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A comprehensive transient thermohydrodynamic analysis for dynamically loaded journal bearings such as engine crankshaft bearings has been developed. A key element in this analysis is consideration of different time scales for the oil film, journal and bushing. Another important element of this analysis is consideration of moving grids in the oil film. Mass conserving cavitation is included via the Elrod cavitation algorithm. The 3-D energy equation is solved without any simplification in the oil film or the bushing. The journal is treated as a lumped thermal element. We found that the time scales for thermal transients in the oil film are of the same order as the period of the dynamic loading (one engine cycle for a crankshaft bearing); consequently, thermal transients in the oil film were considered. However, the time scales for thermal transients in the journal and bushing are several orders of magnitude greater than those for the oil film. Consequently, these elements were treated as if they were in quasi-steady state over one loading cycle. Results from this analysis are presented for an engine crankshaft main bearing under sinusoidal loading. Oil film temperatures are found to vary considerably over time and space.

Non-Newtonian effects of multigrade engine oils in dynamically loaded crankshaft bearings are analyzed. The main focus of this work is on the shear-thinning effect. Viscoelastic effects are also considered over a limited range of the relaxation time. It has been shown that the same generalized Reynolds equation used in the Thermohydrodynamic (THD) analysis can be used for analyzing the shear-thinning effects as well. Consequently the shear thinning effect and the THD effect can be treated together. A mass conserving cavitation algorithm developed earlier for doing the THD analysis is used to solve the generalized Reynolds equation. Non-Newtonian shear-thinning significantly affects the power loss, film thickness, and oil flow of a multigrade oil as compared with a Newtonian oil. Over the range of relaxation times considered, no viscoelastic effects were discernible for crankshaft bearings lubricated with multigrade oils.

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