E.H. Smith

Analysis of lubrication and friction for a complete piston-ring pack with an improved oil availability model: Part 1: Circumferentially uniform film

Abstract The study of the tribological performance of piston rings plays an important role in piston assembly design. In this study, a comprehensive analysis of piston-ring pack lubrication has been developed. The model employs a flow-continuity algorithm and considers relative ring locations in the piston-ring pack as well as oil accumulation in front of the ring in determining the oil availability. The computer model is able to predict the effect that bore distortion and ring conformability have on piston-ring performance. (This influence is discussed in Part 2 of the paper). In this part of the paper (Part 1), the theoretical formulation of the model is briefly described. The model is verified through comparison of the calculated ring-liner film thicknesses with those measured experimentally by Hamilton and Moore on a diesel engine. Then some results, obtained under situations where film thicknesses are circumferentially uniform, are presented to simulate a piston-ring pack in a modern petrol engine as an example to demonstrate the capabilities of the model and to show the effects of some important factors on the performance characteristics of the ring pack. The authors have found that the model developed is a robust one which can be used to analyse the tribological performance of ring packs effectively in both circular and distorted cylinder bores of internal combustion (IC) engines.

Modern measurement techniques in surface metrology: part II; optical instruments

Abstract This review examines the underlying principles behind the construction and operation of a number of optical instruments designed to measure surface topography. A wide range of such devices has been developed in recent years. They offer an operational range and resolution which are usually at least as good as that of stylus instruments and often better. In addition, they are non-contacting thus precluding the possibility of damage to the specimen during measurement.

Modern measurement techniques in surface metrology: part I; stylus instruments, electron microscopy and non-optical comparators

Abstract This paper reviews the operation and characteristics of a range of methods used to measure the surface topography of engineering components. Particular attention is paid to stylus instruments and electron microscopes as these are the devices most commonly used in industry and research.

Experimental methods for measuring the oil-film thickness between the piston-rings and cylinder-wall of internal combustion engines

Abstract Computer models of the lubrication of piston-rings in internal combustion engines normally present an estimate of the minimum oil-film thickness between ring and cylinder wall as a function of crank angle. As a consequence, experimental measurements of film thickness play a critical role in the verification of theoretical models of piston-ring lubrication. A review is presented of the wide range of techniques that have been used to measure this important variable. The strengths and weaknesses of particular techniques are identified and a number of ways in which the techniques could be developed further are proposed

The significance of surface topography in engineering

Abstract All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also disccused.

A Three-Dimensional Analysis of Piston Ring Lubrication Part 1: Modelling

The study of piston ring lubrication in internal combustion engines has remained a very active area in tribology. Theoretical analyses have been developed by many researchers to predict the performance characteristics of piston rings, but almost all previous models established were based upon the assumption that ring/cylinder geometry was axisymmetric. This may not be adequate for modern-day engine design since it is well known that cylinder bores are not perfectly circular. They suffer radial distortions which arise for various reasons. In the current work, a three-dimensional model has been developed to account for the effects of bore out-of-roundness. In order to do this, the three-dimensional Reynolds equation was solved cyclically using the finite difference method in fully flooded lubrication conditions. In this part of the paper, the theoretical model is presented and the effect of bore shape on piston ring performance is examined with three proposed types of bore (circular, elliptical and four-lobe). The results have shown that piston ring performance is significantly dependent on the bore shape or bore out-of-roundness.

Parameters for Characterizing the Surface Topography of Engineering Components

Profile measurements of the surface topography of engineering components are often used in attempts to assess the functional suitability of surfaces. This paper reviews the definitions and properties of a large number of parameters which are used to characterize measurements of this type.

A New Approach to the Calculation of Flash Temperatures in Dry, Sliding Contacts

The work done in overcoming frictional resistance between sliding surfaces is transformed into heat at the separate, very small and very highly loaded asperity contacts that make up the real area of contact. The temperatures at these initial asperity contacts (the ‘flash temperatures’) are usually much higher than the bulk temperatures and, although of very short duration, can cause potentially major local changes at the surfaces, such as softening, chemical transformations, and local melting. A new approach to calculating these flash temperatures is presented, which relies on the solution, by finite-element analysis, of the three-dimensional equation for transient heat flow in an hemispherical asperity. A Design of Experiments (DoE) exercise showed that the major influential factors on flash temperature were the thermal conductivity, the product of friction coefficient and hardness, the velocity of sliding, and the radius and degree of wear/flattening of the hemisphere. The DoE analysis also produced predictions for the flash temperature, which agreed extremely well with the FE calculations. Response surfaces of flash temperatures are presented, which facilitate the determination of flash temperatures without resorting to FE analysis.

A New Approach to the Solution of Elastohydrodynamic Lubrication of Crankshaft Bearings

A study of the elastohydrodynamic lubrication of crankshaft bearings in internal combustion engines is presented in this paper. A new method for simulating the performance of a finite width bearing and two-dimensional flexible structure is developed and introduced. The method is based on a finite element model of the structure and finite difference approximation of the Reynolds equation. In order to reduce the number of unknowns in the derived simultaneous equations, a modified form of the Reynolds equation is employed. The non-linear system of integro-differential equations is solved by a Newton—Raphson method. Analysis of a dynamically loaded Ruston—Hornsby bearing is performed and the method is found to be both rapid and robust. The influence of mesh and time step sizes upon the solution accuracy is studied.

Walsh theory and spectral analysis of engineering surfaces

Abstract The equivalents of Euler-Fourier analysis in the Walsh domain are defined and practical utilization of the resulting theory is discussed. Walsh spectral moments are redefined, together with other parallels between the Euler and Walsh domains including a relation between spectral moments and autocorrelation. The Nayak theory is extended to Walsh spectral moments, and the bandwidth parameters of both Euler and Walsh spectra are applied to non-gaussian non-random surfaces.