N. Biboulet

Piston ring load carrying capacity: Influence of cross-hatching parameters

This work studies the influence of the cross-hatching groove parameters on a model piston ring load carrying capacity. Over 2000 transient calculations were performed varying all parameters (groove depth, groove width, groove angle, and the distance between cross-overs) to obtain the average load carrying capacity. It is shown that the load carrying capacity results fall close to a single master curve when using the Δ parameter that is a combination of the groove parameters. Finally, the influence of the starvation level on load carrying capacity was analyzed.

Hydrodynamic force and moment in pure rolling lubricated contacts. Part 2: Point contacts:

Abstract Hydrodynamic rolling force and moments in point contact have been studied in detail using isoviscousrigid (IVR) and elastohydrodynamic (EHL) models. Using fully flooded assumptions, curve-fitted relationships are given for calculating the IVR and EHL hydrodynamic rolling forces. Both are proportional (or almost proportional in the IVR case) to 2a, the Hertzian contact length being perpendicular to the rolling direction, and are also functions of the dimensionless speed parameter. A single curve-fitted relationship has been derived to cover the full range of operating conditions with a smooth transition from IVR to EHL regime of lubrication. The results obtained are slightly higher than those previously published (the ratio being of the order of 1.5 for usual operating conditions). Point contact and line contact (with a contact length £ being equal to the point contact length 2a) hydrodynamic rolling forces have also been compared. The point contact forces are about 26 per cent larger than those obtained using line contact relationship (published in part 1) because of a larger domain of integration in the lateral direction. By limiting the width of the integration domain to £ (roller length or ball diameter), the effect of 2a/£ on the hydrodynamic rolling force has been studied, leading to the derivation of a truncation factor C. As the load increases, 2a increases and the truncation factor decreases until reaching a limit when ellipse truncation starts because 2a/£ is equal to or larger than one. Using the truncation factor and limiting the 2a/£ ratio to one, it was found that point contact and line contact hydrodynamic forces are the same within a few per cent. A single point contact relationship can therefore be suggested, covering the IVR to EHL operating conditions with a smooth transition between these lubrication regimes, and also a smooth transition from point contact to line contact as the load increases and contact ellipse truncation occurs. Finally, calculations of power losses due to the Poiseuille flow in the rolling direction x and in the perpendicular direction z show that the power loss in the z direction is usually very small for wide elliptical contacts and that most of the power is dissipated in the inlet and outlet, with a 26 per cent contribution of the integration domain defined out the range −a < z < a. This result is in line with the truncation factor defined previously.

Contact stress and rolling contact fatigue of indented contacts: Part II, rolling element bearing life calculation and experimental data of indent geometries

This article presents a brief overview of how the stress risk integrals of indented contacts are combined to calculate a rolling element bearing life and some experimental data concerning measured indentation. The possibility of predicting surface indentation and bearing life from normalized contamination standards is discussed.

Determination of fundamental parameters for the cross-hatched cylinder liner micro-geometry

This paper is part of a project aiming at optimizing the cylinder-liner/piston-ring contact performance: oil consumption, friction and wear. The surface micro-geometry has a major influence on these characteristics. Classical cylinder-liners display cross-hatched patterns. Grooves modify contact pressure distributions and act as lubricant reservoirs and pipes redistributing oil. The load-carrying capacity is greatly influenced by the number of grooves and their geometry. An automatic groove geometry identification (depth, width, angle) is performed on cylinder-liner surface measurements. The surfaces were measured at two instants: new and after a fired engine test. The micro-geometry evolution is discussed.

Contact stress and rolling contact fatigue of indented contacts: Part I, numerical analysis

Based on previous studies concerning pressure perturbations due to indents in dry and elastohydrodynamic lubrication contacts, this article presents the indented contact stress distribution and risk integral calculations. Different stress criteria are discussed and an equation predicting the risk integral is proposed.

Development of Piston and Piston Ring Lubrication Analysis

The reduction of CO2 emissions has become an imperative duty in order to cope with environmental compliance. For car manufacturers, CO2 emission has been set by regulation and many consumers prefer a fuel efficient car because of the increasing fuel price. In such a situation, reducing engine friction is an effective way of improving fuel efficiency. Among engine parts, the piston counts for a large percentage of the friction losses. In this study, we established a calculation model for estimating piston and piston ring friction. This paper shows how the accuracy of the calculation model was improved by validating against measurements.

Piston Ring Load Carrying Capacity: Influence of Cross-Hatching Parameters

Energy and environment are of major concern in internal combustion engine component design. The piston ring-cylinder liner (PRCL) contact plays an essential part in design and is highlighted in this study. In fact, the rings ensure the sealing property, reducing the environmental impact by avoiding lubricant contamination (blow-by) and lubricant consumption. Unfortunately, when sealing, the rings generate between 11 to 24% of the friction losses in an internal combustion engine [1], thus reducing the energy efficiency of the engine.The cylinder liner surface features a special micro-geometry, a classical one is the cross-hatching pattern, obtained by honing. This texturing acts as a micro-bearing, oil reservoir and debris trap. Understanding the influence of texture parameters as groove depth and width or angle, will allow tribological improvements of the PRCL contact.The 2D transient Reynolds equation has to be solved for this kind of surface. The statistical method using the Patir and Cheng [2] flow factors is widely used. This approach lumps the different components of the surface (grooves and plateaux) and does not consider the roughness directionality. Methods decoupling both components, like the homogenization method [3] are also used. Another alternative is to use a deterministic model on measured surfaces, but this is a “hugely” expensive approach. Multigrid methods [4] are used to drastically reduce the calculational cost.The aim of the current study is to facilitate the understanding of measured surface calculations. Hence, analytical surfaces are used. They allow a flexible handling of the cross-hatching parameters. The plateaux are perfectly smooth and the grooves are sinusoidally shaped. The top ring is modelled using a parabolic profile. Periodic boundary conditions are used in the orthoradial direction and zero pressure conditions (Dirichlet) in the axial direction.To investigate the effect of different parameters, various imposed film thicknesses are applied and the mean load carrying capacity (LCC) over time is calculated. When representing the LCC corresponding to each parameter compared to the smooth LCC, as a function of the logarithm of the minimum film thickness, the curves are quite linear for small values of the film thickness and then for larger values they converge to 1.Copyright