The filing trend in this dataset peaked at 31 filings in 2017, held near 30 through 2022, and has since tapered to 8 in the latest partial year. That pattern is consistent with a technology whose core mechanical claim space — rotor and stator construction, in particular — filled up during the mid-2010s rather than one that is losing commercial relevance. Because publication lags filing by roughly 18 months, the most recent one to two years understate true activity, so the drop should not be read as a full stop. Anyone assessing current activity should weight the 2022-2023 data more heavily than the tail years.

Both motor types appear in the same search because they share the core problem this dataset targets: delivering torque without rare-earth magnets while managing acoustic noise and control complexity. Switched reluctance (SRM) filings tend to concentrate on discrete rotor pole geometry and current-waveform control to reduce torque ripple and noise, as seen in the representative Tokyo Institute of Technology filing. Synchronous reluctance filings more often address continuous rotor lamination design and higher torque density for variable-speed drives. The underlying IPC classes (H02K17, H02K19, H02P25) capture both without separating them, so a sub-search within this corpus is needed to isolate one motor type cleanly.

The leading assignees tracked in this dataset include General Electric, Mitsubishi Electric, Aisin Seiki, Switched Reluctance Drives, Toshiba and Virginia Tech Intellectual Properties, spanning industrial motor manufacturers, automotive suppliers and a university IP office. None of these six show filings in the most recent tracked year, which reflects the reporting lag rather than an exit from the field. Virginia Tech's IP office stands out for its co-filing pattern, appearing in the two strongest co-assignee relationships in the dataset alongside named inventors rather than corporate co-assignees.

Relative to the 501-record density in core motor construction (H02K), several adjacent branches carry noticeably lighter claim coverage: radial force harmonic shaping specifically for acoustic noise control, rotor bar geometry aimed at rare-earth-free torque density, control-complexity reduction tailored to SRM drive electronics, and acoustic noise measurement integrated directly into the control feedback loop. These are not unclaimed, but the filing density is thin enough that a well-drafted claim combining a specific harmonic-order target with a measurable noise or torque outcome has room to stand apart from the crowded rotor-geometry prior art.

US11784599B2, assigned to Tokyo Institute of Technology and published in 2023, claims an acoustic noise reduction system that derives an optimum current waveform to minimise radial force amplitude at a specific harmonic order while still meeting an average-torque condition. It does not block all noise-reduction approaches for switched reluctance motors — it blocks that specific mechanism of harmonic-targeted current waveform shaping tied to radial force at stator teeth. Designs that reduce noise through mechanical damping, alternative pole counts, or different control variables (rather than harmonic-order current shaping) sit outside its claim scope, though a freedom-to-operate review of the full claim set is needed before relying on that distinction.