Showing papers on "Fluid bearing published in 1997"

Foil Air/Gas Bearing Technology — An Overview

Abstract: This paper summarizes the chronological progress of foil air bearings for turbomachinery during the last 25 years. Descriptions of various machines which are in production are provided. The foil bearing air cycle machine on the 747 aircraft has demonstrated an MTBF (mean time between failure) in excess of 100,000 hours. Many advantages of foil air bearings are noted. Various designs of foil air bearings presently in use and their relative merits are described. Analytical methods, their limitations, and their relationships with test results are noted. Descriptions of various machines built and tested in process fluids being gases, other than air, and cryogenic liquids are described. Conclusions are drawn that various high speed turbomachines including high temperature applications can be designed and developed using foil air bearings which will increase efficiency and reduce cost of these machines.Copyright © 1997 by ASME

Hydrodynamic Lubrication: Bearings and Thrust Bearings

Abstract: Part 1 Tribology from antiquity to our times: the prehistoric period the Greek and Roman period Middle Ages and Renaissance toward the Industrial Revolution the Industrial Revolution tribology in the 20th century. Part 2 Lubricating oils: base oil additive agents viscosity of lubricants viscosimetry viscosity variation with temperature viscosity variation with pressure lubricants specifications non-Newtonian behaviour of lubricants viscosity of gases. Part 3 General equations in hydrodynamic lubrication with a Newtonian fluid: generalized equations of the mechanics of viscous thin films physical interpretation energy equation in the mechanics of viscous thin films particular forms of the generalized equation of the mechanics of viscous thin films boundary conditions for smooth surfaces solving algorithms calculus of various parameters of the contact study of elementary loading cases applications remark on the Reynolds equation. Part 4 Plane sliders and thrust bearing pads: plane sliders with fixed geometry pad of finite dimensions thrust bearings with fixed geometry tilting pad thrust bearing global thermal effects theory-experiment comparisons. Part 5 Static characteristics of journal bearings: laminar journal bearings general considerations infinitely long journal bearing the short bearing finite journal bearing global thermal effect application to the design of a journal bearing theory-experiment comparison. Part 6 Dynamic characteristics of journal bearings: Reynolds equation in dynamic regime linear modelling - dynamic coefficients infinitely-short bearing infinitely-long bearing finite width bearing stability of journal bearing operation linear analysis theory-experiment comparison. Part 7 Non circular journal bearings with fixed geometry and with tilting pads: multiple-lobe bearing tilting pad journal bearing. Part 8 Journal bearings subjected to dynamic loading: rotor bearings study of connecting-rod bearings. Part 9 Influence of shape defects and of surface deformations: basic equations and general considerations shape defects linked to machining flaws shape defects generated by deformations under dynamic loading shape defects generated by instantaneous deformation in transitory regime. Part 10 Thermal effects in hydrodynamic journal bearings: basic equations numerical methods results theory - experiment comparison. Part 11 Superlaminar flow regimes: inertia forces in bearings in laminar regime Taylor's vortex regime in smooth bearings transition in thrust bearings turbulent flow comparison between theoretical results and experiments application to a turbine bearing thermal effects in non laminar regime. (Part contents)

Three-dimensional direct simulation Monte Carlo method for slider air bearings

Abstract: The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision model. Two-dimensional pressure profiles are obtained across the film thickness direction. The results obtained from the two methods agree well with each other for Knudsen numbers as large as 35 which corresponds to a minimum spacing of 2 nm. The result for contact slider is also obtained by the DSMC simulation and presented in this paper.

Angled Injection—Hydrostatic Bearings Analysis and Comparison to Test Results

Abstract: Hydrostatic/hydrodynamic (hybrid journal bearings handling process liquids have limited dynamic stability characteristics and their application as support elements to high speed flexible rotating systems is severely restricted. Measurements on water hybrid bearings with angled orifice injection have demonstrated improved rotordynamic performance with virtual elimination of cross-coupled stiffness coefficients and null or negative whirl frequency ratios. A bulk-flow model for prediction of the static performance and force coefficients of hybrid bearings with angled orifice injection is advanced. The analysis reveals that the fluid momentum exchange at the orifice discharge produces a pressure rise in the hydrostatic recess which retards the shear flow induced by journal rotation, and thus, reduces cross-coupling forces. The predictions from the model are compared with experimental measurements for a 45 deg angled orifice injection, 5 recess, water hydrostatic bearing operating at 10.2, 17.4, and 24.6 krpm and with supply pressures of 4, 5.5 and 7 MPa. The correlations include recess pressures, flow rates, and rotordynamic force coefficients at the journal centered position. An application example for a liquid oxygen hybrid bearing also demonstrates the advantages of tangential orifice injection on the rotordynamic coefficients and stability indicator for forward whirl motions, and without performance degradation on direct stiffness and damping coefficients.

Optimum design of high-speed, short journal bearings by mathematical programming

Abstract: Generally, the selection of design variables in bearing design is done by a trial and error method using many design charts. However, it is not so easy to successfully select optimum design variables by such a method, and a considerable amount of working time and cost is needed to complete the optimum design of bearings. In this paper, an optimum design procedure for high-speed, short journal bearings operated in both laminar and turbulent flow regimes is developed based on mathematical programming. Under the short bearing assumption, simplified closed-form design formulas are obtained for the eccentricity ratio, maximum film pressure, fluid film temperature rise, supply lubricant quantity and whirl onset velocity. The radial clearance, slenderness ratio and average viscosity of lubricant, which minimize the weighted sum of fluid film temperature rise and supply lubricant quantity for various combinations of journal rotational speed and applied load, are determined by successive quadratic programming, whi...

CFD Based Design Techniques for Thermal Prediction in a Generic Two-Axial Groove Hydrodynamic Journal Bearing

Abstract: There are many physical parameters that influence the thermal condition of a hydrodynamic journal bearing. This remains the case even when appropriate nondimension-alization procedures have been applied. However, two dimensionless parameters are particularly useful, since they embody lubricant shearing, convection, conduction and viscosity temperature variation. In this paper, these parameters are varied to obtain design charts for the maximum bearing shell and journal temperatures. Computational fluid dynamics ( CFD ) techniques are used in this process. They are applied to a generic two-axial groove circular bearing having a section of journal that extends beyond the width of the shell. The results demonstrate the usefullness of the charts through example design studies.

Surface roughness effects in high-speed hydrodynamic journal bearings

Abstract: This paper describes an applicability of modified Reynolds equation considering the combined effects of turbulence and surface roughness, which was derived by Hashimoto and Wada (1989), to high-speed journal bearing analysis by comparing the theoretical results with experimental ones. In the numerical analysis of modified Reynolds equation, the nonlinear simultaneous equations for the turbulent correction coefficients are greatly simplified to save computation time with a satisfactory accuracy under the assumption that the shear flow is superior to the pressure flow in the lubricant films. The numerical results of Sommerfeld number and attitude angle are compared with the experimental results to confirm the applicability of the modified Reynolds equation in the case of two types of bearings with different relative roughness heights. Good agreement was obtained between theoretical and experimental results.

Spindle motor with fluid dynamic bearing having a journal bearing in combination with a conical bearing

Abstract: A hydrodynamic fluid bearing useful in a bearing cartridge which cartridge may be incorporated into a spindle motor or the like, where the bearing includes a shaft, a conical bearing supported on the shaft, and journal bearings located at least on one side and typically both above and below the conical bearing. A sleeve is mounted for rotation relative to the shaft and defines, in cooperation with the shaft, the gaps necessary for both the conical hydrodynamic bearing and the axial, journal bearings. At an end of the shaft, capillary seals are defined between the sleeve and the shaft so that fluid does not escape from the hydrodynamic bearing. The shaft itself includes a central hole, with bores communicating with both the conical bearing and the journal bearings to maintain appropriate pressure balances. In a further desirable feature, in some embodiments the diameter of one end of the shaft can be made greater than the diameter of the other end of the shaft. This allows for making the gaps between the shaft and the surrounding sleeve or journal to be greater where the diameter of the fixed shaft is greater, reducing the need for tight tolerances within at least part of the hydrodynamic bearing. Preferably the top end of the shaft (i.e. the end of the shaft adjacent the wider end of the conical bearing) has the journal bearing with greater diameter.

A Pseudospectral-Finite Difference Analysis of an Infinitely Wide Slider Bearing with Thermal and Inertial Effects

Abstract: A pseudospectral-finite difference solution of the thermal hydraulic flow through an infinitely wide convergent slider bearing configuration is presented. The model includes both thermal and inertial effects. The approach combines a collocation technique with orthogonal polynomial representations of velocities, temperatures and property variations through the thickness of the lubricant film with finite difference representations of derivatives in the streamwise direction. The technique is motivated by the need for general analyses of fluid film bearings which incorporate the before-mentioned effects. Results will be presented that separately demonstrate inertial and thermal effects in laminar flows. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

A Modal Analysis Method For Slider-Air Bearings In Hard Disk Drives

Abstract: A system identification method using modal analysis is proposed to analyze the dynamic characteristics of slider-air bearings in hard disk drives. A procedure for estimating the modal parameters, as well as the stiffness and damping matrices, is presented. The "Nutcracker" slider used as an example is analyzed, and the results are verified. The differences of the stiffness matrices calculated through different methods are found and explained. The results of the example show the assumptions of the method are satisfied in a wide amplitude range. Therefore the technique provides a powerful tool for head-medium interface analysis and experiment.

Spindle motor with multiple thrust plate fluid dynamic bearing

Abstract: A method to create an improved hydrodynamic bearing which is relatively insensitive to changes in load and rotational speed is provided, wherein the hydrodynamic bearing is useful in a spindle motor for a disc drive or the like which is stiffer than known standard spindle motors so that the stability of the system and specifically of the actuator arm and transducer relative to the rotating disc is optimized. The hydrodynamic bearing can also be used as a bearing cartridge or as the cartridge that may be incorporated into a spindle motor or the like, where the bearing includes a shaft and at least two independent bearings each comprising a thrust plate supported on the shaft and a counter plate incorporated in a sleeve which is capable of relative rotation around the shaft.

Analysis of Oil-Film Pressure Distribution in Porous Journal Bearings Under Hydrodynamic Lubrication Conditions Using an Improved Boundary Condition

Abstract: Pressure distributions in the oil film of a porous journal bearing are investigated theoretically and experimentally under hydrodynamic lubrication conditions. The circumferential boundary condition for the oil-film pressure is obtained by applying an integral momentum equation to the oil-film region in the bearing clearance. The oil-film pressure distributions are numerically solved using this momentum equation and taking into consideration the balance between oil fed into the clearance and that lost from it. The present analysis shows the occurrence of a negative film pressure before the trailing end of the oil-film region. The experimental results confirm the existence of this negative film pressure. Furthermore, the angular position of the trailing end of the oil-film region obtained in the present analysis moves toward the downstream region, yielding better agreement with the measured and calculated film regions than was found in out previous analysis based on the quasi-Reynolds boundary condition.

Hybrid combined hydrostatic and hydrodynamic bearing with enhanced stability and reduced flow rate

Abstract: A rotary hybrid bearing that utilizes both hydrostatic and hydrodynamic principles to support a rotatable shaft in which lubricating fluid is fed through orifices or other flow restriction devices to a plurality of recesses, and finally across lands and out of the bearing. The shaft is rotated in such a direction as to pump the fluid back through grooves from lands to recesses, thereby reducing the flow rate of lubricant through the bearing. The recesses are located at an angular position from lands such that a force is generated by hydrostatic action that substantially cancels the destabilizing force generated by hydrodynamic action, thereby greatly enhancing the stability of the bearing and enabling higher rotational speeds.

Self-acting fluid dynamic bearing support and method of assembling thereof

Abstract: A self-acting gas- dynamic or hydrodynamic bearing support for units rotating with a speed of about 10,000 rpm or higher consists of a stationary shaft (16) and a rotating bearing member (20) put on shaft with a radial gap of about 1 to 2 μm. A distinguishing feature of the bearing support of the invention consists in that bearing member (20) is made of a wear-resistant ceramic and the thrust members (12 and 14) and the shaft (16) are made of steel with wear-resistant coating. The difference in coefficients of linear thermal expansion of steel and ceramic is advantageously used in assembling for self-positioning of the thrust members strictly perpendicular to the shaft and strictly parallel to each other and to the end surfaces of the bearing member. The invention also concerns a method of assembling of the bearing support.

Design Of Fluid Bearing Spindle Motors With Controlled Unbalanced Magnetic Forces

Abstract: This paper discusses the beneficial and detrimental effects of unbalanced magnetic forces developed in a fluid bearing spindle motor used for hard disk drives The analysis made in this paper shows that unbalanced forces can be useful for magnetic preloading and stabilizing the fluid bearing system of a hard disk drive spindle motor

Single plate hydrodynamic bearing cartridge

Abstract: Hydrodynamic bearing having a shaft relatively rotatable with respect to a surrounding sleeve and having a thrust plate on one end thereof rotating in a recess of the sleeve. The shaft is preferably interrupted by a equi-pressure groove accessing a central reservoir in the shaft and having journal bearings defined by herringbone patterns above and below the groove to stabilize and provide stiffness to the cartridge. The stiffness of the cartridge is further enhanced by a thrust plate carried at one end of the shaft and rotating in a recess of the sleeve and being used to define thrust bearings on either surface thereof.

Stochastic FEM Analysis of Finite Hydrodynamic Bearings with Rough Surfaces

Abstract: A Reynolds-type equation for finite hydrodynamic bearings, (plane slider and cylindrical journal), with rough surfaces (longitudinal, transverse and isotropic roughnesses), has been solved using the stochastic finite element method considering film thickness to be a stationary, ergodic stochastic process with mean zero. Mean steady-state characteristics have been obtained and compared with those obtained by previous investigators. The effect of a spatially randomly varying component of roughness has been studied by giving different input standard deviations of film thickness and calculating output standard deviation of maximum pressure for different scales of fluctuation using the first-order second-moment method. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing

Abstract: This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

Design of a high speed and high precision 3 DOF linear direct drive

Abstract: Developments in microelectronics, micromechanics and microelectromechanical systems (e.g. micromotors, microsensors) require significant improvements in manufacturing tools for mass productions. Especially the assembling tools have to become faster and more precise. Many assembly devices use XY stages driven by DC servomotors with ball screws or parallel structures; others use linear drives with traditional ball bearings. Only a few devices use linear drives together with air bearings, but always together with an angular guide for X and Y direction. The novel approach presented in this paper is based on linear drives together with a planar air bearing. In contrast to other stages, it doesn't need any angular guide. This reduces the moved mass and leads to higher accelerations. It consists of an arrangement of four identical moving coils attached to a slide, which is suspended by a planar air bearing. This new configuration allows a workspace of 60/spl times/60 mm/sup 2/ and an acceleration exceeding 10 g with a resolution better than 100 nm. This paper gives an overview of the system and focuses on the design and characterization of the moving coils.

Effects of compliance of hydrodynamic thrust bearings in hard disk drives on disk vibration

Abstract: For cantilever-shaft design 2-disk hydrodynamic bearing spindle motors, the compliance of the thrust bearing has little effect on the radial operating vibration amplitudes which are the major contributor to the track misregistration in hard disk drives. At the low frequency range (<300 Hz), the compliance of the thrust bearing has great effect on the axial vibration amplitudes. However, the disk flexibility and/or disk clamping condition have more effects than the compliance of the thrust bearing on the axial operating vibration amplitudes at the frequency range of 300/spl sim/800 Hz. Magnetic preload may contribute equivalent vibration amplitudes but consumes much less power than the hydrodynamic preload does.

A study on engine bearing performance using EHL analysis and experimental analysis

Abstract: In order to efficiently improve engine bearing durability, we investigated the feasibility of predicting the durability of actual engine bearings by means of hydrodynamic lubrication computations. This paper describes a method of predicting the amount of actual engine bearing wear based on the results of a numerical analysis (EHL analysis) which takes into account the pressure dependence of lubricant viscosity and the elastic deformation of the bearing housing. The wear shape predicted by this method serves as input data for the EHL analysis calculations. The results show that variations in bearing performance caused by wear are substantial. Analyses that incorporate wear shape data make it possible to examine durability under conditions that more closely approximate actual conditions.

Hydrodynamic bearing having lubricant particle traps

Abstract: Particle traps (73, 74) in a hydrodynamic bearing unit (200) prevent particles, generated by repeated motor (250) start and stop operations or lubricant cavitation caused by shock loads or introduced by ambient sources, from circulating with the bearing lubricant, thereby preventing accelerated wear of bearing grooves. Each trap (73, 74) is defined by an annular bevel shaped channel defined along the inner radial wall of a shaft sleeve (94). Each trap is located in close proximity to hydrodynamic bearings (34, 36) so that existing particles and any wear particles generated by the bearings (34, 36) may be pumped into the traps (73, 74) by centrifugal force created by rotation of the bearing unit (200) and imparted to the lubricant. The centrifuge-like effect forces the particles against the back wall of each channel while the bevel shaped configuration of the channels prevents particles from migrating out of the channels after the motor (250) stops.

Dynamic pressure fluid bearing

Abstract: PROBLEM TO BE SOLVED: To improve the durability and suppress the run-out of a rotary shaft. SOLUTION: Herringbone grooves 111 are cut in the lower part of the outer peripheral surface of a rotary shaft 106. Plural notches 11 are formed on the outer periphery of a rotary thrust plate 10 in which the rotary shaft 106 is fitted and fixed. Lubricating fluid is sealed between the rotary shaft 106 and the rotary thrust plate 10, and bearing surfaces 113 or the inside surface of a shaft hole. When the rotary shaft 106 and the rotary thrust plate 10 are rotated, pressure is generated by the herringbone grooves 111 to support radial load. Further, pressure is generated by the notches 11 in the neighborhood of the outer periphery of the rotary thrust plate 10 to receive thrust load. Furthermore, since the lubricating fluid is efficiently circulated by the notches 11, the frictional loss is reduced to enhance the durability, and thus to suppress the rotational run-out. COPYRIGHT: (C)1998,JPO

Rotor dynamics of polygonal mirror scanner motor supported by air bearings in digital electrophotography

Abstract: A mathematical analysis has been performed on rotor dynamics of a high-speed polygonal mirror scanner motor in digital electrophotography. The rotor is assumed rigid and vertically supported by air bearings with an effective length that is not negligible compared to the rotor length. The model is a four-degree-of-freedom system that includes the gyroscopic effect and nonorthogonal force of the air bearing. The model also includes the effects of longitudinal bearing length and radially unstable magnetic stiffness of a driving motor and/or a magnetic bearing. A simulation program was coded to calculate complex eigenvalues, static and dynamic stability, critical speeds, unbalance responses, and external excitation responses. The results indicated that although the effects of bearing length and magnetic unstable stiffness were ignored in the past, these simplifications result in substantial error for the evaluation of rotor dynamics. The model is utilized to realize high-performance scanner motors.