REFRIGERATION DEVICE

Abstract

 A refrigerant circuit (11) includes an oil separator (60) configured to separate oil from high pressure refrigerant, and an oil feed circuit (70) configured to feed the oil separated in the oil separator (60) to a compression mechanism (20) so as to cool the refrigerant in the course of a compression phase of the compression mechanism (20). The oil feed circuit (70) includes a recovery mechanism (40) configured to recover energy of the oil separated in the oil separator (60). In the compression mechanism (20), the refrigerant is cooled by the oil, thereby reducing power of the compression mechanism (20). Simultaneously, in the recovery mechanism (40), power required to increase pressure of the oil in the compression mechanism (20) is recovered.

Description

TECHNICAL FIELD

[0001] The present invention relates to refrigeration apparatuses including a refrigerant circuit for circulating refrigerant to perform a refrigeration cycle, particularly to power saving of the refrigeration apparatuses.

BACKGROUND ART

[0002] Refrigeration apparatuses including a refrigerant circuit for performing a refrigeration cycle have widely been used for air conditioners etc. for conditioning air inside a room.

[0003] Patent Document 1 discloses a refrigeration apparatus of this type. A refrigerant circuit of the refrigeration apparatus includes a compressor, a cyclone (an oil separator), a radiator, a utilization-side heat exchanger, etc. A high pressure refrigerant compressed in the compressor flows into the oil separator. The oil separator separates oil from the high pressure refrigerant. The separated oil is cooled as it passes through the radiator, and is fed to a suction side of the compressor. Thus, refrigerant is cooled by the oil in a compression phase of the compressor. Accordingly, during the compression phase of the compressor, the refrigerant hardly increases in temperature, and is compressed almost isothermally. This compression phase of the compressor reduces power of the compressor as compared with a compression phase of a general compressor (a compression phase similar to adiabatic change). Thus, the refrigeration apparatus is configured to improve COP (coefficient of performance) in accordance with reduction in power of the compressor.
Patent Document 1: Japanese Patent Publication No. H04-116348

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0004] In order to cool the refrigerant in the course of the compression phase of the compressor in the same manner as the refrigeration apparatus of Patent Document 1, a large amount of oil separated in the oil separator has to be fed to the compressor. Specifically, as the amount of the oil fed to the compressor increases, the refrigerant is cooled by the oil more effectively, thereby reducing the power required to compress the refrigerant. However, the increase in amount of the oil fed to the compressor increases power required to increase pressure of the oil fed to the compressor. As a result, the compressor disadvantageously wastes power (energy) to increase the pressure of the oil.

[0005] In view of the foregoing, the present invention has been achieved. An object of the invention is to provide a refrigeration apparatus capable of effectively reducing power of a compression mechanism.

SOLUTION TO THE PROBLEM

[0006] A first aspect of the invention is directed to a refrigeration apparatus including: a refrigerant circuit (11) which includes a compression mechanism (20) connected thereto, and performs a refrigeration cycle. The refrigerant circuit (11) includes an oil separating section (60) configured to separate oil from a high pressure refrigerant compressed in the compression mechanism (20), and an oil feed circuit (70) configured to feed the oil separated in the oil separating section (60) to the compression mechanism (20) so as to cool the refrigerant in the course of a compression phase of the compression mechanism (20). The oil feed circuit (70) includes a recovery mechanism (40) which is configured recover energy of the oil flowing in the oil feed circuit (70).

[0007] In the refrigerant circuit (11) according to the first aspect of the invention, the oil separating section (60) separates high pressure oil from the high pressure refrigerant compressed in the compression mechanism (20). The separated oil is fed to the compression mechanism (20) through the oil feed circuit (70) to cool the refrigerant in the course of the compression phase of the compression mechanism (20). This reduces increase in temperature of the refrigerant in the compression phase of the compression mechanism (20), thereby reducing power required to compress the refrigerant in the compression mechanism (20).

[0008] In order to cool the refrigerant in the course of the compression phase of the compression mechanism (20) by the oil as described above, a large amount of oil has to be fed from the oil feed circuit (70) to the compression mechanism (20). For this reason, a conventional compression mechanism has a problem of increase in power required to increase pressure of the oil.

[0009] As a solution to this problem, the oil feed circuit (70) of the present invention includes the recovery mechanism (40) configured to recover energy of the oil. Specifically, the oil separated from the high pressure refrigerant in the oil separating section (60) has power used to increase the pressure of the oil in the compression mechanism (20) as kinetic energy, potential energy, pressure energy, etc. The recovery mechanism (40) recovers the power of the separated oil (i.e., the energy of the oil). Thus, even when a large amount of oil is fed to the compression mechanism (20) through the oil feed circuit (70), and the power required to increase the pressure of the oil increases, the power used to increase the pressure of the oil can be recovered by the recovery mechanism (40). Therefore, the present invention can reduce increase in power required to compress the refrigerant due to the feeding of a large amount of oil to the compression mechanism (20), and can prevent waste of the power used to increase the pressure of the large amount of oil.

[0010] In a second aspect of the invention related to the refrigeration apparatus of the first aspect of the invention, the oil feed circuit (70) feeds the oil to the compression mechanism (20) in such a manner that the refrigerant is isothermally compressed for at least part of a period of the compression phase of the compression mechanism (20).

[0011] The oil feed circuit (70) of the second aspect of the invention feeds the oil to the compression mechanism (20) in such a manner that the refrigerant is isothermally compressed for at least part of the period of the compression phase of the compression mechanism (20). Thus, in the compression phase of the compression mechanism (20), the refrigerant hardly increases in temperature, thereby reducing the power required to compress the refrigerant in the compression mechanism (20). In order to isothermally compress the refrigerant for at least part of the period of the compression phase of the compression mechanism (20), a large amount of oil has to be fed from the oil feed circuit (70) to the compression mechanism (20). This involves in increase in power required to increase the pressure of the oil in the compression mechanism (20). According to the present invention, however, the recovery mechanism (40) recovers the energy of the oil in the oil feed circuit (70). Therefore, the power used to increase the pressure of the oil in the compression mechanism (20) would not be wasted.

[0012] In a third aspect of the invention related to the refrigeration apparatus of the first or second aspect of the invention, the refrigerant circuit (11) is configured to perform a refrigeration cycle in which the refrigerant is compressed in the compression mechanism (20) to a critical pressure or higher.

[0013] The refrigerant circuit (11) of the third aspect of the invention performs a refrigeration cycle in which the high pressure refrigerant is compressed to a critical pressure or higher. In this refrigeration cycle (hereinafter referred to as a supercritical cycle), the power required to compress the refrigerant can more effectively be reduced by the above-described feeding of the low temperature oil to the compression mechanism (20).

[0014] Specifically, in the supercritical cycle, even when the refrigerant is cooled in the course of the compression phase of the compression mechanism (20), the refrigerant increases in pressure in the state of superheated vapor, and would not be condensed. That is, in the compression phase of the supercritical cycle, the refrigerant would not reach a gas-liquid two-phase region (a condensation region). Thus, according to the present invention, the power required to compress the refrigerant can more effectively be reduced by so-called isothermal compression as compared with a general refrigeration cycle (in which the refrigerant is compressed in a pressure range lower than the critical pressure).

[0015] In a fourth aspect of the invention related to the refrigeration apparatus of any one of the first to third aspects of the invention, the oil feed circuit (70) is configured to feed the oil in the course of the compression phase of the compression mechanism (20).

[0016] According to the fourth aspect of the invention, the oil which is cooled in the cooling section (80), and is relatively low in temperature is fed to the compression mechanism (20) in the course of the compression phase (i.e., at a point where the refrigerant has an intermediate pressure between the suction pressure and the discharge pressure). In the course of the compression phase of the compression mechanism (20), the refrigerant is already compressed (adiabatically), and is increased in temperature. When the low temperature oil is fed in this state, the temperature of the refrigerant would not be lower than the temperature of the oil. Thus, in the subsequent part of the compression phase, the refrigerant can be prevented from being heated by the oil, and from overheat compression. Therefore, the power to compress the refrigerant can be effectively reduced without being affected by the overheat compression.

[0017] In a fifth aspect of the invention related to the refrigeration apparatus of any one of the first to third aspects of the invention, the oil feed circuit (70) is configured to feed the oil to a suction side of the compression mechanism (20).

[0018] According to the fifth aspect of the invention, the oil which is cooled in the cooling section (80), and is relatively low in temperature is fed to the suction side of the compression mechanism (20). Thus, the refrigerant is cooled by the oil from the beginning of the compression phase of the compression mechanism (20). This allows effective reduction of the power required to compress the refrigerant.

[0019] In a sixth aspect of the invention related to the refrigeration apparatus of any one of the first to fifth aspects of the invention, the recovery mechanism (40) includes a movable part (50) which is driven to rotate by the oil, and an output shaft (42) coupled to the movable part (50).

[0020] According to the sixth aspect of the invention, the recovery mechanism (40) includes the movable part (50) and the output shaft (42). The movable part (50) of the recovery mechanism (40) is driven to rotate by the oil separated from the high pressure refrigerant. As a result, the output shaft (42) coupled to the movable part (50) also rotates. The rotary power of the output shaft (42) is used as power to drive, for example, a power generator, other components, etc.

[0021] In a seventh aspect of the invention related to the refrigeration apparatus of the sixth aspect of the invention, the compression mechanism (20) is coupled to, and is driven by the output shaft (42) of the recovery mechanism (40).

[0022] According to the seventh aspect of the invention, the power of the oil recovered by the recovery mechanism (40) (i.e., the energy of the oil) is used as a power source for driving the compression mechanism (20) through the output shaft (42). As described above, when the amount of the oil fed to the compression mechanism (20) increases, the power to compress the refrigerant is reduced by the above-described isothermal compression. In this case, the power required to increase the pressure of the oil in the compression mechanism (20) increases. According to the present invention, when the amount of the fed oil increases, the power recovered by the recovery mechanism (40) increases, and the increase in power allows reduction of the power of the compression mechanism (20). Specifically, according to the present invention, the low temperature oil is actively fed to the compression mechanism (20), thereby effectively reducing the power required to compress the refrigerant, and increasing the power recovered by the recovery mechanism (40). Thus, the present invention can effectively reduce general power of the compression mechanism (20), thereby effectively improving efficiency of the compression mechanism (20).

[0023] In an eighth aspect of the invention related to the refrigeration apparatus of the sixth or seventh aspect of the invention, the refrigerant circuit (11) includes an expansion mechanism (30) having a movable part which is driven to rotate by the refrigerant, and is coupled to the output shaft (42) of the recovery mechanism (40).

[0024] The refrigerant circuit (11) of the eighth aspect of the invention includes the expansion mechanism (30) which is driven to rotate by the refrigerant. The movable part of the expansion mechanism (30) is coupled to the output shaft (42) of the recovery mechanism (40). Specifically, the output shaft (42) is driven to rotate by both of the power recovered by the recovery mechanism (40), and the power obtained by expansion of the refrigerant in the expansion mechanism (30) (i.e., expansion power). The rotary power of the output shaft (42) is used as power to drive the compression mechanism (20) of the seventh aspect of the invention etc.

[0025] In a ninth aspect of the invention related to the refrigeration apparatus of any one of the sixth to eighth aspects of the invention, the refrigeration apparatus further includes a power generator (45) which is coupled to, and is driven by the output shaft (42) of the recovery mechanism (40).

[0026] According to the ninth aspect of the invention, the energy of the oil recovered by the recovery mechanism (40) is used as power to drive the power generator (45) through the output shaft (42). Thus, according to the present invention, electric power can be generated by the power generator (45), and the electric power can be used as a power source of the other components etc.

[0027] In a tenth aspect of the invention related to the refrigeration apparatus of the first to ninth aspects of the invention, an oil cooling heat exchanger (80) configured to cool the oil separated in the oil separating section (60) is connected to the oil feed circuit (70).

[0028] According to the tenth aspect of the invention, the oil cooling heat exchanger (80) is connected to the oil feed circuit (70). Specifically, the oil separated in the oil separating section (60) is cooled by heat exchange with predetermined fluid in the oil cooling heat exchanger (80). The cooled oil is fed to the compression mechanism (20) to cool the refrigerant in the course of the compression phase of the compression mechanism (20).

[0029] In an eleventh aspect of the invention related to the refrigeration apparatus of the tenth aspect of the invention, the refrigerant circuit (11) includes an indoor heat exchanger (13) placed inside a room, and is configured to perform heating operation of heating room air by the refrigerant flowing in the indoor heat exchanger (13), and the oil cooling heat exchanger (80) is placed inside the room, and is configured to dissipate heat of the oil into the room air in the heating operation.

[0030] The refrigerant circuit (11) of the eleventh aspect of the invention is configured to perform the heating operation of heating the room air. Specifically, the refrigerant compressed in the compression mechanism (20) is fed to the indoor heat exchanger (13), and is allowed to dissipate heat of the refrigerant into the room air, thereby heating the room.

[0031] The oil cooling heat exchanger (80) of the present invention functions as an auxiliary room heater when placed inside the room. Specifically, in the heating operation, the oil separated in the oil separating section (60) flows into the oil cooling heat exchanger (80), and the oil in the oil cooling heat exchanger (80) exchanges heat with the room air, thereby dissipating heat of the oil into the room air. This allows heating of the room air, thereby improving heating capability. Simultaneously, the oil in the oil cooling heat exchanger (80) is cooled by the room air. The cooled oil is fed to the compression mechanism (20) to cool the refrigerant in the course of the compression phase of the compression mechanism (20).

[0032] In a twelfth aspect of the invention related to the refrigeration apparatus of the tenth aspect of the invention, the refrigerant circuit (11) includes an indoor heat exchanger (13) placed inside a room, and is configured to perform heating operation of heating room air by the refrigerant flowing in the indoor heat exchanger (13), and cooling operation of cooling the room air by the refrigerant flowing in the indoor heat exchanger (13) in a switchable manner, and the oil feed circuit (70) includes a first oil cooling heat exchanger (80a) which is placed inside the room, and dissipates heat of the oil into the room air in the heating operation, and a second oil cooling heat exchanger (80b) which is placed outside the room, and dissipates the heat of the oil into outside air in the cooling operation, both of which are connected to the oil feed circuit (70).

[0033] The refrigerant circuit (11) of the twelfth aspect of the invention is configured to perform the heating operation of heating the room air, and the cooling operation of cooling the room air in a switchable manner. Specifically, the room is heated by feeding the refrigerant compressed in the compression mechanism (20) to the indoor heat exchanger (13) to dissipate the heat of the refrigerant into the room air. Further, the room is cooled by feeding a low pressure gaseous refrigerant to the indoor heat exchanger (13) to absorb the heat of the room air into the refrigerant.

[0034] The oil feed circuit (70) of the present invention includes the first oil cooling heat exchanger (80a) placed inside the room, and the second oil cooling heat exchanger (80b) placed outside the room. In the heating operation, the oil separated in the oil separating section (60) flows into the first oil cooling heat exchanger (80a), and the oil in the first oil cooling heat exchanger (80a) dissipates heat into the room air. This improves heating capability. In the cooling operation, the oil separated in the oil separating section (60) flows into the second oil cooling heat exchanger (80b), and the oil in the second oil cooling heat exchanger (80b) dissipates heat into the outside air. Thus, the heat of the oil would not be dissipated into the room, and cooling capability would not be reduced.

ADVANTAGES OF THE INVENTION

[0035] According to the present invention, the oil is fed to the compression mechanism (20) by the oil feed circuit (70) to cool the refrigerant in the course of the compression phase, thereby reducing the power required to compress the refrigerant in the compression mechanism (20), and recovering the energy of the oil flowing in the oil feed circuit (70) by the recovery mechanism (40). Thus, the present invention allows reduction of the power required to compress the refrigerant by reliably cooling the refrigerant in the course of the compression phase by the oil, and allows recovery of the power of the compression mechanism (20) to increase the pressure of the oil. Specifically, when the oil is actively fed to the compression mechanism (20) to cool the refrigerant, the power required to increase the pressure of the oil in the compression mechanism (20) increases. However, in the present invention, the energy of the oil increased in pressure is recovered as power, thereby significantly reducing general power of the refrigeration apparatus.

[0036] With the increase in amount of the oil fed to the compression mechanism (20), the temperature of the refrigerant discharged from the compression mechanism (20) can be kept low. This can avoid system errors in the refrigeration apparatus resulting from the increase in temperature of the discharged refrigerant, and damage to the compression mechanism (20). Further, temperature increase of sliding parts of the compression mechanism (20) can also be reduced, thereby reliably preventing seizing of the sliding parts, and preventing deterioration of the oil (refrigeration oil). This can improve the reliability of the refrigeration apparatus to a further extent.

[0037] In addition, with the increase in amount of the oil fed to the compression mechanism (20), the temperature around a motor of the compression mechanism (20) can also be kept low. This can improve efficiency of the motor, thereby reducing input of the compression mechanism (20) to a further extent.

[0038] In particular, according to the second aspect of the invention, the oil is fed in such a manner that the refrigerant is isothermally compressed for at least part of the period of the compression phase of the compression mechanism (20). This requires feeding of a relatively large amount of oil to the compression mechanism (20). According to the present invention, the recovery mechanism (40) recovers the energy of the increased amount of oil as power. This can effectively reduce the power required to compress the refrigerant by the advantage of the isothermal compression, and can increase the power (i.e., the energy) recovered by the recovery mechanism (40).

[0039] According to the third aspect of the invention, the low temperature oil is fed to the compression mechanism (20), while the supercritical cycle is performed in which the high pressure refrigerant is compressed to a critical pressure or higher. Thus, the refrigerant would not be condensed, but can be compressed almost isothermally in the compression phase of the compression mechanism (20). This can effectively reduce the power required to compress the refrigerant.

[0040] According to the fourth aspect of the invention, the low temperature oil is fed to the compression mechanism (20) in the course of the compression phase. Thus, according to the present invention, the refrigerant is heated in the compression mechanism (20) to a certain extent, and then the heated refrigerant is cooled by the oil. This allows reliable cooling of the refrigerant by the low temperature oil, and allows more effective reduction of the compression power by the isothermal compression.

[0041] According to the fifth aspect of the invention, the low temperature oil is fed to the suction side of the compression mechanism (20). Thus, according to the present invention, the refrigerant can be cooled by the low temperature oil from the beginning of the compression phase of the compression mechanism (20). This allows more effective reduction of the compression power by the isothermal compression.

[0042] According to the sixth aspect of the invention, the output shaft (42) is allowed to rotate by the energy of the oil recovered by the recovery mechanism (40), and the rotary power can be used as a predetermined power source. According to the seventh aspect of the invention, the rotary power of the output shaft (42) can be used as power to drive the compression mechanism (20). According to the eighth aspect of the invention, the output shaft (42) is allowed to rotate by both of the energy of the refrigerant recovered by the expansion mechanism (30), and the energy of the oil recovered by the recovery mechanism (40), thereby increasing the rotary power generated by the output shaft (42). Further, according to the ninth aspect of the invention, electric power can be generated by the power generator (45) using the rotary power of the output shaft (42), and the electric power can suitably be used as a power source for driving the components of the refrigeration apparatus.

[0043] According to the tenth aspect of the invention, the oil separated in the oil separating section (60) is cooled in the oil cooling heat exchanger (80), and the cooled oil is fed to the compression mechanism (20). This allows effective cooling of the refrigerant in the course of the compression phase of the compression mechanism (20).

[0044] In particular, according to the eleventh aspect of the invention, the oil in the oil cooling heat exchanger (80) dissipates heat into the room air in the heating operation, thereby cooling the oil. Thus, according to the present invention, the room air can be heated by both of the refrigerant and the oil. This improves heating capability to a sufficient degree.

[0045] According to the twelfth aspect of the invention, the oil in the first oil cooling heat exchanger (80a) dissipates heat into the room air in the heating operation, thereby cooling the oil. Further, in the cooling operation, the oil in the second oil cooling heat exchanger (80b) dissipates heat into the outside air, thereby cooling the oil. Thus, according to the present invention, the room air can be heated by both of the refrigerant and the oil in the heating operation, thereby improving the heating capability to a sufficient degree. Further, in the cooling operation, transfer of the heat of the oil to the room air can be prevented, thereby improving cooling capability to a sufficient degree.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 

[FIG. 1] FIG. 1 is a piping diagram schematically illustrating the structure of an air conditioner of a first embodiment.

[FIG. 2] FIG. 2 is a vertical cross-sectional view illustrating an enlarged recovery mechanism.

[FIG. 3] FIGS. 3(A) to 3(D) are horizontal cross-sectional views illustrating the inside of the recovery mechanism, and operation of a piston.

[FIG. 4] FIGS. 4(A) and 4(B) are a P-h diagram and a P-V diagram, respectively, of an ideal refrigeration cycle according to the embodiment.

[FIG. 5] FIGS. 5(A) and 5(B) are a P-h diagram and a P-V diagram, respectively, of a general refrigeration cycle.

[FIG. 6] FIG. 6 is a graph showing relationship between amount of injected oil and power of a compression mechanism.

[FIG. 7] FIG. 7 is a graph showing relationship between amount of injected oil and rate of COP improvement.

[FIG. 8] FIG. 8 is a piping diagram schematically illustrating the structure of an alternative example of the air conditioner of the first embodiment.

[FIG. 9] FIG. 9 is a piping diagram schematically illustrating the structure of an air conditioner of a second embodiment.

[FIG. 10] FIG. 10 is a piping diagram schematically illustrating the structure of an air conditioner of a third embodiment.

[FIG. 11] FIG. 11 is a piping diagram schematically illustrating the structure of an air conditioner of a fourth embodiment.

[FIG. 12] FIG. 12 is a horizontal cross-sectional view illustrating a first state of an operating compression mechanism of an air conditioner of a fifth embodiment.

[FIG. 13] FIG. 13 is a horizontal cross-sectional view illustrating a second state of the operating compression mechanism of the air conditioner of the fifth embodiment.

[FIG. 14] FIG. 14 is a block diagram illustrating the structure of a controller.

[FIG. 15] FIG. 15 is a block diagram illustrating the structure of a controller of an air conditioner of a sixth embodiment.

[FIG. 16] FIG. 16 is a horizontal cross-sectional view illustrating a first state of a compression mechanism.

[FIG. 17] FIG. 17 is a horizontal cross-sectional view illustrating a second state of the compression mechanism.

[FIG. 18] FIG. 18 is a graph showing power reduction by isothermal compression in a compressor of a comparative example.

[FIG. 19] FIG. 19 is a graph showing power reduction by isothermal compression in a compression mechanism of the sixth embodiment.

[FIG. 20] FIG. 20 is a piping diagram schematically illustrating the structure of an air conditioner of a seventh embodiment.

[FIG. 21] FIG. 21 is a piping diagram schematically illustrating the structure of an air conditioner of an eighth embodiment (in heating operation).

[FIG. 22] FIG. 22 is a piping diagram schematically illustrating the structure of the air conditioner of the eighth embodiment (in cooling operation).

[FIG. 23] FIG. 23 is a piping diagram schematically illustrating the structure of an air conditioner according to a first alternative example of other embodiment.

[FIG. 24] FIG. 24 is a piping diagram schematically illustrating the structure of an air conditioner according to a second alternative example of the other embodiment.

[FIG. 25] FIG. 25 is a piping diagram schematically illustrating the structure of an air conditioner according to a third alternative example of the other embodiment.

[FIG. 26] FIG. 26 is a piping diagram schematically illustrating the structure of an air conditioner according to a fourth alternative example of the other embodiment.

[FIG. 27] FIG. 27 is a P-h diagram of an example of a refrigeration cycle in which isothermal compression is performed.

[FIG. 28] FIG. 28 is a horizontal cross-sectional view illustrating a compression mechanism of a comparative example.

DESCRIPTION OF REFERENCE CHARACTERS

[0047] 

10

Air conditioner (refrigeration apparatus)

11

Refrigerant circuit

12

Outdoor heat exchanger

13

Indoor heat exchanger

20

Compression mechanism

30

Expansion mechanism

40

Recovery mechanism

42

Output shaft

45

Power generator

50

Piston (movable part)

60

Oil separator (oil separating section)

70

Oil guiding path (oil feed circuit)

80

Oil cooler (oil cooling heat exchanger)

80a

Indoor oil cooler (first oil cooling heat exchanger)

80b

Outdoor oil cooler (second oil cooling heat exchanger)

DESCRIPTION OF EMBODIMENTS

[0048] Embodiments of the present invention will be described in detail below with reference to the drawings.

[First Embodiment of the Invention]

[0049] A first embodiment of the present invention will be described. A refrigeration apparatus of the invention constitutes an air conditioner (10) for conditioning air inside a room. The air conditioner (10) is configured to perform cooling operation and heating operation in a switchable manner.

<General Structure of Air Conditioner>

[0050] As shown in FIG. 1, the air conditioner (10) includes a refrigerant circuit (11). The refrigerant circuit (11) circulates refrigerant to perform a refrigeration cycle. The refrigerant circuit (11) is filled with carbon dioxide (CO₂) as refrigerant. The refrigerant circuit (11) performs a refrigeration cycle in which the refrigerant is compressed to a critical pressure or higher (a so-called supercritical cycle). The refrigerant circuit (11) contains oil (refrigeration oil) made of PAG (polyalkylene glycol).

[0051] The refrigerant circuit (11) includes an oil power recovering compression unit (C/O), an expansion unit (E), an outdoor heat exchanger (12), an indoor heat exchanger (13), a first four-way switching valve (14), and a second four-way switching valve (15). The refrigerant circuit (11) further includes an oil separator (60), an oil guiding path (70), and an oil cooler (80).

[0052] The oil power recovering compression unit (C/O) includes a compression mechanism (20), a recovery mechanism (40), and an electric motor (25) contained in a casing (not shown). The compression mechanism (20) constitutes a rotary positive displacement compressor. The compression mechanism (20) compresses the refrigerant to a critical pressure or higher in a compression chamber. The recovery mechanism (40) includes a body (41), and an output shaft (42). The body (41) of the recovery mechanism (40) constitutes a rotary positive displacement fluid machine. The compression mechanism (20) and the body (41) are coupled to each other through the output shaft (42). The electric motor (25) is a motor which drives the output shaft (42) to rotate, and is an inverter motor capable of changing an output frequency (i.e., rotation speed of the output shaft).

[0053] The oil power recovering compression unit (C/O) includes a suction pipe (22) through which the refrigerant is sucked into the compression mechanism (20), and a discharge pipe (23) through which the refrigerant compressed in the compression mechanism (20) is discharged. The oil power recovering compression unit (C/O) further includes an oil inlet pipe (43) through which oil (refrigeration oil) flows into the body (41) of the recovery mechanism (40), and an oil outlet pipe (44) through which the oil flows out of the body (41).

[0054] The expansion unit (E) includes an expansion mechanism (30), an expansion output shaft (31), and an expansion power generator (35) contained in a casing (not shown). The expansion mechanism (30) constitutes a rotary positive displacement expansion mechanism. The refrigerant expands, and decreases in pressure in an expansion chamber of the expansion mechanism (30). In the expansion mechanism (30), a piston as a movable part (not shown) is driven to rotate by the refrigerant expanded in the expansion chamber, thereby driving the expansion output shaft (31) coupled to the piston to rotate. This drives the expansion power generator (35) to generate power. Specifically, the expansion power generator (35) is an object which is coupled to, and is driven by the expansion output shaft (31) of the expansion mechanism (30). Electric power generated by the expansion unit (E) is used as power to drive the oil power recovering compression unit (C/O) and the other components. The expansion unit (E) further includes an inlet pipe (33) through which the refrigerant flows into the expansion mechanism (30), and an outlet pipe (34) through which the refrigerant flows out of the expansion mechanism (30).

[0055] The outdoor heat exchanger (12) is an air heat exchanger for performing heat exchange between the refrigerant and outside air. The indoor heat exchanger (13) is an air heat exchanger for performing heat exchange between the refrigerant and room air.

[0056] The first four-way switching valve (14) and the second four-way switching valve (15) have first to fourth ports, respectively. In the first four-way switching valve (14), a first port is connected to the discharge pipe (23) through a discharge line (18), and a second port is connected to the suction pipe (22) through a suction line (17). In the first four-way switching valve (14), a third port is connected to an end of the outdoor heat exchanger (12), and a fourth port is connected to an end of the indoor heat exchanger (13). In the second four-way switching valve (15), a first port is connected to the inlet pipe (33), and a second port is connected to the outlet pipe (34). In the second four-way switching valve (15), a third port is connected to the other end of the outdoor heat exchanger (12), and a fourth port is connected to the other end of the indoor heat exchanger (13).

[0057] Each of the first four-way switching valve (14) and the second four-way switching valve (15) is configured to switch between a first state (a state indicated by a solid line in FIG. 1) in which the first and third ports communicate with each other, and the second and fourth ports communicate with each other, and a second state (a state indicated by a broken line in FIG. 1) in which the first and fourth ports communicate with each other, and the second and third ports communicate with each other.

[0058] The oil separator (60) is arranged on the discharge line (18). The oil separator (60) is comprised of a vertically oriented, substantially cylindrical hermetic container, and functions as an oil separating section configured to separate oil from high pressure refrigerant. A refrigerant/oil inlet pipe (61) is connected to a barrel of the oil separator (60), a refrigerant discharge pipe (62) is connected to the top of the oil separator (60), and an oil discharge pipe (63) is connected to the bottom of the oil separator (60). The oil separator (60) separates the oil from the refrigerant which entered the oil separator through the refrigerant/oil inlet pipe (61). The oil separator (60) can separate the oil by various methods. For example, the oil may be separated by centrifugation using swirling flow, or the oil may be settled by the difference in specific gravity between the refrigerant and the oil, etc. The refrigerant from which the oil is separated is discharged from the oil separator (60) through the refrigerant discharge pipe (62), and the separated oil is discharged through the oil discharge pipe (63).

[0059] An oil guiding path (70) constitutes an oil feed circuit configured to feed the oil separated in the oil separator (60) to the compression mechanism (20). The oil guiding path (70) includes a first oil guiding pipe (71), and a second oil guiding pipe (72).

[0060] The first oil guiding pipe (71) is connected to the oil discharge pipe (63) of the oil separator (60) at a starting end thereof, and is connected to the oil inlet pipe (43) at a terminal end thereof. The oil cooler (80) is arranged on the first oil guiding pipe (71). The oil cooler (80) is a cooling section for cooling the oil separated in the oil separator (60), and constitutes an oil cooling heat exchanger. The oil cooler (80) of the present embodiment is an air-cooled heat exchanger.

[0061] The second oil guiding pipe (72) is connected to the oil outlet pipe (44) at a starting end thereof, and is connected to an oil injection port (24) of the compression mechanism (20) at a terminal end thereof. The oil injection port (24) of the compression mechanism (20) is opened at a position in the compression chamber where a compression phase is performed. Specifically, the oil guiding path (70) of the present embodiment is connected to the compression mechanism (20) in such a manner that the oil separated in the oil separator (60) is fed to the compression mechanism (20) in the course of the compression phase.

[0062] The oil guiding path (70) configured as described above constitutes an oil feed circuit configured to feed the oil separated in the oil separator (60) to the compression mechanism (20) so as to cool the refrigerant in the course of the compression phase of the compression mechanism (20). The oil guiding path (70) is configured to feed the oil to the compression mechanism (20) in such a manner that the refrigerant is isothermally compressed for at least part of a period of the compression phase of the compression mechanism (20).

<Structure of Recovery Mechanism>

[0063] The structure of the recovery mechanism (40) will be described with reference to FIGS. 2 and 3.

[0064] The recovery mechanism (40) recovers power of the oil (i.e., energy of the oil). Specifically, the oil separated from the high pressure refrigerant has power used to increase pressure of the oil in the compression mechanism (20) as kinetic energy, potential energy, pressure energy, etc. The recovery mechanism (40) recovers such energies of the oil as power. The body (41) of the recovery mechanism (40) is a so-called oscillating piston-driven rotary fluid machine. The output shaft (42) is coupled to the body (41) at one end, and is coupled to a movable part (a piston) of the compression mechanism (20) at the other end. Specifically, the compression mechanism (20) is an object which is coupled to, and is driven by the output shaft (42) of the recovery mechanism (40). The output shaft (42) includes a main shaft portion (42a), and an eccentric portion (42b). The eccentric portion (42b) is eccentric relative to the main shaft portion (42a) by a predetermined amount, and has a larger diameter than the main shaft portion (42a).

[0065] The body (41) of the recovery mechanism is provided with a front head (46), a cylinder (47), and a rear head (48) sequentially arranged in the direction from the bottom to the top of the body. The cylinder (47) is in the shape of a tube through which the output shaft (42) penetrates in the vertical direction. A lower end of the cylinder (47) is closed by the front head (46), and an upper end of the cylinder (47) is closed by the rear head (47).

[0066] As shown in FIG. 3, a piston (50) as a movable part is contained in the cylinder (47) (a cylinder chamber). The piston (50) is annular-, or cylindrical-shaped. The eccentric portion (42b) of the output shaft (42) is fitted in, and is coupled to the piston (50). An outer circumferential surface of the piston (50) is slidably in contact with an inner circumferential surface of the cylinder (47), an end face of the piston (50) is slidably in contact with the front head (46), and the other end face of the piston (50) is slidably in contact with the rear head (47). An oil chamber (49) is formed in the cylinder (47) between the inner circumferential surface of the cylinder (47) and the outer circumferential surface of the piston (50). The oil chamber (49) communicates with the oil inlet pipe (43) and the oil outlet pipe (44).

[0067] The piston (50) is integrated with a blade (51). The blade (51) is in the shape of a plate extending in the radial direction of the piston (50), and protrudes outward from the outer circumferential surface of the piston (50). The blade (51) is inserted in a blade groove (52) formed in the cylinder (47). The blade groove (52) of the cylinder (47) is formed to extend in the cylinder (47) in the thickness direction, and is opened in the inner circumferential surface of the cylinder (47).

[0068] The cylinder (47) is provided with a pair of bushings (53). Each of the bushings (53) is a small piece having a planar inner surface, and an arc-shaped outer surface. In the cylinder (47), the paired bushings (53) are inserted in a bushing hole (54) to sandwich the blade (51). The inner surfaces of the bushings (53) are slidably in contact with the blade (51), and the outer surfaces of the bushings (53) slide on the cylinder (47). The blade (51) integrated with the piston (50) is supported by the cylinder (47) through the bushings (53), and is able to swing, and to move back and forth relative to the cylinder (47).

[0069] The oil chamber (49) in the cylinder (47) is divided by the piston (50) and the blade (51). A room on the left of the blade (51) in FIG. 3 communicates with the oil inlet pipe (43), and a room on the right of the blade (51) in FIG. 3 communicates with the oil outlet pipe (44).

-Operation Mechanism-

[0070] An operation mechanism of the air conditioner (10) of the first embodiment will be described below. The air conditioner (10) is able to perform cooling operation and heating operation according to the settings of the first four-way switching valve (14) and the second four-way switching valve (15). First, basic operation of the air conditioner (10) in the cooling operation will be described.

[0071] In the cooling operation, the first four-way switching valve (14) and the second four-way switching valve (15) are set to the first state (a state indicated by a solid line in FIG. 1) in which the refrigerant circulates in the refrigerant circuit (11) to perform a vapor compression refrigeration cycle. Thus, in the cooling operation, a refrigeration cycle is performed in which the outdoor heat exchanger (12) functions as a radiator (a condenser), and the indoor heat exchanger (13) functions as an evaporator. High pressure of the refrigerant circuit (11) is set higher than a critical pressure of carbon dioxide as the refrigerant. That is, a so-called supercritical cycle is established.

[0072] In the oil power recovering compression unit (C/O), the compression mechanism (20) is driven to rotate by the electric motor (25). In the compression mechanism (20), refrigerant sucked into the compression chamber through the suction pipe (22) is compressed, and the compressed refrigerant is discharged through the discharge pipe (23). The refrigerant discharged from the compression mechanism (20) flows through the discharge line (18), and flows into the oil separator (60) through the refrigerant/oil inlet pipe (61).

[0073] In the oil separator (60), oil is separated from the refrigerant. Then, the refrigerant from which the oil is separated stays in an upper portion of the oil separator, while the separated oil stays in a lower portion of the oil separator. The refrigerant after the oil separation flows out of the oil separator through the refrigerant discharge pipe (62), and enters the outdoor heat exchanger (12). In the outdoor heat exchanger (12), the high pressure refrigerant dissipates heat into the outside air. The refrigerant flowing out of the outdoor heat exchanger (12) flows into the expansion mechanism (30) of the expansion unit (E) through the inlet pipe (33).

[0074] In the expansion mechanism (30), the high pressure refrigerant expands in the expansion chamber, thereby driving the expansion output shaft (31) to rotate. This drives the expansion power generator (35) to generate electric power. The electric power is fed to the compression mechanism (20), and the other components. The refrigerant expanded in the expansion mechanism (30) is discharged from the expansion unit (E) through the outlet pipe (34).

[0075] The refrigerant discharged from the expansion unit (E) enters the indoor heat exchanger (13). In the indoor heat exchanger (13), the refrigerant absorbs heat from the room air to evaporate. As a result, the room air is cooled to cool the room. The refrigerant discharged from the indoor heat exchanger (13) is sucked into the compression mechanism (20) through the suction pipe (22), and is compressed again.

[0076] In the cooling operation, oil injection is performed to improve COP (coefficient of performance) of the air conditioner (10). Specifically, the oil separated in the oil separator (60) flows into the first oil guiding pipe (71) through the oil discharge pipe (63). The oil is cooled in the oil cooler (80) to a predetermined temperature. The cooled oil flows through the oil inlet pipe (43) to enter the body (41) of the recovery mechanism (40) of the oil power recovering compression unit (C/O).

[0077] In the body (41) of the recovery mechanism (40), the piston (50) is driven to rotate by the oil flowing in the oil chamber (49). Thus, the piston (50) rotates eccentrically in the cylinder (47) in the order of FIGS. 3(A), 3(B), 3(C), 3(D), 3(A) ... In accordance with the eccentric rotation of the piston (50), the eccentric portion (42b) and the main shaft portion (42a) are driven to rotate. The rotary power is used as power to drive the compression mechanism (20). In this way, in the oil power recovering compression unit (C/O), energy of the oil is recovered by the recovery mechanism (40) as the power to drive the compression mechanism (20), thereby reducing power of the compression mechanism (20).

[0078] The oil whose energy is recovered in the oil chamber (49) is reduced to a predetermined pressure, and is discharged from the body (41) of the recovery mechanism (40) through the oil outlet pipe (44). The discharged oil flows through the second oil guiding pipe (72) to enter the oil injection port (24) of the compression mechanism (20). Thus, in the compression mechanism (20), oil injection is performed by feeding the low temperature oil to the compression chamber of the compression mechanism (20) in the course of the compression phase.

[0079] Due to the oil injection, the refrigerant is compressed in the compression mechanism (20) performing the cooling operation in such a manner that the behavior of the refrigerant is close to the isotherm plot on the P-h diagram, i.e., so-called isothermal compression is performed. This phenomenon will be described with reference to FIGS. 4(A) and 4(B). FIG. 4(A) is a P-h diagram of a refrigeration cycle in which ideal isothermal compression is performed, and FIG. 4(B) is a P-V diagram of the refrigeration cycle of FIG. 4(A).

[0080] In the cooling operation, the refrigerant circuit (11) performs superheat control in which the refrigerant on the suction side of the compression mechanism (20) is superheated by a predetermined temperature. Compression of the sucked refrigerant in the compression mechanism (20) starts from point A in FIG. 4(A) to increase pressure and temperature of the refrigerant by a predetermined amount, and then the compressed refrigerant is mixed with oil at point B. When the refrigerant and the oil are mixed in the compression mechanism (20), the refrigerant is cooled by the low temperature oil cooled in the oil cooler (80). Specifically, in the compression phase, the refrigerant is compressed while being cooled by the oil after passing through point B. As a result, the refrigerant is compressed to follow along the isotherm plot (e.g., about 40°C) shown in FIG. 4(A), thereby reaching a target high pressure (point C). In this way, the refrigerant is compressed to sequentially pass points A, B, and C, thereby effectively reducing power required to compress the refrigerant in the compression mechanism (20). Thus, according to the present embodiment, in the compression phase of compressing the low pressure refrigerant to the high pressure refrigerant in the compression mechanism (20) (i.e., in a phase from point A to point C), the refrigerant is isothermally compressed in part of a period of the phase, i.e., from point B to point C.

[0081] For example, when general adiabatic compression is performed in the compression phase, the refrigerant is compressed to sequentially pass points A, B, and C' in FIG. 4(A). As a result, in this refrigeration cycle, power required to compress the refrigerant increases. In contrast, when the refrigerant is cooled in the compression phase by the oil injection according to the present embodiment, the power to compress the refrigerant in the compression mechanism (20) can be reduced by an area ΔS defined by points B, C, and C' shown in FIG. 4(B) as compared with the case where the general adiabatic compression is performed.

[0082] As described in the present embodiment, when the oil injection is performed in a refrigerant circuit which performs a supercritical cycle using carbon dioxide as the refrigerant, the power to compress the refrigerant in the compression mechanism (20) is effectively reduced. This advantage will be described below.

[0083] In the refrigerant circuit (11) of the present embodiment, the refrigerant is compressed in the compression phase in such a manner that the pressure of carbon dioxide is as high as, or higher than the critical pressure (pressure at point cP in FIG. 4(A)). Therefore, when the refrigerant is compressed while cooling the refrigerant in part of the period of the compression phase from point B to point C, the refrigerant can be prevented from entering a gas-liquid two-phase region (a condensation region). Specifically, in the supercritical cycle, cold of the oil would not be used for condensation of the refrigerant, thereby effectively reducing the temperature of the refrigerant. Thus, the behavior of the refrigerant can be made closer to the isotherm plot.

[0084] In contrast, for example, in a compression phase of a general vapor compression refrigeration cycle shown in FIGS. 5(A) and 5(B) (R410A is used as the refrigerant), the refrigerant is compressed in a pressure range lower than the critical pressure. Therefore, when the oil injection is performed in this refrigeration cycle, the refrigerant enters a gas-liquid two-phase region (a condensation region), while the refrigerant is compressed at point A1, and is cooled by the oil at point B1. Thus, in this refrigeration cycle, isothermal compression is performed only in the range from point B1 to point C1.

[0085] For the above reasons, when the oil injection is performed in the refrigeration cycle shown in FIGS. 5(A) and 5(B), the compression power of the compression mechanism is reduced by an area ΔS' defined by points B1, C1, and C1' shown in FIG. 5(B). In contrast, when the oil injection is performed in the supercritical cycle of the present embodiment, the compression power of the compression mechanism (20) is reduced by an area ΔS, i.e., the compression power is effectively reduced.

[0086] In the present embodiment, the power of the oil is recovered by the recovery mechanism (40) as described above. This allows effective reduction of the power to compress the refrigerant by the oil injection, and reduction of the power to increase the pressure of the oil. These advantages will be described with reference to FIG. 6.

[0087] When the oil injection is performed, the compression mechanism (20) consumes not only the power to compress the refrigerant (Wr in FIG. 6), but also power to increase the pressure of the oil (Wo in FIG. 6). The power to compress the refrigerant Wr is reduced as described above by the isothermal compression caused by the oil injection. Accordingly, the power to compress the refrigerant Wr decreases as the amount of low temperature oil fed to the compression mechanism (20) (an amount of injected oil Goil) increases. With the increase in amount of injected oil Goil, the power to increase the pressure of the oil Wo in the compression mechanism (20) increases. Thus, general power Wt consumed by the compression mechanism (20) (i.e., Wr+Wo) and the amount of injected oil Goil show the relationship as shown in FIG. 6. When the amount of injected oil Goil exceeds the predetermined value (Gb), the general power Wt of the compression mechanism (20) may possibly increase.

[0088] In the present embodiment, the recovery mechanism (40) is used to recover the power to increase the pressure of the oil Wo. Specifically, when the oil injection is performed with the amount of injected oil Goil set higher than the predetermined value Gb, the power to increase the pressure of the oil Wo increases. However, the oil power recovering compression unit (C/O) recovers the power (energy) of the pressure-increased oil as power to drive the compression mechanism (20). Thus, even when the amount of injected oil Goil increases in the present embodiment, the air conditioner (10) can achieve relatively high rate of COP improvement (the advantage of the isothermal compression).

[0089] Specifically, as shown in FIG. 7, in the case where the recovery mechanism (40) does not recover the power of the oil (broken line L-0 in FIG. 7), and the amount of injected oil exceeds the predetermined value Gb, the power to increase the pressure of the oil Wo becomes larger than a cutback of the power to compress the refrigerant Wr achieved by the isothermal compression. This results in reduction in rate of COP improvement. In contrast, in the case where the recovery mechanism (40) recovers the power of the oil, the power of the oil recovered to the compression mechanism (20) increases with the increase in power to increase the pressure of the oil Wo. As a result, for example, in the case where the recovery mechanism (40) recovers the power by 50 % (solid line L-50 in FIG. 7), a high rate of COP improvement rate can be obtained even when the amount of the injected oil increases. The rate of COP improvement increases as the rate of power recovery by the recovery mechanism (40) increases (see, e.g., solid line L-80 in FIG. 7 (80 % oil power recovery rate), and solid line L-100 (100 % oil power recovery rate)), in particular, as the amount of injected oil Goil increases.

-Advantages of First Embodiment-

[0090] In the first embodiment, the oil is separated from the high pressure refrigerant in the oil separator (60), and the energy of the oil is recovered by the recovery mechanism (40) to be used as power to drive the compression mechanism (20). Thus, the power used to increase the pressure of the oil in the compression mechanism (20) can be recovered by the recovery mechanism (40), thereby advantageously saving power of the air conditioner (10).

[0091] In the first embodiment, the oil separated in the oil separator (60) is cooled in the oil cooler (80), and the low temperature oil is fed to the compression mechanism (20). Therefore, in the compression mechanism (20), the refrigerant can be compressed to show a line close to the isotherm shown in FIG. 4(A) (i.e., a line sequentially passing points A, B, and C), thereby significantly reducing the power to compress the refrigerant. In addition, with the increase in amount of injected oil Goil, the refrigerant can effectively be cooled, thereby further reducing the power to compress the refrigerant, and increasing the energy of the oil recovered by the recovery mechanism (40). This can significantly improve the rate of COP improvement of the air conditioner (10), thereby improving power saving. The amount (mass flow) of injected oil which allows effective improvement in rate of COP improvement of the air conditioner (10) is preferably in the range of about 0.5 times to about 6.0 times larger, both inclusive, than the amount (mass flow) of the refrigerant sucked into the compression mechanism (20).

[0092] Increasing the amount of injected oil to actively feed the low temperature oil to the compression mechanism (20) offers additional advantages described below. Specifically, the refrigerant discharged from the compression mechanism (20) can be prevented from increasing in temperature, and malfunction of the air conditioner (10) and mechanical damage to the compression mechanism (20) can be avoided. Further, the sliding parts such as the piston, the bearings, etc. in the compression mechanism (20) can sufficiently be lubricated, and the sliding parts can effectively dissipate heat. This can prevent the sliding parts from increase in friction loss, and seizing. In addition, the oil in the compression mechanism (20) is also kept at a relatively low temperature, thereby preventing deterioration of the oil due to excessive increase in temperature of the oil. Further, temperature around the compression mechanism (20) can also be kept at a relatively low temperature, thereby keeping the temperature in the casing of the oil power recovering compression unit (C/O) at a relatively low temperature. This can reduce temperature around the electric motor (25), thereby improving efficiency of the electric motor (25), and further reducing the input of the compression mechanism (20).

[0093] In the first embodiment, the low temperature oil is fed to the compression mechanism (20) performing the supercritical cycle of compressing the high pressure refrigerant to a critical pressure or higher. Thus, the refrigerant can be compressed to show a line close to the isotherm (see, e.g., FIGS. 4(A) and 4(B)) without condensation in the compression phase of the compression mechanism (20). This can effectively reduce the power to compress the refrigerant as compared with the general refrigeration cycle (see, e.g., FIGS. 5(A) and 5(B)).

[0094] In the first embodiment, the low temperature oil is fed to the compression mechanism (20) in the course of the compression. Accordingly, the refrigerant can be heated in the compression mechanism (20) to a certain degree, and then the heated refrigerant can be cooled by the oil. This can prevent the temperature of the refrigerant mixed with the oil from being lower than the temperature of the oil, and can prevent heating of the refrigerant by the oil. As a result, the refrigerant can reliably be cooled by the low temperature oil, thereby further reducing the compression power by the isothermal compression.

<First Alternative Example of First Embodiment>

[0095] According to the first embodiment, the expansion mechanism (30) comprised of a positive displacement fluid machine is used as an expansion mechanism for expanding the refrigerant. However, as shown in FIG. 8, an electronic expansion valve (38) capable of adjusting the degree of opening may be used to reduce the pressure of the refrigerant.

[Second Embodiment of the Invention]

[0096] A second embodiment of the invention will be described. The second embodiment is different from the first embodiment in the structure of the refrigerant circuit (11). In the refrigerant circuit (11) of the second embodiment shown in FIG. 9, a compression mechanism (20) and an expansion mechanism (30) are integrated, and are incorporated in an expansion/compression unit (C/E), and a recovery mechanism (40) is incorporated in an oil power recovering unit (O).

[0097] Specifically, the expansion/compression unit (C/E) includes a compression mechanism (20), an expansion mechanism (30), an expansion output shaft (31), and an electric motor (25) contained in a casing (not shown). The compression mechanism (20) and the expansion mechanism (30) are coupled to each other through the expansion output shaft (31). Thus, in the compression/expansion unit (C/E), energy of the refrigerant recovered in the expansion mechanism (30) is used as power to drive the compression mechanism (20). That is, the compression mechanism (20) is an object which is coupled to, and is driven by the expansion output shaft (31) of the expansion mechanism (30).

[0098] The oil power recovering unit (O) includes a recovery mechanism (40), and a power generator (45) contained in a casing (not shown). An output shaft (42) of the recovery mechanism (40) is coupled to the power generator (45). Specifically, in the oil power recovering unit (O), the power generator (45) is driven by power of the oil recovered by the recovery mechanism (40) (i.e., energy of the oil), and electric power is generated by the power generator (45). The electric power generated by the power generator (45) is used as power to drive the compression mechanism (20) and other components.

[0099] When the air conditioner (10) of the second embodiment performs cooling operation, the refrigerant compressed in the compression mechanism (20) of the compression/expansion unit (C/E) flows into the oil separator (60). The refrigerant from which the oil is separated in the oil separator (60) dissipates heat in the outdoor heat exchanger (12), and expands in the expansion mechanism (30) of the compression/expansion unit (C/E). Thus, power obtained from the refrigerant expanded in the expansion mechanism (30) (i.e., expansion power) is used as power to drive the compression mechanism (20). The refrigerant expanded in the expansion mechanism (30) evaporates in the indoor heat exchanger (13) to be used to cool the air inside the room, and is sucked into the compression mechanism (20) of the compression/expansion unit (C/E).

[0100] The oil separated in the oil separator (60) is cooled in the oil cooler (80), and then flows into the recovery mechanism (40) of the oil power recovering unit (O). In the recovery mechanism (40), the output shaft (42) is driven to rotate by the oil in the oil chamber (49), thereby driving the power generator (45). Thus, the power generator (45) generates electric power.

[0101] The oil from which the power is recovered by the recovery mechanism (40), and which is reduced in pressure flows into the oil injection port (24) of the compression mechanism (20) of the compression/expansion unit (C/E). In the compression mechanism (20), the oil cools the refrigerant in the course of compression. As a result, the refrigerant is compressed almost isothermally, thereby reducing power required to compress the refrigerant.

[0102] As described above, a relatively large amount of oil is injected also in this embodiment. This causes isothermal compression, thereby reducing the power to compress the refrigerant, and increasing the power of the oil recovered from the pressure-increased oil (i.e., the energy of the oil). Thus, COP of the air conditioner (10) of the second embodiment effectively improves.

[Third Embodiment of the Invention]

[0103] A third embodiment of the invention will be described. The third embodiment is different from the above-described embodiments in the structure of the refrigerant circuit (11). In the refrigerant circuit (11) of the third embodiment shown in FIG. 10, a compression mechanism (20) is incorporated in a compression unit (C), and an expansion mechanism (30) and a recovery mechanism (40) are integrated, and are incorporated in an oil power recovering expansion unit (E/O).

[0104] Specifically, the compression unit (C) includes a compression mechanism (20), a drive shaft (21), and an electric motor (25) contained in a casing (not shown). The compression mechanism (20) and the electric motor (25) are coupled to each other through the drive shaft (21). Thus, the compression mechanism (20) is driven by the electric motor (25) in this compression unit (C).

[0105] The oil power recovering expansion unit (E/O) includes an expansion mechanism (30), a recovery mechanism (40), and a power generator (45) contained in a casing (not shown). The expansion mechanism (30) is coupled to an end of an output shaft (42) of the recovery mechanism (40), and the power generator (45) is coupled to a center portion of the output shaft (42). Specifically, in the oil power recovering expansion unit (E/O), the expansion mechanism (30) recovers energy of the refrigerant, and the recovery mechanism (40) recovers energy of the oil. These energies are used as power to drive the power generator (45) through the output shaft (42). That is, the power generator (45) is an object which is coupled to, and is driven by the recovery mechanism (40) and the expansion mechanism (30) through the output shaft (42). Thus, the power generator (45) generates a larger amount of electric power than the power generator in the expansion unit (E) of the first embodiment. The electric power generated by the power generator (45) is used as power to drive the compression mechanism (20) and other components.

[0106] When the air conditioner (10) of the third embodiment performs cooling operation, the refrigerant compressed in the compression mechanism (20) of the compression unit (C) flows into the oil separator (60). The refrigerant from which the oil is separated in the oil separator (60) dissipates heat in the outdoor heat exchanger (12), and expands in the expansion mechanism (30) of the oil power recovering expansion unit (E/O). Thus, power obtained from the refrigerant expanded in the expansion mechanism (30) is used for power generation by the power generator (45). The refrigerant expanded in the expansion mechanism (30) evaporates in the indoor heat exchanger (13) to be used to cool the air inside the room, and is sucked into the compression mechanism (20) of the compression unit (C).

[0107] The oil separated in the oil separator (60) is cooled in the oil cooler (80), and then flows into the recovery mechanism (40) of the oil power recovering expansion unit (E/O). In the recovery mechanism (40), the output shaft (42) is driven to rotate by the power of the oil in the oil chamber (49), thereby driving the power generator (45). Thus, the power generator (45) generates electric power.

[0108] The oil from which the power is recovered by the recovery mechanism (40), and which is reduced in pressure exits from the oil power recovering expansion unit (E/O), and flows into the oil injection port (24) of the compression mechanism (20) of the compression unit (C). In the compression mechanism (20), the oil cools the refrigerant in the course of compression. As a result, the refrigerant is compressed almost isothermally, thereby reducing power required to compress the refrigerant. As described above, a relatively large amount of oil is injected also in this embodiment. This causes isothermal compression, thereby reducing the power to compress the refrigerant, and increasing the power of the oil recovered from the pressure-increased oil. Thus, COP of the air conditioner (10) of the third embodiment effectively improves.

[Fourth Embodiment of the Invention]

[0109] A fourth embodiment of the invention will be described. The fourth embodiment is different from the above-described embodiments in the structure of the refrigerant circuit (11). In the refrigerant circuit (11) of the fourth embodiment shown in FIG. 11, a compression mechanism (20), an expansion mechanism (30), and a recovery mechanism (40) are integrated, and are incorporated in an oil power recovering expansion/compression unit (C/E/O).

[0110] Specifically, the oil power recovering expansion/compression unit (C/E/O) includes a compression mechanism (20), an expansion mechanism (30), a recovery mechanism (40), and an electric motor (25) contained in a casing (not shown). The expansion mechanism (30) is coupled to an end of an output shaft (42) of the recovery mechanism (40), and the compression mechanism (20) is coupled to a center portion of the output shaft (42). The electric motor (25) is also coupled to the output shaft (42) between the expansion mechanism (30) and the compression mechanism (20). As described above, in the oil power recovering expansion/compression unit (C/E/O), the expansion mechanism (30) recovers energy of the refrigerant, and the recovery mechanism (40) recovers energy of the oil. These energies are used as power to drive and rotate the compression mechanism (20) through the output shaft (42). That is, the compression mechanism (20) is an object which is coupled to, and is driven by the recovery mechanism (40) and the expansion mechanism (30) through the output shaft (42). Thus, as compared with the oil power recovering compression unit (C/O) of the first embodiment, the oil power recovering expansion/compression unit (C/E/O) can reduce electric power of the electric motor (25) to drive the compression mechanism (20).

[0111] When the air conditioner (10) of the fourth embodiment performs cooling operation, the refrigerant compressed in the compression mechanism (20) of the oil power recovering expansion/compression unit (C/E/O) flows into the oil separator (60). The refrigerant from which the oil is separated in the oil separator (60) dissipates heat in the outdoor heat exchanger (12), and expands in the expansion mechanism (30). Thus, energy of the refrigerant expanded in the expansion mechanism (30) is used as power to drive the compression mechanism (20) through the output shaft (42). The refrigerant expanded in the expansion mechanism (30) evaporates in the indoor heat exchanger (13) to be used to cool the air inside the room, and is sucked into the compression mechanism (20) of the compression unit (C).

[0112] The oil separated in the oil separator (60) is cooled in the oil cooler (80), and flows into the recovery mechanism (40). In the recovery mechanism (40), the output shaft (42) is driven to rotate by the oil in the oil chamber (49). The rotary power of the output shaft (42) is used as power to drive the compression mechanism (20).

[0113] The oil from which the power is recovered by the recovery mechanism (40), and which is reduced in pressure flows into the oil injection port (24) of the compression mechanism (20). In the compression mechanism (20), the oil cools the refrigerant in the course of compression. As a result, the refrigerant is compressed almost isothermally, thereby reducing power required to compress the refrigerant. As described above, a relatively large amount of oil is injected also in this embodiment. This causes isothermal compression, thereby reducing the power to compress the refrigerant, and increasing the power of the oil recovered from the pressure-increased oil. Thus, COP of the air conditioner (10) of the fourth embodiment effectively improves.

[Fifth Embodiment of the Invention]

[0114] A fifth embodiment of the invention will be described. An air conditioner (10) of the fifth embodiment is obtained by adding an oil injection mechanism (100) and a controller (95) to the structure described in the above-described embodiment.

<Structure of Compression Mechanism and Oil Injection Mechanism>

[0115] The general structure of a compression mechanism (20) and an oil injection mechanism (100) of the fifth embodiment will be described below. In this example, the oil injection mechanism (100) is provided in the compression mechanism (20) of the air conditioner (10) of the first embodiment.

[0116] As shown in FIG. 12, the compression mechanism (20) is comprised of an oscillating piston-driven rotary fluid machine, like the above-described recovery mechanism (40). The compression mechanism (20) includes a compression chamber (26), and sucks carbon dioxide as refrigerant which is working fluid into the compression chamber (26) for compression. The oil injection mechanism (100) is capable of opening and closing the oil injection port (24), and feeds refrigeration oil to the compression chamber (26) at predetermined timing. The compression mechanism (20) is contained in a casing of the oil power recovering compression unit (C/O) as described above.

[0117] The compression mechanism (20) is configured to suck and compress the refrigerant due to operation of a piston (28) in a cylinder (27) having the compression chamber (26). In the compression mechanism (20), the compression chamber (26) is circular when viewed in section, and the piston (28) is configured to rotate eccentrically in the compression chamber (26).

[0118] The piston (28) includes an annular portion (28a) which is fitted on a crankpin (42c) of a crankshaft (42) as the output shaft to rotate eccentrically, and a blade (28b) integrated with the annular portion (28a). The blade (28b) is in the shape of a plate, and extends radially outward from the annular portion (28a). The cylinder (27) includes an oscillating bushing (29) for holding the blade (28b) in a slidable manner. The oscillating bushing (29) includes a suction bushing (29a) and a discharge bushing (29b), both of which are almost semicircular. The suction bushing (29a) and the discharge bushing (29b) may be integrated by partially coupling them.

[0119] The cylinder (27) includes a suction port (22a) which is opened in the compression chamber (26) at one end to suck the refrigerant into the compression chamber (26). The other end of the suction port (22a) communicates with the suction pipe (22) of the suction line (17). Like the cylinder in the above-described recovery mechanism (40), the cylinder (27) has two end plates (27a, 27b) which cover end faces of the cylinder in the axial direction, respectively (an end plate (27a) near the power generator is referred to as a front head, and an end plate (27b) opposite the power generator is referred to as a rear head). One of the front head (27a) and the rear head (27b) is provided with a discharge port (23a) through which the refrigerant compressed in the compression chamber (26) is discharged into space inside the casing of the oil power recovering compression unit (C/O). The discharge port (23a) has a reed valve (not shown) as a discharge valve. The discharge port (23a) is opened when a difference between the pressure in the compression chamber (26) and the pressure in the casing of the oil power recovering compression unit (C/O) reaches the predetermined value. The discharge pipe (23) is directly connected to the casing of the oil power recovering compression unit (C/O). The refrigerant flowing out of the discharge port (23a) flows through the discharge pipe (23) to enter the discharge line (18) of the refrigerant circuit (11).

[0120] When an upper end of a vertical axis shown in FIG. 12 is regarded as a position of 0°, the position of the suction port (22a) is shifted from the position of 0° to the right at an angle of θs. The oil injection mechanism (100) includes an injection nozzle (101) provided in the cylinder (27). The injection nozzle (101) is arranged at a position of angle θi, and communicates with the compression chamber (26) through the oil injection port (24). Thus, the suction port (22a) and the oil injection port (24) are arranged to communicate with each other through the compression chamber (26) in a suction phase shown in FIG. 13.

[0121] The injection nozzle (101) of the oil injection mechanism (100) includes a cylindrical injection case (102), a spool (103) capable of sliding in the axial direction in the injection case (102), and a drive mechanism (104) for driving the spool (103). An oil spray port (105) communicating with the oil injection port (24) is formed at an end of the injection case (102). An oil feed pipe (106) connected to the second oil guiding pipe (72) of the oil guiding path (70) is connected to the other end of the injection case (102).

[0122] An end of the spool (103) near the oil spray port (105) is formed into a tapered valve element (107). In the oil spray port (105), an inner surface of the injection case (102) is tapered at the same angle with the valve element (107) of the spool (103) to form a valve seat (108). With this configuration, when the spool (103) moves backward, thereby separating an outer circumferential surface of the valve element (107) from the inner circumferential surface of the valve seat (108) of the injection case (102) (the state shown in FIG. 12), the refrigeration oil fed from the oil feed pipe (106) flows through a gap between the valve element (107) and the valve seat (108), and is sprayed into the compression chamber (26) through the oil injection port (24). On the other hand, when the spool (103) moves forward to press the outer circumferential surface of the valve element (107) onto the inner circumferential surface of the valve seat (108) of the injection case (102) (the state shown FIG. 13), space inside the injection case (102) is hermetically sealed, and the refrigeration oil fed from the oil feed pipe (106) is not sprayed into the compression chamber (26).

[0123] A solenoid mechanism (109) is used as a drive mechanism (104) for moving the spool (103) back and forth in the axial direction. The solenoid mechanism (109) includes an iron core (110) fixed to the spool (103), and a coil (111) fixed to the injection case (102). A coil spring (112) for applying spring force in the direction of moving the spool (103) backward is provided in the injection case (102). A spring receiver (113) for receiving an end of the coil spring (112) is fixed to the spool (103). The other end of the coil spring (112) is in contact with an end face of the injection case (102) near the oil spray port (105).

[0124] When the coil (111) of the solenoid mechanism (109) is not energized, the spool (103) moves to a rear end of its movement range. In this case, the iron core (110) is eccentric from the center of the coil (111), thereby forming a gap between the valve element (107) of the spool (103) and the valve seat (108) of the oil spray port (105) (FIG. 12). On the other hand, when the coil (111) of the solenoid mechanism (109) is energized, the iron core (110) is pulled forward of the spool (103) against the spring force of the coil spring (112), thereby bringing the valve element (107) of the spool (103) and the valve seat (108) of the oil spray port (105) into press contact (FIG. 13). In this case, the gap no longer exists, thereby hermetically sealing the space inside the injection case (102).

<Structure of Controller>

[0125] The air conditioner (10) of the fifth embodiment includes a controller (95) as a control section for controlling the oil injection mechanism (100).

[0126] The controller (a control section) (95) for controlling the compression mechanism (20) is configured as shown in a block diagram of FIG. 14. The controller (95) includes an input value (data) reading section (96), a measurement value (or a set value) reading section (97), and a calculated value determining section (98). The input value reading section (96) and the measurement value reading section (97) are connected to the calculated value determining section (98) to send a signal to the calculated value determining section (98). The calculated value determining section (98) calculates injection timing based on the position θs of the suction port (22a), the position θi of the oil injection port (24), rotation speed ω of the crankshaft (42), and a current value θc of a rotation angle of the crankshaft (42), and the controller (95) sends a control signal to the oil injection mechanism (100). The on/off state of the solenoid mechanism (109) is controlled based on the control signal, thereby controlling timing of oil injection.

[0127] Specifically, in a single cycle of the compression mechanism (20) including a suction phase, a compression phase, and a discharge phase, a position of the piston at which the suction phase is finished is regarded as an injection starting position, and a position of the piston before the completion of the discharge phase (in this embodiment, when the piston (28) reaches the oil injection port (24)) is regarded as an injection termination position. In these conditions, the controller (95) controls the oil injection mechanism (100) in such a manner that the oil injection is performed in at least part of the range from the injection starting position to the injection termination position. In particular, the controller (95) is preferably configured in such a manner that the oil injection is performed throughout the range from the injection starting position to the injection termination position for performing the isothermal compression throughout the range.

<Timing of Opening/Closing the Injection Nozzle in Oil Injection>

[0128] Timing of opening/closing the injection nozzle (101) in the oil injection will be described below.

[0129] The position θs of the suction port (22a) and the position θi of the oil injection mechanism (100) are previously input in the input value reading section (96) of the controller (95) as preset positions. The measurement value reading section (97) of the controller (95) measures the rotation speed ω of the crankshaft (42), and the current value θc of the rotation angle of the crankshaft (42). Then, the calculated value determining section (98) calculates the injection timing based on these values.

[0130] In the single cycle including the suction phase, the compression phase, and the discharge phase, a position of the piston at which the suction phase is finished is regarded as an injection starting position θs, and a position of the piston before the completion of the discharge phase (specifically, when the piston (28) reaches the oil injection port (24)) is regarded as an injection termination position θi. In these conditions, the injection timing is determined in such a manner that the oil injection is performed in at least part of the range from the injection starting position θs to the injection termination position θi, or throughout the range. For performing the oil injection throughout the range, the spool (103) of the injection nozzle (101) of the oil injection mechanism (100) is moved backward when the piston (28) is located between the position θs and the position θi, thereby opening the oil spray port (105) as shown in FIG. 12. Then, the spool (103) of the injection nozzle (101) of the oil injection mechanism (100) is moved forward when the piston (28) is located between the position θi and the position θs, thereby closing the oil spray port (105) as shown in FIG. 13.

[0131] The controller (95) determines the injection timing in such a manner that the oil spray port (105) is opened only for injection time Δt calculated by the calculated value determining section (98) shown in FIG. 14. Thus, the oil spray port (105) of the oil injection mechanism (100) is opened/closed to control the oil injection to the compression mechanism (20).

[0132] In a conventional oil injection mechanism (100), the oil spray port (105) is kept open. Therefore, when the piston (28) is located in the range from the position θi to the position θs as shown in FIG. 28, the suction port (22a) and the oil injection port (24) may communicate with each other through the compression chamber (26), and the oil that entered from the oil injection port (24) to the compression chamber (26) may flow back into the suction port (22a).

[0133] According to the present embodiment, in contrast, the spool (103) of the oil injection mechanism (100) is moved backward to open the oil spray port (105) when the piston (28) is located in the range between the position θs and the position θi as shown in FIG. 12. Thus, the oil injection can normally be performed in this range. When the piston (28) is located between the position θi and the position θs as shown in FIG. 13, the spool (103) of the oil injection mechanism (100) is moved forward to close the oil spray port (105). Therefore, wasteful oil injection is not performed in this range.

[0134] According to the fifth embodiment described above, in the single cycle including the suction phase, the compression phase, and the discharge phase of the piston (28), the oil injection port (24) is opened while the suction port (22a) and the oil injection port (24) do not communicate with each other. Therefore, the oil injection can be performed, and the advantage of the isothermal compression described above can sufficiently be obtained in this period. On the other hand, the oil injection port (24) is closed while the suction port (22a) and the oil injection port (24) communicate with each other. In this period, the oil is prevented from flowing into the compression chamber (26). When the oil injection port (24) is opened while the piston (28) is operated, and the suction port (22a) and the oil injection port (24) communicate with each other, the refrigeration oil flowing from the oil injection port (24) to the compression chamber (26) may flow back into the suction port (22a), thereby interfering the suction of the refrigerant. In the present embodiment, however, the refrigeration oil would not flow back into the suction port (22a). This can prevent suction loss.

[0135] In the present embodiment, there is no need to calculate the required cooling amount from various values, such as rotation speed of the compressor, suction pressure, discharge pressure, enthalpy, and the amount of circulating refrigerant, to calculate a period for opening a liquid refrigerant injection device, and the amount of the refrigerant to be injected. Further, a calculation logic for measuring the input of the compressor to minimize the input is not necessary. Instead, the oil injection is performed by simply determining the timing within the range between the position of the suction port (22a) regarded as the injection starting position θs, and the position of the oil injection port (24) regarded as the injection termination position θi. Thus, the injection timing of the oil injection mechanism (100) can easily be calculated, and the oil injection can effectively be performed by merely installing a simple calculation logic.

[0136] Thus, according to the present embodiment, in a compressor which performs the isothermal compression by injecting the oil, a large amount of oil required to cool the refrigerant can be injected without increasing suction loss. Further, the isothermal compression can effectively be performed without complicated control, thereby significantly improving system performance.

[Sixth Embodiment of the Invention]

[0137] A sixth embodiment of the invention will be described below. An air conditioner (10) of the sixth embodiment has the same oil injection mechanism (100) as that of the fifth embodiment, and a controller (95) different from that of the fifth embodiment.

<Structure of Controller>

[0138] The controller (95) of the sixth embodiment is configured as shown in a block diagram of FIG. 15. The controller (95) includes an input value (data) reading section (96), a measurement value (or a set value) reading section (97), and a calculated value determining section (98). The input value reading section (96) and the measurement value reading section (97) are connected to the calculated value determining section (98) to send a signal to the calculated value determining section (98). The calculated value determining section (98) calculates timing of the oil injection based on a volume of the cylinder Vc, a position of the suction port θs, and a position of the oil injection port θi (these are data of the input value reading section (96)), and rotation speed ω of the crankshaft (42), a current value θc of a rotation angle of the crankshaft (42), temperature of sucked gas Ts, low pressure Lp of the refrigerant circuit (11), high pressure Hp of the refrigerant circuit (11), temperature of injected oil To, and pressure of injected oil Po (these are data of the measurement value reading section (97)). Specifically, an injection starting position θ1 which satisfies Tr=To where the temperature of the gaseous refrigerant in the course of compression is Tr, an injection termination position θ2 which satisfies Pr=Po where the pressure of the gaseous refrigerant in the course of the compression is Pr, and injection time Δt from the position θ1 to the position θ2 are obtained, and a control signal indicating these values is sent from the controller (95) to the oil injection mechanism (100). The on/off state of the solenoid mechanism (109) is controlled based on the control signal, thereby controlling timing of the oil injection. The temperature of the gaseous refrigerant in the course of the compression Tr, and the pressure of the gaseous refrigerant in the course of the compression Pr are calculated based on the data of the compressor such as the volume of the cylinder Vc, and the position of the suction port θs, measurement values such as the temperature of sucked gas Ts, the low pressure Lp and the high pressure Hp of the refrigerant circuit (11), and physical data of the refrigerant previously recorded in the controller. The calculation of the injection starting position θ1 and the injection termination position θ2 shown in FIG. 15 includes a process of calculating the temperature of the gaseous refrigerant in the course of the compression Tr, and the pressure of the gaseous refrigerant in the course of the compression Pr (a refrigerant temperature detecting section, and a refrigerant pressure detecting section).

[0139] Specifically, in the single cycle including the suction phase, the compression phase, and the discharge phase, a position at which the temperature of the refrigerant Tr in the compression chamber (26) reaches the temperature of the injected oil To is regarded as the injection starting position θ1, and a position at which the pressure of the refrigerant Pr in the compression chamber (26) reaches the discharge pressure Hp is regarded as the injection termination position θ2. In these conditions, the controller (95) controls the oil injection mechanism (100) in such a manner that the oil injection is performed in at least part of the range from the injection starting position θ1 to the injection termination position θ2. In particular, the controller (95) is preferably configured in such a manner that the oil injection is performed throughout the range from the injection starting position θ1 to the injection termination position θ2 for performing the isothermal compression throughout the range.

<Timing of Opening/Closing the Injection Nozzle in Oil Injection>

[0140] Timing of opening/closing the injection nozzle (101) in the oil injection will be described below.

[0141] The volume of the cylinder Vc, the position of the suction port θs, and the position of the oil injection port θi are previously input in the input value reading section (96) of the controller (95) as preset positions. The measurement value reading section (97) of the controller (95) measures the rotation speed ω of the crankshaft (42), the current value θc of the rotation angle of the crankshaft (42), the temperature of the sucked gas Ts, the low pressure Lp of the refrigerant circuit (11), the high pressure Hp of the refrigerant circuit (11), the temperature of the injected oil To, and the pressure of the injected oil Po. Then, the calculated value determining section (98) calculates the injection timing based on these values. Specifically, the injection starting position θ1 which satisfies Tr=To where the temperature of the gaseous refrigerant in the course of compression is Tr, the injection termination position θ2 which satisfies Pr=Hp where the pressure of the gaseous refrigerant in the course of the compression is Pr, and injection time Δt from the position θ1 to the position θ2 are obtained, and a control signal indicating these values is sent from the controller (95) to the oil injection mechanism (100). The on/off state of the solenoid mechanism (109) is controlled based on the control signal, thereby controlling timing of the oil injection.

[0142] In the single cycle including the suction phase, the compression phase, and the discharge phase, a position at which the temperature of the refrigerant Tr in the compression chamber (26) reaches the temperature of the injected oil To is regarded as the injection starting position θ1, and a position at which the pressure of the refrigerant Pr in the compression chamber (26) reaches the discharge pressure Hp is regarded as the injection termination position θ2. In these conditions, the injection timing is determined in such a manner that the controller (95) performs the oil injection in at least part of the range from the injection starting position θ1 to the injection termination position θ2, or throughout the range. For performing the oil injection throughout the range, the oil injection is performed in the whole range from the position θ1 to the position θ2 in FIG. 16. In this case, the spool (103) of the oil injection mechanism (100) is moved backward to open the oil spray port (105). Further, when the piston (28) is located between the position θ2 and the position θ1 as shown in FIG. 17, the spool (103) of the oil injection mechanism (100) is moved forward to close the oil spray port (105).

[0143] The controller (95) opens or closes the oil spray port (105) of the oil injection mechanism (100) based on the injection timing obtained by the calculated value determining section (98), thereby controlling the oil injection to the compression mechanism (20).

[0144] When the oil injection is performed by a conventional oil injection mechanism (100), the refrigerant is superheated when the temperature of the refrigeration oil To is higher than the temperature of the refrigerant Tr, thereby causing power loss due to overheat compression.

[0145] According to the present embodiment, however, the spool (103) of the oil injection mechanism (100) is moved backward to open the oil spray port (105) when the piston (28) is located in the range from the position θ1 to the position θ2 as shown in FIG. 16. In this range, the temperature of the refrigerant Tr is not higher than the temperature of the refrigeration oil To, thereby sufficiently reducing a workload by the isothermal compression. Further, when the piston (28) has passed the position θ2, and is approaching the position θ1 as shown in FIG. 17, the spool (103) of the oil injection mechanism (100) is moved forward to close the oil spray port (105). Therefore, in this range, wasteful oil injection is not performed, thereby preventing the power loss due to the overheat compression.

[0146] In the sixth embodiment described above, in the single cycle including the suction phase, the compression phase, and the discharge phase of the piston (28), a position of the piston at which the temperature of the refrigerant Tr in the compression chamber (26) reaches the temperature of the injected oil To is regarded as an injection starting position θ1, and a position of the piston at which the pressure of the refrigerant in the compression chamber (26) reaches the discharge pressure is regarded as an injection termination position θ2. In these conditions, the oil injection is performed in at least part the range from the injection starting position θ1 to the injection termination position θ2, or throughout the range. When the oil injection is performed throughout the range from the position θs to the position θi, a workload which cancels the workload reduced by the isothermal compression is generated by the overheat compression as shown in FIG. 18. According to the present embodiment, the oil injection performed only in the range from the position θ1 to the position θ2 prevents the generation of the workload by the overheat compression as shown in FIG. 19, thereby improving the advantage of the isothermal compression. For the above-described reasons, the present embodiment allows injection of a large amount of oil required to cool the refrigerant, and prevents the power loss due to the overheat compression. Therefore, the isothermal compression can effectively be performed, and system performance can significantly improve.

[Seventh Embodiment of the Invention]

[0147] An air conditioner (10) of the seventh embodiment is a heating-only air conditioner which performs heating operation only. As shown in FIG. 20, a refrigerant circuit (11) of the air conditioner (10) includes, like the refrigerant circuit of the first embodiment, an oil power recovering compression unit (C/O), an expansion unit (E), an outdoor heat exchanger (12), an indoor heat exchanger (13), an oil separator (60), etc.

[0148] In the refrigerant circuit (11) of the seventh embodiment, for example, two four-way switching valves (14, 15) used in the structure of the first embodiment are removed. Specifically, in the refrigerant circuit (11), a refrigerant discharge pipe (62) of the oil separator (60) is connected to an inlet end of the indoor heat exchanger (13), and an outlet end of the indoor heat exchanger (13) is connected to an inlet pipe (33) of the expansion unit (E). Further, an outlet pipe (34) of the expansion unit (E) is connected to an inlet end of the outdoor heat exchanger (12), and an outlet end of the outdoor heat exchanger (12) is connected to the suction pipe (22) of the compression mechanism (20) through a suction line (17). The refrigerant circuit (11) of the present embodiment is configured to perform heating operation for heating room air by the refrigerant in the indoor heat exchanger (13).

[0149] An oil cooler (80) of the seventh embodiment constitutes an oil cooling heat exchanger configured to cool the oil separated in the oil separator (60), and also functions as an auxiliary room heater which dissipates heat of the oil into the room during the heating operation. Specifically, the oil cooler (80) is placed inside the room where the indoor heat exchanger (13) is placed.

[0150] In the heating operation of the air conditioner (10) of the seventh embodiment, the refrigerant compressed in the compression mechanism (20) flows into the oil separator (60), and the oil is separated from the refrigerant in the oil separator (60). The refrigerant from which the oil is separated flows into the indoor heat exchanger (13). In the indoor heat exchanger (13), high pressure refrigerant dissipates heat into the room air, thereby heating the room air. Thus, the room is heated. The refrigerant that flowed out of the indoor heat exchanger (13) is reduced in pressure in the expansion unit (E), evaporates in the outdoor heat exchanger (12), and is sucked into the compression mechanism (20).

[0151] In the heating operation of the seventh embodiment, the oil injection is performed in the same manner as described in the foregoing embodiments. Specifically, the oil separated in the oil separator (60) is cooled in the oil cooler (80), and then flows into the recovery mechanism (40). In the recovery mechanism (40), an output shaft (42) is driven to rotate by the oil in the oil chamber (49), and the rotary power of the output shaft (42) is used as power to drive the compression mechanism (20).

[0152] The oil from which the energy is recovered by the recovery mechanism (40), and is reduced in pressure flows into the oil injection port (24) of the compression mechanism (20). In the compression mechanism (20), the refrigerant in the course of the compression is cooled by the oil, and is compressed almost isothermally. This can reduce power required to compress the refrigerant. As described above, a relatively large amount oil is injected also in this embodiment. This causes isothermal compression, thereby reducing the power to compress the refrigerant, and increasing the energy of the oil recovered from the pressure-increased oil.

[0153] Further, in the seventh embodiment, the oil cooler (80) is used as an auxiliary room heater to compensate the reduction in heating capability due to the oil injection. This feature will be described in detail below.

[0154] As described above, the refrigerant is compressed almost isothermally in the compression mechanism (20) performing the heating operation, thereby reducing the power to compress the refrigerant. However, when the refrigerant is compressed almost isothermally, the compressed refrigerant shows lower enthalpy as compared with the refrigerant compressed in a normal refrigeration cycle without performing the oil injection. Accordingly, heat dissipated by the refrigerant is reduced in the indoor heat exchanger (13) of the refrigerant circuit (11) performing the heating operation, thereby reducing the heating capability.

[0155] In the present embodiment, the oil cooler (80) is placed inside the room in such a manner that the oil flowing in the oil cooler (80) can dissipate heat into the room air. Specifically, in the oil injection during the heating operation, the oil separated in the oil separator (60) flows into the oil cooler (80), and the oil in the oil cooler (80) exchanges heat with the room air. As a result, the heat of the relatively high temperature oil is transferred to the room air, thereby further heating the room. The oil flowing in the oil cooler (80) is cooled by the room air. In the heating operation, the oil in the oil cooler (80) is cooled, and at the same time, the room air is heated by the oil. Thus, the oil injection can be performed while preventing the reduction of the heating capability.

[Eighth Embodiment of the Invention]

[0156] An air conditioner (10) of the eighth embodiment is a heat pump air conditioner which performs cooling and heating in a switchable manner. As shown in FIGS. 21 and 22, a refrigerant circuit (11) of the air conditioner (10) includes, like the refrigerant circuit of the first embodiment, an oil power recovering compression unit (C/O), a first four-way switching valve (14), an outdoor heat exchanger (12), an indoor heat exchanger (13), an oil separator (60), etc. In this refrigerant circuit (11), an expansion valve (38) is used as a pressure reducing mechanism in place of the expansion unit (E) of the first embodiment.

[0157] Unlike the oil feed circuits of the above-described embodiments, an oil feed circuit (70) of the eighth embodiment is configured to switch the passage of the oil between the cooling operation and the heating operation. Specifically, the oil feed circuit (70) of the eighth embodiment includes two oil coolers (80, 80), and an oil passage switching mechanism (81).

[0158] The oil passage switching mechanism (81) is comprised of a four-way switching valve having four ports. The oil passage switching mechanism (81) is configured to switch between a state in which first and fourth ports communicate with each other, and second and third ports communicate with each other (a state shown in FIG. 21), and a state in which the first and third ports communicate with each other, and the second and fourth ports communicate with each other (a state shown in FIG. 22).

[0159] The first port of the oil passage switching mechanism (81) is connected to an oil discharge pipe (63) through a first oil guiding pipe (71). The second port of the oil passage switching mechanism (81) is connected to a suction line (17) through a low pressure communication pipe (75). The third port of the oil passage switching mechanism (81) is connected to an oil inlet pipe (43) through an outdoor oil passage (74). The fourth port of the oil passage switching mechanism (81) is connected to an oil inlet pipe (43) through an indoor oil passage (73).

[0160] An indoor oil cooler (80a) placed in the room where the indoor heat exchanger (13) is placed is connected to the indoor oil passage (73). The indoor oil cooler (80a) constitutes a first oil cooling heat exchanger which dissipates heat of the oil into the room air in the heating operation. An outdoor oil cooler (80b) placed outside the room is connected to the outdoor oil passage (74). The outdoor oil cooler (80b) constitutes a second oil cooling heat exchanger which dissipates heat of the oil into the outside air in the cooling operation. In the oil feed circuit (70) configured in this manner, the oil separated in the oil separator (60) is selectively fed to one of the indoor oil cooler (80a) and the outdoor oil cooler (80b).

[0161] When the air conditioner (10) of the eighth embodiment performs the heating operation, the first four-way switching valve (14) and the oil passage switching mechanism (81) are set to the state shown in FIG. 21. The refrigerant compressed in the compression mechanism (20) flows into the oil separator (60), and the oil is separated from the refrigerant in the oil separator (60). The refrigerant from which the oil is separated flows into the indoor heat exchanger (13). In the indoor heat exchanger (13), the high pressure refrigerant dissipates heat into the room air, thereby heating the room air to heat the room. The refrigerant condensed in the indoor heat exchanger (13) is reduced in pressure through the expansion valve (38), evaporates in the outdoor heat exchanger (12), and is sucked into the compression mechanism (20).

[0162] When the heating operation is performed, the oil separated in the oil separator (60) flows into the indoor oil cooler (80a) through the indoor oil passage (73). In the indoor oil cooler (80a), the oil dissipates heat into the room air. Thus, like in the seventh embodiment, the indoor oil cooler (80a) functions as an auxiliary room heater, thereby preventing reduction in heating capability. The oil cooled in the indoor oil cooler (80a) in this manner flows into the recovery mechanism (40). In the recovery mechanism (40), the output shaft (42) is driven to rotate by the oil in the oil chamber (49), and the rotary power of the output shaft (42) is used as power to drive the compression mechanism (20).

[0163] The oil from which the energy is recovered by the recovery mechanism (40), and which is reduced in pressure flows into the oil injection port (24) of the compression mechanism (20). In the compression mechanism (20), the refrigerant in the course of the compression is cooled by the oil, and is compressed almost isothermally. This reduces power required to compress the refrigerant. As described above, a relatively large amount of oil is injected also in this embodiment. This causes isothermal compression, thereby reducing the power required to compress the refrigerant, and increasing the energy of the oil recovered from the pressure-increased oil. In addition, the heat of the oil flowing in the indoor oil cooler (80a) can be used to heat the room. Thus, COP of the air conditioner (10) of the eighth embodiment effectively improves.

[0164] When the air conditioner (10) of the eighth embodiment performs the cooling operation, the first four-way switching valve (14) and the oil passage switching mechanism (81) are set to the state shown in FIG. 22. The refrigerant compressed in the compression mechanism (20) flows into the oil separator (60), and the oil is separated from the refrigerant in the oil separator (60). The refrigerant from which the oil is separated is condensed in the outdoor heat exchanger (12), reduced in pressure through the expansion valve (38), and flows into the indoor heat exchanger (13). In the indoor heat exchanger (13), the refrigerant absorbs heat of the room air to evaporate. Thus, the room air is cooled to cool the room. The refrigerant evaporated in the indoor heat exchanger (13) is sucked into the compression mechanism (20).

[0165] When the cooling operation is performed, the oil separated in the oil separator (60) flows into the outdoor oil cooler (80b) through the outdoor oil passage (74). In the outdoor oil cooler (80b), the oil dissipates heat into the outside air. In this way, the oil flowing in the outdoor oil cooler (80b) is cooled by the outside air. Thus, the oil separated in the oil separator (60) does not flow into the indoor oil cooler (80a) in the cooling operation. Accordingly, the oil in the indoor oil cooler (80a) does not dissipate heat into the room, thereby preventing increase in load to cool the room.

[0166] In the above-described manner, the oil cooled in the outdoor oil cooler (80b) flows into the recovery mechanism (40). In the recovery mechanism (40), the output shaft (42) is driven to rotate by the oil in the oil chamber (49), and the rotary power of the output shaft (42) is used as power to drive the compression mechanism (20).

[0167] The oil from which the energy is recovered by the recovery mechanism (40), and which is reduced in pressure flows into the oil injection port (24) of the compression mechanism (20). In the compression mechanism (20), the refrigerant in the course of the compression is cooled by the oil, and is compressed almost isothermally. This reduces power required to compress the refrigerant.

[0168] The oil power recovering unit (O) and the oil power recovering expansion/compression unit (C/E/O) described above can surely be used in the air conditioner (10) of the seventh or eighth embodiment.

[Other Embodiments]

[0169] The above-described embodiments may be modified as described below.

<First Alternative Example>

[0170] In the embodiments described above, the oil separated from the refrigerant in the oil separator (60) may be fed to the suction side (the low pressure side) of the compression mechanism (20) instead of feeding the oil to the compression mechanism (20) in the course of the compression. Specifically, as shown in FIG. 23, for example, the oil guiding path (70) of the above-described embodiments may be configured to feed the separated oil to the suction side of the compression mechanism (20). In the example shown in FIG. 23, a terminal end of the second oil guiding pipe (72) of the oil guiding path (70) of the first embodiment is connected to the suction line (17). In this alternative example, the refrigerant compressed in the compression mechanism (20) can simultaneously be cooled by the oil cooled in the oil cooler (80), and the above-described advantage of the isothermal compression can be obtained.

<Second Alternative Example>

[0171] In the embodiments described above, the oil cooled in the oil cooler (80) is fed to the recovery mechanism (40). However, the oil from which the energy is recovered by the recovery mechanism (40) may be cooled in the oil cooler (80). Specifically, as shown in FIG. 24, for example, the oil cooler (80) may be arranged downstream of the recovery mechanism (40) on the oil guiding path (70) of the above-described embodiment. In the example shown in FIG. 24, the oil cooler (80) of the first embodiment is arranged downstream of the recovery mechanism (40). Also in this alternative example, the energy of the oil can be recovered by the recovery mechanism (40), and the oil cooled in the oil cooler (80) can be fed to the compression mechanism (20), thereby obtaining the above-described advantage of the isothermal compression. In the alternative example shown in FIG. 24, the oil can be cooled in the oil cooler (80) immediately before the feeding to the compression mechanism (20), thereby allowing stable feeding of the low temperature oil to the compression mechanism (20). This can improve the advantage of the isothermal compression to a further extent.

<Third Alternative Example>

[0172] In the above-described embodiments, for example, the refrigerant circuit (11) may include an internal heat exchanger (90) as shown in FIG. 25. In the example shown in FIG. 25, the internal heat exchanger (90) is connected to the refrigerant circuit (11) of the second alternative example described above (the example shown in FIG. 24).

[0173] Specifically, the internal heat exchanger (90) includes a first passage (91) and a second passage (92) to exchange heat between the refrigerants flowing in the passages (91, 92). The first passage (91) is connected to a high pressure line (19) into which the refrigerant flows after heat dissipation in a radiator (e.g., the outdoor heat exchanger (12) in the cooling operation) in the refrigerant circuit (11), and before entering the expansion mechanism (30). The second passage (92) is connected to the suction line (17). Thus, in the internal heat exchanger (90), the high pressure refrigerant flowing in the first passage (91) is cooled by the low pressure refrigerant flowing in the second passage (92). Accordingly, when the cooling operation is performed in this alternative example, the degree of supercooling of the high pressure refrigerant increases, and the cooling capability of the indoor heat exchanger (13) improves. Further, the low pressure refrigerant flowing in the second passage (92) is superheated by the high pressure refrigerant flowing in the first passage (91), thereby increasing the degree of superheat of the sucked refrigerant. Accordingly, when the low temperature oil is fed to the suction side of the compression mechanism (20) as shown in FIG. 25, the sucked refrigerant can be higher in temperature than the oil, and the oil can sufficiently cool the refrigerant.

<Fourth Alternative Example>

[0174] In the above-described embodiments, for example, the oil separator (60) may be arranged at different position as shown in FIG. 26. In the example shown in FIG. 26, the oil separator (60) of the first embodiment is arranged on the high pressure line (19) described in the third alternative example. In this alternative example, the oil increased in pressure in the compression mechanism (20) accumulates in the oil separator (60). Therefore, sending the oil to the recovery mechanism (40) allows recovery of the energy of the oil. In this alternative example, the oil that accumulates in the oil separator (60) in the cooling operation is the oil that dissipated heat in the outdoor heat exchanger (12). Specifically, the oil that accumulates in the oil separator (60) of this alternative example is lower in temperature than the oil in the oil separator of the above-described embodiments. Therefore, in the oil injection according to this alternative example, the oil which is much lower in temperature can be fed to the compression mechanism (20), thereby further improving the above-described advantage of the isothermal compression.

<Other Alternative Examples>

[0175] In the above-described embodiments, the oil separated in the oil separator (60) is fed to the compression mechanism (20), thereby allowing isothermal compression of the refrigerant in the compression phase of the compression mechanism (20) (see FIG. 4). In the example shown in FIG. 4, the refrigerant is isothermally compressed for at least part of the period of the compression phase (i.e., a period between point B to point C). However, the refrigerant may be isothermally compressed throughout the whole period of the compression phase. The part of the period of the compression phase is not limited to that shown in FIG. 4, but may be a different part.

[0176] In the example shown in FIG. 4, the refrigerant is compressed isothermally in the compression phase to make the behavior of the refrigerant closer to the isotherm plot. However, FIG. 4 merely describes ideal isothermal compression as described above, and the isothermal compression of the present invention is not always the same as that shown in FIG. 4. Specifically, as shown in FIG. 27, for example, in the isothermal compression of the present invention, the refrigerant cooled by the oil may be compressed to show the behavior which is gradually separated from the isotherm. That is, the "isothermal compression" of the present invention indicates that the refrigerant in the compression phase is cooled by the oil, and is compressed to show the behavior closer to the isotherm as compared with the refrigerant which is compressed adiabatically in a general manner (i.e., pseudo isothermal compression is included).

[0177] In the above-described embodiments, the recovery mechanism (40) of the present invention is applied to a refrigerant circuit in which the oil separated in the oil separator (60) is actively fed to the compression mechanism (20) to perform the isothermal compression. However, for example, in a refrigerant circuit in which the oil discharged from the compression mechanism (20) is sent back to the suction side of the compression mechanism (20) through an oil return pipe so as to prevent poor lubrication of the compression mechanism (20), the recovery mechanism (40) of the present invention may be applied to the oil return pipe. Also in this case, the energy of the high pressure oil can be recovered by the recovery mechanism (40), thereby improving COP of the refrigeration apparatus.

[0178] In the above-described embodiments, the body (41) of the recovery mechanism (40) is comprised of a rotary positive displacement fluid machine. However, the body (41) may be comprised of a scroll positive displacement fluid machine, or a non-positive displacement fluid machine (e.g., a turbine non-positive displacement fluid machine). The compression mechanism (20) and the expansion mechanism (30) described above may be replaced with fluid machines of other types.

[0179] In the above-described embodiments, the refrigerant filling the refrigerant circuit (11) may be replaced with other refrigerant. The oil (refrigeration oil) mixed with the refrigerant in the refrigerant circuit (11) may be replaced with other oil.

[0180] In the above-described embodiments, the invention is applied to the air conditioner (10) for conditioning air inside the room. However, the invention may be applied to, for example, a refrigeration apparatus for cooling the inside of a refrigerator or a freezer, and other refrigeration apparatuses.

[0181] The above-described embodiments have been set forth merely for the purposes of preferred examples in nature, and are not intended to limit the scope, applications, and use of the invention.

INDUSTRIAL APPLICABILITY

[0182] As described above, the invention is useful for a refrigeration apparatus including a refrigerant circuit for circulating refrigerant to perform a refrigeration cycle.

Claims

1. A refrigeration apparatus comprising:

a refrigerant circuit which includes a compression mechanism connected thereto, and performs a refrigeration cycle, wherein

the refrigerant circuit includes an oil separating section configured to separate oil from high pressure refrigerant compressed in the compression mechanism, and an oil feed circuit configured to feed the oil separated in the oil separating section to the compression mechanism so as to cool the refrigerant in the course of a compression phase of the compression mechanism, and

the oil feed circuit includes a recovery mechanism configured to recover energy of the oil flowing in the oil feed circuit.

2. The refrigeration apparatus of claim 1, wherein
the oil feed circuit feeds the oil to the compression mechanism in such a manner that the refrigerant is isothermally compressed for at least part of a period of the compression phase of the compression mechanism.

3. The refrigeration apparatus of claim 1 or 2, wherein
the refrigerant circuit is configured to perform a refrigeration cycle in which the refrigerant is compressed in the compression mechanism to a critical pressure.

4. The refrigeration apparatus of claim 1 or 2, wherein
the oil feed circuit is configured to feed the oil in the course of the compression phase of the compression mechanism.

5. The refrigeration apparatus of claim 1 or 2, wherein
the oil feed circuit is configured to feed the oil to a suction side of the compression mechanism.

6. The refrigeration apparatus of claim 1 or 2, wherein
the recovery mechanism includes a movable part which is driven to rotate by the oil, and an output shaft coupled to the movable part.

7. The refrigeration apparatus of claim 6, wherein
the compression mechanism is coupled to, and is driven by the output shaft of the recovery mechanism.

8. The refrigeration apparatus of claim 6, wherein
the refrigerant circuit includes an expansion mechanism having a movable part which is driven to rotate by the refrigerant, and is coupled to the output shaft of the recovery mechanism.

9. The refrigeration apparatus of claim 6, further comprising:

a power generator which is coupled to, and is driven by the output shaft of the recovery mechanism.

10. The refrigeration apparatus of claim 1 or 2, wherein
an oil cooling heat exchanger configured to cool the oil separated in the oil separating section is connected to the oil feed circuit.

11. The refrigeration apparatus of claim 10, wherein
the refrigerant circuit includes an indoor heat exchanger placed inside a room, and is configured to perform heating operation of heating room air by the refrigerant flowing in the indoor heat exchanger, and
the oil cooling heat exchanger is placed inside the room, and is configured to dissipate heat of the oil into the room air in the heating operation.

12. The refrigeration apparatus of claim 10, wherein
the refrigerant circuit includes an indoor heat exchanger placed inside a room, and is configured to perform heating operation of heating room air by the refrigerant flowing in the indoor heat exchanger, and cooling operation of cooling the room air by the refrigerant flowing in the indoor heat exchanger in a switchable manner, and
the oil feed circuit includes a first oil cooling heat exchanger which is placed inside the room, and dissipates heat of the oil into the room air in the heating operation, and a second oil cooling heat exchanger which is placed outside the room, and dissipates the heat of the oil into outside air in the cooling operation, both of which are connected to the oil feed circuit.

Drawing