Influence of misalignment on nonlinear dynamic characteristics for matched bearings-rotor system

Abstract

This paper presents a simplified model of misaligned-installing matched bearings, which is always constituted by two angular contact bearings in machine tools. Aiming at the effect of parallel misalignment arising in practical installing between two matched bearings, the nonlinear restoring force is derived and a matched bearings-rotor system model is established with Timoshenko elements. The Continued-Poincare–Newton–Floquet method is employed to analyze the global nonlinear characteristics with a varying clearance. Compared with the normally installed matched bearings-rotor system, it can be found that the amount of misalignment plays an important factor both on the global stability and vibration amplitude for a misaligned matched bearings-rotor system. The broadest unstable speed region always arise while the amount of misalignment equals to the initial clearance, and a slightly larger misalignment than the initial clearance can easily help the system from unstable dynamic behavior to periodic behavior. Meanwhile, a horizontal increasing misalignment will mainly affect the horizontal dynamic response by the way of magnifying and right shifting the vibration amplitude peak on speed axis obviously, but do a slight opposite effect on vertical normally installed direction. The results show that a proper amount of misalignment may be beneficial for the dynamic characteristic for the matched bearings-rotor system.