In designing of engine bearings for automobiles, we need to establish a mixed lubrication model that considers the solid-to-solid contact between journal surfaces and bearing surfaces with microgroove. However, as far as we know, there is no literature treating such problems. This paper describes theoretical modeling for microgrooved bearings under the mixed lubrication conditions with experimental verifications and prediction of performance in the actual engine bearings. In this modeling, a sectional shape of the microgrooved bearing was approximated to be a circular sectional shape. Contact pressure between the journal surfaces and the bearing surfaces with microgroove was calculated using the Hertzian contact model and the effects of elastic deformation of bearing surface due to hydrodynamic and contact pressures were considered. A numerical calculation model was developed to predict bearing performance under the mixed lubrication condition in microgrooved journal bearings. Oil film thickness distributions, hydrodynamic and contact pressure distributions, and real contact area between the journal surfaces and the bearing surfaces with microgroove were obtained simultaneously by the theoretical model. Moreover, friction coefficients under mixed lubrication conditions were determined by the theoretical model and the calculated results were compared with experimental results using test rig. The calculated results successfully agreed with the experimental results and the applicability of the model was verified. Moreover, the model was applied to predict the performance of engine bearings. In the numerical results, real contact area occurred relative widely under low-speed conditions when engine was started but friction loss was not excessive because of low shearing velocity. On the other hand, under high-speed engine conditions, the friction loss was large in spite of narrow real contact area because of high shearing velocity. Under both low-speed and high-speed conditions, the real contacts will occur severely at the edge of the bearing in the axial direction and at the bearing angles from 50 deg to 110 deg in circumferential direction. In addition, an appropriate design of the microgrooved bearing was examined under mixed lubrication conditions. In the design of the microgrooves, a cooling effect and an enough amount of oil flow to the contact area are needed. As the results from parametric studies using present theoretical model, an influence of the depth of the microgroove was the largest on the cooling effect and the enough amount of oil flow. In the case of typical operation condition, it was found that 1.0 μm of the groove depth was the most appropriate.

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In the design and analysis of engine bearings for automobiles, the elastic deformation of bearing surface due to high pressure and temperature of oil film affects significantly on the bearing characteristics. Thermo-elasto-hydrodynamic lubrication analysis (TEHL) is usually used to consider such effects, but a large amount of calculation time is needed to obtain the numerical solution of oil film temperature by solving the conventional type of 3-dimensional energy equation in TEHL. This paper describes a rapid method of numerical calculation of oil film temperature in engine bearings. In this modeling, it is assumed that the temperature distribution in the oil film thickness direction takes the parabolic form. Under such an assumption, averaging the 3-dimensional energy equation over the film thickness, the 2-dimensional energy equation is newly obtained. The numerical solutions of oil film temperature based on the 2-dimensional model are compared with the solutions based on the 3-dimensional model. It is confirmed that the calculation time is remarkably reduced to obtain the oil film temperature with an allowable accuracy. Moreover, the predicted oil film temperature by the 2-dimentional model is compared with measured data, and the good agreement is seen between them.