Investigation Of Coupling Tribo-dynamic Characteristics Of Helical Gear Based On The Finite Line Contact

Gear transmission is a kind of universal transmission.The lubrication technology of gear has an important influence on the transmission of gear.The traditional theoretical model of helical gear elastohydrodynamic lubrication does not consider the influence of dynamic load on lubrication.Due to the time-varying effect of dynamic load,the distribution of oil film pressure and film thickness along the engagement line presents a fluctuation characteristic.At the same time,the influence of friction on the dynamic characteristics is often ignored in the gear dynamics model,and the latest research finds that the effect of friction can not be ignored.When the rotating speed is low,the oil film shear force is large,and the friction force and friction torque generated thereby have a great influence on the dynamic load.Meanwhile,the friction force and friction torque will make the gear vibration in the direction perpendicular to the meshing line,which will aggravate the wear of the gear surface,increase the temperature,produce fatigue wear and lead to fatigue failure.Therefore,it is necessary to establish the friction dynamics model of gear and study the coupling relationship between gear dynamics and gear lubrication,which is of great significance to the study of fatigue failure and the prediction of fatigue life of gear.The main contents of this paper include:(1)The single degree of freedom and multi-degree of freedom friction dynamics model of helical gear based on finite long line contact is established.The dynamic characteristics of the system considering friction excitation,time-varying meshing stiffness,meshing damping and static transmission error are discussed.A method for calculating the time-varying friction force and friction moment of gears is proposed,and the effects of friction on single-degree-of-freedom and multi-degree-of-freedom systems are discussed respectively.The time-domain and frequeny-domain distributions of dynamic meshing forces of single-DOF system and multi-DOF system are compared and analyzed.Under the multi-degree of freedom system,the distribution law of vibration velocity,vibration acceleration and vibration displacement of the master and slave driving wheels along the transverse,axial and torsional directions is systematically analyzed,and the distribution law of dynamic meshing force and bearing force is discussed.The influence of rotational speed on the single-DOF system and the multi-DOF system is discussed.It is found that in the multi-DOF system,the dynamic meshing force has multiple peak values at different rotational speeds,while in the single-DOF system,only one peak value appears.At low speed,the dynamic loads all have high frequency fluctuations.(2)The unidirectional coupling model of helical gear dynamic load and thermoelastohydrodynamic lubrication based on finite long line contact was established.The lubrication characteristics of gear under dynamic load were studied,and the distribution laws of oil film pressure,film thickness,temperature field and friction coefficient under dynamic load were discussed.It is found that the oil film pressure and film thickness fluctuate during gear meshing because of the time-varying characteristics of dynamic load.The distribution of pressure,average film thickness,friction coefficient and temperature of the central oil film along the meshing line at different rotating speeds and torques are analyzed.The distribution law of oil film pressure,film thickness and stress field on the secondary surface is studied.It is found that the oil film pressure peaks at the rough peak and the stress concentration on the secondary surface.In the roughness valley,the oil film pressure will appear a trough,and the subsurface stress is small.(3)The multi-degree-of-freedom dynamic model of helical gear and the full coupling model of thermoelastohydrodynamic lubrication model are established.The bidirectional coupling mechanism of dynamics and lubrication is deeply analyzed.The coupling between the two is carried out through friction and dynamic load,and the numerical solution is carried out through cyclic iteration.The variation law of time-varying friction force and friction moment is discussed,and the distribution law of dynamic load with or without friction is compared under different rotating speeds and torques.It is found that the friction has a greater effect on dynamic load when the rotating speed is lower.The distribution laws of oil film pressure,film thickness and temperature field under different meshing position coupling model and static state were compared and analyzed.The distribution laws of the center oil film pressure,average film thickness,center oil film temperature and friction coefficient along the meshing line under the coupling model and static state under different rotating speeds are discussed.It is found that,compared with the static condition,high frequency fluctuations of pressure and film thickness appear in the fully coupled model at low speed,and the high frequency fluctuations disappear with the increase of rotational speed.The friction force and friction moment have a great influence on the coiling speed and relative sliding speed of the gear,and then have a great influence on the friction coefficient and temperature field.