• Tribology and Lubricants
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• v.15 no.3
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• pp.248-256
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• 1999

Many tribological components in automobile engine undergo high load and sliding speed with thin film thickness. The lubrication characteristics of the components are regarded as ether hydrodynamic lubrication or boundary lubrication, whereas in a working cycle they actually have both characteristics. Many modem engine lubricants have various additives for better performance which make boundary film formation even under hydrodynamic lubrication regime. Conventional Reynolds equation with the viewpoints of continuum mechanics concerns only bulk viscosity of lubricant, which means that its simulation does not give insights on boundary lubrication characteristics. However, many additives of modern engine lubricant provide mixed modes of boundary lubrication characteristics and hydrodynamic lubrication. Especially, high molecular weight polymeric viscosity index improvers form boundary film on the solid surface and cause non-Newtonian fluid effect of shear thinning. This study has performed the investigation about journal bearing system with the mixed concepts of boundary lubrication and hydrodynamic lubrication which happen concurrently in many engine components under the condition of viscosity index improver added.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.82-90
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• 1998

Machines that normally operate under fluid film lubricated condition also experience surface damage. This is largely due to the failure of the lubricant film which leads to boundary lubrication. Thus, it is important to have a good understanding of boundary lubrication behavior. In this paper the major tribological parameters that influence the boundary lubrication properties are evaluated. It is shown that disk roughness, hardness and normal load affect the friction and wear of metals in boundary lubrication. Also, the mechanism of surface damage is attributed to abrasion and wear particle interaction.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.256-262
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• 1998

Many lubricated systems experience boundary, lubrication condition during operation. However, the friction and wear characteristics of boundary lubrication are not clearly understood. In this work the factors which affect the friction and wear between boundary lubricated metallic surfaces are investigated. Experiments were performed on atuminium, copper, and SM45C with bearing ball using a pin-on disk type tester. The experimental conditions were determined by Taguchi experimental method. From the experimental results, the major factors that influence the friction and wear characteristics of boundary lubrication could be identified.

• Tribology and Lubricants
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• v.15 no.2
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• pp.171-177
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• 1999

Many lubricated systems experience boundary lubrication condition during operation. However, the friction and wear characteristics of boundary lubrication are not clearly understood. In this work the factors which affect the friction and wear between boundary lubricated metallic surfaces are investigated. Experiments were performed using a pin-on-disk type tester with pure aluminum, pure copper, and SM45C steel as the disk material and steel, stainless steel and bearing ball as the ball. The experimental conditions were determined according to the Taguchi experimental method. From the experimental results, the major factors that influence the friction and wear characteristics of boundary lubrication could be identified.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.76-83
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• 2000

Boundary lubrication condition arises in most lubricated systems, especially during motion reversals and start up phase of operation. In this work electric contact resistance variations with respect to sliding conditions under lubrication is investigated The motivation was to improve the understanding of the contact condition in the boundary lubrication regime. It is shown that electrical contact resistance is sensitive to sliding speed and surface condition of the specimens. Also, phenomena such as run-in during the initial phase of sliding and lubricant pile up near the sliding pin could be observed. The results of this work will aid in better understanding of the metal to metal contact condition in lubricated systems.

• Tribology and Lubricants
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• v.16 no.5
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• pp.381-388
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• 2000

Boundary lubrication condition arises in most lubricated systems, especially during motion reversals and start up phase of operation. In this work electric contact resistance variations with respect to sliding conditions under lubrication is investigated. The motivation was to improve the understanding of the contact condition in the boundary lubrication regime. It is shown that electrical contact resistance is sensitive to sliding speed and surface condition of the specimens. Also, phenomena such as run-in during the initial phase of sliding and lubricant pile up near the sliding pin could be observed. The results of this work will aid in better understanding of the metal to metal contact condition in lubricated systems.

• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.928-934
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• 2000

This paper describes a method developed for the simulation of ring pack lubrication characteristic in an internal combustion engine. In general, the quantity of oil supply for piston ring lubrication may be insufficient in filling the entire volume formed at the interference between the piston ring and the cylinder liner. Thus the oil starvation condition should be considered in analyzing piston ring lubrication. In order to reasonably estimate the amount of oil left over on the cylinder liner, the flow rate at the posterior portion of the interface should be calculated with an adequate boundary condition that confirms flow continuity condition. In this analysis, oil starvation and open-end boundary conditions are considered at the inlet and outlet of the piston rings. The lubrication characteristic of each piston ring is obtained by an iterative method with sequential steps. It is revealed that piston rings are operated under oil starvation in most operating cycles and the result under these conditions are quite different from that with the fully-flooded assumption.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2179-2186
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• 2005

The lubrication modes of line contact between the vane and the camring in an oil hydraulic vane pump have been investigated. First, variations of the radial acting force of a vane were calculated from previously measured results of the dynamic internal pressure in four chambers surrounding a vane. Next, distinctions of the lubrication modes were made using Hooke's chart, which represents an improvement over Johnson's chart. Finally, the influence of boundary conditions in the lubrication region on fluid film lubrication was examined by calculating film pressure distributions. The results show that the lubrication modes of the vane tip are a rigid-variable viscosity region. This region discharges pressure higher than 7 MPa, and exerts a great influence on oil film pressure in the large arc section due to the Piezo-viscous effect.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.133-134
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• 2002

The use of low friction wear resistant coatings for machine components is rapidly increasing. These components may operate in any lubrication regime, and less frequently even unlubricated. When run unlubricated it is easy to see the beneficial effect of a low friction coating. However, it has frequently been shown that the coating may also be very beneficial under boundary and mixed lubrication conditions. The present digest briefly presents a few interesting aspects of the use of low friction coatings in lubricated contact illustrated by selected experimental results.

• Tribology and Lubricants
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• v.35 no.6
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• pp.356-361
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• 2019

The friction and wear between machine components directly influence the energy loss and failure in various machines. Therefore, there is always a demand for finding methods to reduce friction and wear. Of the possible methods, lubrication is a widely used method for reducing friction and wear. In the case of lubrication, it is important to analyze the tribological behavior in the boundary lubrication because most of friction and wear occurs in the boundary lubrication regime. Cast iron has been regarded as a good material for industrial applications due to the excellent mechanical properties and high productivity. Especially, nodular cast iron is a material that shows better mechanical properties and wear-resistance compared with cast iron due to inclusion of spheroidal graphite. In this work, we investigated the tribological characteristics of nodular cast iron with respect to different counter parts in boundary lubrication regime. Sliding tests were conducted with SUJ2, ZrO₂, Si₃N₄ balls as counter parts using a pin-on-disk type tribotester. The results showed different friction and wear behaviors with different counter parts. The case of ZrO₂ showed the lowest wear rate in specimen and no significant ball wear. In case of SUJ2, it showed similar wear rate with ZrO₂ case in specimen and the highest friction coefficient. The case of Si₃N₄ showed the lowest friction coefficient, 33% lower than the case of SUJ2. It showed 16.9 times larger wear rate in specimen and 43% larger wear rate in ball compared to that of the SUJ2 case.