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Technical Paper

Hydrodynamic Lubrication Evaluation of Thrust Bearings

2010-10-06
2010-36-0117
The pressure generation within the lubricant fluid present in the clearance between a thrust bearing and the collar attached to the shaft has a fundamental importance to avoid contact between solid parts with axial relative motion. Any existing contact can lead to friction, wear and, as a consequence, failure of elements on a rotating machine. Therefore, in order to design an effective bearing, it is important to know how the pressure is generated within the oil film and the magnitude of the load capacity transmitted from the collar to the bearing throughout the fluid. Thus, it is necessary to solve the Reynolds' Equation to obtain the distribution of pressure on the sections under Hydrodynamic Lubrication. Then several operational parameters can be obtained, such as, the total load capacity, lubricant fluid flow, position of the maximum pressure and so on.
Technical Paper

Influence of Different Geometries of Hydrodynamic Bearings in the Dynamic Response of a Rotating System

2010-10-06
2010-36-0123
Hydrodynamic bearings are widely used in rotating machines, being the element responsible for the interaction between the rotor and the supporting structure. Therefore, in order to describe the dynamic behavior of the rotating shafts, it is necessary to know the journal bearings dynamic characteristics. For this reason, this work aims to analyze the influence of three different geometries of journal bearings when operating in a small turbocharger for vehicular application, which implies in high rotation speed and load capacity. In this paper the analysis will be done through the frequency response of the proposed system and the equivalent damping and stiffness coefficients coming from the oil film present in the bearings. These dynamic coefficients are obtained with a spring-damper approach, in order to represent the inherent flexibility and damping of the oil film.
Technical Paper

Transient Multi-Level Elastohydrodynamic Point Contact Algorithm Experimental Validation

2010-10-06
2010-36-0088
One of the great challenges of engineering teams nowadays is to overcome long and costly project experimentation phases. One effective way of decreasing such project demands is to come up with a firsthand prototype with high success probability. In order to do so, the project team should rely on robust numerical models, which can represent most of the real-life product behaviors, for instance system dynamics. For rolling element bearings, such dynamic models have to consider the dynamic interactions between its components, i.e., rolling elements and raceways. The only vibration transmitting points on rolling element bearings are the lubricated contacts. Therefore, in order to represent the full bearing dynamic behavior on a numerical model, an efficient transient contact model, which depicts the actual contact behavior, is fundamental.
Technical Paper

Sensitivity Analysis for the Lubricant Film in Bearings Under THD Lubrication

2010-10-06
2010-36-0107
The study about the dynamic characteristics of a great number of mechanical parts has been promoted by the necessity of decreasing the vibrational effects in mechanical systems, as the reduction of superficial fatigue. In this way, the research around, even, a simple part like a hydrodynamic bearing is very important, especially in the automotive industry. In this case, the lubricant acts like a flexible liking element between the journal-bearing surfaces. The lubrication is essential for the engine, because it reduces the wear between the internal parts and prevents the metal contact. Due to the shear stresses present in the lubricant, the temperature rises and, consequently, it changes the lubricant properties. The viscosity is strongly dependent on the temperature and it is the parameter that characterizes the fluid flow and its dynamic behavior. Any temperature change induces a consequent modification in the lubricant behavior.
Technical Paper

A Numerical Approach to the Thermal Effect on the Equivalent Dynamic Coefficients of Radial Bearings

2011-10-04
2011-36-0327
To analyze a complete real machine, it can be convenient to divide the system into sub-systems, analyzing each sub-system individually, and then, assembling them together in the whole system. Many of these sub-systems can be found in an automotive engine, being the hydrodynamic bearing one of the most common mechanical components present in all kinds of power generation systems. Journal bearings are linking elements between parts with relative motion, and these linking elements must work to support radial loads with minimal friction and power loss. In 1925, Stodola realized that the bearing is not a rigid support, but it works like a set of springs and dashpots whose characteristics have an expressive effect on the dynamical behavior of the supported rotating shaft.
Technical Paper

Dynamic Analysis of Ball Bearings

2009-10-06
2009-36-0057
The development area of the bearing's industry constantly searches for a better efficiency and a lower film oil thickness in surfaces with high roughness under relative motion. In these cases, operational conditions like high loads and temperatures, as well as low safety margins for weight and size, considering the lubricant viscosity, should be taken into account as fundamental design parameters. In order to know better the elastohydrodinamic lubrication effect, firstly, it is necessary to understand deeply and accurately the applied loads on the ball element bearings. For this purpose, the accurate analysis and study of the performance of these machine components is carried out, using analytical methods and giving special focus on the velocities and accelerations involved, as well as different types of loads applied on the ball element and their distribution and consequences during the ball motion inside the bearing rings.
Technical Paper

Dynamic analysis prediction using Multiobjective Genetic Algorithm in rotor-bearing-coupling systems

2006-11-21
2006-01-2702
The study of rotative machines occupies an outstanding position in the context of machines and structures in view of significant amount of typical phenomena in the operation of those equipments. The existence of a rotative component leaning by bearings and transmitting power and torque creates a family of problems that are found in the most several machines. Therefore, in the study of the dynamic behavior of those systems, it is necessary to be determined the interaction among all the components that affect in a significant way the dynamic behavior of the system. It is proposed, this way, to determine the dynamic behavior of Rotor-Bearing-Coupling system using a Multiobjective Genetic Algorithm coupled with Surface Response Method. The Rotor-Bearing-Coupling system has the support structure or foundation practically rigid, in way to allow the analysis of the transverse or flexional vibrations of the system.
Technical Paper

Dynamic Analysis of Horizontal Rotating Machinery

1999-12-01
1999-01-3037
A software for the management and test of rotors was developedand that is capable to set up models and to generate solutions as frequency response of a rotor on line with the design process. That system can be applied in the study of problems of rotordynamics, taking into account the interaction between the rotor and the supporting structure where it is set up. The Rotortest software is capable of make the management of the input data of each element that composes a rotor: shafts, hydrodynamic and roller bearings, mechanical seals and foundations. Besides, starting from the input data, it presents illustrative outputs as diagrams and schemes, to accomplish the assembly of the mathematical models, and to find the frequency response solution of the complete system, presenting the results graphically.
Technical Paper

Roller Bearing Design Optimization Applying Hertz Contact Theory

1999-12-01
1999-01-3036
In a large part of the mechanical elements used in machines and equipment, the preponderant failure mode is not that of fatigue of the element itself, but certainly the fatigue of a small point where the contact occurs. The prime example of this are the roller bearings, that they fail not by “breaking”, but by surface fatigue at contact points or on the tracks where there is contact between the rings and the rolling bodies. The optimization of the contact geometry, the material and the lubrication used can allow us to have larger admissible loads or lower system's costs where there is great influence of the contact fatigue. To make this optimization easier, a software was developed for a Windows platform, including the whole contact theory, the life calculations under surface fatigue and the lubricating fluid film thickness. In an interactive way, the user can change the data entrances such as material or geometry until an ideal solution is found for its problem.
Technical Paper

Linear Model Updating Applied to Rotating Machines

2000-12-01
2000-01-3189
The present research proposes the use of linear model updating along with unrestricted optimization methods, in order to obtain a methodology, which allows the calibration of mathematical models of rotating systems. An experimental set up of a symmetric rotor, on a rigid foundation supported by two hydrodynamic cylindrical bearings and with a central disk of considerable mass, working as an unbalancing excitation force, was used for this purpose. Once the numeric and experimental values are obtained, error vectors are then defined, which serve as minimization parameters, through the variation of the numeric model parameters. The method presented satisfactory results, as it was able to calibrate the mathematical model and then from that, obtain reliable responses for the physical system studied.
Technical Paper

Hydrodynamic Lubrication Applied to Bearings with Oscillating Motion in Internal Combustion Engines

2005-11-22
2005-01-4004
This work has for purpose to develop a mathematical model for the hydrodynamic lubrication of bearings with oscillating motion. The motivation lies in the tribology of internal combustion engines, specifically the lubrication problem at the bearing existing between the connecting rod and the piston pin. This kind of bearing does not perform a complete rotation, thus characterizing a new class of oscillating motion bearings. For the analysis of lubrication, a viscous fluid flow with negligible inertia inside a narrow gap formed by two surfaces is considered. The surfaces can be considered flat and are inclined to each other. The inner surface is fixed whereas the outer one performs an oscillating motion which generates a combined Couette-Poiseuille flow inside the gap. Using the same assumptions as in classical Reynolds' lubrication equation, the simplified mass and momentum conservation equations are analytically solved to determine the velocity and pressure distributions.
Technical Paper

Development of Software Applying the Hertz Contact Theory to Commercial Rolling Bearings

2005-11-22
2005-01-4031
This paper presents a software developed to apply the Hertz contact formulation to bearings with rolling elements, estimating the occurrence of surface fatigue failure in this kind of parts. Considering the wide range of designs in the automotive industry using this kind of bearings, a dedicated software, using a simple language, becomes a useful tool to reduce the design time, predicting in a satisfactory manner the failure of the bearing. The software developed shows a high level of accuracy, when compared to data provided by rolling bearing manufacturers.
Technical Paper

Experimental Balancing Technique by Trial Masses

2005-11-22
2005-01-4006
This paper approaches the static and dynamic experimental balancing, applied to rotating machinery, considering the trial Weight Balancing. This method uses the Fast Fourier Transform (FFT), intending to determine the vibration signal (amplitude and phase) and to balance the system. This behavior occurs, because of the eccentricity of the center of gravity of th disk. One of the objectives is to allow a precision balancing of rotating systems, in order to apply fitting process to balanced rotating systems, where it is possible to include a known unbalance, which can be use to check some fitting methods in laboratory. The data acquisition is made by proximity sensors located at the disk or at the journal bearings. These data are processed by the software LabView, where the vibration signal is evaluated and the masses necessary to balance and their angular positions on the disk are determined.
Technical Paper

Finite Difference Model for Journal Bearings Applied in the Camshaft Support Elements

2003-11-18
2003-01-3557
The modern passenger cars structure has the valve actuation system with usual application in combustion engines. These mechanisms offer the possibility to change the rotational movement into an oscillating movement, so this simple construction causes an elementary higher dynamic stiffness, but gives costs advantages in opposite of lever controls. Regarding the valve actuation over tribology view increase the cam / tappet friction losses. The friction forces had decreased considerably through the use of roller cam, which in comparison to cams and flat systems is possible to save up to 70% [17]. The friction increased in the camshaft / tappet system leads to an elevate heat stream, that must be derived from the contact with the complete system and the lubricant oil. The objective of this paper is to introduce the oil film pressure distribution in different boundary conditions, the modeling first part.
Technical Paper

Dynamic analysis of flexible couplings in rotor-bearing-coupling systems

2003-11-18
2003-01-3552
The study of rotative machines occupies an outstanding position in the context of machines and structures in view of the significant amount of typical phenomena in the operation of those equipments. The existence of a rotative component leaning by bearings and transmitting power and torque creates a family of problems that are found in the most several machines. Therefore, in the study of the dynamic behavior of those systems, it is necessary to be determined the interaction among all the components that affect in a significant way the dynamic behavior of the system. It is proposed, this way, a simplified mathematical model, through the method of finite elements, of the Rotor-Bearing-Coupling system, considering the support structure or foundation practically rigid, in way to allow the analysis of the transverse or flexional vibrations of the system.
Technical Paper

Reliability Models Fitting and Comparative Study of Accumulated Fault Curves of Roller Bearings

2004-11-16
2004-01-3290
A comparative study involving failure data of life tests of two bearings types is presented. In a first stage, the statistical distribution more adapted for the modeling of the failure process is selected. Soon after, the parameters of the distribution and the confidence intervals are estimate. The approximationed sample size is supplied in function of an interval with a magnitude and specific confidence level. Tests of hypotheses are used for several significant levels, rejecting or accepting the hypothesis of equality among the adjusted curves of accumulated failure to each bearing.
Technical Paper

Methodology Development based on Robust Design and Sensitivity Parametric Analysis to Machine Components

2002-11-19
2002-01-3417
Technological systems are designed to carry out very specific functions. Because of that, their components should have measurements that can guarantee their operability within the range of precision. Furthermore, the current systems are inherent parts of design involving multi-disciplinary aspects. Their development and analysis expose the designer to a series of unknown parameters from several sources such as material properties, environmental and operational conditions. Therefore, the qualification and quantification of these inherent sources of design uncertainties become very important in several aspects in the context of design development and so, a system is reliable and robust if it allows a certain range of uncertainties before the first failure occurs. With this in mind, we propose here the development of a methodology that can identified the sources of uncertainties and parameters that largely influence the whole design.
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