Stress analysis of main bearings under actual working conditions

Abstract

As vehicle engines become lighter, smaller, and more powerful, stress prediction of the main bearings has become an important aspect of strength design measures for the cylinder block. To predict the stress of the engine main bearings under actual working conditions, a flexible multibody dynamics (FMBD) solver was developed with a built-in elastohydrodynamic lubrication solver for the main bearings. The dynamic behavior of the engine system under actual working conditions was then calculated and the results were used to calculate the stress. To reduce the stress calculation cost, rather than inputting the actual working load into a finite element model (FEM) of the whole engine as a boundary condition, the stress was calculated by inputting the dynamic behavior into a small FEM consisting only of the main bearing as a displacement boundary condition. Verification of the test results confirmed that this model is capable of highly precisely predicting the actual working strain of main bearing portions susceptible to fatigue-related fractures. It was confirmed that the developed model could predict the actual working strain if the highest natural frequency of the eigenmode utilized by the FMBD analysis was set to 50kHz or higher.

Keywords

• main bearing
• cylinder block
• stress analysis
• flexible multibody dynamics
• component mode synthesis
• elastohydrodynamic lubrication
• mixed lubrication