The tracked leaderboard includes established compressor and HVAC manufacturers such as Gree, Hitachi, Daikin, Kobe Steel and Kaishan, alongside Carrier working jointly with a named inventor. None of these assignees shows filing activity in the latest tracked year, which reflects both a general slowdown after the 2017 peak and the roughly 18-month lag between filing and publication. No single assignee holds a dominant share of the 78 tracked families; the field reads as fragmented across several established compressor makers rather than led by one company.

The dataset shows filings peaking at 7 in 2017 before settling into a lower, roughly flat pattern, with the 2022 midpoint at 4. This is consistent with a sub-field where the core mechanical approaches — rotor tooth profile control, pulsation damping and vibration isolation — were substantially claimed in the years following that peak, leaving less open ground for new filings. The apparent decline after 2017 should be read alongside publication lag, since the most recent one to two years in any dataset are always understated at the time of capture.

Rotor whine reduction generally targets the tonal noise generated by meshing rotor teeth and gas pulsation at the compression chamber, often addressed through rotor tooth profile design — the subject of the most-cited records in this dataset. Pulsation attenuation instead targets pressure pulsations in the discharge gas stream, typically handled with damper chambers or muffler-type structures downstream of the compression stage, as seen in patents like the pulsation damper record in this set. Both mechanisms contribute to overall compressor noise, but they are addressed with different hardware and are often claimed separately.

This dataset anchors on F04C (rotary-piston pumps), which covers all 78 tracked records and is the primary classification for screw compressor mechanism patents. Supporting classes worth checking include F01C (rotary-piston machines generally), F03C (positive-displacement hydraulic engines), F25B (refrigeration and heat pumps, relevant when the compressor sits inside a refrigeration circuit), F04B (positive-displacement pumps) and F16C (shafts, bearings and couplings) for vibration transfer at the mechanical interface. A thorough freedom-to-operate search should not stop at F04C alone, since noise and vibration solutions sometimes get classified under the downstream application rather than the compressor mechanism itself.

The flat-to-declining filing trend since 2017 and the concentration of citations on decade-old rotor tooth-profile patents suggest the most obvious mechanical routes are already densely claimed, particularly around rotor form and integral pulsation damping. However, the thin IPC spillover into standalone vibration-isolation mounts, bearing-level vibration transfer, and hydraulic-drive variants suggests these adjacent branches carry lighter patent density. A practitioner considering a new filing should map a specific concept against these thinner branches rather than against the crowded rotor-profile core.