S. Boedo

Surface Roughness and Structural Inertia in a Mode-Based Mass-Conserving Elastohydrodynamic Lubrication Model

Detailed formulations are presented for a mass-conserving, mode-based computational model which includes effects of structural inertia and surface roughness. Performance evaluation of a big end connecting rod bearing is shown to require only a few mode shapes, from which it is found that body forces arising from structural motion strongly influence film thickness history at operating engine speeds. Surface roughness effects on nominal film thickness are found to he small, even in assumed regions of partial lubrication.

Optimal shape design of steadily loaded journal bearings using genetic algorithms

This puller describes an implementation of a genetic algorithm scheme suitable to the optimal shape design of finite-width, iso-viscous, fluid film journal bearings under steady load and steady journal rotation. Assuming perfect journal cylindricity, the optimization objective is to determine the circumferential variation of sleeve geometry that maximizes bearing load capacity, subject to specified minimum film thickness. Particular emphasis is placed on the selection of the number of design variables, chromosomes per generation, crossover and mutation probabilities, and the number of generations that promote convergence to one or more optimal designs. Optimal film thickness specifications obtained using this genetic algorithm are found to be generally superior to random search methods and comparable with previously published results based on traditional optimization strategies. For finite-width bearings, optimal bearing geometry is found to offer a small improvement in load capacity and a substantial improvement in oil flow over purely cylindrical designs. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

Classical Bearing Misalignment and Edge Loading: A Numerical Study of Limiting Cases

This paper investigates transient and steady state behavior of grooveless, axially (angularly) misaligned bearings using finite element formulations of the complete two-dimensional Reynolds equation. Performance trends of misaligned bearings are compared with their aligned counterparts within the traditional framework of classical lubrication theory. Elastic/plastic deformations, thermal effects, surface roughness, and pressure-viscosity variations are not taken into account. It is found that axially misaligned bearings have infinite load and moment capacity as the endplane minimum film thickness approaches zero under transient journal squeeze motion and under steady load and speed conditions. These results differ markedly from finite capacity trends reported previously in both numerical and experimental studies. Predictions of squeeze rate and load capacity based on axially aligned bearings are also shown to be sufficient to approximate squeeze rate and load capacity for axially misaligned bearings for an appreciable range of midplane eccentricity ratios.

Cavitation in Normal Separation of Square and Circular Plates

The negative squeeze lubrication problem is investigated by means of a mass-conserving finite element cavitation algorithm (described elsewhere) within the context of a dimensionless study of lubricant film behavior between rigid, parallel separating surfaces. Appropriate mesh geometries which capture spatial and temporal mixture density history and satisfy JFO conditions on the cavitation interface are determined. Present simulation results agree qualitatively with previous experiments, supporting the validity of the algorithm and its utility in the bearing design process

A mass conserving modal analysis for elastohydrodynamic lubrication

A computational model which reflects both bearing elasticity and mass conservation is presented for transient elastohydrodynamic analysis. Bearing deformation is represented by a combination of elastic mode shapes coupled with a finite element film model which conserves lubricant mass everywhere. The formulation is applied to a big-end connecting-rod bearing which is lubricated through a crankpin feed-hole.

Finite element analysis of elastic engine bearing lubrication: theory

This paper reviews the theory of finite element mode-based elastohydrodynamic lubrication analysis (as applied in a companion paper to the bearing and structural design of a dynamically loaded automotive connecting rod).

A Mode-Based Elastohydrodynamic Lubrication Model With Elastic Journal and Sleeve

A mass-conserving, mode-based elastohydrodynamic lubrication model, which includes combined effects of journal and sleeve elasticity, is described. Application to a sample cylindrical bearing system (geometrically similar to automotive main and connecting rod bearings) shows that relative displacement of an elastic journal and sleeve can be represented by a set of mode shapes which are qualitatively similar to those obtained with a rigid journal, while the corresponding mode eigenvalues are found to be dependent on journal elasticity, Performance evaluation under steady and pure squeeze loading shows that a sufficiently compliant hollow journal can reduce film pressure and improve film thickness when compared with its rigid counterpart.

Modal and Nodal EHD Analysis for Gas Journal Bearings

This paper presents a novel finite element elastohydrodynamic lubrication analysis appropriate for gas journal bearings under dynamic conditions. The method employs gas pressure as a state variable, and structural sleeve deformation is represented by a linear combination of preselected mode shapes obtained from a related eigenvalue problem. The method takes into account temporal variation of journal position and velocity, and second-order slip flow boundary effects are included at no additional computational cost. The formulation is subsequently applied to a particular example (flexible large-aspect ratio, high-speed, MEMS-scale journal microbearing), where it is shown that a judicious choice of structural sleeve elasticity can significantly improve bearing performance (as measured by pressure distribution and load capacity) when compared with results obtained using rigid bearing surfaces.

Practical tribological issues in big-end bearings

Abstract: This chapter focuses upon practical design guidelines for big-end connecting rod journal bearings which allow for rapid prediction of three key tribological performance measures: cyclic minimum film thickness, cyclic average oil flow and cyclic average power loss. Design information, provided in both graphical and equation form, apply specifically to a grooveless big-end bearing pressure-lubricated by a single crank-pin feed hole. In addition, this chapter reviews the current state of tribological research aimed at improving design capabilities for big-end bearings and suggests related topics for further study.

Global Stability Analysis of Cylindrical and Dual Offset Rotor Bearing Systems

Extensive numerical simulation studies with a short bearing film model show that a balanced dual offset rotor bearing subjected to a fixed external load can improve bearing performance for load and speed conditions known to produce undesirable half-speed whirl in conventional zero-offset cylindrical systems. For specific values of dimensionless load, offset ratio, and load orientation, parametric changes in speed show that the dual offset bearing can undergo a variety of bifurcations which produce coexisting period 1–4 subharmonic, quasi-periodic, and chaotic attractors, all of which may be driven by lower-order dynamic processes. For a specific set of initial conditions, the transition to chaos via period doubling in the dual offset bearing actually produces lubricant films which are significantly thicker than those found in the corresponding cylindrical system.