Split-phase cooler with expansion piston motion enhancer
The invention described herein may be manufactured, used, and licensed by the U.S. Government for governmental purposes without the payment of any royalties therein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is in the field of split-cycle Stirling-cycle coolers which generally have a compression portion and expansion portion connected by a refrigerant conduit. The expansion portion has a &#34;cold finger&#34; in which expansion of the refrigerant occurs. This cold finger has an ambient end from which the refrigerant towards a cold end. Thus a temperature gradient will exist from the ambient to the cold end of the finger. Typical of such coolers are those shown in the U.S. Pat. Nos. 3,630,041, 3,862,546 and 3,877,239. An improvement in operation of such typical coolers will be realized if the temperature gradient along the cold finger is reduced. The present invention is able to reduce this gradient by providing enhancing motion of the expansion piston. 
     SUMMARY OF THE INVENTION 
     The invention is an improved Stirling-cycle cooler of the split cycle type wherein expansion piston motion enhancement is used for better cooling. The cooler employs a first compressor piston and cylinder connected by a refrigerant conduit to a first expansion space. This expansion space has one end of an expansion piston therein, with a regenerator inside said one end. The motion enhancer employs a second compressor piston and cylinder connected by a refrigerant conduit to a second expansion space. This second expansion space has the other end of said expansion piston therein. The two compressor pistons are driven from a common motor, but at a 180° phase difference. This phase difference insures that one end of the expansion piston is under suction while the other end is under compression, and conversely. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a diagramatic view of one embodiment of the invention. 
     FIG. 2 shows a diagramatic view of a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention may perhaps be best understood by referring to the drawings, in which the embodiment of FIG. 1 includes compressor portion 5, expansion portion 6, and refrigerant conduits 7 and 8. Portion 5 includes first and second cylinders 9 and 10 with respective pistons 11 and 12 therein. Pistons 11 and 12 are connected by arms 13 and 14 to crankshaft 15 supported by bearings 16 and 17. Motor 18 turns crankshaft 15. Rods 13 and 14 are mounted to crankshaft 15 such that pistons 11 and 12 move in the same direction as 15 rotates. This gives a 180° phase difference in the compression-expansion cycles in cylinders 9 and 10. I.e., the refrigerant in cylinder 9 is undergoing compresion at the same time that refrigerant in cylinder 20 is being expanded, and conversely. Conduits 7 and 8 respectively connect cyliners 9 and 10 to spaces 19 and 20 in expansion portion 6. This expansion portion includes housing 6a  with flange 6b and an expansion piston 21 respectively having end 22 and smaller end 23 in respective spaces 19 and 20. Piston 21 is supported by and sealed in housing 6a by 0-rings 24 and 25 (or equivalent) fixed in housing 6a. The rings may be seated in grooves (not shown) in 6a or otherwise held stationary therein. As can be seen in the drawings, end 22 of piston 21 is hollow, with openings 22a and 22b communicating with the interior space of 21. This interior space is filled with material 26 which acts as a regenerator, in the usual manner. 
     The alternate embodiment of FIG. 2 is similar in its compressor portion and conduits to the FIG. 1 embodiment and only expansion portion 6&#39; is shown in detail. Conduits 7&#39; and 8&#39; correspond to respective conduits 7 and 8 of FIG. 1. Portion 6&#39; includes housing 6a&#39;, flange 6b&#39;, and piston 30 in housing 6a&#39;. Piston 30 has ends 31 and 32 in respective spaces 33 and 34. Piston 30 is hollow and has openings 30a and 30b communicating with its interior. Within this interior is regenerator 35, corresponding to regenerator 26 of FIG. 1. Piston 30 is supported by and sealed in housing 6a&#39; by 0-rings 36 and 37 or equivalent fixed to the interior walls of 6a&#39; or in grooves (not shown) in 6a&#39;. 
     OPERATION OF INVENTION 
     Expansion portions 6 and 6&#39; of drawings are the cooling portions of the invention, with the right end of housings 6a and 6a&#39; being the &#34;cold finger&#34; parts. These housings are inserted in the regions to be cooled, with their flanges (6b or 6b&#39;) seated against a wall of the cooled region. The flanges are thus at the ambient zones of the coolers. It is assumed that the cooler(s) contain a proper refrigerant. In FIG. 1, upward movement of the pistons allows the refrigerant to be compressed by piston 11 in cylinder 9, to pass through conduit 7 and to expand through regenerator 26 in space 19. Cylinder 21 tends to move to the left. Thus, a stage of cooling is provided. At the same time, piston 12 moves to provide expansion of fluid (refrigerant) in cylinder 10, and thus produces a suction in space 20. This suction acts on end 23 of cylinder 21 and enhances the leftward movement of cylinder 21. When pistons 11 and 12 move in the opposite direction, fluid is compressed in cylinder 10, passes through conduit 8 and expands in space 20. Piston 11 at the same time is inducing a suction in cylinder 9, conduit 7 and space 19, and piston 21 tends to move to the right. This tendency is enhanced by the expansion of fluid in space 20 against end 23 of piston 21. Operation of the FIG. 2 embodiment is similar to the operation of the FIG. 1 embodiment, except that an optimized operation of the invention can be achieved with end 32 of piston 30 having the same diameter as the rest of the piston.