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Technical Paper

A Proposed New Film Thickness-Roughness Ratio, Λz, in Rolling Bearings: Notes on an Engineer’s Experience with Surface Texture Parameters

The film thickness-roughness ratio Λ has been used since the mid-1960s as a simplified criterion for the lubrication conditions in rolling bearings. However, due to an assumed Gaussian distribution of the roughness height amplitudes of the functional surfaces of rolling bearings and other unsubstantiated assumptions regarding the mechanisms of contact interaction, concerns have arisen about the representability of Λ in terms of lubrication. In this study, a more objective Λ-type ratio that does not depend on the law of roughness height distribution and the peculiarities of contact mechanics is introduced and defined as Λz. The relevant range of the new Λ ratio is lower than that of its conventional counterpart, and it overlaps with contemporary theoretical and experimental results. The study exhibits unique profilometric data of the functional surfaces of the roller bearings, produced by the major bearing manufacturers.
Technical Paper

Friction Temperature of the Piston Rings with Consideration of the Cylinder Wall Thickness

Analysis of the friction temperature of a piston ring in a reciprocating oil-less compressor was presented in the work of V. Dunaevsky and I. Kudish published in 1998 by SAE, Paper 982828. In that work a theoretical analysis of the transient friction temperature at the interface was conducted under a simplifying assumption that the ring slides over the plane which serves as the boundary of a half-space with infinite thickness. In the current paper the simplifying assumption that the cylinder wall has infinite thickness is replaced by the assumption that the wall thickness is finite, i.e. by a finite thickness layer bounded by two parallel planes. A numerical heat transfer model was used to show effects of wall thickness and heat transfer coefficient on transient and steady temperature distribution across the wall.
Technical Paper

Development of Conformability Model of Piston Rings with Consideration of Their Three-Dimensional Torsional Distortions and Fourier Series Representation of Cylinder Bore Geometry

Conformability of a piston ring is a measure of the ring ability to conform to the ever-present cylinder bore deviations from a perfect circle by elastic deformation of the ring. Conformability is usually defined as the limit of bore distortion at which the clearance between the piston ring and bore can be kept at zero by elastic deformation of the piston ring. Retention of good conformability is important for ring/bore sealing and reduction of oil passing and blow-by. The most known technique for conformability analysis was developed almost sixty years ago and considers only two-dimensional deformation of the ring in its plane by the force of piston ring elasticity. It is known, however, that the piston rings with asymmetrical cross-section, a prevalent type of the modern compression piston rings, undergo a complicated three-dimensional installation displacements (twist) which affect many functions of the rings.
Technical Paper

The Effect of Contact Pressure on Piston Ring Twist

The paper is a step in an ongoing work targeted at the development of an engineering methodology to estimate sealing properties of a piston ring, and for the development of ring design guidelines. This work is necessary because the sealing properties of a ring significantly affect oil passing and blow by in the reciprocating air compressors and engines. It is known that the sealing function of a piston ring depends on the ring's ability to elastically deform in its plane under its own tension by conforming to the deviations of the cylinder bore. At the same time, if it has an asymmetrical cross section, the ring fitted in the cylinder bore is subjected to the additional, three-dimensional, distortions called twist. This type of cross section is usually imparted to the ring to further improve its sealing functions by interlocking (because of twist) between the piston groove and the cylinder wall.
Technical Paper

Analysis of Three-Dimensional Distortions of the Piston Rings with Arbitrary Cross-Section

With consideration of the importance (for oil passing and blow-by) of the issue of three-dimensional deformation of piston rings in a cylinder due to either installation stress, or operational gas, friction, and thermal loads the subject of piston ring distortions still generates continuing interest. The current paper demonstrates application of a mathematical model developed in the former works of the authors for analysis of the distortions of arbitrary cross-section rings loaded by tangential force. Applications of the model to the several typical cross-sections are given for illustration. The work is a necessary step for the development of a comprehensive three-dimensional theory of piston ring installation and operational distortions.