Vibration and stability analyses of rotor–bearing-casing system in an axial piston pump subjected to bearing faults

Healthy roller bearings are essential for the safe performance of axial piston pumps. A dynamic failure model of a rotor–bearing-casing system was developed to investigate the effect of bearing damage on the vibration characteristics and stability. This model considers the effect of large-gap circulation on a wet rotor system model, which is closely related to the stirring conditions during actual operation of axial piston pumps. The stator and rotor of the pump were modelled using the centralised parameter technique and finite element method, which were combined to develop the rotor–bearing-casing model. Vibration and stability analyses were performed for the system model with bearing failure, considering the gap annular flow and hydraulic excitation force. The effects of the mass eccentricity, rotational speed, and discharge pressure on the vibration characteristics and stability were analysed under different types of bearing failures. Furthermore, the vibration behaviour of the rotor–bearing-casing system with a bearing fault was measured to validate the established dynamic model. The results indicated that the rotational speed and rotor eccentricity affected the churning and unbalanced effects of the rotor. With an increase in the rotor eccentricity, the rotor first transitioned from nonlinear motion to one-period motion and subsequently to periodic motion. The rotor energy reduction and steady state of the rotor–bearing-casing system were induced by the rotor churning action. As the annular gap decreased, churning losses increased, resulting in a more stable rotor motion.