考虑激振频率的可倾瓦推力轴承动特性理论与试验研究

为了研究激振频率对可倾瓦推力轴承动特性的影响,提出考虑激振频率的动特性建模方法和试验方法。依据可倾瓦轴承刚度和阻尼定义,将激振频率引入可倾瓦推力轴承动特性计算过程,通过建立轴向扰动下的膜厚方程、雷诺方程及瓦块运动方程,推导出包含激振频率的可倾瓦推力轴承动特性数学模型,计算分析刚度和阻尼随扰动频率(激振频率与主轴转频的比值)、转速及载荷的变化规律;采用脉冲激振法在可倾瓦推力轴承试验台进行动特性试验,得到不同激振频率、转速及载荷条件下刚度、阻尼的试验结果,并和相应的理论计算值进行对比分析。结果表明：当扰动频率较小时,可倾瓦推力轴承刚度随其增加而逐步增大,阻尼随其增加而逐步减小;当扰动频率增加到一定程度后,其刚度和阻尼逐步趋于稳定。此外,转速和载荷对其刚度和阻尼随扰动频率的变化幅度基本无影响。     

波箔动压空气径向轴承实验台设计

现有的波箔动压空气径向轴承实验台存在最大工作转速达不到轴承实际工作转速,无法在不影响轴承正常工作的情况下对轴承施加径向载荷,无法测量轴承的阻力距等缺点.为了全面满足波箔动压空气径向轴承的实验需要,设计一种最高转速为60 000 r/min的波箔动压空气径向轴承实验台,可以在不影响轴承正常工作的情况下对轴承施加径向载荷,可以同时测量转轴转速、轴承阻力距、转轴水平和竖直方向的位移、轴承工作温度、冷却空气的压力.     

Steady state and dynamic characteristics of partial journal bearings

The response of the lubricant film of a partial journal bearing to displacements and velocities of its journal for laminar Newtonian flow of the lubricant is presented. The bearing force coefficients (spring and damping coefficients) were evaluated experimentally on a sophisticated test rig, with control over all the essential variables. Test results are presented in non-dimensional form and are applicable to a bearing of 130° arc and with a length-to-diameter ratio of 0.8. Useful design data and a theoretical comparison are given.     

试验台约束对滑动轴承动特性识别精度的影响

在滑动轴承的动特性测试中,试验台参数对动特性测试精度有重要的影响。以某倒置式轴承动特性试验台为研究对象,基于轴承动力学正反问题,提出滑动轴承动特性系数识别精度的仿真评估方法,分析不同激振频率时试验台约束参数对轴承动特性系数识别精度的影响规律,并对激振频率和约束参数的取值范围进行优选。结果表明：在较低激振频率的条件下,当约束刚度和约束阻尼取值较小时,动特性系数的识别精度受测试误差的影响不大,随着约束刚度和约束阻尼取值增大到一定值,动特性系数的识别精度受测试误差的影响迅速增大。针对研究的试验台,选择激振频率在30~300 Hz之间,选择试验台约束刚度小于试验轴承刚度的0.3%,试验台约束阻尼小于试验轴承阻尼的7%时,能够保证较好的轴承动特性系数的测试精度。     

Influence of Particles on the Loading Capacity and the Temperature Rise of Water Film in Ultra-high Speed Hybrid Bearing

Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles...     

超临界二氧化碳动静压径向可倾瓦轴承实验台设计与实验研究

针对超临界二氧化碳(S-CO₂)动力机组在启动和停止阶段气体轴承产生非常大的摩擦磨损,以及气体轴承承载力低、刚度低、阻尼小、稳定性较差等问题,设计并改进一种新型动静压S-CO₂润滑径向可倾瓦轴承结构。设计并搭建S-CO₂润滑轴承实验台,针对于实验台转子刚启动和极低转速工况,对新型S-CO₂润滑动静压径向轴承在静压状态下的动态特性进行实验研究,得到轴承的动态刚度和动态阻尼,并分析静压对轴承动态性能的影响。实验结果表明,设计的S-CO₂动静压径向可倾瓦轴承在启停阶段,在轴瓦与轴颈之间产生了足够的静压压力,可将二者完全分隔开,从而能减少启停阶段的摩擦磨损;随着静压压力的增大,轴承X、Y方向上的整体刚度、主阻尼都增大,且2个方向的主刚度系数差别不大,而交叉刚度和交叉阻尼都接近于0。研究结果为进一步揭示S-CO₂润滑径向轴承动压状态特性提供参考。     

Experimental Determination of the Dynamic Characteristics of a Two-Axial Groove Journal Bearing

A hydrodynamic bearing test rig was used to experimentally study the steady operating characteristics and dynamic coefficient of a plain two-axial groove journal bearing. Using two electrodynamic shakers to generate synchronous sinusoidal excitations, two small independent elliptical displacement orbits were produced for different static equilibrium positions. Data was measured for two fixed shaft speeds, while the steady load was varied to achieve Sommerfeld numbers ranging from 0.063 to 0.344. The four linearized stiffness and four linearized damping coefficients were determined for each speed-load condition by reducing the orbital data using an average magnitude and phase method. The coefficients are presented in dimensionless form as functions of the Sommerfeld number. Typical average uncertainty was found to be 12 percent for the coefficients and 8 percent for the Sommelfeld number. For the speed, load, and temperature ranges tested herein, the dynamic coefficient results for each speed agreed within the uncertainty of the data, supporting the first order approximation that, for the operating range studied, a coefficient's magnitude is independent of the absolute speed, load, and viscosity so long as the Sommerfeld number is matched. The same conclusion was reached for the steady operating location within the bearing clearance space. The overall consistency of these results also lends confidence as to their reliability. Additional experimental results presented include three sets of continuous circumferential oil film thickness and pressure profiles, and discrete temperatures.     

螺旋槽气体轴承动态特性及失稳分析

针对高速动静压气体轴承气膜的复杂非线性动力学行为,以球面螺旋槽动静压气体轴承为研究对象,建立润滑分析数学模型;采用有限差分法与导数积分法进行求解,得到动态扰动压力分布及动态特性系数,并研究切向供气条件下螺旋槽参数、径向偏心率、供气压力、转速对气膜刚度阻尼系数的影响规律;建立线性稳定性计算模型,预测气膜涡动失稳转速,分析运行参数对失稳转速的影响。结果表明:气膜阻尼是一种抑制涡动的因素,气膜的稳定性取决于气膜刚度与阻尼的协同作用;气膜刚度阻尼随着槽宽比、槽深比、螺旋角的增大,整体上呈先增大后减小的趋势;刚度随转速的升高而增大,阻尼则随转速的升高而减小;径向偏心率和供气压力越大,气膜刚度和阻尼越大;在一定范围内,提高供气压力、增大径向偏心率能够提高系统失稳转速;合理地选取轴承结构参数和运行参数,能够优化轴承动态特性,保证气体轴承较高的运行稳定性。     

Rotor dynamics analysis and experiment study of the flywheel spin test system

The strength study of the flywheel is important to the flywheel energy storage. The motor and bearing are the key challenges for the high-speed flywheel spin test device in vacuum. By using a small stiffness pivot-jewel bearing and a spring squeeze film damper as the lower support of the flywheel, a simple spin system was designed at a low cost and is suitable for longtime operation. The auxiliary support at the top was not removed until the flywheel passed the first critical speed. The flywheel that kept its rigid state in sub-critical state was tested at the high speed without the top support. The dynamic model of the flywheel-bearing-damper was built by means of the Lagrangian equation to calculate critical speeds, mode shapes and modal damping ratios at different speeds. The lower damper??s effects on the modal damping ratios and forced vibration were discussed. The vibrations of the flywheel-bearing-damper system were measured at the different damping coefficients in the experiment. When the lower damper was adjusted to be overdamped, the flywheel ran up to 50000 r/min steadily, and the experimental result was in agreement with the theoretical assumption. The sub-critical rotor dynamics design and pivot-jewel bearing proved to be good solutions to the spin test for the composite flywheel.     

Robust rotor dynamics for high-speed air bearing spindles

For ultra-precision machining machine tool components need to operate outside critical frequencies of the machining system to avoid insufficient surface finish caused by vibrations. This particularly applies to tooling spindles as those are generally the component of a machine tool with low stiffness and damping values. Surface finish and shape of a machined part rely directly on the overall accuracy in motion of the tooling spindle over the entire machining parameter and speed range. Thus spindle designs for an operation outside critical frequencies combined with high stiffness and damping values are crucial for ultra-precision machining.For sufficient stiffness properties bearing gaps of gas bearings have to have a size of only a few microns and show a distinct sensitivity on temperature and for journal bearings also on speed. This again means that bearing properties change with temperature and speed. Considering a spindle system comprising a rigid shaft rotating in a radial/axial bearing system with changing stiffness and damping properties leads to a resonance speed map with changing rigid mode resonance speeds.This paper treats the influence of shaft speed and temperature on bearing gaps from which rigid mode resonance speeds for a shaft spinning in a bearing system are derived. The quoted influence of centrifugal load and temperature on bearing stiffness, damping and load capacity can be applied to any kind of gas bearing. Therefore the calculation of bearing stiffness, damping or load capacity is not treated in detail. The reader will be shown that there are simple design rules for air bearing systems and shafts of high-speed tooling spindles to avoid critical speeds through the entire speed range. Finally, methods of how to prove the initial design goals and how to verify dynamics of high-speed spindles in production will be presented to the reader. It will also be shown that there are production high-speed spindles available which do not include any critical speed within their speed range and thus show robust rotor dynamics with extremely low errors in motion.Procedures in design, validation and application treated in this paper shall give the reader not only design guidelines for spindles to avoid critical spindle speeds within its speed range, but also recommendations for machine tool builders and end-users for a machine operation taking machine and rotor dynamics into account. As the knowledge for this paper is predominantly based on the experience and work of the author himself only a few references are used. However presented testing results entirely confirm the approach presented in this paper.     

多跨转子-轴承系统振动稳定性试验研究

在一多跨转子-轴承模拟试验台上进行了轴承不对中对系统阻尼及稳定性影响作用的试验研究。采用扩展Prony方法识别了阻尼参数,从非线性系统动力学角度对试验中若干现象进行了定性分析。     

Influence of lubricants on the performance of journal bearings – a review

ABSTRACT

The lubricant properties have a significant influence on the static and dynamic performance characteristics of journal bearing such as load-carrying capability, minimum fluid film thickness, maximum pressure, lubricant flow rate, damping coefficients, stiffness coefficients, etc. The present document reviews the behaviour of various lubricants such as power-law lubricants, couple stress lubricants, micropolar lubricants, ionic liquid lubricants and space lubricants. The influence of these lubricants on the performance of hydrostatic, hydrodynamic and hybrid journal bearings is discussed. An effort is made to develop the understanding to choose the suitable lubricant for journal bearings for different journal bearing configurations. Journal bearings operated with non-Newtonian lubricants have shown better performance compared to Newtonian lubricants. Ionic liquid lubricants have shown high potential in vacuum applications and extreme temperature environment such as in bearings of spacecraft moving mechanical assemblies.     

Practical determination and use of bearing dynamic coefficients

For four practically important journal bearing designs the stiffness and damping coefficients for ideal operating conditions were determined and their reliability ascertained by vibration measurements on high-speed rotors. The effects of static bearing misalignment, variable lubricant viscosity, inertial forces in the lubricant film and turbulent gap flow were investigated in detail. The significant effects on the static load capacity of the bearing and the stability behaviour of the rotor-bearing systems are illustrated and discussed.     

Elastohydrodynamically Lubricated Ball Bearings with Couple-Stress Fluids,Part II: Dynamic Analysis and Application

Stiffness and damping coefficients of isothermal elastohydrodynamically lubricated point-contact problems are evaluated numerically with couple-stress fluids. A set of equations under steady-state and dynamic conditions is derived from the modified Reynolds equation using a linearized perturbation method. This paper is the second part of the present study; the modified Reynolds equation derived from the Stokes micro-continuum theory is used in the previous article. Dynamic pressures are found after solving the set of perturbed equations using the previously obtained steady-state pressure from the modified Reynolds equation. The stiffness and damping coefficients of the film are determined using the dynamic pressures. Then the overall stiffness and damping matrices of the ball bearing are obtained from load distribution, coordinate transformation, and compatibility relations. The bearing coefficients are introduced into a rotor system to simulate the response. It has been observed that the influence of couple-stress fluids on the dynamics of a rotor supported on lubricated ball bearings is marginal; hence, Newtonian theory can be used instead for simplicity. However, with increasing content of polymer additives in lubricant, for an accurate analysis the effect of couple stresses in a fluid should not be neglected.     

Surface topography and tribology of cast iron in boundary lubrication

This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen.Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test.The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens.     

弹流润滑状态下机床主轴轴承刚度特性分析

圆柱滚子轴承的刚度特性会对机床动态性能产生较大影响.在双列圆柱滚子轴承力学分析的基础上,综合赫兹接触与润滑油膜对轴承刚度的影响,分析了不同工况以及润滑参数下的轴承刚度变化特性.分析结果表明,弹流润滑产生的润滑油膜会使轴承综合刚度下降;随着外载荷的增大,赫兹刚度与油膜刚度均有所提升,轴承综合刚度提高;提升轴承预紧量有利于...     

Evaluation of the finite journal bearing characteristics,using the exact analytical solution of the Reynolds equation

A very recent analysis of the exact analytical solution of the Reynolds equation for the lubrication of the plain journal bearing with finite length is used in the current work in order to evaluate the impedance forces of the fluid film and define them in closed form analytical expressions. The main journal bearing design parameters such as the eccentricity ratio, the location of the minimum fluid film thickness, the location of the maximum pressure and the stiffness and damping coefficients are evaluated under the recent analytical definition of the lubricant pressure distribution and presented in charts as functions of the Sommerfeld number, comparing them with the past and recent literature.     

Identification of Journal Bearing Force Coefficients under High Dynamic Loading Centered Static Operation

Lightly damped rotor bearing systems experience large amplitudes of vibration when traversing critical speeds. Bearing linearized force coefficients, strictly valid for minute motions about an equilibrium position, may not be reliable for design or troubleshooting in rotordynamics predictive analyses. Experiments assessing the dynamic forced response of a plain journal bearing undergoing large orbital motions due to single-frequency excitation forces were conducted in a test rig. The short test bearing of slenderness ratio L/D = 0.25 has a nominal radial clearance of 0.127 mm (5 mils). Tests were conducted at three rotor speeds (900, 1800, and 2700 rpm), three feed pressures (1, 3, and 6 psig), and three excitation frequencies (15, 30, and 45 Hz). Baseline bearing motions due to shaft runout are recorded and subtracted in the parameter identification procedure. The forces exerted on the bearing induce large orbital motions with peak amplitudes exceeding 50% of the nominal bearing clearance. Identified cross-coupled stiffness and direct damping coefficients fall within value bands predicted by the π and 2π models of the fluid film, even for the largest amplitudes of motion. The bearing whirl frequency ratio approaches the typical 50% value at the highest speed tested. Excitation frequency has a marked influence of the test direct dynamic stiffness coefficients with added mass coefficients at least twice as large as predicted values.     

圆锥滚子轴承阻尼的计算方法

在对圆锥滚子轴承进行受力分析的基础上,利用弹性流体动力润滑理论,得到承载最大滚子与内、外滚道间的最小油膜厚度计算式,并将其引入滚动轴承阻尼计算过程,建立了包含轴承滚子阻尼和油膜阻尼的轴承综合阻尼计算模型.     

挤压油膜阻尼器对滑动轴承-转子系统的影响

建立了转子-挤压油膜阻尼器-滑动轴承系统的动力学计算模型,分析了挤压油膜阻尼器对滑动轴承-转子系统的强迫振动的影响、挤压油膜阻尼器的刚度和阻尼搭配关系以及转子-挤压油膜阻尼器-滑动轴承系统的自由振动稳定性问题。研究结果表明,合理的外弹性支承可以使系统的振幅得到有效控制,而且也提高了系统的稳定性;如要减小系统的振幅可以通过一个低的支承刚度和一个合适的阻尼来实现。在小的支撑刚度的情况下,存在一个很宽的支承阻尼域,此域可以获得低幅值的不平衡响应。