Effects of parallel misalignment on performance of hydrodynamic-rolling hybrid bearing

A hydrodynamic-rolling hybrid bearing (HRHB) arranged in parallel is introduced, in which the radial clearance of rolling bearing is used to prevent the rotor and hydrodynamic bearing from contacting during starts and stops. The aim of this study is to investigate the effects of rolling bearing misalignment on performance of HRHB for providing a design guide of machining and assembling tolerance. An analytic model is developed to predict the static performance of HRHBs with a misalignment. The misalignment is represented as an offset and an include angle. Taking the misalignment into account, a force balance equation about oil film force, rolling bearing reaction and external load is derived. The effects of the misalignment on the locus of equilibrium position, the maximum eccentricity, and the transition speed are investigated. The results show that misalignment has significant influences on performance of HRHBs, but there are regions of included angle which are insensitive to the performance of HRHBs; according to the insensitive regions, requirement of alignment errors, machining and concentricity tolerance can be determined; distinct from conventional hydrodynamic bearings, the locus of equilibrium positions of misaligned HRHBs have three variation modes of monotone decreasing, monotone increasing, and increasing first and decreasing afterwards; the monotone decreasing mode of conventional hydrodynamic is not suitable for HRHBs below transition speed; and before the maximum eccentricity ratio, the variation mode of equilibrium positions locus should be determined.