This landscape identifies 202 patent families published between 2015 and mid-2026 that combine reciprocating or piston compressor terminology with cylinder, crankshaft or connecting-rod design claims. That figure counts families rather than raw document publications, which gives a fairer picture of distinct inventions since it neutralises continuation filings and multi-jurisdiction duplicates. The count spans core compressor IPC classes plus adjacent engine, steam, refrigeration and bearing classes where compressor structural hardware is claimed as a sub-assembly.

The trend is flat rather than growing: filings rose from 2 in 2017 to a peak of 9 in 2022, and no subsequent year has exceeded that midpoint. That pattern is more consistent with a mature, already well-claimed structural space than an emerging one. Because patent publication typically lags filing by around 18 months, the apparent drop in the most recent year should not be read as a real decline until later data confirms it.

F04B, covering positive-displacement pumps, carries the largest share at 107 records, followed by F01B reciprocating machines and engines at 52. Adjacent classes — F02B internal-combustion engines, F01K steam and thermal power, F01C rotary-piston machines, F16C shafts and bearings, F01L valve gear and F25B refrigeration — each contribute a meaningful but smaller slice. This spread shows that structural compressor hardware is frequently claimed inside a larger power, thermal or refrigeration system rather than as a standalone device.

The dataset shows filing concentrated among a handful of named assignees and individual inventors, with a long tail of single-filing entrants. Recent-year momentum data shows every tracked assignee, including the most active corporate and individual filers, at zero filings in the latest year — a pattern best explained by publication lag rather than an actual halt in development. Co-assignee analysis found 10 collaborative pairs, the strongest being an inventor pairing appearing together on six filings.

The clearest openings sit in the overlap zones rather than the core: counter-rotating dual-crank balancing hardware, dry-running piston seal geometry, bearing-integrated connecting-rod structures that cross into F16C, valve-timing coupled directly to crank position, and refrigeration-duty cylinder cooling paths. These branches show thinner direct claim density than the core F04B and F01B cylinder-and-crank geometry, making them more promising starting points for a new filing than the heavily claimed core.