Lubrication mechanisms of rubbing interface in internal meshing teeth with small clearance

Abstract

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.

A Review of Mixed Lubrication Modelling and Simulation

“…In the average flow model, for solving Reynold's equation in terms of average pressure between two rough interacting surfaces, film thickness is defined as the thickness of the local film is an addition of nominal film thickness h and wall roughness 𝛿 1 , 𝛿 2 which is a random roughness amplitude measured from the mean level (see figure 4). Wall roughness parameter (𝛿 1 and 𝛿 2 ) assumed to have Gaussian distribution of height with zero mean and standard deviations 𝜎 1 and 𝜎 2 with combined root mean square value 𝜎 = √𝜎 1 2 + 𝜎 2 2 . Surface roughness effect depends on the value of lambda ratio (𝜆 = ℎ 𝜎 ⁄ ).…”

“…Physical conditions between the contact are very complex for example collision of surface asperities, mechanical deformation, lubricant flow, and chemical reactions. The Lubricant theory has been proposed to model and analyses the film thickness and pressure variations between the contact area [2]. REVIEW This tribological area is widespread for example, rolling element bearings, gears, cam and followers, contact between human joints, etc.…”

A Practical Approach to Gear Design and Lubrication: A Review

“…The value of the backlash is a very important parameter since it affects both the stiffness and the lubrication condition of the mating gears [57,58].…”