Analysis Of Dynamic Oil Film Thermal EHL Considering Boundary Temperature Of Bearing Components

Based on rolling bearings,non-Newtonian effect,thermal effect and dynamic effect on elastohydrodynamic lubrication(EHL)are considered.Four parts are included in the present thesis,analysis of non-Newtonian thermal EHL in ball bearings under a load impact,analysis of non-Newtonian thermal EHL in ball bearings with normal vibration,influence of temperature boundary condition of bearing components on non-Newtonian thermal EHL of dynamic oil film,and experimental study on EHL under velocity impact condition.Firstly,taking Ree-Eyring non-Newtonian fluid as an example,a thermal EHL model in ball bearings under a load impact was established.Effects of rotational speed of the inner ring,the initial load and other parameters on the lubricating performance of EHL at the contact point between the inner ring and the rolling element were investigated.Results show that,the increase of the rotational speed of the inner ring has little influence on the pressure of the oil film.And the higher rotational speed of the inner ring causes the oil film temperature rise obviously in the inlet of the contact area.However,the phenomenon of thicker film thickness caused by higher speed does not happen.Secondly,a non-Newtonian thermal EHL model in ball bearings under normal vibration was established,and thermal EHL problem with normal harmonic vibration of a rolling element was simulated numerically.The difference of thermal EHL between Newtonian and non-Newtonian fluid was compared.And effects of the amplitude of normal vibration and the initial load on the properties of dynamic oil film lubrication were analyzed.Results show that,during the squeezing process,the greater the amplitude,the larger the central pressure,the central temperature,the friction coefficient and the load coefficient,but the thinner the central film,However,variation trend is opposite during the separation process.Thirdly,considering temperature boundary conditions of the bearing component,a non-Newtonian thermal EHL model under load impact and normal vibration conditions was established based on the temperature field of rolling bearings.The influence of the bearing component temperature on the lubricating performance was analyzed.Considering the factors that affect the oil film temperature,thermal failure conditions of the dynamic oil film in ball bearings under extreme conditions were investigated.Results show that,when the rolling element temperature is higher,the film is thinner.Under extreme conditions,the first critical temperature of the boundary film desorption is attained for the inner ring,and the mixed lubrication status is for the contact between the inner ring and the rolling element.Finally,with an optical interference EHL test rig,variations in the EHL oil film under the velocity impact were investigated,and the difference of oil film shape and thickness with different oils was compared.Effects of the running time in constant speed phase for the oil film were studied as well.Results show that,in the acceleration phase,the film thickness with different oil products increases from the inlet area,whereas the response of the film thickness is relatively slow in the contact region and at the exit.During the later period of the acceleration and in the constand speed phase,thicker film is generated for higher viscosity oil product.In the deceleration phase,the film thickness of the three oil products begins to decrease in the inlet,and the response speed for PB680 is slower.In addition,the film thickness with different oil products in the constant speed maintenance phase increases firstly and then decreases.