Coupling Research On The Tribo-dynamic Of A Gear Pair Considering The Thermal Elastohydrodynamic Lubrication Contact Characteristics

Gears are widely used in various mechanical equipment due to the advantages of heavy-load capability and smooth transmission,its contact characteristics and dynamic behaviors directly determine the service performance of entire mechanical equipment.As the modern equipment is pointing to the direction of heavy-load and high-speed,the dynamic behavior,lubrication property and transmission efficiency of gear transmission have been becoming the research focus.The traditional gear design method is based on the classic Hertz contact theory,ignoring the lubrication factors between the tooth surfaces and dynamic behaviors.As this method fails to clarify the correlation between the thermal lubrication contact characteristics and the dynamic behaviors of the system,the analysis of system dynamic behaviors is not accurate enough.The result is difficult to support the anti-fatigue design for high performance gears,which significantly affects the safety and reliability of high-end equipment.This research establishes a transient thermal elastohydrodynamic lubrication(EHL)numerical model to predict the pressure,oil film thickness,shear force and temperature field within a complete mesh cycle,which takes the involute spur gear transmission as the object.Based on the lubrication properties,the tooth surface friction force,oil film damping,EHL contact stiffness and other contact characteristics are described.Multi-subjects such as gear meshing theory,the lubrication contact mechanics etc.,are involved.Considering the coupling effect between the contact characteristics of interface lubrication and the dynamic responses of system,the tribo-dynamic coupled model of the gear pair is developed to obtain both dynamic responses with the effect of lubrication contact characterisitcs and lubrication properties with the dynamic boundary condition.This work reveals the interrelation between the interface lubrication and gear dynamic responses,which provides theoretical support for the establishment of modern contact mechanics and dynamic analysis system of gears.The main contents are as follows:(1)Based on the geometric and kinematic analysis of involute spur gear,variations of the equivalent radii of curvature,surface velocities and tooth force along the line of action(LOA)are obtained.A transient thermal EHL numerical model for the gear pair adopting the general Reynolds equation is built,which considers the Ree-Eyring fluid characteristics and thermal effect.The influence of squeezing effect,thermal effect and operating conditions on the lubrication properties is discussed over a tooth mesh cycle.(2)According to the lubrication properties,the time-varying characteristics of thermal EHL contact such as tooth surface friction,oil film damping,EHL contact stiffness etc.are described,which are served as the link between the lubrication sub-model and dynamic sub-model.The influence of working condition,lubricant ambient viscosity,thermal effect on the contact characteristics is analyzed.(3)Based on the coupling interaction of the gear structure stiffness,thin film of lubricant and profile modification,a new analytical model of nonlinear time-varying mesh stiffness for the gear pair under the lubrication condition is proposed,which provides the theoretical basis for accurate simulation of gear nonlinear dynamics.This model can not only realize the effect of EHL contact stiffness on the total mesh stiffness,but also evaluate the effect of the tooth profile modification and operating condition on the gear mesh stiffness.(4)A tribo-dynamic coupled analytical model for the gear pair is established,which combines both the dynamic sub-model considering the time-varying contact characteristics of interface lubrication and the lubrication sub-model taking the dynamic tooth force and actual surface velocities as the dynamic boundary condition.The formula describing the relation among the rigid body displacement,dynamic tooth force and load distribution factor is deduced,and then a time-real iterative scheme for simultaneously obtaining lubrication properties and dynamic responses is proposed.Compared with the traditional dynamic model,the accuracy and applicability of the new model are verified.(5)Based on the tribo-dynamic coupled model,the influence of factors such as contact condition,thermal effect,operating condition,and profile modification on the nonlinear dynamic characteristics of gear system is discussed,which reveals the interaction between the lubrication properties and dynamic responses.The variation trends of gear lubrication properties,temperature field,transmission efficiency under the static and dynamic conditions are compared.