Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
  • F25B49/022—Compressor control arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B1/00—Compression machines, plants or systems with non-reversible cycle
  • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B31/00—Compressor arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B41/00—Fluid-circulation arrangements
  • F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B41/00—Fluid-circulation arrangements
  • F25B41/30—Expansion means; Dispositions thereof
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
  • F25B49/025—Motor control arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/06—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point using expanders
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/10—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point with several cooling stages
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
  • F25B9/145—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle pulse-tube cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2309/00—Gas cycle refrigeration machines
  • F25B2309/005—Gas cycle refrigeration machines using an expander of the rotary type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2600/00—Control issues
  • F25B2600/02—Compressor control
  • F25B2600/021—Inverters therefor
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2600/00—Control issues
  • F25B2600/02—Compressor control
  • F25B2600/025—Compressor control by controlling speed
  • F25B2600/0253—Compressor control by controlling speed with variable speed
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2600/00—Control issues
  • F25B2600/25—Control of valves
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/19—Pressures
  • F25B2700/193—Pressures of the compressor
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/19—Pressures
  • F25B2700/193—Pressures of the compressor
  • F25B2700/1933—Suction pressures

Definitions

• the present invention relates to a method for operating a cryocooler and a cryocooler.
• the cryocooler In order to cool a target object with a cryocooler, first, the cryocooler must be started and the cryocooler must be cooled from the initial temperature to the target cryogenic temperature.
• the initial cooling of such a cryocooler is also referred to as a cooldown. Since the initial cooling is merely a preparation for starting the cooling of the target object, it is desired that the required time is as short as possible.
• a cryocooler includes a first compressor, an expander, and a high pressure line and a low pressure line connecting the first compressor to the expander.
• the method includes: connecting a second compressor in series with a first compressor on a high pressure line or a low pressure line; connecting a buffer volume to the low pressure line via a supply valve; executing initial cooling for cooling an expander from an initial temperature to a cryogenic temperature in a state where the second compressor and the buffer volume are connected to the cryocooler; and executing a steady operation of maintaining the expander at the cryogenic temperature after the initial cooling.
• the execution of the initial cooling includes supplying a working gas to the expander by using the first compressor and the second compressor, and controlling the supply valve to keep a pressure of the high pressure line within a preset appropriate pressure range based on the measured pressure of the high pressure line.
• a cryocooler includes a first compressor, an expander, and a high pressure line and a low pressure line connecting the first compressor to the expander.
• the method includes: connecting a second compressor in series with a first compressor on a high pressure line or a low pressure line; executing initial cooling for cooling an expander from an initial temperature to a cryogenic temperature in a state where the second compressor is connected to the cryocooler; and executing a steady operation of maintaining the expander at the cryogenic temperature after the initial cooling.
• the first compressor or the second compressor has a compressor motor with a variable operating frequency, and is driven by the compressor motor.
• a cryocooler including: an expander capable of executing initial cooling for cooling from an initial temperature to a cryogenic temperature and a steady operation of maintaining the cryogenic temperature after the initial cooling; a high pressure line and a low pressure line connected to the expander; a first pressure sensor that measures a pressure of the high pressure line; a second pressure sensor that measures a pressure of the low pressure line; a buffer volume for storing a working gas; a supply valve that connects the buffer volume to the low pressure line; and a controller that controls the supply valve to keep the pressure of the high pressure line within a preset appropriate pressure range based on the pressure of the high pressure line measured by the first pressure sensor during the initial cooling.
• the initial cooling time of the cryocooler can be shortened.
• Figs. 1 and 2 are views schematically illustrating a cryocooler 10 according to a first embodiment.
• the cryocooler 10 is a two-stage Gifford-McMahon (GM) cryocooler.
• Fig. 1 schematically illustrates a compressor 12 and an expander 14 constituting the cryocooler 10 together with a control device 100
• Fig. 2 illustrates the internal structure of the expander 14 of the cryocooler 10.
• the displacer assembly 18 includes a first displacer 18a and a second displacer 18b connected to each other, and these move integrally.
• the first displacer 18a and the second displacer 18b are members having a cylindrical shape, and the second displacer 18b has a diameter smaller than that of the first displacer 18a.
• the first displacer 18a and the second displacer 18b are disposed coaxially with each other.
• the first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b.
• the first displacer 18a can reciprocate in the axial direction along the first cylinder 16a, and the second displacer 18b can reciprocate in the axial direction along the second cylinder 16b.
• the displacer assembly 18 forms a room temperature chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the cryocooler cylinder 16.
• the expander 14 includes a first cooling stage 33 and a second cooling stage 35 for heat exchange with a desired object or medium to be cooled by the cryocooler 10.
• the room temperature chamber 30 is formed between the upper lid portion of the first displacer 18a and the upper portion of the first cylinder 16a.
• the first expansion chamber 32 is formed between the lower lid portion of the first displacer 18a and the first cooling stage 33.
• the second expansion chamber 34 is formed between the lower lid portion of the second displacer 18b and the second cooling stage 35.
• the first cooling stage 33 is fixed to the lower portion of the first cylinder 16a to surround the first expansion chamber 32
• the second cooling stage 35 is fixed to the lower portion of the second cylinder 16b to surround the second expansion chamber 34.
• the first regenerator 26 is connected to the room temperature chamber 30 through a working gas flow path 36a formed in the upper lid portion of the first displacer 18a, and is connected to the first expansion chamber 32 through a working gas flow path 36b formed in the lower lid portion of the first displacer 18a.
• the second regenerator 28 is connected to the first regenerator 26 through a working gas flow path 36c formed from the lower lid portion of the first displacer 18a to the upper lid portion of the second displacer 18b.
• the second regenerator 28 is connected to the second expansion chamber 34 through a working gas flow path 36d formed in the lower lid portion of the second displacer 18b.
• the pressure switching valve 40 may take the form of a rotary valve. That is, the pressure switching valve 40 may be configured such that the high pressure valve 40a and the low pressure valve 40b are alternately opened and closed by the rotational sliding of the valve disc with respect to the stationary valve body. In that case, an expander motor 42 may be connected to the pressure switching valve 40 to rotate the valve disc of the pressure switching valve 40.
• the pressure switching valve 40 is disposed such that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.
• the high pressure valve 40a and the low pressure valve 40b may be valves that can be individually controlled.
• the pressure switching valve 40 may not be connected to the expander motor 42.
• the expander motor 42 is connected to a displacer drive shaft 44 via a motion conversion mechanism 43 such as a Scotch yoke mechanism.
• the expander motor 42 is attached to the cryocooler housing 20.
• the motion conversion mechanism 43 is accommodated in the cryocooler housing 20 similar to the pressure switching valve 40.
• the motion conversion mechanism 43 converts the rotary motion output by the expander motor 42 into a linear reciprocating motion of the displacer drive shaft 44.
• the displacer drive shaft 44 extends from the motion conversion mechanism 43 into the room temperature chamber 30, and is fixed to the upper lid portion of the first displacer 18a.
• the rotation of the expander motor 42 is converted into an axial reciprocation of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 reciprocates linearly in the cryocooler cylinder 16 in the axial direction.
• the expander 14 may include a temperature sensor 46 that measures the temperature of the second cooling stage 35 (and/or the first cooling stage 33) and outputs a measured temperature signal indicating the measured temperature.
• the high pressure line 63 includes the high-pressure pipe 65 and the high pressure flow path 52
• the low pressure line 64 includes the low-pressure pipe 66 and the low pressure flow path 53.
• the bypass line 56 may be considered to be a part of the gas line 62.
• the bypass line 56 connects the high pressure line 63 to the low pressure line 64 to bypass the expander 14 and return the working gas from the high pressure line 63 to the low pressure line 64.
• the cryocooler 10 When the compressor 12 and the expander motor 42 are operated, the cryocooler 10 generates periodic volume fluctuations and pressure fluctuations of the working gas synchronized with the periodic volume fluctuations in the first expansion chamber 32 and the second expansion chamber 34.
• the low pressure valve 40b is closed and the high pressure valve 40a is opened, whereby the high pressure working gas flows from the compressor 12 into the room temperature chamber 30 through the high pressure valve 40a, is supplied to first expansion chamber 32 through the first regenerator 26, and is supplied to the second expansion chamber 34 through the second regenerator 28.
• the first expansion chamber 32 and the second expansion chamber 34 are pressurized from the low pressure to the high pressure.
• the displacer assembly 18 is moved upward from the bottom dead center to the top dead center, and the volumes of the first expansion chamber 32 and the second expansion chamber 34 are increased.
• the high pressure valve 40a is closed, the intake process ends.
• the upper limit value Pd and the lower limit value Pc of the appropriate pressure range may be selected from, for example, a range of 2 MPa to 3 MPa or a range of 2.1 MPa to 2.7 MPa.
• the width of the appropriate pressure range that is, the difference between the upper limit value Pd and the lower limit value Pc of the appropriate pressure range may be set to a certain value within 0.5 MPa, 0.3 MPa, or 0.1 MPa, for example.
• the appropriate pressure range may be set to 2.45 ⁇ 0.05 MPa. In this case, the width of the appropriate pressure range is 0.1 MPa, the upper limit value Pd is 2.5 MPa, and the lower limit value Pc is 2.4 MPa.
• the controller 110 closes the supply valve 72 when the measured pressure of the high pressure line 63 is restored to an appropriate pressure range (S16). For example, the controller 110 may compare the measured pressure of the high pressure line 63 with the lower limit value Pc of the appropriate pressure range, and close the supply valve 72 when the measured pressure of the high pressure line 63 exceeds the lower limit value Pc (PH > Pc or PH ⁇ Pc).
• Pc lower limit value
• the pressure threshold for closing the supply valve 72 may be different from the lower limit value Pc of the appropriate pressure range, and may be larger than the lower limit value Pc, for example.
• the pressure threshold may be set not to exceed the upper limit value Pd of the appropriate pressure range.
• the pressure threshold may be a value obtained by adding a predetermined ratio of a width of an appropriate pressure range (upper limit value Pd - lower limit value Pc) to the lower limit value Pc.
• the predetermined ratio may be 50% or less, 30% or less, or 10% or less.
• Fig. 4 is a flowchart for describing a method for controlling the cryocooler 10 according to the first embodiment. This method is repeatedly executed by the controller 110 in a predetermined cycle in the initial cooling of the cryocooler 10. This method may be executed in parallel with the method illustrated in Fig. 3 . This method may be continuously executed not only during the initial cooling but also during the steady operation of the cryocooler 10.
• the pressure of the high pressure line 63 is measured using the first pressure sensor 54 (S20).
• the controller 110 receives the first measured pressure signal PH from the first pressure sensor 54, and acquires the measured pressure of the high pressure line 63.
• the measured pressure of the high pressure line 63 is compared with an appropriate pressure range (S22).
• the controller 110 compares the measured pressure of the high pressure line 63 with the upper limit value Pd of the appropriate pressure range, and opens the collection valve 74 when the measured pressure of the high pressure line 63 exceeds the upper limit value Pd (PH > Pd) (S24).
• Pd PH > Pd
• the controller 110 closes the collection valve 74 when the measured pressure of the high pressure line 63 is restored to an appropriate pressure range (S26). For example, the controller 110 may compare the measured pressure of the high pressure line 63 with the upper limit value Pd of the appropriate pressure range, and close the collection valve 74 when the measured pressure of the high pressure line 63 falls below the upper limit value Pd (PH ⁇ Pd or PH ⁇ Pd).
• Pd PH ⁇ Pd or PH ⁇ Pd
• the pressure threshold for closing the collection valve 74 may be different from the upper limit value Pd of the appropriate pressure range, and may be smaller than, for example, the upper limit value Pd.
• This pressure threshold may be selected from an appropriate pressure range, that is, may be larger than the lower limit value Pc of an appropriate pressure range.
• the appropriate pressure range may be changed during the operation of the cryocooler 10.
• the appropriate pressure range in the initial cooling may be different from the appropriate pressure range in the steady operation, and may be higher than the appropriate pressure range in the steady operation, for example.
• the lower limit value Pc in the initial cooling may be higher than the lower limit value Pc in the steady operation
• the upper limit value Pd in the initial cooling may be higher than the upper limit value Pd in the steady operation.
• PHVH + PLVL + PBVB nRT is established.
• PH (MPa) indicates the pressure of the high pressure line 63 in the steady operation at the temperature T
• PL (MPa) indicates the pressure of the low pressure line 64 in the steady operation at the temperature T
• PB (MPa) indicates the pressure of the buffer volume 70 in the steady operation at the temperature T.
• Equation (3) When Equation (3) is solved for PB and substituted into Equation (4), the following relationship is obtained.
• the buffer volume 70 satisfies Equation (5) for any temperature in the temperature range from the initial temperature to the cryogenic temperature.
• a condition desired for the buffer volume 70 is considered.
• PB ⁇ PH is supposed to be satisfied.
• Equation (3) is solved for PB and substituted into Equation (6), the following relationship is obtained.
• the buffer volume 70 satisfies Equation (7) for any temperature in the temperature range from the initial temperature to the cryogenic temperature.
• Fig. 5 is a graph illustrating an example of time-dependent changes in temperature and pressure during the operation of the cryocooler 10 according to the first embodiment.
• the illustrated pressure change is acquired by an experiment, and in the upper part of Fig. 5 , the pressure PH of the high pressure line 63 measured by the first pressure sensor 54 and the pressure PL of the low pressure line 64 measured by the second pressure sensor 55 are illustrated.
• a temperature T1 of the first cooling stage 33 and a temperature T2 of the second cooling stage 35 are illustrated in the lower part of Fig. 5 .
• the horizontal axis represents time.
• both the pressure PH of the high pressure line 63 and the pressure PL of the low pressure line 64 are the filling pressures PI, and the temperature T1 of the first cooling stage 33 and the temperature T2 of the second cooling stage 35 are room temperature (approximately 300K).
• the compressor 12 and the expander 14 work, the pressure PH of the high pressure line 63 is increased from the filling pressure PI, and the pressure PL of the low pressure line 64 decreases from the filling pressure PI. Due to the initial cooling, the temperature T1 of the first cooling stage 33 and the temperature T2 of the second cooling stage 35 decrease.
• the first cooling stage 33 and the second cooling stage 35 are each cooled to the above-described standard cooling temperature (for example, T1 ⁇ 30K, T2 ⁇ 4K), the initial cooling is completed and shifted to the steady operation.
• Fig. 6A schematically illustrates an enlarged portion A illustrated in Fig. 5
• Fig. 6B schematically illustrates an enlarged portion B illustrated in Fig. 5
• Fig. 6A illustrates the pressure PH of the high pressure line 63 immediately after the start of the initial cooling together with the open/closed state of the collection valve 74
• Fig. 6B illustrates the pressure PH of the high pressure line 63 after the portion A together with the open/closed state of the supply valve 72.
• the collection valve 74 is opened. Since the working gas is collected from the high pressure line 63 to the buffer volume 70 through the collection valve 74, the pressure PH of the high pressure line 63 decreases. When the pressure PH of the high pressure line 63 falls below the upper limit pressure Pd, the collection valve 74 is closed. In this manner, excessive pressurization of the high pressure line 63 can be avoided. The risk of an emergency stop of the compressor 12 due to excessive pressurization is reduced. Further, since the buffer volume 70 is pressurized by collecting the working gas, which leads to effective utilization for supplying the working gas from the buffer volume 70 to the low pressure line 64.
• the supply valve 72 is opened.
• the working gas is supplied from the buffer volume 70 to the low pressure line 64 through the supply valve 72. Since the amount of the working gas circulating in the gas line 62 increases, the pressure in the high pressure line 63 is restored. In this manner, when the pressure PH of the high pressure line 63 exceeds the lower limit value Pc, the supply valve 72 is closed.
• the density of the working gas increases in the expander 14 due to the temperature decrease of the expander 14 during the initial cooling, which has the effect of lowering the pressure PH of the high pressure line 63. Therefore, even when the pressure PH of the high pressure line 63 is restored once, the pressure PH falls below the lower limit value Pc again.
• the supply valve 72 is opened again, the pressure in the high pressure line 63 is restored, and the supply valve 72 is closed. In this manner, the supply valve 72 operates to repeatedly open and close to maintain the pressure PH of the high pressure line 63 within an appropriate pressure range.
• the pressure PH of the high pressure line 63 may significantly decrease due to the temperature decrease of the expander 14. Since the cooling capacity of the cryocooler 10 correlates with the pressure PH of the high pressure line 63, the cooling capacity of the cryocooler 10 may decrease as the initial cooling progresses. This can be a factor that increases the time required for the initial cooling.
• the pressure PH of the high pressure line 63 can be maintained within an appropriate pressure range by controlling the supply valve 72 during the initial cooling. Therefore, the cooling capacity of the cryocooler 10 can be appropriately maintained, and an increase in the initial cooling time can be suppressed. Further, by keeping the pressure PH of the high pressure line 63 substantially constant, the cryocooler 10 can provide a stable cooling capacity.
• a method for controlling the supply valve 72 and the collection valve 74 based on the pressure of the low pressure line 64 is also conceivable.
• the pressure of the low pressure line 64 is affected by the cooling temperature of the expander 14 (varies depending on the cooling temperature). Therefore, it is practically indispensable to set an appropriate pressure range of the low pressure line 64, that is, a pressure threshold of the low pressure line 64 for opening and closing the supply valve 72 and the collection valve 74 to a different value depending on the cooling temperature, and the design of the control becomes complicated. Further, even when the low pressure line 64 is within an appropriate pressure range, there may be a case where the pressure of the high pressure line 63 is excessively high depending on the cooling temperature. Therefore, a method based on the pressure of the high pressure line 63 as in the embodiment is advantageous in that such inconvenience is alleviated or prevented.
• Fig. 7 is a graph illustrating an example of changes in temperature and pressure during the operation of the cryocooler 10 according to the first embodiment.
• Fig. 8 is a view schematically illustrating the cryocooler 10 according to the first embodiment.
• the cryocooler 10 includes the compressor 12, the expander 14, the buffer volume 70, and the control device 100.
• the controller 110 controls the supply valve 72 to keep the pressure of the high pressure line 63 within a preset appropriate pressure range based on the pressure of the high pressure line 63 measured by the first pressure sensor 54 during the initial cooling. Further, the controller 110 controls the collection valve 74 to keep the pressure of the high pressure line 63 within an appropriate pressure range based on the pressure of the high pressure line 63 measured by the first pressure sensor 54 during the initial cooling.
• the cryocooler 10 includes a buffer pressure sensor 76 connected to the buffer volume 70 to measure the pressure of the buffer volume 70.
• the buffer pressure sensor 76 is electrically connected to the control device 100, and is configured to output a measured buffer pressure signal PB representing the measured pressure to the control device 100.
• the pressure PB of the buffer volume 70 measured by the buffer pressure sensor 76 is illustrated in the upper part of Fig. 7 .
• the temperature T1 of the first cooling stage 33 and the temperature T2 of the second cooling stage 35 are illustrated in the lower part of Fig. 7 .
• the pressure PH of the high pressure line 63 and the pressure PL of the low pressure line 64 are also stabilized.
• both the supply valve 72 and the collection valve 74 are closed, and the buffer volume 70 is disconnected from the gas line 62. Therefore, the pressure PB of the buffer volume 70 is also constant (final buffer pressure PF illustrated in Fig. 7 ).
• the controller 110 may calculate a difference between the measured pressure PB of the buffer volume 70 and a reference pressure during the initial cooling, and detect the stabilization of the calculated pressure difference, to determine the completion of the initial cooling.
• the reference pressure may be the pressure of the previously measured buffer volume 70, and may be, for example, the maximum value PM of the pressure of the buffer volume 70 measured during the initial cooling. It is understood from Fig. 7 that the pressure of the buffer volume 70 increases from the filling pressure PI and takes the maximum value PM immediately after the start of the initial cooling.
• the controller 110 may compare the calculated pressure difference (that is, the difference between the measured pressure PB of the buffer volume 70 and the reference pressure) with the pressure difference target value, and based on the comparison result, the controller 110 may determine whether or not the calculated pressure difference is equal to the pressure difference target value.
• the controller 110 may complete the initial cooling when a state where the calculated pressure difference is equal to the pressure difference target value continues for a predetermined time.
• the predetermined time may be selected from a range of 1 minute or more and 10 minutes or less.
• a predetermined value for example, 0.05 MPa
• the controller 110 may calculate the difference between the measured pressure PH of the high pressure line 63 and the measured pressure PL of the low pressure line 64, and detect the stabilization of the calculated pressure difference, to determine the completion of the initial cooling.
• the supply valve 72 is controlled (hereinafter, also referred to as high pressure priority control) based on the measured pressure of the high pressure line 63 during the initial cooling, and the pressure of the high pressure line 63 is kept within an appropriate pressure range.
• high pressure priority control also referred to as high pressure priority control
• the controller 110 may be configured to discontinue the control (that is, high pressure priority control) of the supply valve 72 based on the pressure of the high pressure line 63 when the pressure of the low pressure line 64 measured by the second pressure sensor 55 falls below a preset low pressure threshold.
• the controller 110 may be configured to control the supply valve 72 to restore the pressure of the low pressure line 64 to the low pressure threshold based on the pressure of the low pressure line 64 measured by the second pressure sensor 55.
• the control of the supply valve 72 based on the pressure of the low pressure line 64 will also be referred to as low pressure priority control.
• An example of the switching processing from the high pressure priority control to the low pressure priority control will be described later with reference to Fig. 9 .
• Fig. 9 is a flowchart for describing a method for controlling the cryocooler 10 according to the first embodiment. This method is repeatedly executed by the controller 110 in a predetermined cycle in the initial cooling of the cryocooler 10. This method may be continuously executed not only during the initial cooling but also during the steady operation of the cryocooler 10.
• the measured pressure PL of the low pressure line 64 is compared with a low pressure threshold Pe (S32).
• the low pressure threshold Pe may be set as a lower limit value of the pressure of the low pressure line 64 from the viewpoint of guaranteeing stable operation of the compressor 12.
• the low pressure threshold Pe may be selected from a range of 0.2 MPa to 0.4 MPa.
• the low pressure threshold Pe can be appropriately set based on the empirical knowledge of the designer, an experiment or simulation by the designer, or the like.
• the low pressure threshold Pe may be stored in advance in the controller 110 as an initial setting of the cryocooler 10, or may be set in the controller 110 by the user before the cryocooler 10 is operated.
• the supply valve 72 is opened and closed based on the pressure of the low pressure line 64, and the pressure of the low pressure line 64 can be restored to the low pressure threshold Pe.
• the pressure of the high pressure line 63 is not managed. Therefore, during the low pressure priority control, there is a possibility that an undesired phenomenon such that the pressure of the high pressure line 63 becomes extremely low may occur.
• the controller 110 may be configured to discontinue the control of the supply valve 72 based on the pressure of the low pressure line 64 when the pressure of the high pressure line 63 measured by the first pressure sensor 54 falls below the high pressure threshold.
• the controller 110 may be configured to control the supply valve 72 to restore the pressure of the high pressure line 63 to the high pressure threshold based on the pressure of the high pressure line 63 measured by the first pressure sensor 54.
• An example of the return processing from the low pressure priority control to the high pressure priority control will be described later with reference to Fig. 11 .
• Fig. 11 is a flowchart for describing a method for controlling the cryocooler 10 according to the first embodiment. During the execution of the low pressure priority control described above, this method is repeatedly executed by the controller 110 at a predetermined cycle.
• the pressure of the high pressure line 63 is measured (S50).
• the measured pressure of the high pressure line 63 is compared with a high pressure threshold Pf (S52).
• the high pressure threshold Pf may be the lower limit value Pc within an appropriate pressure range.
• the high pressure threshold Pf can be appropriately set based on the empirical knowledge of the designer, an experiment or simulation by the designer, or the like.
• the high pressure threshold Pf may be stored in advance in the controller 110 as an initial setting of the cryocooler 10, or may be set in the controller 110 by the user before the cryocooler 10 is operated.
• the controller 110 compares the measured pressure of the high pressure line 63 with the high pressure threshold Pf, and when the measured pressure of the high pressure line 63 exceeds the high pressure threshold Pf (PH > Pf or PH ⁇ Pf), the low pressure priority control is selected (S54). In this case, the low pressure priority control is continuously executed.
• the controller 110 selects the high pressure priority control (S56). In this manner, the switching processing from the high pressure priority control to the low pressure priority control ends.
• the supply valve 72 is controlled based on the measured pressure of the high pressure line 63, and the pressure of the high pressure line 63 is maintained within an appropriate pressure range.
• the time required for initial cooling can also be shortened.
• the relief valve 60 bypassing the high pressure line 63 and the low pressure line 64 may be an obstacle.
• the relief valve 60 is of a type that is mechanically opened when a differential pressure equal to or higher than a set pressure acts between the inlet and outlet of the relief valve 60, the operating differential pressure of the cryocooler 10 may be limited to this set pressure.
• cryocooler 10 In order to cope with this, additional compressors may be temporarily installed in the cryocooler 10 for initial cooling, as described below.
• the main compressor 12 of the cryocooler 10 will be referred to as a first compressor 12, and the sub-compressor to be added will be referred to as a second compressor 80.
• Figs. 12 and 13 are views schematically illustrating the cryocooler 10 according to a second embodiment.
• Fig. 12 illustrates the settings of the cryocooler 10 in the initial cooling
• Fig. 13 illustrates the basic settings of the cryocooler 10 in steady operation before or after the initial cooling.
• Fig. 14 is a flowchart for describing a method for operating the cryocooler 10 according to the second embodiment.
• the cryocooler 10 and the method for operating the same according to the second embodiment can be the same as the cryocooler 10 and the method for operating method the same according to the first embodiment, except for the second compressor 80. Therefore, in Figs. 12 and 13 , the same reference numerals will be assigned to the configurations common to the first embodiment, and detailed description thereof will be appropriately omitted in order to avoid redundancy.
• the cryocooler 10 takes a basic setting including the first compressor 12 and the expander 14 as illustrated in Fig. 13 before the initial cooling is performed.
• the first compressor 12 and the expander 14 are connected by the high pressure line 63 and the low pressure line 64.
• the second compressor 80 and the buffer volume 70 are not connected to the cryocooler 10.
• the second compressor 80 and the buffer volume 70 are connected to the cryocooler 10 as pretreatment for initial cooling (S60, S61).
• the attachment order of the second compressor 80 and the buffer volume 70 is not limited.
• the buffer volume 70 is connected to the low pressure line 64 via the supply valve 72 and is connected to the high pressure line 63 via the collection valve 74.
• the supply valve 72 and the collection valve 74 may be accommodated in one housing together with the buffer volume 70 to form a buffer volume unit.
• the buffer volume unit and the second compressor 80 may be brought to the site where the cryocooler 10 is operated, for example, by a serviceman and connected to the cryocooler 10.
• the initial cooling is executed in a state where the second compressor 80 and the buffer volume 70 are connected to the cryocooler 10. Therefore, in the initial cooling, the working gas is supplied to the expander 14 by using the first compressor 12 and the second compressor 80.
• the first compressor 12 pressurizes the working gas of the cryocooler 10 collected from the expander 14 through the low pressure line 64, and supplies the pressurized working gas to the second compressor 80.
• the second compressor 80 further pressurizes the working gas from the first compressor 12, and supplies this to the expander 14 again.
• the buffer volume 70 is used to keep the pressure of the high pressure line 63 within an appropriate pressure range, as in the first embodiment. That is, the supply valve 72 performs control to keep the pressure of the high pressure line 63 within an appropriate pressure range based on the pressure of the high pressure line 63 measured by the first pressure sensor 54 during the initial cooling.
• the second compressor 80 and the buffer volume 70 are removed from the cryocooler 10 (S63, S64).
• the order of removal of the second compressor 80 and the buffer volume 70 is not limited.
• the cryocooler 10 is returned to the basic setting illustrated in Fig. 14 . Then, a steady operation of the cryocooler 10 is performed (S65).
• the operating differential pressure of the cryocooler 10 can be increased by adding the second compressor 80.
• the operating differential pressure of the cryocooler 10 can be increased exceeding the limitation caused by the set pressure of the relief valve 60 of the first compressor 12 described above.
• An increase in the operating differential pressure causes an increase in the cooling capacity of the cryocooler 10, and can shorten the time required for initial cooling.
• the cryocooler 10 As another method for increasing the operating differential pressure of the cryocooler 10, it is conceivable to bring a large-sized compressor having a higher output than the first compressor 12 to the site from the outside and replace the first compressor 12 with the large-sized compressor. However, such a large-sized compressor is generally unsuitable for carrying because the large-sized compressor is large in size and weight. On the other hand, since the second compressor 80 is used in combination with the first compressor 12, the second compressor 80 may be relatively small in size and is easy to carry.
• the buffer volume 70 is removed. Also in the second embodiment, similar to the first embodiment, as illustrated in Fig. 1 , a steady operation of the cryocooler 10 may be performed in a state where the buffer volume 70 is connected to the cryocooler 10. Alternatively, also in the first embodiment, similar to the second embodiment, the buffer volume 70 may be removed from the cryocooler 10 after the initial cooling.
• Embodiments of the present invention can also be expressed as follows.

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