing with respect to the supported shaft demonstrate desirable stability characteristics for the range of tests.     

Experimental study of journal bearings with undulating journal surface

A journal bearing test rig was designed and constructed to test the behaviour of journals with wavy surfaces, the circumferential undulations being varied both in amplitude and in number. Results show that wavy journal surfaces may well enhance the load carrying capacity of a bearing. Moreover, surface undulations are shown to move the journal centre locus closer to the load line, ie cause a lower attitude angle. These effects are found to be more pronounced with larger wave amplitudes, and with higher numbers of waves around the journal circumference. In general, friction is found to be reduced with increase in surface wave amplitude.Good agreement is shown to exist between test results and a computer aided analysis conducted by the authors to predict wavy journals performance¹. It has been established that a wavy journal surface may, under certain conditions, display higher load capacity, lower friction and permit safer running of journal than bearings with perfectly smooth surfaces.     

基于流固耦合的多油楔滑动轴承动特性研究

提出了适用于多油楔滑动轴承结构的动网格方法,并实现了轴颈任意扰动(自由振荡运动、脉冲激励运动和偏心涡动)下润滑流场的瞬态计算。通过在润滑流场与转子系统间进行数据传递,形成了多油楔滑动轴承润滑流场与转子动力学之间的耦合计算。讨论了轴颈自由振荡、受脉冲激励以及偏心涡动时轴瓦安装角对多油楔滑动轴承动特性的影响,数值计算表明:当安装角设置在20°~40°之间时,轴承的阻尼较小,稳定性较差;而当轴瓦安装角在100°~120°之间时,轴承阻尼较大,稳定性较好,并且轴瓦数越多,安装角对稳定性的影响越小。     

Contrarotating Journal Bearings for Naval Propulsion Systems

Contrarotating propeller systems offer well-recognized advantages in propulsion efficiency. Unfortunately, circular bore journal bearings have no load capacity when used in contrarotation, but a quasi-squeeze effect may be induced by offset or preloaded sub arcs as these pass through the loaded region of the film. With this type of bearing, even when under steady load, the journal must orbit within the clearance space. The propagation of such orbits is described. The response is quantified by a Fourier analysis of the motion. Contrarotating journal bearings may be designed to support loads of the same general magnitude as conventional circular (non-rotating) bearings.     

Determination of the dynamic coefficients of the coupled journal and thrust bearings by the perturbation method

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. Reynolds equations and their perturbation equations of journal and thrust bearings are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between the journal and the thrust bearings. It also includes the Reynolds boundary condition in the numerical analysis to simulate the cavitation phenomenon. The stiffness and damping coefficients of the proposed mathematical method are compared with those of the numerical differentiation of the bearing force with respect to finite displacements and finite velocities of bearing center. It shows that the proposed method can calculate the dynamic coefficients of a coupled journal and thrust bearing more numerically stable and computationally efficient than the differentiation method. It also investigates the coupling effect of the coupled journal and thrust bearing and it shows that the proposed method makes it possible to calculate the cross-coupled dynamic coefficients in the radial–axial direction of the coupled journal and thrust bearing.     

动压气体轴承的动态刚度和动态阻尼系数

采用偏导数法求解动压气体润滑Reynolds方程,给出动压气体轴承动态刚度和动态阻尼系数普遍适应的计算方法.进行有限元数值仿真,计算动压气体轴承的动态刚度和动态阻尼系数,并重点研究轴颈扰动频率和不同轴颈扰动频率下的轴承静态载荷及轴承数对这些系数的影响.从理论上解释动压气体轴承的动态刚度和动态阻尼系数与轴颈扰动频率的密切相关性.     

Thermal effects in cylindrical journal bearings of high‐speed gearboxes

The high rotational speeds and loads of gears operating in acceleration gearboxes causes problems related to the correct choice and design of journal or rolling bearings. In the case of journal bearings, these problems are connected with thermoelastohydrodynamic lubrication theory and the dynamics of the bearing system. However, of major importance is the problem of thermal effects in journal bearings. This has been considered for bearings used in a double‐helical gearbox with the pinion and output shaft operating in cylindrical journal bearings. The oil film pressure, temperature, viscosity distributions, and maximum and mean oil film temperatures have been determined. In calculations, laminar adiabatic and turbulent adiabatic models of oil films have been applied. The results of the calculations can be used in the design of cylindrical or other types of journal bearing in rotating machinery, including acceleration or reduction gearboxes.     

Comparison of tribological characteristics between aluminum alloys and polytetrafluoroethylene composites journal bearings under mineral oil lubrication

This study examined the tribological behavior of journal bearings made from polytetrafluoroethylene (PTFE) composites and aluminum (Al) alloys. The PTFE composite journal bearings consisted of a steel backing with a thickness of 1.6 mm, a middle layer of sintered porous bronze with a thickness of 0.24～0.27 mm, and a surface layer of PTFE filled with fluorinated ethylene propylene (FEP) powder and carbon fibers with a thickness 0.06～0.14 mm. The other was an aluminum alloy journal bearing consisted of a steel backing with a thickness of 1.5 mm and a surface layer of an Al-6Sn-6Si alloy with a thickness 0.35～0.75 mm. A series of lubrication tests were performed using a journal bearing tester under various normal loads. The tribological properties for each journal bearing were evaluated by measuring the lubricant oil temperature and friction coefficient as a function of the applied normal load. In addition, the chemical compositions and microstructures of the journal bearing materials used in this study was analyzed by inductively coupled plasma (ICP), optical microscopy (OM), and scanning electron microscopy (SEM), respectively. The experimental results showed that the Al alloy journal bearings reduce the friction coefficient by 28 % compared to the PTFE composites bearings. In addition, the Al alloy journal bearing worked properly at the maximum load of ～ 8,000 N without adhesion. However, the PTFE composite journal bearings exhibited strong adhesion at the loads ranging from 6300 to 8000 N. This suggests that the Al alloy is a more promising material in journal bearings than PTFE composites.     

气体动压径向短轴承动力学和分岔分析

径向气体润滑轴承是精确定位以及微旋转机械中的重要部件,其非线性动力学特性对整个器件的稳定性和可靠性具有重要的影响。文中以气体动压径向短轴承—转子系统为研究对象,建立气体轴承—转子系统耦合非线性动力学方程,以轴承数为分岔参数,分析长径比为0.75时在不同初始偏心率条件下,系统动力学特性随转子转速变化的影响。