JP6998776B2 - GM freezer - Google Patents

Description

The present invention relates to a GM (Gifford-McMahon) refrigerator.

GM refrigerators are roughly classified into two types, motor-driven type and gas-driven type, depending on the drive source of the displacer. In the motor-driven type, the displacer is mechanically connected to the motor and driven by the motor. In the gas-driven type, the displacer is driven by gas pressure.

Japanese Unexamined Patent Publication No. 2014-139498

In a typical gas-driven GM refrigerator, the load on the compressor tends to be larger than that of the motor-driven GM refrigerator. In the motor-driven GM refrigerator, the compressor only needs to supply the working gas to the expansion chamber, whereas in the gas-driven GM refrigerator, the compressor not only supplies the working gas to the expansion chamber but also drives the displacer. Because it has to be.

One of the exemplary objects of an aspect of the present invention is to reduce the load on the compressor in a gas driven GM refrigerator.

According to an aspect of the present invention, the GM refrigerating machine accommodates a displacer capable of reciprocating in the axial direction, a drive piston connected to the displacer so as to drive the reciprocating movement of the displacer in the axial direction, and the drive piston. The drive chamber is connected to the drive chamber, the drive chamber pressure switching valve that is connected to the drive chamber and generates periodic pressure fluctuations of high pressure and low pressure in the drive chamber, and the drive chamber pressure switching valve are connected to the drive chamber in parallel with the drive chamber pressure switching valve. It comprises an intermediate pressure source having an intermediate pressure between the high pressure and the low pressure during the periodic pressure fluctuations in the drive chamber.

It should be noted that any combination of the above components or components or expressions of the present invention that are mutually replaced between methods, devices, systems, etc. are also effective as aspects of the present invention.

According to the present invention, the load on the compressor can be reduced in the gas-driven GM refrigerator.

It is a figure which shows schematically the gas drive type GM refrigerator which concerns on embodiment. It is a figure which illustrates the valve timing and pressure fluctuation of the GM refrigerator shown in FIG.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are designated by the same reference numerals, and duplicate description will be omitted as appropriate. The scales and shapes of the illustrated parts are set for convenience of explanation and are not limitedly interpreted unless otherwise specified. The embodiments are exemplary and do not limit the scope of the invention in any way. Not all features and combinations thereof described in the embodiments are essential to the invention.

FIG. 1 is a schematic view showing a GM refrigerator 10 according to an embodiment.

The GM refrigerator 10 includes a compressor 12 for compressing a working gas (for example, helium gas) and a cold head 14 for cooling the working gas by adiabatic expansion. The compressor 12 has a compressor discharge port 12a and a compressor suction port 12b. The compressor discharge port 12a and the compressor suction port 12b function as a high-pressure source and a low-pressure source of the GM refrigerator 10, respectively. The cold head 14 is also called an expander.

As will be described in detail later, the compressor 12 supplies a high-pressure (PH) working gas to the cold head 14 from the compressor discharge port 12a. The cold head 14 is provided with a cold storage device 15 for precooling the working gas. The precooled working gas is further cooled by expansion in the cold head 14. The working gas is collected in the compressor suction port 12b through the cool storage device 15. The working gas cools the cooler 15 as it passes through the cooler 15. The compressor 12 compresses the recovered low-pressure (PL) working gas and supplies it to the cold head 14 again.

The cold head 14 shown is a single-stage type. However, the cold head 14 may be of a multi-stage type.

The cold head 14 is a gas drive type. Therefore, the cold head 14 includes an axially movable body 16 as a free piston driven by gas pressure, and a cold head housing 18 that is airtightly configured and accommodates the axially movable body 16. The cold head housing 18 supports the axially movable body 16 so as to be reciprocating in the axial direction. Unlike the motor-driven GM refrigerator, the cold head 14 does not have a motor and a coupling mechanism (eg, a Scotch yoke mechanism) that drives the axially movable body 16.

The axially movable body 16 includes a displacer 20 capable of reciprocating in the axial direction (vertical direction in FIG. 1, indicated by an arrow C) and a drive piston 22 connected to the displacer 20 so as to drive the displacer 20 in the axial direction. , Equipped with. The drive piston 22 is arranged coaxially with the displacer 20 and apart from each other in the axial direction.

The cold head housing 18 includes a displacer cylinder 26 that houses the displacer 20 and a piston cylinder 28 that houses the drive piston 22. The piston cylinder 28 is arranged coaxially with the displacer cylinder 26 and adjacent to the displacer cylinder 26 in the axial direction. Although the details will be described later, the drive unit of the cold head 14 which is a gas drive type includes a drive piston 22 and a piston cylinder 28.

Further, the axially movable body 16 includes a connecting rod 24 that rigidly connects the displacer 20 to the drive piston 22 so that the displacer 20 reciprocates in the axial direction integrally with the drive piston 22. The connecting rod 24 also extends from the displacer 20 to the drive piston 22 coaxially with the displacer 20 and the drive piston 22.

The drive piston 22 has a smaller dimension than the displacer 20. The axial length of the drive piston 22 is shorter than that of the displacer 20, and the diameter of the drive piston 22 is also smaller than that of the displacer 20. The diameter of the connecting rod 24 is smaller than that of the drive piston 22.

The volume of the piston cylinder 28 is smaller than that of the displacer cylinder 26. The axial length of the piston cylinder 28 is shorter than that of the displacer cylinder 26, and the diameter of the piston cylinder 28 is also smaller than that of the displacer cylinder 26.

The dimensional relationship between the drive piston 22 and the displacer 20 is not limited to the above, and may be different from the above. Similarly, the dimensional relationship between the piston cylinder 28 and the displacer cylinder 26 is not limited to the above, and may be different from the above. For example, the drive piston 22 may be the tip end portion of the connecting rod 24, and the diameter of the drive piston 22 may be equal to the diameter of the connecting rod 24.

The axial reciprocating movement of the displacer 20 is guided by the displacer cylinder 26. Typically, the displacer 20 and the displacer cylinder 26 are axially extending cylindrical members, respectively, and the inner diameter of the displacer cylinder 26 matches or is slightly larger than the outer diameter of the displacer 20. Similarly, the axial reciprocating movement of the drive piston 22 is guided by the piston cylinder 28. Typically, the drive piston 22 and the piston cylinder 28 are axially extending cylindrical members, respectively, and the inner diameter of the piston cylinder 28 matches or is slightly larger than the outer diameter of the drive piston 22.

Since the displacer 20 and the drive piston 22 are rigidly connected by the connecting rod 24, the axial stroke of the drive piston 22 is equal to the axial stroke of the displacer 20, and both move integrally over the entire stroke. The position of the drive piston 22 with respect to the displacer 20 remains unchanged during the axial reciprocation of the axially movable body 16.

Further, the cold head housing 18 includes a connecting rod guide 30 for connecting the displacer cylinder 26 to the piston cylinder 28. The connecting rod guide 30 extends from the displacer cylinder 26 to the piston cylinder 28 coaxially with the displacer cylinder 26 and the piston cylinder 28. The connecting rod 24 penetrates the connecting rod guide 30. The connecting rod guide 30 is configured as a bearing that guides the axial reciprocating movement of the connecting rod 24.

The displacer cylinder 26 is airtightly connected to the piston cylinder 28 via the connecting rod guide 30. Thus, the cold head housing 18 is configured as a pressure vessel for the working gas. The connecting rod guide 30 may be regarded as a part of either the displacer cylinder 26 or the piston cylinder 28.

The first seal portion 32 is provided between the connecting rod 24 and the connecting rod guide 30. The first seal portion 32 is attached to either the connecting rod 24 or the connecting rod guide 30, and slides on the other of the connecting rod 24 or the connecting rod guide 30. The first seal portion 32 is composed of, for example, a seal member such as a slipper seal or an O-ring. The piston cylinder 28 is hermetically configured with respect to the displacer cylinder 26 by the first seal portion 32. In this way, the piston cylinder 28 is fluidly isolated from the displacer cylinder 26, and the internal pressure of the piston cylinder 28 and the internal pressure of the displacer cylinder 26 can have different magnitudes. Since the first seal portion 32 is provided, direct gas flow between the piston cylinder 28 and the displacer cylinder 26 does not occur.

The displacer cylinder 26 is divided into an expansion chamber 34 and a room temperature chamber 36 by the displacer 20. The displacer 20 forms an expansion chamber 34 with the displacer cylinder 26 at one end in the axial direction, and a room temperature chamber 36 with the displacer cylinder 26 at the other end in the axial direction. The room temperature chamber 36 can also be called a compression chamber. The expansion chamber 34 is arranged on the bottom dead center LP1 side of the displacer 20, and the room temperature chamber 36 is arranged on the top dead center UP1 side of the displacer 20. Further, the cold head 14 is provided with a cooling stage 38 fixed to the displacer cylinder 26 so as to enclose the expansion chamber 34.

The cold storage 15 is built in the displacer 20. The displacer 20 has an inlet flow path 40 at its upper lid, which communicates the cool storage device 15 with the room temperature chamber 36. Further, the displacer 20 has an outlet flow path 42 in the cylinder portion thereof, which communicates the cold storage device 15 with the expansion chamber 34. Alternatively, the outlet flow path 42 may be provided in the lower lid portion of the displacer 20. In addition, the cold storage 15 includes an inlet retainer 41 inscribed in the upper lid portion and an outlet retainer 43 inscribed in the lower lid portion. The cold storage material may be, for example, a copper wire mesh. The retainer may be a wire mesh that is coarser than the cold storage material.

The second seal portion 44 is provided between the displacer 20 and the displacer cylinder 26. The second seal portion 44 is, for example, a slipper seal, and is attached to the cylinder portion or the upper lid portion of the displacer 20. Since the clearance between the displacer 20 and the displacer cylinder 26 is sealed by the second seal portion 44, there is no direct gas flow between the room temperature chamber 36 and the expansion chamber 34 (that is, the gas flow bypassing the cool storage 15).

When the displacer 20 moves axially, the expansion chamber 34 and the room temperature chamber 36 complementarily increase or decrease the volume. That is, when the displacer 20 moves downward, the expansion chamber 34 becomes narrower and the room temperature chamber 36 becomes wider. The reverse is also true.

The working gas flows from the room temperature chamber 36 into the cool storage device 15 through the inlet flow path 40. More precisely, the working gas flows from the inlet flow path 40 through the inlet retainer 41 into the cooler 15. The working gas flows from the cold storage 15 into the expansion chamber 34 via the outlet retainer 43 and the outlet flow path 42. When the working gas returns from the expansion chamber 34 to the room temperature chamber 36, it follows the reverse route. That is, the working gas returns from the expansion chamber 34 to the room temperature chamber 36 through the outlet flow path 42, the cold storage device 15, and the inlet flow path 40. The working gas that bypasses the cool storage 15 and tries to flow through the clearance is shut off by the second seal portion 44.

The piston cylinder 28 includes a drive chamber 46 whose pressure is controlled to drive the drive piston 22. The drive chamber 46 corresponds to the internal space of the piston cylinder 28. The drive chamber 46 is divided into an upper section 46a and a lower section 46b by the drive piston 22. The drive piston 22 forms an upper section 46a with the piston cylinder 28 at one end in the axial direction and a lower section 46b with the piston cylinder 28 at the other end in the axial direction. When the drive piston 22 moves axially, the upper compartment 46a and the lower compartment 46b complementarily increase or decrease the volume. The connecting rod 24 extends from the lower surface of the drive piston 22 through the lower section 46b to the connecting rod guide 30. Further, the connecting rod 24 extends through the room temperature chamber 36 to the upper lid portion of the displacer 20.

A third seal portion 50, which is a clearance between the drive piston 22 and the piston cylinder 28, is provided between the drive piston 22 and the piston cylinder 28. The third seal portion 50 acts as a flow path resistance with respect to the gas flow in the upper section 46a and the lower section 46b. The third seal portion 50 may have a seal member such as a slipper seal mounted on the side surface of the drive piston 22 so as to seal this clearance. In that case, the lower section 46b of the drive chamber 46 will be sealed by the first seal portion 32 and the third seal portion 50.

When the drive piston 22 moves downward, the lower section 46b becomes narrower. At this time, the gas in the lower section 46b is compressed and the pressure increases. The pressure in the lower compartment 46b acts upward on the lower surface of the drive piston 22. Therefore, the lower section 46b generates a gas spring force that opposes the downward movement of the drive piston 22. The lower section 46b can also be referred to as a gas spring chamber. On the contrary, when the drive piston 22 moves upward, the lower section 46b expands. The pressure in the lower section 46b decreases, and the gas spring force acting on the drive piston 22 also decreases.

The cold head 14 is installed in the orientation shown in the illustration at the site where it is used. That is, the cold head 14 is installed vertically so that the displacer cylinder 26 is arranged vertically downward and the piston cylinder 28 is arranged vertically upward. As described above, when the cooling stage 38 is installed in a posture facing downward in the vertical direction, the GM refrigerator 10 has the highest refrigerating capacity. However, the arrangement of the GM refrigerator 10 is not limited to this. On the contrary, the cold head 14 may be installed in a posture in which the cooling stage 38 faces upward in the vertical direction. Alternatively, the cold head 14 may be installed sideways or in any other orientation.

The driving force acting on the drive piston 22 due to the working gas pressure acts downward on the drive piston 22 when the drive piston 22 moves downward. Since the gravity due to the weight of the axially movable body 16 also acts downward, when the cold head 14 is installed in a posture in which the cooling stage 38 is directed downward in the vertical direction, the driving force during downward movement is in the same direction as the gravity. On the contrary, the driving force at the time of upward movement is opposite to the gravity. The gas spring force acting on the drive piston 22 from the gas spring chamber (that is, the lower section 46b of the drive chamber 46) alleviates or prevents a difference in behavior between the upward movement and the downward movement of the axially movable body 16. Useful for.

Further, the GM refrigerator 10 includes a working gas circuit 52 that connects the compressor 12 to the cold head 14. The working gas circuit 52 is configured to generate a pressure difference between the piston cylinder 28 (ie, drive chamber 46) and the displacer cylinder 26 (ie, expansion chamber 34 and / or room temperature chamber 36). This pressure difference causes the axially movable body 16 to move in the axial direction. If the pressure of the displacer cylinder 26 is lower than that of the piston cylinder 28, the drive piston 22 moves downward, and the displacer 20 also moves downward accordingly. On the contrary, if the pressure of the displacer cylinder 26 is higher than that of the piston cylinder 28, the drive piston 22 moves upward, and the displacer 20 also moves upward accordingly.

The working gas circuit 52 includes a valve portion 54. The valve portion 54 may be disposed in the cold head housing 18 and may be connected to the compressor 12 by piping. The valve portion 54 may be disposed outside the cold head housing 18 and may be connected to each of the compressor 12 and the cold head 14 by piping.

The valve portion 54 includes an expansion chamber pressure switching valve (hereinafter, also referred to as a main pressure switching valve) 60 and a drive chamber pressure switching valve (hereinafter, also referred to as an auxiliary pressure switching valve) 62. The main pressure switching valve 60 has a main intake opening / closing valve V1 and a main exhaust opening / closing valve V2. The auxiliary pressure switching valve 62 has an auxiliary intake opening / closing valve V3 and an auxiliary exhaust opening / closing valve V4.

The working gas circuit 52 includes a high pressure line 13a and a low pressure line 13b that connect the compressor 12 to the valve portion 54. The high pressure line 13a extends from the compressor discharge port 12a, branches in the middle, and is connected to the main intake opening / closing valve V1 and the sub intake opening / closing valve V3. The low-pressure line 13b extends from the compressor suction port 12b, branches in the middle, and is connected to the main exhaust opening / closing valve V2 and the sub-exhaust opening / closing valve V4.

Further, the working gas circuit 52 includes a main passage 64 and a sub-passage 66 that connect the cold head 14 to the valve portion 54. The main passage 64 connects the displacer cylinder 26 to the main pressure switching valve 60. The main passage 64 extends from the room temperature chamber 36, branches in the middle, and is connected to the main intake opening / closing valve V1 and the main exhaust opening / closing valve V2. The auxiliary passage 66 connects the drive chamber 46 to the auxiliary pressure switching valve 62. The auxiliary passage 66 extends from the upper section 46a of the drive chamber 46, branches in the middle, and is connected to the auxiliary intake opening / closing valve V3 and the auxiliary exhaust opening / closing valve V4.

The main pressure switching valve 60 is configured to selectively communicate the compressor discharge port 12a or the compressor suction port 12b to the room temperature chamber 36 of the displacer cylinder 26. In the main pressure switching valve 60, the main intake opening / closing valve V1 and the main exhaust opening / closing valve V2 are exclusively opened. That is, it is prohibited to open the main intake opening / closing valve V1 and the main exhaust opening / closing valve V2 at the same time. The main intake opening / closing valve V1 and the main exhaust opening / closing valve V2 may be temporarily closed together.

When the main intake opening / closing valve V1 is open, the main exhaust opening / closing valve V2 is closed. Working gas flows from the compressor discharge port 12a to the displacer cylinder 26 through the high-pressure line 13a and the main passage 64. As described above, the working gas flows from the room temperature chamber 36 to the expansion chamber 34 through the cool storage device 15. In this way, the working gas of the high-pressure PH is supplied from the compressor 12 to the expansion chamber 34, and the expansion chamber 34 is boosted. On the contrary, when the main intake opening / closing valve V1 is closed, the supply of the working gas from the compressor 12 to the expansion chamber 34 is stopped.

On the other hand, when the main exhaust opening / closing valve V2 is open, the main intake opening / closing valve V1 is closed. First, the working gas of high-pressure PH expands in the expansion chamber 34 and is depressurized. Working gas flows from the expansion chamber 34 to the room temperature chamber 36 through the cool storage device 15. Working gas flows from the displacer cylinder 26 to the compressor suction port 12b through the main passage 64 and the low pressure line 13b. In this way, the working gas of the low pressure PL is recovered from the cold head 14 to the compressor 12. When the main exhaust open / close valve V2 is closed, the recovery of the working gas from the expansion chamber 34 to the compressor 12 is stopped.

The auxiliary pressure switching valve 62 is configured to selectively communicate the compressor discharge port 12a or the compressor suction port 12b to the drive chamber 46 of the piston cylinder 28. The sub-pressure switching valve 62 is configured such that the sub-intake opening / closing valve V3 and the sub-exhaust opening / closing valve V4 are exclusively opened. That is, it is prohibited to open the sub-intake open / close valve V3 and the sub-exhaust open / close valve V4 at the same time. The sub-intake open / close valve V3 and the sub-exhaust open / close valve V4 may be temporarily closed together.

When the sub-intake open / close valve V3 is open, the sub-exhaust open / close valve V4 is closed. Working gas flows from the compressor discharge port 12a to the piston cylinder 28 through the high-pressure line 13a and the auxiliary passage 66. In this way, the working gas of the high-pressure PH is supplied from the compressor 12 to the drive chamber 46, and the drive chamber 46 is boosted. When the sub intake opening / closing valve V3 is closed, the supply of the working gas from the compressor 12 to the drive chamber 46 is stopped.

On the other hand, when the sub-exhaust open / close valve V4 is open, the sub-intake open / close valve V3 is closed. The working gas is recovered from the drive chamber 46 to the compressor suction port 12b through the auxiliary passage 66 and the low pressure line 13b, and the drive chamber 46 is stepped down to the low pressure PL. When the sub-exhaust open / close valve V4 is closed, the collection of the working gas from the drive chamber 46 to the compressor 12 is stopped.

In this way, the main pressure switching valve 60 generates periodic pressure fluctuations of high pressure PH and low pressure PL in the expansion chamber 34. Further, the auxiliary pressure switching valve 62 generates periodic pressure fluctuations of high pressure PH and low pressure PL in the drive chamber 46.

The auxiliary pressure switching valve 62 is configured to control the pressure in the drive chamber 46 so that the drive piston 22 drives the axial reciprocating movement of the displacer 20. Typically, the pressure fluctuations in the drive chamber 46 are generated in the same period and in substantially opposite phases as the pressure fluctuations in the expansion chamber 34. When the expansion chamber 34 has a high voltage PH, the drive chamber 46 becomes a low voltage PL, and the drive piston 22 can move the displacer 20 upward. When the expansion chamber 34 has a low pressure PL, the drive chamber 46 becomes a high pressure PH, and the drive piston 22 can move the displacer 20 downward.

The valve portion 54 may take the form of a rotary valve. In this case, a group of valves (V1 to V4) are incorporated in the valve portion 54 and are driven synchronously. The valve portion 54 is configured so that the valve (V1 to V4) is properly switched by the rotational sliding of the valve disc (or valve rotor) with respect to the valve body (or valve stator). A group of valves (V1 to V4) are switched at the same cycle during operation of the GM refrigerator 10, whereby the four open / close valves (V1 to V4) periodically change the open / close state. The four on-off valves (V1 to V4) are opened and closed in different phases.

The GM refrigerator 10 may include a rotation drive source 56 connected to the valve portion 54 so as to rotate the valve portion 54. The rotary drive source 56 is mechanically connected to the valve portion 54. The rotary drive source 56 is, for example, a motor. However, the rotary drive source 56 is not mechanically connected to the axially movable body 16. Further, the GM refrigerator 10 may include a control unit 58 that controls the valve unit 54. The control unit 58 may control the rotation drive source 56.

In certain embodiments, the group of valves (V1 to V4) may take the form of a plurality of individually controllable valves. Each valve (V1 to V4) may be an electromagnetic on-off valve. In this case, the rotary drive source 56 is not provided, and each valve (V1 to V4) is electrically connected to the control unit 58. The control unit 58 may control the opening and closing of each valve (V1 to V4).

Further, the GM refrigerator 10 includes an intermediate pressure source 100 connected to the drive chamber in parallel with the auxiliary pressure switching valve 62. The intermediate pressure source 100 is connected to the drive chamber 46 so that the working gas can flow between the intermediate pressure source 100 and the drive chamber 46. The intermediate pressure source 100 branches from the auxiliary passage 66 at the branch point 68. The branch point 68 is located between the auxiliary pressure switching valve 62 and the drive chamber 46 on the auxiliary passage 66. Alternatively, the intermediate pressure source 100 may be connected to the drive chamber 46 without going through the auxiliary passage 66.

In this way, the intermediate pressure source 100 communicates with the drive chamber 46 via (or without) the sub-communications 66. The intermediate pressure source 100 does not communicate with the displacer cylinder 26, that is, the expansion chamber 34 and the room temperature chamber 36, and the main communication passage 64. Further, the intermediate pressure source 100 is merely connected to the high pressure line 13a and the low pressure line 13b via the auxiliary pressure switching valve 62, and does not directly communicate with the high pressure line 13a and the low pressure line 13b.

The intermediate pressure source 100 is configured such that the pressure of the intermediate pressure source 100 is lower than the pressure of the drive chamber 46 at the time when the intake air of the drive chamber 46 ends, that is, at the time when the auxiliary intake opening / closing valve V3 is closed. Further, the intermediate pressure source 100 is configured such that the pressure of the intermediate pressure source 100 exceeds the pressure of the drive chamber 46 at the time when the exhaust of the drive chamber 46 ends, that is, at the time when the sub-exhaust opening / closing valve V4 is closed.

More specifically, the intermediate pressure source 100 has an intermediate pressure between the high pressure PH and the low pressure PL during periodic pressure fluctuations between the high pressure PH and the low pressure PL in the drive chamber 46. The intermediate pressure source 100 is configured to maintain an intermediate pressure between the high pressure PH and the low pressure PL during periodic pressure fluctuations in the drive chamber 46.

Therefore, the intermediate pressure source 100 can preliminarily recover the working gas from the drive chamber 46 immediately after closing the auxiliary intake opening / closing valve V3 as an auxiliary gas storage tank provided separately from the compressor 12. .. Further, the intermediate pressure source 100 can preliminarily supply the working gas to the drive chamber 46 immediately after closing the sub-exhaust opening / closing valve V4 as an auxiliary gas storage tank.

As an example, the intermediate pressure source 100 includes a flow path resistance member 102 connected to the drive chamber 46 in parallel with the auxiliary pressure switching valve 62, and a buffer volume 104 connected to the drive chamber 46 via the flow path resistance member 102. , Equipped with. The flow path resistance member 102 is connected between the buffer volume 104 and the branch point 68.

The flow path resistance member 102 is an element having a function of delaying the fluctuation of the pressure (hereinafter, also referred to as the buffer pressure) of the buffer volume 104 with respect to the periodic pressure fluctuation in the drive chamber 46, and is, for example, an orifice. The flow path resistance member 102 has a drive chamber 46 such that the pressure of the buffer volume 104 becomes lower when the drive chamber 46 has a high pressure PH, and the pressure of the buffer volume 104 becomes higher when the drive chamber 46 has a low pressure PL. It is designed to form a pressure difference between and the buffer volume 104. The flow path resistance member 102 may be a flow rate control valve or any other member that provides flow path resistance.

The buffer volume 104 is configured to store an intermediate pressure working gas between the high pressure PH and the low pressure PL. The buffer volume 104 is configured as, for example, a buffer tank. The shape of the buffer volume 104 is arbitrary. The intermediate pressure may be, for example, the average pressure PM of the high pressure PH and the low pressure PL. By doing so, it is possible to generate a larger differential pressure with each of the high pressure PH and the low pressure PL. The intermediate pressure may be any pressure between the high pressure PH and the low pressure PL.

When the sub-intake open / close valve V3 is open, the high-pressure PH working gas flows into not only the drive chamber 46 but also the buffer volume 104. However, since the flow path resistance member 102 is provided, the degree of pressure increase in the buffer volume 104 is smaller than that in the drive chamber 46. Therefore, when the sub intake opening / closing valve V3 is closed, the pressure in the buffer volume 104 is lower than the pressure in the drive chamber 46. Further, when the sub-exhaust open / close valve V4 is open, the working gas flows out not only from the drive chamber 46 but also from the buffer volume 104, but the degree of pressure reduction of the buffer volume 104 due to the flow path resistance member 102 is the degree of pressure reduction in the drive chamber. It is smaller than 46. Therefore, when the sub-exhaust open / close valve V4 is closed, the pressure in the buffer volume 104 exceeds the pressure in the drive chamber 46. In this way, the combination of the flow path resistance member 102 and the buffer volume 104 connected in series functions as the intermediate pressure source 100 of the drive chamber 46.

The buffer volume 104 is sufficiently larger than the drive chamber 46, so that the buffer pressure is ideally maintained constant during operation of the GM refrigerator 10 (intermediate pressures such as high pressure PH and low pressure PL). The average pressure is maintained at PM). In reality, the volume of the buffer volume 104 is finite, and the pressure of the buffer volume 104 fluctuates somewhat depending on the pressure of the drive chamber 46 and the open / closed state of the auxiliary pressure switching valve 62, but is still maintained substantially constant (still. Maintained in an intermediate pressure zone containing average pressure PM).

As an example, the buffer volume 104 may have a volume more than twice that of the drive chamber 46. By doing so, the pressure fluctuation of the buffer volume 104 can be reduced. It is possible to avoid excessive boosting of the buffer volume 104 due to the opening of the sub-intake opening / closing valve V3 and excessive step-down due to opening of the sub-exhaust opening / closing valve V4. Further, in order to suppress the increase in size of the GM refrigerator 10, the buffer volume 104 may have a volume 10 times or less that of the drive chamber 46. From this point of view, the buffer volume 104 may have, for example, 3 to 7 times the volume of the drive chamber 46, for example, about 5 times the volume.

The buffer volume 104 may be installed in the cold head housing 18. Alternatively, the buffer volume 104 may be installed away from the cold head housing 18.

FIG. 2 is a diagram illustrating valve timing and pressure fluctuation of the GM refrigerator 10 shown in FIG. The upper part of FIG. 2 shows the valve timing of each valve (V1 to V4) over one cycle of the refrigerating cycle of the GM refrigerator 10, and the lower part of FIG. 2 shows the pressure fluctuation in the cold head 14. One cycle of the refrigerating cycle of the GM refrigerator 10 is divided into four periods: a first period T1, a second period T2, a third period T3, and a fourth period T4. The second period T2 follows the first period T1, the third period T3 follows the second period T2, the fourth period T4 follows the third period T3, and the first period of the next cycle of the refrigeration cycle. T1 follows the fourth period T4. The pressures of the expansion chamber 34, the drive chamber 46, and the buffer volume 104 in the first period T1 to the fourth period T4 are shown. In the valve timing illustration, the solid line indicates that the valve is open, and the dashed line indicates that the valve is closed.

When the displacer 20 is at or near the bottom dead center LP1, the intake process of the GM refrigerator 10 is started. The illustrated first period T1 and second period T2 correspond to the intake process of the GM refrigerator 10. The main intake open / close valve V1 is open, and the main exhaust open / close valve V2 is closed. The expansion chamber 34 has a high pressure PH.

The drive chamber 46 is exhausted at the same time as the intake air to the expansion chamber 34. In the first period T1, both the sub-intake open / close valve V3 and the sub-exhaust open / close valve V4 are closed. Since the drive chamber 46 is boosted to the high pressure PH in the fourth period T4 immediately before, the pressure (PH) of the drive chamber 46 is higher than the pressure (PM) of the buffer volume 104 at the start of the first period T1. Therefore, the working gas is discharged from the drive chamber 46 to the buffer volume 104. In the first period T1, the drive chamber 46 is stepped down to the pressure of the buffer volume 104. In the middle of the intake process of the GM refrigerator 10, the first period T1 is shifted to the second period T2. The sub-intake open / close valve V3 remains closed, but the sub-exhaust open / close valve V4 is opened. Therefore, in the second period T2, the working gas is discharged from the drive chamber 46 to the compressor 12, and the drive chamber 46 is stepped down to the low pressure PL.

Since the flow path resistance member 102 is provided between the buffer volume 104 and the sub-exhaust open / close valve V4 as described above, the pressure of the buffer volume 104 is maintained substantially constant. In the second period T2, the pressure decrease of the buffer volume 104 is suppressed as compared with the drive chamber 46.

Therefore, in the intake process, the driving force due to the differential pressure between the driving chamber 46 and the expansion chamber 34 acts upward on the driving piston 22. In the first period T1, a driving force proportional to the differential pressure PH-PM acts on the drive piston 22, and in the second period T2, a driving force proportional to the differential pressure PH-PL acts on the drive piston 22. Therefore, the displacer 20 moves from the bottom dead center LP1 to the top dead center UP1 together with the drive piston 22. In this way, the volume of the expansion chamber 34 is increased and filled with high-pressure gas.

When the displacer 20 is at or near top dead center UP1, the exhaust process of the GM refrigerator 10 is started. The illustrated third period T3 and fourth period T4 correspond to the exhaust process of the GM refrigerator 10. The main exhaust open / close valve V2 is open, and the main intake open / close valve V1 is closed. The high-pressure gas expands and is cooled in the expansion chamber 34. The expanded gas is recovered in the compressor 12 through the room temperature chamber 36 while cooling the cool storage device 15. The expansion chamber 34 becomes a low pressure PL.

At the same time as the exhaust from the expansion chamber 34, the intake air to the drive chamber 46 is performed. In the third period T3, both the sub-intake open / close valve V3 and the sub-exhaust open / close valve V4 are closed. At the start of the third period T3, the pressure (PL) of the drive chamber 46 is lower than the pressure (PM) of the buffer volume 104. Therefore, the working gas is supplied from the buffer volume 104 to the drive chamber 46. In the third period T3, the drive chamber 46 is boosted to the pressure of the buffer volume 104. In the middle of the exhaust process of the GM refrigerator 10, the transition from the third period T3 to the fourth period T4. The sub-exhaust open / close valve V4 remains closed, but the sub-intake open / close valve V3 is opened. Therefore, in the fourth period T4, the working gas is supplied from the compressor 12 to the drive chamber 46, and the drive chamber 46 is boosted to the high pressure PL.

Since the flow path resistance member 102 is provided between the buffer volume 104 and the sub intake opening / closing valve V3 as described above, the pressure of the buffer volume 104 is maintained substantially constant. In the fourth period T4, the pressure increase of the buffer volume 104 is suppressed as compared with the drive chamber 46.

Therefore, in the exhaust process, the driving force due to the differential pressure between the drive chamber 46 and the expansion chamber 34 acts downward on the drive piston 22. In the third period T3, a driving force proportional to the differential pressure PM-PL acts on the drive piston 22, and in the fourth period T4, a driving force proportional to the differential pressure PH-PL acts on the drive piston 22. Therefore, the displacer 20 moves from the top dead center UP1 to the bottom dead center LP1 together with the drive piston 22. In this way, the volume of the expansion chamber 34 is reduced and the low pressure gas is discharged.

The GM refrigerator 10 cools the cooling stage 38 by repeating such a refrigerating cycle (that is, a GM cycle). Thereby, the GM refrigerator 10 can cool the superconducting device or other object to be cooled (not shown) thermally coupled to the cooling stage 38.

The valve timings depicted at the same time in the figure do not have to be exactly at the same time and may be slightly different. For example, it is not essential that the main intake opening / closing valve V1 and the sub-exhaust opening / closing valve V4 are closed at the same time. Further, it is not essential that the main exhaust opening / closing valve V2 is closed and the sub intake opening / closing valve V3 is closed at the same time.

In the GM refrigerator 10 according to the embodiment, the intermediate pressure source 100 is connected to the drive chamber 46 in parallel with the auxiliary pressure switching valve 62, and the high pressure PH and the low pressure PL are connected during the periodic pressure fluctuation in the drive chamber 46. Has an intermediate pressure with. Since the intermediate pressure source 100 can be used as an auxiliary gas source, the work supplied from the compressor 12 to the drive chamber 46 can be reduced, and the load on the compressor 12 can be reduced. As a result, the efficiency of the compressor is increased, and the efficiency of the entire system of the gas-driven GM refrigerator is improved.

The flow path resistance member 102 is connected to the drive chamber in parallel with the auxiliary pressure switching valve 62, and the buffer volume 104 is connected to the drive chamber 46 via the flow path resistance member 102. With such a configuration, a part of the work input to the drive chamber 46 by supplying the working gas from the compressor 12 can be collected in the buffer volume 104, and the collected work can be reused in the next refrigeration cycle. It will be possible.

In a typical gas-driven GM refrigerator, the sub-exhaust open / close valve V4 is also normally open while the main intake open / close valve V1 is open. Further, the sub intake opening / closing valve V3 is also open during the opening of the main exhaust opening / closing valve V2.

On the other hand, in the GM refrigerator 10 according to the embodiment, since the buffer volume 104 and the flow path resistance member 102 are provided as described above, the timing for opening the sub-exhaust open / close valve V4 is set to the main intake open / close valve V1. It is possible to delay the opening of the sub-exhaust opening / closing valve V4 and shorten the opening time of the sub-exhaust opening / closing valve V4 as compared with the main intake opening / closing valve V1. Further, the timing of opening the sub intake opening / closing valve V3 can be delayed from the opening of the main exhaust opening / closing valve V2, and the opening time of the sub intake opening / closing valve V3 can be shortened as compared with the main exhaust opening / closing valve V2.

The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above embodiment, various design changes are possible, various modifications are possible, and such modifications are also within the scope of the present invention. By the way.

10 GM refrigerator, 20 displacer, 22 drive piston, 46 drive chamber, 100 intermediate pressure source, 102 flow path resistance member, 104 buffer volume.

Claims (6)

A displacer that can reciprocate in the axial direction and
A drive piston connected to the displacer so as to drive the axial reciprocating motion of the displacer,
A drive chamber accommodating the drive piston and
A drive chamber pressure switching valve that is connected to the drive chamber and generates periodic pressure fluctuations between high pressure and low pressure in the drive chamber.
Provided with an intermediate pressure source connected to the drive chamber in parallel with the drive chamber pressure switching valve and having an intermediate pressure between the high pressure and the low pressure during the periodic pressure fluctuations in the drive chamber. The featured GM refrigerator. The intermediate pressure source includes a flow path resistance member connected to the drive chamber in parallel with the drive chamber pressure switching valve, and a buffer volume connected to the drive chamber via the flow path resistance member. The GM refrigerator according to claim 1. The GM refrigerator according to claim 1 or 2, wherein the drive piston is rigidly connected to the displacer by a connecting rod. A claim further comprising a displacer cylinder accommodating the displacer and a seal portion provided on a connecting rod or a guide for axially guiding the connecting rod and separating the drive chamber from the displacer cylinder. Item 3. The GM refrigerator according to item 3. The drive chamber is divided into a first section and a second section by the drive piston, the drive chamber pressure switching valve and the intermediate pressure source are connected to the first section, and the connecting rod passes through the second section. Extends to the displacer
3. The second compartment functions as a gas spring chamber that generates a gas spring force that opposes the movement of the drive piston when the drive piston moves so as to narrow the second compartment. Or the GM refrigerator according to 4. The drive chamber is divided into a first section and a second section by the drive piston.
One of claims 1 to 5, wherein a clearance acting as a flow path resistance to the gas flow of the first section and the second section is provided between the drive piston and the drive chamber. The described GM refrigerator.

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