Hydrodynamic journal bearings are critical power transmission components that are carrying increasingly high loads because of the increasing power density in various machines. Therefore, knowing the true operating conditions of hydrodynamic journal bearings is essential to machine design. Oil film pressure is one of the key operating parameters describing the operating conditions in hydrodynamic journal bearings. Measuring the oil film pressure in bearings has been a demanding task and therefore the subject has been studied mainly by mathematical means. The aim of this study was to determine the oil film pressure in real hydrodynamic journal bearings under realistic operating conditions. The study focused on engine bearings. Test rig experiments, simulations and calculations were carried out to determine the oil film pressure and to understand its relationship with other operating parameters. The main test apparatus was a versatile bearing test rig with a hydraulic loading system. The operating ranges of the bearings were determined by a novel method and the friction loss was determined by a heat flow analysis. The oil film pressure was measured by optical pressure sensors integrated in the bearings. The Author was a member of the research team that developed these sensors. The realistic oil film pressure was measured under hydrodynamic lubrication in realistic operating conditions. Significant differences between the measured and simulated oil film pressure distributions were found. Typically, the measured area of high pressure in the lubricating oil film was wider than the simulated one. The results can be used in the development and validation of mathematical methods for research into hydrodynamic journal bearings.
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