VIBRATION TRANSMISSION THROUGH SELF-ALIGNING (SPHERICAL) ROLLING ELEMENT BEARINGS: THEORY AND EXPERIMENT

Abstract

Interest in vibration control in systems employing rolling element bearings, ranging from rotor systems used in energy conversion/transmission to high-precision, multi-degree-of-freedom optical positioning systems, has focused attention on the modelling of bearing dynamic stiffness properties. While modelling a rolling element bearing either as an ideal boundary condition for a shaft or as a simple translational element may suffice in understanding basic rotor system dynamics, such simple models are inadequate in explaining how vibratory energy may be transmitted from, for example, transverse shaft vibrations to perpendicular, out-of-plane casing vibrations. Recently, researchers have begun to address this issue for conventional single row ball or cylindrical rolling element bearings which exhibit a strong moment–coupling stiffness. The study reported in this article focuses on double row spherical (self-aligning) rolling element bearings where moment stiffnesses are negligible, but translational cross-coupling stiffnesses between axial and radial bearing directions are present. A new theoretical model for the direct and cross-coupling stiffness coefficients of spherical rolling element bearings is developed and partially validated using new experimental techniques. It is shown that the coefficient values are complicated functions dependent on radial and axial preloads. While cross-coupling stiffness coefficients are negligible with simple radialoraxial preloads, under the combined radialplusaxial preload condition, the cross-coupling stiffness coefficient between the axial direction and the direction of the radial preload becomes significant.