Numerical Modelling And Analysis Of Elastohydrodynamic Lubrication And Dynamic Characteristics On Line Contact Friction Pairs

With the demand of further acceleration of high-speed trains,higher performance requirements are required for key transmission parts such as bearings and gears.The friction contact form between roller and raceway,gear tooth is line contact.In order to reducing the friction wear,absorbing vibration and heat that generated in the operating process,lubricating system usually concluded to improving the working performances and reducing the service life of mechanical system.The film lubricating state between the contact interfaces not only determines the tribological performances of the components and mechanisms,but also affects the dynamic characteristics.However,in the conventional sense,the EHL effect is ignored in the dynamic analysis due to the high complexity of modelling and expense of computing.Therefore,it is important to conduct the coupling research of elastohydrodynamic lubrication and dynamics for line contact,which has great significance for improving the accuracy of theoretical analysis and provide a reference in the design process.This work established the coupling model of EHL and dynamics under isothermal conditions and proposed a calculation method of stiffness and damping for line contact friction pairs.And the effects of main working conditions and structural parameters to lubricating performance and dynamic characteristics were discussed.Then,thermal effect was included in the coupling model of EHL and dynamics.Based on the proposed method,the thermal effects to dynamic characteristics and temperature increase were studied.Finally,surrogate model of EHL stiffness and damping to load was established,which was verified through universal contact model by Newmark-β method.The relationship between bearing rotation and entrainment velocity in the established model was derived and obtained the stiffness and damping surrogate model.The main contents of this thesis are as follows:(1)Established the coupling model of elastohydrodynamic and dynamics for line contact and proposed an evaluation method for stiffness and damping parameters based on the Reynolds equation,the fundamental of elastic contact and dynamics theory.Specifically,the multi-level multiintegration method was adopted to calculate the elastic deformation of the contact body and the Newmark-β theory was employed to solve the dynamic responses during the transient contact process.Then,the stiffness force part is separated according to the established function relationship under steady-state condition,and damping value can be obtained consequently.The results show that the stiffness force plays an increasingly important role over the applied load conditions while the damping effects is gradually weakened.EHL stiffness is obviously smaller than dry contact stiffness,but the discrepancy is decreasing with the increasing load.Moreover,the higher entrainment velocity,lubricant viscosity and larger curvature radii leads to smaller stiffness and damping.The elastic modulus generates little effect on dynamic characteristics when the load is light while dominates the maximum level of the contact stiffness.(2)Combined the energy equation to establish the coupling model of thermal elastohydrodynamic lubrication and dynamics for line contact.The temperature of the lubricant oil film in middle,upper and lower contact surface and the close surface can be solved in each iteration process via the distribution of oil film pressure and thickness.The results show that the temperature of lubricating oil film obviously increased with the increasing of external load and entrainment velocity.Moreover,the increase in slippery ration leads to the increase in the temperature of lubricant.(3)Investigated the thermal effect to EHL dynamic characteristics based on the thermal EHL system and the proposed stiffness and damping evaluation method.The results show that the thermal EHL stiffness and damping value was larger than that under isothermal conditions.And the thermal effect was more obvious with the larger entrainment velocity,which leads to a larger stiffness gap when the temperature increase considered.(4)Established the surrogate model based on the EHL stiffness and damping results and verified the reliability by comparing the dynamic responses calculated through universal contact model.Finally,the function relationship between the applied load and stiffness damping parameters can be obtained on the basis of the kinematic relations of roller bearings,which provides theoretical reference for the establishment of EHL dynamic model of roller bearings.