# US 4,380,902 A · Sealed oil-backed displacer suspension diaphragm

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- Number: US 4,380,902 A
- Document ID: US4380902A
- Status: Granted
- Kind: A
- Application number: 06/270,892
- Filed: 1981-06-05
- Granted: 1983-04-26
- Earliest claimed: 1981-06-05
- Assignees: Mechanical Technology Incorporated
- Inventors: Nicholas G. Vitale
- Web page: https://patentgrep.com/patent/US4380902A

## CPC

- F02G 1/053: Component parts or details
- F02G 1/0435: {the engine being of the free piston type}
- F02G 2243/24: with free displacers
- F02G: HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS (steam engine plants, special vapour plants, plants operating on either hot gas or combustion-product gases together with other fluid F01K; gas-turbine plants F02C; jet-propulsion plants F02K); USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR

## Abstract

A diaphragm suspension system for a free piston Stirling engine includes a transverse wall across the cold end of the displacer. An upper diaphragm is attached to the displacer shell above the transverse wall, and a support diaphragm is attached at its center to a partition fixed to the engine vessel, and is attached at its peripheral edge to the lower end of the displacer. A lower oil cavity is defined between the transverse wall and the support diaphragm, and an upper oil cavity is defined between the upper diaphragm and the transverse wall. A cylinder is formed in the transverse wall communicating between the oil cavities, and a piston is disposed in the cylinder and is fixed to the partition. When the displacer moves, the piston remains stationary and compensates for the oil displacement caused by the support diaphragm flexing into and out of the oil cavity, so the support diaphragm experiences only or primarily displacement induced stress rather than pressure induced stress. The top oil cavity ensures that leakage past the piston will be equal in both directions, and also provides an additional spring effect to return the displacer toward its midstroke position.

## Claims

### Claim 1

A displacer suspension system for a free piston Stirling engine having a hermetic vessel enclosing a working space adapted to contain a working gas and in which oscillates a displacer for displacing working gas back and forth between an expansion space in said working space serially through a heater, a regenerator, a cooler, and into a compression space in said working space, and then back again; said suspension system comprising:
a first diaphragm fixed at its center and outer edge to said vessel and said displacer so that said diaphragm flexes between concave and convex shapes when said displacer oscillates;
a rigid wall fastened to said displacer and extending generally parallel to said diaphragm; said rigid wall and said diaphragm bounding two sides of a first cavity adapted to be filled with an incompressible liquid;
a piston mounted in said vessel and axially fixed with respect thereto;
a cylinder formed in said rigid wall and receiving said piston for relative axial movement therewith;
a second diaphragm sealed at its outer peripheral edge to said vessel and having one face defining with said rigid wall a second cavity adapted to be filled with said incompressible liquid, said cylinder communicating between said cavities and being substantially sealed by said piston, said second diaphragm flexing when said displacer moves from its center position and storing energy in so flexing that is returned to said displacer to restore said displacer from an extreme axial position toward said center position;
whereby axial oscillation of said displacer causes said cylinder to reciprocate relative to said piston and causes said first diaphragm to flex between said concave and convex shapes, thereby displacing liquid in said first cavity, which liquid displacement is accommodated by movement of said piston in said cylinder, and leakage between said cylinder and said piston being contained by and returned from said second cavity.

### Claim 2 (depends on 1)

The displacer suspension system defined in claim 1, wherein said first diaphragm is connected at the outer peripheral edge thereof to said displacer, and connected at its center to said vessel.

### Claim 3 (depends on 2)

The displacer suspension system defined in claim 2, further comprising a rigid, aperatured partition fastened to said vessel between said first diaphragm and said power piston and attached to said center of said displacer.

### Claim 4 (depends on 1)

The displacer suspension system defined in claim 1, further comprising a top rigid wall facing the other face of said second diaphragm and defining therewith a gas spring cavity.