• Tribology and Lubricants
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• 제29권6호
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• pp.353-359
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• 2013

The rollers and/or races in cylindrical and tapered roller bearings should be profiled to relieve high edge stress concentrations caused by their finite lengths and misalignment. In this study, a numerical analysis was performed to investigate the elastohydrodynamic lubrication (EHL) of a Lundberg profile-type cylindrical roller. A finite difference method with fully nonuniform grids and the Newton-Raphson method were used to present detailed EHL pressure distributions and film shapes, as well as the variations in the minimum and central film thicknesses with the profile modification coefficient. In the Lundberg profile, the maximum pressure and minimum film thickness always occurred near the edges. Proper modification of the Lundberg profile considerably increased the minimum film thickness.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.686-689
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• 2003

Many technologies are applied to the measurement of elastohydrodynamic lubrication (EHL) film thickness. In particular, optical in-situ interferometric method has many advantages in making the actual contact behaviors realized with the experimental apparatus. Careful selection of incident lights greatly enhances the fringe resolution up to nanometer scale by using image processing technology. In this work, it is found that dichromatic incident light can provide much finer resolution of EHL film thickness than monochromatic incident light, because it has much more variables of color components to be discriminated among the wavelengths of colors according the variations of EHL film thickness. Some simulated interferometric images are shown how the film thickness is resolutionized in nanometer scale

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제28회 추계학술대회
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• pp.212-218
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• 1998

This paper presents a study of the elastohydrodynamic lubrication of elliptical contacts where lubricant entrainment coincides with the major axis of the Hertzian contact ellipse. A finite difference method and the Newton-Raphson method are applied to analyze the problem. Film contours and pressure distributions are compared with the results for lubricant entrainment coincides with the minor axis. Variations of the minimum and central film thicknesses with the radius ratio are also examined. Therefore, the present numerical scheme can be used generally in the analysis of the EHL of elliptical contacts where the lubricant entraining vector did not coincide with either of the principal axis of the conjunction.

• Tribology and Lubricants
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• 제23권2호
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• pp.49-55
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• 2007

A numerical analysis of elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning has been carried out. A finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. The velocity vectors resulting from combined spinning and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. The spin motion have large effect on variations of the minimum film thickness with load parameter which are small in pure rolling/sliding cases. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• Tribology and Lubricants
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• 제29권4호
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• pp.228-234
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• 2013

This paper presents analysis of elastohydrodynamic lubrication (EHL) of ball bearings, in which surface roughness is considered. A lot of time is required to obtain a solution in the case of EHL analysis where surface roughness is considered, because the analysis requires a variety of analytic nodes. To save time, we use the full approximation scheme (FAS) among multilevel methods. We analyze the results of EHL and contact analyses in terms of pressure. We also compare the results for smooth and rough surfaces with respect to film thickness. We confirm that the film pressure decreases as compared to contact pressure because of the presence of lubricants between the ball and the raceway. Furthermore, in the case when surface roughness is considered, the film pressure increases because of contact asperities. Therefore, surface roughness should be considered when designing ball bearings.

• 드라이브 ㆍ 컨트롤
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• 제10권3호
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• pp.7-13
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• 2013

Hydraulic vane pumps are widely used in various hydraulic systems because of its compactness and light weight. It is well known that the vanes and cam ring are separated by very thin liquid films which result in the EHL state. Contrary to the case of cylindrical roller bearings, the inlet and side boundary pressures are much higher than the atmospheric pressure. In this paper, a numerical solution of the EHL of finite line contacts between the cam ring and vane tip with profiled ends is presented. Using a finite difference method with non-uniform grids and the Newton-Raphson method, converged solutions are obtained for moderate load and material parameters. The EHL pressure distribution and film shape are considerably affected by pump delivery pressure and the side boundary condition applied. Both the maximum pressure and the minimum film thickness always occurred near the edge regions. The present results can be used in the design of optimum vane profile in hydraulic vane pump.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.36-41
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• 2004

The purpose of this paper is analyzing the oil film pressure distribution and the minimum oil film thickness for a connecting rod bearing using an A VL's EXCITE program. It is very important to understand optimized oil supplying holes and oil groove dimensions for supporting sufficiently inertia forces and gas pressures from the combustion chamber for a Diesel engine. The computed results indicate that the optimized oil groove width of a bearing and oil hole of a journal are recommended for high performance of a connecting rod bearing at the elastohydrodynamic lubrication zone. These results as design parameters are very useful data for a bearing designer as a firm reference of an automotive engine.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.121-128
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• 1999

In this study, a numerical procedure to analyze 3-dimensional unsteady elastohydrodynamic lubrication was developed. The procedure was applied to the actual cam and roller follower of the valve mechanism for a marine diesel engine. The pressure distribution between the cam and roller follower was calculated for the several cam rotating angles. The pressure spike is shown near the roller edge and it is getting higher as the external load is increased. The roller profile for reducing the pressure spike was suggested by the Hertzian contact analysis.

• Tribology and Lubricants
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• 제17권2호
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• pp.138-145
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• 2001

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present analysis is a part of research program directed toward maximizing these advantages of refrigerant compressors. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressors. Therefore, theoretical investigation of the lubrication characteristics of a rotary compressor used for refrigeration and air-conditioning systems is studied. Newton-Raphson method is used for the partial elastohydrodynamic lubrication analysis between vane and rolling piston in the rotary compressor. The results show that the rotational speed of a shaft and the discharge pressure influence significantly the friction force and the energy loss between vane and rolling piston.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.323-330
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• 1999

The conventional analysis for the numerical computation of fluid film thickness with elastic deformation of contact region. is performed by Newton-Rephson method for its 18st convergence characteristics. However, both high load and relatively low sliding velocity frequently make it impossible for Newton-Rahpson method to get both converged and stable solutions. In particular, this method cannot provide converged Solution under the condition of high load above 1.0 GPa which frequently occurs in line contact of EHL problem. Multigird multi-level method for the solver of non-linear partial differential equation including solid deformation is preferred to Newton-Rshpson method for better convergence and stability and is applied to line contact EHL behavior in this study.