Calculation of dynamic coefficients in a hydrodynamic bearing considering five degrees of freedom for a general rotor-bearing system

A complete method is presented to calculate the stiffness and the damping coefficients in a hydrodynamic bearing considering five degrees of freedom for a general rotor-bearing system. Perturbation equations are obtained from Reynolds equation by assuming the small amplitude motion of a bearing center, and are solved by the finite element method. Their characteristics due to eccentricity and misalignment are investigated for herringbone groove journal and thrust bearings in the spindle motor of a hard disk drive. This research shows that the dynamic coefficients increase with increasing the misalignment as well as the eccentricity due to the wedge effect. It also shows that the moment coefficients, which have been neglected in most of the previous analyses, are of significant magnitude in a journal bearing and have even bigger values for the thrust bearing when they are compared with the ball bearing in the same type of a spindle motor.