| Rolling bearing is one of the important basic components in rotating equipment.Its performance and life directly affect the working performance,reliability and safety of the equipment.The thermal characteristics of the bearing and its influence are very important to the performance and life of the bearing.At present,it is still a difficult and hot issue to accurately calculate the working temperature of the rolling bearing.The theoretical and experimental analysis of the stress,deformation,stiffness change of the bearing due to heat and the impact on the vibration of the rotor system are insufficient.There are still many gaps in the understanding of its law and lack of targeted experimental means.The thermal characteristics of the bearing and its influence mechanism are very complex,and the theoretical and technical research is also very difficult and challenging.Therefore,it is of great scientific significance and engineering application value to carry out the research on the thermal and vibration characteristics and their experiments.In this paper,the typical form of cylindrical roller bearing used in the main shaft of aero-engine is taken as the research object.The thermal characteristics of the bearing and the vibration characteristics of the rotor system with the changes of the thermal bearing stiffness and clearance are studied.The method of combining theoretical analysis with experimental research is adopted.The thermal analysis model of cylindrical roller bearing system,the finite element analysis model of contact mechanics and the thermal time-varying stiffness analysis model are established.The effects of load,rotational speed,structure,environment,lubrication and heat generation on bearing temperature,displacement distribution of inner and outer rings,stress of raceway and stiffness characteristics are studied.The rotor dynamic model considering the changes of thermal stiffness and clearance of bearing is established.The influence of bearing stiffness and clearance on the vibration of rotor system during the warm-up and under the action of hot oil is studied.The main research results are as follows:The coupling relationship between heat generation and lubrication,structure,installation and temperature in the process of bearing operation is studied,and the thermal analysis model of bearing system considering the thermal-solid coupling effect is established.In this model,the quasi statics method is used to analyze the motion and mechanical relationship between the bearing components,the local method is used to calculate the heat generation rate of each friction surface,and the thermal network method is used to establish the differential equations of bearing system temperature,so as to realize the theoretical analysis method of bearing transient temperature.The test rig and test system of bearing thermal characteristics are built,and the characteristics of bearing temperature change under typical working conditions are obtained.The results are compared with the theoretical calculation results,and the accuracy of bearing temperature calculation model is verified.Based on the bearing thermal analysis model and combined with the test,the influence factors of the thermal characteristics of the bearing system are studied.The effects of heat generation characteristics,oil film,clearance and slip rate on the thermal balance of bearings are analyzed.The effects of rotational speed,load,ambient temperature,structural parameters and lubrication parameters on the heat generation rate and bearing temperature are obtained.The results show that the rotational speed and the temperature of the oil have a significant effect on the heat generation rate of the bearing.During the warm-up,the oil film thickness decreases rapidly first and then becomes stable gradually.Rotational speed and temperature of oil have great influence on bearing temperature,while load and ambient temperature have little influence on bearing temperature.Too low temperature and flow rate of oil will lead to a significant increase in bearing temperature.The variation trend of the bearing clearance is mainly related to the temperature difference between the inner and outer rings of the bearing,and the clearance has obvious influence on the bearing temperature when the load is small.The interference between the inner and outer ring of the bearing has some influence on the temperature of the bearing seat and the shaft.The finite element models of static and dynamic analysis of cylindrical roller bearing system are established respectively,and the bearing thermal analysis model is introduced to study the displacement of inner and outer rings and the stress distribution characteristics of raceway under the influence of many factors.Under the action of load,the inner and outer rings of the bearing deform irregularly,and the displacement of the inner and outer rings fluctuates with the angle.The thermal expansion increases the stress at the contact between the bearing roller and the race.With the increase of rotational speed,the displacement of inner and outer rings of bearing increases gradually and the temperature of lubricating oil has obvious influence on the displacement of inner and outer rings.With the increase of oil temperature,the displacement of inner and outer rings first decreases and then increases,and the oil flow rate has little influence on the displacement of inner and outer rings and the stress of raceway.In the process of bearing thermal balance,the displacement of inner and outer rings increases rapidly and then becomes stable.Based on the bearing thermal analysis model,the bearing thermal time-varying stiffness calculation model is established,and the effects of speed,load,environmental temperature,structure and lubrication on the bearing stiffness are studied.The method of applying incremental load to the bearing and testing the relative displacement of the inner and outer rings is used to identify the stiffness of the bearing.The test method of identifying the bearing stiffness by applying incremental load to the bearing is adopted.The stiffness characteristics of the bearing during the warm-up and in the condition of different lubricating oil temperature were studied.The results show that the change of oil film thickness leads to the obvious change of bearing stiffness.During the warm-up,the stiffness shows strong non-linear and time-varying characteristics.In the early stage of operation,the stiffness of the bearing decreases rapidly,but in the start-up state,the stiffness of the bearing increases with the increase of the rotational speed;After reaching the thermal balance state,the stiffness of the bearing decreases with the increase of the rotational speed.Heating oil also has a significant impact on the bearing stiffness.With the increase of oil temperature,the bearing stiffness drops sharply.The dynamic model of rotor bearing system considering the change of thermal stiffness and clearance of bearing is established.The identification method of bearing stiffness and clearance based on rotor vibration response is proposed.Through the theoretical analysis and experimental study of the vibration of the rotor system,the response law of the unbalanced vibration of the rotor in the process of bearing thermal balance and the influence law of different oil temperature on it are obtained.The results show that during the warm-up,the amplitude,peak value and effective value of rotor unbalance vibration increase gradually,the bearing stiffness decreases gradually,and the clearance changes little.The increase of oil temperature will cause the vibration amplitude of rotor to decrease gradually and the identified bearing stiffness and clearance decrease.The temperature of oil also has an obvious influence on the peak value and effective value of bearing vibration.Through the research in this paper,the change law of oil film and bearing stiffness in the process of heat generation and during the warm-up is revealed and the influence law of load,rotational speed,structure,environment and lubrication conditions on the deformation of inner and outer rings of the bearing and the stress of raceway are obtained.Furthermore,the influence law of bearing stiffness due to thermal effect on the vibration characteristics of rotor system is revealed.The results of this paper can provide theoretical and technical basis for the thermal characteristics analysis,static and dynamic analysis of cylindrical roller bearing,as well as the dynamic analysis of rotor system. |
PDF Full Text Request