Fast thermo-elasto-hydrodynamic modeling approach for mixed lubricated journal bearings in internal combustion engines

Abstract

Journal bearings are key components in internal combustion engines. Their reliability, durability, and economy are of highest importance. Especially, the accurate prediction of friction loss power and wear are essential for the development of an engine. For an appropriate representation of the hydrodynamic load-carrying capacity and also the friction behavior, both the dynamics of the contacting components, the shape of the contacting component surfaces, the amount of the available lubricant, and the properties of the lubricant itself are of importance. A Reynolds-averaged equation with laminar flow conditions in combination with an asperity contact model is a typical modeling approach for that purpose. The lubricant properties are in particular influenced by its thermal conditions on one hand. On the other hand, the thermal conditions are influenced by the mixed lubricated contact conditions as well. These interactions require a coupled modeling approach, which combines the component flexibility and its interaction with load-carrying capacity as well as the thermal behavior of the lubricant and the component surfaces. In this work, a thermo-elasto-hydrodynamic contact model is presented, which computes the oil film temperature using a 2D energy equation. The 2D equation is derived from the equivalent 3D energy equation by integration over the clearance gap height. Besides component material properties such as specific heat capacity, density, heat conductivity for lubricant and structures, also heat transfer through mixed lubricated regimes and partly filled clearance gaps, as implied in cavitation regions, are being considered. The presented method is applied for a typical engineering task of a sensitivity analysis for oils with different viscosity index (VI) improvers in a main bearing of a four-cylinder inline diesel engine. The influence of the oil film temperature on the oil film viscosity and therefore on the load-carrying capacity is shown. Furthermore, the simplified 2D approach is compared with a 3D approach both in terms of obtained result data and in terms of elapsed calculation times. The presented results show similar accuracy of the 2D approach with significantly reduced simulation time compared to the equivalent 3D case.

Thermal analysis of hydrodynamic lubricated journal bearings in internal combustion engines

“…The next two sections describe the mixed lubricated bearing contact, both for hydrodynamic lubrication and for asperity contact. These parts of the model correspond to the former bearing model 18 where more details can be found.…”

“…Averaging of the oil film temperature equation. According to Lorenz et al, 18 the 3D approach (9) can be reduced to a simplified 2D one by averaging of the equation and incorporation of an efficient density eff :¼ due to partly filled clearance gaps. 20,28 This yields the following equation for an average temperature distribution T m ðx, z, tÞ ¼ 1 h R h 0 Tðx, y, z, tÞdy in the fluid film (Remark: owing to the difference in the corresponding equation in Lorenz et al, 18 this formulation includes no domain transformation)…”

“…The 2D oil film energy equation is derived from the equivalent 3D energy equation by integration over the clearance gap height. 18 The calculation of the oil film temperature is necessary because bearings rarely operate in the isothermal mode. In almost all cases of practical bearing operations, sufficient heat is generated by dissipation, which invalidates an isothermal assumption (cf.…”

“…26 The model in this paper represents a further development of a former model developed and published by the same authors. 18 The improvement is focused on the thermal behavior of the lubrication oil; therefore the model is extended by a model for the temperature distribution in the solid bearing structures, which includes thermal interface conditions between lubrication oil and structures, considers the mixing process of the oil in supply areas, and incorporates a model for the asperity friction power source. However, the model has some overlapping parts, which are briefly included for understanding matters.…”

Lubrication Performance of Connecting-Rod and Main Bearing in Different Engine Operating Conditions

“…Refs. [15][16][17][18] study the thermo-elastohydrodynamic lubrication of engine crankshaft bearing. Tabrizi et al [19] compared three kinds of simulation models of connecting rod bearing.…”