US3744261A

US3744261A - Cryogenic refrigerator

Info

Publication number: US3744261A
Application number: US00235170A
Authority: US
Inventors: G Lagodmos
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1972-03-16
Filing date: 1972-03-16
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10

Abstract

The substantially ambient temperature volume of the Vuilleumier refrigerator, which comprises a crank volume, is reduced to a minimum by employing a cylindrical disc in a cylindrical crank cavity, with a pin carried on eccentric race on the disc. A slider carries the pin and drives the piston. By this construction, metal occupies most of the crank volume.

Description

I Umted statfiS Patent 1 1111 3,744,261

Lagodmos 45 J l 1%, 1973 CRYOGENIC REFRIGERATOR 3,157,024 11 1964 McCrory 62 6 3,220,178 ll 1965 S' 62 6 [751 Inventor: George hgmlms, 3,282,064 11/1966 mean 62/45 Callf- 3,523,427 8/1970 62/6 Assigneez Hughes p y Culver Aldridge E City, Calif. Primary Examiner-William J. Wye [22] Filed 1 Attorney-W. H. MacAllister, Jr. and Allen A. [21] Appl. No.: 235,170 Dicke, lr.

[52] US. Cl 62/6, 60/24, 92/72, [57] ABSTRACT 92/138, 123/44, 417/415 [51] Int. Cl. F25b 9/00 The substamlany ambem temperature volume of the [58] Field of Search 62/6. 60/24. 92/138 Vuilleumier refrigerator, which comprises a crank vol- 92/72. 125/44 ume, is reduced to a minimum by employing a cylindrical disc in a cylindrical crank cavity, with a pin carried [56] References Cited on eccentric race on the disc. A slider carries the pin UNITED STATES PATENTS and drives the piston. By this construction, metal occupies most of the crank volume. 2,982,088 5/l96l Meijer 62/6 10 Claims, 11 Drawing Figures PATENIED 1 3. 744.261

SIIEIJBF Fig. 6.

PATENIEU L 1 0 ma sm wr d Volume 28 Fig. ll.

oSmmmtm Volume 22 CRYOGENIC REFRIGERATOR BACKGROUND This invention is directed to the crank volume construction in a cryogenic refrigerator for the reduction of gas volume thereof.

U. S. Pat. No. 1,275,507 describes a three chamber refrigerator cycle, commonly known as the Vuilleumier cycle, or the VM cycle, being named after the inventorpatentee. A more modern refrigeration machine employing this cycle is shown in Cowans US. Pat. No. 3,423,948 (reissue application Ser. No. 48,755). The equipment described in these patents for performing the cycle is subject to redesign for improvement of cycle efficiency. Further background on this cycle is found in the publication Miniature Vuilleumier-Cycle Refrigerator, by G. K. Pitcher and F. K. DuPre', published in ADVANCES IN CRYOGEN ENGINEER- ING, Vol. 15, Plenum Press, New York, 1970, at pages 447 through 451.

SUMMARY In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a cryogenic refrigerator apparatus wherein the volume of the crank chamber is minimized by employing a cylindrical crank disc in a cylindrical crank chamber. The crank disc carries an eccentric ring set in one side thereof, with an attachment between a sliding piston rod and the eccentric ring.

Accordingly, it is an object of this invention to provide a cryogenic refrigerator apparatus of improved design. It is a further object to provide a refrigerator apparatus specifically designed for employing the Vuilleumier cycle, wherein the crankcase volume is incorporated in the cryogen system, wherein reduction of volume of the crankcase volume increases the cycle efficiency. It is a further object to provide a refrigerator apparatus which is economic to produce and is of long, trouble-free life. Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, the claims, and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a cryogenic refrigerator apparatus in accordance with this invention.

FIG. 2 is a section taken generally along the line 2-2 of FIG. 1.

FIG. 3 is an enlarged partial section, with parts broken away, taken generally along the line 3--3 of FIG. 2.

FIG. 4 is a partial section, with parts broken away, taken generally along the line 4-4 of FIG. 1.

FIG. 5 is an enlarged partial elevational view, with parts broken away, as seen generally along line 5-5 of I FIG. 4.

FIGS. 6, 7, and 8 are sections similar to FIG. 2 showing the apparatus in progressive positions.

FIG. 9 is a schematic diagram of the refrigerator showing the several volumes and the interconnection thereof.

FIGS. 10 and 11 are P-V diagrams showing the conditions in the cold and hot volumes, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to fully understand the significance of the design, the Vuilleumier cycle should be understood so that the improvement in efficiency by reduction of the intermediate volume can be fully appreciated. Referring principally to FIGS. 1, 2, 4, 6, 7, and 8, the cryogenic refrigerator apparatus 10 is shown therein. The apparatus 10 has a hot cylinder 12 and a cold cylinder 14. These are both mounted upon a crankcase, or crank housing 16. Hot displacer 18 is mounted in hot cylinder 12, while cold displacer 20 is mounted in cold cyclinder 14. As the hot displacer 18 moves through the hot cylinder 12, it divides the interior of the cylinder into a hot volume 22 and an ambient volume 24. While it is called an ambient volume, the temperature of volume 24 is slightly above the ambient temperature of the environment, because heat is rejected from the cryogen gas at the temperature of the ambient volume to the exterior environment. However, this volume is called an ambient volume, because it is neither purposely elevated nor at the point of refrigeration.

I-Ieater 26 is provided to heat the cryogen gas in the hot volume 22. Hot displacer 18 contains a regenerator therein, as indicated schematically in FIG. 9, so that as the hot displacer sweeps through the cylinder 12, heat is exchanged between the cryogen gas and the regenen ator mass.

Similarly, cold displacer 20 divides the cold cylinder 18 into a cold volume 28 and an ambient volume 30. A regenerator 21 is built into cold displacer 20, with access through top and

bottom ports

23 and 25, see FIGS. 2 and 3, so that heat is exchanged between the cryogen gas and the regenerator mass as the cryogen moves through the displacer and the displacer sweeps the cold cylinder.

The cold spot at which refrigeration is developed is shown at 34.

In the manner which is subsequently described, the hot and cold displacers are mechanically connected so that they operate at substantially a phase angle with respect to each other. This is illustrated by the mechanical configuration of the exterior of the device, where the cylinders are postioned at 90 with respect to each other. On the other hand, the cylinders may be positioned in other orientations with the phase angle regulated by the relative position of the cranks.

The refrigerator is a constant volume device. The total volume of the cold chamber 28, the hot chamber 22, and the total ambient volume comprised of

chambers

24 and 30 and the interconnecting passageways, including the ambient volume 32 in crank housing 16 is constant. However, the volume is divided in different fractions, depending upon the positions of the hot and cold displacers l8 and 20. In spite of, the fact that the motion of the two pistons cannot vary the total volume, pressure varies as the displacers move because of changes in the average temperature of the gas that fills the total volume. Considering the displacers individually, as the hot displacer 18 moves toward the crankshaft, it forcesgas from the ambient chamber 24 to the hot side of hot displacer 18, which is hot chamber 22. Since this movement causes an increase in the average temperature of the gas in these two portions of the total volume, the average pressure in the entire refrigerator increases. Likewise, as the cold displacer 20 moves toward the crankshaft, it forces some of the gas from the ambient volume 30 to the cold end of displacer 20 into cold volume 28. As the gas is thus cooled, the pressure decreases.

In operation, the crankshaft 30 rotates in the clockwise direction, as seen in FIGS. 2, 6, 7, and 8. The relative volume sizes of cold volume 28 and hot volume 22 are shown in FIGS. and 11 as the displacers move through their cycles. As the crank moves in the clockwise direction, the pressure-volume characteristics of these two volumes change as indicated. Starting from the position of FIG. 7, the cold displacer is in its extended position in cold cylinder 14, while the hot displacer 18 is in an intermediate position within its hot cylinder 12, and moving toward the crankshaft. As the crank moves 90 to the position of FIG. 8, the cold displacer 20 moves to its central position, and the hot displacer 18 moves to its bottom dead center position. While moving through this quadrant, both pistons are moving toward the center line of the crankshaft. As previously discussed, motion in this direction by the hot displacer 18 tends to cause an increase in pressure, and motion in this direction by cold displacer 22 tends to cause decrease in pressure. These actions are essentially balanced, and the average pressure does not substantially change, as indicated in FIGS. 10 and 11. The net effect is that a certain amount of the working cryogen gas is transferred to the cold volume 28 without undergoing any substantial change in pressure.

Further movement of the crank in the clockwise direction to the position of FIG. 2 brings the cold displacer 20 to its bottom dead center, and hot displacer 18 to an intermediate position. During crank motion through this quadrant, the hot displacer 18 is moving away from the crank, while cold displacer 20 is moving toward the crank. As previously discussed, motion of the pistons in this direction both cause cooling of the gas and the pressure falls from a substantially constant high value, P in FIGS. 10 and 11, to a new, substantially constant low value of P, in FIGS. 10 and 11. This is the refrigeration portion of the cycle by gas expansion in cold volume 28. As the crank moves from the position of FIG. 2 to the position of FIG. 6, the hot displacer 18 moves to its top dead center position, while the cold displacer 20 moves to an intermediate position. During this motion, the cold displacer 20 moves gas to a warmer region, and the hot displacer 18 moves gas to a cooler region, substantially without affecting the pressure, as indicated in FIGS. 10 and 11. Thus, the pressure remains substantially at the low value P,, and gas is transferred from hot chamber 22 to cold chamber 28.

In the next quadrant of motion, from the position of FIG. 6 to the position of FIG. 7, cold displacer 20 is moved to the top dead center position, reducing cold volume 28, and the hot displacer is moved to an intermediate position toward the crank to thus arrive at the initiation point of the refrigeration phase of the cycle. This motion causes both pistons to cause increase in pressure of the gas to raise the pressure from P, to P The pressure-volume curves of FIGS. 10 and '1 1 show that the amount of work that has been done by the gas in the cold volume exactly matches the amount of work that has been supplied to the gas in the hot volume. The mechanical P-V work of the cryogen gases in the volumes act upon each other so that they are coupled and are equal. The work done in the expansion of the cold cryogen is equal to the work done in compression of the hot cryogen. Therefore, thermodynamic heat addition by heater 26 causes an equal thermodynamic extraction or cooling at cold point 34.

It must be noted, however, that the change in pressure is strongly influenced by the size of the ambient volume. With the same temperature change, a lesser pressure change will occur when the ambient volume is larger. Therefore, the ambient volume should be minimized. It is the thrust of this invention to minimize the ambient volume and thus achieve higher pressure ratios on the cycle and thus achieve more refrigeration per unit equipment size.

Since the total of

volumes

24, 30, and 32 comprises the volume at ambient temperature which is just sufficiently higher than the temperature of the environment so that heat can be rejected from the ambient volume to the environment, this volume does not contribute to pressure changes resulting from the average temperature of the entire cryogen mass. Instead, the crank volume reduces the pressure ratio and thus is detrimental to refrigerator efficiency. With reduction of crank volume 32 to zero, all of the volumes are swept volumes so that all volumes contribute to the cycle operation. Thus, zero volume of the crank volume 32 would produce the maximum pressure changes in the system with the movement of the cryogen gas from one volume to another, in the manner previously described. With the highest compression ratio, the greatest amount of refrigeration is obtainable from a cryogenic refrigerator of a particular size. While a zero ambient volume 32 is not possible, because there must be a connection between the

volumes

24 and 30, the ambient volume 32 of the crank chamber can be minimized. FIGS. 3, 4, and 5 show the structure of this invention which produces a minimum crankcase volume.

Crank housing 16 carries motor 36 thereon. Motor 36 is principally a speed control device which regulates the refrigerator cycle speed. While it has a power input thereto, the power input is small and principally overcomes friction. The power input is not the principal power input of this system. Motor shaft 38 extends into crank housing 16 and is rotatably mounted therein on the usual bearings and is equipped with the usual seals to prevent the escape of cryogen gas.

Discs

40 and 42 are mounted on the end of motor shaft 38 and are rotated thereby. They are pinned together by means of pin 44.

Separate discs

40 and 42 are illustrated for the convenience in machining operations. If desired, a single disc can be employed. Eccentric groove 47 is machined in disc 40, while eccentric groove 47 is machined'in disc 42.

Bearings

48 and 50 are respectively pressed into these grooves at the interior thereof. Eccentric drive rings 52 and 54 are respectively mounted on

bearings

48 and 50, and substantially till the

grooves

46 and 47, respectively. The outer race of the bearings and the eccentric drive rings have a small running clearance thereabout.

The entire structure of

discs

40 and 42 is mounted within cavity 56 within crank housing 16. Cavity 56 is cylindrical and is in a close running fit with respect to the

discs

40 and 42. Thus, minimum clearance volume is provided. Guide bores 58 and 60 are formed in a suitable bearing material, such as bearing

sleeves

62 and 64, see FIG. 2.

Piston rods

66 and 68 are respectively slidably located in these bearing sleeves. The guide bores intersect with the cavity 56 so that the piston rods can interconnect with the eccentric drive rings. The relative positioning is such that the center line of guide bore 58 is substantially in a line with the left side of the cavity 56, as seen in FIG. 3, while the center line of the guide bore 60 is substantially in line with the right side of the cavity 56, as seen in FIG. 3. In this way, the piston rods have a flat machined surface on one side thereof so that the surface is a diameter. These flats are shown at 70 and 72. The end of the machining which results in these flats produces

surfaces

74 and 76 which are portions of cylindrical surfaces having substantially the same radius as the discs. The

surfaces

74 and 76 are positioned along the piston rods so that, when the piston rod is in its fully retracted position, such as rod 66 in FIG. 3, thereis a close running fit between the surface 74 and the outer surface of disc 40. Similarly, the terminal ends of the piston rods closely fit the bottom of the guide bores, when in retracted position.

Interconnection between the piston rods and the eccentric drive rings is accomplished by

drive pins

78 and 80, respectively. They are mounted in suitable bearings in the piston rods. Since there is oscillatory motion between the drive pins and their bores in the piston rods, ball bearings, as illustrated, can be employed to reduce friction. The running clearances illustrated are exaggerated to show the spacing between parts to show which were movable with respect to others without touching. Clearances are minimized, particularly between

bores

58 and 60, in order to minimize the crankcase volume 32. Gas interconnection between the

volumes

24 and 32 is accomplished by providing small flats along the sides of piston rod 66 to permit gas passage from the swept volume under piston 18 to the crank chamber cavity 56. Running spaces are adequate to permit passage of the cryogen gas.

It can be seen that this structure produces the minimum crank housing volume 32, because most of the space is filled with metal. Minimum dimensioned running fits provide what crank volume 32 remains. Even the volumes at the inner ends of the piston rods are swept by piston rod motion so that minimum fixed volume remains. This improves the efficiency of the cryogenic refrigerator, as compared to one with a greater crankcase volume 32.

As an example of particular dimensions and fits, in a small VM cryogenic refrigerator, the stroke of both the pistons is 0.25 inch. With this stroke, convenient diameter for the

discs

40 and 42 of 1.50 inches and a convenient total axial length thereof is 0.25 inch, the spacing between the discs and the cavity can be made as little as 0.002 inch. Similarly, the spacing between the ends of the piston rods and the bottoms of their guide bores can be as little as 0.002 inch, and the spacing between the

surfaces

74 and 76 and the outer diameter of the discs can be as little as 0.002 inch. With small flats provided on the piston rod 66 to communicate with the cavity 56, this spacing within the cavity 56 is sufficient to permit cryogen gas flow between the two cylinders.

This invention having been described in its preferred embodiment, it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of I the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

What is claimed is: 1. Apparatus for acting on cryogen gas for a cryogenic refrigerator comprising:

a crank housing, first and second cylinders for containing cyogenic fluid carried on said crank housing, first and second pistons respectively mounted for reciprocation within said cylinders for acting on cryogen gas within said cylinders, a cavity within said crank housing, cryogen gas connections between said cylinders and said cavity, actuating means positioned within said cavity for connection to said pistons for controlling the motion of and position of said pistons within said cylinders for controlling the flow of cryogen gas between said cylinders and said cavity, the improvement comprising:

said cavity in said crank housing being substantially cylindrical, and said actuating means having a cylindrical disc positioned within said cylindrical cavity to substantially fill said cavity, whereby cryogen gas volume within said cavity is minimized said crank housing cavity being interconnected with said cylinder so that they both can contain cryogen gas.

2. The cryogenic refrigerator apparatus of claim 1 wherein said disc rotates on an axis, said axis passing substantially along the axis of said cylindrical cavity.

3. The cryogenic refrigerator apparatus of claim 2 wherein said disc has an eccentric groove in'an axial face thereof, said disc carrying a laterally-extending drivepin thereon, said drivepin extending into said groove.

4. The cryogenic refrigerator apparatus of claim 3 wherein an eccentric drive ring is positioned in said eccentric groove in said disc, and said drivepin is mounted in said eccentric drive ring, said eccentric drive ring being rotatably mounted with respect to said disc within said eccentric groove.

5. The cryogenic refrigerator apparatus of claim 4 wherein said eccentric drive ring is mounted on an antifriction bearing with respect to said disc within said eccentric groove.

6. The cryogenic refrigerator apparatus of claim 2 wherein a first piston rod is connected to said first piston, said first piston rod extending into a guidebore within said crank housing, said guidebore intersecting said cylindrical cavity so that said first piston rod can interengage with said actuating means so that first piston position is controlled by said disc.

7. The cryogenic refrigerator apparatus of claim 6 wherein said first piston rod is cylindrical and its axis substantially intersects with the axis of rotation of said disc at substantially right angles, said axis of said first piston rod lying substantially on an axial face of said disc.

8. The cryogenic refrigerator apparatus of claim 7 wherein said first piston rod is axially positioned along its guidebore in accordance with said eccentric groove, and when said first piston rod is positioned closest to the axis of said disc, the portion of said first piston rod radially closest to said disc is in a non-engaging closerunning fit with respect to said disc.

9.-The cryogenic refrigerator apparatus of claim 8 wherein the end of said first piston rod toward the axis of rotation of said disc has an axially-directed flat positioned thereon, said flat being substantially formed along a diameter of said first piston rod and terminating in a surface which has a curvature substantially equal to the cylindrical curvature of said disc and said cavity in said crank housing.

said first and second drivepins-respectively engaging said first and second eccentric drive rings, and first and second drivepins being respectively carried by piston rods of said first and second pistons.

Claims

1. Apparatus for acting on cryogen gas for a cryogenic refrigerator comprising: a crank housing, first and second cylinders for containing cyogenic fluid carried on said crank housing, first and second pistons respectively mounted for reciprocation within said cylinders for acting on cryogen gas within said cylinders, a cavity within said crank housing, cryogen gas connections between said cylinders and said cavity, actuating means positioned within said cavity for connection to said pistons for controlling the motion of and position of said pistons within said cylinders for controlling the flow of cryogen gas between said cylinders and said cavity, the improvement comprising: said cavity in said crank housing being substantially cylindrical, and said actuating means having a cylindrical disc positioned within said cylindrical cavity to substantially fill said cavity, whereby cryogen gas volume within said cavity is minimized said crank housing cavity being interconnected with said cylinder so that they both can contain cryogen gas.

3. The cryogenic refrigerator apparatus of claim 2 wherein said disc has an eccentric groove in an axial face thereof, said disc carrying a laterally-extending drivepin thereon, said drivepin extending into said groove.

5. The cryogenic refrigerator apparatus of claim 4 wherein said eccentric drive ring is mounted on an anti-friction bearing with respect to said disc within said eccentric groove.

8. The cryogenic refrigerator apparatus of claim 7 wherein said first piston rod is axially positioned along its guidebore in accordance with said eccentric groove, and when said first piston rod is positioned closest to the axis of said disc, the portion of said first piston rod radially closest to said disc is in a non-engaging close-running fit with respect to said disc.

9. The cryogenic refrigerator apparatus of claim 8 wherein the end of said first piston rod toward the axis of rotation of said disc has an axially-directed flat positioned thereon, said flat being substantially formed along a diameter of said first piston rod and terminating in a surface which has a curvature substantially equal to the cylindrical curvature of said disc and said cavity in said crank housing.

10. The cryogenic refrigerator apparatus of claim 4 wherein there are first and second axially facing eccentric grooves in said disc and there are first and second eccentric drive rings respectively positioned in said first and second grooves and rotatably mounted therein, said first and second drivepins respectively engaging said first and second eccentric drive rings, and first and second drivepins being respectively carried by piston rods of said first and second pistons.