F02B 71/00
Free-piston engines
Official title: Free-piston engines; Engines without rotary main shaft
F02B71/00 (Free-piston engines) appears on 445 US grants and 275 published applications in this corpus.
Search patents in F02B- Granted patents
- 445
- Published applications
- 275
- Assignees
- 134
- Inventors
- 518
- Latest grant
- 25 Aug 2026
Filings by year
| Year | Granted patents | Published applications |
|---|---|---|
| 1976 | 9 | 0 |
| 1977 | 7 | 0 |
| 1978 | 5 | 0 |
| 1979 | 4 | 0 |
| 1980 | 4 | 0 |
| 1981 | 2 | 0 |
| 1982 | 7 | 0 |
| 1983 | 13 | 0 |
| 1984 | 7 | 0 |
| 1985 | 5 | 0 |
| 1986 | 6 | 0 |
| 1987 | 11 | 0 |
| 1988 | 8 | 0 |
| 1989 | 8 | 0 |
| 1990 | 7 | 0 |
| 1991 | 2 | 0 |
| 1992 | 4 | 0 |
| 1993 | 3 | 0 |
| 1994 | 5 | 0 |
| 1995 | 6 | 0 |
| 1996 | 8 | 0 |
| 1997 | 4 | 0 |
| 1998 | 7 | 0 |
| 1999 | 8 | 0 |
| 2000 | 14 | 0 |
| 2001 | 19 | 4 |
| 2002 | 16 | 10 |
| 2003 | 11 | 11 |
| 2004 | 8 | 6 |
| 2005 | 19 | 20 |
| 2006 | 11 | 15 |
| 2007 | 8 | 6 |
| 2008 | 7 | 6 |
| 2009 | 6 | 10 |
| 2010 | 4 | 9 |
| 2011 | 3 | 12 |
| 2012 | 8 | 13 |
| 2013 | 9 | 13 |
| 2014 | 11 | 14 |
| 2015 | 12 | 4 |
| 2016 | 8 | 13 |
| 2017 | 12 | 18 |
| 2018 | 13 | 5 |
| 2019 | 14 | 21 |
| 2020 | 18 | 15 |
| 2021 | 13 | 9 |
| 2022 | 11 | 17 |
| 2023 | 19 | 9 |
| 2024 | 10 | 7 |
| 2025 | 8 | 4 |
| 2026 | 3 | 4 |
By publication year. Applications have been published since 2001. 2026 runs to 8 Oct.
Subgroups
Granted patents
Recent patents
- High-power core system25 Aug 2026US 12,719,334 B2Mainspring Energy, Inc.
- Integrated piston assembly for an electric machine2 Jun 2026US 12,646,997 B2Hyliion Holdings Corp.
- Integrated linear generator system17 Feb 2026US 12,556,063 B2Mainspring Energy, Inc.
- Energy storage and conversion in linear generators18 Nov 2025US 12,473,855 B2Mainspring Energy, Inc.
- Linear electromagnetic machine with a stator having stator teeth arranged to provide an anti-clocking force14 Oct 2025US 12,445,029 B2Mainspring Energy, Inc.
- Gas propulsion thrust device1 Oct 2026US 2026/0298134 A1
- Energy storage and conversion in linear generators9 Jul 2026US 2026/0194003 A1Mainspring Energy, Inc.
- Linear electromagnetic machine system5 Mar 2026US 2026/0066758 A1Mainspring Energy, Inc.
- Free piston engine12 Feb 2026US 2026/0043344 A1
- Integrated piston assembly for an electric machine16 Oct 2025US 2025/0323552 A1Hyliion Holdings Corp.
Most cited
By later US patents
- External combustion slidable vane motor with air cushions149US 4,672,813 A1987
- Free-piston engine103US 6,199,519 B1Sandia Corporation · 2001
- Fluid bearing with compliant linkage for centering reciprocating bodies84US 5,525,845 ASunPower Corporation · 1996
- Two stroke cycle engine80US 4,876,991 A1989
- Internal combustion powered tool for driving fastening elements79US 5,213,247 AHilti Aktiengesellschaft · 1993