Oil-lubricated plain hybrid journal bearings have been investigated theoretically and experimentally to determine the hybrid (hydrostatic/hydrodynamic) performance. The paper consists of two parts: Part I deals with the theoretical treatment of results, and Part II describes the experimental investigation. It is demonstrated that when two rows of inlet lubricant sources are employed in a plain hybrid bearing, greater load-carrying capacity is obtained by positioning the entries near the ends of the bearing rather than at the center or at quarter stations. These results extend previous work by presenting data for a wide range of power ratio (K). The parameter K is defined as the ratio of friction power to pumping power. Increasing K has the same effect as increasing speed for a particular bearing system. A new basis for optimizing hybrid bearings is described. The bearings to be optimized are compared with a reference bearing, on a basis of load/total power; a technique which is not required in other bearings where load does not increase rapidly with power ratio. Plain hybrid bearings are compared with conventional recessed hydrostatic journal bearings and with axial groove hydrodynamic journal bearings. It is found that plain hybrid bearings are superior in performance to recessed journal bearings at low eccentricity ratio and low speed. Also plain hybrid bearings are comparable to axial groove hydrodynamic journal bearings at a high eccentricity ratio and high speed with advantages for variable directions of loading. Furhermore the hydrostatic effect tends to raise the whirl onset speed.
