HEAT PUMP DEVICE, TWO-STAGE COMPRESSOR, AND METHOD OF OPERATING HEAT PUMP DEVICE

Abstract

 To improve the efficiency of a two-stage compressor and of a heat pump apparatus employing a two-stage compressor when a load is small. The heat pump apparatus includes a main refrigerant circuit formed by connecting a two-stage compressor 100, a first heat exchanger, a first expansion mechanism, and a second heat exchanger sequentially with piping. When a load is higher than a predetermined load, the two-stage compressor 100 discharges a refrigerant, which is compressed twice by a low-stage compressor portion 10 and a high-stage compressor portion 30, to the refrigerant circuit. When the load is lower than the predetermined load, the two-stage compressor 100 discharges the refrigerant compressed by the low-stage compressor portion 10 to the main refrigerant circuit while bypassing the high-stage compressor portion 30 so the refrigerant is not compressed by the high-stage compressor portion 30.

Description

Technical Field

[0001] The present invention relates to a two-stage compressor including two compressor portions connected in series, and a heat pump apparatus employing a two-stage compressor.

Background Art

[0002] In a two-stage compressor including a low-stage compressor portion and high-stage compressor portion connected in series, the low-stage compressor portion compresses a refrigerant sucked from a heat pump cycle to a predetermined pressure (pressure to be reached). The pressure to be reached is determined by setting the compressor chamber capacity of the low-stage compressor portion and the compressor chamber capacity of the high-stage compressor portion. The high-stage compressor portion further compresses the refrigerant compressed by the low-stage compressor portion. The refrigerant compressed by the high-stage compressor portion is discharged from the high-stage compressor portion to the internal space of the hermetically sealed container, and discharged from the hermetically sealed container to the heat pump cycle.
As described above, in the two-stage compressor, the compressor chamber capacity of the low-stage compressor portion and the compressor chamber capacity of the high-stage compressor portion determine the pressure to be reached in the low-stage compressor portion. Depending on the operating conditions of the heat pump cycle, an over-compression state may undesirably occur where the refrigerant is compressed by compression of only the low-stage compressor portion to the discharge pressure at which the refrigerant is to be discharged to the heat pump cycle. In an over-compression state, the compression of the high-stage compressor portion is a waste, and efficiency suffers. The over-compression state tends to occur in a small-load state, e.g., heating operation is performed while the outer temperature is high. In other words, the over-compression state lowers the efficiency in a small-load state.

[0003] Patent Document 1 describes a two-stage compressor provided with a bypass route which connects a communication channel, where a refrigerant flows from a low-stage compressor portion to a high-stage compressor portion, to the discharge side space of the high-stage compressor portion. In this two-stage compressor, when an over-compression state occurs, the refrigerant in the communication channel bypasses the high-stage compressor portion and flows to the discharge side space of the high-stage compressor portion. This improves the efficiency in the over-compression state.

[0004] Patent Document 2 describes a heat pump apparatus provided with a release mechanism which returns part of a refrigerant compressed by a low-stage compressor portion to the suction side of the low-stage compressor portion. In this heat pump apparatus, when the load is low, the release mechanism is actuated, thus improving the efficiency of the compressor in a low-load state.

Citation List

Patent Literature

[0005] 

Patent Literature 1: JP 5-133367 A

Patent Literature 2: JP 2-11886 A

Summary of Invention

Technical Problem

[0006] In the two-stage compressor described in Patent Document 1, the refrigerant discharged from the low-stage compressor portion passes through a long, narrow communication channel and is discharged to the discharge side space of the high-stage compressor portion via the bypass route. While the refrigerant passes through the long, narrow communication path, a pressure loss is caused. Although this two-stage compressor may be effective in avoiding a temporary over-compression state, it does not provide much effect in reducing the over-compression loss in a steady operation.
Particularly, when the load is small, the discharge pressure is low, and accordingly the refrigerant gas has a large specific volume and a large volumetric quantity of flow. This causes a large pressure loss due to the insufficient flow channel area.

[0007] In the heat pump apparatus described in Patent Document 2, when the release mechanism is actuated, the suction side and discharge side of the low-stage compressor portion are directly connected, and part of the refrigerant compressed in the low-stage compressor portion returns to the suction side of the low-stage compressor portion. Even when the release mechanism is actuated, however, a compression equal to or exceeding a predetermined amount occurs in the low-stage compressor portion. Also, the refrigerant is heated as it passes through the low-stage compressor portion, causing a so-called preheat loss. Namely, a loss (preheat loss) is resulted from heating the refrigerant before compressing it in the high-stage compressor portion. Therefore, when the load is low, the efficiency is not much improved.

[0008] It is an object of the present invention to improve the efficiency of a two-stage compressor and of a heat pump apparatus employing a two-stage compressor in a small-load operation.

Solution to Problem

[0009] A heat pump apparatus according to the present invention comprises
a main refrigerant circuit formed by connecting a compressor, a first heat exchanger, a first expansion mechanism, and a second heat exchanger sequentially with piping,
the compressor including
a low-stage compressor portion which compresses a refrigerant flowed therein,
a high-stage compressor portion which further compresses the refrigerant compressed by the low-stage compressor portion, and
a bypass mechanism which discharges the refrigerant compressed by the low-stage compressor portion and the high-stage compressor portion to the main refrigerant circuit when a necessary load as a quantity of heat needed to set a fluid which is to be heat-exchanged with the refrigerant flowing in the main refrigerant circuit in the first heat exchanger to have a predetermined temperature is higher than a first load predetermined, and discharges the refrigerant compressed by the low-stage compressor portion to the main refrigerant circuit while bypassing the high-stage compressor portion so that the refrigerant is not compressed by the high-stage compressor portion when the necessary load is lower than the first load.

Advantageous Effects of Invention

[0010] In the heat pump apparatus according to the present invention, when the load is low, the refrigerant compressed by the low-stage compressor portion is discharged to the main refrigerant circuit while bypassing the high-stage compressor portion so the refrigerant is not compressed by the high-stage compressor portion. This can decrease the over-compression loss which may occur in a low-load state.

Brief Description of Drawings

[0011] 

[Fig. 1] is a plan view of a two-stage compressor 100 according to the first embodiment.

[Fig. 2] Fig. 2 is a sectional view taken along the line A- A' of Fig. 1.

[Fig. 3] is an enlarged view showing a compressor mechanism portion 3 in Fig. 2 and a portion around the compressor mechanism portion 3.

[Fig. 4] is a sectional view taken along the line B - B' of Fig. 1.

[Fig. 5] is a sectional view taken along the line C - C' of Fig. 2.

[Fig. 6] is a sectional view taken along the line D - D' of Fig. 2.

[Fig. 7] is a sectional view taken along the line E - E' of Fig. 2.

[Fig. 8] is a sectional view taken along the line F - F' of Fig. 2.

[Fig. 9] shows an example of the circuit configuration of a heat pump apparatus equipped with an injection circuit.

[Fig. 10] is a Mollier diagram illustrating a state of a refrigerant in the heat pump apparatus shown in Fig. 9.

[Fig. 11] shows a two-stage compressor 100 according to the second embodiment.

[Fig. 12] is a sectional view of a portion of a compressor mechanism portion 3 of a two-stage compressor 100 according to the third embodiment.

[Fig. 13] is a view explaining forces acting on a low-stage vane 13.

[Fig. 14] is a graph showing torque fluctuations in an ordinary twin rotary compressor.

[Fig. 15] is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the first embodiment operates normally.

[Fig. 16] is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the first embodiment performs over-compression relief operation.

[Fig. 17] is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the second embodiment performs high-stage direct suction operation.

Description of Embodiments

Embodiment 1.

[0012] In the first embodiment, a two-stage compressor 100 having a bypass port for bypassing a high-stage compressor portion will be described.

[0013] Fig. 1 is a plan view of the two-stage compressor 100 according to the first embodiment.
Fig. 2 is a sectional view taken along the line A - A' of Fig. 1. In Fig. 2, an intermediate connection pipe 51 portion is illustrated as a section taken along the line a - a'.
Fig. 3 is an enlarged view showing a compressor mechanism portion 3 in Fig. 2 and a portion around the compressor mechanism portion 3.
Fig. 4 is a sectional view taken along the line B - B' of Fig. 1.
Fig. 5 is a sectional view taken along the line C - C' of Fig. 2.
Fig. 6 is a sectional view taken along the line D - D' of Fig. 2.
Fig. 7 is a sectional view taken along the line E - E' of Fig. 2.
Fig. 8 is a sectional view taken along the line F - F' of Fig. 2.

First, the two-stage compressor 100 will be described.

[0014] As shown in Fig. 2, the two-stage compressor 100 includes, in a hermetically sealed container 1, an electric motor 2 having a stator 2a and a rotor 2b, the compressor mechanism portion 3 provided with two compressor portions, i.e., a low-stage compressor portion 10 and high-stage compressor portion 30, and a crank shaft 4. A discharge pipe 5 is fitted in the upper portion of the hermetically sealed container 1. The lower portion of the hermetically sealed container 1 forms a lubricating oil storage 6 where a lubricating oil is sealed.
The two-stage compressor 100 includes a suction muffler 7 outside the hermetically sealed container 1. A suction pipe 8 connects the suction muffler 7 to the low-stage compressor portion 10 of the compressor mechanism portion 3 in the hermetically sealed container 1.

[0015] As shown in Fig. 3, the low-stage compressor portion 10 of the compressor mechanism portion 3 has a low-stage compression chamber 15 formed by a low-stage cylinder 11, a low-stage frame 14 which closes the upper side of the low-stage cylinder 11, and an intermediate partition 50 which closes the lower side of the low-stage cylinder 11. The low-stage compressor portion 10 includes a low-stage rolling piston 12 which eccentrically rotates in the low-stage compression chamber 15, and a low-stage vane 13 (see Fig. 7) which partitions the low-stage compression chamber 15 into a suction side space and a discharge side space. The suction pipe 8 is connected to a low-stage suction port 21 of the low-stage compression chamber 15.
Similarly, the high-stage compressor portion 30 has a high-stage compression chamber 35, having a capacity smaller than that of the low-stage compression chamber 15, formed by a high-stage cylinder 31, a high-stage frame 34 which closes the lower side of the high-stage cylinder 31, and the intermediate partition 50 which closes the upper side of the high-stage cylinder 31. The high-stage compressor portion 30 includes a high-stage rolling piston 32 which eccentrically rotates in the high-stage compression chamber 35, and a high-stage vane 33 (see Fig. 8) which partitions the high-stage compression chamber 35 into a suction side space and a discharge side space.
In other words, the two-stage compressor 100 is a rotary two-stage compressor.
The direction of eccentricity of the low-stage rolling piston 12 and that of the high-stage rolling piston 32 are shifted from each other by about 180° (see Figs. 7 and 8).

[0016] The compressor mechanism portion 3 includes a low-stage cover 19 (low-stage discharge portion) which forms a low-stage discharge space 20 with respect to the low-stage frame 14, and a high-stage cover 39 (high-stage discharge portion) which forms a high-stage discharge space 40 with respect to the high-stage frame 34. The compressor mechanism portion 3 is also provided with the intermediate connection pipe 51 which connects an intermediate outflow port 22 of the low-stage cover 19 to a high-stage suction port 41 of the high-stage cylinder 31. This allows the low-stage discharge space 20 to communicate with the high-stage compression chamber 35.
A low-stage discharge port 16 through which the low-stage compression chamber 15 communicates with the low-stage discharge space 20 is formed in the low-stage frame 14. The low-stage discharge port 16 has a low-stage discharge valve 17 and low-stage valve stopper 18 attached using a rivet 28, thus forming a lead valve (see Fig. 6). Similarly, a high-stage discharge port 36 through which the high-stage compression chamber 35 communicates with the high-stage discharge space 40 is formed in the high-stage frame 34. The high-stage discharge port 36 has a high stage discharge valve 37 and high-stage valve stopper 38 attached using a rivet, thus forming a lead valve.
The low-stage cover 19 has a bypass port 23 through which the low-stage discharge space 20 communicates with a discharge pressure space 53 as the internal space of the hermetically sealed container 1. The bypass port 23 has a bypass valve 24 and bypass valve stopper 25 attached using a rivet 29, thus forming a lead valve (see Fig. 5). This structure constitutes a bypass mechanism.
A discharge flow channel 52 is formed to extend through the high-stage frame 34, high-stage cylinder 31, intermediate partition 50, low-stage cylinder 11, low-stage frame 14, and low-stage cover 19 and allows the high stage discharge space 40 and discharge pressure space 53 to communicate with each other.

[0017] As shown in Fig. 4, the low-stage cover 19 is provided with an injector 60. The injector 60 is connected to an injection pipe 61.

[0018] The operation of the two-stage compressor 100 will now be described.
When electric power is supplied, the electric motor 2 operates. The electric motor 2 and compressor mechanism portion 3 are connected to each other by the crank shaft 4, so power generated by the electric motor 2 is transmitted to the compressor mechanism portion 3 via the crank shaft 4. More specifically, upon reception of the electric power, the rotor 2b of the electric motor 2 rotates. When the rotor 2b rotates, the crank shaft 4 inserted in the rotor 2b also rotates. When the crank shaft 4 rotates, the low-stage rolling piston 12 and high-stage rolling piston 32 in which the crank shaft 4 is inserted eccentrically rotate in the low-stage compression chamber 15 and high-stage compression chamber 35, respectively. The eccentric rotation of the low-stage rolling piston 12 and high-stage rolling piston 32 compresses the refrigerant in the low-stage compressor portion 10 and high-stage compressor portion 30.

[0019] The flow of refrigerant in the two-stage compressor 100 will be described.
First, a low-pressure refrigerant flows into the suction muffler 7 from the outside. The low-pressure refrigerant flowing in the suction muffler 7 is sucked into the low-stage compression chamber 15 through the suction pipe 8. The sucked low-pressure refrigerant is compressed in the low-stage compression chamber 15 until its pressure reaches an intermediate pressure. When the refrigerant is compressed to the intermediate pressure, the pressure difference between the refrigerant in the low-stage compression chamber 15 and that in the low-stage discharge space 20 opens the low-stage discharge valve 17 to discharge the refrigerant in the low-stage compression chamber 15 through the low-stage discharge port 16 to the low-stage discharge space 20. The intermediate pressure is a pressure determined by the ratio of the capacity of the suction chamber of the low-stage compression chamber 15 to the capacity of the suction chamber of the high-stage compression chamber 35.
The intermediate-pressure refrigerant discharged to the low-stage discharge space 20 is sucked into the high-stage compression chamber 35 through the intermediate connection pipe 51. The sucked intermediate-pressure refrigerant is compressed in the high-stage compression chamber 35 until its pressure reaches a discharge pressure. When the refrigerant is compressed to the discharge pressure, the pressure difference between the refrigerant in the high-stage compression chamber 35 and that in the high-stage discharge space 40 opens the high-stage discharge valve 37 to discharge the refrigerant in the high-stage compression chamber 35 through the high-stage discharge port 36 to the high-stage discharge space 40.
The discharge-pressure refrigerant discharged to the high-stage discharge space 40 is discharged to the discharge pressure space 53 above the low-stage compressor portion 10 through the discharge flow channel 52. The discharge-pressure refrigerant in the discharge pressure space 53 is discharged through the discharge pipe 5 to the outside.
When the heat pump apparatus equipped with the two-stage compressor 100 performs injection operation, an injection refrigerant from the injection pipe 61 shown in Fig. 4 is injected into the low-stage discharge space 20 through the injector 60. In the low-stage discharge space 20, the injection refrigerant mixes with the intermediate-pressure refrigerant discharged from the low-stage compression chamber 15, and the mixture is compressed in the high-stage compressor portion 30.

[0020] When, e.g., a heat pump apparatus 101 has a small load, an over-compression state may occur where the refrigerant is compressed by compression of only the low-stage compressor portion 10 to the discharge pressure. Namely, the intermediate pressure of the refrigerant described above may undesirably become higher than the necessary discharge pressure.
In this case, the pressure difference between the refrigerant in the low-stage discharge space 20 and that in the discharge pressure space 53 opens the bypass valve 24, and the refrigerant in the low-stage discharge space 20 is discharged through the bypass port 23 to the discharge pressure space 53. In other words, the refrigerant discharged from the low-stage compressor portion 10 to the low-stage discharge space 20 is not compressed by the high-stage compressor portion 30 but bypasses the high-stage compressor portion 30 and is discharged to the discharge pressure space 53.
In the over-compression state, the discharge pressure is obtained by compression of only the low-stage compressor portion 10. Compression by the high-stage compressor portion 30 is a waste. If the high-stage compressor portion 30 performs compression, the efficiency suffers. In the two-stage compressor 100, however, when the over-compression state occurs, the refrigerant compressed in the low-stage compressor portion 10 bypasses the high-stage compressor portion 30 and is discharged. This can suppress a loss (over-compression loss) accompanying an over-compression state.

[0021] In particular, the bypass port 23 is formed in the low-stage cover 19. The refrigerant is discharged to the discharge pressure space 53 in the hermetically sealed container 1 through the bypass port 23 without passing through the intermediate connection pipe 51. In other words, as the refrigerant discharged to the discharge pressure space 53 through the bypass port 23 does not flow in the long, narrow intermediate connection pipe 51, it is free from compression loss. Consequently, over-compression loss can be suppressed effectively in normal operation.

[0022] As described above, the lower portion of the hermetically sealed container 1 forms the lubricating oil storage 6 where the lubricating oil is sealed. The lubricating oil is supplied to the mechanical portion of the compressor mechanism portion 3. For this purpose, an amount of lubricating oil sufficient to immerse at least the compressor portion (the low-stage compressor portion 10 in Fig. 2) positioned on the upper side is sealed.
In a general two-stage compressor, the low-stage compressor portion is under the high-stage compressor portion, and accordingly the low-stage discharge space is under the low-stage compressor portion. In other words, the low-stage cover is formed under the low-stage compressor portion. As a result, the low-stage discharge cover is dipped in the lubricating oil. In this case, the lubricating oil may enter the low-stage discharge space through the bypass port 23. Also, when the refrigerant is discharged via the bypass port 23, the lubricating oil may get involved in the refrigerant, so that the amount of lubricating oil flowing out from the compressor increases undesirably. Therefore, the bypass port cannot be formed in the low-stage cover. The bypass port can be formed only in the narrow flow channel that connects the low-stage discharge space and the high-stage compressor portion, as in Patent Literature 1.
In the two-stage compressor 100, however, the low-stage compressor portion 10 is above the high-stage compressor portion 30, which is opposite to the conventional arrangement. Accordingly, the low-stage discharge space 20 is above the low-stage compressor portion 10, so that the low-stage cover 19 can be located at such a height that it will not be dipped in the lubricating oil. Consequently, the bypass port 23 can be formed in the low-stage cover 19.

[0023] The bypass port 23 is formed not in the intermediate connection pipe 51 but in the low-stage cover 19. This allows the bypass valve 24 to form a lead valve having a simple structure. Hence, the bypass valve 24 can be a component of the same type as the low-stage discharge valve 17, and the bypass valve stopper 25 can be a component of the same type as the low-stage valve stopper 18. Since the number of types of the components is decreased, the cost can be suppressed. Since the structure of the bypass valve 24 is simplified, the assembly cost can also be suppressed.

[0024] The heat pump apparatus 101 equipped with the two-stage compressor 100 will be described.
Fig. 9 shows an example of a circuit configuration of a heat pump apparatus equipped with an injection circuit. Fig. 10 is a Mollier diagram illustrating a state of a refrigerant in the heat pump apparatus 101 of Fig. 9. Referring to Fig. 10, the horizontal axis indicates specific enthalpy and the vertical axis indicates refrigerant pressure.

[0025] The heat pump apparatus 101 includes a main refrigerant circuit formed by connecting the two-stage compressor 100, a heat exchanger 71 (second heat exchanger), a first expansion valve 72, a receiver 78, a third expansion valve 74, and a heat exchanger 76 (first heat exchanger) sequentially with piping. The heat pump apparatus 101 also includes an injection circuit formed by connecting with piping a portion between the receiver 78 and third expansion valve 74 to the injection pipe 61 of the two-stage compressor 100. The injection circuit is equipped with a second expansion valve 75 midway along the piping. The heat pump apparatus 101 includes an internal heat exchanger 73 which exchanges the heat of the refrigerant in the main refrigerant circuit with the heat of the refrigerant in the injection circuit. The heat pump apparatus 101 also includes a four-way valve 77 which changes the direction in which the refrigerant flows.

[0026] First, an operation of the heat pump apparatus 101 performed during heating is described. During heating operation, the four-way valve 77 is set in a course indicated by solid lines. Heating operation, in the description, indicates not only air heating in air conditioning but also water heating in hot water supply to provide hot water.
The high-temperature high-pressure gas refrigerant (a point 1 in Fig. 10) at the two-stage compressor 100 is discharged through the discharge pipe 5 of the two-stage compressor 100. The high-temperature high-pressure gas refrigerant is then sent through the heat exchanger 71, as a condenser or a radiator, where the gas liquefies (a point 2 in Fig. 10). During this process, the heat of the refrigerant increases the temperature of air or water to be used for air conditioning or hot water supply.
The liquid refrigerant from the heat exchanger 71 is sent through the first expansion valve 72 (a decompression mechanism) where the pressure of the liquid refrigerant is reduced, thereby turning into a two-phase gas-liquid refrigerant (a point 3 in Fig. 10). The two-phase gas-liquid refrigerant from the first expansion valve 72 is sent through the receiver 78 where its heat is exchanged with the heat of a refrigerant to be sucked in the two-stage compressor 100, thereby cooled and liquefied (a point 4 in Fig. 10). Then, the flow of the liquid refrigerant in the receiver 78 is divided to the main refrigerant circuit on the side of the internal heat exchanger 73 and third expansion valve 74 and to the injection circuit on the side of the second expansion valve 75.
The liquid refrigerant in the main refrigerant circuit is sent through the internal heat exchanger 73 where its heat is exchanged with the heat of a two-phase gas-liquid refrigerant from the second expansion valve 75, where the pressure of the refrigerant in the injection circuit is reduced, and thereby the liquid refrigerant is further cooled (a point 5 in Fig. 10). The liquid refrigerant cooled at the internal heat exchanger 73 is sent through the third expansion valve 74 (a decompression mechanism) where the pressure is reduced, and thereby the liquid turns into two-phase gas-liquid (a point 6 in Fig. 10). The two-phase gas-liquid refrigerant from the third expansion valve 74 is sent through the heat exchanger 76 as an evaporator, where the gas-liquid refrigerant is heated (a point 7 in Fig. 10). The heated refrigerant from the heat exchanger 76 is then sent through the receiver 78 where it is further heated (a point 8 in Fig. 10). Then, the heated refrigerant is sucked into the two-stage compressor 100 through the suction pipe 8.
Meanwhile, the refrigerant flowing in the injection circuit is sent through the second expansion valve 75 (a decompression mechanism) where its pressure is reduced (a point 9 in Fig. 10), and then through the internal heat exchanger 73 for heat exchange (a point 10 in Fig. 10), as described earlier. The two-phase gas-liquid refrigerant (an injection refrigerant) after heat exchange at the internal heat exchanger 73 flows without changing its phase in the low-stage discharge space 20 via the injection pipe 61 of the two-stage compressor 100.
In the two-stage compressor 100, the refrigerant flowing in the main refrigerant circuit and sucked in through the suction pipe 8 (the point 8 in Fig. 10) is compressed by the low-stage compressor portion 10 to have the intermediate pressure and heated (a point 11 in Fig. 10). The heated and compressed refrigerant having the intermediate pressure and discharged to the low-stage discharge space 20 (the point 11 in Fig. 10) joins the injection refrigerant (the point 8 in Fig. 10) and cools (a point 12 in Fig. 10). The cooled refrigerant (the point 12 in Fig. 10) is then compressed and heated by the high-stage compressor portion 30 to increase its temperature and pressure, and discharged to the discharge pressure space 53 via the discharge flow channel 52 (point 1 in Fig. 10).

[0027] It is to be noted that the opening of the second expansion valve 75 is totally closed when the injection operation is not performed. More specifically, during injection operation, the second expansion valve 75 is set so that the size of its opening is larger than a predetermined size of opening. When the injection operation is not performed, the size of the opening of the second expansion valve 75 is set so that it is smaller than a predetermined size of opening. This may prevent the refrigerant from flowing into the injection pipe 61 of the two-stage compressor 100. In other words, all the amount of refrigerant passing through the heat exchanger 71, the first expansion valve 72, and the receiver 78 is sucked in the two-stage compressor 100 via the suction pipe 8.
It is to be noted that the size of the opening of the second expansion valve 75 may be electronically controlled by a controller. The controller is a microcomputer, for example.

[0028] An operation performed by the heat pump apparatus 101 during cooling is now described. The four-way valve 77 is set in a course indicated by broken lines during cooling operation.
The high-temperature high-pressure gas refrigerant (the point 1 in Fig. 10) at the two-stage compressor 100 is discharged through the discharge pipe 5 of the two-stage compressor 100. The high-temperature high-pressure gas refrigerant is then sent through the heat exchanger 76, as a condenser or a radiator, where the gas liquefies by heat exchange (the point 2 in Fig. 10). The liquid refrigerant from the heat exchanger 76 is then sent through the third expansion valve 74 where its pressure is reduced, and thereby turns into two-phase gas-liquid (the point 3 in Fig. 10). The two-phase gas-liquid refrigerant from the third expansion valve 74 is then sent through the internal heat exchanger 73 where the gas-liquid refrigerant cools by heat exchange and thereby liquefies (the point 4 in Fig. 10). In the internal heat exchanger 73, the heat of the two-phase gas-liquid refrigerant from the third expansion valve 74 is exchanged with the heat of the two-phase gas-liquid refrigerant from the second expansion valve 75 (the point 9 in Fig. 10) where the pressure of the liquid refrigerant from the internal heat exchanger 73 is reduced. The flow of the liquid refrigerant passed through the internal heat exchanger 73 (the point 4 in Fig. 10) is divided to the main refrigerant circuit on the receiver 78 side and the injection circuit on the internal heat exchanger 73 side.
The liquid refrigerant flowing in the main refrigerant circuit is sent through the receiver 78 where its heat is exchanged with the heat of the refrigerant to be sucked in the two-stage compressor 100, thereby further cooled (the point 5 in Fig. 10). The cooled liquid refrigerant from the receiver 78 is then sent through the first expansion valve 72 where the pressure is reduced, and turns into two-phase gas-liquid (the point 6 in Fig. 10). The two-phase gas-liquid refrigerant from the first expansion valve 72 is sent through the heat exchanger 71 as an evaporator to be heated by heat exchange (the point 7 in Fig. 10). During this process, the refrigerant absorbs heat, thereby cooling air or water. This allows room air to be cooled, or water to be chilled or iced. This may also be used for refrigeration.
The heated refrigerant from the heat exchanger 71 is sent through the receiver 78 where it is further heated (the point 8 in Fig. 10), and then sucked in the two-stage compressor 100 via the suction pipe 8.
Meanwhile, the refrigerant flowing in the injection circuit is sent through the second expansion valve 75 where the pressure is reduced (the point 9 in Fig. 10), and then heat-exchanged through the internal heat exchanger 73 (the point 10 in Fig. 10), as described earlier. The two-phase gas-liquid refrigerant (the injection refrigerant) from the internal heat exchanger 73 flows without changing its phase into the low-stage discharge space 20 via the injection pipe 61 of the two-stage compressor 100.
It is to be noted that the compression operation in the two-stage compressor 100 is performed in the same manner as that during heating operation.

[0029] It is to be noted that when the injection operation is not performed, the second expansion valve 75 is totally closed to stop the refrigerant from flowing into the injection pipe 61 of the two-stage compressor 100, like during heating operation.

[0030] As mentioned above, the heat exchanger 71 may be of a type that exchanges heat between a high-temperature high-pressure gas refrigerant or a low-temperature low-pressure liquid refrigerant and liquid such as water. Alternatively, another type of a heat exchanger that exchanges heat between a high-temperature high-pressure gas refrigerant or a low-temperature low-pressure liquid refrigerant and a gas such as air may be employed instead. In other words, the heat pump apparatus 101 illustrated in Fig. 9 may alternatively be an air conditioner, a water heater, a freezer, or a refrigerator.

[0031] It is also to be noted that the injection operation is performed when the load is high. The load refers to the necessary load as a quantity of heat needed to set the temperature of the fluid, the heat of which is be exchanged with the heat of the refrigerant flowing in the main refrigerant circuit in the heat exchanger 71, to a predetermined temperature. The necessary load can be measured by referring to the outside temperature, the rotation frequency of the compressor, or the like as an index. Assume that a necessary load detector (not shown in the figure) detects the necessary load by detecting the outside temperature, the rotation frequency of the compressor, or the like.
For example, the injection operation is performed during heating operation when the outside temperature is the same or below a predetermined temperature (e.g., 2°C) or when the rotation frequency of the compressor is the same or above a predetermined frequency (e.g., 60 Hz). Then, heating capacity may be enhanced when the outside temperature is low. This may result in achieving a heat pump apparatus having excellent performance in heating room air or water. In other cases where the injection operation is not needed, the second expansion valve 75 is totally closed, so the injection operation is not performed even during heating operation.

[0032] As described above, in the two-stage compressor 100, the bypass mechanism is actuated when the load decreases to reach an over-compression state. Then, the refrigerant compressed in the low-stage compressor portion 10 bypasses the high-stage compressor portion 30 so the refrigerant is not compressed by the high-stage compressor portion 30, and is discharged to the discharge pressure space 53, and then to the refrigerant circuit via the discharge pipe 5.

[0033] More specifically, the heat pump apparatus 101 selectively performs the following control operations (1) to (3) in accordance with the intensity of the load.

(1) When the load is high (when the load is higher than the second load predetermined), the size of the opening of the second expansion valve 75 is increased, and injection operation is performed.

(2) When the load is of an intermediate level (when the load is lower than the second load and higher than the first load which is predetermined to be lower than the second load), the size of the opening of the second expansion valve 75 is decreased, no injection operation is performed, and the refrigerant is compressed by two-stage compression using the low-stage compressor portion 10 and high-stage compressor portion 30.

(3) When the load is low (when the load is lower than the first load), the bypass valve 24 is opened, so that the refrigerant bypasses the high-stage compressor portion 30 and is compressed mainly in only the low-stage compressor portion 10.

Hence, when the load is high, an operation that exhibits a high capacity can be performed; when the load is low, the capacity is suppressed, and efficient operation can be performed.

Embodiment 2.

[0034] In the second embodiment, a two-stage compressor 100 will be described which has a mechanism in which a refrigerant in a suction muffler 7 is sucked into a high-stage compressor portion 30 by bypassing a low-stage compressor portion 10.

[0035] Fig. 11 shows the two-stage compressor 100 according to the second embodiment.
Only the portions of the two-stage compressor 100 according to the second embodiment which are different from their equivalents of the two-stage compressor 100 according to the first embodiment will be described.
The two-stage compressor 100 is provided with a four-way valve 54 (selector portion) at a portion corresponding to a midway portion along a suction pipe 8 which connects the suction muffler 7 to a low-stage suction port 21 of the low-stage compressor portion 10 and a midway portion along an intermediate connection pipe 51 which connects an intermediate outflow port 22 of a low-stage cover 19 to a high-stage suction port 41 of the high-stage compressor portion 30.
The four-way valve 54 performs switching operation between a state (flow channels indicated by solid lines) in which the suction muffler 7 is connected to the low-stage suction port 21 and the intermediate outflow port 22 is connected to the high-stage suction port 41 and a state (flow channels indicated by broken lines) in which the suction muffler 7 is connected to the high-stage suction port 41 and the low-stage suction port 21 is connected to the intermediate outflow port 22. In particular, the four-way valve 54 connects the suction muffler 7 to the low-stage suction port 21 and the intermediate outflow port 22 to the high-stage suction port 41 (the flow channels indicated by the solid lines) during normal operation. When the load is low, the four-way valve 54 connects the suction muffler 7 to the high-stage suction port 41 and the low-stage suction port 21 to the intermediate outflow port 22 (the flow channels indicated by the broken lines). In other words, during normal operation, the refrigerant flowing into the suction muffler 7 is sucked by the low-stage compressor portion 10. When the load is low, the refrigerant flowing into the suction muffler 7 bypasses the low-stage compressor portion 10 so it is sucked by the high-stage compressor portion 30 without compression by the low-stage compressor portion 10.

[0036] The two-stage compressor 100 according to the second embodiment can compress the refrigerant with only the high-stage compressor portion 30 when the load is low and compression by both the low-stage compressor portion 10 and high-stage compressor portion 30 is not necessary. Thus, the two-stage compressor 100 can have an improved compressor efficiency when the load is low.
In the two-stage compressor 100 according to the second embodiment, the refrigerant flowing into the suction muffler 7 can be sucked by the high-stage compressor portion 30 directly without passing through the low-stage compressor portion 10. This eliminates preheat loss by the low-stage compressor portion 10.

[0037] In a so-called inverter type compressor in which the rotation frequency of the electric motor is variable, the circulation amount of the refrigerant is adjusted by changing the rotation frequency of the electric motor in accordance with the load fluctuations of the heat pump apparatus. More specifically, when the load is low and the circulation amount of the refrigerant must be decreased, it is done so by decreasing the rotation frequency of the electric motor. When the load is large and the circulation amount of the refrigerant must be increased, it is done so by increasing the rotation frequency of the electric motor.
In general, the electric motor is designed such that its efficiency characteristics reach the peak at the rated rotation frequency. It is thus desirable to operate the electric motor at a rotation frequency close to the rated value from the viewpoint of the efficiency of the compressor.

[0038] As described in the first embodiment, when the load is low, the two-stage compressor 100 discharges the refrigerant through the bypass port 23, so that the refrigerant can be compressed mainly with only the low-stage compressor portion 10. In the second embodiment, as mentioned above, when the load is low, the two-stage compressor 100 switches the four-way valve 54, so that the refrigerant can be compressed with only the high-stage compressor portion 30. In other words, the two-stage compressor 100 can compress the refrigerant using mainly only the low-stage compressor portion 10 or only the high-stage compressor portion 30.
The compressor chamber capacity of the high-stage compressor portion 30 (the capacity of the high-stage compression chamber 35) is smaller than the compressor chamber capacity of the low-stage compressor portion 10 (the capacity of the low-stage compression chamber 15), as described in the first embodiment. To obtain the same refrigerant circulation amount in a compressor having a large compressor chamber capacity and in a compressor having a small compressor chamber capacity, the electric motor of the compressor having the large compressor chamber capacity must have a lower rotation frequency than the rotation frequency of the electric motor of the compressor having the small compressor chamber capacity. In other words, in the two-stage compressor 100, when the refrigerant is to be compressed using mainly only the low-stage compressor portion 10, to obtain the same refrigerant circulation amount as that obtained when the refrigerant is to be compressed using only the high-stage compressor portion 30, the electric motor of the two-stage compressor 100 must have a lower rotation frequency because the compressor chamber capacity of the low-stage compressor portion 10 is larger.
For this reason, when the load is low, the two-stage compressor 100 is switched between operation of compressing the refrigerant using mainly only the low-stage compressor portion 10 and operation of compressing the refrigerant using only the high-stage compressor portion 30 in accordance with how low the load is. More specifically, when the load is not very low, the four-way valve 54 is not switched but the bypass mechanism is actuated, so that the refrigerant is compressed using mainly only the low-stage compressor portion 10. When the load is very low, the four-way valve 54 is switched, and the refrigerant is compressed using only the high-stage compressor portion 30.
Assume a case in which if the refrigerant is to be compressed using the low-stage compressor portion 10, the rotation frequency must be lower than the rated rotation frequency. In this case, the four-way valve 54 is switched so the refrigerant is compressed using only the high-stage compressor portion 30. Then, the rotation frequency of the electric motor can be increased to become close to the rated rotation frequency. Consequently, a higher efficiency can be obtained.

[0039] More specifically, a heat pump apparatus 101 provided with the two-stage compressor 100 according to the second embodiment selectively performs the following control operations (1) to (4) in accordance with the intensity of the load.

(1) When the load is high (when the load is higher than the second load predetermined), the size of the opening of a second expansion valve 75 is increased, and injection operation is performed.

(2) When the load is of an intermediate level (when the load is lower than the second load but higher than the first load which is predetermined to be lower than the second load), the size of the opening of the second expansion valve 75 is decreased. No injection operation is performed. The refrigerant is compressed by two-stage compression using the low-stage compressor portion 10 and high-stage compressor portion 30.

(3) When the load is low (when the load is lower than the first load but higher than the third load which is predetermined to be lower than the first load), a bypass valve 24 is opened, so that the refrigerant bypasses the high-stage compressor portion 30 and is compressed mainly with only the low-stage compressor portion 10.

(4) When the load is very low (when the load is lower than the third load), the four-way valve 54 is switched. The refrigerant bypasses the low-stage compressor portion 10 and is sucked in the high-stage compressor portion 30 via the suction muffler 7, so it is compressed using only the high-stage compressor portion 30.

[0040] Hence, the heat pump apparatus 101 equipped with the two-stage compressor 100 according to the second embodiment can have an improved efficiency when the load is very low.
Note that the four-way valve 54 is electronically controlled by a controller.

Embodiment 3.

[0041] In the third embodiment, a two-stage compressor 100 will be described in which a refrigerant sucked in a high-stage compressor portion 30 is supplied to a low-stage back pressure chamber 26 of a low-stage vane 13 of a low-stage compressor portion 10.

[0042] Fig. 12 is a sectional view of a portion of a compressor mechanism portion 3 of the two-stage compressor 100 according to the third embodiment.
Only the portions of the two-stage compressor 100 according to the third embodiment which are different from their equivalents of the two-stage compressor 100 according to the second embodiment will be described.
The two-stage compressor 100 is provided with a pressure inlet channel 55 extending through an intermediate partition 50. A high-stage suction flow channel 42 from a high-stage suction port 41 to a high-stage compression chamber 35 communicates with the low-stage back pressure chamber 26 of the low-stage compressor portion 10 through the pressure inlet channel 55.
With the pressure inlet channel 55, the refrigerant to be sucked in the high-stage compression chamber 35 flows into the low-stage back pressure chamber 26. Namely, the pressure in the low-stage back pressure chamber 26 is equal to that of the refrigerant to be sucked in the high-stage compressor portion 30.

[0043] Forces acting on the low-stage vane 13 will be described.
Fig. 13 is a view explaining the forces acting on the low-stage vane 13.
A force "Pv × v" expressed as the product of a pressure "Pv" in the low-stage back pressure chamber 26 and an area "v" of the portion of the low-stage vane 13 where the pressure "Pv" works, and a force Psp of a spring 27 act on the low-stage vane 13 from the low-stage back pressure chamber 26 side toward a low-stage compression chamber 15 side. That is, a force "Pv × v + Psp" acts on the low-stage vane 13 from the low-stage back pressure chamber 26 side toward the low-stage compression chamber 15 side.
A force "Ps × a" expressed as the product of a pressure "Ps" of the suction refrigerant and an area "a" of the portion of the low-stage vane 13 where the pressure "Ps" works, and a force "Pc × b" expressed as the product of a pressure "Pc" of the discharge refrigerant and an area "b" of the portion of the low-stage vane 13 where the pressure "Pc" works also act on the low-stage vane 13 from the low-stage compression chamber 15 side toward the low-stage back pressure chamber 26 side. In addition, a pushing force "x" (vane centrifugal force) generated upon eccentric rotation of a low-stage rolling piston 12 acts on the low-stage vane 13 from the low-stage compression chamber 15 side toward the low-stage back pressure chamber 26 side. In other words, a force "(Ps × a) + (Pc × b) + x" acts on the low-stage vane 13 from the low-stage compression chamber 15 side toward the low-stage back pressure chamber 26 side.
In fine, a force "Fv = (Pv × v + Psp) - ((Ps × a) + (Pc × b) + x)" acts on the low-stage vane 13. Note that the area "v" = area "a" + area "b".

[0044] Forces acting on the low-stage vane 13 when a four-way valve 54 is set in a course indicated by the solid lines in Fig. 11 (during normal operation) will be described.
The pressure "Pv" in the low-stage back pressure chamber 26 will be described first.
During normal operation, the refrigerant compressed by the low-stage compressor portion 10 and discharged to a low-stage discharge space 20 is sucked in the high-stage compression chamber 35 of the high-stage compressor portion 30 via an intermediate connection pipe 51 and the high-stage suction flow channel 42. As the refrigerant passes in the high-stage suction flow channel 42, it partly flows into the low-stage back pressure chamber 26 via the pressure inlet channel 55. Hence, an intermediate-pressure refrigerant compressed in the low-stage compressor portion 10 flows into the low-stage back pressure chamber 26. More precisely, the pressure "Pv" of the refrigerant in the low-stage back pressure chamber 26 is not the intermediate pressure of the refrigerant discharged from the low-stage compressor portion 10, but the pressure obtained by enhancing the intermediate pressure by a value corresponding to the resistance of the intermediate connection pipe 51 which is generated as the refrigerant passes in the intermediate connection pipe 51. Namely, the pressure "Pv" of the refrigerant in the low-stage back pressure chamber 26 is slightly higher than the intermediate pressure.
The pressure in the low-stage compression chamber 15 will be described.
During normal operation, the low-stage compressor portion 10 compresses a low-pressure refrigerant to an intermediate pressure. The pressure "Ps" of the suction refrigerant is the low pressure, and the pressure "Pc" of the discharge refrigerant is the intermediate pressure.
During normal operation, the pressure "Pv" (the pressure slightly higher than the intermediate pressure) in the low-stage back pressure chamber 26 is higher than the pressure "Ps" (low pressure) or the pressure "Pc" (intermediate pressure) in the low-stage compression chamber 15.

[0045] Forces acting on the low-stage vane 13 when the four-way valve 54 is set in a course indicated by the broken lines in Fig. 11 (when the low-stage compressor portion 10 is bypassed) will be described.
First, the pressure "Pv" in the low-stage back pressure chamber 26 will be described.
When the low-stage compressor portion 10 is bypassed, the refrigerant flowing in a suction muffler 7 bypasses the low-stage compressor portion 10 and is sucked into the high-stage compression chamber 35 via the intermediate connection pipe 51 and high-stage suction flow channel 42. While the refrigerant passes in the high-stage suction flow channel 42, it partly flows into the low-stage back pressure chamber 26 via the pressure inlet channel 55. Accordingly, a low-pressure refrigerant flowing in the suction muffler 7 flows into the low-stage back pressure chamber 26. In other words, the pressure "Pv" in the low-stage back pressure chamber 26 is a low pressure.
The pressure in the low-stage compression chamber 15 will now be described.
When the low-stage compressor portion 10 is bypassed, the low-stage compressor portion 10 does not suck the refrigerant through the suction muffler 7, and the refrigerant in the low-stage compressor portion 10 is the refrigerant circulating between the low-stage compression chamber 15 and low-stage discharge space 20. Thus, the same refrigerant is repeatedly compressed in the low-stage compressor portion 10. When, however, the refrigerant reaches a pressure higher than the discharge pressure, it is discharged to a discharge pressure space 53 via a bypass port 23. The pressure in the low-stage compression chamber 15 hence varies between the low pressure and the discharge pressure.
When the low-stage compressor portion 10 is bypassed, the pressure "Pv" (low pressure) in the low-stage back pressure chamber 26 is equal to or lower than the pressure "Ps" or "Pc" in the low-stage compression chamber 15. Although the pressure "Pv" in the low-stage back pressure chamber 26 may occasionally become equal to the pressure in the low-stage compression chamber 15, it soon becomes lower than the pressure in the low-stage compression chamber 15.

[0046] By adjusting the force "Psp" of the spring 27 or the vane centrifugal force "x", the force "Fv" acting on the low-stage vane 13 becomes larger than 0 during normal operation. When the low-stage compressor portion 10 is bypassed, the force "Fv" acting on the low-stage vane 13 can be decreased to be smaller than 0. More specifically, during normal operation, the force acting on the low-stage vane 13 from the low-stage back pressure chamber 26 side toward the low-stage compression chamber 15 side is set to be larger than the force acting from the low-stage compression chamber 15 side toward the low-stage back pressure chamber 26 side. When the low-stage compressor portion 10 is bypassed, the force acting on the low-stage vane 13 from the low-stage back pressure chamber 26 side toward the low-stage compression chamber 15 side is set to be smaller than the force acting from the low-stage compression chamber 15 side toward the low-stage back pressure chamber 26 side.
With this setting operation, the low-stage vane 13 is pressed against the low-stage rolling piston 12 during normal operation. This means that the low-stage vane 13 follows the revolution of the low-stage rolling piston 12 well. When the low-stage compressor portion 10 is bypassed, the low-stage vane 13 is hardly pressed against the low-stage rolling piston 12. Namely, the friction loss between the low-stage vane 13 and low-stage rolling piston 12 decreases.

[0047] As the friction loss between the low-stage vane 13 and low-stage rolling piston 12 decreases, a heat pump apparatus 101 equipped with the two-stage compressor 100 according to the third embodiment has a much better efficiency when the load is very low.

Embodiment 4.

[0048] In the fourth embodiment, a two-stage compressor 100 will be described which controls a torque to be generated in accordance with a necessary torque.

[0049] Fig. 14 is a graph showing torque fluctuations in an ordinary twin rotary compressor. The twin rotary compressor is a compressor in which two compressor portions operate in parallel.
Fig. 15 is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the first embodiment performs normal operation. The normal operation refers to an operation of sucking the refrigerant into the low-stage compressor portion 10 from the suction muffler 7. In this operation, the bypass valve 24 is closed and the refrigerant is not discharged via the bypass port 23.
Fig. 16 is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the first embodiment performs an over-compression relief operation. The over-compression relief operation refers to an operation of sucking the refrigerant into the low-stage compressor portion 10 from the suction muffler 7. In this operation, the bypass mechanism is actuated so the refrigerant is discharged via the bypass port 23.
Fig. 17 is a graph showing torque fluctuations occurring when the two-stage compressor 100 according to the second embodiment performs a high-stage direct suction operation. The high-stage direct suction operation refers to an operation of switching the four-way valve 54 to the flow channels indicated by the broken lines in Fig. 11 so the refrigerant is sucked from the suction muffler 7 into the high-stage compressor portion 30.

[0050] As shown in Figs. 14 to 17, the rotation torque fluctuations accompanying a change in crank angle of the crank shaft 4 in the two-stage compressor are larger than those in a twin rotary compressor. If the rotation-torque accompanying the change in crank angle fluctuates greatly, the efficiency of the electric motor decreases and the vibration increases. In particular, a decrease in efficiency of the electric motor due to the large rotation torque fluctuations accompanying the change in crank angle affects the efficiency greatly adversely when the electric motor is operated at a low rotation frequency, that is, when the load is small. If the vibration increases, it produces noise and leads to a low reliability of the piping of the heat pump apparatus.

[0051] In the twin rotary compressor, as the two compressor portions having the same compressor chamber capacities are arranged such that the phases of eccentricity of their rolling pistons are shifted from each other by 180°, their torques cancel each other. Therefore, in the twin rotary compressor, the torque fluctuations accompanying a change in crank angle are small, as shown in Fig. 14.
In contrast to this, in the two-stage compressor 100, the compression chamber capacity of the high-stage compressor portion 30 is smaller than that of the low-stage compressor portion 10, as described in the first embodiment. In other words, the compression differs between the low-stage compressor portion 10 and the high-stage compressor portion 30. Consequently, the rotation torque fluctuations accompanying the change in crank angle in the two-stage compressor 100 are larger than those in the twin rotary compressor, as shown in Fig. 15. In particular, the rotation torque fluctuates greatly at a timing at which the refrigerant is discharged from the low-stage compression chamber 15 to the low-stage discharge space 20 and a timing at which the refrigerant is discharged from the high-stage compression chamber 35 to the high-stage discharge space 40.
As shown in Fig. 16, rotation torque fluctuations accompanying the change in crank angle in the over-compression relief operation become slightly larger than rotation torque fluctuations in the normal operation shown in Fig. 14. This is because, as the refrigerant is compressed mainly only in the low-stage compressor portion 10, the torque behaves in a manner close to the torque of a single rotary compressor having only one compressor portion. In other words, this is because torque cancellation hardly occurs between the two compression portions.
Furthermore, as shown in Fig. 17, when the compressor performs a high-stage direct suction operation, it behaves in a manner close to that of the single rotary compressor, as in the case of over-compression relief operation shown in Fig. 16. Thus, the rotation torque fluctuations accompanying the change in crank angle increase.

[0052] To cope with this, the two-stage compressor 100 controls an electric motor 2 by a controller so that a torque (output torque) is generated in accordance with the necessary torque as the torque (load torque) needed for the operation. This control operation suppresses the torque fluctuations. The necessary torque can be determined from, e.g., the rotation frequency, a change in current, a change in vibration, and the crank angle of the compressor.
For example, the controller determines the necessary torque from the rotation frequency and crank angle of the compressor. The controller stores a table that records torques necessary for the respective rotation frequencies and crank angles of the compressor in advance in the memory. During operation, the controller detects the rotation frequency and crank angle of the compressor and reads from the memory the necessary torque corresponding to the detected rotation frequency and crank angle of the compressor. The controller then controls the electric motor 2 so that the readout necessary torque is generated. Alternatively, the controller may performs learning control operation of learning necessary torques respectively corresponding to various indices such as the rotation frequency and crank angle of the compressor during operation, and control the torque based on the learned result.

[0053] By minimizing the torque fluctuations, the efficiency of the compressor can be further enhanced, and the vibration can be reduced.

[0054] The above description will be summarized as follows.
The two-stage compressor 100 is a rotary two-stage compressor having the low-stage compressor portion 10 on the upper side and the high-stage compressor portion 30 on the lower side. The bypass port 23 which communicates with the discharge pressure space 53, and the bypass valve 24 are formed in the low-stage cover 19 that forms the low-stage discharge space 20 of the low-stage compressor portion 10.

[0055] Also, in the two-stage compressor 100, the suction pipe connected to the suction muffler 7, the suction pipe of the low-stage compressor portion 10, the discharge pipe of the low-stage compressor portion 10, and the suction pipe of the high-stage compressor portion 30 are connected to each other via the four-way valve 54, and the suction pipe connected to the suction muffler 7 communicates with the suction pipe of the high-stage compressor portion 30, so that the sucked refrigerant gas is sucked in the high-stage compressor portion 30 directly without flowing in the low-stage compressor portion 10.

[0056] Also, in the two-stage compressor 100, the suction pressure of the high-stage compressor portion 30 is communicated to the low-stage back pressure chamber 26 of the low-stage compressor portion 10.

[0057] Furthermore, in the two-stage compressor 100, torque control is performed in accordance with the fluctuations of the rotation torque.

Reference Signs List

[0058] 1: hermetically sealed container; 2: electric motor; 2a: stator; 2b: rotor; 3: compressor mechanism portion; 4: crank shaft; 5: discharge pipe; 6: lubricating oil storage; 7: suction muffler; 8: suction pipe; 10: low-stage compressor portion; 11: low-stage cylinder; 12: low-stage rolling piston; 13: low-stage vane; 14: low-stage frame; 15: low-stage compression chamber; 16: low-stage discharge port; 17: low-stage discharge valve; 18: low-stage valve stopper; 19: low-stage cover; 20: low-stage discharge space; 21: low-stage suction port; 22: intermediate outflow port; 23: bypass port; 24: bypass valve; 25: bypass valve stopper; 26: low-stage back pressure chamber; 27: spring; 28, 29: rivet; 30: high-stage compressor portion; 31: high-stage cylinder; 32: high-stage rolling piston; 33: high-stage vane; 34: high-stage frame; 35: high-stage compression chamber; 36: high-stage discharge port; 37: high-stage discharge valve; 38: high-stage valve stopper; 39: high-stage cover; 40: high-stage discharge space; 41: high-stage suction port; 42: high-stage suction flow channel; 46: high-stage back pressure chamber; 50: intermediate partition; 51: intermediate connection pipe; 52: discharge flow channel; 53: discharge pressure space; 54: four-way valve; 55: pressure inlet channel; 60: injector; 61: injection pipe; 71: heat exchanger; 72: first expansion valve; 73: internal heat exchanger; 74: third expansion valve; 75: second expansion valve; 76: heat exchanger; 77: four-way valve; 78: receiver; 100: two-stage compressor; 101: heat pump apparatus

Claims

1. A heat pump apparatus comprising
a main refrigerant circuit formed by connecting a compressor, a first heat exchanger, a first expansion mechanism, and a second heat exchanger sequentially with piping,
the compressor including
a low-stage compressor portion which compresses a refrigerant flowed therein, a high-stage compressor portion which further compresses the refrigerant compressed by the low-stage compressor portion, and
a bypass mechanism which discharges the refrigerant compressed by the low-stage compressor portion and the high-stage compressor portion to the main refrigerant circuit when a necessary load as a quantity of heat needed to set a fluid which is to be heat-exchanged with the refrigerant flowing in the main refrigerant circuit in the first heat exchanger to have a predetermined temperature is higher than a first load predetermined, and discharges the refrigerant compressed by the low-stage compressor portion to the main refrigerant circuit while bypassing the high-stage compressor portion so that the refrigerant is not compressed by the high-stage compressor portion when the necessary load is lower than the first load.

2. The heat pump apparatus according to claim 1, further comprising:

an injection circuit formed by connecting with piping a portion between the first heat exchanger and first expansion mechanism in the main refrigerant circuit to an injection pipe connected to an intermediate flow channel that connects the low-stage compressor portion and the high-stage compressor portion in the compressor, the injection circuit being provided with a second expansion mechanism midway along the piping; and

a controller which performs control operation of enlarging an opening of the second expansion mechanism provided to the injection circuit to not less than a predetermined size, when the necessary load is higher than a second load which is predetermined to be higher than the first load, so part of the refrigerant, flowing in the main refrigerant circuit from the first heat exchanger toward the expansion mechanism, is injected from the injection pipe to the intermediate flow channel of the compressor via the injection circuit.

3. The heat pump apparatus according to claim 1, further comprising:

a switching portion which causes the refrigerant flowing from the main refrigerant circuit to bypass the low-stage compressor portion, when the necessary load is lower than a third load which is predetermined to be lower than the first load, so the refrigerant is sucked into the high-stage compressor portion without compression by the low-stage compressor portion.

4. The heat pump apparatus according to claim 1, further comprising:

an intermediate flow channel including a low-stage discharge portion and an intermediate connection pipe, the low-stage discharge portion being formed above the low-stage compressor portion and forming a discharge space into which the refrigerant compressed by the low-stage compressor portion is discharged, and the intermediate connection pipe serving to connect the low-stage discharge portion to the high-stage discharge portion; and

a hermetically sealed container for forming an internal space which stores the low-stage compressor portion, the high-stage compressor portion, and the low-stage discharge portion and into which the refrigerant compressed by the high-stage compressor portion is discharged, so the refrigerant discharged into the internal space is discharged to the main refrigerant circuit,

wherein the high-stage compressor portion is formed under the low-stage compressor portion, and sucks the refrigerant discharged to the discharge space formed by the low-stage discharge portion into a compressor chamber thereof via the intermediate connection pipe and compresses the refrigerant, and

the bypass mechanism comprises a bypass port formed in the low-stage discharge portion to connect the discharge space to the internal space of the hermetically sealed container, the bypass port being provided with an on/off valve which opens when the necessary load is lower than the first load.

5. A two-stage compressor comprising:

a low-stage compressor portion which compresses a refrigerant sucked into a compressor chamber via a suction port and discharges the compressed refrigerant via a discharge port;

a low-stage discharge portion which is formed above the low-stage compressor portion and forms a discharge space into which the refrigerant compressed by the low-stage compressor portion is discharged via the discharge port;

an intermediate connection pipe having one end connected to the discharge space formed by the low-stage discharge portion;

a high-stage compressor portion which is formed under the low-stage compressor portion, is connected to the other end of the intermediate connection pipe, and sucks the refrigerant discharged in the discharge space into a compression chamber via the intermediate pipe and compresses the refrigerant; and

a hermetically sealed container which forms an internal space for storing the low-stage compressor portion, the high-stage compressor portion, and the low-stage discharge portion and into which the refrigerant compressed by the high-stage compressor portion is discharged,

the low-stage discharge portion having a bypass port which connects the discharge space to the internal space of the hermetically sealed container, the bypass port being provided with an on/off valve which opens when the refrigerant in the discharge space has a pressure higher than a pressure of the refrigerant in the internal space.

6. The two-stage compressor according to claim 5, wherein
the discharge port of the low-stage compressor portion is provided with an on/off valve which opens when the refrigerant in the compression chamber of the low-stage compressor portion has a pressure higher than the pressure of the refrigerant in the discharge space, and
the on/off valve provided to the bypass port of the low-stage discharge portion has a structure identical to that of the on/off valve provided to the discharge port of the low-stage compressor portion.

7. The two-stage compressor according to claim 6, wherein
each of the on/off valve provided to the discharge port of the low-stage compressor portion and the on/off valve provided to the bypass port of the low-stage discharge portion comprises a lead valve.

8. The two-stage compressor according to claim 5, further comprising:

a suction muffler into which the refrigerant flows from an outside;

a suction pipe which connects the suction muffler to the suction port of the low-stage compressor portion; and

a switching portion which performs selective switching operation between a flow channel along which the refrigerant flowing into the suction muffler is sucked in the low-stage compressor portion from the suction port via the suction pipe, and a flow channel which connects a middle portion of the suction pipe to a middle portion of the intermediate connection pipe and causes the refrigerant flowing into the suction muffler to bypass the low-stage compressor portion so the refrigerant is sucked in the high-stage compressor portion without compression by the low-stage compressor portion.

9. The two-stage compressor according to claim 8, wherein
the switching portion performs selective switching operation between a flow channel which connects the suction muffler to the suction port of the low-stage compressor portion with the suction pipe and connects the low-stage discharge portion to the suction port of the high-stage compressor portion with the intermediate connection pipe, and a flow channel which connects a mid portion of the suction pipe to a mid portion of the intermediate connection pipe to connect the suction muffler to the suction port of the high-stage compressor portion and connects the low-stage discharge portion to the suction port of the low-stage compressor portion.

10. The two-stage compressor according to claim 8, wherein the compressor chamber of the high-stage compressor portion has a capacity smaller than a capacity of the compressor chamber of the low-stage compressor portion.

11. The two-stage compressor according to claim 5, wherein
the low-stage compressor portion comprises
a back pressure chamber and
a vane which projects toward the compression chamber upon being pressed by a pressure in the back pressure chamber and partitions the compression chamber into a space on a side of the suction port and a space on a side of the discharge port, and
the two-stage compressor further comprises an inflow channel along which part of the refrigerant to be sucked in the compression chamber of the high-stage compressor portion flows into the back pressure chamber provided to the low-stage compressor portion.

12. The two-stage compressor according to claim 5, further comprising:

an electric motor which operates the low-stage compressor portion and the high-stage compressor portion; and

a controller which controls operation of the electric motor to generate a necessary torque in accordance with a torque needed to operate the low-stage compressor portion and the high-stage compressor portion.

13. A method of operating a heat pump apparatus including a main refrigerant circuit formed by connecting a two-stage compressor, a first heat exchanger, a first expansion mechanism, and a second heat exchanger sequentially with piping, the two-stage compressor including a low-stage compressor portion and a high-stage compressor portion connected in series,
the method comprising:

discharging a refrigerant compressed by the low-stage compressor portion and the high-stage compressor portion to the main refrigerant circuit when a necessary load as a quantity of heat needed to set a fluid which is to be heat-exchanged with a refrigerant flowing in the main refrigerant circuit in the first heat exchanger to have a predetermined temperature is higher than a first load predetermined; and

discharging the refrigerant compressed by the low-stage compressor portion to the main refrigerant circuit by bypassing the high-stage compressor portion so the refrigerant is not compressed by the high-stage compressor portion when the necessary load is lower than the first load.

14. The method of operating a heat pump apparatus according to claim 13, the heat pump apparatus further comprising
an injection circuit formed by connecting a portion between the first heat exchanger and first expansion mechanism in the main refrigerant circuit to an injection pipe connected to an intermediate flow channel that connects the low-stage compressor portion and the high-stage compressor portion in the compressor,
wherein the method of operating a heat pump apparatus further comprises injecting part of the refrigerant, flowing in the main refrigerant circuit from the first heat exchanger toward the expansion mechanism, from the injection circuit to the intermediate flow channel when the necessary load is higher than a second load which is predetermined to be higher than the first load.

15. The method of operating a heat pump apparatus according to claim 13, comprising causing the refrigerant flowing from the main refrigerant circuit to bypass the low-stage compressor portion, when the necessary load is lower than a third load which is predetermined to be lower than the first load, so the refrigerant is sucked into the high-stage compressor portion having a compression chamber with a capacity smaller than that of the low-stage compressor portion without compression by the low-stage compressor portion.

Drawing