GB2583666A

GB2583666A - Refrigeration cycle device

Info

Publication number: GB2583666A
Application number: GB2010975.7A
Authority: GB
Inventors: Miura Ken; Imato Naoki
Original assignee: Toshiba Carrier Corp
Current assignee: Toshiba Carrier Corp
Priority date: 2018-02-16
Filing date: 2018-02-16
Publication date: 2020-11-04
Anticipated expiration: 2038-02-16
Also published as: CN111712677A; GB2583666B; JP6859461B2; JPWO2019159335A1; GB202010975D0; WO2019159335A1; CN111712677B

Abstract

Provided is a refrigeration cycle device which has excellent reliability and can appropriately and quickly solve lubricant shortages in each outdoor unit. When the amount of lubricant in any one compressor is less than a set value, the amount of refrigerant circulating in the outdoor unit in which said compressor is present is made larger than the amount of refrigerant circulating in the other outdoor units.

Description

DESCRIPTION

REFRIGERATION CYCLE DEVICE

Technical Field

Embodiments described herein relate generally to a refrigeration cycle apparatus comprising a plurality of outdoor units.

Background Art

A multitype refrigeration cycle apparatus which comprises a plurality of outdoor units including a compressor and an outdoor heat exchanger, and a plurality of indoor units including an indoor heat exchanger, and controls the number of operating compressors and the capacity in the outdoor units in accordance with the sum of the request capacity of each indoor unit is known.

The compressor of each outdoor unit accommodates a motor, cylinder, etc., in a sealed casing together with a lubricant. The lubricant partially flows into the refrigeration cycle from the sealed casing in association with the discharge of a refrigerant. Thus, the lubricant may be insufficient in any one of the outdoor units. If the lubricant is insufficient, sliding portions such as a motor and a cylinder are in a state where oil has run out. Thus, the life of the compressor is adversely affected.

As a measure, controls for providing an oil separator in the refrigeration cycle and returning the lubricant stored in the oil separator to each compressor as needed are adopted.

Citation List Patent Literature Patent Literature 1: JP 2011-2160 A

Summary of Invention

Technical Problem By only returning the lubricant from the oil separator, lubricant shortages cannot be appropriately solved.

Embodiments described herein aim to provide a refrigeration cycle apparatus which has excellent reliability and can appropriately and quickly solve lubricant shortages in each outdoor unit.

Solution to Problem According to claim 1, a refrigeration cycle apparatus comprises a plurality of outdoor units including a compressor and an outdoor heat exchanger, a plurality of indoor units including an indoor heat exchanger, and a controller which, when an amount of lubricant in one of the compressors is less than a set value, makes an amount of refrigerant circulating in the outdoor unit in which the compressor is present greater than an amount of refrigerant circulating in the other outdoor units.

Brief Description of Drawings

FIG. 1 is a diagram showing the structure of a first embodiment.

FIG. 2 is a diagram showing the relationship between the ratio of the amount of refrigerant circulating in each outdoor unit of each embodiment and the rate of deviation of lubricant in each outdoor unit.

FIG. 3 is a flowchart showing the control of the first embodiment.

FIG. 4 is a diagram showing the structure of a second embodiment.

FIG. 5 is a flowchart showing the control of the second embodiment.

FIG. 6 is a diagram showing the structure of a third embodiment.

FIG. 7 is a flowchart showing the control of the third embodiment.

FIG. 8 is a diagram showing the structure of a fourth embodiment.

FIG. 9 is a flowchart showing the control of the fourth embodiment.

FIG. 10 is a flowchart following FIG. 9.

FIG. 11 is a diagram showing the structure of a fifth embodiment.

FIG. 12 is a flowchart showing the control of the fifth embodiment.

Mode for Carrying Out the Invention

[1] First Embodiment The first embodiment of the present invention is explained with reference to FIG. 1 to FIG. 3.

As shown in FIG. 1, a plurality of outdoor units Al and A2 are parallelly connected by piping, and a plurality of outdoor units Bl, B2..... Bn are connected to these outdoor units Al and A2 by piping.

By this piping connection, a refrigeration cycle apparatus for an air conditioner is structured.

<Structure of Outdoor Unit Al> Outdoor unit Al comprises a compressor la, high-pressure-side pipes 2a and 2 in which the discharged refrigerant of compressor la flows, an oil separator 3 into which the gaseous refrigerant of high-pressure-side pipe 2 flows, a four-way valve 4 in which the gaseous refrigerant having passed through the oil separator 3 flows, an outdoor heat exchanger 5 into which the gaseous refrigerant having passed through the four-way valve 4 flows, an electric expansion valve 6 which reduces the pressure of a liquid refrigerant supplied from the outdoor heat exchanger 5 to indoor units Bl, B2, . . . , Bn, a liquid-side packed valve 7a and a gas-side packed valve 7b for piping connection, an accumulator 8 in which the gaseous refrigerant having passed through indoor units Bl, B2, . . . , Bn flows via the above four-way valve 4, low-pressure-side pipes 9 and 9a which lead the gaseous refrigerant flowing out from the accumulator 8 to the inlet of compressor la, an outdoor fan 10 provided near the outdoor heat exchanger 5, a high-pressure-side temperature sensor 41 and a high-pressure-side pressure sensor 42 attached to the above high-pressure-side pipe 2, a low-pressure-side pressure sensor 43 attached to the above low-pressure-side pipe 9, a main controller 50, an inverter 51, etc. The above compressor la is a hermetic compressor which accommodates a motor M, a cylinder Q, etc., in a sealed casing together with a lubricant La. The above oil separator 3 separates the lubricant L contained in the gaseous refrigerant supplied from high-pressure-side pipe 2, internally retains the separated lubricant L and supplies the gaseous refrigerant after the separation to the four-way valve 4 side. The electric expansion valve 6 is a pulse motor valve in which the opening continuously changes in accordance with the number of input drive pulses.

Outdoor unit Al further comprises a gas returning pipe 11 having an end connected to high-pressure-side pipe 2, a gas returning pipe lla extending from the other end of gas returning pipe 11 and connected to low-pressure-side pipe 9a, a decompressor, for example, a capillary tube 12, provided in gas returning pipe 11, a capillary tube 13a provided in gas returning pipe lla, and a temperature sensor 44 attached to a downstream-side position as compared with a capillary tube 12 in gas returning pipe 11. Gas returning pipes 11 and lla return part of the gaseous refrigerant in high-pressure-side pipe 2a to low-pressure-side pipe 9a. Temperature sensor 44 detects temperature T1 of the gaseous refrigerant which passes through gas returning pipe 11 and whose pressure is reduced in capillary tube 12.

Outdoor unit Al further comprises an oil returning pipe 21a connected between a side portion of the sealed casing of compressor la and the other end of gas returning pipe 11, a check valve 12a and a decompressor, for example, a capillary tube 23a, provided in oil returning pipe 21a, and a temperature sensor 45a attached to a downstream-side position as compared with capillary tube 23a in oil returning pipe 21a. Oil returning pipe 21a is connected to a position having a predetermined height from the lower part of the sealed casing of compressor la. This connected position is the criterion for determining whether or not the amount of lubricant La in the sealed casing is greater than or equal to a set value.

For example, when the oil level of lubricant La reaches the connected position of oil returning pipe 21a, lubricant La flows in oil returning pipe 21a, and a gaseous refrigerant flows in gas returning pipe 11. The temperature of lubricant La flowing in oil returning pipe 21a is not decreased even when the pressure is reduced in capillary tube 23a. The temperature of the gaseous refrigerant flowing in gas returning pipe 11 is decreased when the pressure is reduced in capillary tube 12. In this case, detection temperature T1 of temperature sensor 44 is different from detection temperature T2a of temperature sensor 45a. Thus, the main controller 50 is allowed to determine that the current state is not a state of lubricant shortages in which the amount of lubricant La is less than a set value.

When the oil level of lubricant La does no reach the connected position of oil equalization pipe 21a, a gaseous refrigerant flows in oil returning pipe 21a, and a gaseous refrigerant also flows in gas returning pipe 11. The temperature of the gaseous refrigerant flowing in oil returning pipe 21a is decreased when the pressure is reduced in capillary tube 23a. The temperature of the gaseous refrigerant flowing in gas returning pipe 11 is also decreased when the pressure is reduced in capillary tube 12. In this case, detection temperature T1 of temperature sensor 44 is substantially equal to detection temperature T2a of temperature sensor 45a. Thus, the main controller 50 is allowed to determine that the current state is a state of lubricant shortages in which the amount of lubricant La is less than a set value.

An oil amount detection unit which detects the amount of lubricant La in the sealed casing of compressor la is structured by gas returning pipes 11 and lla, capillary tubes 12 and 13a, oil returning pipe 21a, check valve 22a, capillary tube 23a, temperature sensors 44 and 45a and the main controller 50.

Outdoor unit Al further comprises an oil returning pipe 14 connected between a side portion of the oil separator 3 and the other end of gas returning pipe 11, a resistor, for example, a capillary tube 15 provided in oil returning pipe 14 for controlling the oil amount, an oil returning pipe 16 connected to a downstream-side position as compared with capillary tube 15 in oil returning pipe 14 from the bottom portion of the oil separator 3, a resistor, for example, a capillary tube 17 provided in oil returning pipe 16 for adjusting the oil amount, an electromagnetic on-off valve 18 provided at a downstream-side position as compared with capillary tube 17 in oil returning pipe 16, the main controller 50 and inverter 51.

When a defined amount or greater amount of lubricant L is stored in the oil separator 3, the above oil returning pipe 14 returns lubricant L exceeding the defined amount to the inlet side of compressor la. The above oil returning pipe 16 is used to forcibly return lubricant L in the oil separator 3 to the inlet side of compressor la, and is electrically continuous by the release of the electromagnetic on-off valve 18. The above main controller 50 controls outdoor units Al and A2 and indoor units B1, B2, . . . , Bn as a whole. Inverter 51 converts the alternating voltage of a commercial alternating-current power supply into direct voltage, converts the direct voltage into a predetermined frequency Fa (Hz) and alternating voltage at a level corresponding to the predetermined frequency Fa, and outputs the alternating voltage as drive power for the motor M of compressor la. The predetermined frequency Fa is referred to as operation frequency Fa.

<Structure of Outdoor Unit A2> Outdoor unit A2 comprises a compressor lc, a lubricant Lc, a high-pressure-side pipe 2c, a lowpressure-side pipe 9c, an oil returning pipe 21c, a check valve 22c, a capillary tube 23c, a temperature sensor 45c, a controller 60, an inverter 61, etc., instead of compressor la, lubricant La, high-pressure-side pipe 2a, low-pressure-side pipe 9a, oil returning pipe 21a, check valve 22a, capillary tube 23a, temperature sensor 45a, the main controller 50 and inverter 51 of outdoor unit Al.

An oil amount detection unit which detects the amount of lubricant Lc in the sealed casing of compressor lc is structured by gas returning pipes 11 and 11c, capillary tubes 12 and 13c, oil returning pipe 21c, check valve 22c, capillary tube 23c, temperature sensors 44 and 45c and the main controller 50. Controller 60 notifies the main controller 50 of the result of detection of each temperature sensor and each pressure sensor of outdoor unit A2, and controls the operation of outdoor unit A2 based on an instruction from the main controller 50. Inverter 61 converts the alternating voltage of a commercial alternating-current power supply into direct voltage, converts the direct voltage into a predetermined frequency Fc (Hz) and alternating voltage at a level corresponding to the predetermined frequency Fc, and outputs the alternating voltage as drive power for the motor M of compressor lc. The predetermined frequency Fc is referred to as operation frequency Fc.

The other structures are the same as those of outdoor unit Al. Therefore, the detailed description thereof is omitted.

<Piping Structure> The liquid-side packed valve 7a of outdoor unit Al is connected to liquid-side packed valve 7a of outdoor unit A2 by a connection pipe P1. The gas-side packed valve 7b of outdoor unit Al is connected to the gas-side packed valve 7b of outdoor unit A2 by a connection pipe P2. An end of the indoor heat exchanger 32 of each of indoor units B1, B2, . . . Bn is connected to connection pipe P1 by piping via the electric expansion valve 31 of each of indoor units B1, B2..... Bn. The other end of each of the indoor heat exchangers 32 is connected to connection pipe P2 by piping.

By the above piping connection, a heat-pump-type refrigeration cycle is structured. The rated capacity of outdoor unit Al (the capacity of compressor la) is equal to the rated capacity of outdoor unit A2 (the capacity of compressor 1c).

Each of indoor units Bl, B2, . . . Bn comprises a controller 30. Controller 30 notifies the main controller 50 of the difference between the indoor temperature of the room in which each indoor unit is provided and a preset temperature set in advance as a request capacity, and controls the operation of each indoor unit based on an instruction from the main controller 50.

<Function of Main Controller 50> The main controller 50 comprises control sections 50a, 50b and 50c as the main functions.

Control section 50a is a structural element of the oil amount detection unit in each of outdoor units Al and A2, and detects the amounts of lubricants La and Lc in compressors la and lc by the above detection method based on detection temperature T1 of temperature sensor 44 in each of outdoor units Al and A2 and detection temperatures T2a and T2c of temperature sensors 45a and 45c.

When one of the amounts of lubricants La and Lc in compressors la and lc detected in control section 50a is in a shortage state less than a set value, control section 50b makes the amount of refrigerant circulating in the outdoor unit in which the compressor in a shortage state is present greater than the amount of refrigerant circulating in the other outdoor unit. Specifically, when the amount of lubricant La of compressor la is in a shortage state less than a set value, the capacity of outdoor unit Al in which compressor la is present (operation frequency Fa of compressor la) is increased, and the capacity of outdoor unit A2 (operation frequency Fc of compressor lc) is reduced by only the increase. When the amount of lubricant Lc of compressor lc is in a shortage state less than a set value, the capacity of outdoor unit A2 in which compressor lc is present is increased, and the capacity of outdoor unit Al is reduced by only the increase.

When both of the amounts of lubricants La and Lc detected in control section 50a are in a shortage state less than a set value, control section 50c sets the amount of refrigerant circulating in outdoor unit Al so as to be in the same state as the amount of refrigerant circulating in outdoor unit A2. Specifically, the capacity of outdoor unit Al (operation frequency Fc of compressor la) and the capacity of outdoor unit A2 (operation frequency Fc of compressor lc) are set to a predetermined capacity for oil collection (operation frequency Fo) in common.

FIG. 2 shows the relationship between the ratio of the amount of refrigerant circulating in each of outdoor units Al and A2 and the rate of deviation of lubricant L in each of outdoor units Al and A2 for reference. In the ratio of the amount of circulation "0.5" where the amount of refrigerant circulating in outdoor unit Al is equal to the amount of refrigerant circulating in outdoor unit A2, the rate of deviation of lubricant L to outdoor unit Al is 50%, and the rate of deviation of lubricant L to outdoor unit A2 is also 50. In an area greater than the ratio of the amount of circulation "0.5" where the amount of refrigerant circulating in outdoor unit Al is greater than the amount of refrigerant circulating in outdoor unit A2, the rate of deviation of lubricant L to outdoor unit Al is greater than or equal to 50%, and the rate of deviation of lubricant L to outdoor unit A2 is less than 50(o. In an area less than the ratio of the amount of circulation "0.5" where the amount of refrigerant circulating in outdoor unit Al is less than the amount of refrigerant circulating in outdoor unit A2, the rate of deviation of lubricant L to outdoor unit Al is less than 50%, and the rate of deviation of lubricant L to outdoor unit A2 is greater than or equal to <Control of Main Controller 50> The control of the main controller 50 is explained with reference to the flowchart of FIG. 3. Symbols S1 to S18 in the flowchart show processing steps.

The main controller 50 starts time count tl (S1), and compares time count tl with a predetermined certain time tls set in advance, for example, 10 minutes (S2).

When time count tl reaches the predetermined time tls (YES in S2), the main controller 50 detects the amounts of lubricants La and Lc in compressors la and lc by the above detection method based on detection temperatures T1 and T2a of temperature sensors 44 and 45a under the determination of an oil amount detection time point (S3). When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to a set value (NO in S4), the main controller 50 returns to the process of the first step S1 and starts time count tl again (S1).

When one of the detected amounts of lubricants La and Lc, for example, the amount of lubricant Lc, is in a shortage state less than the set value (YES in S4), the main controller 50 opens the electromagnetic on-off valve 18 of outdoor unit A2, and collects lubricant L of the oil separator 3 of outdoor unit A2 in compressor lc via oil returning pipe 16, capillary tube 17, oil returning pipe 14, oil returning pipes 11 and llc, capillary tube 13c and low-pressure-side pipe 9c (S5).

The main controller 50 starts time count t2 at the same time as the collection (S6), and compares time count t2 with a predetermined time t2s set in advance (S7). When time count t2 reaches the predetermined time t2s (YES in S7), the main controller 50 closes the electromagnetic on-off valve 18 of outdoor unit A2 and finishes the collection of lubricant L in compressor lc (S8).

In association with the end of the collection, the main controller 50 detects the amounts of lubricants La and Lc in compressors la and lc again based on detection temperatures Ti and T2a of temperature sensors 44 and 45a (S9). When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to a set value (YES in S10 and YES in S11), the main controller 50 returns to the process of the first step S1 and starts time count tl again (S1).

When, of the amounts of lubricants La and Lc detected in the above process of S9, the amount of lubricant La is in an appropriate state greater than or equal to the set value (YES in S10), and the amount of lubricant Lc is still in a shortage state less than the set value (NO in S11), the main controller 50 increases operation frequency Fc of compressor lc by only a predetermined value AF (S12), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases operation frequency Fa of compressor la by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2. By this decrease, in spite of the increase in the capacity of outdoor unit A2, the total capacity of outdoor units Al and A2 is maintained so as to be a value suitable for the sum of the request capacities of indoor units Bl, B2, . . . Bn.

When the capacity of outdoor unit A2 is increased, the amount of refrigerant returning to outdoor unit A2 from outdoor units Bl, B2, . . . Bn via connection pipe P2 is increased. When the amount of refrigerant circulating in outdoor unit A2 is increased, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amount of lubricant Lc in compressor lc is increased. Thus, lubricant shortages of compressor lc are solved.

In association with the above increase in operation frequency Fc, the main controller 50 starts time count t3 (S16), and compares time count t3 with a predetermined time t3s set in advance (S17). When time count t3 reaches the predetermined time t3s (YES in S17), the main controller 50 cancels the increase in the capacity of outdoor unit A2 by the increase in operation frequency Fc and the reduction in the capacity of outdoor unit Al by the decrease in operation frequency Fa (S18). Subsequently, the main controller 50 returns to the process of S9 and detects the amounts of lubricants La and Lc again (S9). When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to the set value (YES in S10 and YES in S11), the main controller 50 returns to the process of the first step S1 and restarts time count tl (S1).

When, of the detected amounts of lubricants La and Lc, the amount of lubricant La is in a shortage state less than the set value (NO in S10), and the amount of lubricant Lc is in an appropriate state greater than or equal to the set value (YES in S13), the main controller 50 increases operation frequency Fa of compressor la by only a predetermined value LE (S14), thereby increasing the capacity of outdoor unit Al. At the same time, the main controller 50 decreases operation frequency Fc of compressor lc by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al. By this decrease, in spite of the increase in the capacity of outdoor unit Al, the total capacity of outdoor units Al and A2 is maintained so as to be a value suitable for the sum of the request capacities of indoor units Bl, B2, . . . , Bn.

When the capacity of outdoor unit Al is increased, the amount of refrigerant returning to outdoor unit Al from indoor units Bl, B2, . . . , Bn is increased. When the amount of refrigerant circulating in outdoor unit Al is increased, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amount of lubricant La in compressor la is increased. Thus, the lubricant shortages of compressor la are solved.

In association with the above increase in operation frequency Fa, the main controller 50 starts time count t3 (S16), and compares time count t3 with a predetermined time t3s set in advance (S17). When time count t3 reaches the predetermined time t3s (YES in S17), the main controller 50 cancels the increase in the capacity of outdoor unit Al by the increase in operation frequency Fa and the reduction in the capacity of outdoor unit A2 by the decrease in operation frequency Fc (S18). In accordance with this cancel, the main controller 50 returns to the process of S9, and detects the amounts of lubricants La and Lc in compressors la and lc again based on detection temperatures Tl and T2a of temperature sensors 44 and 45a (S9). When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to the set value (YES in S10 and YES in S11), the main controller 50 returns to the process of the first step S1 and restarts time count tl (S1).

When both of the amounts of lubricants La and Lc detected in the above process of S9 are in a shortage state less than the set value (NO in S10 and NO in S13), the main controller 50 sets operation frequency Fa of compressor la and operation frequency Fc of compressor lc to operation frequency Fo for oil collection in common (S15). Operation frequency Fo is a value variably and sequentially set by the main controller 50 in accordance with the sum of the request capacities of indoor units B1, B2, . . . , Bn on the assumption that the total capacity of outdoor units Al and A2 based on operation frequencies Fa and Fc is maintained so as to be a value suitable for the sum of the request capacities of indoor units Bl, B2, Bn.

In this way, operation frequencies Fa and Fc are set to operation frequency Fo for oil collection in common. Thus, the capacity of outdoor unit Al and the capacity of outdoor unit A2 are set to a predetermined capacity corresponding to operation frequency Fo.

Accordingly, the amount of refrigerant circulating in outdoor unit Al is equal to the amount of refrigerant circulating in outdoor unit A2 (the ratio of the amount of circulation "0.5"). As a result, both the rate of deviation of lubricant L to outdoor unit Al and the rate of lubricant L to outdoor unit A2 are equalized so as to be 50'. In this structure, lubricant L flowing out in the refrigeration cycle uniformly and effectively returns to both compressor la and compressor lc, and the lubricant shortages of compressors la and lc are solved.

In association with the above setting of operation frequency Fo, the main controller 50 starts time count t3 (S16), and compares time count t3 with a predetermined time t3s set in advance (S17). When time count t3 reaches the predetermined time t3s (YES in S17), the main controller 50 cancels the setting of operation frequency Fo (S18). In accordance with this cancel, the main controller 50 returns to the process of S9, and detects the amounts of lubricants La and Lc again (S9).

As described above, when lubricant La of compressor la is in a shortage state, the capacity of outdoor unit Al in which compressor la is present is increased, thereby increasing the amount of refrigerant circulating in outdoor unit Al. When lubricant Lc of compressor lc is in a shortage state, the capacity of outdoor unit A2 in which compressor lc is present is increased, thereby increasing the amount of refrigerant circulating in outdoor unit A2. When both lubricants La and Lc of compressors la and lc are in a shortage state, the capacities of outdoor units Al and A2 are set to a predetermined capacity for oil collection, thereby setting the amounts of refrigerant circulating in outdoor units Al and A2 so as to be in the same state. In this way, the lubricant shortages of outdoor units Al and A2 can be appropriately and quickly solved.

[2] Second Embodiment The second embodiment of the present invention is explained with reference to FIG. 4 and FIG. 5. The structures of outdoor units Al and A2 are explained only with regard to portions different from those of the first embodiment.

As shown in FIG. 4, outdoor unit Al comprises two compressors la and lb, high-pressure-side pipes 2a and 2b in which the discharged refrigerant of compressors la and lb flows, a high-pressure-side pipe 2 which the refrigerant of high-pressure-side pipes 2a and 2b meets, low-pressure-side pipes 9a and 9b leading the gaseous refrigerant of a low-pressure-side pipe 9 to the inlets of compressors la and lb, gas returning pipes lia and llb leading the gaseous refrigerant of a gas returning pipe 11 to low-pressure-side pipes 9a and 9b, oil returning pipes 21a and 21b connected between side portions of sealed casings of compressors la and lb and the other end of gas returning pipe 11, check valves 12a and 12b and decompressors, for example, capillary tubes 23a and 23b, provided in oil returning pipes 21a and 21b, temperature sensors 45a and 45b attached to downstream-side positions as compared with capillary tubes 23a and 23b in oil returning pipes 21a and 12b, inverters 51 and 52, etc. Inverter 52 converts the alternating voltage of a commercial alternating-current power supply into direct voltage, converts the direct voltage into a predetermined frequency Fb (Hz) and alternating voltage at a level corresponding to the predetermined frequency Fb, and outputs the alternating voltage as drive power for the motor M of compressor lb. The predetermined frequency Fb is referred to as operation frequency Fb.

An oil amount detection unit which detects the amount of lubricant La in the sealed casing of compressor la is structured by gas returning pipes 11 and 11a, capillary tubes 12 and 13a, oil returning pipe 21a, check valve 22a, capillary tube 23a, temperature sensors 44 and 45a and a main controller 50. An oil amount detection unit which detects the amount of lubricant Lb in the sealed casing of compressor lb is structured by gas returning pipes 11 and 11b, capillary tubes 12 and 13b, oil returning pipe 21b, check valve 22b, capillary tube 23b, temperature sensors 44 and 45b and the main controller 50.

Outdoor unit A2 comprises two compressors lc and ld, high-pressure-side pipes 2c and 2d in which the discharged refrigerant of compressors lc and id flows, a high-pressure-side pipe 2 which the refrigerant of high-pressure-side pipes 2c and 2d meets, low-pressure-side pipes 9c and 9d leading the gaseous refrigerant of a low-pressure-side pipe 9 to the inlets of compressors lc and ld, gas returning pipes llc and lld leading the gaseous refrigerant of a gas returning pipe 11 to lowpressure-side pipes 9c and 9d, oil returning pipes 21c and 21d connected between side portions of sealed casings of compressors lc and ld and the other end of gas returning pipe 11, check valves 12c and 12d and decompressors, for example, capillary tubes 23c and 23d, provided in oil returning pipes 21c and 21d, temperature sensors 45c and 45d attached to downstream-side positions as compared with capillary tubes 23c and 23d in oil returning pipes 21c and 12d, inverters 61 and 62, etc. Inverter 62 converts the alternating voltage of a commercial alternating-current power supply into direct voltage, converts the direct voltage into a predetermined frequency Fd (Hz) and alternating voltage at a level corresponding to the predetermined frequency Fd, and outputs the alternating voltage as drive power for the motor M of compressor ld. The predetermined frequency Ed is referred to as operation frequency Fd.

An oil amount detection unit which detects the amount of lubricant Lc in the sealed casing of compressor lc is structured by gas returning pipes 11 and llc, capillary tubes 12 and 13c, oil returning pipe 21c, check valve 22c, capillary tube 23c, temperature sensors 44 and 45c and the main controller 50. An oil amount detection unit which detects the amount of lubricant Ld in the sealed casing of compressor ld is structured by gas returning pipes 11 and 11d, capillary tubes 12 and 13d, oil returning pipe 21d, check valve 22d, capillary tube 23d, temperature sensors 44 and 45d and the main controller 50.

A controller 60 notifies the main controller 50 of the result of detection of each temperature sensor and each pressure sensor of outdoor unit A2, and controls the operation of outdoor unit A2 based on an instruction from the main controller 50.

Control section 50a of the main controller 50 is a structural element of the oil amount detection unit in each of outdoor units Al and A2, and detects the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld based on detection temperature T1 of each temperature sensor 44 and detection temperatures T2a, T2b, T2c and T2d of temperature sensors 45a, 45b, 45c and 45d in outdoor units Al and A2.

When one of the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld detected in control section 50a is in a shortage state less than a set value, a control section 50b makes the amount of refrigerant circulating in the outdoor unit in which the compressor in a shortage state is present greater than the amount of refrigerant circulating in the other outdoor unit. Specifically, when only the amount of lubricant La of compressor la is less than a set value, the capacity of outdoor unit Al in which compressor la is present (total operation frequency Fl of operation frequency Fa and operation frequency Fb) is increased, and the capacity of outdoor unit A2 (total operation frequency F2 of operation frequency Fc and operation frequency Fd) is reduced by only the increase. When only the amount of lubricant Lc of compressor lc is less than a set value, the capacity of outdoor unit A2 in which compressor lc is present (total operation frequency F2) is increased, and the capacity of outdoor unit Al (total operation frequency Fl) is reduced by only the increase.

When all the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld detected in control section 50a are in a shortage state less than a set value, a control section 50c sets the amount of refrigerant circulating in outdoor unit Al so as to be in the same state as the amount of refrigerant circulating in outdoor unit A2. Specifically, when all the amounts of lubricants La, Lb, Lc and Ld are in a shortage state less than a set value, on the condition that the number of operating compressors la and lb at the current time point in outdoor unit Al is equal to the number of operating compressors lc and ld at the current time point in outdoor unit A2, the capacity of outdoor unit Al (total operation frequency Fl) and the capacity of outdoor unit A2 (total operation frequency F2) are set to a predetermined capacity for oil collection (operation frequency Fo) in common.

As supplementary controls, when all the amounts of lubricants La, Lb, Lc and Ld are in a shortage state less than a set value, and the number of operating compressors la and lb at the current time point in outdoor unit Al is greater than the number of operating compressors lc and ld at the current time point in outdoor unit A2, control section 50c preferentially increases the capacity of outdoor unit Al (total operation frequency Fl) and reduces the capacity of outdoor unit A2 (total operation frequency F2) by only the increase. When all the amounts of lubricants La, Lb, Lc and Ld are in a shortage state less than a set value, and the number of operating compressors lc and ld at the current time point in outdoor unit A2 is greater than the number of operating compressors la and lb in outdoor unit Al, the capacity of outdoor unit A2 (total operation frequency F2) is preferentially increased, and the capacity of outdoor unit Al (total operation frequency Fl) is reduced by only the increase.

The other structures are the same as those of the first embodiment. Therefore, the detailed description thereof is omitted.

The control performed by the main controller 50 is explained below with reference to the flowchart of FIG. 5. The explanation of the same control as the control of the first embodiment is omitted, and only control different from the control of the first embodiment is explained.

When time count tl reaches a predetermined time tls (YES in S2), the main controller 50 detects the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld based on the determination of an oil amount detection time point (S3). When the detected amounts of lubricants La, Lb, Lc and Ld are in an appropriate state greater than or equal to a set value (NO in S4), the main controller 50 returns to the process of the first step S1 and starts time count tl again (S1).

When, of the detected amounts of lubricants La, Lb, Lc and Ld, for example, the amount of lubricant Lc is in a shortage state less than the set value (YES in S4), the main controller 50 opens the electromagnetic on-off valve 18 of outdoor unit A2, and collects lubricant L of the oil separator 3 of outdoor unit A2 in compressors lc and ld via an oil returning pipe 16, a capillary tube 17, an oil returning pipe 14, oil returning pipes 11, 11c and 11d, capillary tubes 13c and 13d and low-pressure-side pipes 9c and 9d (S5). After the completion of this collection, the main controller 50 detects the amounts of lubricants La, Lb, Lc and Ld again (S9).

When the detected amounts of lubricants La, Lb, Lc and Ld are in an appropriate state greater than or equal to a set value (YES in S10 and YES in S11), the main controller 50 returns to the process of the first step S1 and starts time count tl again (S1).

When the above detected amount of lubricant Lc is still in a shortage state less than a set value (YES in S10 and NO in S11), the main controller 50 increases total operation frequency F2 of operation frequency Fc of compressor lc and operation frequency Fd of compressor ld by only a predetermined value LB' (S12), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases total operation frequency Fl of operation frequency Fa of compressor la and operation frequency Fb of compressor lb by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

When the capacity of the outdoor unit A2 is increased, the amount of refrigerant returning to outdoor unit A2 from indoor units Bl, B2, . . . , Bn via a connection pipe P2 is increased. When the amount of refrigerant circulating in outdoor unit A2 is increased, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. Thus, the lubricant shortages of compressor lc are solved.

When, of the amounts of lubricants La, Lb, Lc and Ld detected in the above process of S9, for example, the amount of lubricant La is in a shortage state (NO in S10 and YES in S13), the main controller DO increases total operation frequency Fl by only a predetermined value AF (S14), thereby increasing the capacity of outdoor unit Al. At the same time, the main controller 50 decreases total operation frequency F2 by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

When the capacity of outdoor unit Al is increased, the amount of refrigerant returning to outdoor unit Al from indoor units Bl, B2, . . . , Bn is increased. When the amount of refrigerant circulating in outdoor unit Al is increased, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. Thus, the lubricant shortages of compressor la are solved.

When all the amounts of lubricants La, Lb, Lc and Ld detected in the above process of S9 are in a shortage state less than the set value (NO in S10 and NO in S13), the main controller 50 determines the great/less relationship between the number of operating compressors la and lb in outdoor unit Al and the number of operating compressors lc and ld in outdoor unit A2 (S21 and S23).

When the number of operating compressors la and lb in outdoor unit Al is equal to the number of operating compressors lc and ld in outdoor unit A2 (NO in S21 and No in S23), the main controller 50 sets total operation frequencies Fl and F2 to operation frequency Fo for oil collection in common (S15).

In this way, total operation frequencies Fl and F2 are set to operation frequency Fo for oil collection in common. Thus, the capacity of outdoor unit Al and the capacity of outdoor unit A2 are set to a predetermined capacity corresponding to operation frequency Fo. Accordingly, the amount of refrigerant circulating in outdoor unit Al is equal to the amount of refrigerant circulating in outdoor unit A2. As a result, both the rate of deviation of lubricant L to outdoor unit Al and the rate of deviation of lubricant oil L to outdoor unit A2 are equalized so as to be 50-3. In this structure, lubricant L flowing out in the refrigeration cycle uniformly and effectively returns to both outdoor unit Al and outdoor unit A2, and the lubricant shortages of compressors la, lb, lc and ld are solved.

When the number of operating compressors la and lb in outdoor unit Al is greater than the number of operating compressors lc and ld in outdoor unit A2 (YES in S21), the main controller 50 increases total operation frequency Fl by only a predetermined value AF (S22), thereby increasing the capacity of outdoor unit Al. At the same time, the main controller 50 decreases total operation frequency F2 by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

The rate of deviation of lubricant L to outdoor unit Al is increased by increasing the capacity of outdoor unit Al in which the number of operating compressors is great and preferentially increasing the amount of refrigerant circulating in outdoor unit Al. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. Thus, at least the lubricant shortages on the compressor la side are solved.

When the number of operating compressors lc and ld in outdoor unit A2 is greater than the number of operating compressors la and lb in outdoor unit Al (NO in S21 and YES in S23), the main controller 50 increases total operation frequency F2 by only a predetermined value AF (S24), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases total operation frequency Fl by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

The rate of deviation of lubricant L to outdoor unit A2 is increased by increasing the capacity of outdoor unit A2 in which the number of operating compressors is great and preferentially increasing the amount of refrigerant circulating in outdoor unit A2. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. Thus, at least the lubricant shortages on the outdoor unit A2 side are solved.

As described above, when a lubricant is insufficient on the outdoor unit Al side, the capacity of outdoor unit Al is increased, thereby increasing the amount of refrigerant circulating in outdoor unit Al. When a lubricant is insufficient on the outdoor unit A2 side, the capacity of outdoor unit A2 is increased, thereby increasing the amount of refrigerant circulating in outdoor unit A2. In this way, the lubricant shortages of outdoor units Al and A2 can be appropriately and quickly solved.

When all lubricants La, Lb, Lc and Ld are in a shortage state, and the number of operating compressors in outdoor unit Al is equal to the number of operating compressors in outdoor unit A2, the lubricant shortages in outdoor units Al and A2 can be appropriately and quickly solved by setting the capacities of outdoor units Al and A2 to a predetermined capacity for oil collection and equalizing the amounts of refrigerant circulating in outdoor units Al and A2. When all lubricants La, Lb, Lc and Ld are in a shortage state, and the number of operating compressors in outdoor unit Al is different from the number of operating compressors in outdoor unit A2, the lubricant shortages of at least one outdoor unit can be appropriately and quickly solved by increasing the capacity of the outdoor unit in which the number of operating compressors is great and preferentially increasing the amount of refrigerant circulating in the outdoor unit.

[3] Third Embodiment The third embodiment of the present invention is explained with reference to FIG. 6 and FIG. 7. The structures of outdoor units Al and A2 are explained only with regard to portions different from those of the first embodiment.

As shown in FIG. 6, outdoor unit Al comprises a compressor la, a bypass pipe 71 which bypasses the refrigerant of a high-pressure-side pipe 2a to an accumulator 8 connected to a low-pressure-side pipe 9, and an electromagnetic on-off value 72 provided in the bypass pipe 71. Outdoor unit A2 comprises a compressor lc, a bypass pipe 71 which bypasses the refrigerant of a high-pressure-side pipe 2c to an accumulator 8 connected to a low-pressure-side pipe 9, and an electromagnetic on-off value 72 provided in the bypass pipe 71.

Control section 50a of a main controller 50 is a structural element of an oil amount detection unit in each of outdoor units Al and A2, and detects the amounts of lubricants La and Lc in compressors la and lc based on detection temperature T1 of a temperature sensor 44 in each of outdoor units Al and A2 and detection temperatures T2a and T2c of temperature sensors 45a and 45c.

When one of the amounts of lubricants La and Lc in compressors la and lc detected in control section 50a is in a shortage state less than a set value, a control section 50b determines whether or not an increase in the capacity of the outdoor unit in which the compressor in a shortage state is present is allowable. When it is allowable, control section 50b increases the capacity of the outdoor unit and reduces the capacity of the other outdoor unit by only the increase. When it is not allowable, control section 50b opens the electromagnetic on/off valve 72 in the other outdoor unit and bypasses the gaseous refrigerant on the high-pressure side to the low-pressure side. Specifically, when only the amount of lubricant La of compressor la is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in operation frequency Fa) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit Al is increased, and the capacity of outdoor unit A2 (operation frequency Fc) is reduced by only the increase. When it is not allowable, the electromagnetic on/off valve 72 of outdoor unit A2 is opened to bypass the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. When only the amount of lubricant Lc of compressor lc is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in operation frequency Fc) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit A2 is increased, and the capacity of outdoor unit Al (operation frequency Fa) is reduced by only the increase. When it is not allowable, the electromagnetic on/off valve 72 of outdoor unit Al is opened to bypass the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side.

When both of the amounts of lubricants La and Lc detected in control section 50a are in a shortage state less than a set value, a control section 50c sets the amount of refrigerant circulating in outdoor unit Al so as to be in the same state as the amount of refrigerant circulating in outdoor unit A2. Specifically, the capacity of outdoor unit Al (operation frequency Fc) and the capacity of outdoor unit A2 (operation frequency Fc) are set to a predetermined capacity for oil collection (operation frequency Fo) in common.

The control performed by the main controller 50 is explained with reference to the flowchart of FIG. 7. The explanation of the same control as the control of the first embodiment is omitted, and only control different from the control of the first embodiment is explained.

When, of the amounts of lubricants La and Lc detected in the process of S9, the amount of lubricant La is in an appropriate state greater than or equal to a set value (YES in S10), and the amount of lubricant Lc is in a shortage state less than the set value (NO in S11), the main controller 50 determines whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in operation frequency Fc) is allowable at the current time point (S12a). For example, when the cooling load is not large and operation frequency Fc has a sufficient increase allowable width for the upper limit in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit A2 is allowable (YES in S12a). When the cooling load is large because of an increase in external temperature, etc., and operation frequency Fc reaches the upper limit or its vicinity in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit A2 is not allowable (NO in Sl2a).

When an increase in the capacity of outdoor unit A2 is allowable (YES in Sl2a), the main controller 50 increases operation frequency Fc by only a predetermined value AF (S12b), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases operation frequency Fa by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

When the capacity of outdoor unit A2 is increased, the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amount of lubricant Lc in compressor lc is increased. The lubricant shortages of compressor lc are solved.

When an increase in the capacity of outdoor unit A2 is not allowable (NO in S12a), the main controller opens the electromagnetic on/off valve 72 of outdoor unit Al and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side. By this bypass, in other words, high-pressure release, the capacity of compressor Al is reduced. When the capacity of outdoor unit Al is reduced, the capacity of outdoor unit A2 is relatively increased, and the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amount of lubricant Lc in compressor lc is increased. The lubricant shortages of compressor lc are solved.

When, of the amounts of lubricants La and Lc detected in the process of S9, the amount of lubricant Lc is in an appropriate state greater than or equal to a set value (NO in S10), and the amount of lubricant La is in a shortage state less than a set value (YES in S13), the main controller 50 determines whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in operation frequency Fa) is allowable at the current time point (S14a). When the cooling load is not very large and operation frequency Fa of compressor la has a sufficient increase allowable width for the upper limit in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit Al is allowable (YES in Sl4a). When the cooling load is large because of an increase in external temperature, etc., and operation frequency Fa of compressor la reaches the upper limit or its vicinity in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit Al is not allowable (NO in Sl4a).

When an increase in the capacity of outdoor unit Al is allowable (YES in S14a), the main controller 50 increases operation frequency Fa by only a predetermined value tF (S14b), thereby increasing the capacity of outdoor unit Al. At the same time, the main controller 50 decreases operation frequency Fc by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

When the capacity of outdoor unit Al is increased, the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amount of lubricant La in compressor la is increased. The lubricant shortages of compressor la are solved.

When an increase in the capacity of outdoor unit A2 is not allowable (NO in S14a), the main controller 50 opens the electromagnetic on/off valve 72 of outdoor unit A2 and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. By this bypass, in other words, high-pressure release, the capacity of compressor A2 is reduced. When the capacity of outdoor unit A2 is reduced, the capacity of outdoor unit Al is relatively increased, and the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amount of lubricant La in compressor la is increased. The lubricant shortages of compressor la are solved.

[4] Fourth Embodiment The fourth embodiment of the present invention is explained with reference to FIG. 8 to FIG. 10. The structures of outdoor units Al and A2 are explained only with regard to portions different from those of the first embodiment.

As shown in FIG. 8, outdoor unit Al comprises two compressors la and lb, a bypass pipe 71 which bypasses the refrigerant of a high-pressure-side pipe 2a to an accumulator 8 connected to a low-pressure-side pipe 9, and an electromagnetic on-off value 72 provided in the bypass pipe 71. Outdoor unit A2 comprises two compressors lc and lb, a bypass pipe 71 which bypasses the refrigerant of a high-pressure-side pipe 2c to an accumulator 8 connected to a low-pressure-side pipe 9, and an electromagnetic on-off value 72 provided in the bypass pipe 71.

Control section 50a of a main controller 50 is a structural element of an oil amount detection unit in outdoor units Al and A2, and detects the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld based on detection temperature Ti of each temperature sensor 44 and detection temperatures T2a, T2b, T2c and T2d of temperature sensors 45a, 45b, 45c and 45d in outdoor units Al and A2.

When one of the amounts of lubricants La, Lb, Lc and Ld in compressors la, lb, lc and ld detected in control section 50a is in a shortage state less than a set value, a control section 50b determines whether or not an increase in the capacity of the outdoor unit in which the compressor in a shortage state is present is allowable. When it is allowable, control section 50b increases the capacity of the outdoor unit and reduces the capacity of the other outdoor unit by only the increase. When it is not allowable, control section 50b opens the electromagnetic on/off valve 72 in the other outdoor unit and bypasses the gaseous refrigerant on the high-pressure side to the low-pressure side. Specifically, when only the amount of lubricant La of compressor la is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in total operation frequency Fl) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit Al is increased, and the capacity of outdoor unit A2 (total operation frequency F2) is reduced by only the increase. When it is not allowable, the electromagnetic on/off valve 72 of outdoor unit A2 is opened to bypass the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. When only the amount of lubricant Lc of compressor lc is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in total operation frequency F2) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit A2 is increased, and the capacity of outdoor unit Al (total operation frequency Fl) is reduced by only the increase. When it is not allowable, the electromagnetic on/off valve 72 of outdoor unit Al is opened to bypass the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side.

When all the amounts of lubricants La, Lb, Lc and Ld detected in control section 50a are in a shortage state less than a set value, a control section 50c sets the amount of refrigerant circulating in outdoor unit Al so as to be in the same state as the amount of refrigerant circulating in outdoor unit A2.

Specifically, when all the amounts of lubricants La, Lb, Lc and Ld are in a shortage state less than a set value, on the condition that the number of operating compressors la and lb at the current time point in outdoor unit Al is equal to the number of operating compressors lc and ld at the current time point in outdoor unit A2, the capacity of outdoor unit Al (total operation frequency Fl) and the capacity of outdoor unit A2 (total operation frequency F2) are set to a predetermined capacity for oil collection (operation frequency Fo) in common.

As supplementary controls, when all the amounts of lubricants La, Lb, Lc and Ld are in a shortage state less than a set value, and the number of operating compressors la and lb at the current time point is greater than the number of operating compressors lc and ld at the current time point, control section 50c determines whether or not an increase in the capacity of outdoor unit Al (an increase in total operation frequency Fl) is allowable at the current time point.

When it is allowable, control section 50c preferentially increases the capacity of outdoor unit Al (total operation frequency Fl) and reduces the capacity of outdoor unit A2 (total operation frequency F2) by only the increase. When it is not allowable, control section 50c opens the electromagnetic on/off valve 72 of outdoor unit A2 and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. When the number of operating compressors lc and ld at the current time point is greater than the number of operating compressors la and lb at the current time point, whether or not an increase in the capacity of outdoor unit A2 in which compressors lc and ld are present (an increase in total operation frequency F2) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit A2 (total operation frequency F2) is preferentially increased, and the capacity of outdoor unit Al (total operation frequency Fl) is reduced by only the increase. When it is not allowable, the electromagnetic on/off valve 72 of outdoor unit Al is opened to bypass the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side.

The control performed by the main controller 50 is explained with reference to the flowchart of FIG. 9 and the flowchart of FIG. 10 following FIG. 9. The explanation of the same control as the control of the second embodiment is omitted, and only control different from the control of the second embodiment is explained.

When, of the amounts of lubricants La, Lb, Lc and Ld detected in the process of S9, only the amount of lubricant Lc is in a shortage state less than a set value (YES in S10 and NO in S11), the main controller 50 determines whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in total operation frequency F2) is allowable at the current time point (512x). For example, when the cooling load is not very large and total operation frequency F2 has a sufficient increase allowable width for the upper limit in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit A2 is allowable (YES in S12x). When the cooling load is large because of an increase in external temperature, etc., and total operation frequency F2 reaches the upper limit or its vicinity in terms of control, the main controller 50 determines that an increase the capacity of outdoor unit A2 is not allowable (NO in S12x).

When an increase in the capacity of outdoor unit A2 is allowable (YES in S12x), the main controller 50 increases total operation frequency F2 by only a predetermined value tF (S12y), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases total operation frequency Fl by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

When the capacity of outdoor unit A2 is increased, the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. The lubricant shortages of compressor lc are solved.

When an increase in the capacity of outdoor unit A2 is not allowable, (NO in S12x), the main controller 50 opens the electromagnetic on/off valve 72 of outdoor unit Al and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side. By this bypass, in other words, high-pressure release, the capacity of compressor Al is reduced. When the capacity of outdoor unit Al is reduced, the capacity of outdoor unit A2 is relatively increased, and the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. The lubricant shortages of compressor lc are solved.

When, of the amounts of lubricants La, Lb, Lc and Ld detected in the process of S9, only the amount of lubricant La is in a shortage state less than a set value (NO in S10 and NO in S13), the main controller 50 determines whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in total operation frequency Fl) is allowable at the current time point (S14x). For example, when the cooling load is not very large and total operation frequency Fl has a sufficient increase allowable width for the upper limit in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit Al is allowable (YES in S14x). When the cooling load is large because of an increase in external temperature, etc., and total operation frequency Fl reaches the upper limit or its vicinity in terms of control, the main controller 50 determines that an increase in the capacity of outdoor unit Al is not allowable (NO in S14x).

When an increase in the capacity of outdoor unit Al is allowable (YES in S14x), the main controller 50 increases total operation frequency Fl by only a predetermined value AF (S14y), thereby increasing the capacity of outdoor unit Al. At the same time, the main controller 50 decreases total operation frequency F2 by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

When the capacity of outdoor unit Al is increased, the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. The lubricant shortages of compressor la are solved.

When an increase in the capacity of outdoor unit A2 is not allowable, (NO in S14s), the main controller 50 opens the electromagnetic on/off valve 72 of outdoor unit A2 and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. By this bypass, in other words, high-pressure release, the capacity of compressor A2 is reduced. When the capacity of outdoor unit A2 is reduced, the capacity of outdoor unit Al is relatively increased, and the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. The lubricant shortages of compressor la are solved.

When all the amounts of lubricants La, Lb, Lc and Ld detected in the above process of S9 are in a shortage state less than a set value (NO in S10 and NO in S13), the main controller 50 determines the great/less relationship between the number of operating compressors la and lb in outdoor unit Al at the current time point and the number of operating compressors lc and ld in outdoor unit A2 at the current time point (S21 and S23).

When the number of operating compressors la and lb at the current time point is equal to the number of operating compressors lc and ld at the current time point (NO in S21 and NO in S23), the main controller 50 sets total operation frequency Fl and total operation frequency F2 to operation frequency Fo for oil collection in common (S15).

When the number of operating compressors la and lb at the current time point is greater than the number of operating compressors lc and ld at the current time point (YES in S21), whether or not an increase in total operation frequency Fl of compressors la and lb is allowable is determined (S22x). When an increase in total operation frequency Fl is allowable (YES in S22x), the main controller 50 increases total operation frequency Fl by only a predetermined value AF (S22y), thereby preferentially increasing the capacity of outdoor unit Al. At the same time, the main controller decreases total operation frequency F2 by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

When the capacity of outdoor unit Al is increased, the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. At least the lubricant shortages on the outdoor unit Al side are solved.

When an increase in the capacity of outdoor unit Al is not allowable (NO in S22x), the main controller opens the electromagnetic on/off valve 72 of outdoor unit A2 and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit A2 to the low-pressure side. By this bypass, in other words, high-pressure release, the capacity of compressor A2 is reduced. When the capacity of outdoor unit A2 is reduced, the capacity of outdoor unit Al is relatively increased, and the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased. As a result, the amounts of lubricants La and Lb in compressors la and lb are increased. At least the lubricant shortages on the outdoor unit Al side are solved.

When the number of operating compressors lc and ld at the current time point is greater than the number of operating compressors la and lb at the current time point (NO in S21 and YES in S23), whether or not an increase in total operation frequency F2 of compressors lc and ld is allowable is determined (S24x). When an increase in total operation frequency F2 is allowable (YES in 524x), the main controller 50 increases total operation frequency F2 by only a predetermined value AF (S24y), thereby preferentially increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases total operation frequency Fl by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

When the capacity of outdoor unit A2 is increased, the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. At least the lubricant shortages on the outdoor unit A2 side are solved.

When an increase in total operation frequency F2 is not allowable (NO in 324x), the main controller 50 opens the electromagnetic on/off valve 72 of outdoor unit Al and bypasses the gaseous refrigerant on the high-pressure side in outdoor unit Al to the low-pressure side. By this bypass of gaseous refrigerant, in other words, high-pressure release, the capacity of compressor Al is reduced. When the capacity of outdoor unit Al is reduced, the capacity of outdoor unit A2 is relatively increased, and the amount of refrigerant circulating in outdoor unit A2 is increased.

Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased. As a result, the amounts of lubricants Lc and Ld in compressors lc and ld are increased. At least the lubricant shortages on the outdoor unit A2 side are solved.

[5] Fifth Embodiment The fifth embodiment of the present invention is explained with reference to FIG. 11 and FIG. 12. The structures of outdoor units Al and A2 are explained only with regard to portions different from those of the first embodiment.

As shown in FIG. 11, outdoor unit Al comprises a compressor la, a heat exchanger 81, a bypass pipe 82 and an electric expansion valve 83. The bypass pipe 82 is connected from a liquid-side pipe between an outdoor heat exchanger 5 and outdoor units Bl, B2, . . . Bn to a low-pressure-side pipe between a four-way valve 4 and an accumulator 8. The electric expansion valve 83 is a pulse monitor valve in which the opening is variable, and is provided in the bypass pipe 82. The heat exchanger 81 includes a first flow path 81a provided in the liquid-side pipe between the outdoor heat exchanger 5 and outdoor units Bl, B2, . . . , Bn, and a second flow path 81b provided at a downstream-side position as compared with the electric expansion valve 83 in the bypass pipe 82, and performs heat exchange of refrigerant between the first flow path 81a and the second flow path 81b.

When the electric expansion valve 83 is opened, a liquid refrigerant in the liquid-side pipe flows into the flow channel 81b of the heat exchanger 81. The supplied refrigerant takes heat from the liquid refrigerant of the flow path 81a, evaporates and becomes a gaseous refrigerant. The gaseous refrigerant passes through the bypass pipe 82 and flows into the low-pressure-side pipe between the four-way valve 4 and the accumulator 8.

Outdoor unit A2 comprises a compressor lc, and comprises a heat exchanger 81, a bypass pipe 82 and an electric expansion valve 83 which are the same as those of outdoor unit Al.

Control section 50a of a main controller 50 is a structural element of an oil amount detection unit in outdoor units Al and A2, and detects the amounts of lubricants La and Lc in compressors la and lc based on detection temperature T1 of each temperature sensor 44 and detection temperatures T2a and T2c of temperature sensors 45a and 45c in outdoor units Al and A2.

When one of the amounts of lubricants La and Lc in compressors la and lc detected in control section 50a is in a shortage state less than a set value, a control section 50b determines whether or not an increase in the capacity of the outdoor unit in which the compressor in a shortage state is present is allowable. When it is allowable, control section 50b increases the capacity of the outdoor unit and reduces the capacity of the other outdoor unit by only the increase. When it is not allowable, control section 50b opens the electric expansion valve 83 in the other outdoor unit with a predetermined opening and bypasses the refrigerant of the liquid-side pipe to the low-pressure side. Specifically, when only the amount of lubricant La of compressor la is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in operation frequency Fa) is allowable at the current time point is determined. When it is allowable, the capacity of outdoor unit Al is increased, and the capacity of outdoor unit A2 (operation frequency Fc) is reduced by only the increase. When it is not allowable, the electric expansion valve 83 of outdoor unit A2 is opened with a predetermined opening, and the opening of the electric expansion valve 83 which bypasses the liquid refrigerant of the liquid-side pipe in outdoor unit A2 to the low-pressure side is increased in stages by each predetermined amount. When only the amount of lubricant Lc of compressor lc is in a shortage state less than a set value, whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in operation frequency Fc) is allowable at the current time point is determined.

When it is allowable, the capacity of outdoor unit A2 is increased, and the capacity of outdoor unit Al (operation frequency Fa) is reduced by only the increase. When it is not allowable, the electric expansion valve 83 of outdoor unit Al is opened with a predetermined opening, and the liquid refrigerant of the liquid-side pipe in outdoor unit Al is bypassed to the low-pressure side, and the opening of the electric expansion valve 83 is increased in stages by each predetermined amount.

When both of the amounts of lubricants La and Lc detected in control section 50a are in a shortage state less than a set value, control section 50c sets the amount of refrigerant circulating in outdoor unit Al so as to be in the same state as the amount of refrigerant circulating in outdoor unit A2. Specifically, the capacity of outdoor unit Al (operation frequency Fc) and the capacity of outdoor unit A2 (operation frequency Fc) are set to a predetermined capacity for oil collection (operation frequency Fo) in common.

The control performed by the main controller 50 is explained with reference to the flowchart of FIG. 12. The explanation of the same control as the control of the first embodiment is omitted, and only control different from the control of the first embodiment is explained.

When, of the amounts of lubricants La and Lc detected in the process of S9, the amount of lubricant Lc is in a shortage state less than a set value (YES in S10 and NO in S11), the main controller 50 determines whether or not an increase in the capacity of outdoor unit A2 in which compressor lc is present (an increase in operation frequency Fc) is allowable at the current time point (S12a).

When an increase in the capacity of outdoor unit A2 is allowable (YES in S12a), the main controller 50 increases operation frequency Fc by only a predetermined value tF (S12b), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases operation frequency Fa by only the predetermined value to reduce the capacity of outdoor unit Al by only the increase in the capacity of outdoor unit A2.

When an increase in the capacity of outdoor unit A2 is not allowable (NO in S12a), the main controller 50 opens the electric expansion valve 83 of outdoor unit Al with a predetermined opening (initial opening) and bypasses the liquid refrigerant of the liquid-side pipe in outdoor unit Al to the low-pressure side (S12c). By this bypass, the capacity of compressor Al is reduced. When the capacity of outdoor unit Al is reduced, the capacity of outdoor unit A2 is relatively increased, and the amount of refrigerant circulating in outdoor unit A2 is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit A2 is increased, and the rate of deviation of lubricant L to outdoor unit Al is decreased.

At the time of this bypass, the main controller 50 increases count value N by one (S31). The main controller 50 starts time count t3 (S16), and compares time count t3 with a predetermined time t3s set in advance (S17). When time count t3 reaches the predetermined time t3s (YES in S17), the main controller 50 cancels the bypass applied by the release of the electric expansion valve 83 (S18).

Subsequently, the main controller 50 returns to the process of S9 and detects the amounts of lubricants La and Lc again (S9). When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to a set value (YES in S10 and YES in S11), the main controller 50 clears count value N so as to be zero (S30), returns to the first process of S1 and restarts time count tl (S1).

When the detected amount of lubricant Lc is still in a shortage state less than a set value (YES in S10 and NO in S11), and further, an increase in the capacity of outdoor unit A2 (an increase in operation frequency Fc) is not allowable (NO in S12a), the main controller 50 opens the electric expansion valve 83 of outdoor unit Al again and bypasses the liquid refrigerant of the liquid-side pipe in compressor Al to the low-pressure side (S12c). At this time, the main controller 50 sets the opening of the electric expansion valve 83 so as to be greater than the initial predetermined opening (initial opening) by only a predetermined amount proportional to count value N (= "1"). In this way, the opening of the electric expansion valve 83 is increased in stages, thereby increasing the amount of bypass of refrigerant. Thus, the reduction in the capacity of outdoor unit Al is accelerated. Thus, the amount of lubricant Lc in compressor is is assuredly increased, and the lubricant shortages of compressor lc are quickly solved.

When, of the amounts of lubricants La and Lc detected in the process of S9, the amount of lubricant La is in a shortage state less than a set value (NO in S10 and YES in S13), the main controller 50 determines whether or not an increase in the capacity of outdoor unit Al in which compressor la is present (an increase in operation frequency Fa) is allowable at the current time point (S14a).

When an increase in the capacity of outdoor unit Al is allowable (YES in S14a), the main controller 50 increases operation frequency Fa by only a predetermined value AF (S14b), thereby increasing the capacity of outdoor unit A2. At the same time, the main controller 50 decreases operation frequency Fa by only the predetermined value to reduce the capacity of outdoor unit A2 by only the increase in the capacity of outdoor unit Al.

When an increase in the capacity of outdoor unit Al is not allowable (NO in S14a), the main controller 50 opens the electric expansion valve 83 of outdoor unit A2 with a predetermined opening (initial opening) and bypasses the liquid refrigerant of the liquid-side pipe in outdoor unit A2 to the low-pressure side (S14c). By this bypass, the capacity of compressor A2 is reduced. When the capacity of outdoor unit A2 is reduced, the capacity of outdoor unit Al is relatively increased, and the amount of refrigerant circulating in outdoor unit Al is increased. Accordingly, the rate of deviation of lubricant L to outdoor unit Al is increased, and the rate of deviation of lubricant L to outdoor unit A2 is decreased.

At the time of this bypass, the main controller 50 increases count value N by one (S31). The main controller 50 starts time count t3 (S16), and compares time count t3 with a predetermined time t3s set in advance (S17). When time count t3 reaches the predetermined time t3s (YES in S17), the main controller 50 cancels the bypass applied by the release of the electric expansion valve (S18). Subsequently, the main controller 50 returns to the process of S9 and detects the amounts of lubricants La and Lc again (S9).

When the detected amounts of lubricants La and Lc are in an appropriate state greater than or equal to the set value (YES in S10 and YES in S11), the main controller 50 clears count value N so as to be zero (S30), returns to the first process of Si and restarts time count tl (S1).

When the detected amount of lubricant La is still in a shortage state less than the set value (NO in S10 and YES in S13), and further, an increase in the capacity of outdoor unit Al (an increase in operation frequency Fa) is not allowable (NO in S14a), the main controller 50 opens the electric expansion valve 83 of outdoor unit A2 again and bypasses the liquid refrigerant of the liquid-side pipe in compressor A2 to the low-pressure side (S14c). At this time, the main controller 50 sets the opening of the electric expansion valve 83 so as to be greater than the initial predetermined opening (initial opening) by only a predetermined amount proportional to count value N (-"1"). In this way, the opening of the electric expansion valve 83 is increased in stages, thereby increasing the amount of bypass of refrigerant. Thus, the reduction in the capacity of outdoor unit A2 is accelerated. Thus, the amount of lubricant La in compressor la is assuredly Increased. The lubricant shortages of compressor la are quickly solved.

In this fifth embodiment, this specification explains a case where each of outdoor units Al and A2 comprises a compressor. However, the fifth embodiment can be also implemented in a case where each of outdoor units Al and A2 comprises two compressors in a manner similar to that of the above fourth embodiment.

[6] Modification Example In each of the embodiments described above, when a lubricant is insufficient, lubricant L from the oil separator 3 is collected. When lubricant shortages are not solved in spite of the collection, the amount of refrigerant circulating in outdoor units is controlled. However, when a lubricant is insufficient, the amount of refrigerant circulating in outdoor units may be immediately controlled.

Each of the embodiments described above is explained with an example in which the amount of lubricant is detected based on the temperature of refrigerant and the temperature of oil. However, various detection methods may be adopted. For example, the amount of lubricant may be detected, using a float floating on the oil surface in a compressor. The amount of lubricant may be detected by dielectric constant.

The above embodiments and modification example have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments and modification example described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments and modification example described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. Reference Signs List Al, Bl la 2, A2 to Bn to ld Outdoor unit Indoor unit 3 2a, 2b Compressor High-pressure-side pipe Oil separator Four-way valve Outdoor heat exchanger 6 Electric expansion valve 11, 11a, llb Oil returning pipe Controller 44, 45a to 45d Temperature sensor Main controller 60 Controller 51, 52, 61, 62 Inverter 71 Bypass pipe 72 Electromagnetic on/off valve 81 Heat exchanger 82 Bypass pipe 83 Electric expansion valve

Claims

CLAIMS1. A refrigeration cycle apparatus characterized by comprising: a plurality of outdoor units including a compressor and an outdoor heat exchanger; a plurality of indoor units including an indoor heat exchanger; and a controller which, when an amount of lubricant in one of the compressors is less than a set value, makes an amount of refrigerant circulating in the outdoor unit in which the compressor is present greater than an amount of refrigerant circulating in the other outdoor units.
2. The refrigeration cycle apparatus of claim 1, characterized in that the controller sets the amounts of refrigerant circulating in the outdoor units so as to be in a same state, when all the amounts of lubricant in the compressors are less than the set value.
3. The refrigeration cycle apparatus of claim 1, characterized in that the controller increases a capacity of the outdoor unit in which the compressor is present, and reduces a capacity of the other outdoor units by only the increase, when the amount of lubricant in one of the compressors is less than the set value.
4. The refrigeration cycle apparatus of claim 1, characterized in that each of the outdoor units includes a high-pressure-side pipe in which a discharged refrigerant of the respective compressors flows, a low-pressure-side pipe in which the refrigerant sucked into the compressor flows, a bypass pipe connected between the high-pressure-side pipe and the low-pressure-side pipe, and an on/off valve provided in the bypass pipe, and when the amount of lubricant in one of the compressors is less than the set value, the controller determines whether an increase in a capacity of the outdoor unit in which the compressor is present is allowable, and increases the capacity of the outdoor unit and reduces the capacity of the other outdoor units by only the increase when the increase is allowable, and opens the on/off valve in the other outdoor units when the increase is not allowable.
5. The refrigeration cycle apparatus of claim 1, characterized in that each of the outdoor units includes a liquid-side pipe between the respective outdoor heat exchangers and the indoor units, a low-pressure-side pipe in which refrigerant sucked into the respective compressor flows, a bypass pipe connected between the liquid-side pipe and the low-pressure-side pipe, and an electric expansion valve provided in the bypass pipe, and when an amount of lubricant in one of the compressors is less than the set value, the controller determines whether an increase in a capacity of the outdoor unit in which the compressor is present is allowable, and increases the capacity of the outdoor unit and reduces the capacity of the other outdoor units by only the increase when the increase is allowable, and opens the electric expansion valve in the other outdoor units when the increase is not allowable.
6. The refrigeration cycle apparatus of claim 5, characterized in that each of the outdoor units includes a heat exchanger which includes a first flow path provided in the liquid-side pipe, and a second flow path provided at a downstream-side position as compared with the electric expansion valve in the bypass pipe, and performs heat exchange of refrigerant between the first flow path and the second flow path.
7. The refrigeration cycle apparatus of claim 5, characterized in that the controller opens the electric expansion valve in the other outdoor units with a predetermined opening and increases the opening of the electric expansion valve in stages by each predetermined amount when the increase is not allowable.