Cryogenic refrigerator

The cryogenic refrigerator includes a movable displacer within an enclosure having first and second chambers of variable volume. A refrigerant fluid is circulated in a fluid path between said chambers by movement of the displacer. A spool valve controls introduction of high pressure fluid and low pressure fluid. The displacer movement is controlled by an electric motor.

BACKGROUND 
The present invention is an improvement on the Gifford-McMahon cycle. 
Familiarity with said cycle is assumed. Representative prior art patents 
teaching such cycle include U.S. Pat. Nos. 2,966,035; 3,188,818; 
3,218,815; and 4,305,741. 
For maximum efficiency and reliability, it is important to have maximum gas 
volume transfer through the regenerator. In order that this may be 
attained, it is important that the direction of gas flow be reversed when 
the displacer is at top dead center or bottom dead center. The present 
invention is directed to a solution of that problem by utilizing an 
electric motor to control the position of the displacer adjacent top dead 
center and bottom dead center in combination with a slidable pressure 
responsive valve for controlling fluid flow. 
SUMMARY OF THE INVENTION 
The present invention is directed to a cryogenic refrigerator in which a 
movable displacer defines within an enclosure first and second chambers of 
variable volume. A refrigerant fluid is circulated in a fluid flow path 
between the first chamber and the second chamber by movement of the 
displacer. 
The refrigerator includes chamber means for guiding a slide having an axial 
passage. The slide is connected to the displacer. A motor is connected to 
the slide for controlling movement of the displacer. 
The passage in the slide has a restriction. A valve is provided with a 
spool valve member for controlling flow of the high and low pressure 
fluid. Means is provided including a conduit communicating one end of the 
spool valve member with the end of said chamber means remote from said 
displacer for introducing high fluid pressure into the conduit to shift 
the spool valve member when the displacer is at bottom dead center. 
It is an object of the present invention to provide a cryogenic 
refrigerator wherein efficiency and reliability are improved by 
controlling movement of the displacer by the combination of a motor which 
controls the displacer at top dead center and bottom dead center. 
It is another object of the present invention to provide a cryogenic 
refrigerator which has both a refrigeration mode and a heat generating 
mode. 
Other objects and advantages will appear hereinafter.

DETAILED DESCRIPTION OF FIRST EMBODIMENT 
Referring to the drawings in detail, wherein like numerals indicate like 
elements, there is shown a refrigerator in accordance with the present 
invention designated generally as 10. As illustrated, the refrigerator 10 
has a first stage 12 and a second stage 14. When in use said stages are 
disposed within a vacuum housing not shown. It is within the scope of the 
present invention to have one or more of such stages. Each stage includes 
a housing such as housing 16 within which is provided a displacer 18. The 
displacer 18 has a length less than the length of the housing 16 so as to 
define a warm chamber 20 thereabove and a cold chamber 22 therebelow. The 
designations warm and cold are relative as is well known to those skilled 
in the art. 
A heat station 24 in the form of a tube having a flanged ring and made from 
a good heat conductive material is attached to the housing 16 and 
surrounds the cold chamber 22. Heat station 24 may have other 
constructions as is well known to those skilled in the art. 
Within the displacer 18, there is provided a regenerator 26 containing a 
matrix. Ports 28 communicate the upper end of the matrix in regenerator 26 
with the warm chamber 20. See FIG. 2. Radially disposed ports 30 
communicate the lower end of the matrix in regenerator 26 with a clearance 
space 32 disposed between the outer periphery of the lower end of the 
displacer 18 and the inner periphery of the housing 16. Thus, the lower 
end of the matrix in regenerator 26 communicates with the cold chamber 22 
by way of ports 30 and clearance 32 which is an annular gap heat 
exchanger. 
The matrix of the regenerator 26 is preferably a stack of 250 mesh material 
having high specific heat such as oxygen free copper. The matrix has low 
void area and low pressure drop. The matrix may be other materials such as 
lead spheres, nylon, glass, etc. may be used. 
The second stage 14 is substantially the same as the first stage 12. In the 
second stage, the cold chamber is designated 34 and is surrounded by the 
heat station 36. Insofar as the second stage 14 is concerned, the warm 
chamber thereof is chamber 22. The displacer 37 of the second stage 14 is 
fixedly connected to the displacer 18. The regenerator of the second stage 
14 communicates with the chamber 22 by way of the ports 39 and contains a 
matrix of lead spheres. 
An electrical motor 40 is disposed within a motor housing 38. Housing 16 
depends downwardly from housing 38. The output of motor 40 is connected to 
a cam 44. Cam 44 has a follower disposed within a transverse slot of slide 
46. Slide 46 is of uniform diameter and is connected to the upper end of 
the displacer 18. 
The slide 46 is surrounded by and guided by clearance seal sleeve bearings 
48 and 49 attached to the housing 38. Bearings 48 and 49 are preferably 
made from a ceramic material. Slide 46 has cylindrical bearing inserts 50 
in sliding contact with the inner periphery of the sleeve bearing 48. An 
axial flow passage 52 is provided in the slide 46. Slide 46 is longer than 
the sleeve bearing 48 and has radial ports 55 located above a restriction 
54 in the passage 52. When the slide 46 is below top dead center, as shown 
in FIG. 2, the chamber means thereabove and within the bearing 48 is 
designated 56. 
The housing 38 includes a bore 58 parallel to the slide 46. Within the bore 
58 there is provided a clearance seal sleeve bearing 60 preferably made 
from a ceramic material. Within the sleeve bearing 60, there is provided a 
reciprocable spool valve member 62 having an axial flow passage 64. It 
will be noted that the member 62 has a length less than the length of the 
sleeve bearing 60 so that passage 64 communicates with chamber 65 
therebelow. 
Adjacent the upper end of member 62, there is provided a restriction 66 in 
passage 64. The upper end of the passage 64 communicates with chamber 56 
by way of conduit 67. A groove 68 is provided on the outer periphery of 
spool valve member 62. In the position of spool valve member 62 as shown 
in FIG. 1, one end of groove 68 communicates with the warm chamber 20 by 
way of passage 70. Passage 70 communicates with chamber 65 via passage 71. 
A high pressure port 74 is provided in housing 38 and is blocked by the 
spool valve member 62 in the position thereof as shown in FIG. 1. As will 
be made clear hereinafter, port 74 is adapted to communicate with chamber 
means 56 by way of passage 76 when the displacer 18 is at bottom dead 
center. 
In the position of the spool valve member 62 as shown in FIG. 1, the upper 
end of the groove 68 communicates with a port 78 on the inner periphery of 
the sleeve bearing 60. Port 78 communicates directly with chamber 80. 
Ports 55 of slide 46 communicate with chamber 80 when slide 46 is at top 
dead center. See FIG. 1. Chamber 80 communicates directly with chamber 42 
within which the motor 40 is disposed. Chamber 42 communicates by way of 
port 82 with the suction side of a compressor 84. The output from 
compressor 84 communicates by way of conduit 86 with the high pressure 
port 74. 
The housing 38 is constructed of a number of components so as to facilitate 
machining of the housing, assembly, and access to the spool valve member 
62 and slide 46. The manner in which housing 38 is comprised of a 
plurality of components is not illustrated but will be obvious to those 
skilled in the art. The refrigerator 10 is preferably designed for use 
with a cryogenic fluid such as helium but other fluids such as air and 
nitrogen may be used. The refrigerator 10 was designed to have a wattage 
output of at least 65 watts at 77.degree. K. from stage 12 and a minimum 
of 5 watts at 20.degree. K. at stage 14. 
Multi-staging is a thermodynamically efficient process to attain cryogenic 
refrigeration temperatures at different levels. For a given refrigeration 
requirement, there is a decreased power requirement. 
Operation Of First Embodiment 
As shown in FIG. 1, the displacers 18 and 37 are at top dead center and 
under the control of the motor 40. Spool valve member 62 has just moved to 
its uppermost position wherein chamber 20 communicates with the suction 
side of compressor 84 by way of passage 70, ports 78, and chambers 80 and 
42. Motor 40 is cooled by the gas flowing through chamber 42. The chamber 
65 below spool valve member 62 is also exhausted by way of passage 64, 
conduit 67, passage 52 and chamber 80. 
As the displacers begin to move downwardly by motor 40, the cold low 
pressure gas in chambers 22, 34 moves upwardly through the respective 
regenerators and is exhausted. As the gas moves up through passage 32 into 
the regenerators, it absorbs heat from heat station 24 and the 
regenerators thereby cooling the regenerators. As shown in FIG. 2, the 
displacers are moving down and approaching bottom dead center. When the 
upper end of slide 46 uncovers passage 76, the displacers will be at 
bottom dead center. Accuracy in locating the passage 76 directly effect 
efficiency. High pressure gas from port 74 now flows from passage 76 to 
chamber means 56 and conduit 67. The pressure between restrictors 54 and 
66 increases. When the high pressure gas overcomes the low pressure fluid 
trapped in chamber 65, member 62 descends to the position shown in FIG. 3. 
Now the entire system contains high pressure gas. The displacers are at 
bottom dead center. 
The function of the regenerators in said displacers 18 and 37 is to cool 
the gas passing downwardly therethrough and to heat gas passing upwardly 
therethrough. In passage downwardly through the regenerators, the gas is 
cooled thereby causing the pressure to decrease and further gas to enter 
the system to maintain the maximum cycle pressure. The decrease in 
temperature of the gas in the chambers 22, 34 is useful refrigeration 
which is sought to be attained by the apparatus at heat stations 24, 36. 
As the gas flows upwardly through the regenerators, it is heated by the 
matrix to near ambient temperature thereby cooling the matrix. 
The side 46 is moved upwardly from bottom dead center as shown in FIG. 3 
with the displacers 18 and 37 by motor 40 as high pressure gas moves 
downwardly into chambers 20 and 34. Port 55 communicates with chamber 80 
just before top dead center is reached. The upper end of bearing 49 may be 
removed and machined or made vertically adjustable to fine tune the timing 
of communication between port 55 and chamber 80. This immediately places 
passage 52 and conduit 67 in communication with the suction side of the 
compressor 84. The high pressure gas trapped in chamber 65 raises the 
spool valve member 62 from the position shown in FIG. 3 to the position 
shown in FIG. 1 as the displacers reach top dead center. One cycle is now 
complete. A typical embodiment operates at the rate of 72-80 cycles per 
minute. The length of the stroke of the movable members is short such as 
12 mm for valve member 62 and 30 mm for the displacers. Valve member 62 
need not have axial flow passage 64 but instead may be a solid spool valve 
member which responds to differential pressure. 
The refrigeration available at heat stations 24 and 36 may be used in 
connection with a wide variety of devices. As shown in FIG. 7, heat 
station 24 is used to cool chevron vanes 90 supported on cryopump housing 
92 and heat station 36 is used to cool charcoal 94 in pan 96. In a 
cryopump, vanes 90 are optically dense and cause gases such as oxygen and 
nitrogen to adhere thereto. Nobel gases are absorbed by the charcoal 94. 
Description Of Second Embodiment 
In FIGS. 4-8 there is illustrated another embodiment designated generally 
as 10'. The refrigerator 10' is the same as refrigerator 10 except as will 
be set forth hereinafter. Hence, corresponding elements of refrigerator 
10' are designated with corresponding primed numerals. 
A pilot valve 100 is provided between the slide 46' and the valve member 
62'. The valve 100 includes a spool valve member 102 within a ceramic 
bearing 104. The valve member 102 has a circumferential groove 106 which 
may selectively interrupt the communication along passage 76. As 
illustrated in FIG. 4, high pressure is provided in conduit 77, groove 106 
and passage 120 but blocked by the slide 46' and valve member 52'. The 
remainder of the system is at low pressure. 
The spool valve member 102 remains in the position as illustrated in FIG. 4 
during the entire refrigeration cycle as described above. When the 
charcoal 94' can no longer absorb nobel gases, due to reaching a 
saturation point, the nobel gases have no place to go. The nobel gases 
collide around and find their way back into the pump. This puts a 
conductive load on the second stage which heats up. When the temperature 
of the second stage reaches about 20.degree. K., a diode 108 is triggered. 
Diode 108 closes contacts in solenoid 110. Solenoid 110 is connected to 
rod 112 which in turn is connected to the valve member 102. As a result 
thereof, the valve member 102 is shifted from the position shown in FIG. 4 
to the position shown in FIG. 5. This immediately reverses the effect of 
valve member 62' whereby the apparatus is now in a heating mode. 
As shown in FIG. 5, it is assumed that the shifting of valve member 102 
occurred while the slide 46' was at top dead center. Due to the slight 
pressure differential, the high pressure gas in passage 67' causes the 
slide valve member 62' to move from the position shown in FIG. 5 to the 
position shown in FIG. 6. The apparatus 10' is now in a heating mode 
instead of a refrigerating mode with the displacers at top dead center. 
High pressure gas exists in all of the passages except for passages 114 
and 116. As the pressure in the cold volume increases, the temperature of 
the gas rises. 
As the displacer begins to move downwardly toward the cold end, the 
relatively warm gas is moved upwardly through the regenerator matrix 
thereby heating the matrix material in each of the stages. As the 
displacers are continued to move downwardly to a bottom dead center, the 
low pressure control port is about to open as shown in FIG. 7. As shown in 
FIG. 8, the displacers are at bottom dead center. 
As shown in FIG. 8, when the displacers are at bottom dead center chamber 
56' communicates with passage 114 which in turn communicates with chamber 
80 whereby the space above valve member 62', conduit 67', chamber 56', and 
passage 52' down to the restriction is at low pressure. High pressure gas 
is communicated by way of passage 70' to the first and second stages. Due 
to a slight momentary pressure differential across valve member 62' it is 
forced upwardly from the position shown in FIG. 8 to the position shown in 
FIG. 5. At this point in time, the entire system is connected low pressure 
except for conduit 76' which communicates through the valve member 102 but 
is blocked at the lefthand end by the slide 46'. The high pressure warm 
gas above the displacers is expanded out passage 70', groove 68', through 
passage 118' to the chamber 80 and through the motor housing, to the inlet 
or suction side of the compressor 84'. Thereafter, the displacers begin to 
move upwardly under the influence of motor 40' thereby forcing the low 
pressure relatively warm gas down through the regenerators in the first 
and second stages. 
As the displacers are moved upwardly, the slide 46' closes off the lefthand 
end of passage 114 and thereafter continue moving toward top dead center. 
When the displacers reach top dead center as shown in FIG. 4, high 
pressure will be introduced from conduit 76' into groove 106, through 
passage 120 to port 55', through passage 52', chamber 56', conduit 67' and 
to the restriction in the valve member 62'. The remainder of the system 
will be at low pressure communicating with the inlet side of the 
compressor 84'. One cycle has now been completed. In an operative 
embodiment, there would approximately 72 to 80 cycles per minute. 
The heating cycle will be terminated wherever the solenoid 110 moves the 
valve member 102 to the position shown in FIG. 4 thereby placing the 
apparatus back into a refrigerating mode. The diode 108 will trigger the 
solenoid 110 when it is desired to revert to a refrigeration mode. The 
heating mode will take approximately 35 minutes. All gases and moisture 
liberated within housing 92' will be pumped away. Regeneration of charcoal 
94' within approximately 35 minutes is a substantial advancement over 
present techniques which require at least 31/2 hours. Embodiment 10' 
utilizes the existing flow passages in connection with the pilot valve 100 
to provide more efficient use of sizes of passages and associated flow 
rates. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.