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

Interest in vibration control in systems employing rolling element bea rings, ranging from rotor systems used in energy conversion/transmissi on to high-precision, multi-degree-of-freedom optical positioning syst ems, has focused attention on the modelling of bearing dynamic stiffne ss properties. While modelling a rolling element bearing either as an ideal boundary condition for a shaft or as a simple translational elem ent may suffice in understanding basic rotor system dynamics, such sim ple models are inadequate in explaining how vibratory energy may be tr ansmitted from, for example, transverse shaft vibrations to perpendicu lar, 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 stiffn ess. The study reported in this article focuses on double row spherica l (self-aligning) rolling element bearings where moment stiffnesses an negligible, but translational cross-coupling stiffnesses between axia l and radial bearing directions are present. A new theoretical model f or the direct and cross-coupling stiffness coefficients of spherical r olling 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 cr oss-coupling stiffness coefficients are negligible with simple radial or axial preloads, under the combined radial plus axial preload condit ion, the cross-coupling stiffness coefficient between the axial direct ion and the direction of the radial preload becomes significant. (C)) 1998 Academic Press.