• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.859-865
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• 2001

This paper reports on the theoretical analysis of mixed lubrication for the piston ring. The analytical model is presented by using the average flow and asperity contact model. The cyclic variations of the nominal minimum oil film thickness are obtained by numerical iterative method. The total friction is calculated by using the hydrodynamic and asperity contact theory. The effect of the roughness height, pattern, and engine speed on the nominal minimum film thickness, friction force, ad frictional power losses are investigated. As the roughness height increases, the nominal oil film thickness and total friction force increase. Also, the effect of the surface roughness on the boundary friction is dominant at low engine speed and high asperity height. The longitudinal roughness pattern shows lower mean oil film pressure and thinner oil film thickness compared to the case of the isotropic and transverse roughness patterns.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.4
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• pp.66-74
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• 1990

Friction between piston-ring assembly and cylinder wall of a spark ignition engine was evaluated under various engine operating conditions utilizing a grasshopper linkage system. The friction force was estimated by the force balance relation at the small end of connecting rod. Three forces were chosen to be measured for the objective. They were gas pressure inside the cylinder, inertia force of the piston-ring assembly, and the force exerted by the connecting rod. These forces were measured by a piezo type pressure sensor, an accelerometer and strain gauges, respectively. Comparisons were made with the frictional force evaluated by the conventional method where the assumption of constant rotational speed of engines was adopted. Due to the variation of rotational speed of engines, the conventional method was found to lead to a large error in the evaluation of the frictional force.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.294-297
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• 2009

The frictional behaviors of Cermets/Cr-Ceramics and Cu-Al coatings of piston ring were investigated. Friction tests were carried out by pin-on-disk test and materials properties of coating layer were analyzed by nano indentation tester. Higher friction coefficient was obtained at harder coating with rougher surface. In case of hard-coating, the scratch depth, width and pile-up height had close relationship with indentation hardness. So the scratch width, depth and pile-up height increases with decreasing friction coefficient. But in case of soft-coating, the friction coefficients are strongly dependent on the morphological characteristics after nano scratching more than indentation hardness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1183-1188
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• 2001

This paper reports on the starved lubrication for the piston ring. In this analysis, two types of inlet boundary conditions, fully flooded and starved condition, are considered at the leading edge. The inlet position of effective lubrication and squeeze term are obtained by numerically iterative method. The effective lubricated region is reduced due to the starved condition at the inlet. The starved condition at the inlet significantly reduced the minimum oil film thickness(MOFT) at the midstroke of piston, and the friction force is also increased due to the thin oil film thickness. In the starved conditions, the power loss is significantly increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.89-102
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• 1993

In this experimental investigation, various plasma-sprayed zirconia contained coatings and a kind of alumina-zirconia coating were studied to gain a better understanding of their tribological behaviour under dry contact condition in a reciprocating motion at temperature of 200℃. Particular attention was made for finding appropriate coatings in cylinder liner/piston ring application with an emphasis on the antiwear property. In order to identify the wear mechanism, SEM(Scanning Electron Microscope), optical micrograph, and roughness tester were used. Alumina-zirconia and 8% yttria-zirconia were found to be most appropriate for the application to the cylinder liner/piston ring and, especially, alumina-zirconia exhibited highest wear-resistance and also showed good friction characteristics. Wear mechanisms of ceramic coatings identified.

• KSTLE International Journal
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• v.6 no.2
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• pp.58-64
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• 2005

An OEM driven working group started in January 2004 to elaborate the philosophies, concepts and test procedures for testing piston ring and cylinder liner materials as well as engine oils outside the engine using the $SRV^{(R)}$ test equipment. The different $SRV^{(R)}$ test philosophies in use by OEMs are compiled. The working group focuses on a.) ASTM sequence VIB (Fuel economy by aging oils), b.) friction and wear in the top dead region under mixed/boundary lubrication, c.) extreme pressure load under mixed/boundary lubrication and d.) hydrodynamic friction. Tribological test result and precision data are presented.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.5
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• pp.81-88
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• 1999

In order to understand the relationship between the phase angle of piston ring and oil consumption was measured by analyzing $CO_2$concentration in exhaust gas. The use of hydrogen fuel not gasoline makes this possible because all of the carbon component in exhaust gas can be assumed to be produced from oil. As a result of experiment, it is known that the oil consumption varies periodically and a specific location of ring end gap was found at each peak of oil consumption. Therefore, it was found that the oil consumption was not constant even at the same operating conditions and this is because the relative locations of top and 2'nd ring end gap change arbitrarily.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.114-120
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• 2000

Friction forces of piston rings for a typical SI engine were independently measured while excluding the effects of cylinder pressure, oil starvation and piston secondary motion using a floating liner system. Friction patterns, represented by the measured friction forces, were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(mid-stroke and dead centers). The modes were identified on the Stribeck diagram of the dimensionless bearing parameter and friction coefficients which were evaluated at the mid-stroke and at the dead centers. And the frictional modes were estimated to the full operation range. The compression rings behave in the mode where hydrodynamic lubrication is dominant at the mid-stroke and mixed lubrication is dominant at the dead centers under steady operating conditions. However, the oil control ring behave in the mode where mixed lubrication is dominant throughout the entire stroke.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.100-106
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• 1998

The wide open throttle performance and piston temperatures were measured by the change of fuel : gasoline and liquefied petroleum gas(LPG). Bench test method was developed and experimented to study the effect of temperature on the formation of carbon deposit. The bench test results were confirmed by measuring the piston temperature and observing the deposit production rate at an actual engine running condition. Results show that if the fuel of spark ignition engine is changed from gasoline to LPG, the output power decreases about 10% and the piston temperatures increase about 40~55$^{\circ}C$. In actual engine tests, because of this temperature increase, it was observed that the quantity of carbon deposit in the top ring groove increased in a big degree. Consuquently, it is known that the fing sticking may occur if the gasoline engine was rebuilt to LPG fuelled engine. Therefore, in order to preserve the durability of LPG fuelled engine, it is necessary to lower the piston temperature by hardware modificationor to reduce the carbon deposit by the improvement of engine oil.

• Tribology and Lubricants
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• v.1 no.1
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• pp.46-58
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• 1985

The basic mechanism of lubrication between the piston ring and the cylinder wall is developed theoretically under the assumption of a reciprocating and dynamically loaded slider-bearing pair of parabolic form and smooth plane. A numerical computation for the prediction in cyclic variations of film thickness, net lubricant flow and frictional behaviour is attempted, and the influenec on the performance characteristics due to the ring height, ring face radius of curvature and the degree of offset, is also examined. The computational procedures develeped for a single ring system are extended and applied further to the complex problem of a ring pack system. It is well known that the ring pressure which is the total load on a ring, can be obtained from either an experimental measurement or a gas flow analysis. In this work, the latter of a gas low analysis method was used to calculate the pressures. It is remarked that the work done was focused on the role of flow continuity and lubricant starvation within the ring pack lubrication.