Homer Rahnejat

Fundamentals of tribology

Description of Surfaces Contact Mechanics Dry Contact Friction Lubricant Rheology Principles of Hydrodynamics Thermohydrodynamics Elastohydrodynamics Thrust Bearings Journal Bearings Externally Pressurized Bearings Hydrostatic Bearings Aerostatic Bearings Ball and Rolling Element Bearings Fatigue Wear Adhesion Transient Elastohydrodynamics Valve Trains Pistons Biotribology of Natural Joints Joint Replacements Nanotribology Van Der Waals Forces Electrostatics Meniscus Action Solvation Hydration MEMS Hard Disk Drives.

The Vibrations of Radial Ball Bearings

This paper presents a theoretical analysis of the vibration response of a rotating rigid shaft supported by two radial deep-groove lubricated ball bearings. The bearings and their oil films are approximated to a set of non-linear elastic springs and dampers rotating relative to the shaft when it is subjected to a rotating unbalance or inner race surface waviness. Under gravity load, the shafts initial vibration is damped down to a limit cycle operating at a quasi-simple harmonic frequency of small amplitude. Rotating unbalance and surface features introduce further significant frequencies which influence the output response.

A five degrees of freedom analysis of vibrations in precision spindles

Abstract This paper outlines a five degrees of freedom model of a rigid shaft supported by a pair of angular contact ball bearings. The model simulates an existing precision grinding machine tool spindle. It enables the study of various loading arrangements to be carried out.

Multi-body dynamics: historical evolution and application

Abstract The historical developments in the discipline of engineering dynamics are briefly reviewed, with attention paid to the formulation and solution of the dynamic behaviour of multi-body systems. It is shown that the dynamic characteristics of practical multi-body systems are dependent upon the interactions of many physical phenomena that can induce, restrain or constrain motion of parts. The long process of understanding and formulating the physics of multi-body motions, in some cases with pioneering contributions centuries old, together with continual refinements in numerical techniques and enhanced computing power has resulted in the solution of quite complex and practical engineering problems. Linking the historical developments to the fundamental physical phenomena and their interactions, the paper presents solutions to two complex multi-body dynamic problems. The practical implications of the approach in design of these systems are highlighted.

Multi-body dynamics in full-vehicle handling analysis under transient manoeuvre

This paper presents a 94 degrees of freedom non-linear multi-body dynamics model of a vehicle comprising front and rear suspensions, steering system, road wheels, tyres and vehicle inertia. The model incorporates all sources of compliance: stiffness and damping, all with non-linear characteristics. The model is used for the purpose of vehicle handling analysis. A simulation run, pertaining to a double lane change is undertaken in-line with the ISO 3888 standard.

The “QFD/FMEA interface”

The intention of this paper is to propose a methodology for interactions between the two quality tools of quality function deployment (QFD) and failure mode effects analysis (FMEA), and place an emphasis on their common features. The paper will also emphasise the value that both tools have when used throughout the product development cycle. An example of the method described will be highlighted within Ford Motor Company that will demonstrate the quality and resource benefits achievable when these two tools are used in conjunction with one another. This example will illustrate how, through the use of crossfunctional and multidisciplined teamwork, QFD and FMEA can be linked into systems engineering and a quality operating system with far‐reaching benefits.

Transient elastohydrodynamic lubrication of rough new or worn piston compression ring conjunction with an out-of-round cylinder bore

Real cylinder bores are out-of-round and axially asymmetrical. The top compression ring, nominally an incomplete circle, is subjected to ring tension and cyclic combustion force in order to conform to the bore surface. The bounding surfaces are rough and their conjunction is subject to a transient tribological state. Therefore, the ring–bore conjunction is only partially conforming for most of the engine cycle. The conjunction may be viewed as a problem of scale, depending on the analysis carried out at a certain bore order (out-of-roundness). Therefore, the contact may be viewed as a multi-lobed rough conjunction, where the regime of lubrication may vary from hydrodynamics to mix with dominant asperity friction at piston reversals. Measured bores and ring profiles are used to predict conjunctional power loss and percentage fuel energy consumed. Furthermore, lubricant’s flow through the ring is predicted throughout the engine cycle. These measures are key industrial design drivers for fuel efficiency and reduction of emissions. The results show that the effect of bore out-of-roundness can be even more significant than the surface topography.

Tribology of the ring–bore conjunction subject to a mixed regime of lubrication

Abstract This paper provides a detailed analysis of the compression ring—bore/liner conjunction. The analysis includes ring—bore conformability and global in-plane deformation of ring fitted in situ. The analysis for fitted ring in an out-of-round bore shows very good agreement with precise measurements, using a coordinate measuring machine. The analysis also includes the lubricated conjunction under a transient regime of lubrication, taking into account combined elastohydrodynamics and asperity interactions. The transient nature of the tribological conjunction has been demonstrated, particularly the prevalent mixed/boundary regime of lubrication at the top and bottom dead centres. The analysis is applied to a high performance motorbike engine subjected to very high impact loads and engine speeds of the order of 13 000 r/min. Furthermore, the predictions of the model show good conformance to the measurements of friction reported by other research workers.

In-Cylinder Friction Reduction Using a Surface Finish Optimization Technique

Abstract The paper describes the importance of reducing frictional losses in internal combustion (IC) engines, thereby improving engine efficiency. One of the main sources contributing significantly to engine friction is the interaction between the piston compression and oil rings and the cylinder bore/liner. Improving the tribological performance in these conjunctions has the greatest potential for performance improvement in the IC engine. Traditionally, the approaches used to tackle this problem have relied heavily on empirical engineering judgement. These have resulted in many inconclusive studies, involving a large number of alternatives, including the introduction of cylinder liners with surface modification work and/or with special coatings. This paper highlights a fundamental investigation of surface modification and coating and its impact on frictional performance. The study combines numerical and experimental approaches. Very good agreement is found between the conclusions of numerical predictions and those of engine test bed work.

Vibration monitoring of high speed spindles using spectral analysis techniques

Abstract A significant source of noise and vibration in precision high speed machine tool spindles is bearing induced vibration, which is caused by inherent geometrical characteristics, as well as out-of-balance assembly and interactions between rolling mating members with surface irregularities. The multitude of causes often makes a diagnostic approach quite arduous, particularly due to insufficient information obtained from frequency domain analysis alone. Furthermore, the averaging nature of Fourier analysis and its poor frequency resolution make the task in complex vibration spectra more difficult. The paper presents a new approach in use of auto-correlation analysis with good frequency resolution, combined with windowing capability to isolate significant causes for subsequent remedial actions. The method is applied to a routing spindle with special reference to primary induced bearing frequencies.