Research On Thermal Elastohydrodynamic Lubrication Characteristics Of Rolling Bearings

Rolling bearings are widely used in high-end mechatronic systems with rotating motion.The lubrication conditions affect the tribological characteristics of the bearing and the motion stability of the mechatronic system directly.The contact lubrication characteristics of rolling elements and inner and outer races in rolling bearings can be solved and calculated by elastohydrodynamic lubrication theory.In previous studies,many scholars considered the thermal effect and roughness in order to obtain a numerical solution that is more appropriate to the true value.Taking rolling bearing as object,the lubrication properties,thermal stress and thermal elastic deformation on the contact surface are studied by considering some influence factors including micro roughness,thermal elastic deformation,elastic modulus,which can provide valuable theoretical reference for rolling bearing lubrication analysis and structural design.The main contents of the dissertation include:（1）The full approximate scheme of the multi-grid method is introduced,and the 4-layer W loop structure is used to analyze the influence on the number of cycles and the maximum error.The thermal stress expression and thermal deformation expression of the cylinder are derived by using the stress function method and the Bessel function,and a numerical example is given to solve the Bessel function parameters.（2）The micro thermal elastohydrodynamic lubrication of elliptical point contact of the ball and the inner race of deep groove ball bearings is modeled,and the lubrication characteristics of6206 deep groove ball bearings with different types of roughness are studied.The influences of speed and combined elastic modulus on elastohydrodynamic lubrication characteristics are investigated.（3）Considering the effect of the thermal deformation,the finite-length line contact of cylindrical roller and inner race of cylindrical roller bearing is modeled.The principle of heat-force conversion is introduced.Taking the NU204 cylindrical roller bearing as an object,the thermal elastohydrodynamic lubrication characteristics,thermal elastic deformation and thermal stress are calculated.The influences of speed,load,and viscosity on lubrication characteristics are studied,and then the thermal elastic deformation and the thermal stress are also studied.（4）Considering the effects of micro roughness and thermal deformation,the micro thermal elastohydrodynamic lubrication model of elliptical point contact of angular contact ball bearing is established.Taking 7032C angular contact ball bearing as an object,the effects of speed,load and viscosity on the oil film pressure,thickness,temperature rise are studied.The lubrication characteristics,the thermal elastic deformation and thermal stress are also studied.（5）Considering the combined effects of roughness,thermal deformation and elastic modulus,the thermal elastohydrodynamic lubrication model of the finite-length line contact of the needle and the inner race of needle bearing is established,and then a new numerical method is proposed to calculate the lubrication characteristics.The elastic modulus field is calculated numerically by introducing the relationship between elastic modulus and temperature.Taking the NAV4004 needle bearing as an object,the film pressure,thickness,temperature rise,elastic modulus and thermal elastic deformation are calculated.The influences of load and entrainment speed on the elastic modulus,film pressure and film thickness are further studied.（6）The proposed numerical method is verified by the film thickness experiments of rolling bearings of other scholars.In their works,the oil film thickness of D1842926N₁Q₁ and N2312cylindrical roller bearings are measured using the resistance-capacitance oscillation technique and the ultrasonic method.The experimental operation parameters of these two types of rolling bearings are used to solve the minimum film thickness by the proposed finite-length line contact thermal elastohydrodynamic lubrication method.The numerical results show that the obtained solutions by the proposed method are in good agreement with the experimental results.