Rolling Element Bearing Vibration Transfer Characteristics: Effect of Stiffness

Vibration transmission through rolling element bearings was investigated in order to aid signal interpretation for use in machinery condition monitoring studies. The relationship between bearing nonlinear stiffness and frequency response function was derived for bearings of types commonly used in rotating machinery. By considering the contact deformation of individual elements the stiffness characteristic for a complete bearing was evaluated for the case of a radially applied load. Variation in stiffness of the complete bearing as elements moved through the load zone was calculated for bearings of a specified type and size. These values were also used to dynamically model typical rolling element bearing nonlinear behavior. Derived nonlinear stiffness coefficients were substituted into the equations of motion for a model bearing. Solution was obtained by digital integration, and the bearing frequency response function was then evaluated for discrete increments of static loading. Rolling element bearing frequency response was found to be very dependent on load. For operation under light load the bearings had especially strong nonlinear vibration transfer characteristics. At this operating condition a small increase in radial load produced a significant change in the bearing transfer characteristic (due to an increase in resonance frequency).