Numericalanalysis Of Transient Thermoelastic Lubrication Under Large Sliding-rolling-ratios

The objective of this thesis is to explore the properties of elastohydrodynamic lubrication(EHL)considering thermal,non-Newtonian and transient effects which are simultaneously encountered in eccentric wheel or cam-follower contacts.Eccentric wheel or cam-follower mechanism is widely used in machinery.However,superposed transition effects are presented in this contact type due to the variations of velocity,load and geometry with time.Moreover,large sliding-rolling-ratios(SRR)are frequently subjected in contacts,which induce obvious non-Nowtonian and thermal effects and poor lubrication states.Consequently,numerical simulations of such contacts are tough to be performed even though it is of huge important and essential issue.The numerical studies on eccentric or cam-follower contacts simultaneously considering transient,non-Newtonian and thermal effects,are still not adequate.Especially,only little work using novel lubricants and practical parameters has been carried out.Therefore,the present work will focus on the numerical simulations of such contacts.In combination with experimental observation,the influences of primary parameters on the lubricating performance will be explored.The main contents cover:I.A transient non-Newtionan thermal numerical model of point EHL contacts is established and a numerical program is compiled.Solutions of pressure,elastic deformation and temperature field are achieved using multi-grid algorithm,multi-grid integration algorithm and column scanning,respectively.II.Performance of thermal EHL contacts lubricated by novel ionic liquids(IL)under large SRR conditions.The viscosity-pressure coefficient is first obtained based on pure rolling EHL film thickness measurement and numerical fitting.Subsequently,the behaviors of film thickness and friction are numerically observed.The results present that the performance of IL is superior to that of traditional lubricant with similar viscosity.The IL gives an acceptable film thickness but much lower friction coefficient and temperature rise.The advantages of IL over traditional lubricants are further confirmed by comparing both of the measured friction curves.III.Performance of transient non-Newtonian EHL films in eccentric sphere-disc contacts.Film thickness and friction coefficient are simultaneously measured using a new eccentric sphere-disc optical EHL test rig.An acceptable agreement is achieved between test results and transient non-Newtonian numerical simulations.Further analysis of the lubricities of eccentric sphere-disc contacts is given based on the numerical results.IV.Numerical analysis of transient non-Newtonian thermal EHL films in roller-cam and flat-cam contacts.According to the motion of valve encountered in practical applications,the profiles of the two types of cam are obtained via a kinematic inversion approach.Taking the geometry,practical load spectrum and velocity as input parameter,numerical solutions of film thickness,pressure,temperature field and friction coefficient are obtained in a whole motion period.The results show that the film thickness is primarily influenced by speed and geometry parameters,whilst the variations of temperature rise are closely related to the load parameter.The SRR changes in a large scope in flat-cam contacts.An abnormal EHL contact with dimple is found near the zero entrainment velocity.The crown dimension of flat base follower largely affects the lubrication state.A smaller crown will induce poor lubrication state.The present work is beneficial to understand the tribological performance of IL under large SRR conditions,as well as the lubricities of eccentric wheel or cam-follower contacts under practical running and geometry parameters.