Investigation On Compound Fault Mechanism And Skidding Characteristics Of Rolling Element Bearings

Rolling element bearings are essential basic components of rotating machines,its service status will have an immediate impact on the performance and reliability of the whole mechanical system.Since rolling element bearings are often affected by severe working conditions such as high speed and heavy load,the rolling elements and raceway surfaces are prone to local faults,which will evolve into group faults or multi-point compound faults in severe cases.Besides,it is inevitable that bearings skidding during operation,which will accelerate bearing wear,reduce bearing rotation accuracy and cause vibration and noise.Hence,it is of great theoretical significance and engineering application value to carry out dynamic modeling of rolling element bearings to study the compound fault mechanism and skidding characteristics.In the paper,deep groove ball bearing is used as a research object,the vibration characteristics induced by compound faults of bearings and the skidding characteristics of healthy bearings under thermal elastohydrodynamic lubrication(EHL)are studied.The main research contents are summarized as follows:(1)A dynamic model of rolling element bearing with compound fault of both inner and outer raceway surface is developed.The impact force excitation function varying with shaft speed and defect width is derived by comprehensively considering the influence of revolution and rotation speed of rolling element.Combined with the influence of film thickness,stiffness and damping of oil film under thermal EHL condition,and time-varying displacement,a dynamic model of rolling element bearing of compound fault with local faults on both inner and outer raceway surface is proposed.The dynamic differential equations are solved by the fourth-order Runge-Kutta method,and the simulation signals are obtained.The bearing fault simulation experiment is carried out by using the Machinery Fault Simulation(MFS)test rig,and the signals characteristics of simulation and experiment are compared and analyzed,which verified the correctness of the model.(2)The vibration response characteristics of rolling element bearings under different working conditions and different contact conditions between the same rolling element and inner and outer raceway defects are explored.The influence of different shaft speeds and defect widths on the vibration response of rolling element bearing are analyzed.A mapping method from defect-rolling element-defect behavior to time is proposed,and the dynamic characteristics of the bearing under the simultaneous or successive collision of the same rolling element with inner and outer raceway defects in the load zone by combining with the simulation model.The results show that the vibration amplitude of the bearing increases with the increase of shaft speed and defect width.Secondly,in the load area,the vibration amplitude of the bearing decreases when the same rolling element collides with the inner and outer raceway defects at the same time,and the vibration amplitude of the bearing increases when the same rolling element collides with the inner and outer raceway defects successively.(3)A skidding dynamic model of rolling element bearing is built.The cage pocket clearance is introduced into the bearing model.The cage model is simplified as flexible cage units with the same number of rolling elements,and the between flexible cage units are connected by springs.The interaction between cage units and rolling elements,cage units and cage units,and rolling element and inner and outer raceways are described.A skidding dynamic model of rolling element bearing under thermal EHL condition is proposed.The simulation signals of the model are obtained by solving the dynamic differential equations with numerical method.Finally,the model simulation results are analyzed in detail.(4)The skidding characteristics of rolling element bearings under different working conditions and bearing parameters are explored.The trend of sliding speed between the rolling element and inner raceway and the cage slip ratio under different shaft speeds,radial loads,equivalent stiffness between flexible cage units and cage pocket clearance are investigated.The results show that with the increase of shaft speed or the decrease of radial load,the sliding speed between the rolling element and inner raceway and the cage slip ratio increase.With the increase of equivalent stiffness between flexible cage units,the sliding speed between the rolling element and inner raceway and the cage slip ratio decrease.With the decrease of cage pocket clearance,the sliding speed between the rolling element and inner raceway and the cage slip ratio decrease.However,when the cage pocket clearance is zero,the sliding speed between the rolling element and inner raceway increases.