TWO PISTON V-TYPE STIRLING ENGINE

Abstract: A two piston Stirling engine which includes a heat exchanger arrangement placing the cooler (26) and regenerator (28) directly adjacent the compression space (22) for minimal cold duct volume; a sealing arrangement (54) and (56) which eliminates the need for piston seals, crossheads and piston rods; and a simplified power control system (60).

Description: TWO PISTON V-TYPE STIRLING ENGINE FIELD OF THE INVENTION The present invention is directed towards providing a Stirling engine, particularly one which is a two piston V-type. BACKGROUND OF THE INVENTION With the renewed and ever expanding interest in Stir¬ ling engines, efforts have been made to continually improve upon their design. Basic Stirling engine princi¬ pals of operations are set forth in a text entitled "Stir¬ ling Engines" by G. Walker, 1st Edition, 1980. Essentially in this regard, a Stirlng engine operates on the principal of heating and cooling a working fluid (gas), with the expansion and compression of the gas utilized to perform useful work. A variety of designs are illustrated in the aforenoted text with their attendant advantages; A typical Stirling cycle consists of a contained volume divided into the following adjacent regions: compression (or cold) space, cooler, regenerator, heater and expansion (or hot) space. In actual construction though these spaces are necessarily connected by ineffec¬ tive regions or connecting ducts. Ther odynamically, it is less severe when occurring between the regions where working fluid is hot and less dense than when occurring in the cooler regions where the working fluid is more dense. In most cases, the largest connecting volumes are between heater and expansion space, and cooler and cold space. Of these two, the cold duct is the " most disadvantageous to power density and efficiency, so it is an object of this design to minimize that volume. In addition, the majority of present Stirling engines utilize lighter-than-air gases such as hydrogen or helium as the working fluid due to their relatively high conduc¬ tivity, high specific heat and low viscosity. However, a disadvantage of a lighter-than-air Stirling engine is that a fixed inventory of the gas is required and there¬ fore also fairly completed sealing between the working spaces and ambient conditions. Current hydrogen and helium engines use a sliding seal on a rod between the pistons and the crossheads (which absorb side loads), to prevent oil leakage from the crankcase into the working space and working fluid leakage from working space to crankcase. Such an arrangement adds complexity, weight and volume to the engine. Other designs envision the use of air as a working fluid. While such air-cycle engines avoid certain of the sealing requirements of the lighter-than-air engines and have other advantages to compensate for air's relatively poor fluid properties, a variety of design hurdles must be overcome, particularly providing an efficient power to weight ratio, since many of such air-cycle engines tend to be relatively heavy and need to be improved and simpli¬ fied. In either situation, air or lighter-than-air cycle Stirling engines, it is desirable to streamline them, simplifying their design and reducing their weight, while maintaining or improving their operating efficiencies. While many of the prior designs of Stirling engines have proven acceptable in certain applications, there exists an ever present need to improve on such designs to provide a more efficient and less expensive engine. SUMMARY OF THE INVENTION It is a principal object of the present invention to provide for a Stirling engine, which is relatively simple and inexpensive yet efficient. It is another object of the present invention to reduce dead volume space in a Stirling engine thereby improving its thermodynamic efficiency. It is further object of the present invention to eliminate complicated piston seal designs and their attendant disadvantages, heretofore utilized. Another object is to.provide for a simplified control therefor, adding to its simplicity and reducing its cost. The present invention provides for a Stirling engine design, particularly suitable for a two piston single acting 90° V-type, which positions the cooler and regen¬ erator directly over the cold piston adjacent the compression space so as to minimize cold compression duct volume. Also, a piston and sealing arrangement which includes pressuring the crankcase is provided which elim¬ inates the need for piston seals, crossheads or piston rods. In addition, a simpli ied power control system is included. The design provided is relatively simple, yet effi¬ cient and may utilize air or lighter-than-air working fluids in operation. Furthermore, due to the nature of the design, it is modular and can be readily applied in multiples to produce a larger engine. BP.I5F DESCRIPTION OF THE DRAWINGS Thus, by the present invention, the aforenoted objects, advantages and others will be realized, the description of which should be taken in conjunction with the drawings, wherein: Figure 1 is a schematic view of a single acting two piston V-type Stirling engine, incorporating the teach¬ ings of the present invention; Figure 2 is an exploded view of the major components of the Stirling cycle engine, incorporating the teachings of the present invention; and Figure 3 is a schematic view of the compression control, incorporating the teachings of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMOBODIMENT With more particular reference to the drawings, in Figure 1 there is shown the basic layout for two piston Stirling engine or cycle 10. In this regard, a two piston arrangement is utilized rather than a piston-displacer type so as to allow for the maximum volume change during the cycle. The engine includes a flat head compression piston 12 and dome shaped expansion piston 14 which are driven by connecting rods 16 and 18 coupled to the same crankshaft 20. The piston axes are arranged to be sepa¬ rated by an angle of crank rotation equal to the desired phase separation between the two pistons. Typically, the ideal angle is about 90°, expansion side leading to provide manufacturing ease and improved balancing. ' As shown, the compression piston 12 is positioned in a cylindrical compression space 22 with the expansion space defined by housing 24. Each of the pistons is provided with piston rings 25 which provide cycle-to-crankcase sealing. Immediately adjacent the compression space 22 there is provided a cooler 26 and regenerator 28 which may be constructed in accordance with standard procedures. In addition, while any cooler construction suitable for purpose may be utilized, a cooler constructed in accordance with my copending U.S. Patent Application (Serial No. 605,473 ) filed April 30, 1984 entitled, "Heat Exchanger for a Stirling Engine", commonly assigned herein, is particularly appropriate. Regenerator 28 is positioned in housing 30 with the cooler 26 including perhaps its own housing 32. A connecting duct 34 couples the regenerator to the heater tubes 36. The expansion space 24 is also coupled to the heating tubes 36 via connecting duct 38. Note that the shape of the heater tubes forms a tunnel appropriate for insertion into a fluestack however this is merely illustrative since any heating arrangement suitable for the purpose may be utilized. The pistons are provided with low friction plastic pads such as polytetrafluorethylene on the piston skirts at 40 and 42 as currently used in oilless air compressors. Since there is no use of piston rods, rod seals or crossheads, it is desirable to eliminate the use of oil as a lubricant which might leak into the Stirling cycle. In this regard, the connecting rods 16 and 18 are coupled to the crankshaft 20 by way of roller bearings 44 which are either greased and sealed or utilize dry lubricant (gra- phite cages). This eliminates the need for oil to lubri¬ cate these members. However, since the loading on this engine will be relatively high, active cooling of the roller bearings is desired. This can be accomplished by passing a coolant through the crankshaft 20 (hollow) which serves as the inner race 46 (only one. is shown) for the piston roller bearings and also serves as part of the cooling loop 48. Alternatively, air pumped by the motion of the pistons could be directed at the roller bearing and outer races. If necessary, a check-valving means could be incorporated to carry the air through an external cooler by creating a net flo„w loop. The crankcase area 50 of cylinder block 52 is pres¬ surized to the mean cycle pressure which serves to relieve the bearings and rings of much of their loading. In this regard, and as shown in Figure 2, pressure seals 54 are provided in addition to end caps 56, with the crankshaft 20 supported by main bearings 58 in the crankcase. With reference now to Figure 3, there is shown a control system 60. This control system 60, while less efficient -than the complicated systems heretofore utilized (see e.g., U.S. Patent No. 3,999,388, issued December 28, 1976), performs satisfactorily and has the advantage of being inexpensive. A simple multi-orificed (for linear response) flow diversion valve 62 is provided which is coupled via conduit 64 to the cold space between the cooler 26 and compression piston 12 and conduit 66 to the crankcase. 50. This valve 62 may merely comprise a multi-orifice plate occluded by a guillotin valve plate and provides a bypass around the compression piston. For less than maximum power, the valve 62 is opened to the desired degree allowing some portion of the working gas flow to be diverted into the crankcase 50 (at mean pres¬ sure) and back out again instead of through the heat exchangers thus reducing the pressure wave of the cycle. Activation of the valve would require little effort and could be by a manual lever etc. As is apparent, the construction of this design is very simple and of relative low cost while being reliable. This engine is modular and can be readily coupled with others sharing a common combustor and arranged on a common crankshaft axis. Note, that in a multiple cycle engine, the compression control system would simply be used in a ganged manner for all. Also, the coupling of similar cycles ^ allows the assembly to be g.ven a full dynamic balance. Thus by the present invention, its objects and advan¬ tages, are realized and although a preferred embodiment has been disclosed and described in detail herein, its scope should not be limited thereby, rather its scope should be determined by that of the appended claims.

Claims: WHAT IS CLIAMSD IS: 1. A Stirling cycle comprising: compression piston reciprocal in a cold compression space and expansion piston reciprocal in an expansion space at approximately 90° out of phase with respect to each other; cooling means; regenerator means; said regenerator means being positioned immediately adjacent the cooling means which is axially aligned immediately adjacent with the cold compression space so as to minimize cold duct volume; and heating means coupled with said regenerator and said expansion space completing the Stirling cycle. 2., A Stirling cycle comprising.- an engine housing which includes compression and expansion cylinders and a crankcase area; compression piston and expansion piston positioned in respective cylinder in said housing and coupled to a crankshaft via bearing means; said crank¬ shaft being positioned in the crankcase area which is defined by said pistons and said housing; said pistons include pad means between said pistons and their respec¬ tive cylinders to minimize the friction therebetween during reciprocal movement thereof; said crankcase being pressurized inhibiting the passing of working gas past the pistons; and means for cooling said crankshaft and said bearing means eliminating the need for oil in the crankcase. 3. The invention in accordance with claim 2, wherein said pistons are skirted and said pad means comprise plas¬ tic pads positioned thereon. 4. The invention in accordance with claim 3, wherein said cooling means comprises a hollow crankshaft through which a cooling medium passes. 5. The invention in accordance with claim 4, further including cooling means and regenerator means respective¬ ly positioned axially and immediately adjacent the compression space so as to minimize cold duct dead volume, and heater means coupled with said regenerator and expan¬ sion cylinders completing the Stirling cycle. 6. The invention in accordance with claim 5, which includes control means comprising flow diversion valve in a conduit which allows the working gas to bypass the compression cylinder, with the regulation of the flow diversion valve determining the average amount of working gas in the cycle thus regulating the pressure wave of the cycle and accordingly the power output * 7. The invention in accordance with claim 1, which includes control means comprising flow diversion valve in a conduit which allows the working gas to bypass the compression cylinder, with the regulation of .the flow diversion valve determining the average amount of working gas in the cycle thus regulating the pressure wave of the cycle and accordingly the power output. 8. The invention in accordance with claim 1, wherein a plurality.of said Stirling cycles are arranged together to form a common multi-cylinder Stirling cycle machine. 9. The invention in accordance with claim 2, wherein a plurality of said Stirling cycles are arranged together to form a common multi-cylinder Stirling cycle machine. 10. A Stirling cycle machine including one or more Stirling cycles each of which Stirling cycles comprises: (a) a compression piston reciprocal in a low temperature compression space; (b) an expansion piston reciprocal in a high temperature expansion space and arranged to be approxi¬ mately 90° out of phase with respect to said compression piston; (c) cooling means;. (d) regenerator means, said regenerator means being positioned immediately adjacent the low temperature compression space so as to minimize low temperature duct volume; and (e) heating means coupled with said regenerator means and said expansion space completing said Stirling cycle.

Inventors: COREY JOHN A, COREY, JOHN, A.
Applicants: MECHANICAL TECH INC, MECHANICAL TECHNOLOGY INCORPORATED
Application year: 1985
Main classification: F02G1
IPC codes: F02G1