Abstract
This paper proposes a novel approach to analyze the inverse problems of elastohydrodynamic lubrication (EHL). First, a finite-difference method is employed to discretize the elastic deformation and the force balance equations. The discretizing equations can be rearranged into a matrix form. The pressure distribution can be expressed in an appropriate function and then substituting it into the matrix form. The least-squares error method is adopted to find the undetermined coefficients, which generates a smooth pressure distribution based upon a small number of measuring points on the film thickness map and overcomes the problems of pressure fluctuations obtained from the traditional methods. The apparent viscosity can be solved from the Reynolds equations by using the least-squares method to predict the optimum value of the pressure-viscosity index ( ). The proposed method is applied to analyze four kinds of the inverse problems, namely, EHL of line contacts, EHL of point contacts, pure squeeze EHL motion of circular contacts, and elastohydrodynamic thin film lubrication (EHTFL).
This paper discusses the effects of the implemented errors on the predicted value of apparent viscosity. The errors are implemented at the film thickness, the load, the effective elastic modulus, the viscosity at ambient pressure, and the mean velocity. Results show that the implemented errors in load and effective elastic modulus have a significant influence on the accuracy of the results, but the errors in average velocity and in the viscosity at ambient pressure do not have a significant effect. In these implemented errors, the resolution of the film thickness measurement plays the most important role in determining the accuracy of the apparent viscosity. Even when errors in the film thickness measurements are deliberately introduced, the inverse approach still provides a satisfactory value of the pressure-viscosity index. The resulting apparent viscosity errors are much smaller than those generated when using the traditional inverse method. The inverse approach can allow higher measurement error than traditional inverse method, and the allowable resolution range can be increased to about 3-10 times.
Base on the viscous adsorption theory, the modified Reynolds equation is derived for EHTFL. In this theory, the film thickness between lubricated surfaces is simplified as three fixed layers across the film, and the viscosity and the density of lubricant vary with pressure in each layer. The difference between classical EHL and EHTFL is investigated to find the important parameters of EHTFL. Results show that the proposed model can reasonably calculate the film thickness and the viscosity under EHTFL. Adsorbent layer thickness and viscosity significantly influence the lubrication characteristics of the contact conjunction. The inverse approach is developed to evaluate the pressure of contact region, pressure-viscosity index ( ) of oil film, and the film thickness and viscosity of adsorbent layer under EHTFL.
This paper also uses a self-development EHL tester with the optical interferometry equipment to observe the EHL film thickness map of circular contacts under the steady state and the pure squeeze motion. The inverse approach can be used to estimate the pressure distribution on a film thickness map obtained from optical EHL tester. By using this pressure distribution, the estimated pressure-viscosity index can be obtained. Result shows that the inverse approach predicts a larger value of the pressure-viscosity index than the actual value. The error between the actual and the estimated values of is less than 7 percent. When the minimum film thickness is less than 30 nm, the inverse approach based on EHTFL theory can reduce the error between the actual and the estimated values of .
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0728103-115946 |
| Date | 28 July 2003 |
| Creators | Chu, Hsiao-Ming |
| Contributors | none, none, Yuang-Cherng Chiou, Rong-Tsong Lee, Yeong-Maw Hwang, Jao-Hwa Kuang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0728103-115946 |
| Rights | withheld, Copyright information available at source archive |
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