Showing papers on "Fluid bearing published in 2012"

Direct Observation of Cavitation Phenomenon and Hydrodynamic Lubrication Analysis of Textured Surfaces

Abstract: When a textured ring rotates relatively against the other texture-free ring in a parallel thrust bearing, cavitation of liquid lubricant may occur in the divergent zones of the dimples or grooves on the textured surface due to local pressure drops. The Reynolds and Jakobsson–Floberg–Olsson (JFO) models are two widely used cavitation models in hydrodynamic lubrication theory, where the former lacks mass conservation while the latter enforces it. In order to investigate the applicability of the two models to the hydrodynamic lubrication analysis of parallel thrust bearings with surface textures, comparison between experiment and simulation results has been carried out on parallel thrust bearings in terms of cavitation zone morphology in a groove, friction coefficient, and bearing clearance. The results have shown that the observed cavitation morphology in steady state is more similar to the prediction from the JFO model than that from the Reynolds model.

The Effect of Texture Shape on the Load-Carrying Capacity of Gas-Lubricated Parallel Slider Bearings

Abstract: Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between gas-lubricated parallel sliding surfaces. The shape, geometry, and density of the patterned microtexture features (“dimples”) play a key role in the tribological performance of the textured slider bearings. The objective of this paper is to compare the load-carrying capacity of commonly used dimple shapes for gas-lubricated textured parallel slider bearings. Six different texture shapes are considered, including spherical, ellipsoidal, circular, elliptical, triangular, and chevron-shaped dimples. The pressure distribution and load-carrying capacity generated by different texture shapes are simulated using the compressible Reynolds equation over a domain containing a column of ten dimples. The texture geometry and density are optimized in terms of maximum load-carrying capacity for each individual dimple shape, as a function of operating parameters such as relative velocity and spacing between the two sliding surfaces. The maximum load-carrying capacity of each individual texture shape—with optimized geometry and density—is then compared relative to each other. It is concluded that the ellipsoidal shape results in the highest load-carrying capacity, and the optimal geometry and density are found to be almost independent of the operating conditions.

Numerical investigation on the influence of surface texture on the performance of hydrodynamic journal bearing

Abstract: Many researchers have adopted various techniques for improving the performance characteristics of journal bearing. Apart from other parameters, incorporation of different forms of surface texture (sinusoidal, dimple, spherical etc.) on bearing or shaft also helps to increase the load carrying capacity and reduce the friction coefficient etc. in the journal bearing. Present study investigates the influence of different forms of surface texture on finite journal bearing which has been considered in the form of negative texture (micro cavities) at different locations of bearing surface. The Governing equations are solved numerically through finite difference approach for analysis of texture effects on bearing characteristics. It has been observed that the presence of micro cavities at different locations of bearing surface help in enhancing the bearing performance. It has also been found that the negative half wave texture enhances the bearing performance more in comparison to full wave texture on bearing surface.

Performance of inherently compensated flat pad aerostatic bearings subject to dynamic perturbation forces

Abstract: The importance of air bearing design is growing in engineering. As the trend to precision and ultra precision manufacture gains pace and the drive to higher quality and more reliable products continues, the advantages which can be gained from applying aerostatic bearings to machine tools, instrumentation and test rigs is becoming more apparent. The inlet restrictor design is significant for air bearings because it affects the static and dynamic performance of the air bearing. For instance pocketed orifice bearings give higher load capacity as compared to inherently compensated orifice type bearings, however inherently compensated orifices, also known as laminar flow restrictors are known to give highly stable air bearing systems (less prone to pneumatic hammer) as compared to pocketed orifice air bearing systems. However, they are not commonly used because of the difficulties encountered in manufacturing and assembly of the orifice designs. This paper aims to analyse the static and dynamic characteristics of inherently compensated orifice based flat pad air bearing system. Based on Reynolds equation and mass conservation equation for incompressible flow, the steady state characteristics are studied while the dynamic state characteristics are performed in a similar manner however, using the above equations for compressible flow. Steady state experiments were also performed for a single orifice air bearing and the results are compared to that obtained from theoretical studies. A technique to ease the assembly of orifices with the air bearing plate has also been discussed so as to make the manufacturing of the inherently compensated bearings more commercially viable. (c) 2012 Elsevier Inc. All rights reserved.

Steady-State Hydrodynamic Lubrication Modeled With the Payvar-Salant Mass Conservation Model

Abstract: Steady-state smooth surface hydrodynamic lubrications of a pocketed pad bearing, an angularly grooved thrust bearing, and a plain journal bearing are simulated with the mass-conservation model proposed by Payvar and Salant. Three different finite difference schemes, i.e., the harmonic mean scheme, arithmetic mean scheme, and middle point scheme, of the interfacial diffusion coefficients for the Poiseuille terms are investigated by using a uniform and nonuniform set of meshes. The research suggests that for the problems with continuous film thickness and pressure distributions, the results obtained with these numerical schemes generally well agree with those found in the literatures. However, if the film thickness is discontinuous while the pressure is continuous, there may be an obvious deviation. Compared with both the analytical solution and other two schemes, the harmonic mean scheme may overestimate or underestimate the pressure. In order to overcome this problem artificial nodes should be inserted along the wall of the bearings where discontinuous film thickness appears. Moreover, the computation efficiency of the three solvers, i.e., the direct solver, the line-by-line the tridiagonal matrix algorithm (TDMA) solver, and the global successive over-relaxation (SOR) solver, are investigated. The results indicate that the direct solver has the best computational efficiency for a small-scale lubrication problem (around 40 thousand nodes). TDMA solver is more robust and requires the least storage, but the SOR solver may work faster than TDMA solver for thrust bearing lubrication problems. Numerical simulations of a group of grooved thrust bearings were conducted for the cases of different outer and inner radii, groove depth and width, velocity, viscosity, and reference film thickness. A curve fitting formula has been obtained from the numerical results to express the correlation of load, maximum pressure, and friction of an angularly grooved thrust bearing in lubrication.

Temporal and Convective Inertia Effects in Plain Journal Bearings With Eccentricity, Velocity and Acceleration

Abstract: This paper extends the theory originally developed by Tichy (Tichy and Bou-Said, 1991, Hydrodynamic Lubrication and Bearing Behavior With Impulsive Loads,” STLE Tribol. Trans. 34 , pp. 505–512) for impulsive loads to high reduced Reynolds number lubrication. The incompressible continuity equation and Navier-Stokes equations, including inertia terms, are simplified using an averaged velocity approach to obtain an extended form of short bearing Reynolds equation which applies to both laminar and turbulent flows. A full kinematic analysis of the short journal bearing is developed. Pressure profiles and linearized stiffness, damping and mass coefficients are calculated for different operating conditions. A time transient solution is developed. The change in the rotor displacements when subjected to unbalance forces is explored. Several comparisons between conventional Reynolds equation solutions and the extended Reynolds number form with temporal inertia effects are presented and discussed. In the specific cases considered in this paper, the primary conclusion is that the turbulence effects are significantly more important than inertia effects.

Experimental Investigations of Active Air Bearings

Abstract: Along with traditional oil lubrication, increasing demand for high-speed applications has renewed attention to gas bearings technology Traditional aerostatic and aerodynamic gas lubrication has been widely used in a variety of applications, ranging from high-speed spindles to micro and meso-scale turbo-machinery The present paper deals with experimental rotordynamic testing of a flexible rotor supported by hybrid aerostatic-aerodynamic gas journal bearing equipped with an electronic radial air injection system From a rotordynamic point of view there are two phenomena that limit the widespread of traditional gas lubrication: 1) Low damping makes operation across critical speed dangerous, as even low level of unbalance can generate large vibration responses This is especially problematic for gas bearing applications, which often operate in the supercritical region Moreover, 2) An upper bound to supercritical operation is determined by the appearance of subsynchronous whirl instability Due to the sudden increase in amplitude with respect to speed, this most often corresponds to the maximal attainable rotational speed of the system Postponing the onset speed of instability poses therefore one of the greatest challenges in a high-speed gas bearing design A great deal of research is devoted to attack such issues, where most propose passive designs such as compliant foil bearings, tilting pad and flexure pivot gas bearings These solutions proved to be effective in improving static and dynamic properties of the bearings, however issues related to the manufacturing and accuracy of predictions has so far limited their applications Another drawback is that passive bearings offer a low degree of flexibility, meaning that an accurate optimization is necessary for each application The developed prototype active bearing offers several promising performance enhancements Synchronous vibrations can be effectively addressed ensuring safe operation across the critical speeds; whirling instability is suppressed; intervening on the software, rather than the hardware can modify the response of the system Implementing active lubrication adds however a considerable number of parameters and variables The performance of a good control system lays most importantly on a good choice of control gains, which in general are different depending on the goal of the controller Optimum tuning of the control loop is addressed experimentally, showing dependency on the supply pressure and, less prominently, the rotational velocityCopyright © 2012 by ASME

Preliminary study of pressure profile in hydrodynamic lubrication journal bearing

Abstract: In hydrodynamic lubrication, the pressure condition of the fluid is critical to ensure good performance of the lubricated machine elements such as journal bearings. In the present study, an experimental work was conducted to determine the pressure distribution around the circumference of a journal bearing and fluid frictional force of the bearing caused by shearing actions. A journal diameter of 100mm with a 1/2 length-to-diameter ratio was used. Pressure results for 600 RPM speed at different radial loads were obtained. The experimental results were compared to predicted values from established Raimondi and Boyd charts. It was observed that the location of the maximum pressure for the given operating conditions is close to the predicted value.

A Study on the Performance of a Magnetic-Fluid-Based Hydrodynamic Short Journal Bearing

Abstract: Efforts have been made to study and analyze the performance of a hydrodynamic short journal bearing under the presence of a magnetic fluid lubricant. With the usual assumptions of hydrodynamic lubrication, the associated Reynolds equation for the fluid pressure is solved with appropriate boundary conditions. In turn, this is then used to calculate the load-carrying capacity which results in the calculation of friction. The computed results presented in graphical form suggest that the bearing system registers an improved performance owing to the magnetic fluid as compared to the conventional lubricant. It is clearly observed that the load-carrying capacity increases nominally while the coefficient of friction decreases significantly. Besides, it is seen that the bearing can support a load even when there is no flow of lubricant. In addition, this type of study may offer an additional degree of freedom from design point of view in terms of the forms of the magnitude of the magnetic fluid.

Water Lubricated Bearings

Abstract: The increasing ecological awareness and stringent requirements for environmental protection have led to the development of water lubricated bearings in many applications where oil was used as the lubricant. The chapter details the theoretical analysis to determine both the static and dynamic characteristics, including the stability (using both the linearised perturbation method and the nonlinear transient analysis) of multiple axial groove water lubricated bearings. Experimental measurements and computational fluid dynamics (CFD) simulations by the Tribology research group at Queensland University of Technology, Australia and Manipal Institute of Technology, India, have highlighted a significant gap in the understanding of the flow phenomena and pressure conditions within the lubricating fluid.

Centrifugal inertia effects in high-speed hydrostatic air thrust bearings

Abstract: A modified Reynolds equation for compressible flow is used to model the dynamics of pressurised air bearings in a simplified axisymmetric geometry. The formulation incorporates the effect of centrifugal inertia for high-speed operation. A steady-state analysis is presented with a fixed rotor–stator clearance. The load-carrying capacity of the bearing is assessed for both inward and outward pressurisation and the air-flow characteristics are seen to depend on the level and direction of pressurisation. A critical shaft speed is identified that maintains no-net flow by balancing inertia and pressurisation effects. The nonlinear air–rotor–stator dynamics are investigated by modelling the axial stator position using a spring–mass–damper system coupled to the air-film dynamics. Solutions are presented to illustrate the effect of various frequencies and amplitudes of forcing for a range of rotation speeds. The time-averaged axial force and mass flow of air are used as characteristic measures of bearing performance, and further numerical results are presented as part of a parameter space analysis. Using the method of arc-length continuation key measures of the numerical solutions are tracked for changing values of the physical parameters. The minimum rotor–stator clearance is used to evaluate the limit of stable periodic operation without resonant stator dynamics and incorporating high operating speeds.

Radial oil injection applied to main engine bearings: evaluation of injection control rules

Abstract: The performance of main bearings in a combustion engine affects key functions such as durability, noise and vibration. Thus, with the aim of reducing friction losses and vibrations between the crankshaft and the bearings, the work reported here evaluates different strategies for applying controllable radial oil injection to main crankshaft journal bearings. In an actively lubricated bearing, conventional hydrodynamic lubrication is combined with controllable hydrostatic lubrication, where the oil injection pressures can be modified depending on the operational conditions. In this study, the dynamic behaviour of the main bearing of a medium-size engine is theoretically analysed when the engine operates with controllable radial oil injection and four different injection control rules. The theoretical investigation is based on a single-cylinder combustion engine model. The performance of the actively lubricated bearing is compared with the performance of the conventional lubricated bearing, giving some insig...

A magnetically suspended miniature spindle and its application for tool orbit control

Abstract: This paper reports the design, analysis, and experimental results of a miniature spindle using magnetic bearings for very high-speed micromachining. To ensure stable high-speed rotation, the shaft was designed such that the first flexible natural frequency was higher than 9 kHz. Four-pole radial magnetic bearings with a permanent magnet bias were located in front of and behind the spindle, and axial air bearings at the spindle covers were used to hold the shaft in the axial direction. Additionally, to ensure small tools were clamped effectively, a clamping mechanism with a shape memory alloy was added at the nose of the shaft. The designed miniature spindle has an outer diameter of 62 mm and a total length of 94 mm, including the housing. The spindle was controlled with a digital signal processor (DSP)-based control system and rotated at up to 200,000 rpm using a built-in air turbine. The stability and ability of the spindle to control the tool orbit to generate micro-features was evaluated.

Fluid-dynamic bearing system for rotary mounting of spindle motor that is utilized for rotary driving of magnetic storage disk of hard disk drive, has stopper element arranged at end of shaft and partially formed as integral part of shaft

Abstract: The system has radial bearings (22a, 22b) formed along an axially extending portion of a bearing gap (20). A fluid-dynamic thrust bearing (26) is arranged along a radially extending portion of the bearing gap. Sealing gaps (32, 34) outwardly seal an end of the bearing gap. A stopper element (18) is arranged at an end of a shaft (12) and joined to one of the sealing gaps. The stopper element is partially formed as an integral part of the shaft. A rotor component (14) has an annular groove for receiving a hollow cylindrical portion of a component of the stopper element. Independent claims are also included for the following: (1) a spindle motor (2) a hard disk drive.

Controllable Lubrication for Main Engine Bearings Using Mechanical and Piezoelectric Actuators

Abstract: Although mechatronic systems are nowadays implemented in a large number of systems in vehicles, active lubrication systems are still incipient in industrial applications. This study is an attempt to extend the active lubrication concept to combustion engines and gives a theoretical contribution to this field. One refers to active lubrication when conventional hydrodynamic lubrication is combined with dynamically modified hydrostatic lubrication. In this study, two different schemes for the oil injection system in actively lubricated main engine bearings are presented. The use of active lubrication in journal bearings helps to enhance the hydrodynamic fluid film by increasing the fluid film thickness and consequently reducing viscous friction losses and vibrations. In this study, the hydrostatic lubrication is modified by injecting oil at controllable pressures through orifices circumferentially located around the bearing surface. The main equations that govern the dynamics of the injection for a piezo-actuated oil injector and a mechanical-actuated oil injector are presented. It is shown how the dynamics of the oil injection system is coupled to the dynamics of the bearing fluid film through equations. The global system is numerically solved using as a case study a single-cylinder combustion engine, where the conventional lubrication of the main bearing is modified by applying radial oil injection using piezo-actuated injection. The performance of such a hybrid bearing is compared to an equivalent conventional lubricated bearing in terms of the maximum fluid film pressures, minimum fluid film thicknesses, and reduction of viscous friction losses.

On the elastohydrodynamic lubrication performance of crankshaft bearing based on the effect of whole engine block deformation

Abstract: Purpose – The elastic deformation of crankshaft bearing surface will be caused when acted by oil film pressure, which will affect the lubrication performance of crankshaft bearing. The model of the single bearing housing was usually used in the calculation of the elastic deformation of bearing surface. In actual internal combustion engine, the main bearing housing is combined together with engine block; deformation of the main bearing surface will be affected by deformation of the engine block. The purpose of this paper is to investigate the effect of deformation of the whole engine block on the hydrodynamic lubrication performance of main bearings.Design/methodology/approach – The loads of main bearings were calculated by the whole crankshaft beam‐element finite element method. The lubrication of crankshaft bearings was analyzed by dynamic method. The elastic deformations of bearing surface under oil film pressure were calculated by compliance matrix method. The compliance matrix was established by finit...

Method for controlling a wind turbine and wind turbine

Abstract: Method for controlling a wind turbine (1) with a plain/sliding bearing (2) and bearing lubrication means (7), comprising the steps of: operating the bearing (2) as a hydrodynamic bearing (HD) in normal operation; and operating the bearing (2) as a hydrostatic bearing (HS) when the friction of the bearing (2) reaches a threshold.

Sliding bearing with micro holes on inner wall thereof

Abstract: The invention discloses a sliding bearing with micro holes on the inner wall thereof, which is prepared through the steps of welding a bearing bush and a bearing lining the surface of which is uniformly provided with micro through holes; and then rolling, wherein the bearing lining is arranged in the bearing bush; the total area of the micro through holes on the surface of the bearing lining accounts for 10 to 20 percent of the surface area of the inner wall of the bearing lining; and the ratio of depth to diameter of the micro through holes on the surface of the bearing lining is 0.05 to 0.2. The sliding bearing disclosed by the invention has the advantages that the micro through holes on the bearing lining form micro grooves on the inner wall of the sliding bearing, and the micro grooves are used for storing the lubricating oil, and when sufficient lubricating oil is stored in the micro grooves, a dynamic pressure oil film is formed between the bearing bush of the sliding bearing and an axle journal rubbing pair, thereby reducing the rubbing wear; the elastic deformation of the bearing lining is enlarged, the rubbing pair is in an elastic hydrodynamic lubrication state, and the bearing is good in abrasion resistance and obvious in lubrication effect; and the bearing is simple in processing and easy to manufacture.

Hydrodynamic Lubrication Effects of Multiple Circular Bump Pattern for a Thrust Sliding Bearing of a Scroll Compressor

Abstract: The optimum texturing pattern for a thrust sliding bearing of a scroll compressor was investigated. As the basis of lubrication analysis for multiple circular bumps pattern, fundamental hydrodynamic lubrication effects of the axisymmetric circular geometry expressed by the power law formula were analyzed using elastohydrodynamic lubrication (EHL) analysis. The optimum geometry to improve the load carrying capacity and reduce frictional force for the model geometry was discussed. Frictional properties of the proposed thrust bearings were experimentally evaluated and compared with numerically predicted properties. In order to clarify the robustness against accidental high load, seizure limits of a circular bump pattern were experimentally evaluated. These results show that the initial frictional properties are able to control by the crowning profile, the proposed pattern has a sufficiently low friction coefficient and quite a high seizure limits.

Lateral Vibration Analysis of Flexible Shafts Supported on Elliptical Journal Bearings

Abstract: This paper presents the development of a finite element procedure for the dynamic analysis of flexible rotors supported on fluid-film elliptical journal bearings operating under several operating conditions. The rotating shaft is modeled by using Timoshenko beam theory and the coupled rotating components, such as disks and impellers, are modeled by using lumped masses. The modeling of the elliptical journal bearings is performed by solving the lubrication equations generated from the application of a linearized perturbation method on the classical Reynolds equation. The bearing carrying-load capacity and the linearized dynamic force coefficients can be predicted for elliptical bearings with different preloads and journal eccentricities. The rotor transient whirling unbalance response is estimated by performing the time integration of the finite element equations using Newmark method. Experimental whirling unbalance response of a rotating shaft supported at two identical journal bearings is used to validate the finite element procedure. A comparative analysis of the dynamic response of flexible rotors supported on both cylindrical and elliptical journal bearings is performed to show that some elliptical bearings are capable of attenuating the rotor unbalance response more efficiently than cylindrical bearings are.

Hydrodynamic bearing assembly and spindle motor including the same

Abstract: There are provided a hydrodynamic bearing assembly and a spindle motor including the same. The hydrodynamic bearing assembly includes: a sleeve including a shaft hole to have a shaft rotatably installed therein; and a cover member covering the shaft hole at a lower portion of the shaft hole in an axial direction, wherein an inner surface of the sleeve is provided with depression parts depressed in an outer diameter direction between upper and lower portions of the sleeve and portions in which radial bearings are formed, such that the portions in which the radial bearings are formed are provided with bearing closure adhesion parts allowing the portions in which the radial bearings are formed to be closer to the shaft than portions other than the portions in which the radial bearings are formed.

Robust Optimum Design of Thrust Hydrodynamic Bearings for Hard Disk Drives

Abstract: This paper describes the robust optimum design which combines the geometrical optimization method proposed by Hashimoto and statistical method. Recently, 2.5″ hard disk drives (HDDs) are widely used for mobile devices such as laptops, video cameras and car navigation systems. In mobile applications, high durability towards external vibrations and shocks are essentials to the bearings of HDD spindle motor. In addition, the bearing characteristics are influenced by manufacturing error because of small size of the bearings of HDD. In this paper, the geometrical optimization is carried out to maximize the bearing stiffness using sequential quadratic programming to improve vibration characteristics. Additionally, the bearing stiffness is analyzed considering dimensional tolerance of the bearing using statistical method. The dimensional tolerance is assumed to distribute according to the Gaussian distribution, and then the bearing stiffness is estimated by combining the expectation and standard deviation. As a result, in the robust optimum design, new groove geometry of bearing can be obtained in which the bearing stiffness is four times higher than the stiffness of conventional spiral groove bearing. Moreover, the bearing has lower variability compared with the result of optimum design neglecting dimensional tolerance.

A miniature pump with a fluid dynamic bearing

Abstract: This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic bearing. Tests verify that the miniature pump is stable and quiet for rotational speeds larger than 4000 min-1. The three-dimensional turbulent flow in the entire pump flow passage and the laminar flow in the fluid dynamic bearing were then simulated numerically. The average pump performance was well predicted by the simulations. Both the tests and the simulations show that there is no obvious Reynolds effect for the miniature pump within the tested range of rotational speeds. The numerical results also show that the bearing capacity of the fluid dynamic bearing increases with the pump rotor rotational speed and the eccentricity ratio of the journal to the bushing. This pump is very compact, so it is a promising device for surgical use.