A Design-of-Experiments Framework for Characterizing Functional Surface Parameters Relevant to Pitting and Micropitting in Shaving-Finished Planetary Gear Flanks

 Pitting and micropitting are dominant surface-fatigue failure modes observed in shaving-finished automotive planetary gearsets, yet current production drawings regulate flank roughness solely through the arithmetic mean parameter Ra (ISO 4287), which cannot distinguish between peak-dominant and valley-dominant surface topologies at equal Ra. This ambiguity limits the ability to predict and manage pitting-related damage during volume production, motivating the need for a more discriminative surface characterization approach.

 A design of experiments (DOE) is proposed to evaluate the influence of ISO 13565-2 functional surface parameters - core roughness depth (Rk), reduced peak height (Rpk), reduced valley depth (Rvk) - together with skewness (Rsk), on pitting and micropitting behavior in a six-speed automatic transmission planetary gearset. Two primary factors are considered: surface group (neutral, peak-dominant, and valley-dominant) and sun–planet roughness matching (symmetric versus asymmetric pairing). Testing is to be conducted on a previously validated planetary-gearset pitting-reproduction rig, with surface topology measured at both the pitch-circle-diameter and true-involute-form locations using a gear-measuring instrument equipped with a roughness-extension module capable of outputting the full ISO 4287/ISO 13565-2 parameter set.

 Instrumentation validation on production gear flanks confirms that the functional surface parameters Rk, Rpk, Rvk, and Rsk can be reliably measured and are relevant to characterizing pitting and micropitting susceptibility in planetary gear contacts, capturing asymmetries in surface height distribution that are not resolved by Ra alone. This measurement capability establishes the technical basis required for the subsequent full-scale DOE evaluation of their statistical influence.

 This paper establishes the measurement and experimental basis for extending gear-flank roughness regulation beyond Ra to functional parameters, offering a pathway toward manufacturing-relevant, pitting- and micropitting-resistant surface specifications without requiring any change to the existing shaving process.