Numerical Analysis of Wear on Hypoid Gears: Influence of Lubrication properties and Wear Partition Factor

Of all the mechanisms designed for crossed axes transmission, hypoid gears are known to show high sliding speeds, resulting from screwing relative motion, that can affect the resistance of the teeth surface to damage, as pitting. Thus, manufacturers of hypoid gears invest in complex and expensive machinery for optimizing the flank micro-geometry, to achieve higher mechanical resistance to pitting and ensure smoother operations. High sliding speeds associated with hypoid gears also cause more severe wear, which can affect the desired teeth micro-topography after a certain amount of meshing cycles, typically in the order of millions. Therefore, wear needs to be carefully considered for gears operating in long-life applications. Expensive experimental tests can be limited by exploiting numerical wear predictions, particularly in the design phase, to estimate the duration and quality degradation of surface topology. Numerical wear models require a wear law for estimating the amount and distribution of the material removed from the contact surfaces. In case of adhesive/abrasive wear, the Archard wear law is commonly adopted; it provides a simple relation between wear depth, sliding distance, and contact pressure. The more complex part of the procedure involves the discretization of three main steps: wear estimation, geometry update due to material removal and the contact analysis on the worn surfaces. These steps are mutually dependent in a continuous process: wear changes the geometry of mating teeth that in turn can significantly alter the pressure pattern and the area of the sliding zone. This, in turn, affects the evolution of wear depth. Reducing this complex phenomenon in a sequence of discrete steps should therefore be carefully checked. A previous work [1] presented wear predictions for both the gear and pinion teeth of a hypoid gear, focusing on the impact of the frequency at which the surface geometry is updated on contact and wear parameters. The analysis yielded both predictable and unpredictable results: while the pattern spread along both the profile and the lengthwise direction, it also exhibited an unexpected concentration of contact pressures and a shift towards the tip. Further analysis is needed to verify the validity of these findings.