Patent Application
20170115036
Priority is claimed to Japanese Patent Application No. 2015-208614, filed Oct. 23, 2015, and Japanese Patent Application No. 2016-116329, filed Jun. 10, 2016, the entire content of each of which is incorporated herein by reference.
Technical Field
The present invention in particular embodiments relates to Gifford-McMahon (GM) cryocoolers.
Description of Related Art
GM cryocoolers, which are typifying examples of cryogenic refrigerators, generate extremely low temperatures using the GM cycle. That means that GM cryocoolers are configured so as to appropriately synchronize periodic pressure fluctuations in the expansion space—deriving from intake of the working gas into, its adiabatic expansion in, and its exhausting from, the expansions space—with periodic variation in volume of the expansion space due to the reciprocating movement of the displacer.
One embodiment of the present invention affords a GM cryocooler including: a first cold head including an axially reciprocatory first displacer, and a first cylinder between the first displacer and which a first gas chamber is formed; a second cold head including a second displacer disposed coaxially with respect to the first displacer and axially reciprocatory unitarily with the first displacer, and a second cylinder between the second displacer and which a second gas chamber is formed, and disposed opposing the first cold head; a common drive mechanism connected to the first displacer and the second displacer such as to drive axial reciprocation of the first displacer and the second displacer; and a working gas circuit connected to the first cold head and the second cold head such as to generate between the first gas chamber and the second gas chamber a pressure differential assisting the common drive mechanism.
Another embodiment of the present invention affords a GM cryocooler including; a first cold head including an axially reciprocatory first displacer, and a first cylinder between the first displacer and which a first gas chamber is formed; and a second cold head including a second displacer disposed coaxially with respect to the first displacer and axially reciprocatory unitarily with the first displacer, and a second cylinder between the second displacer and which a second gas chamber is formed, and disposed opposing the first cold head.
A general basic configuration of a GM cryocooler includes one compressor and one expander (that is, combination between one displacer and a drive portion thereof). As a configuration example derived from this basic configuration, a cryocooler is suggested which includes two displacers which are disposed for one displacer drive portion in parallel and in which intake operations to expansion spaces corresponding to the two displacers are alternately performed. The alternate intake operations of two expanders decrease the pressure fluctuation in a compressor, and improve the efficiency of the compressor. Accordingly, this contributes to improvement in the efficiency of the cryocooler.
However, in order to drive two displacers by one drive portion, a relatively large drive portion which generates a corresponding drive torque is required. In addition, an area of floor for installation of the cryocooler is liable to be increased due to the parallel disposition of the two expanders.
In a GM cryocooler having a plurality of displacers, it is desirable to realize improvement in the efficiency of a compressor while decreasing a drive torque of the displacers.
In addition, arbitrary combinations of the above-described components, or components or expression of the present invention may be replaced by each other in methods, devices, systems, or the like, and these replacements are also included in aspects of the present invention.
According to the present invention, in a GM cryocooler having a plurality of displacers, it is possible to realize improvement in the efficiency of a compressor while decreasing drive torque of the displacers.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in descriptions, the same reference numerals are assigned to the same elements, and overlapping descriptions thereof are appropriately omitted. Moreover, configurations described below are exemplified, and do not limit the scope of the present invention.
The GM cryocooler 10 includes a compressor 12 which compresses a working gas (for example, helium gas), and a plurality of cold heads which are cooled by adiabatic expansion of the working gas. The cold head is referred to as an expander. As described in detail below, the compressor 12 supplies a high-pressure working gas to the cold heads. A regenerator which pre-cools the working gas is provided in the cold head. The pre-cooled working gas is cooled by expansion in the cold head again. The working gas is recovered to the compressor 12 through the regenerator. When the working gas passes through the regenerator, the regenerator is cooled. The compressor 12 compresses the recovered working gas, and supplies the compressed working gas to the expander again.
The GM cryocooler 10 includes a first cold head 14a and a second cold head 14b which are disposed so as to face each other. In addition, the GM cryocooler 10 includes a common drive mechanism 40 for the first cold head 14a and the second cold head 14b. The first cold head 14a is disposed on one side with respect to the common drive mechanism 40, and the second cold head 14b is disposed on the other side with respect to the common drive mechanism 40. In addition, the GM cryocooler 10 includes a working gas circuit 70 which connects the compressor 12 to the first cold head 14a and the second cold head 14b.
The first cold head 14a is a single staged cold head. The first cold head 14a includes a first displacer 16a which can axially reciprocate, and a first cylinder 18a which accommodates the first displacer 16a. The axial reciprocation of the first displacer 16a is guided by the first cylinder 18a. In general, each of the first displacer 16a and the first cylinder 18a is a cylindrical member which axially extends, and the inner diameter of the first cylinder 18a is slightly greater than the outer diameter of the first displacer 16a. Here, an axial direction is an upward-downward direction in
A first expansion chamber 20a is formed between the first displacer 16a and the first cylinder 18a on one end in the axial direction, and a first room-temperature chamber 22a is formed between the first displacer 16a and the first cylinder 18a on the other end in the axial direction. The first room-temperature chamber 22a is positioned near the common drive mechanism 40, and the first expansion chamber 20a is positioned far from the common drive mechanism 40. This means that the first room-temperature chamber 22a is formed on a proximal end of the first cold head 14a and the first expansion chamber 20a is formed on a distal end of the first cold head 14a. A first cooling stage 24a, which is fixed to the first cylinder 18a so as to enclose the first expansion chamber 20a, is provided on the distal end of the first cold head 14a.
When the first displacer 16a axially moves, the first expansion chamber 20a and the first room-temperature chamber 22a complementarily increase and decrease the volume. That is, when the first displacer 16a moves upward, the first expansion chamber 20a is widened, and the first room-temperature chamber 22a is narrowed, and vice versa.
The first displacer 16a includes a first regenerator 26a which is built therein. The first displacer 16a includes a first inlet flow path 28a, which allows the first regenerator 26a to communicate with the first room-temperature chamber 22a, on the upper lid portion of the first displacer 16a. In addition, the first displacer 16a includes a first outlet flow path 30a, which allows the first regenerator 26a to communicate with the first expansion chamber 20a, on the tubular portion of the first displacer 16a. Alternatively, the first outlet flow path 30a may be provided on the lower lid portion of the first displacer 16a. Moreover, the first displacer 16a includes a first inlet flow-straightener 32a which is in inner-contact with the upper lid portion, and a first outlet flow-straightener 34a which is in inner-contact with the lower lid portion. The first regenerator 26a is interposed between the pair of flow-straighteners.
The first cold head 14a includes a first seal portion 36a which blocks a clearance formed between the first cylinder 18a and the first displacer 16a. For example, the first seal portion 36a is a slipper seal, and is mounted on the tubular portion or the upper lid portion of the first displacer 16a.
In this way, the first seal portion 36a is positioned near the common drive mechanism 40, and the first outlet flow path 30a is away from the common drive mechanism 40 and is positioned near the first cooling stage 24a. In other words, the first seal portion 36a is attached to a proximal portion of the first displacer 16a, and the above-described first outlet flow path 30a is formed in a distal portion of the first displacer 16a.
The working gas flows from the first room-temperature chamber 22a into the first regenerator 26a through the first inlet flow path 28a. More specifically, the working gas flows from the first inlet flow path 28a into the first regenerator 26a through the first inlet flow-straightener 32a. The working gas flows from the first regenerator 26a into the first expansion chamber 20a via the first outlet flow-straightener 34a and the first outlet flow path 30a. The working gas goes through a reverse pathway with respect to the above-described pathway when the working gas is returned from the first expansion chamber 20a to the first room-temperature chamber 22a. That is, the working gas is returned from the first expansion chamber 20a to the first room-temperature chamber 22a through the first outlet flow path 30a, the first regenerator 26a, and the first inlet flow path 28a. The working gas, which bypasses the first regenerator 26a and flows into the clearance, is interrupted by the first seal portion 36a.
As described above, the second cold head 14b is disposed on the side opposite to the first cold head 14a with respect to the common drive mechanism 40. Except for this, the configuration of the second cold head 14b is similar to that of the first cold head 14a. Accordingly, similarly to the first cold head 14a, the second cold head 14b is a single staged cold head, and has the shape and size similar to those of the first cold head 14a.
The second cold head 14b includes a second displacer 16b which is coaxially disposed with respect to the first displacer 16a and is able to axially reciprocate integrally with the first displacer 16a, and a second cylinder 18b which accommodates the second displacer 16b. The axial reciprocation of the second displacer 16b is guided by the second cylinder 18b. In general, each of the second displacer 16b and the second cylinder 18b is a cylindrical member which axially extends, and the inner diameter of the second cylinder 18b is slightly greater than the outer diameter of the second displacer 16b.
A second expansion chamber 20b is formed between the second displacer 16b and the second cylinder 18b on one end in the axial direction, and a second room-temperature chamber 22b is formed between the second displacer 16b and the second cylinder 18b on the other end in the axial direction. The second room-temperature chamber 22b is positioned near the common drive mechanism 40, and the second expansion chamber 20b is positioned far from the common drive mechanism 40. This means that the second room-temperature chamber 22b is formed on a proximal end of the second cold head 14b and the second expansion chamber 20b is formed on a distal end of the second cold head 14b. A second cooling stage 24b, which is fixed to the second cylinder 18b so as to enclose the second expansion chamber 20b, is provided on the distal end of the second cold head 14b.
When the second displacer 16b axially moves, the second expansion chamber 20b and the second room-temperature chamber 22b complementarily increase and decrease the volume. That is, when the second displacer 16b moves upward, the second expansion chamber 20b is widened, and the second room-temperature chamber 22b is narrowed, and vice versa.
The second displacer 16b includes a second regenerator 26b which is built therein. The second displacer 16b includes a second inlet flow path 28b, which allows the second regenerator 26b to communicate with the second room-temperature chamber 22b, on the upper lid portion of the second displacer 16b. In addition, the second displacer 16b includes a second outlet flow path 30b, which allows the second regenerator 26b to communicate with the second expansion chamber 20b, on the tubular portion of the second displacer 16b. Alternatively, the second outlet flow path 30b may be provided on the lower lid portion of the second displacer 16b. Moreover, the second displacer 16b includes a second inlet flow-straightener 32b which is in inner-contact with the upper lid portion, and a second outlet flow-straightener 34b which is in inner-contact with the lower lid portion. The second regenerator 26b is interposed between the pair of flow-straighteners.
The second cold head 14b includes a second seal portion 36b which blocks a clearance formed between the second cylinder 18b and the second displacer 16b. For example, the second seal portion 36b is a slipper seal, and is mounted on the tubular portion or the upper lid portion of the second displacer 16b.
In this way, the second seal portion 36b is positioned near the common drive mechanism 40, and the second outlet flow path 30b is away from the common drive mechanism 40 and is positioned near the second cooling stage 24b. In other words, the second seal portion 36b is attached to a proximal portion of the second displacer 16b, and the above-described second outlet flow path 30b is formed in the distal portion of the second displacer 16b.
The working gas flows from the second room-temperature chamber 22b into the second regenerator 26b through the second inlet flow path 28b. More specifically, the working gas flows from the second inlet flow path 28b into the second regenerator 26b through the second inlet flow-straightener 32b. The working gas flows from the second regenerator 26b into the second expansion chamber 20b via the second outlet flow-straightener 34b and the second outlet flow path 30b. The working gas goes through a reverse pathway with respect to the above-described pathway when the working gas is returned from the second expansion chamber 20b to the second room-temperature chamber 22b. That is, the working gas is returned from the second expansion chamber 20b to the second room-temperature chamber 22b through the second outlet flow path 30b, the second regenerator 26b, and the second inlet flow path 28b. The working gas, which bypasses the second regenerator 26b and flows into the clearance, is interrupted by the second seal portion 36b.
The GM cryocooler 10 is installed in the shown direction in the use site thereof. That is, the first cold head 14a is disposed downward in the vertical direction, the second cold head 14b is disposed upward in the vertical direction, and thus, the GM cryocooler 10 is installed in a longitudinal direction. The second cold head 14b is installed with a posture inverted to that of the first cold head 14a. The second expansion chamber 20b is disposed upward in the vertical direction in the second cold head 14b while the first expansion chamber 20a is disposed downward in the vertical direction in the first cold head 14a. Alternatively, the GM cryocooler 10 may be installed in a horizontal direction or in other directions.
The common drive mechanism 40 includes a reciprocation drive source 42 which drives the axial reciprocation of the first displacer 16a and the second displacer 16b. The reciprocation drive source 42 includes a rotation drive source 44 (for example, motor) having a rotation output shaft 46, and a Scotch yoke 48 which is connected to the rotation output shaft 46 so as to convert the rotation of the rotation output shaft 46 into axial reciprocation.
The common drive mechanism 40 includes a first connection rod 50a and a second connection rod 50b. The first connection rod 50a axially extends from the reciprocation drive source 42 and connects the reciprocation drive source 42 to the first displacer 16a. The second connection rod 50b axially extends from the reciprocation drive source 42 on the side opposite to the first connection rod 50a and connects the reciprocation drive source 42 to the second displacer 16b. The first displacer 16a, the first connection rod 50a, the second connection rod 50b, and the second displacer 16b are coaxially disposed with respect to each other.
More specifically, the first connection rod 50a axially extends from the Scotch yoke 48 to the first displacer 16a and connects the Scotch yoke 48 to the first displacer 16a. The first connection rod 50a rigidly connects the proximal portion of the first displacer 16a to the Scotch yoke 48. The first connection rod 50a is supported by a first bearing portion 38a so as to be movable in the axial direction. The first bearing portion 38a is disposed between the Scotch yoke 48 and the first displacer 16a.
The second connection rod 50b axially extends from the Scotch yoke 48 to the second displacer 16b and connects the Scotch yoke 48 to the second displacer 16b. The second connection rod 50b rigidly connects the proximal portion of the second displacer 16b to the Scotch yoke 48. The second connection rod 50b is supported by a second bearing portion 38b so as to be movable in the axial direction. The second bearing portion 38b is disposed between the Scotch yoke 48 and the second displacer 16b.
As shown in
The reciprocation drive source 42 and the Scotch yoke 48 shown in
In this way, the common drive mechanism 40 is connected to the first displacer 16a and the second displacer 16b so as to drive the axial reciprocation of the first displacer 16a and the second displacer 16b. The first displacer 16a and the second displacer 16b configure a single displacer connector 16 which is fixedly connected to each other. A relative position of the second displacer 16b with respect to the first displacer 16a is not changed during the axial reciprocation of the first displacer 16a and the second displacer 16b.
Accordingly, the axial reciprocation of the first displacer 16a and the axial reciprocation of the second displacer 16b have phases opposite to each other. When the first displacer 16a is positioned at the top dead center (that is, the dead center on the proximal end side), the second displacer 16b is positioned at the bottom dead portion (that is, the dead center on the distal end side). When the first displacer 16a moves from the top dead center to the bottom dead center (that is, when the first displacer 16a moves from the proximal end of the first cold head 14a to the distal end thereof so as to narrow the first expansion chamber 20a), the second displacer 16b moves from the bottom dead center to the top dead center (that is, the second displacer 16b moves from the distal end of the second cold head 14b to the proximal end thereof so as to widen the second expansion chamber 20b).
As shown in
The refrigerant circulation circuit 54 includes a first refrigerant cooling unit 54a which is thermally coupled to the first cold head 14a, a second refrigerant cooling unit 54b which is thermally coupled to the second cold head 14b, and a connection refrigerant pipe 54c which connects the first refrigerant cooling unit 54a to the second refrigerant cooling unit 54b. In addition, the refrigerant circulation circuit 54 includes a supply pipe 54d and a recovery pipe 54e. Each of the first refrigerant cooling unit 54a and the second refrigerant cooling unit 54b is a spiral refrigerant pipe which is wound around the first cooling stage 24a and the second cooling stage 24b. The first refrigerant cooling unit 54a is cooled by the first cooling stage 24a, and the second refrigerant cooling unit 54b is cooled by the second cooling stage 24b. The connection refrigerant pipe 54c is connected to one end of the first refrigerant cooling unit 54a, and the supply pipe 54d is connected to the other end thereof. The connection refrigerant pipe 54c is connected to one end of the second refrigerant cooling unit 54b, and the recovery pipe 54e is connected to the other end thereof.
A detachable connection mechanism 54f is provided in the connection refrigerant pipe 54c. Accordingly, when the connection mechanism 54f is removed, the portion of the connection refrigerant pipe 54c on the first refrigerant cooling unit 54a side and the portion of the connection refrigerant pipe 54c on the second refrigerant cooling unit 54b side are separated from each other. According to the connection mechanism 54f, disassembly of the refrigerant circulation circuit 54 is easily performed. This contributes to an increase in efficiency of maintenance work of the GM cryocooler 10.
Flow directions of the refrigerant in the refrigerant circulation circuit 54 are shown by arrows. The refrigerant flows from the recovery pipe 54e to the supply pipe 54d through the second refrigerant cooling unit 54b, the connection refrigerant pipe 54c, and the first refrigerant cooling unit 54a. In this way, first, the refrigerant is cooled by the second refrigerant cooling unit 54b, and thereafter, is cooled by the first refrigerant cooling unit 54a.
The cold head has a highest freeze capacity when the cold head is installed in a posture in which the expansion chamber is positioned downward in the vertical direction. As described above, the first cold head 14a has first expansion chamber 20a on the lower side in the vertical direction. However, the second cold head 14b does not have the second expansion chamber on the lower side in the vertical direction. Accordingly, the temperature of the second cooling stage 24b is higher than the temperature of the first cooling stage 24a. According to the above-described refrigerant circuit configuration, first, the recovered refrigerant having a relatively high temperature is cooled by the second cold head 14b having a high temperature, and thereafter, is cooled by the first cold head 14a having a low temperature. Accordingly, it is possible to improve heat exchange efficiency between the refrigerant and the GM cryocooler 10.
In addition, the GM cryocooler 10 includes an auxiliary vacuum vessel 56 in which the second cold head 14b and the second refrigerant cooling unit 54b are accommodated, and a flanged portion 60 for attaching the first cold head 14a to a main vacuum vessel 58 separated from the auxiliary vacuum vessel 56. The first cold head 14a and the first refrigerant cooling unit 54a are accommodated in the main vacuum vessel 58.
The auxiliary vacuum vessel 56 is attached to the proximal end of the second cylinder 18b, and the flanged portion 60 is attached to the proximal end of the first cylinder 18a. The auxiliary vacuum vessel 56 is connected to the flanged portion 60 by a connection pipe 62 which allows the auxiliary vacuum vessel 56 to airtightly communicate with the main vacuum vessel 58. The connection pipe 62 provided a passage through which the supply pipe 54d and the connection refrigerant pipe 54c are introduced from the main vacuum vessel 58 to the auxiliary vacuum vessel 56. The connection pipe 62 has a bellows portion midway.
The second cold head 14b and the second refrigerant cooling unit 54b are covered with the auxiliary vacuum vessel 56, and only the first cold head 14a and the first refrigerant cooling unit 54a are exposed. Therefore, in an operation in which the GM cryocooler 10 is attached to the main vacuum vessel 58, an operator can handle the GM cryocooler 10 as a general GM cryocooler having a single cold head.
The working gas circuit 70 shown in
The working gas circuit 70 includes a valve portion 72. The valve portion 72 includes a first intake valve V1, a first exhaust valve V2, a second intake valve V3, and a second exhaust valve V4. The valve portion 72 is accommodated in the drive mechanism housing 52 shown in
The first intake valve V1 is configured so as to determine a first intake period A1 of the first cold head 14a. The first intake valve V1 is disposed in a first intake flow path 74a which connects a discharge port of the compressor 12 to the first room-temperature chamber 22a of the first cold head 14a. In the first intake period A1 (that is, when the first intake valve V1 opens), the working gas flows from the discharge port of the compressor 12 into the first room-temperature chamber 22a. Inversely, when the first intake valve V1 is closed, the supply of the working gas from the compressor 12 to the first room-temperature chamber 22a is stopped.
The first exhaust valve V2 is configured so as to determine a first exhaust period A2 of the first cold head 14a. The first intake valve V2 is disposed in a first exhaust flow path 76a which connects a suction port of the compressor 12 to the first room-temperature chamber 22a of the first cold head 14a. In the first exhaust period A2 (that is, when the first exhaust valve V2 opens), the working gas flows from the first room-temperature chamber 22a into the suction port of the compressor 12. When the first exhaust valve V2 is closed, the recovery of the working gas from the first room-temperature chamber 22a to the compressor 12 is stopped. As shown in
Similarly, the second intake valve V3 is configured so as to determine a second intake period A3 of the second cold head 14b. The second intake valve V3 is disposed in a second intake flow path 74b which connects the discharge port of the compressor 12 to the second room-temperature chamber 22b of the second cold head 14b. In the second intake period A3 (that is, when the second intake valve V3 opens), the working gas flows from the discharge port of the compressor 12 into the second room-temperature chamber 22b. When the second intake valve V3 is closed, the supply of the working gas from the compressor 12 to the second room-temperature chamber 22b is stopped. As shown in
The second exhaust valve V4 is configured so as to determine a second exhaust period A4 of the second cold head 14b. The second exhaust valve V4 is disposed in a second exhaust flow path 76b which connects the suction port of the compressor 12 to the second room-temperature chamber 22b of the second cold head 14b. In the second exhaust period A4 (that is, when the second exhaust valve V4 opens), the working gas flows from the second room-temperature chamber 22b to the suction port of the compressor 12. When the second exhaust valve V4 is closed, the recovery of the working gas from the second room-temperature chamber 22b to the compressor 12 is stopped. As shown in
In
The first intake period A1 and the second exhaust period A4 are within a range from 0° to 135°, and the first exhaust period A2 and the second intake period A3 are within a range from 180° to 315°. The first intake period A1 and the first exhaust period A2 are alternately positioned to each other, and the second intake period A3 and the second exhaust period A4 are alternately positioned to each other. The first (second) displacer 16a (16b) is positioned at the bottom (top) dead center or in the vicinity thereof at 00, and the first (second) displacer 16a (16b) is positioned at the top (bottom) dead center or in the vicinity thereof at 1800.
The operation of the GM cryocooler 10 having the above-described configuration will be described. When the first displacer 16a is positioned at the bottom dead center of the first cylinder 18a or in the vicinity thereof, the first intake period A1 starts (0° in
When the first displacer 16a positioned at the top dead center or in the vicinity thereof, the first exhaust period A2 starts (180° in
The first cold head 14a repeats the cooling cycle (that is, GM cycle), and thus, the first cooling stage 24a is cooled. Accordingly, the refrigerant is cooled by the first refrigerant cooling unit 54a.
Simultaneously with the above-described operation of the first cold head 14a, the second cold head 14b is operated. When the second displacer 16b positioned at the top dead center or in the vicinity thereof, the second exhaust period A4 starts (0° in
When the second displacer 16b positioned at the bottom dead center of the second cylinder 18b or in the vicinity thereof, the second intake period A3 starts (180° in
In this way, in the second cold head 14b, the cooling cycle (that is, GM cycle) which has a phase opposite to the phase of the first cold head 14a but is similar to the cycle of first cold head 14a is repeated. Accordingly, the second cooling stage 24b is cooled, and the refrigerant is cooled by the second refrigerant cooling unit 54b.
In the expander of the GM cryocooler, there is a technology referred to as so-called “gas assist” using a gas pressure in order to decrease the drive torque. Typical gas assist is realized by distributing a portion of the supplied working gas to a gas assist chamber inside the expander separated from the expansion space. The working gas supplied to the gas assist chamber cannot contribute to PV work in the expansion space. Accordingly, in the gas assist, there is a disadvantage that a decrease in the PV work may occur, that is, a decrease in freezing capacity may occur.
However, in the above-described embodiment, the first intake period A1 overlaps the second exhaust period A4. Accordingly, when gas is supplied from the compressor 12 to the first cold head 14a, the gas is recovered from the second cold head 14b to the compressor 12. In this case, the pressure of the first expansion chamber 20a is higher than the pressure of the second expansion chamber 20b, and this pressure difference biases the displacer connector 16 upward in the
In addition, since the first exhaust period A2 overlaps the second intake period A3, when gas is recovered from the first cold head 14a, gas is supplied to the second cold head 14b, and the pressure of the first expansion chamber 20a is lower than the pressure of the second expansion chamber 20b. This pressure difference biases the displacer connector 16 downward in
Accordingly, operations of the first cold head 14a and the second cold head 14b themselves provide the gas assist to the displacer connector 16. As the above-described typical gas assist configuration, the working gas is not consumed in the dedicated gas assist chamber, and thus, loss of the PV work does not occur. Therefore, it is possible to decrease the drive torque generated by the common drive mechanism 40 to drive the displacer connector 16, and thus, a decrease in a size of the drive mechanism can be obtained.
In order to obtain the above-described advantages, the first intake period A1 and the second exhaust period A4 may not correctly coincide with each other. The second exhaust period A4 may at least partially overlap the first intake period A1. Similarly, the first exhaust period A2 and the second intake period A3 may not correctly coincide with each other. The second intake period A3 may at least partially overlap the first exhaust period A2.
In the above-described embodiment, the second intake period A3 does not overlap the first intake period A1. In addition, the second exhaust period A4 does not overlap the first exhaust period A2. In this way, the intake-exhaust cycle from the compressor 12 to the first cold head 14a is completely deviated from the intake-exhaust cycle from the compressor 12 to the second cold head 14b. Accordingly, variation between a high pressure and a low pressure of the compressor 12 decreases, and thus, it is possible to improve efficiency of the compressor 12.
In order to obtain the advantages, the intake-exhaust cycles of the two cold heads need not be completely deviated from each other. Preferably, the second intake period A3 may be later than first intake period A1 by 150° or more. Along with this, or instead of this, preferably, the second exhaust period A4 may be later than the first exhaust period A2 by 150° or more.
In addition, lengths of the first intake period A1 and the second exhaust period A4 may be different from each other. Similarly, lengths of the first exhaust period A2 and the second intake period A3 may be different from each other. For example, the difference between the intake period and the exhaust period may be within 20° or 5°. In this way, the difference between freezing capacities of the first cold head 14a and the second cold head 14b may be adjusted.
In addition, the lengths of the first intake period A1 and the first exhaust period A2 may be different from each other. Similarly, the lengths of the second intake period A3 and the second exhaust period A4 may be different from each other. In this case, for example, the difference between the intake period and the exhaust period may be within 20° or 5°.
Moreover, in the above-described embodiment, since the GM cryocooler 10 is installed such that the two cold heads disposed to face each other are positioned in the longitudinal direction, it is possible to reduce the area of floor for installation of the GM cryocooler 10.
In the GM cryocooler 10 described with reference to
The first connection rod 50a and the second connection rod 50b configure a single connection rod 50 which is fixedly connected to each other. Alternatively, the first connection rod 50a and the second connection rod 50b may be fixedly connected to each other via an intermediate member.
The first connection rod 50a has a first cross-sectional area S1 in a plane perpendicular to the axial direction, and the second connection rod 50b has a second cross-sectional area S2 in a plane perpendicular to the axial direction. The first cross-sectional area S1 is the same as the second cross-sectional area S2. For example, the first connection rod 50a may have a circular cross-section having a first diameter, and the second connection rod 50b may have a circular cross-section having a second diameter which is the same as the first diameter. Typically, the first connection rod 50a and the second connection rod 50b have the same cross-sectional shape as each other. However, both may have cross-sectional shapes different from each other.
The working gas circuit 70 is configured so as to drive the axial reciprocation of the first displacer 16a and the second displacer 16b. The working gas circuit 70 is connected to the first cold head 14a and the second cold head 14b so as to generate the pressure difference between the first gas chamber and the second gas chamber.
Similarly to the GM cryocooler 10 shown
The first intake period A1 overlaps the second exhaust period A4. Accordingly, when gas is supplied from the compressor 12 to the first cold head 14a, the gas is recovered from the second cold head 14b to the compressor 12. In this case, the pressure of the first expansion chamber 20a is higher than the pressure of the second expansion chamber 20b. In this way, it is possible to move the displacer connector 16 upward by the pressure difference.
In addition, the first exhaust period A2 overlaps the second intake period A3. Gas is supplied to the second cold head 14b when gas is recovered from the first cold head 14a, and thus, the pressure of the first expansion chamber 20a is lower than the pressure of the second expansion chamber 20b. It is possible to move the displacer connector 16 downward by the pressure difference.
In this way, it is possible to provide the GM cryocooler 10 which does not have the common drive mechanism 40. The GM cryocooler 10 is configured of a gas differential-pressure drive type cryocooler. In addition, in a case where the valve portion 72 is configured of a rotary valve, as described above, the GM cryocooler 10 may include a drive source (for example, rotation drive source 44) which is connected to a rotary valve so as to rotationally drive the rotary valve.
In addition, in the GM cryocooler 10 shown in
The first connection rod 50a has the first cross-sectional area S1 in a plane perpendicular to the axial direction, and the second connection rod 50b has the second cross-sectional area S2 in a plane perpendicular to the axial direction. The first cross-sectional area S1 is different from the second cross-sectional area S2. For example, the first cross-sectional area S1 is greater than the second cross-sectional area S2. For example, the first connection rod 50a has a circular cross-section having a first diameter, and the second connection rod 50b has a circular cross-section having a second diameter. The second diameter is smaller than the first diameter.
Accordingly, the working gas circuit 70 can generate a pressure difference assisting the common drive mechanism 40. The operations of the first cold head 14a and the second cold head 14b themselves provide the gas assist to the displacer connector 16.
Moreover, the GM cryocooler 10 shown in
The Scotch yoke 48 is accommodated in an internal space 53 of the drive mechanism housing 52. As described above, the first bearing portion 38a and the second bearing portion 38b respectively seal the first room-temperature chamber 22a and the second room-temperature chamber 22b from the internal space 53. The internal space 53 communicates with the discharge port of the compressor 12 shown in
When the displacer connector 16 moves upward, since the first room-temperature chamber 22a is a high pressure PH and the second room-temperature chamber 22b is a low pressure PL, the upward assist force Fup is represented by Fup=(PH−PL) S1. Meanwhile, when the displacer connector 16 moves upward, since the first room-temperature chamber 22a is a low pressure PL and the second room-temperature chamber 22b is a high pressure PH, the downward assist force Fdown is represented by Fdown=(PH−PL) S2. Accordingly, in a case where the first cross-sectional area S1 is greater than the second cross-sectional area S2, the upward assist force Fup is greater than the downward assist force Fdown.
The GM cryocooler 10 is installed in the shown direction in the use site thereof. That is, the first cold head 14a is disposed downward in the vertical direction, the second cold head 14b is disposed upward in the vertical direction, and thus, the GM cryocooler 10 is installed in a longitudinal direction. In this case, the load of the drive source (for example, rotation drive source 44) may be different from each other according to the movement directions of the displacer connector 16. For example, due to the weight of the displacer connector 16 itself, the load of the drive source (for example, the rotation drive source 44) when the displacer connector 16 moves upward may be greater than the load of the drive source when the displacer connector 16 moves downward.
The GM cryocooler 10 shown in
In an embodiment, the internal space 53 of the drive mechanism housing 52 may be maintained to a predetermined pressure different from the low pressure PL. Similarly, it is possible to apply assist forces different from each other to the displacer connector 16 according to the movement direction of the displacer connector 16.
In an embodiment, the first cross-sectional area S1 of the first connection rod 50a may be smaller than the second cross-sectional area S2 of the second connection rod 50b. For example, the first connection rod 50a has a circular cross-section having a first diameter, the second connection rod 50b has a circular cross-section having a second diameter, and the first diameter may be smaller than the second diameter. In this way, the upward assist force Fup can be smaller than the downward assist force Fdown.
The GM cryocooler 10 includes the first connection rod 50a and the second connection rod 50b, and the first connection rod 50a and the second connection rod 50b are axially connected to each other. The first displacer 16a is connected to the second displacer 16b via the first connection rod 50a and the second connection rod 50b such that the axial reciprocation of the first displacer 16a has the phase opposite to the phase of the axial reciprocation of the second displacer 16b. The relative position of the second displacer 16b with respect to the first displacer 16a is not changed during the axial reciprocation of the first displacer 16a and the second displacer 16b.
The first connection rod 50a and the second connection rod 50b configure a single connection rod 50 which is fixedly connected to each other. Alternatively, the first connection rod 50a and the second connection rod 50b may be fixedly connected to each other via an intermediate member.
The first connection rod 50a has the first cross-sectional area S1 in a plane perpendicular to the axial direction, and the second connection rod 50b has the second cross-sectional area S2 in a plane perpendicular to the axial direction. The first cross-sectional area S1 is different from the second cross-sectional area S2. For example, the first cross-sectional area S1 is greater than the second cross-sectional area S2. For example, the first connection rod 50a has a circular cross-sectional area having a first diameter, and the second connection rod 50b has a circular cross-section having a second diameter. The second diameter is smaller than the first diameter.
Similarly to the GM cryocooler 10 shown
In this way, the GM cryocooler 10 can be configured of a gas differential-pressure drive type cryocooler. In addition, it is possible to apply drive forces different from each other to the displacer connector 16 according to the movement direction of the displacer connector 16. Accordingly, the upward movement and the downward movement of the displacer connector 16 can be symmetrized to each other. It is possible to uniformize the freezing performance of the first cold head 14a and the second cold head 14b.
It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.
For example, two cold heads may have configurations different from each other. The first cold head 14a and the second cold head 14b have sizes different from each other, and thus, may have freezing capacities different from each other. Alternatively, one or both of the first cold head 14a and the second cold head 14b may be multiple-staged cold head (for example, two-staged cold head).
The reciprocation drive source 42 may have a linear motor which drives the axial reciprocation of the first displacer 16a and the second displacer 16b.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-208614 | Oct 2015 | JP | national |
| 2016-116329 | Jun 2016 | JP | national |
