JP5978045B2 - Decompression system - Google Patents

Description

  In the present invention, a drive unit is operated by a first electric motor, a cooling unit is cooled to a predetermined temperature corresponding to the number of rotations of the first electric motor, and a refrigerant is expanded in the cooling unit to capture a gas. And a single compression unit that operates the compression unit with a second electric motor and supplies the refrigerant compressed by the compression unit to each decompression unit at a flow rate corresponding to the rotation speed of the second motor, The present invention relates to a decompression system comprising measuring means for measuring the temperature of the cooling part of each decompression means.

  There is a cryopump unit as one of vacuum pumps that evacuate to a pressure in a high vacuum region, and such a cryopump unit is known from, for example, Patent Document 1. 5 (a) and 5 (b), the cryopump unit is a mechanical refrigeration built in a cylindrical pump case 1 that is mounted on a pressure reduction target W such as a vacuum chamber via a gate valve GV. A compressor Cp (pressure reduction means) and a second motor (not shown) that is provided outside the object to be reduced pressure W and circulates helium gas as a refrigerant through the helium inlets / outlets 21i and 21o of the mechanical refrigerator Cp. Machine Cm (compression means). The mechanical refrigerator Cp includes a cold head first stage 22 and a cold head second stage 23 as a cooling unit, and a cylindrical shield 22a along the inner side of the pump case 1 is attached to the cold head first stage 22. A cryopanel 23a is attached to the second stage 23 of the cold head, and a baffle 22b that is cooled to the same temperature as the first stage 22 of the cold head is provided at the opening of the shield 22a.

Inside the cold head first stage 22 and the cold head second stage 23, as shown in FIG. 5B, a first stage regenerator 24 and a first stage expansion chamber 25, and a second stage regenerator 26 and a second stage expansion chamber 27 are provided. A displacer 28 as a drive unit is provided so as to be reciprocally movable by a first electric motor 3 such as a motor. Then, after opening the high-pressure valve 41 and sending the compressed helium gas from the compressor Cm to the displacer 28, when the expansion chambers 25 and 27 are moved so as to expand, they are cooled by the regenerators 24 and 26. However, the high pressure gas flows into the expansion chambers 25 and 27. Next, when the high pressure valve 41 is closed and the low pressure valve 42 is opened and the displacer 28 is moved so as to reduce the expansion chambers 25 and 27, the helium gas in the expansion chambers 25 and 27 expands and the regenerators 24 and 26 are expanded. Return to the compressor Cm while cooling. Thereby, among the gas molecules present in the object to be decompressed W, H ₂ O having a high condensation temperature is condensed on the baffle 22b and the shield 22a of 80K, and Ar and N _{2 having} a low condensation temperature are 12 to 13K. It is condensed and exhausted to the cryopanel 23a.

  A temperature sensor TC is provided in each of the cold head first stage 22 and the cold head second stage 23, and the operations of both the first and second electric motors are controlled in accordance with the temperature detected by the temperature sensor TC. And, for example, in a vacuum processing apparatus such as a cluster tool, as many decompression means as the number of vacuum processing chambers and vacuum transfer chambers used for processing and transport are required, so that the space for the vacuum processing apparatus is reduced. It is common to construct a decompression system that supplies helium gas to a plurality of mechanical refrigerators mounted in a vacuum processing chamber or a vacuum transfer chamber by a single compressor.

  By the way, in recent years, energy saving is strongly demanded for the above-described vacuum processing apparatus, and energy saving of the decompression system itself is indispensable for this energy saving. However, in the above-described conventional decompression system, the refrigerant is supplied to each decompression unit at an equal flow rate by a single compression unit and the drive unit of each decompression unit is continuously operated uniformly. It was a hindrance to energy. In other words, for each vacuum processing chamber in which the decompression means is installed, the exhaust performance required depending on the internal processing (heat treatment, plasma treatment, cooling treatment) and the internal environment (heat input to the decompression means, etc.) Regardless of the difference (including the cooling performance of the cooling unit), the refrigerant is supplied uniformly, etc., so that depending on the decompression means, more refrigerant than necessary is supplied, or the refrigerant supply is insufficient, and all decompression As a result, the operation time required to exhibit the exhaust performance required by the means becomes longer, resulting in an increase in power consumption, which hinders energy saving.

JP 2002-298966 A

  In view of the above points, an object of the present invention is to provide a decompression system capable of reducing power consumption and saving energy.

  In order to solve the above-described problem, the drive unit is operated by the first electric motor, the cooling unit is cooled to a predetermined temperature corresponding to the rotation speed of the first electric motor, and the refrigerant is expanded in the cooling unit to generate gas. A plurality of decompression means for capturing the refrigerant, and a single motor that operates the compression section by the second motor and supplies the refrigerant compressed by the compression section to each decompression means at a flow rate corresponding to the rotational speed of the second motor. The decompression system of the present invention comprising the compression means and the measurement means for measuring the temperature of the cooling unit of each decompression means cools between the first threshold and the second threshold lower than the first threshold. Control means for controlling the operation of both the first and second electric motors so that the temperature of each part is maintained, and the control means operates both the first and second electric motors to cool the cooling parts of the respective decompression means. Between the first threshold value and the second threshold value, One of the cooling units having the slowest cooling rate is selected, and the number of rotations of the first electric motors of the remaining decompression units is decreased, and when the cooling unit of each decompression unit reaches the second threshold value, The first electric motors of all the decompression means are stopped.

  According to the present invention, when any one of the decompression means reaches a temperature higher than the first threshold value and the cooling unit needs to be cooled, the second electric motor of the compression unit is activated to the cooling unit of each decompression unit. The refrigerant supply is restarted, and the first electric motors of the decompression units are operated. Here, for each vacuum processing chamber in which the decompression means is mounted, the cooling rate of the cooling part of each decompression means varies depending on the processing performed internally and the internal environment. Therefore, by selecting the one decompression means having the slowest temperature decrease rate among the cooling parts of each decompression means, and lowering the number of rotations of the first electric motor of the remaining decompression means, respectively, Refrigerant is preferentially supplied, and the amount of refrigerant supplied to a relatively fast cooling rate is reduced, so that the cooling rate at the cooling part of each decompression means is averaged. At this time, the power consumption is reduced by the amount that the rotation speed of the first electric motor is lowered, and the slowest cooling rate can be lowered to the second threshold at an early stage. The power consumption is further reduced by that amount. In the present invention, “reducing the rotational speed of the electric motor” includes stopping the operation of the electric motor at which the rotational speed becomes zero.

  By the way, in a vacuum processing chamber in which each decompression means is mounted, since a certain process is normally repeated, the decompression device reduces the temperature from the first threshold value to the second threshold value. It can be seen whether the temperature rises to the first threshold after both the first and second electric motors are stopped. For this reason, the temperature decreasing rate and the temperature increasing rate per unit time are measured in advance for each decompression unit and stored in the control unit, and the operation of the first electric motor of each decompression unit is controlled accordingly. In this way, for example, it is possible to control the on / off of each first electric motor to average the rate of temperature drop in the cooling section of each decompression means, thereby further reducing power consumption. In this case, the first electric motor is an AC motor, which is advantageous in terms of cost as compared with an inverter that controls the rotational speed.

  In the present invention, an accumulator for storing the compressed refrigerant is further provided, and the control means is configured such that after all the first electric motors are deactivated, a predetermined volume of the refrigerant is stored in the accumulator. In this state, when the temperature of the cooling unit of each decompression unit rises, at least one decompression unit having a relatively high temperature rise rate is selected from the cooling units of each decompression unit. It is preferable to increase the rotational speed of the first electric motor of the decompression means and supply the refrigerant stored in the accumulator to selectively cool only the cooling part of the decompression means. According to this, it is possible to delay the start of the operation of the first electric motor of the decompression means that has not been selected, and also to delay the operation of the second electric motor, thereby further reducing power consumption. When the stored refrigerant runs out, for example, when the rotational speed of the first electric motor of the decompression unit is lowered again and becomes higher than the second threshold value of the cooling unit of each decompression unit, both the first and second What is necessary is just to operate an electric motor again.

  In the present invention, the control means calculates the temperature rise rate per unit time in the cooling part of each decompression means, restarts the operation of the second electric motor, and has a fast time to reach the first threshold value. It is preferable to restart the operation of the first electric motor sequentially. According to this, when the temperature rises from the second threshold value to the first threshold value, it is possible to individually delay the start of operation of the first electric motor of each decompression means, and it is possible to further reduce power consumption.

The figure which shows the structure of the pressure reduction system of this invention typically. The figure explaining the operation | movement procedure of the pressure reduction system corresponded to a prior art example. The figure explaining the operation | movement procedure of the pressure reduction system in this invention. The figure explaining a part of operation | movement procedure of the pressure reduction system which concerns on the modification of this invention. (A) is a figure explaining the structure of the cryopump unit as a pressure reduction means. (B) is an enlarged view of the main part.

  Hereinafter, referring to the drawings, an example of a decompression system configured to supply helium to a plurality of mechanical refrigerators using a compressor as a single compression means is a mechanical refrigerator. An embodiment of the present invention will be described. In the following, the same reference numerals are used for the same members and elements as those of the conventional example.

  Referring to FIG. 1, PS is a decompression system according to the present embodiment. The decompression system PS compresses a plurality of mechanical refrigerators Cp and helium gas (refrigerant) to each mechanical refrigerator Cp. A compressor Cm, a high-pressure accumulator 5 that is interposed between the compressor Cm and the gas inlet 21i of each mechanical refrigerator Cp, and temporarily stores the compressed helium gas, and each mechanical refrigerator Cp. The low-pressure side accumulator 6 where helium gas from the gas outlet 21o merges, the temperature sensors TC provided in each mechanical refrigerator Cp, and the control for overall control of the operations of each mechanical refrigerator Cp and compressor Cm. Means Cu.

  In the present embodiment, among the mechanical refrigerators Cp, the one constituted by the cold head first stage 22 and the cold head second stage 23 is provided so as to be reciprocally movable by the first electric motor 3 such as a cooling unit or a motor. The displacer 28 is a drive unit. As the first electric motor 3, a known motor such as a DC motor or an AC motor can be used. When an AC motor is used, an inverter circuit (not shown) is provided and the output frequency to the AC motor is changed by the inverter circuit. You may make it change the rotation speed. Then, the displacer 28 is operated by the first electric motor 3, and the cold head first stage 22 and the cold head second stage 23 are cooled to predetermined temperatures in accordance with the rotation speed of the first electric motor 3, respectively, and helium as a refrigerant The gas existing in the reduced pressure object W is expanded by expanding the gas.

  A known compressor can be used as the compressor Cm, and the helium gas compressed by the compressor 72 by operating the compressor 72 by the second motor 71 at a flow rate corresponding to the rotational speed of the second motor 71 is increased on the high pressure side. Compressed helium gas is supplied to the accumulator 5. As the second electric motor 71, a known motor such as a DC motor or an AC motor can be used. Similarly to the above, when an AC motor is used, an inverter circuit (not shown) is provided, and the output frequency to the AC motor is controlled by the inverter circuit. You may make it change and change the rotation speed. As will be described later, the high-pressure side accumulator 5 has a volume capable of storing an amount of helium necessary to supply the cooling units 22 and 23 when only the specific first electric motor 3 is operated. The control means Cu is a well-known one provided with a microcomputer, a sequencer, a memory, etc., and controls the operation of the first and second electric motors 3 and 71 and receives an output from the temperature sensor TC. It has come to be. Hereinafter, an operation procedure of the decompression system PS will be described in detail with reference to FIGS. 2 and 3.

In the case of condensing H ₂ O or the like having a high condensation temperature among the gas molecules present in the reduced pressure object W to the baffle 22b or the shield 22a as an example, the memory (not shown) of the control means Cu includes Based on the cooling temperature (80K) of the baffle 22b and the shield 22a, a predetermined temperature higher than this temperature is preset as a first threshold T1, and a predetermined temperature higher than this temperature is preset as a second threshold T2. And the 1st electric motor 3 and the 2nd electric motor 71 are act | operated, and the cooling parts 22 and 23 of each mechanical refrigerator Cp are cooled. Next, when the temperature detected by the temperature sensor TC falls from the first threshold value T1 and becomes lower than the second threshold value T2, the first electric motor 3 and the second electric motor 71 are deactivated. When the temperature detected by the temperature sensor TC becomes higher than the first threshold value T1, the operations of the first electric motor 3 and the second electric motor 71 are restarted.

  Here, as shown in FIG. 2, when helium is supplied to each mechanical refrigerator Cp at a substantially equal flow rate by a single compressor Cm, the cooling units 22 and 23 are moved from the first threshold value T1 to the second threshold value. Depending on the processing performed in the reduced pressure object W to which each mechanical refrigerator Cp is mounted and the internal environment until cooling to the threshold value T2, the cooling rate (lines a, b, c in FIG. 2). Are different from each other). Specifically, when the heat treatment is performed in the object to be decompressed W and the inside is at a relatively high temperature (for example, 415 ° C.), the cooling rate is low as shown by the line a. When the interior is at a relatively low temperature (for example, room temperature), the cooling rate is fast as shown by line c, and the second threshold value T2 is reached early. In this case, if the temperature detected by the temperature sensor TC is not lower than the second threshold value T2 in all the mechanical refrigerators Cp, the first motor 3 and the second motor 71 are not stopped. Energy cannot be achieved.

  Therefore, in the present embodiment, the first electric motor 3 and the second electric motor 71 are operated in the memory of the control means Cu in a predetermined environment of the object to be depressurized W, and the second threshold value from the first threshold value T1. The cooling rate per unit time when the cooling units 22 and 23 are cooled to T2 is measured for each mechanical refrigerator Cp and stored in advance as data. Note that “preliminarily” may be determined using, for example, a result obtained by prior verification, or by referring to a temperature decrease rate from the first threshold T1 to the second threshold T2. May be. After any mechanical refrigerator Cp reaches a temperature exceeding the first threshold value T1, the first electric motor 3 and the second electric motor 71 are operated to cool the cooling units 22, 23 of the mechanical refrigerator Cp. In the case of further cooling, the control means Cu selects one mechanical refrigerator Cp (for example, line a in FIG. 2) having the slowest cooling rate from the above data. Then, the first electric motors of the remaining mechanical refrigerators Cp (on the lines b and c in FIG. 2) are intermittently turned on and off, respectively.

  The time for ON / OFF control of the first electric motors 3 of the remaining mechanical refrigerators Cp is calculated in advance from the previously acquired data and the temperature decrease rate of the one mechanical refrigerator Cp having the slowest temperature decrease rate. Further, the first electric motors of the remaining mechanical refrigerators Cp can be used in accordance with the outputs of the temperature sensors TC of the cooling units 22 and 23 of the one mechanical refrigerator Cp having the slowest cooling rate. 3 can be controlled on and off. As a result, as shown in FIG. 3, since the refrigerant is preferentially supplied to the slowest cooling rate, the cooling units 22 and 23 of the mechanical refrigerator Cp cool down early (in FIG. 3). , And the cooling units 22 and 23 of the remaining mechanical refrigerators Cp cool down stepwise ((shown by lines b ′ and c ′ in FIG. 3), and the result The cooling rate at the cooling units 22 and 23 of each mechanical refrigerator Cp is averaged.

  Next, when the detected temperature of the temperature sensor TC becomes lower than the second threshold value T2 in all the mechanical refrigerators Cp, all the first electric motors 3 are deactivated, and then a predetermined volume is added to the high-pressure side accumulator 5. When the compressed helium is stored, the second electric motor 71 is deactivated. If left in this state, the cooling units 22 and 23 are heated by heat input to the mechanical refrigerators Cp. Here, as shown in FIG. 2, when the inside of the depressurized object W is at a relatively high temperature (for example, 415 ° C.), the rate of temperature rise is fast as shown by line a, and the first threshold value T1 is early. Thus, the temperature of the cooling units 22 and 23 rises, and this shortens the time during which the first electric motor 3 and the second electric motor 71 are deactivated.

  Therefore, the temperature increase rate per unit time when the temperature of the cooling units 22 and 23 is increased from the second threshold value T2 to the first threshold value T1 in a predetermined environment of the decompression target W is determined for each mechanical refrigerator Cp. Each is measured and stored in advance as data. When the cooling units 22 and 23 of each mechanical refrigerator Cp are heated, the control means Cu has a relatively high heating rate among the cooling units of each mechanical refrigerator Cp (in FIG. a), the operation of only the first electric motor 3 of the selected mechanical refrigerator Cp is resumed, and helium stored in the high-pressure side accumulator 5 is supplied to the mechanical refrigerator. Only the Cp cooling sections 22 and 23 were selectively cooled once. Thereby, as shown by line a 'in FIG. 3, it is possible to lengthen the time until the first threshold T1 is reached. Note that the number of the first electric motors 3 whose operation is resumed can be appropriately set in consideration of the amount of helium stored in the high-pressure side accumulator 5 or the like. When the cooling units 22 and 23 of each mechanical refrigerator Cp further rise in temperature, the control means Cu determines from the measured temperature of the temperature sensor TC per unit time in the cooling units 22 and 23 of each mechanical refrigerator Cp. The temperature increase rate is calculated, and the operation of the first electric motor 3 is sequentially restarted from the earliest time to reach the first threshold before reaching the first threshold. Thereafter, during the operation of the decompression system PS, the above operation is repeated, and the cooling units 22, 23 of each mechanical refrigerator Cp are between the first threshold T1 and the second threshold T2 lower than the first threshold. The operations of the first electric motor 3 and the second electric motor 71 are controlled so that the respective temperatures are maintained. In general, the cooling capacity of the cooling units 22 and 23 of each mechanical refrigerator Cp deteriorates due to a change with time. For this reason, you may make it change the time which carries out on-off control of the 1st electric motor 3 according to the operation time of the cooling parts 22 and 23, for example.

  According to the above, when any one of the mechanical refrigerators Cp reaches a temperature higher than the first threshold T1 and the cooling units 22 and 23 need to be cooled, the second electric motor 71 of the compressor Cm is activated. Then, helium is supplied to the cooling units 22 and 23 of each mechanical refrigerator Cp, and the first electric motor 3 of each mechanical refrigerator Cp is operated. Then, one mechanical refrigerator Cp having the slowest cooling rate is selected from the cooling units 22 and 23 of each mechanical refrigerator Cp, and the first electric motor 3 of the remaining mechanical refrigerators Cp is controlled to be turned on / off. Thus, the refrigerant having the slowest cooling rate is preferentially supplied with the refrigerant, and the cooling rate in each of the cooling units 22 and 23 is averaged. At this time, the power consumption is reduced by the amount that the first electric motor 3 is deactivated, and the slowest cooling rate can be lowered to the second threshold at an early stage, so that the entire operation time is shortened. The power consumption is further reduced by that amount. Further, since the first electric motor 3 is intermittently turned on / off, it is advantageous in terms of cost as compared with the case where the rotation speed is controlled by providing an inverter.

Furthermore, when the temperature of each mechanical refrigerator Cp rises after both the first and second electric motors 3 and 71 are stopped, the pressure reducing means having a relatively fast temperature-decreasing speed in the cooling part of each mechanical refrigerator Cp. At least one of them, only the first electric motor 3 of the selected mechanical refrigerator Cp is temporarily turned on, and the mechanical refrigerator Cp is temporarily cooled by helium stored in the high-pressure accumulator 5. Since only the parts 22 and 23 are selectively cooled, the start of the operation of the first motor 3 of each mechanical refrigerator Cp that is not selected can be delayed, and the operation of the second motor 71 can also be delayed. It is possible to further reduce power consumption. Note that when helium is stored is eliminated, for example, turning off the first motor 3 of the mechanical refrigerator Cp, higher than the second threshold value of H ₂ cooling portions 22 and 23 of the mechanical refrigerator Cp Then, both the first and second electric motors 3, 71 may be operated again. Further, in order to restart the operation of the first electric motor 3 in order from the earliest time to reach the first threshold T1, when the temperature rises from the second threshold T2 to the first threshold T1, each mechanical refrigerator The start of operation of the Cp first electric motor 3 can be individually delayed, and the power consumption can be further reduced.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited above. In the present invention, the case where both the first and second electric motors 3, 71 are controlled to be turned on and off has been described as an example. However, both electric motors are AC motors, and an inverter is provided to reduce the power consumption by changing the rotation speed. In any case, the present invention can be applied naturally. In the above embodiment, the mechanical refrigerator as a cryopump is described as an example of the decompression means. However, the present invention is not limited to this, and the present invention is also applied to, for example, a cryopanel provided in a vacuum chamber. Can be applied.

  Furthermore, in the said embodiment, although demonstrated as an example what controls each operation | movement of the 1st electric motor 3 and the 2nd electric motor 71 based on what was previously memorize | stored as data in the memory of the control means Cu, It is not limited. For example, the cooling unit 22 of each mechanical refrigerator Cp is operated from the first threshold T1 to the second threshold T2 by operating the first electric motor 3 and the second electric motor 71 in a predetermined environment of the object to be decompressed W. , 23 is measured in real time for each cooling unit 22, 23 of each mechanical refrigerator Cp, and the operation of the first electric motor 3 and the second electric motor 71 is appropriately determined according to the measured value. You may make it control. With reference to FIG. 4, the case where the operation of the two mechanical refrigerators Cp is controlled will be described as an example. One mechanical refrigerator Cp (for example, line d in FIG. 4) having the slowest cooling rate determined from the measured value is selected. Then, the first electric motor 3 of another mechanical refrigerator Cp (in FIG. 4, line e) is intermittently turned on / off, and the temperature lowering speeds in the cooling units 22 and 23 are averaged.

  Here, while the first electric motor 3 of each mechanical refrigerator Cp is controlled to be turned on / off as described above, the other mechanical refrigerators Cp are not cooled, so that the measured value becomes one machine. There is a risk that a problem may occur in which the selection of the mechanical refrigerator Cp that exceeds the measured temperature of the mechanical refrigerator Cp and has the slowest temperature decrease rate is switched. In this case, the refrigerant is not supplied to the first mechanical refrigerator Cp, which is originally the slowest cooling rate, and is inappropriate. Therefore, it is preferable that on / off control is performed so that the measured temperature of the other mechanical refrigerator Cp does not exceed the measurement of the one mechanical refrigerator Cp having the slowest cooling rate determined first by the control means Cu. (See FIG. 4).

  Specifically, the on / off control appropriately takes into account the response speed of the device, for example, the difference between the measured temperature of one mechanical refrigerator Cp and the measured temperature of another mechanical refrigerator Cp is -5 ° C. Then, the first electric motor 3 is turned off, and when the difference between the measured temperature of one mechanical refrigerator Cp and the measured temperature of the other mechanical refrigerator Cp becomes −1 ° C., the first electric motor 3 is turned on. That's fine. Thereby, since the refrigerant is preferentially supplied to the slowest cooling rate, the cooling units 22 and 23 of the one mechanical refrigerator Cp cool down early (indicated by a line d in FIG. 4). The cooling units 22 and 23 of the other mechanical refrigerators Cp are stepped down in a step-like manner without becoming higher than the cooling units 22 and 23 of one mechanical refrigerator Cp ((FIG. 4 As a result, the cooling rate at the cooling units 22 and 23 of each mechanical refrigerator Cp is reliably averaged.

PS: Decompression system, Cp: Mechanical refrigerator (decompression unit), Cm: Compressor (compression unit), 22: Cold head 1 stage (cooling section), 23: Cold head 2 stages (cooling section), 28: Display Sir (drive unit), 3... First electric motor, 5... High-pressure side accumulator (accumulator), first electric motor, 71... Second electric motor, 72. Cu: control means, T1: first threshold, T2: second threshold.

Claims (3)

A plurality of decompression means for operating the drive unit by the first electric motor, cooling the cooling unit to a predetermined temperature corresponding to the number of rotations of the first electric motor, and expanding the refrigerant in the cooling unit to capture the gas; A single compressor that operates the compressor by the second motor and supplies the refrigerant compressed by the compressor to each decompressor at a flow rate corresponding to the rotational speed of the second motor; and A decompression system comprising measuring means for measuring the temperature of each cooling section,
Provided with control means for controlling the operation of both the first and second electric motors so that the temperature of the cooling section is maintained between the first threshold and a second threshold lower than the first threshold. In
The control means activates both the first and second electric motors until the temperature of the cooling section of each decompression means reaches the second threshold value from the first threshold value. When one pressure reducing means having a slow temperature drop rate is selected, the number of rotations of the first motors of the remaining pressure reducing means is decreased, and the cooling unit of each pressure reducing means reaches the second threshold value, the first of all the pressure reducing means A decompression system characterized in that the operation of each electric motor is stopped. An accumulator for storing the compressed refrigerant;
The control means reduces the rotational speed of the second electric motor when a predetermined volume of refrigerant is stored in the accumulator after all the first electric motors are deactivated. When the temperature rises, at least one pressure reducing means having a relatively high temperature rising speed is selected from the cooling parts of each pressure reducing means, and the rotational speed of the first electric motor of the selected pressure reducing means is increased, and the accumulator is The decompression system according to claim 1, wherein the stored refrigerant is supplied and only the cooling part of the decompression means is selectively cooled. The control means calculates the temperature increase rate per unit time in the cooling part of each decompression means, restarts the operation of the second electric motor, and in order from the earliest time to reach the first threshold, The decompression system according to claim 1 or 2, wherein the operation is resumed.

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