3D Transient Line-contact EHL Modeling Of Involute Spur Gears

Gear is among the key components of modern transmissions; they transmit motionand power in mechanical transmission for navigation, aviation, transportation vehicles.Proper design of gear lubrication status is very important for guarantee the service lifeof gears.The work reported in this thesis is a portion in the projects from the State KeyLaboratory of Mechanical Transmission of Chongqing University, titled “Study onmechanical transmission performance under typical working conditions” and “Typicaltransmission contact failure and basis of material change.” Exploration of the latestaccomplishments in elastohydrodynamic lubrication (EHL) research and the frontier ofrelated fields suggest the proper lubrication modeling of line-contact gears, such as spurgears, should consider the real surface topography from machining, The research aimsto develop a three-dimensional (3D) transient line-contact EHL model of spur gears forin-depth understanding of gear lubrication and supporting design of gears with longservice life.First, a smooth-surface point-contact EHL model is studied, and the influences ofload and entraining speed on contact pressure, film thickness and other tribologicalparameters are analyzed. The results show the horseshoe feature in the film thicknesscontour and the spike in the pressure distribution. The total load and entraining speedhave notable influences on fluid pressure, film thickness and friction coefficient.Secondly, the basic characteristics of3D transient line-contact EHL model areexplored and the influences of entraining speed, surfaces topography and roughnessorientation are studied. The results show that the3D transient line-contact model cansuccessfully deal with different surfaces in lubrication problems, such as those ofsmooth surface, sinusoidal surface, and real machined engineering surfaces. Entrainingspeed and roughness orientation greatly affect the film thickness.Then, a novel3D transient line-contact EHL model for involute spur gears is builtbased on the above3D line-contact EHL model. This model enables the analyses ofcontact pressure and film thickness along the line of action with the consideration of allthe time-dependent parameters, such as load, surface velocities, radii of curvature andslid to roll ratio. The influence of pinion rotating speed, torque, and surface topographyon film thickness are investigated. In addition, the influence of root mean square (RMS) roughness and surface topography on the film thickness ratio and contact ratio are alsostudied. The results suggest that the torque has a more significant influence on the filmthickness distribution along the line of action, than that of the pinion rotating speed. Thefilm thickness ratio and contact ratio are greatly affected by the RMS roughness andsurface topography.