Comprehensive method of thermo-elastohydrodynamic lubrication analysis is proposed to predict performance of connecting rod bearing such as minimum film thickness, maximum film pressure, heat dissipation rate and oil flow rates. This method appropriately deals with elastic and thermal distortion of the bearing surface as well as cavitation phenomenon, temperature and viscosity variation in the lubrication film.
Relationship between the elastic deformation of the bearing surface and the pressure generated in the lubrication film is determined by three-dimensional finite element stress analysis. Newton-Raphson iterative method is used to solve the nonlinear Reynolds equation and the equations of motion of the journal center simultaneously.
Mass-conserving cavitation algorithm is used to solve the Reynolds equation taking into account the effect of the cavitation phenomenon in the oil film. The algorithm is based on the idea of the biphase mixture lubricant with properties intermediate between those of its two constituents. In this algorithm, the lubrication film is divided into pressure-generated region and cavitation region on the basis of lubricant density value. The time derivative of the lubricant density is treated as unknown value which must be determined from the Reynolds equation as well as the film pressure.
Lubrication film temperature is treated as a time-dependent, two-dimensional variable which is averaged over the film thickness, while temperature of connecting rod big end is assumed to be time-independent and three-dimensional. It is assumed that a portion of the heat generated by viscous dissipation in the lubrication film is absorbed by the film itself, and the remainder flows into the bearing surface. The proportion of the heat absorbed by the lubrication film is determined so that the average film temperature over one load cycle and the average temperature of the bearing surface are identical. Thermal distortion of the bearing surface is also determined by three-dimensional finite element stress analysis. The effect of variable viscosity is included with the appropriate temperature-viscosity relationship to solve the Reynolds equation.
Simulation results of the connecting rod bearing of internal combustion engine are presented. It is shown that the cavitation phenomenon, temperature and viscosity variation in the lubrication film, and elastic and thermal distortion of the bearing surface have significant effects on the performance of connecting rod bearing. It is concluded from the simulation results that the thermo-elastohydrodynamic lubrication analysis is strongly recommended to predict the bearing performance of connecting rod big end in internal combustion engine, and that the proposed method can be used as a design tool of connecting rod bearings.
