A comparative analysis of the measured sound pressure levels for dry and grease-lubricated conditions in Steel–POM and POM–PA66 gear pairs is presented in Figure 13, with corresponding vibration levels summarized in Figure 14. While differences at the lowest tested rotational speed were relatively minor, a marked improvement in NVH performance was observed at intermediate (L3, L4) and high (L5, L6) speed levels under lubricated conditions.

Overall, the application of grease exhibited a beneficial effect, acting as an additional damping medium within the gear tooth contact zone. This led to a reduction in impact-induced noise and vibration, as well as a suppression of stick-slip phenomena. The improved dynamic response is attributed to the lubricating film’s capacity to mitigate direct surface interactions and absorb vibratory energy during meshing. In between measured sound pressure level for dry and grease lubricated tests with Steel–POM and POM–PA66 combinations are shown in Fig. 13. Measured vibration levels are summarized in Fig. 14. While at the lowest tested rotational speed the differences were not so evident a quite significant improvement could be observed at the medium (L3, L4) and high (L5, L6) rotational speeds. In general, a beneficial impact of grease could be observed, which can be considered as an effect of an additional damping element in the contact, generating less impact noise and vibrations, while also reducing the stick-slip effect.