Internal gears with small tooth number difference are widely used as core component in robotics, medical, and other fields. The clearance between the entire meshing teeth is much smaller compared with other gear transmissions, indicating that the entire tooth profile can significantly affect the mixed elastohydrodynamic lubrication (EHL) state of a certain meshing point. Thereby, available lubrication analysis is limited with the assumption of effective radius at each meshing point. In the present study, the entire tooth profile with gear flank modification is studied to improve lubricating characteristics. A mixed EHL model for predicting the film, pressure, power loss, and subsurface stress is presented with consideration of the entire tooth geometry. We find that the tooth geometry away from the meshing location shows a remarkable influence on the film and pressure distribution as well as power loss of tooth rubbing interface, which is commonly unrecognised in previous study. Optimization of modification parameters is observed under different operating conditions, highlighting the critical role of entire tooth geometry in mixed EHL behaviour for internal gears with small tooth number difference.
Existing studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions. However, most lubricated transmission components operate in the mixed lubrication region, indicating that both the asperity contact and film lubrication exist on the rubbing surfaces. Herein, a novel method is proposed to evaluate the time-varying contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions. This method is sufficiently robust for addressing any mixed lubrication state regardless of the severity of the asperity contact. Based on this method, the transient mixed contact stiffness and damping of spiral bevel gears are investigated systematically. The results show a significant difference between the transient mixed contact stiffness and damping and the results from Hertz (dry) contact. In addition, the roughness significantly changes the contact stiffness and damping, indicating the importance of film lubrication and asperity contact. The transient mixed contact stiffness and damping change significantly along the meshing path from an engaging-in to an engaging-out point, and both of them are affected by the applied torque and rotational speed. In addition, the middle contact path is recommended because of its comprehensive high stiffness and damping, which maintained the stability of spiral bevel gear transmission.
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