Research On Dynamic Behavior Of High-speed Rolling Bearings In Aeroengines

To satisfy the trending of aeroengine for high thrust-weight ratio, long life andhigh reliability, high-speed rolling bearings of aeroengine is required more and morerigorous on speed and loads. Due to high contact pressure and temperature rise, kinds ofsurface failures, such as surface scratch and surface burning, even serious consequencessuch as journal sticking the on severe case, occur on rolling bearings that operates onthe high speed and heavy load conditions. Although materials and structures of spindlebearings have been gradually improved to meet requirements of aeroengine, limitationof the materials has come in the applications in critical conditions. In addition,instability of high-speed rolling bearings, which makes the cage fracture and rotorinstability happened, becomes more and more important while the aeroengine workingon different conditions. Therefore, analysis of dynamic properties and behaviors ofhigh-speed rolling bearings are basic to optimize the bearing design and key researchfor improve the reliability and life of bearings. The objects of this dissertation arehigh-speed rolling bearings of aeroengines under typical rigorous working conditions.Dynamic performances of bearings are investigated according to establishment ofdynamic model and simulation. The results provide the checking basis for bearingdesign and theoretical basis to reliability and stability growth of bearing-rotor system inaeroengine.According to the geometry and kinematic relationship of bearing elements, modelsof interaction between elements were established. Dynamic models of high speedrolling bearings were established and solved by integration method of Runge-Kutta andNewtown-Raphson which is proposed to improve the calculation efficiency and keepingprecision of dynamic results. The results could provide the basis data to analyze thebearing dynamic behavior on different conditions. The dynamic model is applied on oillubricated and solid lubricated bearing. This model can be used to analyze the influenceof assembling, temperature differential and centrifugal force. The effects of ellipticalcage pocket in ball bearing and roller profile modification in roller bearing can beinvestigated by this model.Aiming at the misalignment between inner ring and outer ring caused byassembling error, effect of tilted misalignment on loading characteristics of rollerbearings was investigated based on the dynamic model of roller bearings. The resultsshown: The deflection between inner and outer rings caused eccentric loads on rollers,generating excessive contact pressure. In addition, the fluctuation of maximum contactpressure during the running process of bearings influenced by deflection between rings.With the increase of deflection angle between inner and outer rings, the maximumcontact stress in loading zone gradually went up and then got stabilized when deflection reached to a certain angle. While during bearing running, the fluctuation range ofmaximum contact stress first gradually decreased and then modestly increased. Forimproving the loading characteristics of roller bearings under the condition of tiltmisalignment, the quantity design basis that increasing the number of roller and usinglogarithmic roller profile modification were proposed.Based on the dynamic model of rolling bearings, characteristics of rolling bearingsin steady conditions were analyzed from two aspects: deviation ratio of cage whirlspeed and cage sliding ratio. The results have significance for bearing failure analysis.The results shown: increasement of bearing velocity improves the cage stability butmakes cage sliding ratio increased meanwhile. It is available for decrease the cagesliding ratio and improves the cage stability through control the ratio of radial loads toaxial load. Increasement of radial loads on roller bearings decreases the cage slidingratio but makes cage stability become weak.According to the aeroengine features that switching between several workingconditions, transitional dynamic performance of high speed bearings in starting,accelerating and loading processes were investigated. The results shown: Initial status ofbearing has great influence on cage stability. In starting process, cage motion completeddepends on the push of rolling elements, the force on cage are less. Cage stability isworse in the beginning of bearing starting process. In the accelerating process andloading process, cage motion is influenced by rolling elements and guiding ring. Therub and impact between cage and rolling elements increased with the raising of bearingspeeds and loads.Based on the features of working condition, including high speed, heavy load andhigh temperature, of rolling bearings in aeroengines, the calculation model of bearingworking clearance, considering the assembling, temperature differential and centrifugalforce, was established. The working clearance and its effcts on bearing performancewere investigated. The model and analysis results can be used to guide the design ofbearing assembling parameters.Dynamic analysis software of rolling bearings was developed through hybridprogramming of Visual Basic and Matlab. According to the example calculation,accuracy of the dynamic model and software were validated by comparing the resultscalculated by this dissertation to the results calculated by SHABERTH and ADORE.Base on the calculation method of bearing fatigue life considering the contact loadon micro area, bearing structure optimization model, which the fatigue life as the goalfunction, the cage sliding ratio, race curvature factor and ball filling angle as theconstraint condition, was established. Effect of bearing structure on bearing stabilitywas studied. In addition, effect of rotation modes of bearings, including rotation bysingle and double rings, on bearing performance was investigated. Analysis resultsapplies theory basis for life extension of high speed rolling bearings in aeroengines.Coupling dynamic model of rolling bearing-rotor system was established to analyze the influence of rotor on dynamic behavior of bearings. The results shown:vibration of rotor makes contact loads and relative sliding of bearing between rollingelement and rings increased, and thus influence on bearing life and temperature rise.The results are basis to analyze the micro-failure behaviors of heavy-load friction pairon micro contact area.