IP Library Granted Patent US 12,421,890
Granted Patent B2
US 12,421,890 · App. 18/651,352 · Granted Sep 23, 2025

High-efficiency linear generator

Inventors: Adam Simpson (San Francisco, CA); Shannon Miller (Belmont, CA); Matt Svrcek (Redwood City, CA)
Assignee: Mainspring Energy, Inc.
F02B71/04F01B11/001F02B25/08F02B63/041F02B71/00F02B75/282H02K7/1892H02K35/02F01B7/02F01B11/007F02B1/12
View Patent ↗
Loading inventors, assignments & file history…
Monitor This Case
Get email alerts when status or documents change.
Order Certified Copies
Most orders are placed with the USPTO same day — all within 24 business hours.
Order via The Patent Place →
Pre-filled with this patent's details
Quick Facts
Patent No.
US 12,421,890
App. No.
18/651,352
Granted
Sep 23, 2025
Kind
B2
Abstract

Various embodiments of the present invention are directed toward a linear generator, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a reaction section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the reaction section opposite the other piston assembly, each piston assembly including a spring rod and a piston comprising a solid front section adjacent the reaction section and a gas section; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke.

Claims (54)

1. A linear generator comprising:

a piston assembly to reciprocate along a longitudinal axis, the piston assembly comprising:

a rod;

a pair of pistons coupled to opposite ends of the rod;

a translator attached to the piston assembly;

a stator arranged to convert kinetic energy of the piston assembly into electrical energy;

a first section in contact with a first axial side of the piston assembly in which a first force is generated that acts on the piston assembly in a first axial direction;

a second section in contact with a second axial side of the piston assembly, opposite to the first axial side in which a second force is generated that acts on the piston assembly in a second axial direction, opposite the first axial direction,

wherein:

the first force and the second force cause the piston assembly to translate in the first axial direction or the second axial direction,

the linear generator operates according to a two stroke cycle comprising a first stroke and a second stroke,

the first force is sufficient to complete the first stroke, and

the second force is sufficient to complete the second stroke.

2. The linear generator of claim 1 , wherein the first axial side of the piston assembly comprises a first axial side of a first piston of the pair of pistons, and wherein the second axial side of the piston assembly comprises a second axial side of the second piston of the pair of pistons, the linear generator further comprising:

a first back section in contact with a second axial side of the first piston of the pair of pistons;

a second back section in contact with a second axial side of the second piston of the pair of pistons, wherein the first back section comprises pressurized gas.

3. The linear generator of claim 2 , wherein the second back section comprises gas.

4. The linear generator of claim 1 , wherein the stator is arranged between the pair of pistons.

5. The linear generator of claim 4 , wherein the translator is attached to the rod.

6. The linear generator of claim 1 , wherein a first intake port and a second intake port deliver a fuel mixture to the first section and to the second section, respectively.

7. The linear generator of claim 1 , further comprising one or more gas make-up ports, wherein each of a first exhaust port and a second exhaust port are to provide exhaust gas to the one or more gas make-up ports for exhaust gas recycling.

8. The linear generator of claim 7 , further comprising:

a first back section in contact with a second axial side of the first piston of the pair of pistons; and

a second back section in contact with a second axial side of the second piston of the pair of pistons, wherein at least one of the one or more gas make-up ports is in communication with at least one of the first section, the second section, or the first back section.

9. The linear generator of claim 1 , wherein the first section comprises an ignition section.

10. The linear generator of claim 1 , wherein the first section and the second section each comprise one or more of a respective gas removal port or a respective gas make-up port.

11. The linear generator of claim 1 , wherein the first section comprises a gas, and wherein a compression of the gas occurs as the piston assembly approaches top-dead-center.

12. A method of operating a linear generator, the linear generator comprising:

a piston assembly to reciprocate along a longitudinal axis, the piston assembly comprising:

a rod;

a pair of pistons coupled to opposite ends of the rod;

a translator attached to the piston assembly;

a stator arranged to convert kinetic energy of the piston assembly into electrical energy;

a first section in contact with a first axial side of the piston assembly in which a first force is generated that acts on the piston assembly in a first axial direction; and

a second section in contact with a second axial side of the piston assembly, opposite to the first axial side in which a second force is generated that acts on the piston assembly in a second axial direction, opposite the first axial direction;

the method comprising:

causing, using the first force and the second force, the piston assembly to translate in the first axial direction or the second axial direction, and

operating the linear generator operates according to a two stroke cycle comprising a first stroke and a second stroke, wherein:

the first force is sufficient to complete the first stroke, and

the second force is sufficient to complete the second stroke.

13. The method of claim 12 , wherein the first axial side of the piston assembly comprises a first axial side of a first piston of the pair of pistons, and wherein the second axial side of the piston assembly comprises a second axial side of the second piston of the pair of pistons, the linear generator further comprising:

a first back section in contact with a second axial side of the first piston of the pair of pistons;

a second back section in contact with a second axial side of the second piston of the pair of pistons, wherein the first back section comprises pressurized gas.

14. The method of claim 13 , wherein the second back section comprises gas.

15. The method of claim 12 , wherein the stator is arranged between the pair of pistons.

16. The method of claim 15 , wherein the translator is attached to the rod.

17. The method of claim 12 , wherein a first intake port and a second intake port deliver a fuel mixture to the first section and to the second section, respectively.

18. The method of claim 17 , further comprising providing exhaust gas to one or more gas make-up ports of the linear generator for exhaust gas recycling using at least one of a first exhaust port or a second exhaust port of the linear generator.

19. The method of claim 18 , the linear generator further comprising:

a first back section in contact with a second axial side of the first piston of the pair of pistons; and

a second back section in contact with a second axial side of the second piston of the pair of pistons, wherein at least one of the one or more gas make-up ports is in communication with at least one of the first section, the second section, or the first back section.

20. The method of claim 12 , wherein the first section comprises an ignition section.

21. The method of claim 12 , wherein the first section and the second section each comprise one or more of a respective gas removal port or a respective gas make-up port.

22. The linear generator of claim 12 , further comprising compressing a gas within the first section as the piston assembly approaches top-dead-center.

Assignments (3)
SECURITY INTEREST Recorded Jun 6, 2025
From: MAINSPRING ENERGY, INC.
To: AVENUE VENTURE OPPORTUNITIES FUND II, L.P., AS AGENT
Reel/Frame 071499/0428 →
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded May 1, 2024
From: SIMPSON, ADAM; MILLER, SHANNON; SVRCEK, MATT
To: ETAGEN, INC.
Reel/Frame 067283/0877 →
CHANGE OF NAME Recorded May 1, 2024
From: ETAGEN, INC.
To: MAINSPRING ENERGY, INC.
Reel/Frame 067288/0673 →
Continuity (12)
Continuation 18077007 · Dec 7, 2022
Continuation 17106695 · Nov 30, 2020
Continuation 16274003 · Feb 12, 2019
Continuation 16016393 · Jun 22, 2018
Continuation 15390431 · Dec 23, 2016
Continuation 14964463 · Dec 9, 2015
Continuation 14160359 · Jan 21, 2014
Continuation 13298206 · Nov 16, 2011
Continuation In Part 13102916 · May 6, 2011
Continuation In Part 12953277 · Nov 23, 2010
Continuation In Part 12953270 · Nov 23, 2010
Related Publication 20240287930A1 · Aug 29, 2024
References Cited (36)
US 2814551A · Jan et al. · 1957 [cited by applicant]
US 4924956A · Deng et al. · 1990 [cited by applicant]
US 5775273A · Beale · 1998 [cited by applicant]
US 6199519B1 · Van Blarigan · 2001 [cited by applicant]
US 6532916B2 · Kerrebrock · 2003 [cited by applicant]
US 6748907B2 · Malmquist et al. · 2004 [cited by applicant]
US 7082909B2 · Graef et al. · 2006 [cited by applicant]
US 20020139323A1 · Kerrebrock · 2002 [cited by applicant]
US 20050081805A1 · Novotny · 2005 [cited by applicant]
US 20050109295A1 · Kaneko et al. · 2005 [cited by applicant]
US 20060124083A1 · Niiyama et al. · 2006 [cited by applicant]
US 20060196456A1 · Hallenbeck · 2006 [cited by applicant]
US 20080036312A1 · Max et al. · 2008 [cited by applicant]
US 20080271711A1 · Cheeseman · 2008 [cited by examiner]
US 20090031991A1 · Lindgarde · 2009 [cited by applicant]
US 20090179424A1 · Yaron · 2009 [cited by examiner]
US 20100212311A1 · McQuary et al. · 2010 [cited by applicant]
US 20120001499A1 · Makino et al. · 2012 [cited by applicant]
US 20120024264A1 · Mikalsen et al. · 2012 [cited by applicant]
US 20120112468A1 · Najt et al. · 2012 [cited by applicant]
US 20150295485A1 · Sutani et al. · 2015 [cited by applicant]
CN 101473106A · 2009 [cited by applicant]
EP 0037631A1 · 1981 [cited by applicant]
GB 2476495A · 2011 [cited by applicant]
JP 2004301138A · 2004 [cited by applicant]
JP 2012202386A · 2012 [cited by applicant]
JP 2012202387A · 2012 [cited by applicant]
WO 9901651A1 · 1999 [cited by applicant]
WO 0145977A2 · 2001 [cited by applicant]
U.S. Appl. No. 18/518,321, filed Nov. 22, 2023, Christopher Gadda. [cited by applicant]
Ashley, Steven, “Free-Piston IC Generator Developed for Range-Extender Hybrids,” Automotive Engineering Magazine, Jul. 3, 2013, pp. 1-2, SAE International. [cited by applicant]
Blarigan; “Adanced Internal Combustion Engine Research,” DOE Hydrogen Program Review NREL-CP-570-28890 (2000); pp. 1-19. [cited by applicant]
Blarigan; “Free-Piston Engine, Transportation Energy Center” FY 2009 DOE Vehicle Technologies Program Annual Merit Review; May 19, 2009. [cited by applicant]
Kim, “Specific Power Estimations for Free-Piston Stirling Engines,” American Institute of Aeronautics & Astronautics, (Jun. 2006); pp. 1-8. [cited by applicant]
Mikalsen et al., “A Review of Free-Piston Engine History and Applications,” Applied Thermal Engineering 27 (2007); pp. 2339-2352. [cited by applicant]
Schreiber, “Development Considerations on the Free-Piston Stirling Power Converter for Use in Space,” NASA/TM (May 2007) 214805; 39 pgs. [cited by applicant]