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
1997-07-14
2001-09-04
Lazarus, Ira S. (Department: 3743)
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...
C060S517000, C060S526000, C062S006000, C165S145000, C165S176000, C165S910000, C029S888010, C029S888060, C029S890046, C029S890052
Reexamination Certificate
active
06282895
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This invention is related to a heat engine and particularly to an improved Stirling cycle engine incorporating numerous refinements and design features intended to enhance engine performance, manufacturability, and reliability.
The basic concept of a Stirling engine dates back to a patent registered by Robert Stirling in 1817. Since that time, this engine has been the subject of intense scrutiny and evaluation. Various Stirling engine systems have been prototyped and put into limited operation throughout the world. One potential application area for Stirling engines is for automobiles as prime mover or engine power units for hybrid electric applications. Such applications place extreme demands on Stirling engine design. Due to the wide acceptance of spark ignition and Diesel engines, to gain acceptance, a Stirling engine must show significant advantages over those types, such as a dramatic enhancement in fuel efficiency or other advantages. In addition, reliability and the ability to manufacture such an engine at a low cost are of paramount importance in automotive applications. Similar demands are present in other fields of potential use of a Stirling engine such as stationary auxiliary power units, marine applications, solar energy conversion, etc.
Stirling engines have a reversible thermodynamic cycle and therefore can be used as a means of delivering mechanical output energy from a source of heat, or acting as a heat pump through the application of mechanical input energy. Using various heat sources such as combusted fossil fuels or concentrated solar energy, mechanical energy can be delivered by the engine. This energy can be used to generate electricity or be directly mechanically coupled to a load. In the case of a motor vehicle application, a Stirling engine could be used to directly drive traction wheels of the vehicle through a mechanical transmission. Another application in the automotive environmental is for use with a so-called “hybrid” vehicle in which the engine drives an alternator for generating electricity which charges storage batteries. The batteries drive the vehicle through electric motors coupled to the traction wheels. Perhaps other technologies for energy storage could be coupled to a Stirling engine in a hybrid vehicle such as flywheel or thermal storage systems, etc.
The Assignee of the present application, Stirling Thermal Motors, Inc. has made significant advances in the technology of Stirling machines for a number of years. Examples of such innovations include the development of a compact and efficient basic Stirling machine configuration employing a parallel cluster of double acting cylinders which are coupled mechanically through a rotating swashplate. In many applications, a swashplate actuator is implemented to enable the swashplate angle and therefore the piston stroke to be changed in accordance with operating requirements.
Although the Assignee has achieved significant advances in Stirling machine design, there is a constant need to further refine the machine, particularly if the intended application is in large volume production. For such applications, for example in motor vehicles, great demands are placed on reliability and cost. It is well known that motor vehicle manufacturers around the world have made great strides in improving the reliability of their products. The importance of a vehicle engine continuing to operate reliably cannot be overstated. If a Stirling engine is to be seriously considered for motor vehicle applications, it must be cost competitive with other power plant technologies. This is a significant consideration given the mature technology of the spark ignition and Diesel internal combustion engines now predominately found in motor vehicles today.
During the past several decades, significant improvements in exhaust pollution and fuel economy have been made for spark ignition and Diesel engines. However, there are fundamental limits to the improvements achievable for these types of internal combustion engines. Due to the high temperature intermittent combustion process which takes place in internal combustion engines, pollutants are a significant problem. Particularly significant are NO
x
and CO emissions. Although catalytic converters, engine control, and exhaust treatment technologies significantly improve the quality of emissions, there remains room for improvement. Fuel efficiency is another area of concern for the future of motor vehicles which will require that alternative technologies be studied seriously. It is expected that the ultimate thermal efficiency achievable with the spark ignition internal combustion engines is on the order of 20%, with Diesel engines marginally exceeding this value. However, in the case of Stirling engines, particularly if advanced ceramic or other high temperature materials are implemented, thermal efficiencies in the neighborhood of 40% to 50% appear achievable. The external combustion process which could be implemented in an automotive Stirling engine would provide a steady state combustion process which allows precise control and clean combustion. Such a combustion system allows undesirable pollutants to be reduced.
In view of the foregoing, there is a need to provide a Stirling cycle engine having design features enabling it to be a viable candidate for incorporation into large scale mass production such as for automobiles and for other applications. The present invention relates to features for a Stirling engine which achieves these objects and goals.
The Stirling engine in accordance with the present invention has a so-called “modular” construction. The major components of the engine, comprising the drive case and cylinder block, are bolted together along planar mating surfaces. Piston rod seals for the pistons traverse this mating plane. A sliding rod seal can be used which is mounted either to the drive case or cylinder block. The rod seal controls leakage of the high pressure engine working gas at one end of the rod to atmosphere. Sliding contact rod seals provide adequate sealing for many applications. For example, in an automotive engine such an approach might be used. The sliding contact seal would, however, inevitably allow some leakage of working fluid, if only on a molecular level. In solar energy conversion or other applications where the engine must operate over an extremely long life, other types of sealing technology may be necessary to provide a hermetic, i.e., non-leaking, seal. In the engine of this invention, if other rod sealing approaches are required, it would be a simple matter to insert a plate between the drive case and cylinder block which supports a bellows or other type of hermetic sealing element. Thus the same basic engine componentry could be implemented for various applications.
The Stirling engine of the present invention further includes a number of features which enable it to be manufactured efficiently in terms of component costs, processing, and parts assembly. The drive case and cylinder block feature a number of bores and passageways which can be machined at 90° from their major mounting face surfaces, thus simplifying machining processes. Designs which require castings to be machined at multiple compound angles and with intersecting passageways place more demands on production machinery, tools, and operators, and therefore negatively impact cost.
The Stirling engine according to this invention provides a number of features intended to enhance its ease of assembly. An example of such a feature is the use of a flat top retaining plate which mounts the cylinder extensions and regenerator housings of the engine in place on the cylinder block. The use of such flat surfaces and a single piece retaining plate simplifies machining and assembly. The retaining plate design further lowers cost by allowing a reduction in the high temperature alloy content of the engine. Furthermore, the one-piece retaining plate provides superior component retention as compared with separate retainers for each cylinder extens
Houtman William H.
Johansson Lennart N.
Matthews Stephen C.
Roy Amedee
Brinks Hofer Gilson & Lione
Ciric Ljiljana V.
Lazarus Ira S.
STM Power, Inc.
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