Thermal Elastohydrodynamic Lubrication Study For Angular Contact Ball Bearing Based On Modified Quasi-statics Model

The angular contact ball bearing is widely used in engineering fields such as aerospace,weapon equipment,and railway transportation.Under high-speed and heavy-load conditions,this type of bearing is prone to lubrication failure,thermal instability and so no.Great efforts have been made by researchers at home and abroad to solve these problems,but the combined effects of the relative thermal displacement between raceways and elastohydrodynamic lubrication(EHL)on the bearing’s quasi-static performances are still not covered.Besides,effects of the inertial forces of the fluid and thermal deformations on the bearing surfaces have not been considered in the past point-contact thermal EHL(TEHL)researches for the bearing.Therefore,sponsored by the National Key R&D Program of China(No.2018YFB2000604)and the National Natural Science Foundation of China(No.51775067),the present thesis builds a modified quasi-statics model for the angular contact ball bearing.Based on this model,the point-contact TEHL analyses with the consideration of fluid inertial force,thermal deformation and surface roughness are carried out for this type of bearing.The main contents are listed as follows:First,a modified quasi-statics model that considers the relative thermal displacement between raceways and EHL central film thickness is established.The differences between the modified quasi-statics and traditional quasi-statics models are studied.It is found that both the thermal displacement and central film thickness affect the mechanic properties of the ball bearing.The higher the rotational speed,the more notable the impact of the thermal displacement on the mechanic properties.Then,a non-Newtonian TEHL model for point contacts is established with the consideration of the fluid inertial force.Effects of the applied load,entrainment velocity,slide-roll ratio and ambient temperature on TEHL performances of the bearing are analyzed without and with inertial forces considered.Meanwhile,the central film thickness measurement is conducted.It is revealed that with the inertial force considered,the secondary peak pressure under the relatively small slide-roll ratio slightly increases,the mid-layer temperature rise zone distinctly expands and the maximum film temperature increases,the film thickness rises up and the countercurrent of the film enhances.The numerical central film thickness under the inertial situation is closer to the experimental result than that under the inertialess situation.Next,a point-contact non-Newtonian TEHL model is established,into which the thermal deformations on the bearing surfaces are incorporated.At the varied applied load,entrainment velocity,slide-roll ratio,and ambient temperature,effects of the thermal deformation on TEHL performances of the bearing are analyzed.In doing so,the ITD(Internal Temperature Distribution-based)method is proposed to evaluate the thermal deformation.It is revealed that the proposed ITD method can accurately and quickly evaluate the thermal deformation of the bearing.With the thermal deformation considered,for the contact zone of the bearing,the secondary peak pressure and the film temperature near the outlet decrease significantly under the relatively large slide-roll ratio,the film thickness decreases and the film thickness curve inclines towards the outlet.Afterwards,based on the above modified quasi-statics model and the TEHL model,effects of the operating and structural parameters on the bearing’s mechanic and TEHL performances are studied.The numerical results indicate that proper increments of the initial contact angle and ball number and a proper decrement of the inner curvature radius coefficient can help to reduce the film pressure and temperature,to increase the film thickness.Finally,the influence of operating,structural and roughness parameters on TEHL performances of the bearing with surface roughness are studied.It is found that an increment of rotational speed,initial contact angle,ball diameter or ball number causes a smaller film pressure and a larger film thickness.An increment of rotational speed induces a higher film temperature,and an increment of ball diameter a lower one.Increasing the wavelength of the surface roughness contributes to improve the lubrication performance of the bearing.