JP2015163823A

JP2015163823A - Freezer unit

Info

Publication number: JP2015163823A
Application number: JP2014039303A
Authority: JP
Inventors: 岡本　哲也; Tetsuya Okamoto; 哲也岡本; 古庄　和宏; Kazuhiro Kosho; 和宏古庄; 岩田　育弘; Yasuhiro Iwata; 育弘岩田; 隆平加治; Ryuhei Kaji
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2014-02-28
Filing date: 2014-02-28
Publication date: 2015-09-10
Anticipated expiration: 2034-02-28
Also published as: JP6354209B2

Abstract

PROBLEM TO BE SOLVED: To secure an amount of an oil returning from an oil separator 28 to a fourth compression part 24 even when a difference between a suction pressure and a discharge pressure of the fourth compression part 24 is small.SOLUTION: An air conditioner 10 includes: a four stage compressor 20; an outdoor heat exchanger 40; an expansion mechanism 70; an indoor heat exchanger 12a; an oil separator 28; oil return passages 28a, 28b; and an oil return bypass electromagnetic valve SV28. In the four stage compressor 20, multiple low stage compression parts 21, 22, 23 and one high stage fourth compression part 24 are connected in one line. The oil separator 28 is provided at a fourth discharge pipe 24b. The oil return passages 28a, 28b connect a fourth suction tube 24a with the oil separator 28 and return an oil from the oil separator 28 to the fourth compression part 24. The oil return bypass electromagnetic valve SV28 changes passage areas of the oil return passages 28a, 28b.

Description

本発明は、冷凍装置、特に、複数の圧縮部を有する複数段圧縮機構を備えた冷凍装置に関する。 The present invention relates to a refrigeration apparatus, and more particularly to a refrigeration apparatus including a multistage compression mechanism having a plurality of compression units.

従来から、多段圧縮冷凍サイクルを行う冷凍装置であって、油分離器を備えたものが存在する。例えば、特許文献１（特開２０１１−２１４７５７号公報）に記載の冷凍装置は、４段の圧縮部を有しており、最高段の圧縮部から吐出される高圧の冷媒から冷凍機油（以下、単に油という。）の分離を行わせる油分離器を備えている。油分離器で冷媒から分離された油は、油戻し管を通って最高段の圧縮部の吸入配管に戻る。 Conventionally, there are refrigeration apparatuses that perform a multistage compression refrigeration cycle and that include an oil separator. For example, the refrigeration apparatus described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-214757) has a four-stage compression unit, and a refrigerating machine oil (hereinafter, It is equipped with an oil separator that simply separates oil). The oil separated from the refrigerant by the oil separator returns to the suction pipe of the highest stage compression section through the oil return pipe.

３段以上の多段圧縮を行う冷凍装置においては、最高段の高圧の圧縮部（以下、高段圧縮部という。）が殆ど冷媒を圧縮しない運転が存在することを、本発明の発明者は見いだしている。例えば、４段の圧縮を行う圧縮機構を備えた空気調和装置において、熱負荷が小さく効率を向上させるために冷媒の高圧値を小さく保つ運転を行っているときには、１〜３段の圧縮部で必要な圧縮仕事を終えてしまい、４段目の高段圧縮部の吸入圧力と吐出圧力との差が小さくなってしまうことがある。空気調和装置の場合、熱負荷が大きいときの冷房運転に合わせて多段圧縮の圧縮機構を設計すると、暖房運転や、外気温が低いときの冷房運転を行うときには、高段圧縮部に吸入される冷媒の圧力と吐出される冷媒の圧力との差が非常に小さくなってしまう。 The inventor of the present invention has found that in a refrigeration apparatus that performs multi-stage compression of three or more stages, there is an operation in which the highest-stage high-pressure compression section (hereinafter referred to as a high-stage compression section) hardly compresses the refrigerant. ing. For example, in an air conditioner equipped with a compression mechanism that performs four-stage compression, when performing an operation of keeping the high pressure value of the refrigerant small in order to reduce the heat load and improve efficiency, The necessary compression work is finished, and the difference between the suction pressure and the discharge pressure in the fourth stage high-stage compression section may become small. In the case of an air conditioner, if a compression mechanism for multi-stage compression is designed in accordance with the cooling operation when the heat load is large, when performing the heating operation or the cooling operation when the outside air temperature is low, it is sucked into the high-stage compression unit The difference between the pressure of the refrigerant and the pressure of the discharged refrigerant becomes very small.

このように、高段圧縮部の吸入圧力と吐出圧力との差が小さくなった場合、その高段圧縮部の吐出側に設けられた油分離器から高段圧縮部に戻る油の量が少なくなる。すると、余分な油が熱交換器などに流れ出てしまい、圧縮機構に油不足が生じて運転停止に至ってしまうことも考えられる。 As described above, when the difference between the suction pressure and the discharge pressure of the high-stage compression section becomes small, the amount of oil returning from the oil separator provided on the discharge side of the high-stage compression section to the high-stage compression section is small. Become. Then, it is also conceivable that excess oil flows out to a heat exchanger or the like, resulting in a shortage of oil in the compression mechanism, resulting in operation stop.

本発明の課題は、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも油分離器から高段圧縮部に戻る油の量を確保することができる冷凍装置、を提供することにある。 An object of the present invention is to provide a refrigeration apparatus capable of ensuring the amount of oil that returns from the oil separator to the high-stage compression section even when the difference between the suction pressure and the discharge pressure of the high-stage compression section is small. It is in.

本発明の第１観点に係る冷凍装置は、複数段圧縮機構と、放熱器と、膨張部と、蒸発器と、油分離器と、油戻し流路と、流路面積変更部とを備えている。複数段圧縮機構は、複数の低段圧縮部と１つの高段圧縮部とが１列に接続された圧縮機構である。言い換えれば、各低段圧縮部と高段圧縮部とが直列に接続されている。放熱器は、複数段圧縮機構から吐出された冷媒に、放熱をさせる。膨張部は、放熱器を出た冷媒を減圧する。蒸発器は、膨張部を出た冷媒を、蒸発させる。油分離器は、高段吐出配管に設けられている。高段吐出配管は、高段圧縮部から吐出された冷媒が流れる配管である。油戻し流路は、高段吸入配管と油分離器とを結ぶ流路であって、油分離器から高段圧縮部へと油を戻す。高段吸入配管は、高段圧縮部に吸入される冷媒が流れる配管である。そして、流路面積変更部は、油戻し流路の流路面積を変える。 A refrigeration apparatus according to a first aspect of the present invention includes a multi-stage compression mechanism, a radiator, an expansion unit, an evaporator, an oil separator, an oil return channel, and a channel area changing unit. Yes. The multi-stage compression mechanism is a compression mechanism in which a plurality of low-stage compression units and one high-stage compression unit are connected in a row. In other words, each low stage compression part and high stage compression part are connected in series. The radiator causes the refrigerant discharged from the multistage compression mechanism to radiate heat. The expansion part decompresses the refrigerant that has exited the radiator. The evaporator evaporates the refrigerant that has exited the expansion section. The oil separator is provided in the high stage discharge pipe. The high stage discharge pipe is a pipe through which the refrigerant discharged from the high stage compression section flows. The oil return channel is a channel connecting the high stage suction pipe and the oil separator, and returns oil from the oil separator to the high stage compression unit. The high stage suction pipe is a pipe through which the refrigerant sucked into the high stage compression section flows. The flow channel area changing unit changes the flow channel area of the oil return flow channel.

ここでは、複数段圧縮機構の高段圧縮部から吐出された冷媒が、放熱器で放熱し、膨張部で減圧し、蒸発器で蒸発して、再び複数段圧縮機構の低段圧縮部に吸入される。高段圧縮部から吐出されて高段吐出配管を流れる冷媒は、油分離器において油が分離され、その油は、油戻し流路を通って高段吸入配管から高段圧縮部に吸入される。これによって、高段吐出配管を流れる冷媒と高段吸入配管を流れる冷媒との圧力差が大きい場合には、油分離器から高段圧縮部へと確実に油が戻る。一方、高段吐出配管を流れる冷媒と高段吸入配管を流れる冷媒との圧力差が小さい場合には、油分離器から高段圧縮部へと戻る油の量が少なくなることが心配されるが、第１観点に係る冷凍装置では、流路面積変更部によって油戻し流路の流路面積を変えることができる。油戻し流路の流路面積を変えて大きくすることで、高段吐出配管を流れる冷媒と高段吸入配管を流れる冷媒との圧力差が小さい場合にも、油分離器から高段圧縮部へと油を確実に戻すことができるようになる。すなわち、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも、油分離器から高段圧縮部に戻る油の量を確保できる。 Here, the refrigerant discharged from the high-stage compression part of the multistage compression mechanism dissipates heat in the radiator, depressurizes in the expansion part, evaporates in the evaporator, and sucks again into the low-stage compression part of the multistage compression mechanism Is done. The refrigerant discharged from the high stage compression section and flowing through the high stage discharge pipe is separated in the oil separator, and the oil is sucked into the high stage compression section from the high stage suction pipe through the oil return passage. . Accordingly, when the pressure difference between the refrigerant flowing through the high stage discharge pipe and the refrigerant flowing through the high stage suction pipe is large, the oil reliably returns from the oil separator to the high stage compression unit. On the other hand, when the pressure difference between the refrigerant flowing through the high-stage discharge pipe and the refrigerant flowing through the high-stage suction pipe is small, there is a concern that the amount of oil returning from the oil separator to the high-stage compression section will decrease. In the refrigeration apparatus according to the first aspect, the channel area of the oil return channel can be changed by the channel area changing unit. Even if the pressure difference between the refrigerant flowing through the high-stage discharge pipe and the refrigerant flowing through the high-stage suction pipe is small by changing the flow area of the oil return flow path to be large, the oil separator is moved to the high-stage compression section. And it will be possible to return the oil reliably. That is, even when the difference between the suction pressure and the discharge pressure of the high-stage compression section is small, it is possible to ensure the amount of oil that returns from the oil separator to the high-stage compression section.

本発明の第２観点に係る冷凍装置は、第１観点の冷凍装置であって、油戻し流路は、第１油戻し流路と第２油戻し流路とを有している。第１油戻し流路は、キャピラリーチューブを含む流路である。第２油戻し流路の流路面積は、第１油戻し流路のキャピラリーチューブの流路面積よりも大きい。第１油戻し流路と第２油戻し流路とは、並列している。そして、流路面積変更部は、第２油戻し流路に設けられた開閉弁である。 The refrigeration apparatus according to the second aspect of the present invention is the refrigeration apparatus according to the first aspect, wherein the oil return channel includes a first oil return channel and a second oil return channel. The first oil return channel is a channel including a capillary tube. The channel area of the second oil return channel is larger than the channel area of the capillary tube of the first oil return channel. The first oil return channel and the second oil return channel are in parallel. The flow path area changing unit is an on-off valve provided in the second oil return flow path.

ここでは、流路面積が小さいキャピラリーチューブを含む第１油戻し流路と、流路面積が大きい第２油戻し流路とを並列させて、第２油戻し流路に、流路面積変更部としての機能を果たす開閉弁を設けている。このような油戻し流路の構成を採ることによって、開閉弁を閉じているときには、流路面積が小さいキャピラリーチューブを油が流れることになり、開閉弁を開けているときには、主として、圧力損失が小さい流路面積の大きな第２油戻し流路を油が流れることになる。したがって、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合に、開閉弁を開けることで、油分離器から高段圧縮部に戻る油の量を確保することができる。 Here, a first oil return channel including a capillary tube having a small channel area and a second oil return channel having a large channel area are arranged in parallel, and a channel area changing unit is provided in the second oil return channel. An on-off valve that fulfills the function of is provided. By adopting such an oil return passage configuration, when the on-off valve is closed, oil flows through the capillary tube having a small passage area, and when the on-off valve is opened, pressure loss mainly occurs. The oil flows through the second oil return channel having a small channel area. Therefore, when the difference between the suction pressure and the discharge pressure of the high-stage compression unit is small, the amount of oil returning from the oil separator to the high-stage compression unit can be ensured by opening the on-off valve.

本発明の第３観点に係る冷凍装置は、第１観点又は第２観点の冷凍装置であって、放熱器は、冷房運転のときには、熱源によって冷媒を冷やす熱源ユニットの熱源側熱交換器であり、暖房運転のときには、冷媒に放熱をさせる利用ユニットの利用側熱交換器である。蒸発器は、冷房運転のときには、冷媒を蒸発させる利用側熱交換器であり、暖房運転のときには、熱源から熱を奪って冷媒を蒸発させる熱源側熱交換器である。また、第３観点に係る冷凍装置は、切換機構をさらに備えている。切換機構は、高段圧縮部を出た冷媒が熱源側熱交換器に流れる冷房運転の状態と、高段圧縮部を出た冷媒が利用側熱交換器に流れる暖房運転の状態とを切り換える。そして、油分離器は、高段圧縮部と切換機構との間に配置される。 A refrigeration apparatus according to a third aspect of the present invention is the refrigeration apparatus according to the first aspect or the second aspect, wherein the radiator is a heat source side heat exchanger of a heat source unit that cools the refrigerant with a heat source during cooling operation. In the heating operation, it is a utilization side heat exchanger of the utilization unit that radiates heat to the refrigerant. The evaporator is a use-side heat exchanger that evaporates the refrigerant during the cooling operation, and a heat source-side heat exchanger that evaporates the refrigerant by removing heat from the heat source during the heating operation. Moreover, the refrigeration apparatus according to the third aspect further includes a switching mechanism. The switching mechanism switches between a cooling operation state in which the refrigerant that has exited the high stage compression section flows to the heat source side heat exchanger and a heating operation state in which the refrigerant that has exited the high stage compression section flows to the use side heat exchanger. And an oil separator is arrange | positioned between a high stage compression part and a switching mechanism.

ここでは、切換機構によって冷房運転と暖房運転とを切り換えることができる冷凍装置、すなわち、冷暖房可能な空気調和装置に本発明を適用している。そして、油分離器を高段圧縮部と切換機構との間に配置しているので、冷房運転の状態でも暖房運転の状態でも油が高段圧縮部に戻る。高段圧縮部の吸入圧力と吐出圧力との差は、冷房運転と暖房運転とで異なっていることが多いが、運転に応じて油戻し流路の流路面積を変えることで、いずれの運転においても油分離器から高段圧縮部に戻る油の量を確保することができる。 Here, the present invention is applied to a refrigeration apparatus capable of switching between a cooling operation and a heating operation by a switching mechanism, that is, an air conditioner capable of cooling and heating. And since the oil separator is arrange | positioned between the high stage compression part and the switching mechanism, oil returns to a high stage compression part in the state of air_conditionaing | cooling operation and the state of heating operation. The difference between the suction pressure and the discharge pressure of the high-stage compression section is often different between the cooling operation and the heating operation, but any operation can be performed by changing the flow area of the oil return passage according to the operation. The amount of oil returning from the oil separator to the high-stage compression section can be ensured.

本発明の第４観点に係る冷凍装置は、第３観点の冷凍装置であって、複数段圧縮機構は、共通回転軸を有している。共通回転軸は、複数の低段圧縮部それぞれの圧縮部材を回転させるとともに、高段圧縮部の圧縮部材を回転させる。 A refrigeration apparatus according to a fourth aspect of the present invention is the refrigeration apparatus according to the third aspect, wherein the multistage compression mechanism has a common rotating shaft. The common rotation shaft rotates the compression member of each of the plurality of low-stage compression units and rotates the compression member of the high-stage compression unit.

ここでは、共通回転軸によって各低段圧縮部の圧縮部材および高段圧縮部の圧縮部材を回転させているため、低段、高段の各圧縮部の容積比を制御的に変更することができない。したがって、回転数を調整することによって高段圧縮部の吸入圧力と吐出圧力との差を大きくすることはできない。しかし、暖房運転、冷房運転のいずれかの運転に合わせて共通回転軸の回転数を決めており、運転の状況によって高段圧縮部の吸入圧力と吐出圧力との差が小さくなってしまう場合にも、本発明によれば、油分離器から高段圧縮部に戻る油の量を確保することができる。 Here, since the compression member of each low-stage compression unit and the compression member of the high-stage compression unit are rotated by the common rotation shaft, the volume ratio of each of the low-stage and high-stage compression units can be controlled in a controlled manner. Can not. Therefore, the difference between the suction pressure and the discharge pressure of the high-stage compression unit cannot be increased by adjusting the rotation speed. However, when the number of rotations of the common rotating shaft is determined in accordance with either the heating operation or the cooling operation, and the difference between the suction pressure and the discharge pressure of the high-stage compression unit becomes small depending on the operation status In addition, according to the present invention, the amount of oil that returns from the oil separator to the high-stage compression section can be ensured.

本発明の第５観点に係る冷凍装置は、第３観点又は第４観点の冷凍装置であって、中間インジェクション機構をさらに備えている。中間インジェクション機構は、暖房運転のときに、複数の低段圧縮部のうちの１つの低段圧縮部から吐出され次段の低段圧縮部に吸入される冷媒を、冷やす。一方、暖房運転のときに、高段圧縮部に吸入される冷媒の冷却は行われない。 The refrigeration apparatus according to the fifth aspect of the present invention is the refrigeration apparatus according to the third aspect or the fourth aspect, and further includes an intermediate injection mechanism. The intermediate injection mechanism cools the refrigerant that is discharged from one of the plurality of low-stage compression units and sucked into the next-stage low-stage compression unit during heating operation. On the other hand, during the heating operation, the refrigerant sucked into the high-stage compression unit is not cooled.

ここでは、暖房運転時には、１つの低段圧縮部と次段の低段圧縮部との間に中間インジェクション機構が配置され、圧縮途中の冷媒の温度が下げられる。この中間インジェクションによって、冷凍サイクルの効率が上がり、圧縮機に投入するエネルギーを削減できる。この中間インジェクションを行う冷凍装置において、仮に、高段圧縮部から吐出されて油分離器で冷媒から分離された油を、高段圧縮部ではなく、低段圧縮部に戻す構成を採った場合、油が低段圧縮部に滞留してしまうことも心配される。 Here, during the heating operation, an intermediate injection mechanism is arranged between one low-stage compression section and the next-stage low-stage compression section, and the temperature of the refrigerant being compressed is lowered. This intermediate injection increases the efficiency of the refrigeration cycle and reduces the energy input to the compressor. In the refrigeration apparatus that performs the intermediate injection, if the configuration is adopted in which the oil discharged from the high-stage compression unit and separated from the refrigerant in the oil separator is returned to the low-stage compression unit instead of the high-stage compression unit, There is also a concern that the oil stays in the low-stage compression section.

しかし、第５観点に係る冷凍装置では、暖房運転のときに、高段圧縮部に吸入される冷媒の冷却は行われず、高段圧縮部から吐出されて油分離器から高段圧縮部に戻る油は、流路面積が大きくなるように変更された油戻し流路を通ることができる。このため、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも、冷媒圧力が小さい低段圧縮部に油を戻す必要がなくなり、高段圧縮部が必要量の油を保持することができる。 However, in the refrigeration apparatus according to the fifth aspect, during the heating operation, the refrigerant sucked into the high stage compression unit is not cooled, and is discharged from the high stage compression unit and returned from the oil separator to the high stage compression unit. The oil can pass through an oil return channel that has been modified to increase the channel area. For this reason, even when the difference between the suction pressure and the discharge pressure of the high-stage compression section is small, it is not necessary to return the oil to the low-stage compression section where the refrigerant pressure is small, and the high-stage compression section holds the required amount of oil. be able to.

本発明の第６観点に係る冷凍装置は、第３観点から第５観点のいずれかの冷凍装置であって、制御部をさらに備えている。制御部は、流路面積変更部を制御して、第１状態と第２状態とを切り換える。第１状態では、油戻し流路の流路面積が第１流路面積になる。第２状態では、油戻し流路の流路面積が、第１流路面積よりも大きな第２流路面積になる。そして、制御部は、暖房運転のときに、複数段圧縮機構の起動時、複数段圧縮機構の起動後の通常運転開始時、或いは、複数段圧縮機構の起動時と複数段圧縮機構の起動後の通常運転開始時との両方で、流路面積変更部を第２状態にする。 A refrigeration apparatus according to a sixth aspect of the present invention is the refrigeration apparatus according to any one of the third to fifth aspects, and further includes a control unit. The control unit controls the flow path area changing unit to switch between the first state and the second state. In the first state, the channel area of the oil return channel is the first channel area. In the second state, the oil return passage has a second passage area that is larger than the first passage area. The control unit is configured to start the multi-stage compression mechanism, start the normal operation after the multi-stage compression mechanism is started, or start the multi-stage compression mechanism and the multi-stage compression mechanism during the heating operation. The flow path area changing unit is set to the second state both at the start of normal operation.

冷暖房が可能な冷凍装置において複数段圧縮機構を採用した場合、暖房運転のときに高段圧縮部の吸入圧力と吐出圧力との差が小さくなることを、本発明の発明者は見いだしている。特に、複数段圧縮機構の起動時や、その後の通常運転開始時において、油戻し流路の流路面積が小さければ、油分離器から高段圧縮部へと油があまり戻らなくなる。これに鑑み、第６観点に係る冷凍装置では、暖房運転における複数段圧縮機構の起動時、および／又は、暖房運転における複数段圧縮機構の起動後の通常運転開始時に、流路面積変更部を第２状態にして、油戻し流路の流路面積を大きくしている。これにより、高段圧縮部の吸入圧力と吐出圧力との差が小さくなりがちな暖房運転の所定時においても、油分離器から高段圧縮部に戻る油の量を確保することができる。 The inventors of the present invention have found that when a multistage compression mechanism is employed in a refrigeration apparatus capable of cooling and heating, the difference between the suction pressure and the discharge pressure of the high-stage compression section is reduced during heating operation. In particular, when the multistage compression mechanism is started up or when normal operation starts thereafter, if the flow area of the oil return flow path is small, the oil does not return much from the oil separator to the high stage compression section. In view of this, in the refrigeration apparatus according to the sixth aspect, at the time of starting the multi-stage compression mechanism in the heating operation and / or at the time of starting the normal operation after starting the multi-stage compression mechanism in the heating operation, the flow path area changing unit is In the second state, the flow area of the oil return flow path is increased. Thereby, the amount of oil returning from the oil separator to the high-stage compression section can be ensured even at a predetermined time of the heating operation in which the difference between the suction pressure and the discharge pressure of the high-stage compression section tends to be small.

本発明の第７観点に係る冷凍装置は、第６観点の冷凍装置であって、制御部は、冷房運転のときに、複数段圧縮機構の起動時、複数段圧縮機構の起動後の通常運転開始時、或いは、複数段圧縮機構の起動時と複数段圧縮機構の起動後の通常運転開始時との両方で、流路面積変更部を第１状態にする。 A refrigeration apparatus according to a seventh aspect of the present invention is the refrigeration apparatus according to the sixth aspect, wherein the control unit performs normal operation after activation of the multistage compression mechanism during activation of the multistage compression mechanism during cooling operation. The flow path area changing unit is set to the first state both at the time of starting or at the time of starting the multistage compression mechanism and at the time of starting normal operation after the start of the multistage compression mechanism.

冷暖房が可能な冷凍装置において複数段圧縮機構を採用した場合、暖房運転のときに高段圧縮部の吸入圧力と吐出圧力との差が小さくなる一方、熱負荷が大きい冷房運転のときには高段圧縮部の吸入圧力と吐出圧力との差が十分に大きくなることを、本発明の発明者は見いだしている。これに鑑み、第７観点に係る冷凍装置では、冷房運転における複数段圧縮機構の起動時、および／又は、冷房運転における複数段圧縮機構の起動後の通常運転開始時に、流路面積変更部を第１状態にして、油戻し流路の流路面積を小さくしている。これにより、高段圧縮部の吸入圧力と吐出圧力との差が十分に大きい冷房運転の所定時において、油分離器から高段吸入配管に油だけではなく多くの冷媒まで戻ってしまう不具合を抑えられる。 When a multi-stage compression mechanism is used in a refrigeration system capable of cooling and heating, the difference between the suction pressure and the discharge pressure of the high-stage compression unit is reduced during heating operation, while high-stage compression is performed during cooling operation with a large heat load. The inventor of the present invention has found that the difference between the suction pressure and the discharge pressure of the section becomes sufficiently large. In view of this, in the refrigeration apparatus according to the seventh aspect, at the time of starting the multistage compression mechanism in the cooling operation and / or at the time of starting the normal operation after starting the multistage compression mechanism in the cooling operation, the flow path area changing unit is In the first state, the flow area of the oil return flow path is reduced. This suppresses the problem that not only the oil but also a large amount of refrigerant returns from the oil separator to the high-stage intake pipe at the predetermined time of the cooling operation where the difference between the suction pressure and the discharge pressure of the high-stage compression section is sufficiently large. It is done.

本発明の第１観点に係る冷凍装置によれば、油戻し流路の流路面積を変えて大きくすることで、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも油分離器から高段圧縮部に戻る油の量を確保できる。 According to the refrigeration apparatus according to the first aspect of the present invention, oil separation can be achieved even when the difference between the suction pressure and the discharge pressure of the high-stage compression unit is small by changing and increasing the flow area of the oil return flow path. The amount of oil returning from the vessel to the high stage compression section can be secured.

本発明の第２観点に係る冷凍装置では、開閉弁を開けているときには、圧力損失が小さい流路面積の大きな第２油戻し流路を油が流れることになって、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも、油分離器から高段圧縮部へと油を確実に戻すことができる。 In the refrigeration apparatus according to the second aspect of the present invention, when the on-off valve is opened, the oil flows through the second oil return channel having a large channel area with a small pressure loss, so that the suction of the high-stage compression unit Even when the difference between the pressure and the discharge pressure is small, the oil can be reliably returned from the oil separator to the high-stage compression section.

本発明の第３観点に係る冷凍装置では、運転に応じて油戻し流路の流路面積を変えることで、冷房、暖房、いずれの運転においても、油分離器から高段圧縮部に戻る油の量を確保することができる。 In the refrigeration apparatus according to the third aspect of the present invention, the oil returning from the oil separator to the high-stage compression unit in any of the cooling and heating operations by changing the flow passage area of the oil return flow passage according to the operation. Can be secured.

本発明の第４観点に係る冷凍装置では、共通回転軸を採用しているために低段、高段の各圧縮部の容積比を制御的に変更することができないけれども、流路面積変更部を設けているため、高段圧縮部の吸入圧力と吐出圧力との差が小さい場合にも油分離器から高段圧縮部に戻る油の量を確保することができる。 In the refrigeration apparatus according to the fourth aspect of the present invention, since the common rotating shaft is employed, the volume ratio of the low-stage and high-stage compression sections cannot be changed in a controllable manner. Therefore, even when the difference between the suction pressure and the discharge pressure of the high stage compression section is small, it is possible to secure the amount of oil that returns from the oil separator to the high stage compression section.

本発明の第５観点に係る冷凍装置では、より圧力が低い低段圧縮部に油分離器からの油を戻して高段圧縮部で油が不足気味になるという構成を採る必要がなくなり、高段圧縮部から吐出されて油分離器へと流れた油を、高段圧縮部に所定量だけ確実に戻すことができる。 In the refrigeration apparatus according to the fifth aspect of the present invention, there is no need to adopt a configuration in which the oil from the oil separator is returned to the low-stage compression section having a lower pressure and the oil becomes insufficient in the high-stage compression section. The oil discharged from the stage compression section and flowing to the oil separator can be reliably returned to the high stage compression section by a predetermined amount.

本発明の第６観点に係る冷凍装置によれば、高段圧縮部の吸入圧力と吐出圧力との差が小さくなりがちな暖房運転の所定時においても、油分離器から高段圧縮部に戻る油の量を確保することができる。 According to the refrigeration apparatus according to the sixth aspect of the present invention, the difference between the suction pressure and the discharge pressure of the high-stage compression section is returned from the oil separator to the high-stage compression section even during a predetermined heating operation. The amount of oil can be secured.

本発明の第７観点に係る冷凍装置によれば、高段圧縮部の吸入圧力と吐出圧力との差が十分に大きい冷房運転の所定時において、油分離器から高段吸入配管に油だけではなく多くの冷媒まで戻ってしまう不具合を抑えられる。 According to the refrigeration apparatus according to the seventh aspect of the present invention, at a predetermined time of the cooling operation in which the difference between the suction pressure and the discharge pressure of the high stage compression unit is sufficiently large, the oil alone is not supplied from the oil separator to the high stage suction pipe. The problem of returning to a large number of refrigerants can be suppressed.

本発明の一実施形態に係る空気調和装置の冷房運転時の冷媒回路図である。It is a refrigerant circuit figure at the time of air conditioning operation of the air harmony device concerning one embodiment of the present invention. 図１の冷房運転時（高負荷）の冷凍サイクルの圧力−エンタルピ線図である。FIG. 2 is a pressure-enthalpy diagram of the refrigeration cycle during the cooling operation (high load) of FIG. 1. 図１の冷房運転時（低負荷）の冷凍サイクルの圧力−エンタルピ線図である。FIG. 2 is a pressure-enthalpy diagram of the refrigeration cycle during the cooling operation (low load) of FIG. 1. 空気調和装置の暖房運転時の冷媒回路図である。It is a refrigerant circuit figure at the time of heating operation of an air harmony device. 図４の暖房運転時の冷凍サイクルの圧力−エンタルピ線図である。It is a pressure-enthalpy diagram of the refrigerating cycle at the time of heating operation of FIG. 空気調和装置の制御ブロック図である。It is a control block diagram of an air conditioning apparatus.

本発明の一実施形態に係る冷凍装置である空気調和装置１０について、以下、図面を参照しながら説明する。 An air conditioner 10 that is a refrigeration apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

（１）空気調和装置の構成
図１および図４は、空気調和装置１０の構成を示す冷媒回路図である。空気調和装置１０は、超臨界状態の二酸化炭素冷媒を使用して四段圧縮冷凍サイクルを行う冷凍装置である。空気調和装置１０は、熱源ユニットである室外ユニット１１と、利用ユニットである複数の室内ユニット１２とが、連絡冷媒配管１３，１４によって結ばれた装置であり、冷房運転サイクルと暖房運転サイクルとが切り換わる冷媒回路を有する。図１の矢印は、冷房運転において冷媒回路を循環する冷媒の流れを表している。図４の矢印は、暖房運転において冷媒回路を循環する冷媒の流れを表している。 (1) Configuration of Air Conditioner FIG. 1 and FIG. 4 are refrigerant circuit diagrams showing the configuration of the air conditioner 10. The air conditioning apparatus 10 is a refrigeration apparatus that performs a four-stage compression refrigeration cycle using a supercritical carbon dioxide refrigerant. The air conditioner 10 is an apparatus in which an outdoor unit 11 that is a heat source unit and a plurality of indoor units 12 that are utilization units are connected by communication refrigerant pipes 13 and 14, and a cooling operation cycle and a heating operation cycle are provided. It has a refrigerant circuit that switches. The arrows in FIG. 1 represent the flow of the refrigerant circulating in the refrigerant circuit in the cooling operation. The arrows in FIG. 4 represent the flow of the refrigerant circulating through the refrigerant circuit in the heating operation.

空気調和装置１０の冷媒回路は、主として、四段圧縮機２０、第１〜第４切換機構３１〜３４、室外熱交換器４０、第１〜第４油分離器２５〜２８、第１および第２室外電動弁５１，５２、ブリッジ回路５５、エコノマイザ熱交換器６１、内部熱交換器６２、膨張機構７０、レシーバ８０、過冷却熱交換器９０、室内熱交換器１２ａ、室内電動弁１２ｂ、および、各機器や弁を結ぶ冷媒配管群から成る。室外熱交換器４０は、図５に示すように、縦に並べて配置された、第１熱交換器４１、第２熱交換器４２、第３熱交換器４３および第４熱交換器４４から成る。 The refrigerant circuit of the air conditioner 10 mainly includes a four-stage compressor 20, first to fourth switching mechanisms 31 to 34, an outdoor heat exchanger 40, first to fourth oil separators 25 to 28, first and first. 2 outdoor motorized valves 51, 52, bridge circuit 55, economizer heat exchanger 61, internal heat exchanger 62, expansion mechanism 70, receiver 80, supercooling heat exchanger 90, indoor heat exchanger 12a, indoor motorized valve 12b, It consists of a refrigerant piping group that connects each device and valve. As shown in FIG. 5, the outdoor heat exchanger 40 includes a first heat exchanger 41, a second heat exchanger 42, a third heat exchanger 43, and a fourth heat exchanger 44 that are arranged vertically. .

以下、冷媒回路の各構成要素を詳細に説明する。 Hereinafter, each component of the refrigerant circuit will be described in detail.

（１−１）四段圧縮機
四段圧縮機２０は、密閉容器内に、第１圧縮部２１、第２圧縮部２２、第３圧縮部２３、第４圧縮部２４および圧縮機駆動モータ（図示せず）が収容された、密閉式の圧縮機である。圧縮機駆動モータは、共通回転軸によって、４つの圧縮部２１〜２４の各圧縮部材を回転させる。すなわち、四段圧縮機２０は、４つの圧縮部２１〜２４の圧縮部材が単一の共通回転軸に連結された、一軸四段の圧縮構造を有している。四段圧縮機２０では、第１圧縮部２１、第２圧縮部２２、第３圧縮部２３および第４圧縮部２４が、この順番で直列に配管接続される。すなわち、第１圧縮部２１、第２圧縮部２２、第３圧縮部２３および第４圧縮部２４は、１列に接続される。第１圧縮部２１は、第１吸入管２１ａから冷媒を吸い込み、第１吐出管２１ｂへと冷媒を吐出する。第２圧縮部２２は、第２吸入管２２ａから冷媒を吸い込み、第２吐出管２２ｂへと冷媒を吐出する。第３圧縮部２３は、第３吸入管２３ａから冷媒を吸い込み、第３吐出管２３ｂへと冷媒を吐出する。第４圧縮部２４は、高段吸入配管である第４吸入管２４ａから冷媒を吸い込み、一旦密閉空間に吐出し、そこから高段吐出配管である第４吐出管２４ｂへと冷媒を吐出する。すなわち、最高段の圧縮部である第４圧縮部２４に吸入される冷媒は、第４圧縮部２４の吸入ポートに接続された第４吸入管２４ａを流れてくる。また、第４圧縮部２４から吐出された冷媒は、第４圧縮部２４の吐出ポートに接続された第４吐出管２４ｂを流れていく。 (1-1) Four-stage compressor The four-stage compressor 20 includes a first compression section 21, a second compression section 22, a third compression section 23, a fourth compression section 24, and a compressor drive motor ( (Not shown) is a hermetic compressor. A compressor drive motor rotates each compression member of the four compression parts 21-24 with a common rotating shaft. That is, the four-stage compressor 20 has a uniaxial four-stage compression structure in which the compression members of the four compression units 21 to 24 are connected to a single common rotation shaft. In the four-stage compressor 20, the 1st compression part 21, the 2nd compression part 22, the 3rd compression part 23, and the 4th compression part 24 are pipe-connected in series in this order. That is, the 1st compression part 21, the 2nd compression part 22, the 3rd compression part 23, and the 4th compression part 24 are connected to 1 row. The first compressor 21 sucks the refrigerant from the first suction pipe 21a and discharges the refrigerant to the first discharge pipe 21b. The second compressor 22 sucks the refrigerant from the second suction pipe 22a and discharges the refrigerant to the second discharge pipe 22b. The third compressor 23 sucks the refrigerant from the third suction pipe 23a and discharges the refrigerant to the third discharge pipe 23b. The fourth compressor 24 sucks the refrigerant from the fourth suction pipe 24a that is the high stage suction pipe, discharges the refrigerant into the sealed space, and then discharges the refrigerant to the fourth discharge pipe 24b that is the high stage discharge pipe. That is, the refrigerant sucked into the fourth compression section 24 that is the highest stage compression section flows through the fourth suction pipe 24 a connected to the suction port of the fourth compression section 24. Further, the refrigerant discharged from the fourth compression unit 24 flows through the fourth discharge pipe 24 b connected to the discharge port of the fourth compression unit 24.

第１圧縮部２１は、最低段の圧縮機構であり、冷媒回路を流れる最も低圧の冷媒を圧縮する。第２圧縮部２２は、第１圧縮部２１によって圧縮された冷媒を吸い込んで圧縮する。第３圧縮部２３は、第２圧縮部２２によって圧縮された冷媒を吸い込んで圧縮する。第４圧縮部２４は、最高段の圧縮機構であり、第３圧縮部２３によって圧縮された冷媒を吸い込んで圧縮する。第４圧縮部２４によって圧縮され第４吐出管２４ｂへと吐出された冷媒は、冷媒回路を流れる最も高圧の冷媒となる。 The first compression unit 21 is a lowest-stage compression mechanism, and compresses the lowest pressure refrigerant flowing through the refrigerant circuit. The second compression unit 22 sucks and compresses the refrigerant compressed by the first compression unit 21. The third compression unit 23 sucks and compresses the refrigerant compressed by the second compression unit 22. The fourth compression unit 24 is the highest stage compression mechanism, and sucks and compresses the refrigerant compressed by the third compression unit 23. The refrigerant compressed by the fourth compressor 24 and discharged to the fourth discharge pipe 24b becomes the highest pressure refrigerant that flows through the refrigerant circuit.

なお、本実施形態において、各圧縮部２１〜２４は、ロータリー式やスクロール式などの容積式の圧縮機構である。また、圧縮機駆動モータは、制御部９４（図６参照）によってインバータ制御される。 In addition, in this embodiment, each compression parts 21-24 are positive displacement type compression mechanisms, such as a rotary type and a scroll type. The compressor drive motor is inverter-controlled by the control unit 94 (see FIG. 6).

また、第２吸入管２２ａには、第１切換機構３１に向かう冷媒の流れを止める逆止弁が、第３吸入管２３ａには、第２切換機構３２に向かう冷媒の流れを止める逆止弁が、第４吸入管２４ａには、第３切換機構３３に向かう冷媒の流れを止める逆止弁が、それぞれ設けられている。 Further, a check valve for stopping the flow of the refrigerant toward the first switching mechanism 31 is provided in the second suction pipe 22a, and a check valve for stopping the flow of the refrigerant toward the second switching mechanism 32 is provided in the third suction pipe 23a. However, the fourth suction pipe 24 a is provided with a check valve that stops the flow of the refrigerant toward the third switching mechanism 33.

（１−２）第１〜第４切換機構
第１切換機構３１、第２切換機構３２、第３切換機構３３および第４切換機構３４は、冷媒回路内における冷媒の流れの方向を切り換えて、冷房運転サイクルと暖房運転サイクルとを切り換えるために設けられている機構で、それぞれ四路切換弁である。 (1-2) 1st-4th switching mechanism The 1st switching mechanism 31, the 2nd switching mechanism 32, the 3rd switching mechanism 33, and the 4th switching mechanism 34 switch the direction of the flow of the refrigerant | coolant in a refrigerant circuit, A mechanism provided for switching between a cooling operation cycle and a heating operation cycle, each of which is a four-way switching valve.

第１切換機構３１の４つのポートは、第１吐出管２１ｂ、第２吸入管２２ａ、第１熱交換器４１の高温側配管４１ｈおよび低圧冷媒配管１９の枝管１９ａと接続されている。低圧冷媒配管１９は、室外ユニット１１内の低圧のガス冷媒が流れる冷媒配管であり、内部熱交換器６２を介して第１吸入管２１ａに冷媒を送る。枝管１９ａは、第１切換機構３１と低圧冷媒配管１９とを結ぶ配管である。 The four ports of the first switching mechanism 31 are connected to the first discharge pipe 21b, the second suction pipe 22a, the high temperature side pipe 41h of the first heat exchanger 41, and the branch pipe 19a of the low pressure refrigerant pipe 19. The low-pressure refrigerant pipe 19 is a refrigerant pipe through which the low-pressure gas refrigerant in the outdoor unit 11 flows, and sends the refrigerant to the first suction pipe 21 a via the internal heat exchanger 62. The branch pipe 19 a is a pipe connecting the first switching mechanism 31 and the low-pressure refrigerant pipe 19.

第２切換機構３２の４つのポートは、第２吐出管２２ｂ、第３吸入管２３ａ、第２熱交換器４２の高温側配管４２ｈおよび直列接続用第１配管４１ｂと接続されている。直列接続用第１配管４１ｂは、第２切換機構３２と、第１熱交換器４１の低温側配管４１ｉとを結ぶ配管である。 The four ports of the second switching mechanism 32 are connected to the second discharge pipe 22b, the third suction pipe 23a, the high-temperature side pipe 42h of the second heat exchanger 42, and the first pipe 41b for series connection. The first pipe 41b for series connection is a pipe connecting the second switching mechanism 32 and the low temperature side pipe 41i of the first heat exchanger 41.

第３切換機構３３の４つのポートは、第３吐出管２３ｂ、第４吸入管２４ａ、第３熱交換器４３の高温側配管４３ｈおよび直列接続用第２配管４２ｂと接続されている。直列接続用第２配管４２ｂは、第３切換機構３３と、第２熱交換器４２の低温側配管４２ｉとを結ぶ配管である。 The four ports of the third switching mechanism 33 are connected to the third discharge pipe 23b, the fourth suction pipe 24a, the high-temperature side pipe 43h of the third heat exchanger 43, and the second pipe 42b for series connection. The second pipe 42b for series connection is a pipe connecting the third switching mechanism 33 and the low temperature side pipe 42i of the second heat exchanger 42.

第４切換機構３４の４つのポートは、第４吐出管２４ｂ、連絡冷媒配管１４、第４熱交換器４４の高温側配管４４ｈおよび低圧冷媒配管１９と接続されている。 The four ports of the fourth switching mechanism 34 are connected to the fourth discharge pipe 24b, the communication refrigerant pipe 14, the high temperature side pipe 44h of the fourth heat exchanger 44, and the low pressure refrigerant pipe 19.

切換機構３１〜３４は、冷房運転において、四段圧縮機２０によって圧縮された冷媒の冷却器として熱交換器４１〜４４を機能させ、かつ、膨張機構７０および室内電動弁１２ｂを通過して膨張した冷媒の蒸発器（加熱器）として室内熱交換器１２ａを機能させるように、図１に示す状態になる。また、切換機構３１〜３４は、暖房運転において、四段圧縮機２０によって圧縮された冷媒の冷却器（放熱器）として室内熱交換器１２ａを機能させ、かつ、膨張機構７０および室外電動弁５１，５２を通過して膨張した冷媒の蒸発器として室外熱交換器４０を機能させるように、図４に示す状態になる。 In the cooling operation, the switching mechanisms 31 to 34 allow the heat exchangers 41 to 44 to function as coolers for the refrigerant compressed by the four-stage compressor 20, and pass through the expansion mechanism 70 and the indoor motor-operated valve 12 b to expand. The state shown in FIG. 1 is set so that the indoor heat exchanger 12a functions as an evaporator (heater) of the refrigerant. Further, the switching mechanisms 31 to 34 function the indoor heat exchanger 12a as a refrigerant cooler (radiator) compressed by the four-stage compressor 20 in the heating operation, and the expansion mechanism 70 and the outdoor motor operated valve 51. , 52 so that the outdoor heat exchanger 40 functions as an evaporator for the refrigerant that has expanded through the state shown in FIG.

すなわち、切換機構３１〜３４は、冷媒回路の構成要素として四段圧縮機２０、室外熱交換器４０、膨張機構７０および室内熱交換器１２ａのみに着目すると、四段圧縮機２０、室外熱交換器４０、膨張機構７０、室内熱交換器１２ａの順に冷媒を循環させる冷房運転サイクルと、四段圧縮機２０、室内熱交換器１２ａ、膨張機構７０、室外熱交換器４０の順に冷媒を循環させる暖房運転サイクルとを切り換える役割を果たす。 That is, the switching mechanisms 31 to 34 focus on only the four-stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, and the indoor heat exchanger 12a as components of the refrigerant circuit. The cooling operation cycle in which the refrigerant is circulated in the order of the compressor 40, the expansion mechanism 70, and the indoor heat exchanger 12a, and the refrigerant is circulated in the order of the four-stage compressor 20, the indoor heat exchanger 12a, the expansion mechanism 70, and the outdoor heat exchanger 40. It plays a role of switching between heating operation cycles.

（１−３）室外熱交換器
熱源側熱交換器である室外熱交換器４０は、上述のように、第１熱交換器４１、第２熱交換器４２、第３熱交換器４３および第４熱交換器４４から成る。冷房運転時には、第１〜第３熱交換器４１〜４３が、それぞれ、圧縮途中の冷媒（中間圧冷媒）を冷やすインタークーラとして機能し、第４熱交換器４４が、最も高圧の冷媒を冷やすガスクーラとして機能する。第４熱交換器４４は、第１〜第３熱交換器４１〜４３よりも容量が大きい。また、暖房運転時には、第１〜第４熱交換器４１〜４４の全てが、低圧の冷媒の蒸発器（加熱器）として機能する。 (1-3) Outdoor Heat Exchanger As described above, the outdoor heat exchanger 40 that is a heat source side heat exchanger includes the first heat exchanger 41, the second heat exchanger 42, the third heat exchanger 43, and the first heat exchanger 43. 4 heat exchangers 44. During the cooling operation, the first to third heat exchangers 41 to 43 each function as an intercooler that cools the refrigerant (intermediate pressure refrigerant) being compressed, and the fourth heat exchanger 44 cools the highest pressure refrigerant. Functions as a gas cooler. The fourth heat exchanger 44 has a larger capacity than the first to third heat exchangers 41 to 43. Further, during the heating operation, all of the first to fourth heat exchangers 41 to 44 function as low-pressure refrigerant evaporators (heaters).

室外熱交換器４０は、第１熱交換器４１、第２熱交換器４２、第３熱交換器４３、第４熱交換器４４の順で下から上に積み上げられ、一体化されている。この室外熱交換器４０には、内部を流れる冷媒と熱交換を行う冷却源あるいは加熱源として、室外空気が供給される。図示しない回転数可変の室外ファンが、室外空気を室外熱交換器４０に供給する。 The outdoor heat exchanger 40 is stacked and integrated in the order of a first heat exchanger 41, a second heat exchanger 42, a third heat exchanger 43, and a fourth heat exchanger 44 in this order. The outdoor heat exchanger 40 is supplied with outdoor air as a cooling source or a heat source for exchanging heat with the refrigerant flowing inside. A non-illustrated outdoor fan having a variable rotation speed supplies outdoor air to the outdoor heat exchanger 40.

また、第１熱交換器４１、第２熱交換器４２および第３熱交換器４３の低温側配管４１ｉ，４２ｉ，４３ｉからは、第２吸入管２２ａ、第３吸入管２３ａおよび第４吸入管２４ａに向かって、分岐管である第１インタークーラ管４１ａ、第２インタークーラ管４２ａおよび第３インタークーラ管４３ａがそれぞれ延びている。第１インタークーラ管４１ａ、第２インタークーラ管４２ａおよび第３インタークーラ管４３ａには、図１に示すように、それぞれ逆止弁が設けられている。 Further, from the low temperature side pipes 41i, 42i, 43i of the first heat exchanger 41, the second heat exchanger 42, and the third heat exchanger 43, the second suction pipe 22a, the third suction pipe 23a, and the fourth suction pipe. A first intercooler pipe 41a, a second intercooler pipe 42a, and a third intercooler pipe 43a, which are branch pipes, extend toward 24a. As shown in FIG. 1, each of the first intercooler pipe 41a, the second intercooler pipe 42a, and the third intercooler pipe 43a is provided with a check valve.

（１−４）第１〜第４油分離器
四段圧縮機２０の第１圧縮部２１、第２圧縮部２２、第３圧縮部２３および第４圧縮部２４から吐出された冷媒に含まれる油を四段圧縮機２０に戻すために、空気調和装置１０の冷媒回路には第１〜第４油分離器２５〜２８が設けられている。第１〜第４油分離器２５〜２８は、冷媒に含まれる油（潤滑油）を分離するための小容器である。 (1-4) 1st-4th oil separator It is contained in the refrigerant | coolant discharged from the 1st compression part 21, the 2nd compression part 22, the 3rd compression part 23, and the 4th compression part 24 of the four-stage compressor 20. In order to return the oil to the four-stage compressor 20, first to fourth oil separators 25 to 28 are provided in the refrigerant circuit of the air conditioner 10. The first to fourth oil separators 25 to 28 are small containers for separating oil (lubricating oil) contained in the refrigerant.

第１油分離器２５は、冷房運転時に第１圧縮部２１から吐出された冷媒を気液分離して、油を含む液（以下、単に油という。）を油戻し流路２５ａおよび第１インタークーラ管４１ａを介して、第２吸入管２２ａに流し、第２圧縮部２２に吸入させる。第１油分離器２５は、第１熱交換器４１の高温側配管４１ｈに設けられている。油戻し流路２５ａは、銅製の毛細管であるキャピラリーチューブを含んでいる。 The first oil separator 25 gas-liquid separates the refrigerant discharged from the first compression unit 21 during the cooling operation, and a liquid containing oil (hereinafter simply referred to as oil) is supplied to the oil return flow path 25a and the first interface. The air flows into the second suction pipe 22a through the cooler pipe 41a and is sucked into the second compression section 22. The first oil separator 25 is provided in the high temperature side pipe 41 h of the first heat exchanger 41. The oil return channel 25a includes a capillary tube which is a copper capillary tube.

第２油分離器２６は、冷房運転時に第２圧縮部２２から吐出された冷媒を気液分離して、油を油戻し流路２６ａおよび第２インタークーラ管４２ａを介して、第３吸入管２３ａに流し、第３圧縮部２３に吸入させる。第２油分離器２６は、第２熱交換器４２の高温側配管４２ｈに設けられている。油戻し流路２６ａは、銅製の毛細管であるキャピラリーチューブを含んでいる。 The second oil separator 26 gas-liquid-separates the refrigerant discharged from the second compression unit 22 during the cooling operation, and supplies the oil to the third suction pipe via the oil return passage 26a and the second intercooler pipe 42a. It is made to flow into 23 a and is sucked into the third compression part 23. The second oil separator 26 is provided in the high temperature side pipe 42 h of the second heat exchanger 42. The oil return channel 26a includes a capillary tube which is a copper capillary tube.

第３油分離器２７は、冷房運転時に第３圧縮部２３から吐出された冷媒を気液分離して、油を油戻し流路２７ａおよび第３インタークーラ管４３ａを介して、第４吸入管２４ａに流し、第４圧縮部２４に吸入させる。第３油分離器２７は、第３熱交換器４３の高温側配管４３ｈに設けられている。油戻し流路２７ａは、銅製の毛細管であるキャピラリーチューブを含んでいる。 The third oil separator 27 gas-liquid separates the refrigerant discharged from the third compressor 23 during the cooling operation, and supplies the oil to the fourth suction pipe via the oil return passage 27a and the third intercooler pipe 43a. It is made to flow into 24a and is made to inhale to the 4th compression part 24. The third oil separator 27 is provided in the high temperature side pipe 43 h of the third heat exchanger 43. The oil return channel 27a includes a capillary tube that is a copper capillary tube.

第４油分離器２８は、冷房運転時にも暖房運転時にも機能する油分離器である。第４油分離器２８は、第４圧縮部２４の吐出ポートに接続された第４吐出管２４ｂに設けられ、第４圧縮部２４と第４切換機構３４との間に配置されている。第４油分離器２８は、第４圧縮部２４から吐出された冷媒を気液分離して、油を、油戻しメイン流路２８ａ或いは油戻しバイパス流路２８ｂを介して第４吸入管２４ａに流し、第４圧縮部２４に吸入させる。油戻しメイン流路２８ａと、油戻しバイパス流路２８ｂとは、並列している。油戻しメイン流路２８ａは、銅製の毛細管であるキャピラリーチューブＣＡ２８を含んでいる。油戻しバイパス流路２８ｂには、流路の開状態と閉状態とを切り換える油戻しバイパス電磁弁ＳＶ２８が設けられている。キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａよりも、油戻しバイパス流路２８ｂのほうが、流路面積が大きい。油戻しバイパス電磁弁ＳＶ２８が閉じているときには、第４油分離器２８から第４吸入管２４ａに流れる油は、油戻しメイン流路２８ａを通る。一方、油戻しバイパス電磁弁ＳＶ２８が開いているときには、油戻しメイン流路２８ａよりも油戻しバイパス流路２８ｂのほうが流路抵抗が小さいため、第４油分離器２８から第４吸入管２４ａに流れる油は、主として油戻しバイパス流路２８ｂを通る。キャピラリーチューブＣＡ２８のない油戻しバイパス流路２８ｂは、流路抵抗が小さいため、油戻しバイパス電磁弁ＳＶ２８が開いて第４油分離器２８から油戻しバイパス流路２８ｂを通って第４吸入管２４ａに油が流れるときには、第４吐出管２４ｂを流れる冷媒の圧力（以下、第４吐出圧力という。）と第４吸入管２４ａを流れる冷媒の圧力（以下、第４吸入圧力という。）との差が小さいときでも、油の戻り量が十分に確保される。すなわち、後に詳述するが、第４吐出圧力と第４吸入圧力との差が大きいときには油戻しメイン流路２８ａで油を戻し、第４吐出圧力と第４吸入圧力との差が小さいときには、油戻しバイパス流路２８ｂで油を戻す制御が行われる。 The fourth oil separator 28 is an oil separator that functions during both the cooling operation and the heating operation. The fourth oil separator 28 is provided in the fourth discharge pipe 24 b connected to the discharge port of the fourth compression unit 24, and is disposed between the fourth compression unit 24 and the fourth switching mechanism 34. The fourth oil separator 28 gas-liquid-separates the refrigerant discharged from the fourth compression unit 24, and supplies the oil to the fourth suction pipe 24a via the oil return main flow path 28a or the oil return bypass flow path 28b. Poured and sucked into the fourth compression section 24. The oil return main flow path 28a and the oil return bypass flow path 28b are arranged in parallel. The oil return main channel 28a includes a capillary tube CA28 which is a copper capillary tube. The oil return bypass passage 28b is provided with an oil return bypass solenoid valve SV28 that switches between an open state and a closed state of the passage. The oil return bypass flow path 28b has a larger flow area than the oil return main flow path 28a including the capillary tube CA28. When the oil return bypass solenoid valve SV28 is closed, the oil flowing from the fourth oil separator 28 to the fourth suction pipe 24a passes through the oil return main flow path 28a. On the other hand, when the oil return bypass solenoid valve SV28 is open, the oil return bypass flow path 28b has a smaller flow resistance than the oil return main flow path 28a, and therefore the fourth oil separator 28 to the fourth suction pipe 24a. The flowing oil mainly passes through the oil return bypass passage 28b. Since the oil return bypass flow path 28b without the capillary tube CA28 has a low flow resistance, the oil return bypass solenoid valve SV28 is opened, and the fourth suction pipe 24a passes from the fourth oil separator 28 through the oil return bypass flow path 28b. When oil flows into the tank, the difference between the pressure of the refrigerant flowing through the fourth discharge pipe 24b (hereinafter referred to as the fourth discharge pressure) and the pressure of the refrigerant flowing through the fourth suction pipe 24a (hereinafter referred to as the fourth suction pressure). Even when is small, the return amount of oil is sufficiently secured. That is, as will be described in detail later, when the difference between the fourth discharge pressure and the fourth suction pressure is large, the oil is returned by the oil return main flow path 28a, and when the difference between the fourth discharge pressure and the fourth suction pressure is small, Control is performed to return oil in the oil return bypass passage 28b.

言い換えれば、第４油分離器２８から第４吸入管２４ａへと油を戻すための油戻しメイン流路２８ａおよび油戻しバイパス流路２８ｂから成る油戻し流路は、油戻しバイパス電磁弁ＳＶ２８の開閉に応じて、その流路面積が変わり、流路抵抗が変わる。油戻しバイパス電磁弁ＳＶ２８が開いているときには、流路面積が大きくなって、流路抵抗が小さくなる。一方、油戻しバイパス電磁弁ＳＶ２８が閉じているときには、キャピラリーチューブＣＡ２８を通るために流路面積が小さくなり、流路抵抗が大きくなる。 In other words, the oil return flow path composed of the oil return main flow path 28a and the oil return bypass flow path 28b for returning the oil from the fourth oil separator 28 to the fourth suction pipe 24a is the oil return bypass solenoid valve SV28. Depending on the opening and closing, the channel area changes and the channel resistance changes. When the oil return bypass solenoid valve SV28 is open, the flow path area increases and the flow path resistance decreases. On the other hand, when the oil return bypass solenoid valve SV28 is closed, the passage area is reduced because the capillary tube CA28 is passed, and the passage resistance is increased.

（１−５）第１および第２室外電動弁
第１および第２室外電動弁５１，５２は、室外熱交換器４０とブリッジ回路５５との間に配備されている。具体的には、第１室外電動弁５１は、第４熱交換器４４とブリッジ回路５５との間に、第２室外電動弁５２は、第３熱交換器４３とブリッジ回路５５との間に、配備されている。暖房運転時にブリッジ回路５５から室外熱交換器４０へと流れてくる冷媒は、２つに分流され、第１室外電動弁５１／第２室外電動弁５２で膨張し、第４熱交換器４４／第３熱交換器４３へと流れ込む。 (1-5) First and Second Outdoor Motorized Valves The first and second outdoor motorized valves 51 and 52 are disposed between the outdoor heat exchanger 40 and the bridge circuit 55. Specifically, the first outdoor motor operated valve 51 is between the fourth heat exchanger 44 and the bridge circuit 55, and the second outdoor motor operated valve 52 is between the third heat exchanger 43 and the bridge circuit 55. Have been deployed. The refrigerant flowing from the bridge circuit 55 to the outdoor heat exchanger 40 during the heating operation is divided into two and expanded by the first outdoor motor-operated valve 51 / second outdoor motor-operated valve 52, and the fourth heat exchanger 44 / It flows into the third heat exchanger 43.

冷房運転時、第２室外電動弁５２は閉じられ、第１室外電動弁５１は全開状態にされる。暖房運転時、第１および第２室外電動弁５１，５２は、第４熱交換器４４／第３熱交換器４３へと流れ込む冷媒の量が適正になるように（偏流しないように）開度調整が為され、それぞれ膨張機構としての役割も果たす。 During the cooling operation, the second outdoor motor-operated valve 52 is closed and the first outdoor motor-operated valve 51 is fully opened. During heating operation, the first and second outdoor motor operated valves 51 and 52 are opened so that the amount of refrigerant flowing into the fourth heat exchanger 44 / third heat exchanger 43 is appropriate (so as not to drift). Adjustments are made and each also serves as an expansion mechanism.

なお、上述の第３インタークーラ管４３ａは、第３熱交換器４３と第２室外電動弁５２との間から分岐している。 The third intercooler pipe 43a is branched from between the third heat exchanger 43 and the second outdoor motor operated valve 52.

（１−６）ブリッジ回路
ブリッジ回路５５は、室外熱交換器４０と室内熱交換器１２ａとの間に設けられており、エコノマイザ熱交換器６１、内部熱交換器６２および膨張機構７０を介してレシーバ８０の入口管８１に接続されるとともに、過冷却熱交換器９０を介してレシーバ８０の出口管８２に接続されている。 (1-6) Bridge Circuit The bridge circuit 55 is provided between the outdoor heat exchanger 40 and the indoor heat exchanger 12a, and passes through the economizer heat exchanger 61, the internal heat exchanger 62, and the expansion mechanism 70. It is connected to an inlet pipe 81 of the receiver 80 and is connected to an outlet pipe 82 of the receiver 80 via a supercooling heat exchanger 90.

ブリッジ回路５５は、４つの逆止弁５５ａ、５５ｂ、５５ｃ、５５ｄを有している。入口逆止弁５５ａは、室外熱交換器４０からレシーバ８０の入口管８１へ向かう冷媒の流れのみを許容する逆止弁である。入口逆止弁５５ｂは、室内熱交換器１２ａからレシーバ８０の入口管８１へ向かう冷媒の流れのみを許容する逆止弁である。出口逆止弁５５ｃは、レシーバ８０の出口管８２から室外熱交換器４０へ向かう冷媒の流れのみを許容する逆止弁である。出口逆止弁５５ｄは、レシーバ８０の出口管８２から室内熱交換器１２ａへ向かう冷媒の流れのみを許容する逆止弁である。すなわち、入口逆止弁５５ａ，５５ｂは、室外熱交換器４０および室内熱交換器１２ａの一方からレシーバ８０の入口管８１に冷媒を流す機能を果たし、出口逆止弁５５ｃ、５５ｄは、レシーバ８０の出口管８２から室外熱交換器４０および室内熱交換器１２ａの他方に冷媒を流す機能を果たす。 The bridge circuit 55 has four check valves 55a, 55b, 55c, and 55d. The inlet check valve 55a is a check valve that allows only the flow of refrigerant from the outdoor heat exchanger 40 toward the inlet pipe 81 of the receiver 80. The inlet check valve 55b is a check valve that allows only a refrigerant flow from the indoor heat exchanger 12a to the inlet pipe 81 of the receiver 80. The outlet check valve 55 c is a check valve that allows only the flow of refrigerant from the outlet pipe 82 of the receiver 80 toward the outdoor heat exchanger 40. The outlet check valve 55d is a check valve that allows only the flow of refrigerant from the outlet pipe 82 of the receiver 80 toward the indoor heat exchanger 12a. In other words, the inlet check valves 55a and 55b function to flow the refrigerant from one of the outdoor heat exchanger 40 and the indoor heat exchanger 12a to the inlet pipe 81 of the receiver 80, and the outlet check valves 55c and 55d The outlet pipe 82 serves to flow the refrigerant to the other of the outdoor heat exchanger 40 and the indoor heat exchanger 12a.

（１−７）エコノマイザ熱交換器
エコノマイザ熱交換器６１は、ブリッジ回路５５から膨張機構７０およびレシーバ８０へと向かう高圧の冷媒と、その高圧の冷媒の一部を分岐させ膨張させた中間圧の冷媒との間で熱交換を行わせる。ブリッジ回路５５から膨張機構７０へ冷媒を流す主冷媒配管から分岐した配管（インジェクション配管６１ａ）には、第３室外電動弁６１ｂが配備されている。この第３室外電動弁６１ｂを通って膨張し、エコノマイザ熱交換器６１で蒸発した冷媒は、第２インタークーラ管４２ａに向かって延びるインジェクション配管６１ａを通って、第２インタークーラ管４２ａの逆止弁よりも第３吸入管２３ａに近い部分に流れ込み、第３吸入管２３ａから第３圧縮部２３へ吸い込まれる冷媒を冷やす。すなわち、エコノマイザ熱交換器６１、インジェクション配管６１ａおよび第３室外電動弁６１ｂは、第２圧縮部２２から吐出され次段の第３圧縮部２３へと流れる冷媒を冷やす中間インジェクション機構として機能する。但し、エコノマイザ熱交換器６１で蒸発した冷媒は、第３圧縮部２３へ吸い込まれる冷媒のみを冷やし、第４圧縮部２４に吸い込まれる冷媒を冷やすことはない。暖房運転時、第４圧縮部２４に吸い込まれる冷媒には、中間インジェクションが行われない。 (1-7) Economizer Heat Exchanger The economizer heat exchanger 61 has a high-pressure refrigerant heading from the bridge circuit 55 to the expansion mechanism 70 and the receiver 80, and an intermediate pressure obtained by branching and expanding a part of the high-pressure refrigerant. Exchange heat with the refrigerant. A third outdoor motor-operated valve 61b is disposed in a pipe (injection pipe 61a) branched from the main refrigerant pipe that flows the refrigerant from the bridge circuit 55 to the expansion mechanism 70. The refrigerant which has expanded through the third outdoor motor-operated valve 61b and evaporated in the economizer heat exchanger 61 passes through the injection pipe 61a extending toward the second intercooler pipe 42a, and the check of the second intercooler pipe 42a. The refrigerant that flows into the portion closer to the third suction pipe 23a than the valve and cools the refrigerant sucked into the third compression section 23 from the third suction pipe 23a is cooled. That is, the economizer heat exchanger 61, the injection pipe 61a, and the third outdoor motor operated valve 61b function as an intermediate injection mechanism that cools the refrigerant that is discharged from the second compression section 22 and flows to the third compression section 23 at the next stage. However, the refrigerant evaporated in the economizer heat exchanger 61 cools only the refrigerant sucked into the third compression unit 23 and does not cool the refrigerant sucked into the fourth compression unit 24. During the heating operation, intermediate injection is not performed on the refrigerant sucked into the fourth compression unit 24.

（１−８）内部熱交換器
内部熱交換器６２は、ブリッジ回路５５から膨張機構７０およびレシーバ８０へと向かう高圧の冷媒と、膨張機構７０等を通過し室内熱交換器１２ａあるいは室外熱交換器４０で蒸発して低圧冷媒配管１９を流れる低圧のガス冷媒と、の間で熱交換を行わせる。内部熱交換器６２は、液ガス熱交換器と呼ばれることもある。ブリッジ回路５５を出た高圧の冷媒は、まずエコノマイザ熱交換器６１を通過し、次に内部熱交換器６２を通過して、膨張機構７０およびレシーバ８０へと向かう。 (1-8) Internal Heat Exchanger The internal heat exchanger 62 passes through the expansion mechanism 70 and the high-pressure refrigerant from the bridge circuit 55 to the expansion mechanism 70 and the receiver 80, and passes through the indoor heat exchanger 12a or the outdoor heat exchange. Heat exchange is performed with the low-pressure gas refrigerant that evaporates in the vessel 40 and flows through the low-pressure refrigerant pipe 19. The internal heat exchanger 62 is sometimes called a liquid gas heat exchanger. The high-pressure refrigerant that has exited the bridge circuit 55 first passes through the economizer heat exchanger 61, then passes through the internal heat exchanger 62, and travels toward the expansion mechanism 70 and the receiver 80.

（１−９）膨張機構
膨張機構７０は、ブリッジ回路５５から流れてきた高圧の冷媒を減圧・膨張させ、気液二相状態の中間圧の冷媒をレシーバ８０へと流す。すなわち、膨張機構７０は、冷房運転時には、高圧冷媒のガスクーラ（放熱器）として機能する室外の第４熱交換器４４から、低圧冷媒の蒸発器として機能する室内熱交換器１２ａに送られる冷媒を減圧し、暖房運転時には、高圧冷媒のガスクーラ（放熱器）として機能する室内熱交換器１２ａから、低圧冷媒の蒸発器として機能する室外熱交換器４０に送られる冷媒を減圧する。膨張機構７０は、膨張機７１および第４室外電動弁７２から構成される。膨張機７１は、冷媒の減圧過程の絞り損失を有効な仕事（エネルギー）として回収する役割を果たす。 (1-9) Expansion Mechanism The expansion mechanism 70 depressurizes and expands the high-pressure refrigerant that has flowed from the bridge circuit 55, and causes the intermediate-pressure refrigerant in a gas-liquid two-phase state to flow to the receiver 80. That is, during the cooling operation, the expansion mechanism 70 receives the refrigerant sent from the outdoor fourth heat exchanger 44 functioning as a high-pressure refrigerant gas cooler (heat radiator) to the indoor heat exchanger 12a functioning as an evaporator of low-pressure refrigerant. During the heating operation, the refrigerant sent from the indoor heat exchanger 12a functioning as a high-pressure refrigerant gas cooler (radiator) to the outdoor heat exchanger 40 functioning as a low-pressure refrigerant evaporator is decompressed. The expansion mechanism 70 includes an expander 71 and a fourth outdoor electric valve 72. The expander 71 plays a role of recovering the throttle loss in the decompression process of the refrigerant as effective work (energy).

（１−１０）レシーバ
レシーバ８０は、膨張機構７０を出て入口管８１から内部空間に入ってきた気液二相状態の中間圧の冷媒を、液冷媒とガス冷媒とに分離する。分離されたガス冷媒は、低圧戻し配管９１ａに設けられた第５室外電動弁９１を通過して低圧のガスリッチな冷媒となり、過冷却熱交換器９０に送られる。分離された液冷媒は、出口管８２によって過冷却熱交換器９０に送られる。 (1-10) Receiver The receiver 80 separates the intermediate-pressure refrigerant in the gas-liquid two-phase state that has exited the expansion mechanism 70 and entered the internal space from the inlet pipe 81 into liquid refrigerant and gas refrigerant. The separated gas refrigerant passes through the fifth outdoor motor-operated valve 91 provided in the low-pressure return pipe 91 a to become a low-pressure gas-rich refrigerant and is sent to the supercooling heat exchanger 90. The separated liquid refrigerant is sent to the supercooling heat exchanger 90 through the outlet pipe 82.

（１−１１）過冷却熱交換器
過冷却熱交換器９０は、低圧のガス冷媒と、レシーバ８０の出口管８２から出た中間圧の液冷媒との間で熱交換を行わせる。レシーバ８０の出口管８２から出た中間圧の液冷媒の一部は、冷房運転時には、レシーバ８０と過冷却熱交換器９０との間から分岐する分岐管９２ａを流れ、第６室外電動弁９２を通過して、気液二相状態の低圧の冷媒となる。冷房運転時に第６室外電動弁９２で減圧された低圧冷媒は、第５室外電動弁９１で減圧された低圧冷媒と合流し、過冷却熱交換器９０において、レシーバ８０の出口管８２からブリッジ回路５５に向かう中間圧の液冷媒と熱交換され、過熱がついた状態で過冷却熱交換器９０から低圧戻し配管９１ａを通って低圧冷媒配管１９へと流れていく。一方、レシーバ８０の出口管８２からブリッジ回路５５に向かう中間圧の液冷媒は、過冷却熱交換器９０において熱を奪われ、過冷却がついた状態でブリッジ回路５５へ流れていく。 (1-11) Supercooling Heat Exchanger The supercooling heat exchanger 90 performs heat exchange between the low-pressure gas refrigerant and the intermediate-pressure liquid refrigerant output from the outlet pipe 82 of the receiver 80. Part of the intermediate-pressure liquid refrigerant that has exited from the outlet pipe 82 of the receiver 80 flows through the branch pipe 92a that branches from between the receiver 80 and the supercooling heat exchanger 90 during the cooling operation, and the sixth outdoor motor-operated valve 92 And becomes a low-pressure refrigerant in a gas-liquid two-phase state. The low-pressure refrigerant depressurized by the sixth outdoor motor-operated valve 92 during the cooling operation merges with the low-pressure refrigerant depressurized by the fifth outdoor motor-operated valve 91, and in the supercooling heat exchanger 90, the bridge circuit is connected from the outlet pipe 82 of the receiver 80. The heat is exchanged with the intermediate-pressure liquid refrigerant heading 55, and flows from the supercooling heat exchanger 90 to the low-pressure refrigerant pipe 19 through the low-pressure return pipe 91 a while being superheated. On the other hand, the intermediate-pressure liquid refrigerant from the outlet pipe 82 of the receiver 80 toward the bridge circuit 55 is deprived of heat in the supercooling heat exchanger 90 and flows to the bridge circuit 55 with supercooling.

なお、暖房運転時には、第６室外電動弁９２が閉まり、分岐管９２ａには冷媒が流れないが、レシーバ８０の出口管８２から出た中間圧の液冷媒と、第５室外電動弁９１で減圧された低圧冷媒とが、過冷却熱交換器９０において熱交換を行うことになる。 During the heating operation, the sixth outdoor motor-operated valve 92 is closed, and the refrigerant does not flow into the branch pipe 92a. However, the intermediate-pressure liquid refrigerant from the outlet pipe 82 of the receiver 80 is reduced by the fifth outdoor motor-operated valve 91. The low-pressure refrigerant that has been subjected to heat exchange in the supercooling heat exchanger 90.

（１−１２）室内熱交換器
利用側熱交換器である室内熱交換器１２ａは、複数の室内ユニット１２それぞれに設けられており、冷房運転時には冷媒の蒸発器として機能し、暖房運転時には冷媒の冷却器として機能する。これらの室内熱交換器１２ａには、内部を流れる冷媒と熱交換を行う冷房対象あるいは暖房対象として、水や空気が流される。ここでは、室内熱交換器１２ａの周囲に、室内ファンからの室内空気が流れ、冷却あるいは加熱された空調空気が室内へと供給される。 (1-12) Indoor Heat Exchanger The indoor heat exchanger 12a, which is a use side heat exchanger, is provided in each of the plurality of indoor units 12, functions as a refrigerant evaporator during cooling operation, and refrigerant during heating operation. Acts as a cooler. Water and air are flown through these indoor heat exchangers 12a as cooling targets or heating targets that exchange heat with the refrigerant flowing in the interior. Here, indoor air from the indoor fan flows around the indoor heat exchanger 12a, and cooled or heated conditioned air is supplied into the room.

室内熱交換器１２ａの一端は室内電動弁１２ｂに、室内熱交換器１２ａの他端は連絡冷媒配管１４に接続されている。 One end of the indoor heat exchanger 12a is connected to the indoor motor-operated valve 12b, and the other end of the indoor heat exchanger 12a is connected to the communication refrigerant pipe 14.

（１−１３）室内電動弁
室内電動弁１２ｂは、複数の室内ユニット１２それぞれに設けられており、室内熱交換器１２ａに流す冷媒の量を調整したり冷媒の減圧・膨張を行ったりする。室内電動弁１２ｂは、連絡冷媒配管１３と室内熱交換器１２ａとの間に配置されている。 (1-13) Indoor motor-operated valve The indoor motor-operated valve 12b is provided in each of the plurality of indoor units 12, and adjusts the amount of refrigerant flowing to the indoor heat exchanger 12a or performs decompression / expansion of the refrigerant. The indoor motor operated valve 12b is disposed between the communication refrigerant pipe 13 and the indoor heat exchanger 12a.

（１−１４）制御部
図６に示すように、制御部９４は、室外ユニット１１に設けられた室外制御部９５と、室内ユニット１２に設けられた室内制御部９６とが伝送線９４ａによって結ばれて構成されるものであり、各種の制御を行う。室外制御部９５および室内制御部９６は、各種センサや四段圧縮機２０の圧縮機駆動モータ、種々の弁と接続されるマイクロコンピュータである。制御部９４は、リモコン９９等から入力された室内設定温度などの情報に基づいて、圧縮機駆動モータの回転数制御や冷房運転サイクルと暖房運転サイクルとの切り換え、弁開度の調節などを行う。 (1-14) Control Unit As shown in FIG. 6, the control unit 94 connects the outdoor control unit 95 provided in the outdoor unit 11 and the indoor control unit 96 provided in the indoor unit 12 through a transmission line 94a. It is configured and performs various controls. The outdoor control unit 95 and the indoor control unit 96 are microcomputers connected to various sensors, the compressor drive motor of the four-stage compressor 20, and various valves. The control unit 94 controls the rotational speed of the compressor drive motor, switches between the cooling operation cycle and the heating operation cycle, and adjusts the valve opening based on information such as the indoor set temperature input from the remote controller 99 or the like. .

室外制御部９５には、高段吸入温度センサ９７および高段吐出温度センサ９８を含むセンサ群が接続され、冷媒回路の温度や圧力、室外温度などのデータが入力されてくる。室内制御部９６にも、室内温度センサなどのセンサ群が接続される。高段吸入温度センサ９７は、第４吸入管２４ａに装着され、第４吸入管２４ａを流れる冷媒の温度である第４吸入冷媒温度を計測する。具体的には、図１の点Ｈの冷媒の温度を計る。高段吐出温度センサ９８は、第４吐出管２４ｂに装着され、第４吐出管２４ｂを流れる冷媒の温度である第４吐出冷媒温度を計測する。具体的には、図１の点Ｉの冷媒の温度を計る。これらのセンサ群からの温度や圧力の情報に基づき、制御部９４は、室外制御部９５に接続された第１〜第６室外電動弁５１，５２，６１ｂ、７２，９１，９２、四段圧縮機２０、室外ファン、第１〜第４切換機構３１〜３４、油戻しバイパス電磁弁ＳＶ２８を制御する。また、室内制御部９６は、室内ファンや室内電動弁１２ｂを制御する。 A sensor group including a high-stage suction temperature sensor 97 and a high-stage discharge temperature sensor 98 is connected to the outdoor control unit 95, and data such as the temperature and pressure of the refrigerant circuit and the outdoor temperature are input. A sensor group such as an indoor temperature sensor is also connected to the indoor control unit 96. The high stage suction temperature sensor 97 is attached to the fourth suction pipe 24a, and measures the fourth suction refrigerant temperature, which is the temperature of the refrigerant flowing through the fourth suction pipe 24a. Specifically, the temperature of the refrigerant at point H in FIG. 1 is measured. The high-stage discharge temperature sensor 98 is attached to the fourth discharge pipe 24b, and measures the fourth discharge refrigerant temperature that is the temperature of the refrigerant flowing through the fourth discharge pipe 24b. Specifically, the temperature of the refrigerant at point I in FIG. 1 is measured. Based on the temperature and pressure information from these sensor groups, the control unit 94 includes first to sixth outdoor motor-operated valves 51, 52, 61b, 72, 91, 92 connected to the outdoor control unit 95, and four-stage compression. The machine 20, the outdoor fan, the first to fourth switching mechanisms 31 to 34, and the oil return bypass solenoid valve SV28 are controlled. Moreover, the indoor control part 96 controls an indoor fan and the indoor motor operated valve 12b.

（２）空気調和装置の動作
空気調和装置１０の動作について、図１〜図５を参照しながら説明する。図２は、負荷が高いときの冷房運転時における冷凍サイクルの圧力−エンタルピ線図（ｐ−ｈ線図）である。図３は、外気温が低いときや負荷が低いときの冷房運転時における冷凍サイクルの圧力−エンタルピ線図である。図５は、暖房運転時における冷凍サイクルの圧力−エンタルピ線図である。図２、図３および図５において、上に凸の一点鎖線で示す曲線は、冷媒の飽和液線および乾き飽和蒸気線である。また、冷凍サイクル上の英文字が付された点は、それぞれ、図１および図４において同じ英文字で表される点における冷媒の圧力およびエンタルピを表している。例えば、図１の点Ｂにおける冷媒は、図２の点Ｂにおける圧力およびエンタルピの状態になっている。なお、空気調和装置１０の冷房運転時および暖房運転時における各運転制御は、制御部９４によって行われる。 (2) Operation of Air Conditioner The operation of the air conditioner 10 will be described with reference to FIGS. FIG. 2 is a pressure-enthalpy diagram (ph diagram) of the refrigeration cycle during cooling operation when the load is high. FIG. 3 is a pressure-enthalpy diagram of the refrigeration cycle during cooling operation when the outside air temperature is low or the load is low. FIG. 5 is a pressure-enthalpy diagram of the refrigeration cycle during heating operation. 2, 3, and 5, the curves indicated by the one-dot chain line that protrudes upward are the saturated liquid line and the dry saturated vapor line of the refrigerant. Moreover, the point which the English letter on the refrigerating cycle was attached | subjected represents the pressure and enthalpy of the refrigerant | coolant in the point represented by the same English letter in FIG. 1 and FIG. 4, respectively. For example, the refrigerant at point B in FIG. 1 is in the state of pressure and enthalpy at point B in FIG. In addition, each operation control in the cooling operation and the heating operation of the air conditioner 10 is performed by the control unit 94.

（２−１）冷房運転時の動作
（２−１−１）負荷が高いときの冷房運転時の動作
冷房運転時は、図１に示す冷媒配管に沿った矢印の方向に、冷媒が、四段圧縮機２０、室外熱交換器４０、膨張機構７０、室内熱交換器１２ａの順に冷媒回路内を循環する。以下、負荷が高いときの冷房運転時における空気調和装置１０の動作について、図１および図２を参照しながら説明する。 (2-1) Operation at the time of cooling operation (2-1-1) Operation at the time of cooling operation when the load is high At the time of cooling operation, the refrigerant flows in the direction of the arrow along the refrigerant pipe shown in FIG. The inside of the refrigerant circuit is circulated in the order of the stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, and the indoor heat exchanger 12a. Hereinafter, the operation of the air conditioning apparatus 10 during the cooling operation when the load is high will be described with reference to FIGS. 1 and 2.

第１吸入管２１ａから四段圧縮機２０に吸い込まれる低圧のガス冷媒（点Ａ）は、第１圧縮部２１で圧縮されて、第１吐出管２１ｂへと吐出される（点Ｂ）。吐出された冷媒は、第１切換機構３１を通過し、インタークーラとして機能する第１熱交換器４１で冷却された後、第１インタークーラ管４１ａを介して第２吸入管２２ａに流れ込む（点Ｃ）。 The low-pressure gas refrigerant (point A) sucked into the four-stage compressor 20 from the first suction pipe 21a is compressed by the first compression section 21 and discharged to the first discharge pipe 21b (point B). The discharged refrigerant passes through the first switching mechanism 31, is cooled by the first heat exchanger 41 functioning as an intercooler, and then flows into the second suction pipe 22a via the first intercooler pipe 41a (point) C).

第２吸入管２２ａから第２圧縮部２２に吸い込まれた冷媒は、圧縮されて第２吐出管２２ｂに吐出される（点Ｄ）。吐出された冷媒は、第２切換機構３２を通過し、インタークーラとして機能する第２熱交換器４２で冷却された後、第２インタークーラ管４２ａに流れる（点Ｅ）。第２インタークーラ管４２ａを流れる冷媒は、エコノマイザ熱交換器６１において熱交換されてインジェクション配管６１ａを流れてくる中間圧の冷媒（点Ｌ）と合流した後、第３吸入管２３ａに流れ込む（点Ｆ）。 The refrigerant sucked into the second compression part 22 from the second suction pipe 22a is compressed and discharged to the second discharge pipe 22b (point D). The discharged refrigerant passes through the second switching mechanism 32, is cooled by the second heat exchanger 42 functioning as an intercooler, and then flows to the second intercooler pipe 42a (point E). The refrigerant flowing through the second intercooler pipe 42a is heat-exchanged in the economizer heat exchanger 61 and merged with the intermediate pressure refrigerant (point L) flowing through the injection pipe 61a, and then flows into the third suction pipe 23a (point). F).

第３吸入管２３ａから第３圧縮部２３に吸い込まれた冷媒は、圧縮されて第３吐出管２３ｂに吐出される（点Ｇ）。吐出された冷媒は、第３切換機構３３を通過し、インタークーラとして機能する第３熱交換器４３で冷却された後、第３インタークーラ管４３ａを介して第４吸入管２４ａに流れ込む（点Ｈ）。 The refrigerant sucked into the third compression section 23 from the third suction pipe 23a is compressed and discharged to the third discharge pipe 23b (point G). The discharged refrigerant passes through the third switching mechanism 33, is cooled by the third heat exchanger 43 functioning as an intercooler, and then flows into the fourth suction pipe 24a via the third intercooler pipe 43a (point) H).

第４吸入管２４ａから第４圧縮部２４に吸い込まれた冷媒は、圧縮されて第４吐出管２４ｂに吐出される（点Ｉ）。吐出された高圧の冷媒は、第４切換機構３４を通過し、ガスクーラとして機能する第４熱交換器４４で冷却され、全開状態の第１室外電動弁５１およびブリッジ回路５５の入口逆止弁５５ａを通ってエコノマイザ熱交換器６１へと流れていく（点Ｊ）。 The refrigerant sucked into the fourth compression section 24 from the fourth suction pipe 24a is compressed and discharged to the fourth discharge pipe 24b (point I). The discharged high-pressure refrigerant passes through the fourth switching mechanism 34, is cooled by the fourth heat exchanger 44 functioning as a gas cooler, and is fully opened in the first outdoor motor-operated valve 51 and the inlet check valve 55a of the bridge circuit 55. And flows to the economizer heat exchanger 61 (point J).

ブリッジ回路５５の入口逆止弁５５ａを通過した高圧冷媒は、エコノマイザ熱交換器６１に流れ込むとともに、その一部が分岐して第３室外電動弁６１ｂへと流れる。第３室外電動弁６１ｂで減圧・膨張して気液二相状態となった中間圧冷媒（点Ｋ）は、エコノマイザ熱交換器６１において、ブリッジ回路５５から内部熱交換器６２に向かう高圧冷媒（点Ｊ）と熱交換し、中間圧のガス冷媒（点Ｌ）となって上述のようにインジェクション配管６１ａから第２インタークーラ管４２ａへと流れ込む。 The high-pressure refrigerant that has passed through the inlet check valve 55a of the bridge circuit 55 flows into the economizer heat exchanger 61, and a part thereof branches to flow to the third outdoor motor-operated valve 61b. The intermediate-pressure refrigerant (point K) that has been reduced in pressure and expanded by the third outdoor motorized valve 61b into a gas-liquid two-phase state is converted into a high-pressure refrigerant (point K) from the bridge circuit 55 to the internal heat exchanger 62 in the economizer heat exchanger 61. It exchanges heat with the point J) and becomes an intermediate-pressure gas refrigerant (point L) and flows from the injection pipe 61a into the second intercooler pipe 42a as described above.

第３室外電動弁６１ｂを出た中間圧冷媒と熱交換をし、更に温度が下がった状態でエコノマイザ熱交換器６１を出た高圧冷媒（点Ｍ）は、次に内部熱交換器６２を流れ、膨張機構７０へと流れていく（点Ｎ）。内部熱交換器６２では、後述する低圧冷媒配管１９から四段圧縮機２０の第１吸入管２１ａへと流れる低圧冷媒と熱交換を行い、点Ｍの状態の高圧冷媒が、温度が下がって点Ｎの状態の高圧冷媒となる。 The high-pressure refrigerant (point M) that has exchanged heat with the intermediate-pressure refrigerant that has exited the third outdoor motor-operated valve 61b and has exited the economizer heat exchanger 61 in a state where the temperature has further decreased, then flows through the internal heat exchanger 62. And flows to the expansion mechanism 70 (point N). In the internal heat exchanger 62, heat exchange is performed with the low-pressure refrigerant flowing from the low-pressure refrigerant pipe 19 described later to the first suction pipe 21 a of the four-stage compressor 20, and the high-pressure refrigerant in the state of point M drops in temperature. It becomes a high-pressure refrigerant in the N state.

内部熱交換器６２を出た高圧冷媒（点Ｎ）は、２つに分岐され、それぞれ膨張機構７０の膨張機７１、膨張機構７０の第４室外電動弁７２に流れる。膨張機７１で減圧・膨張した中間圧冷媒（点Ｐ）と、第４室外電動弁７２で減圧・膨張した中間圧冷媒（点Ｏ）とは、合流した後に入口管８１からレシーバ８０の内部空間へと流れ込む（点Ｑ）。このレシーバ８０に流れ込んだ気液二相状態の中間圧冷媒は、レシーバ８０の内部空間において液冷媒とガス冷媒とに分離される。 The high-pressure refrigerant (point N) exiting the internal heat exchanger 62 is branched into two and flows to the expander 71 of the expansion mechanism 70 and the fourth outdoor motor-operated valve 72 of the expansion mechanism 70, respectively. The intermediate pressure refrigerant (point P) decompressed / expanded by the expander 71 and the intermediate pressure refrigerant (point O) decompressed / expanded by the fourth outdoor motor-operated valve 72 are joined from the inlet pipe 81 to the internal space of the receiver 80. (Point Q). The gas-liquid two-phase intermediate pressure refrigerant flowing into the receiver 80 is separated into liquid refrigerant and gas refrigerant in the internal space of the receiver 80.

レシーバ８０で分離された液冷媒（点Ｒ）は、出口管８２を通ってそのまま過冷却熱交換器９０へと流れ、レシーバ８０で分離されたガス冷媒（点Ｕ）は、第５室外電動弁９１で減圧され低圧冷媒（点Ｗ）となって過冷却熱交換器９０へと流れていく。レシーバ８０の出口管８２から過冷却熱交換器９０に向かう中間圧冷媒は、過冷却熱交換器９０の手前で分岐し、一方が過冷却熱交換器９０を通ってブリッジ回路５５に向かい、他方が分岐管９２ａの第６室外電動弁９２へと流れる。第６室外電動弁９２を通過して減圧された気液二相状態の低圧冷媒（点Ｓ）は、第５室外電動弁９１を通過した低圧冷媒（点Ｗ）と合流し（点Ｘ）、過冷却熱交換器９０を経て低圧冷媒配管１９へと流れる。過冷却熱交換器９０での熱交換によって、低圧冷媒配管１９に向かって流れる低圧冷媒（点Ｘ）は、蒸発して過熱のついた低圧冷媒（点Ｙ）となり、ブリッジ回路５５に向かって流れる中間圧冷媒（点Ｒ）は、熱を奪われて過冷却のついた中間圧冷媒（点Ｔ）となる。 The liquid refrigerant (point R) separated by the receiver 80 flows directly to the supercooling heat exchanger 90 through the outlet pipe 82, and the gas refrigerant (point U) separated by the receiver 80 is the fifth outdoor motor valve. The pressure is reduced at 91 to form a low-pressure refrigerant (point W) and flow to the supercooling heat exchanger 90. The intermediate pressure refrigerant from the outlet pipe 82 of the receiver 80 toward the supercooling heat exchanger 90 is branched before the supercooling heat exchanger 90, and one of the refrigerants passes through the supercooling heat exchanger 90 toward the bridge circuit 55 and the other. Flows to the sixth outdoor motor-operated valve 92 of the branch pipe 92a. The low-pressure refrigerant (point S) in the gas-liquid two-phase state that has been decompressed after passing through the sixth outdoor motor-operated valve 92 merges with the low-pressure refrigerant (point W) that has passed through the fifth outdoor motor-operated valve 91 (point X), It flows to the low-pressure refrigerant pipe 19 through the supercooling heat exchanger 90. The low-pressure refrigerant (point X) flowing toward the low-pressure refrigerant pipe 19 due to heat exchange in the supercooling heat exchanger 90 evaporates to become a superheated low-pressure refrigerant (point Y) and flows toward the bridge circuit 55. The intermediate-pressure refrigerant (point R) becomes an intermediate-pressure refrigerant (point T) that is deprived of heat and supercooled.

過冷却熱交換器９０で過冷却のついた中間圧冷媒（点Ｔ）は、ブリッジ回路５５の出口逆止弁５５ｄを通って、連絡冷媒配管１３へと流れていく。連絡冷媒配管１３から室内ユニット１２に入った冷媒は、室内電動弁１２ｂを通過するときに膨張し、気液二相の低圧冷媒（点Ｖ）となって室内熱交換器１２ａに流れ込む。この低圧冷媒は、室内熱交換器１２ａで室内空気から熱を奪い、過熱のついた低圧のガス冷媒（点Ｚ）になる。室内ユニット１２を出た低圧冷媒は、連絡冷媒配管１４および第４切換機構３４を経て低圧冷媒配管１９へと流れていく。 The intermediate pressure refrigerant (point T) that has been supercooled by the supercooling heat exchanger 90 flows through the outlet check valve 55d of the bridge circuit 55 to the communication refrigerant pipe 13. The refrigerant that has entered the indoor unit 12 from the communication refrigerant pipe 13 expands when passing through the indoor motor-operated valve 12b, and flows into the indoor heat exchanger 12a as a gas-liquid two-phase low-pressure refrigerant (point V). This low-pressure refrigerant takes heat from the indoor air in the indoor heat exchanger 12a and becomes a superheated low-pressure gas refrigerant (point Z). The low-pressure refrigerant that has exited the indoor unit 12 flows to the low-pressure refrigerant pipe 19 via the communication refrigerant pipe 14 and the fourth switching mechanism 34.

室内ユニット１２から戻ってきた低圧冷媒（点Ｚ）と、過冷却熱交換器９０から流れてくる低圧冷媒（点Ｙ）とは、低圧冷媒配管１９で合流し（点ＡＢ）、内部熱交換器６２を通って第１吸入管２１ａから四段圧縮機２０へと戻っていく。上述のように、内部熱交換器６２では、四段圧縮機２０に向かう低圧冷媒（点ＡＢ）と、ブリッジ回路５５からレシーバ８０へと向かう高圧冷媒（点Ｍ）とが熱交換を行う。 The low-pressure refrigerant (point Z) returned from the indoor unit 12 and the low-pressure refrigerant (point Y) flowing from the supercooling heat exchanger 90 merge at the low-pressure refrigerant pipe 19 (point AB), and the internal heat exchanger. The first suction pipe 21 a returns to the four-stage compressor 20 through 62. As described above, in the internal heat exchanger 62, the low-pressure refrigerant (point AB) that goes to the four-stage compressor 20 and the high-pressure refrigerant (point M) that goes from the bridge circuit 55 to the receiver 80 perform heat exchange.

以上のように冷媒が冷媒回路内を循環することにより、空気調和装置１０は冷房運転サイクルを行う。 As described above, the refrigerant circulates in the refrigerant circuit, so that the air conditioner 10 performs the cooling operation cycle.

（２−１−２）負荷が低いときの冷房運転時の動作
負荷が低いときの冷房運転時における空気調和装置１０の動作も、上述の負荷が高いときの冷房運転時における空気調和装置１０の動作と基本的には同じである。負荷が低いときにも、図１に示す冷媒配管に沿った矢印の方向に、冷媒が、四段圧縮機２０、室外熱交換器４０、膨張機構７０、室内熱交換器１２ａの順に冷媒回路内を循環する。但し、負荷が低いときには、制御部９４は、高圧を小さく保つ省エネ制御を行う。以下、その制御について説明する。 (2-1-2) Operation at the time of cooling operation when the load is low The operation of the air conditioner 10 at the time of cooling operation when the load is low is also the operation of the air conditioner 10 at the time of cooling operation when the load is high. The operation is basically the same. Even when the load is low, the refrigerant flows in the direction of the arrow along the refrigerant pipe shown in FIG. 1 in the order of the four-stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, and the indoor heat exchanger 12a. Circulate. However, when the load is low, the control unit 94 performs energy saving control that keeps the high pressure small. Hereinafter, the control will be described.

冷房運転の負荷が低いときには、四段圧縮機２０の回転数を抑えて運転効率を上げるために、高圧を小さくする制御が行われる。高圧を小さくした省エネ運転では、低圧も大きくなって、高低差圧（高圧−低圧）が小さくなる。図２と図３とを比較すると判るように、低負荷のときの冷房運転の冷凍サイクル（図３）では、高負荷のときに比べて、高圧がＨＰ１からＨＰ２に下がり、低圧がＬＰ１からＬＰ２に上がる。このとき、高負荷の冷房運転においては低段の第１〜第３圧縮部２１〜２３と同様の圧縮仕事を行っていた高段の第４圧縮部２４が、殆ど圧縮仕事をしなくなる。これは、共通回転軸を採用した一軸四段の四段圧縮機２０を、高負荷時の冷房運転を基準として各圧縮部２１〜２４の容積比を決める設計手法を用いていることに起因している。しかし、３段以上の圧縮機構を用いる場合、通常は高負荷の冷房運転を基準にして設計を行うため、高段の圧縮部が低負荷時に圧縮を殆ど行わなくなることは仕方がないことである。 When the cooling operation load is low, control is performed to reduce the high pressure in order to suppress the rotation speed of the four-stage compressor 20 and increase the operation efficiency. In energy-saving operation with a small high pressure, the low pressure also increases and the high-low differential pressure (high pressure-low pressure) decreases. As can be seen from a comparison between FIG. 2 and FIG. 3, in the refrigeration cycle of the cooling operation at low load (FIG. 3), the high pressure decreases from HP1 to HP2 and the low pressure decreases from LP1 to LP2 compared to the high load. Go up to. At this time, in the high-load cooling operation, the high-stage fourth compression section 24 that has been performing the same compression work as the low-stage first to third compression sections 21 to 23 hardly performs the compression work. This is because the single-shaft four-stage four-stage compressor 20 adopting a common rotating shaft uses a design method for determining the volume ratio of the compression sections 21 to 24 based on the cooling operation at the time of high load. ing. However, when using a compression mechanism of three or more stages, since the design is usually based on a high-load cooling operation, it is inevitable that the high-stage compression section will hardly perform compression when the load is low. .

低負荷の冷房運転では上述のように高圧をＨＰ２に下げた運転を行うため、第４吸入管２４ａ（点Ｈ参照）を流れ第４圧縮部２４に吸入される冷媒の圧力である高段吸入圧力と、第４圧縮部２４から吐出され第４吐出管２４ｂ（点Ｉ参照）を流れる冷媒の圧力である高段吐出圧力との差圧ＤＰ２（図３参照）が、小さくなる。図２に示すように、高負荷の冷房運転では、高段吸入圧力と高段吐出圧力との差圧ＤＰ１が、差圧ＤＰ２よりも大きい。 In the low-load cooling operation, the high pressure is reduced to HP2 as described above. Therefore, the high-stage suction that is the pressure of the refrigerant that flows through the fourth suction pipe 24a (see point H) and is sucked into the fourth compression unit 24. The differential pressure DP2 (see FIG. 3) between the pressure and the high-stage discharge pressure that is the pressure of the refrigerant discharged from the fourth compression section 24 and flowing through the fourth discharge pipe 24b (see point I) becomes small. As shown in FIG. 2, in the high-load cooling operation, the differential pressure DP1 between the high stage suction pressure and the high stage discharge pressure is larger than the differential pressure DP2.

（２−２）暖房運転時の動作
暖房運転時は、図４に示す冷媒配管に沿った矢印の方向に、冷媒が、四段圧縮機２０、室内熱交換器１２ａ、膨張機構７０、室外熱交換器４０の順に冷媒回路内を循環する。以下、暖房運転時における空気調和装置１０の動作について、図４および図５を参照しながら説明する。 (2-2) Operation at the time of heating operation During the heating operation, the refrigerant moves in the direction of the arrow along the refrigerant pipe shown in FIG. 4, the four-stage compressor 20, the indoor heat exchanger 12 a, the expansion mechanism 70, and the outdoor heat. It circulates in the refrigerant circuit in the order of the exchanger 40. Hereinafter, operation | movement of the air conditioning apparatus 10 at the time of heating operation is demonstrated, referring FIG. 4 and FIG.

第１吸入管２１ａから四段圧縮機２０に吸い込まれる低圧のガス冷媒（点Ａ）は、第１圧縮部２１で圧縮されて、第１吐出管２１ｂに吐出される（点Ｂ）。吐出された冷媒は、第１切換機構３１を通過し、第２吸入管２２ａを流れる（点Ｃ）。 The low-pressure gas refrigerant (point A) sucked into the four-stage compressor 20 from the first suction pipe 21a is compressed by the first compression section 21 and discharged to the first discharge pipe 21b (point B). The discharged refrigerant passes through the first switching mechanism 31 and flows through the second suction pipe 22a (point C).

第２吸入管２２ａから第２圧縮部２２に吸い込まれた冷媒は、圧縮されて第２吐出管２２ｂに吐出される（点Ｄ）。吐出された冷媒は、第２切換機構３２を通過し、第３吸入管２３ａを流れる。なお、第３吸入管２３ａには、エコノマイザ熱交換器６１において熱交換されてインジェクション配管６１ａを流れてくる中間圧の冷媒（点Ｌ）も流れ込んでくるため、冷媒の温度が下がる（点Ｆ）。 The refrigerant sucked into the second compression part 22 from the second suction pipe 22a is compressed and discharged to the second discharge pipe 22b (point D). The discharged refrigerant passes through the second switching mechanism 32 and flows through the third suction pipe 23a. In addition, since the intermediate pressure refrigerant (point L) that is heat-exchanged in the economizer heat exchanger 61 and flows through the injection pipe 61a also flows into the third suction pipe 23a, the temperature of the refrigerant decreases (point F). .

第３吸入管２３ａから第３圧縮部２３に吸い込まれた冷媒は、圧縮されて第３吐出管２３ｂに吐出される（点Ｇ）。吐出された冷媒は、第３切換機構３３を通過し、第４吸入管２４ａを流れる（点Ｈ）。 The refrigerant sucked into the third compression section 23 from the third suction pipe 23a is compressed and discharged to the third discharge pipe 23b (point G). The discharged refrigerant passes through the third switching mechanism 33 and flows through the fourth suction pipe 24a (point H).

第４吸入管２４ａから第４圧縮部２４に吸い込まれた冷媒は、圧縮されて第４吐出管２４ｂに吐出される（点Ｉ）。吐出された高圧の冷媒は、第４切換機構３４を通過し、連絡冷媒配管１４を介して室内ユニット１２に流入する（点Ｚ）。 The refrigerant sucked into the fourth compression section 24 from the fourth suction pipe 24a is compressed and discharged to the fourth discharge pipe 24b (point I). The discharged high-pressure refrigerant passes through the fourth switching mechanism 34 and flows into the indoor unit 12 through the communication refrigerant pipe 14 (point Z).

連絡冷媒配管１４から室内ユニット１２に入った高圧冷媒は、冷媒の冷却器として機能する室内熱交換器１２ａで室内空気に放熱し、室内空気を暖める。室内熱交換器１２ａでの熱交換によって温度が下がった高圧冷媒（点Ｖ）は、室内電動弁１２ｂを通過する際にわずかに減圧され、連絡冷媒配管１３を通って室外ユニット１１のブリッジ回路５５へと流れ、入口逆止弁５５ｂからエコノマイザ熱交換器６１へ向かう（点Ｊ）。 The high-pressure refrigerant that has entered the indoor unit 12 from the communication refrigerant pipe 14 radiates heat to the indoor air in the indoor heat exchanger 12a that functions as a refrigerant cooler, and warms the indoor air. The high-pressure refrigerant (point V) whose temperature has dropped due to heat exchange in the indoor heat exchanger 12a is slightly decompressed when passing through the indoor motor-operated valve 12b, passes through the communication refrigerant pipe 13, and the bridge circuit 55 of the outdoor unit 11 To the economizer heat exchanger 61 from the inlet check valve 55b (point J).

ブリッジ回路５５を出た高圧冷媒（点Ｊ）は、エコノマイザ熱交換器６１に流れ込むとともに、その一部が分岐して第３室外電動弁６１ｂへと流れる。第３室外電動弁６１ｂで減圧・膨張して気液二相状態となった中間圧冷媒（点Ｋ）は、エコノマイザ熱交換器６において、ブリッジ回路５５から内部熱交換器６２に向かう高圧冷媒（点Ｊ）と熱交換し、中間圧のガス冷媒（点Ｌ）となってインジェクション配管６１ａから第２インタークーラ管４２ａへと流れ込む。 The high-pressure refrigerant (point J) that has exited the bridge circuit 55 flows into the economizer heat exchanger 61, and part of the high-pressure refrigerant branches to the third outdoor motor-operated valve 61b. The intermediate-pressure refrigerant (point K) that has been reduced in pressure and expanded by the third outdoor motorized valve 61b into a gas-liquid two-phase state is converted into a high-pressure refrigerant (point K) from the bridge circuit 55 toward the internal heat exchanger 62 in the economizer heat exchanger 6. It exchanges heat with the point J) and becomes an intermediate-pressure gas refrigerant (point L) and flows from the injection pipe 61a into the second intercooler pipe 42a.

レシーバ８０で分離された液冷媒（点Ｒ）は、出口管８２を通ってそのまま過冷却熱交換器９０へと流れ、レシーバ８０で分離されたガス冷媒（点Ｕ）は、第５室外電動弁９１で減圧され低圧冷媒（点Ｗ）となって過冷却熱交換器９０へと流れていく。レシーバ８０の出口管８２から過冷却熱交換器９０に向かう中間圧冷媒は、第６室外電動弁９２が閉められているため分岐管９２ａには流れず、全量が過冷却熱交換器９０に流れ込む。過冷却熱交換器９０では、レシーバ８０の出口管８２から流れてくる中間圧冷媒（点Ｒ）と、第５室外電動弁９１で減圧された低圧冷媒（点Ｗ，Ｘ）との間で熱交換が行われる。この熱交換によって、低圧冷媒配管１９に向かって流れる低圧冷媒（点Ｘ）は、蒸発して過熱のついた低圧冷媒（点Ｙ）となり、レシーバ８０からブリッジ回路５５に向かう中間圧冷媒（点Ｒ）は、熱を奪われて過冷却のついた中間圧冷媒（点Ｔ）となる。 The liquid refrigerant (point R) separated by the receiver 80 flows directly to the supercooling heat exchanger 90 through the outlet pipe 82, and the gas refrigerant (point U) separated by the receiver 80 is the fifth outdoor motor valve. The pressure is reduced at 91 to form a low-pressure refrigerant (point W) and flow to the supercooling heat exchanger 90. The intermediate pressure refrigerant from the outlet pipe 82 of the receiver 80 toward the supercooling heat exchanger 90 does not flow into the branch pipe 92a because the sixth outdoor motor-operated valve 92 is closed, and the entire amount flows into the supercooling heat exchanger 90. . In the subcooling heat exchanger 90, heat is generated between the intermediate pressure refrigerant (point R) flowing from the outlet pipe 82 of the receiver 80 and the low pressure refrigerant (points W and X) decompressed by the fifth outdoor motor-operated valve 91. Exchange is performed. By this heat exchange, the low-pressure refrigerant (point X) flowing toward the low-pressure refrigerant pipe 19 evaporates to become a superheated low-pressure refrigerant (point Y), and the intermediate-pressure refrigerant (point R) from the receiver 80 toward the bridge circuit 55. ) Becomes an intermediate pressure refrigerant (point T) which is deprived of heat and supercooled.

過冷却熱交換器９０を出てブリッジ回路５５の出口逆止弁５５ｄを通過した中間圧冷媒は、２路に分流し、第１および第２室外電動弁５１，５２でそれぞれ減圧・膨張され気液二相の低圧冷媒となる（点ＡＣ）。このとき、第１および第２室外電動弁５１，５２の開度は、直列に接続される第１〜第３熱交換器４１〜４３の圧力損失量と、第４熱交換器４４の圧力損失量とに応じて調節されており、いずれかの一方の流路に冷媒が偏流してしまうことが抑制されている。 The intermediate-pressure refrigerant that has exited the supercooling heat exchanger 90 and passed through the outlet check valve 55d of the bridge circuit 55 is divided into two passages, and is decompressed and expanded by the first and second outdoor motor-operated valves 51 and 52, respectively. It becomes a liquid two-phase low-pressure refrigerant (point AC). At this time, the opening degree of the 1st and 2nd outdoor motor operated valves 51 and 52 is the pressure loss amount of the 1st-3rd heat exchangers 41-43 connected in series, and the pressure loss of the 4th heat exchanger 44. The amount of the refrigerant is adjusted in accordance with the amount, and the drift of the refrigerant in any one of the flow paths is suppressed.

室外熱交換器４０の第４熱交換器４４に流入した低圧冷媒は、外気から熱を奪って蒸発し、第４熱交換器４４の高温側配管４４ｈから第４切換機構３４を経て低圧冷媒配管１９へと流れていく。一方、室外熱交換器４０の第３熱交換器４３に流入した低圧冷媒は、第２熱交換器４２、第１熱交換器４１を順に流れ、枝管１９ａを介して低圧冷媒配管１９へ流れ、第４熱交換器４４を出た冷媒と合流する。具体的には、第３熱交換器４３を出た冷媒は、第３熱交換器４３の高温側配管４３ｈ、第３切換機構３３、直列接続用第２配管４２ｂ、第２熱交換器４２の低温側配管４２ｉ、第２熱交換器４２、第２熱交換器４２の高温側配管４２ｈ、第２切換機構３２、直列接続用第１配管４１ｂ、第１熱交換器４１の低温側配管４１ｉ、第１熱交換器４１、第１熱交換器４１の高温側配管４１ｈ、第１切換機構３１を順に流れ、第３熱交換器４３だけではなく順に第２熱交換器４２、第１熱交換器４１で外気から熱を奪って蒸発し、枝管１９ａから低圧冷媒配管１９へと流れる。 The low-pressure refrigerant that has flowed into the fourth heat exchanger 44 of the outdoor heat exchanger 40 takes heat from the outside air and evaporates, and passes from the high-temperature side pipe 44h of the fourth heat exchanger 44 through the fourth switching mechanism 34 to the low-pressure refrigerant pipe. It will flow to 19. On the other hand, the low-pressure refrigerant flowing into the third heat exchanger 43 of the outdoor heat exchanger 40 sequentially flows through the second heat exchanger 42 and the first heat exchanger 41, and then flows into the low-pressure refrigerant pipe 19 through the branch pipe 19a. The refrigerant that has exited the fourth heat exchanger 44 joins. Specifically, the refrigerant that has exited the third heat exchanger 43 passes through the high temperature side pipe 43h of the third heat exchanger 43, the third switching mechanism 33, the second pipe 42b for series connection, and the second heat exchanger 42. Low temperature side pipe 42i, second heat exchanger 42, high temperature side pipe 42h of second heat exchanger 42, second switching mechanism 32, first pipe 41b for series connection, low temperature side pipe 41i of first heat exchanger 41, The first heat exchanger 41, the high-temperature side pipe 41h of the first heat exchanger 41, and the first switching mechanism 31 sequentially flow, and not only the third heat exchanger 43 but also the second heat exchanger 42 and the first heat exchanger in order. At 41, heat is taken from the outside air to evaporate, and flows from the branch pipe 19a to the low-pressure refrigerant pipe 19.

第４熱交換器４４および直列に接続された第１〜第３熱交換器４１〜４３で蒸発して過熱もついた低圧のガス冷媒は、図４に示すように室外熱交換器４０の下流側の低圧冷媒配管１９で合流し（点ＡＤ）、更に過冷却熱交換器９０から流れてくる低圧冷媒（点Ｙ）と合流して（点ＡＢ）、内部熱交換器６２を通って第１吸入管２１ａから四段圧縮機２０へと戻っていく。上述のように、内部熱交換器６２では、四段圧縮機２０に向かう低圧冷媒（点ＡＢ）と、ブリッジ回路５５からレシーバ８０へと向かう高圧冷媒（点Ｍ）とが熱交換を行う。 The low-pressure gas refrigerant evaporated and overheated in the fourth heat exchanger 44 and the first to third heat exchangers 41 to 43 connected in series is downstream of the outdoor heat exchanger 40 as shown in FIG. In the low-pressure refrigerant pipe 19 (point AD), further merged with the low-pressure refrigerant (point Y) flowing from the supercooling heat exchanger 90 (point AB), and passes through the internal heat exchanger 62 for the first suction. It returns to the four-stage compressor 20 from the pipe 21a. As described above, in the internal heat exchanger 62, the low-pressure refrigerant (point AB) that goes to the four-stage compressor 20 and the high-pressure refrigerant (point M) that goes from the bridge circuit 55 to the receiver 80 perform heat exchange.

以上のように冷媒が冷媒回路内を循環することにより、空気調和装置１０は暖房運転サイクルを行う。 As described above, the refrigerant circulates in the refrigerant circuit, whereby the air conditioner 10 performs the heating operation cycle.

なお、上述のように四段圧縮機２０の設計において、高負荷時の冷房運転を基準として各圧縮部２１〜２４の容積比を決めているため、暖房運転では、図５に示すように、第４吸入管２４ａ（点Ｈ参照）を流れる冷媒の高段吸入圧力と、第４吐出管２４ｂ（点Ｉ参照）を流れる冷媒の高段吐出圧力との差圧ＤＰ３が小さくなる。高負荷時の冷房運転を基準として四段圧縮機２０を設計すると、暖房運転では２段目と４段目、すなわち第２圧縮部２２と第４圧縮部２４とは、あまり圧縮仕事をしない状態となる。これに鑑み、暖房運転では、上述のように第３吸入管２３ａを流れる冷媒だけを中間インジェクションによって冷やし（図５の点Ｄ、点Ｌ、点Ｆを参照）、第２吸入管２２ａや第４吸入管２４ａを流れる冷媒の冷却は行われない（図５の点Ｂおよび点Ｃ、点Ｇおよび点Ｈを参照）。 In addition, in the design of the four-stage compressor 20 as described above, since the volume ratio of the compression units 21 to 24 is determined based on the cooling operation at the time of high load, in the heating operation, as illustrated in FIG. The differential pressure DP3 between the high-stage suction pressure of the refrigerant flowing through the fourth suction pipe 24a (see point H) and the high-stage discharge pressure of the refrigerant flowing through the fourth discharge pipe 24b (see point I) becomes small. When the four-stage compressor 20 is designed based on the cooling operation at the time of high load, the second and fourth stages, that is, the second compression section 22 and the fourth compression section 24 do not perform much compression work in the heating operation. It becomes. In view of this, in the heating operation, as described above, only the refrigerant flowing through the third suction pipe 23a is cooled by intermediate injection (see points D, L, and F in FIG. 5), and the second suction pipe 22a and the fourth Cooling of the refrigerant flowing through the suction pipe 24a is not performed (see points B and C, points G and H in FIG. 5).

（３）油戻しの動作および油戻しバイパス電磁弁の制御
（３−１）冷房運転時の油戻し
冷房運転のときには、第１〜第４油分離器２５〜２８が全て機能する。第１油分離器２５は、上述のように、第１圧縮部２１から吐出された冷媒を気液分離して、油を、油戻し流路２５ａおよび第１インタークーラ管４１ａを介して第２吸入管２２ａに流し、第２圧縮部２２に吸入させる。第１インタークーラ管４１ａを流れる冷媒の圧力は、第１熱交換器４１の圧力損失の分だけ第１油分離器２５内の冷媒の圧力よりも小さく、その差圧によって油が第１油分離器２５から油戻し流路２５ａを通って第１インタークーラ管４１ａへと流れる。同様に、第２熱交換器４２の圧力損失の分の差圧によって、第２油分離器２６から油戻し流路２６ａを通って第２インタークーラ管４２ａへと油が流れ、第３熱交換器４３の圧力損失の分の差圧によって、第３油分離器２７から油戻し流路２７ａを通って第３インタークーラ管４３ａへと油が流れる。 (3) Oil return operation and control of oil return bypass solenoid valve (3-1) Oil return during cooling operation During the cooling operation, the first to fourth oil separators 25 to 28 all function. As described above, the first oil separator 25 gas-liquid-separates the refrigerant discharged from the first compression unit 21, and supplies the oil to the second through the oil return passage 25a and the first intercooler pipe 41a. It flows into the suction pipe 22a and is sucked into the second compression part 22. The pressure of the refrigerant flowing through the first intercooler pipe 41a is smaller than the pressure of the refrigerant in the first oil separator 25 by the pressure loss of the first heat exchanger 41, and the oil is separated into the first oil by the differential pressure. Flows from the container 25 through the oil return passage 25a to the first intercooler pipe 41a. Similarly, oil flows from the second oil separator 26 through the oil return flow path 26a to the second intercooler pipe 42a by the differential pressure corresponding to the pressure loss of the second heat exchanger 42, and third heat exchange is performed. Oil flows from the third oil separator 27 through the oil return passage 27a to the third intercooler pipe 43a due to the pressure difference corresponding to the pressure loss of the vessel 43.

第４油分離器２８は、上述のように、第４圧縮部２４から吐出された冷媒を気液分離して、油を、第４吸入管２４ａに流し、第４圧縮部２４に吸入させる。第４油分離器２８から第４吸入管２４ａへと流れる油は、並列に配置されている油戻しメイン流路２８ａおよび油戻しバイパス流路２８ｂの少なくとも一方を通る。油戻しバイパス電磁弁ＳＶ２８が閉じているときには、キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａを油が流れ、油戻しバイパス電磁弁ＳＶ２８が開いているときには、油戻しメイン流路２８ａよりも流路面積が大きく流路抵抗が小さい油戻しバイパス流路２８ｂを主として油が流れる。 As described above, the fourth oil separator 28 performs gas-liquid separation on the refrigerant discharged from the fourth compression unit 24, causes the oil to flow through the fourth suction pipe 24 a, and causes the fourth compression unit 24 to suck the oil. The oil flowing from the fourth oil separator 28 to the fourth suction pipe 24a passes through at least one of the oil return main flow path 28a and the oil return bypass flow path 28b arranged in parallel. When the oil return bypass solenoid valve SV28 is closed, oil flows through the oil return main flow path 28a including the capillary tube CA28, and when the oil return bypass solenoid valve SV28 is open, the flow path is more than the oil return main flow path 28a. Oil mainly flows through the oil return bypass passage 28b having a large area and a small passage resistance.

制御部９４は、図１および図２の点Ｈの冷媒の温度を計る高段吸入温度センサ９７と、図１および図２の点Ｉの冷媒の温度を計る高段吐出温度センサ９８とから、第４圧縮部２４の吸入側の第４吸入冷媒温度および第４圧縮部２４の吐出側の第４吐出冷媒温度を取得する。これらの第４吸入冷媒温度および第４吐出冷媒温度の差が所定の閾値よりも大きいときには、第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との差が十分に大きく、バイパス電磁弁ＳＶ２８が開かなくても十分な量の油が第４油分離器２８から第４吸入管２４ａへと流れるため、制御部９４は、油戻しバイパス電磁弁ＳＶ２８を閉じた状態にする。反対に、第４吸入冷媒温度および第４吐出冷媒温度の差が閾値よりも小さければ、第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との差も小さく、キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａでは十分な量の油を流すことができないため、制御部９４は、油戻しバイパス電磁弁ＳＶ２８を開けた状態にする。 The control unit 94 includes a high stage suction temperature sensor 97 that measures the temperature of the refrigerant at point H in FIGS. 1 and 2, and a high stage discharge temperature sensor 98 that measures the temperature of the refrigerant at point I in FIGS. The fourth suction refrigerant temperature on the suction side of the fourth compression unit 24 and the fourth discharge refrigerant temperature on the discharge side of the fourth compression unit 24 are acquired. When the difference between the fourth suction refrigerant temperature and the fourth discharge refrigerant temperature is larger than a predetermined threshold, the difference between the refrigerant pressure in the fourth suction pipe 24a and the refrigerant pressure in the fourth discharge pipe 24b is sufficiently large, and the bypass Even if the solenoid valve SV28 is not opened, a sufficient amount of oil flows from the fourth oil separator 28 to the fourth suction pipe 24a, so the control unit 94 closes the oil return bypass solenoid valve SV28. On the other hand, if the difference between the fourth suction refrigerant temperature and the fourth discharge refrigerant temperature is smaller than the threshold value, the difference between the refrigerant pressure in the fourth suction pipe 24a and the refrigerant pressure in the fourth discharge pipe 24b is also small. Since a sufficient amount of oil cannot flow through the included oil return main flow path 28a, the control unit 94 opens the oil return bypass solenoid valve SV28.

また、制御部９４は、冷房運転において四段圧縮機２０を起動するときには、第４圧縮部２４から吐出された冷媒が、第４油分離器２８および油戻しバイパス流路２８ｂを介して第４吸入管２４ａへと戻り過ぎてしまうことを避けるため、油戻しバイパス電磁弁ＳＶ２８を閉じた状態にする。四段圧縮機２０の起動制御が終了し、通常の冷房運転が始まるときも、その時点では熱負荷が大きく第４圧縮部２４が圧縮仕事を多く行っているため、制御部９４は、油戻しバイパス電磁弁ＳＶ２８を閉じた状態のままで維持する。 Further, when starting the four-stage compressor 20 in the cooling operation, the control unit 94 causes the refrigerant discharged from the fourth compression unit 24 to pass through the fourth oil separator 28 and the oil return bypass passage 28b. In order to avoid returning too much to the suction pipe 24a, the oil return bypass solenoid valve SV28 is closed. Even when the start-up control of the four-stage compressor 20 is finished and the normal cooling operation is started, since the heat load is large and the fourth compression unit 24 performs a lot of compression work at that time, the control unit 94 returns the oil return. The bypass solenoid valve SV28 is kept closed.

（３−２）暖房運転時の油戻し
暖房運転のときには、第１〜第３油分離器２５〜２７は単に低圧の冷媒を通す流路として機能し、油戻し流路２５ａ，２６ａ，２７ａには何も流れない。油戻し流路２５ａ，２６ａ，２７ａは、第２〜第４吸入管２２ａ，２３ａ，２４ａと接続されているが、油戻し流路２５ａ，２６ａ，２７ａが逆止弁を備えているため（図４参照）、油戻し流路２５ａ，２６ａ，２７ａから第１〜第３油分離器２５〜２７へと冷媒が流入することもない。 (3-2) Oil return during heating operation During the heating operation, the first to third oil separators 25 to 27 simply function as flow paths through which low-pressure refrigerant passes, and the oil return paths 25a, 26a, and 27a Nothing flows. The oil return passages 25a, 26a, and 27a are connected to the second to fourth suction pipes 22a, 23a, and 24a, but the oil return passages 25a, 26a, and 27a include check valves (see FIG. 4), the refrigerant does not flow into the first to third oil separators 25 to 27 from the oil return passages 25a, 26a, and 27a.

第４油分離器２８は、冷房運転のときと同様に暖房運転においても、第４圧縮部２４から吐出された冷媒を気液分離し、第４吸入管２４ａへと油を戻して第４圧縮部２４に吸入させる。また、バイパス電磁弁ＳＶ２８の開閉制御についても、運転中は冷房運転のときと同様である。すなわち、制御部９４は、暖房運転のときにも、第４吸入冷媒温度および第４吐出冷媒温度の差が閾値よりも大きいときには、油戻しバイパス電磁弁ＳＶ２８を閉じた状態にして、第４吸入冷媒温度および第４吐出冷媒温度の差が閾値よりも小さければ、油戻しバイパス電磁弁ＳＶ２８を開けた状態にする。 The fourth oil separator 28 gas-liquid separates the refrigerant discharged from the fourth compression unit 24 in the heating operation as in the cooling operation, and returns the oil to the fourth suction pipe 24a to perform the fourth compression. The part 24 is inhaled. Also, the opening / closing control of the bypass solenoid valve SV28 is the same as during the cooling operation during operation. That is, even during the heating operation, when the difference between the fourth suction refrigerant temperature and the fourth discharge refrigerant temperature is larger than the threshold value, the control unit 94 closes the oil return bypass solenoid valve SV28 and closes the fourth suction. If the difference between the refrigerant temperature and the fourth discharge refrigerant temperature is smaller than the threshold value, the oil return bypass solenoid valve SV28 is opened.

但し、冷房運転のときと異なり、暖房運転では、四段圧縮機２０を起動するときには、油戻しバイパス電磁弁ＳＶ２８を開けた状態にする。また、四段圧縮機２０の起動制御が終了し、通常の暖房運転が始まるときも、制御部９４は、油戻しバイパス電磁弁ＳＶ２８を開けた状態のままで維持する。これは、暖房運転において第４圧縮部２４の吸入側と吐出側との差圧（第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との差）が大きくなることは少なく、起動時においても差圧が確保されることが少ないため、初期の油戻しバイパス電磁弁ＳＶ２８の状態として、制御部９４は、開の状態を選択している。 However, unlike the cooling operation, in the heating operation, when the four-stage compressor 20 is started, the oil return bypass solenoid valve SV28 is opened. Further, when the start control of the four-stage compressor 20 is finished and the normal heating operation is started, the control unit 94 maintains the oil return bypass solenoid valve SV28 in an opened state. This is because the difference in pressure between the suction side and the discharge side of the fourth compression section 24 in the heating operation (the difference between the refrigerant pressure in the fourth suction pipe 24a and the refrigerant pressure in the fourth discharge pipe 24b) is rarely increased. Since the differential pressure is rarely secured even at the time of starting, the control unit 94 selects the open state as the initial state of the oil return bypass solenoid valve SV28.

（４）空気調和装置の特徴
（４−１）
本実施形態に係る空気調和装置１０では、第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との圧力差が大きい場合には、第４圧縮部２４から吐出されて第４吐出管２４ｂを流れる冷媒は、第４油分離器２８において油が分離され、その油が、キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａを通って、第４吸入管２４ａから第４圧縮部２４に吸入される。 (4) Features of the air conditioner (4-1)
In the air conditioning apparatus 10 according to the present embodiment, when the pressure difference between the refrigerant pressure in the fourth suction pipe 24a and the refrigerant pressure in the fourth discharge pipe 24b is large, the fourth discharge section 24 discharges from the fourth compression section 24. The refrigerant flowing in the pipe 24b is separated in the fourth oil separator 28, and the oil passes through the oil return main flow path 28a including the capillary tube CA28 to the fourth compression section 24 from the fourth suction pipe 24a. Inhaled.

一方、第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との圧力差が小さい場合には、第４油分離器２８から第４圧縮部２４へと戻る油の量が少なくなることが危惧されるが、本実施形態に係る空気調和装置１０では、油戻しバイパス電磁弁ＳＶ２８を開けることによって流路面積がより大きな油戻しバイパス流路２８ｂに油を通すことができる。油の流路を、キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａから、流路面が大きく抵抗が小さい油戻しバイパス流路２８ｂに切り換えることで、第４吸入管２４ａの冷媒圧力と第４吐出管２４ｂの冷媒圧力との圧力差が小さい場合（図３の差圧ＤＰ２および図５の差圧ＤＰ３を参照）にも、第４油分離器２８から第４圧縮部２４へと油を確実に戻すことができるようになっている。 On the other hand, when the pressure difference between the refrigerant pressure in the fourth suction pipe 24a and the refrigerant pressure in the fourth discharge pipe 24b is small, the amount of oil returning from the fourth oil separator 28 to the fourth compression section 24 is reduced. However, in the air conditioning apparatus 10 according to the present embodiment, the oil return bypass passage 28b having a larger flow passage area can be passed by opening the oil return bypass solenoid valve SV28. By switching the oil flow path from the oil return main flow path 28a including the capillary tube CA28 to the oil return bypass flow path 28b having a large flow path surface and low resistance, the refrigerant pressure and the fourth discharge pipe of the fourth suction pipe 24a are switched. Even when the pressure difference from the refrigerant pressure of 24b is small (see differential pressure DP2 in FIG. 3 and differential pressure DP3 in FIG. 5), the oil is reliably returned from the fourth oil separator 28 to the fourth compressor 24. Be able to.

（４−２）
本実施形態では、第１〜第４切換機構３１〜３４によって冷房運転と暖房運転とを切り換えることができる空気調和装置１０に本発明を適用している。そして、第４油分離器２８を第４圧縮部２４と第４切換機構３４との間に配置しているので、冷房運転の状態でも暖房運転の状態でも油が第４油分離器２８から第４圧縮部２４に戻る。第４圧縮部２４の吸入圧力と吐出圧力との差は、冷房運転と暖房運転とで異なっていることが多いが、運転に応じて、制御部９４が、油戻しメイン流路２８ａおよび油戻しバイパス流路２８ｂから成る油戻し流路の流路面積を変えることで、いずれの運転においても第４油分離器２８から第４圧縮部２４に戻る油の量を確保することができている。 (4-2)
In the present embodiment, the present invention is applied to the air conditioner 10 that can switch between the cooling operation and the heating operation by the first to fourth switching mechanisms 31 to 34. And since the 4th oil separator 28 is arrange | positioned between the 4th compression part 24 and the 4th switching mechanism 34, oil is the 4th oil separator 28 from the 4th oil separator 28 in the state of air_conditionaing | cooling operation or heating operation. 4 Return to the compression unit 24. The difference between the suction pressure and the discharge pressure of the fourth compression unit 24 is often different between the cooling operation and the heating operation. However, according to the operation, the control unit 94 controls the oil return main flow path 28a and the oil return. By changing the flow area of the oil return flow path composed of the bypass flow path 28b, the amount of oil returning from the fourth oil separator 28 to the fourth compression section 24 can be ensured in any operation.

（４−３）
本実施形態に係る空気調和装置１０では、共通回転軸によって４つの圧縮部２１〜２４の各圧縮部材を回転させる、一軸四段の四段圧縮機２０を採用している。すなわち、第１〜第３の低段の圧縮部２１〜２３それぞれの圧縮部材の回転数と、高段の第４圧縮部２４の圧縮部材の回転数とが、同じになる。したがって、四段圧縮機２０では、低段、高段の各圧縮部２１〜２４の容積比を制御的に変更することができない。 (4-3)
In the air conditioning apparatus 10 according to the present embodiment, a four-stage compressor 20 with one shaft and four stages is employed, in which the compression members of the four compression units 21 to 24 are rotated by a common rotation shaft. That is, the rotation speed of the compression member of each of the first to third low-stage compression sections 21 to 23 is the same as the rotation speed of the compression member of the high-stage fourth compression section 24. Therefore, in the four-stage compressor 20, the volume ratio of the low-stage and high-stage compressors 21 to 24 cannot be changed in a controllable manner.

その結果、冷房運転の低負荷時や暖房運転時において、第４圧縮部２４の吸入圧力と吐出圧力との差が殆どなくなってしまう状況（図３の差圧ＤＰ２および図５の差圧ＤＰ３を参照）が生まれる。 As a result, there is almost no difference between the suction pressure and the discharge pressure of the fourth compression section 24 at the time of low load in cooling operation or heating operation (the differential pressure DP2 in FIG. 3 and the differential pressure DP3 in FIG. 5 are reduced). See) is born.

しかし、空気調和装置１０では、油戻しメイン流路２８ａおよび油戻しバイパス流路２８ｂから成る油戻し流路の流路面積を変えることで、そのような状況においても第４油分離器２８から第４圧縮部２４に戻る油の量を確保することができている。 However, in the air conditioner 10, by changing the flow area of the oil return flow path including the oil return main flow path 28a and the oil return bypass flow path 28b, even in such a situation, the fourth oil separator 28 can 4 The amount of oil returning to the compression unit 24 can be secured.

（４−４）
本実施形態に係る空気調和装置１０では、暖房運転時には、第２圧縮部２２と次段の第３圧縮部２３との間に、中間インジェクション機構が配置されている。具体的には、第３室外電動弁６１ｂを通って膨張し、エコノマイザ熱交換器６１で蒸発した冷媒が、インジェクション配管６１ａを通って第３吸入管２３ａに流れ込み、第３吸入管２３ａから第３圧縮部２３へ吸い込まれる冷媒を冷やすという機構が存在する。この中間インジェクションによって、冷凍サイクルの効率が上がり、四段圧縮機２０に投入するエネルギーを削減することができている。 (4-4)
In the air conditioner 10 according to the present embodiment, an intermediate injection mechanism is disposed between the second compression unit 22 and the third compression unit 23 at the next stage during the heating operation. Specifically, the refrigerant that has expanded through the third outdoor motor-operated valve 61b and evaporated in the economizer heat exchanger 61 flows into the third suction pipe 23a through the injection pipe 61a, and passes through the third suction pipe 23a. There is a mechanism for cooling the refrigerant sucked into the compression unit 23. This intermediate injection increases the efficiency of the refrigeration cycle and reduces the energy input to the four-stage compressor 20.

この空気調和装置１０において、仮に、第４圧縮部２４から吐出されて第４油分離器２８で冷媒から分離された油を、第４圧縮部２４ではなく、低段の第３圧縮部２３に戻す構成を採った場合、油が第３圧縮部２３に滞留してしまうことも危惧される。 In the air conditioner 10, suppose that the oil discharged from the fourth compression unit 24 and separated from the refrigerant by the fourth oil separator 28 is not supplied to the fourth compression unit 24 but to the lower third compression unit 23. When the returning configuration is adopted, there is a concern that the oil may stay in the third compression unit 23.

しかし、空気調和装置１０では、暖房運転のときに、第４圧縮部２４に吸入される冷媒の冷却は行われず、第４圧縮部２４から吐出されて第４油分離器２８から第４圧縮部２４に戻る油は、流路面積が大きい油戻しバイパス流路２８ｂを通ることができる。このため、第４圧縮部２４の吸入圧力と吐出圧力との差が小さい場合にも、冷媒圧力が小さい第３圧縮部２３に油を戻す必要がなくなり、第４圧縮部２４が必要量の油を保持することができている。 However, in the air conditioner 10, during the heating operation, the refrigerant sucked into the fourth compression unit 24 is not cooled, and is discharged from the fourth compression unit 24 and is discharged from the fourth oil separator 28 to the fourth compression unit. The oil returning to 24 can pass through the oil return bypass channel 28b having a large channel area. For this reason, even when the difference between the suction pressure and the discharge pressure of the fourth compression section 24 is small, it is not necessary to return the oil to the third compression section 23 where the refrigerant pressure is small, and the fourth compression section 24 has a necessary amount of oil. Can hold.

（４−５）
冷暖房が可能な空気調和装置１０において四段圧縮機２０のような３段以上の圧縮機構を採用した場合、暖房運転のときに高段圧縮部（第４圧縮部２４）の吸入圧力と吐出圧力との差が小さくなることを、本発明の発明者は見いだしている。特に、圧縮機構の起動時や、その後の通常運転開始時において、油戻し流路の流路面積が小さければ、第４油分離器２８から第４圧縮部２４へと油があまり戻らなくなる。 (4-5)
When the air conditioning apparatus 10 capable of cooling and heating employs a compression mechanism having three or more stages such as the four-stage compressor 20, the suction pressure and the discharge pressure of the high-stage compression section (fourth compression section 24) during the heating operation. The inventor of the present invention has found that the difference from the above becomes smaller. In particular, when the compression mechanism is started up or when the normal operation is started thereafter, if the flow area of the oil return flow path is small, the oil does not return so much from the fourth oil separator 28 to the fourth compression section 24.

これに鑑み、本実施形態に係る空気調和装置１０では、暖房運転における四段圧縮機２０の起動時、および、暖房運転における四段圧縮機２０の起動後の通常運転開始時に、流路面積が大きい油戻しバイパス流路２８ｂを油が通る状態にして、油戻し量を確保している。これにより、第４圧縮部２４の吸入圧力と吐出圧力との差が小さくなりがちな暖房運転の所定時においても、第４油分離器２８から第４圧縮部２４に戻る油の量を確保することができている。 In view of this, in the air conditioner 10 according to the present embodiment, the flow path area is large when the four-stage compressor 20 is started in the heating operation and when the normal operation is started after the four-stage compressor 20 is started in the heating operation. The amount of oil return is ensured by allowing oil to pass through the large oil return bypass passage 28b. Thus, the amount of oil returning from the fourth oil separator 28 to the fourth compression unit 24 is ensured even during a predetermined heating operation when the difference between the suction pressure and the discharge pressure of the fourth compression unit 24 tends to be small. Is able to.

一方、本発明の発明者は、３段以上の圧縮機構を採用した場合、暖房運転のときに高段圧縮部の吸入圧力と吐出圧力との差が小さくなる一方、熱負荷が大きい冷房運転のときには高段圧縮部（第４圧縮部２４）の吸入圧力と吐出圧力との差が十分に大きくなることを見いだしている。これに鑑み、本実施形態に係る空気調和装置１０では、冷房運転における四段圧縮機２０の起動時、および、冷房運転における四段圧縮機２０の起動後の通常運転開始時に、油戻しバイパス流路２８ｂに設けた油戻しバイパス電磁弁ＳＶ２８を閉じた状態にして、キャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａを油が流れるようにしている。これにより、高段の第４圧縮部２４の吸入圧力と吐出圧力との差が十分に大きい冷房運転の所定時（図２の差圧ＤＰ１を参照）において、第４油分離器２８から第４圧縮部２４に油だけではなく多くの冷媒まで戻ってしまう不具合が抑制されている。 On the other hand, when the inventor of the present invention employs a compression mechanism having three or more stages, the difference between the suction pressure and the discharge pressure of the high stage compression unit is reduced during heating operation, while the cooling operation with a large heat load is performed. In some cases, it has been found that the difference between the suction pressure and the discharge pressure of the high-stage compression section (fourth compression section 24) becomes sufficiently large. In view of this, in the air conditioner 10 according to the present embodiment, the oil return bypass flow at the start of the four-stage compressor 20 in the cooling operation and at the start of normal operation after the start of the four-stage compressor 20 in the cooling operation. The oil return bypass solenoid valve SV28 provided in the path 28b is closed so that oil flows through the oil return main flow path 28a including the capillary tube CA28. As a result, the fourth oil separator 28 to the fourth oil pressure at the predetermined time of the cooling operation (see the differential pressure DP1 in FIG. 2) where the difference between the suction pressure and the discharge pressure of the high-stage fourth compression section 24 is sufficiently large. The malfunction which returns not only to oil but many refrigerant | coolants to the compression part 24 is suppressed.

（５）変形例
（５−１）変形例Ａ
上記実施形態では、第４油分離器２８から第４圧縮部２４へと戻る油の流路の流路面積を変える油戻しバイパス電磁弁ＳＶ２８の開閉を、第４圧縮部２４の吸入側の第４吸入冷媒温度および第４圧縮部２４の吐出側の第４吐出冷媒温度から判断している。 (5) Modification (5-1) Modification A
In the above embodiment, the opening and closing of the oil return bypass solenoid valve SV28 that changes the flow area of the oil flow path returning from the fourth oil separator 28 to the fourth compression section 24 is performed on the suction side of the fourth compression section 24. This is determined from the four suction refrigerant temperatures and the fourth discharge refrigerant temperature on the discharge side of the fourth compressor 24.

これに代えて、制御部９４は、他のセンサ値を用いて油戻しバイパス電磁弁ＳＶ２８の開閉を制御してもよい。例えば、第４吐出管２４ｂに圧力センサ（高圧センサ）が設けられている場合には、その冷媒の高圧値を基に油戻しバイパス電磁弁ＳＶ２８を開閉すればよい。高圧値が大きいときには、油戻しバイパス電磁弁ＳＶ２８を閉じて流路面積を小さくし、高圧値が小さいときには、油戻しバイパス電磁弁ＳＶ２８を開いて流路面積を大きくすることになる。また、冷房運転において、外気温度が閾値よりも低く、且つ、四段圧縮機２０の回転数が小さいときに、低負荷であると判断して油戻しバイパス電磁弁ＳＶ２８を開く制御を行ってもよい。 Instead of this, the controller 94 may control the opening and closing of the oil return bypass solenoid valve SV28 using other sensor values. For example, when a pressure sensor (high pressure sensor) is provided in the fourth discharge pipe 24b, the oil return bypass solenoid valve SV28 may be opened and closed based on the high pressure value of the refrigerant. When the high pressure value is large, the oil return bypass solenoid valve SV28 is closed to reduce the flow path area, and when the high pressure value is small, the oil return bypass solenoid valve SV28 is opened to increase the flow path area. Further, in the cooling operation, when the outside air temperature is lower than the threshold value and the rotation speed of the four-stage compressor 20 is small, it is determined that the load is low, and control is performed to open the oil return bypass solenoid valve SV28. Good.

（５−２）変形例Ｂ
上記実施形態に係る空気調和装置１０では、第４油分離器２８から第４圧縮部２４に油を戻す油戻し流路として、流路面積が小さいキャピラリーチューブＣＡ２８を含む油戻しメイン流路２８ａと、キャピラリーチューブＣＡ２８よりも流路面積が大きい油戻しバイパス流路２８ｂとを並列させている。そして、油戻しバイパス流路２８ｂに、油戻しバイパス電磁弁ＳＶ２８を設けている。このような並列する２つの流路２８ａ，２８ｂで第４油分離器２８と第４吸入管２４ａとを結ぶ構成を採ることによって、油戻しバイパス電磁弁ＳＶ２８を閉じているときには、流路面積が小さいキャピラリーチューブＣＡ２８を油が流れることになり、油戻しバイパス電磁弁ＳＶ２８を開けているときには、主として、圧力損失が小さい流路面積の大きな油戻しバイパス流路２８ｂを油が流れることになる。これにより、第４圧縮部２４の吸入圧力と吐出圧力との差が小さい場合に、油戻しバイパス電磁弁ＳＶ２８を開けることで、第４油分離器２８から第４圧縮部２４に戻る油の量を確保することができている。 (5-2) Modification B
In the air conditioner 10 according to the above embodiment, the oil return main flow path 28a including the capillary tube CA28 having a small flow path area as the oil return flow path for returning the oil from the fourth oil separator 28 to the fourth compression unit 24; The oil return bypass channel 28b having a channel area larger than that of the capillary tube CA28 is arranged in parallel. An oil return bypass solenoid valve SV28 is provided in the oil return bypass passage 28b. When the oil return bypass solenoid valve SV28 is closed by adopting such a configuration in which the fourth oil separator 28 and the fourth suction pipe 24a are connected by the two flow paths 28a and 28b arranged in parallel, the flow area is large. When oil flows through the small capillary tube CA28 and the oil return bypass solenoid valve SV28 is opened, the oil mainly flows through the oil return bypass channel 28b having a small channel loss and a large channel area. Accordingly, when the difference between the suction pressure and the discharge pressure of the fourth compression unit 24 is small, the amount of oil returning from the fourth oil separator 28 to the fourth compression unit 24 by opening the oil return bypass solenoid valve SV28. Can be secured.

このような２つの流路２８ａ，２８ｂが並列する構成に代えて、１つの流路２８ａだけを用いて、キャピラリーチューブＣＡ２８の代わりに、開度が可変の電動膨張弁を設けるという構成を採ることも可能である。この場合には、制御部９４が、第４圧縮部２４の吸入圧力と吐出圧力との差が大きければ、油戻し用の流路２８ａの電動膨張弁の開度が小さくなるように制御し、第４圧縮部２４の吸入圧力と吐出圧力との差が小さくなれば、油戻し用の流路２８ａの電動膨張弁の開度を大きくする。これにより、冷房運転時の高負荷時も低負荷時も暖房運転時も、第４油分離器２８から第４圧縮部２４へと適量の油が戻るようになる。 Instead of the configuration in which the two flow paths 28a and 28b are arranged in parallel, a configuration in which only one flow path 28a is used and an electric expansion valve having a variable opening degree is provided instead of the capillary tube CA28 is adopted. Is also possible. In this case, if the difference between the suction pressure and the discharge pressure of the fourth compression unit 24 is large, the control unit 94 performs control so that the opening degree of the electric expansion valve of the oil return flow path 28a is small. If the difference between the suction pressure and the discharge pressure of the fourth compression section 24 becomes small, the opening degree of the electric expansion valve of the oil return flow path 28a is increased. As a result, an appropriate amount of oil returns from the fourth oil separator 28 to the fourth compression unit 24 at the time of high load, low load, and heating operation during the cooling operation.

（５−３）変形例Ｃ
上記実施形態では、暖房運転における四段圧縮機２０の起動時も、暖房運転における四段圧縮機２０の起動後の通常運転開始時も、油戻しバイパス流路２８ｂの油戻しバイパス電磁弁ＳＶ２８の初期状態を開の状態にしている。 (5-3) Modification C
In the above embodiment, the oil return bypass solenoid valve SV28 of the oil return bypass flow path 28b is activated both at the start of the four-stage compressor 20 in the heating operation and at the start of normal operation after the start of the four-stage compressor 20 in the heating operation. The initial state is open.

しかし、空気調和装置１０の設置場所や、四段圧縮機２０の各圧縮部２１〜２４の容量設計によっては、これらの時に第４圧縮部２４の吸入圧力と吐出圧力との差が確保されることもある。 However, depending on the installation location of the air conditioner 10 and the capacity design of the compression units 21 to 24 of the four-stage compressor 20, the difference between the suction pressure and the discharge pressure of the fourth compression unit 24 is ensured at these times. Sometimes.

したがって、空気調和装置１０の設置場所などに応じて、暖房運転における四段圧縮機２０の起動時の油戻しバイパス電磁弁ＳＶ２８の初期状態を開の状態にしてもよいし、暖房運転における四段圧縮機２０の起動後の通常運転開始時の油戻しバイパス電磁弁ＳＶ２８の初期状態を開の状態にしてもよい。 Therefore, the initial state of the oil return bypass solenoid valve SV28 when starting the four-stage compressor 20 in the heating operation may be set to an open state or the four-stage in the heating operation depending on the installation location of the air conditioner 10 or the like. The initial state of the oil return bypass solenoid valve SV28 at the start of normal operation after the start of the compressor 20 may be set to an open state.

（５−４）変形例Ｄ
上記実施形態では、一軸四段の四段圧縮機２０を採用した空気調和装置１０を示しているが、高段の圧縮部の吸入圧力と吐出圧力との差が小さくなることがある冷凍装置であれば、他の構造を持った圧縮機構を採用した冷凍装置でも本発明は有用である。 (5-4) Modification D
In the above-described embodiment, the air conditioner 10 employing the four-stage compressor 20 with four uniaxial shafts is shown. However, in the refrigeration apparatus in which the difference between the suction pressure and the discharge pressure of the high-stage compression unit may be small. If present, the present invention is useful even in a refrigeration apparatus employing a compression mechanism having another structure.

１０空気調和装置（冷凍装置）
１２ａ室内熱交換器（利用側熱交換器；蒸発器／放熱器）
２０四段圧縮機（複数段圧縮機構）
２１第１圧縮部（低段圧縮部）
２２第２圧縮部（低段圧縮部）
２３第３圧縮部（低段圧縮部）
２４第４圧縮部（高段圧縮部）
２４ａ第４吸入管（高段吸入配管）
２４ｂ第４吐出管（高段吐出配管）
２８第４油分離器（油分離器）
２８ａ油戻しメイン流路（油戻し流路；第１油戻し流路）
２８ｂ油戻しバイパス流路（油戻し流路；第２油戻し流路）
３１第１切換機構
３２第２切換機構
３３第３切換機構
３４第４切換機構（切換機構）
４０室外熱交換器（熱源側熱交換器；放熱器／蒸発器）
６１エコノマイザ熱交換器（中間インジェクション機構）
６１ａインジェクション配管（中間インジェクション機構）
６１ｂ第３室外電動弁（中間インジェクション機構）
７０膨張機構（膨張部）
９４制御部
ＳＶ２８油戻しバイパス電磁弁（流路面積変更部；開閉弁） 10 Air conditioning equipment (refrigeration equipment)
12a Indoor heat exchanger (use side heat exchanger; evaporator / heat radiator)
20 Four-stage compressor (multi-stage compression mechanism)
21 1st compression part (low stage compression part)
22 2nd compression part (low stage compression part)
23 3rd compression part (low stage compression part)
24 4th compression part (high stage compression part)
24a Fourth suction pipe (high suction pipe)
24b Fourth discharge pipe (high-stage discharge pipe)
28 4th oil separator (oil separator)
28a Oil return main channel (oil return channel; first oil return channel)
28b Oil return bypass channel (oil return channel; second oil return channel)
31 First switching mechanism 32 Second switching mechanism 33 Third switching mechanism 34 Fourth switching mechanism (switching mechanism)
40 Outdoor heat exchanger (heat source side heat exchanger; radiator / evaporator)
61 Economizer heat exchanger (intermediate injection mechanism)
61a Injection piping (intermediate injection mechanism)
61b Third outdoor motor operated valve (intermediate injection mechanism)
70 Expansion mechanism (expansion part)
94 Control part SV28 Oil return bypass solenoid valve (Flow path area changing part; On-off valve)

特開２０１１−２１４７５７号公報JP 2011-214757 A

Claims

複数の低段圧縮部（２１，２２，２３）と、１つの高段圧縮部（２４）とが１列に接続された、複数段圧縮機構（２０）と、
前記複数段圧縮機構から吐出された冷媒に放熱をさせる、放熱器（４０，１２ａ）と、
前記放熱器を出た冷媒を減圧する、膨張部（７０）と、
前記膨張部を出た冷媒を蒸発させる、蒸発器（１２ａ，４０）と、
前記高段圧縮部（２４）から吐出された冷媒が流れる高段吐出配管（２４ｂ）に設けられた油分離器（２８）と、
前記高段圧縮部（２４）に吸入される冷媒が流れる高段吸入配管（２４ａ）と前記油分離器（２８）とを結び、前記油分離器（２８）から前記高段圧縮部（２４）へと油を戻す、油戻し流路（２８ａ，２８ｂ）と、
前記油戻し流路（２８ａ，２８ｂ）の流路面積を変える流路面積変更部（ＳＶ２８）と、
を備える、冷凍装置（１０）。 A multi-stage compression mechanism (20) in which a plurality of low-stage compression sections (21, 22, 23) and one high-stage compression section (24) are connected in a row;
A radiator (40, 12a) for radiating heat to the refrigerant discharged from the multistage compression mechanism;
An expansion section (70) for depressurizing the refrigerant exiting the radiator;
An evaporator (12a, 40) for evaporating the refrigerant exiting the expansion section;
An oil separator (28) provided in a high stage discharge pipe (24b) through which the refrigerant discharged from the high stage compression section (24) flows;
The high stage suction pipe (24a) through which the refrigerant sucked into the high stage compression section (24) flows is connected to the oil separator (28), and the high stage compression section (24) is connected from the oil separator (28). An oil return channel (28a, 28b) for returning oil to
A flow path area changing unit (SV28) that changes a flow path area of the oil return flow path (28a, 28b);
A refrigeration apparatus (10) comprising:

前記油戻し流路は、キャピラリーチューブ（ＣＡ２８）を含む第１油戻し流路（２８ａ）と、前記キャピラリーチューブの流路面積よりも大きな流路面積である第２油戻し流路（２８ｂ）とを有しており、
前記第１油戻し流路と前記第２油戻し流路とは、並列しており、
前記流路面積変更部（ＳＶ２８）は、前記第２油戻し流路に設けられた開閉弁である、
請求項１に記載の冷凍装置。 The oil return channel includes a first oil return channel (28a) including a capillary tube (CA28), and a second oil return channel (28b) having a channel area larger than the channel area of the capillary tube. Have
The first oil return channel and the second oil return channel are in parallel,
The flow path area changing portion (SV28) is an on-off valve provided in the second oil return flow path.
The refrigeration apparatus according to claim 1.

前記放熱器は、冷房運転のときには、熱源によって冷媒を冷やす熱源ユニットの熱源側熱交換器（４０）であり、暖房運転のときには、冷媒に放熱をさせる利用ユニットの利用側熱交換器（１２ａ）であり、
前記蒸発器は、前記冷房運転のときには、冷媒を蒸発させる前記利用側熱交換器（１２ａ）であり、前記暖房運転のときには、熱源から熱を奪って冷媒を蒸発させる前記熱源側熱交換器（４０）であり、
前記高段圧縮部（２４）を出た冷媒が前記熱源側熱交換器（４０）に流れる前記冷房運転の状態と、前記高段圧縮部（２４）を出た冷媒が前記利用側熱交換器（１２ａ）に流れる前記暖房運転の状態とを切り換える、切換機構（３４）
をさらに備え、
前記油分離器（２８）は、前記高段圧縮部（２４）と前記切換機構（３４）との間に配置される、
請求項１又は２に記載の冷凍装置。 The radiator is a heat source side heat exchanger (40) of a heat source unit that cools the refrigerant with a heat source during cooling operation, and a utilization side heat exchanger (12a) of a utilization unit that radiates heat to the refrigerant during heating operation. And
The evaporator is the use-side heat exchanger (12a) that evaporates the refrigerant during the cooling operation, and the heat source-side heat exchanger that evaporates the refrigerant by removing heat from the heat source during the heating operation ( 40)
The cooling operation state in which the refrigerant that has exited the high stage compression section (24) flows to the heat source side heat exchanger (40), and the refrigerant that has exited the high stage compression section (24) is the use side heat exchanger. A switching mechanism (34) for switching between the heating operation state flowing in (12a).
Further comprising
The oil separator (28) is disposed between the high stage compression section (24) and the switching mechanism (34).
The refrigeration apparatus according to claim 1 or 2.

前記複数段圧縮機構（２０）は、複数の前記低段圧縮部（２１，２２，２３）それぞれの圧縮部材を回転させるとともに前記高段圧縮部（２４）の圧縮部材を回転させる共通回転軸、を有している、
請求項３に記載の冷凍装置。 The multi-stage compression mechanism (20) rotates a compression member of each of the plurality of low-stage compression sections (21, 22, 23) and rotates a compression member of the high-stage compression section (24), have,
The refrigeration apparatus according to claim 3.

前記暖房運転のときに、複数の前記低段圧縮部（２１，２２，２３）のうちの１つの前記低段圧縮部（２２）から吐出され次段の前記低段圧縮部（２３）に吸入される冷媒を冷やす、中間インジェクション機構（６１，６１ａ，６１ｂ）
をさらに備え、
前記暖房運転のときに、前記高段圧縮部（２４）に吸入される冷媒の冷却は行われない、
請求項３又は４に記載の冷凍装置。 During the heating operation, one of the plurality of low-stage compression sections (21, 22, 23) is discharged from the low-stage compression section (22) and sucked into the next-stage low-stage compression section (23). Injection mechanism (61, 61a, 61b) for cooling the refrigerant
Further comprising
During the heating operation, the refrigerant sucked into the high-stage compression unit (24) is not cooled.
The refrigeration apparatus according to claim 3 or 4.

前記流路面積変更部（ＳＶ２８）を制御して、前記油戻し流路（２８ａ，２８ｂ）の流路面積が第１流路面積になる第１状態と、前記油戻し流路（２８ａ，２８ｂ）の流路面積が前記第１流路面積よりも大きな第２流路面積になる第２状態とを切り換える、制御部（９４）、
をさらに備え、
前記制御部（９４）は、前記暖房運転のときに、前記複数段圧縮機構（２０）の起動時、および／又は、前記複数段圧縮機構（２０）の起動後の通常運転開始時に、前記流路面積変更部（ＳＶ２８）を前記第２状態にする、
請求項３から５のいずれかに記載の冷凍装置。 A first state in which the flow area of the oil return flow path (28a, 28b) becomes the first flow path area by controlling the flow path area changing unit (SV28), and the oil return flow path (28a, 28b). ) To switch to a second state in which the flow path area becomes a second flow path area larger than the first flow path area,
Further comprising
The controller (94) is configured to perform the flow at the time of the heating operation, at the time of starting the multi-stage compression mechanism (20) and / or at the time of starting normal operation after the start of the multi-stage compression mechanism (20). The road area changing unit (SV28) is set to the second state,
The refrigeration apparatus according to any one of claims 3 to 5.

前記制御部（９４）は、前記冷房運転のときに、前記複数段圧縮機構（２０）の起動時、および／又は、前記複数段圧縮機構（２０）の起動後の通常運転開始時に、前記流路面積変更部（ＳＶ２８）を前記第１状態にする、
請求項６に記載の冷凍装置。 The controller (94) is configured to perform the flow at the time of the cooling operation, at the time of starting the multistage compression mechanism (20) and / or at the time of starting normal operation after the start of the multistage compression mechanism (20). The road area changing unit (SV28) is set to the first state.
The refrigeration apparatus according to claim 6.