Power plants – Motor operated by expansion and/or contraction of a unit of... – Unit of mass is a gas which is heated or cooled in one of a...
Reexamination Certificate
2000-01-03
2001-03-27
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Unit of mass is a gas which is heated or cooled in one of a...
C060S519000
Reexamination Certificate
active
06205782
ABSTRACT:
The invention relates to Stirling cycle machines and in particular to a piston employed in such a machine. In referring to a Stirling cycle machine we include those machines which operate on a cycle resembling the Stirling cycle but with some overlap and merging of the individual phases of the classical Stirling cycle. The invention will be described primarily by reference to Stirling cycle heat engines which generate mechanical power from applied heat but also applies to Stirling cycle heat pumps. Typically the invention is applied to the kind of piston often referred to as a displacer. As an alternative or in addition, in a Stirling cycle engine of the kind having a separate power piston connected to the hot end of the displacement volume, the invention may also be applied to the power piston. The invention will be described primarily in connection with its application to a displacer piston.
The Stirling cycle engine has well known attractions as compared with an internal combustion engine but has not been adopted generally because of certain practical difficulties. One such difficulty is provision of an effective long-life seal for a piston in its cylinder at the hot end of the engine in an environment where conventional lubricants cannot be used. One established practice is to employ a piston with a deep domed crown and to provide seals well below the crown and thus well away from the main hot area. However, the radiused and divergent upper part of the annular gap around the piston encourages hot charge gas to enter the annulus between the cylinder wall and the piston. Pumping losses occur in this annulus. In addition, the transfer of hot gas into the annulus tends to transfer heat down towards the seal, reducing the life and efficiency of the seal. Also, shuttle losses occur on reciprocation of the piston by heat transfer of a generally conductive nature from the hot cylinder wall to the piston when near top dead centre and corresponding heat transfer from the heated piston to a cooler part of the cylinder wall when the piston is the heated piston to a cooler part of the cylinder wall when the piston is near bottom dead centre.
An object of the invention is to provide an improved arrangement of piston.
According to one aspect of the invention a Stirling cycle machine in which a piston reciprocates in a cylinder to define a hot chamber of the machine and in which heat exchange for working fluid in the hot chamber is effected while the working fluid is outside the hot machine chamber in a flow path communicating with that chamber, the piston having a concave crown forming a surface of the hot chamber characterised in that the concave crown surface of the piston joins a cylindrical external surface of the piston to define an acute outer peripheral edge to the piston.
In order to establish a small volume in the hot chamber at top dead centre of the piston, the end wall of a cylinder forming the hot chamber has a generally corresponding convex internal surface.
According to a second aspect of the invention a Stirling machine of the kind to which the invention specifically relates is characterised in that the piston incorporates a land of larger diameter than the general diameter of the piston around its upper periphery.
REFERENCES:
patent: 1524894 (1925-02-01), Thomson
patent: 3760592 (1973-09-01), Neelen
patent: 4285665 (1981-08-01), Enga
patent: 5433078 (1995-07-01), Shin
patent: 5857436 (1999-01-01), Chen
patent: 0252026 (1988-01-01), None
patent: 1044103 (1953-11-01), None
patent: 1306911 (1963-02-01), None
patent: 91/16534 (1991-10-01), None
Davis and Bujold
Nguyen Hoang
Sustainable Engine Systems Ltd.
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