Turbo fluid machinery and refrigeration equipment

Abstract

To restrain a decrease in machine efficiency.SOLUTION: A turbo fluid machine (10) comprises: a rotating shaft (40); an electric motor (30) for driving the rotating shaft (40); a pair of impellers (50a and 50b) for compressing fluid sucked into compression chambers (61a and 66a) by rotating integrally with the rotating shaft (40), and arranged in such a manner that front surfaces (51) provided with blades (53) face each other across the electric motor (30); a casing (20) comprising the compression chambers (61a and 66a) corresponding to the pair of impellers (50a and 50b) respectively; a communication passage (11a) for allowing a pair of the compression chambers (61a and 66a) to communicate with each other; and a reduction part (71 or 76) for reducing pressure in a back space (61b or 66b) of one impeller (50a or 50b) out of the pair of impellers (50a and 50b).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a turbofluid machine and a refrigeration device. [Background technology]

[0002] The turbo compressor of Patent Document 1 accommodates a drive motor, a drive shaft, and two impellers in a sealed container. The drive motor is disposed in a motor chamber formed in the center of the sealed container. The drive shaft is inserted through the drive motor, with one end inserted in the first compression chamber and the other end inserted in the second compression chamber. The impellers are disposed on both ends of the drive shaft. The two impellers are disposed so that their front faces face each other.

[0003] In the turbo compressor of Patent Document 1, gas that flows into the motor chamber is drawn into a first compression chamber in which one impeller is disposed, where the gas undergoes primary compression, and the gas that has undergone primary compression is drawn into a second compression chamber in which the other impeller is disposed, where the gas undergoes secondary compression.

[0004] In the turbo compressor of Patent Document 1, the front faces of the two impellers are arranged to face each other, and therefore the gap between the motor chamber and the second compression chamber is sealed to prevent the primarily compressed gas from leaking into the motor chamber. In this way, the flow paths through which the compressed gas leaks are reduced, improving volumetric efficiency and thereby improving the efficiency of the compressor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-230098 Summary of the Invention [Problem to be solved by the invention]

[0006] In a turbo fluid machine such as that described in Patent Document 1, the front faces of two impellers are arranged facing each other, so that the pressure of the gas compressed in each compression chamber acts on the entire back face of each impeller. When the difference in pressure acting on the back faces of each impeller increases depending on the operating conditions of the compressor, the thrust load acting from one impeller and the thrust load acting from the other impeller cannot be balanced, and a large load is applied to the thrust bearing provided on the drive shaft. In order to handle such a load, the thrust bearing needs to be large.

[0007] However, when the thrust bearing is enlarged, friction occurs between the drive shaft and the gas in the sealed container when the drive shaft rotates at high speed, and windage loss increases. The increased windage loss reduces the efficiency of the compressor. Furthermore, when the thrust bearing is enlarged, the rigidity of the entire drive shaft decreases, limiting the high-speed rotation speed at which the compressor can be operated and narrowing the operating range of the compressor. Thus, when the thrust bearing is enlarged, there is a problem that the mechanical efficiency of the turbo fluid machine decreases.

[0008] An object of the present disclosure is to reduce the loss of mechanical efficiency. [Means for solving the problem]

[0009] The first aspect is directed to a turbo fluid machine that compresses an introduced fluid at an suction pressure to an intermediate pressure that is higher than the suction pressure, and then compresses the fluid at the intermediate pressure to a discharge pressure that is higher than the intermediate pressure. The turbo fluid machine includes a rotating shaft (40), an electric motor (30) that drives the rotating shaft (40), a pair of impellers (50a, 50b) that rotate integrally with the rotating shaft (40) to compress a fluid sucked into a compression chamber (61a, 66a) and are arranged such that their front faces (51) on which blades (53) are provided face each other across the electric motor (30), a casing (20) having the compression chambers (61a, 66a) corresponding to each of the pair of impellers (50a, 50b), a communicating passage (11a) that communicates the pair of compression chambers (61a, 66a) with each other, and a reduction section (71, 76) that reduces the pressure in a back space (61b, 66b) of one of the pair of impellers (50a, 50b).

[0010] In the first aspect, the pressure reducing portion (71, 76) can reduce the pressure in the rear space (61b, 66b) of one of the impellers (50a, 50b), thereby reducing the difference in pressure acting on the respective rear surfaces (52) of the pair of impellers (50a, 50b). This makes it possible to prevent the thrust bearing from becoming large. As a result, it is possible to prevent a decrease in the mechanical efficiency of the turbo fluid machine (10).

[0011] The second aspect is the first aspect, further comprising an intake passage (12a) for introducing a fluid into the casing (20), and the reduction section (71, 76) has a seal section (72, 77) for dividing the rear space (61b, 66b) into a first space (S1) and a second space (S2), and a bypass passage (73a, 78a) for bypassing the fluid in the second space (S2) to the intake passage (12a), wherein the pressure in the first space (S1) is equivalent to the discharge pressure of the compression chamber (61a, 66a) corresponding to one of the impellers (50a, 50b), and the pressure in the second space (S2) is lower than the pressure in the first space (S1).

[0012] In the second aspect, the bypass passages (73a, 78a) make the pressure in the second space (S2) equivalent to the suction pressure and lower the pressure in the second space (S2) than the pressure in the first space (S1). Therefore, the pressure acting on the entire back surface (52) of one of the impellers (50a, 50b) is smaller than that in the case where the second space (S2) is not formed. This makes it possible to reduce the difference in pressure acting on the respective back surfaces (52) of the pair of impellers (50a, 50b).

[0013] In a third aspect, in the second aspect, the one of the impellers (50a, 50b) has a cylindrical first member (80) extending axially away from a back surface (52) of the one of the impellers (50a, 50b), the casing (20) has a first surface (92, 96) facing an outer peripheral surface of the first member (80), and the seal portion (72, 77) is defined by a gap (A) formed between the outer peripheral surface of the first member (80) and the first surface (92, 96).

[0014] In the third aspect, the seal portion (72, 77) is formed by a gap (A) formed between a first member (80) provided on one of the impellers (50a, 50b) and a first surface (92, 96) of the casing (20), and therefore the seal portion (72, 77) can be formed with a small number of additional parts.

[0015] The fourth aspect is the second aspect, wherein the casing (20) has a wall portion (25) facing the back surface (52) of one of the impellers (50a, 50b), the wall portion (25) has an annular protrusion (97) protruding toward the back surface (52) of the one of the impellers (50a, 50b), and the sealing portion (72, 77) is constituted by a gap (B) formed between the back surface (52) of the one of the impellers (50a, 50b) and a tip surface (97a) of the protrusion (97).

[0016] In the fourth aspect, a gap (B) is formed between the back surface (52) of one of the impellers (50a, 50b) and the tip surface (97a) of the protrusion (97) provided on the casing (20). Since the gap (B) constitutes the seal portion (72, 77), it is possible to form the seal portion (72, 77) without adding any new parts.

[0017] A fifth aspect is any one of the second to fourth aspects, wherein the reduction section (71, 76) further includes a valve (74, 79) disposed in the bypass passage (73a, 78a).

[0018] In the fifth aspect, the pressure in the second space (S2) can be adjusted by opening / closing the valves (74, 79) or by changing the degree of opening of the valves (74, 79).

[0019] In a sixth aspect, the compressor of the fifth aspect further includes a control unit (110) that controls the valves (74, 79). The control unit (110) adjusts the opening / closing or the opening degree of the valves (74, 79) based on the suction pressure of the fluid introduced into each of the pair of compression chambers (61a, 66a), the discharge pressure of the fluid discharged from the casing (20), and the back pressure of one of the impellers (50a, 50b).

[0020] In the sixth aspect, the control unit (110) adjusts the opening / closing or opening degree of the valves (74, 79) based on the pressure, which is a direct indicator of the thrust load acting on the rotating shaft (40), thereby improving the reliability of the turbo fluid machine (10).

[0021] A seventh aspect is any one of the first to sixth aspects, wherein the pair of impellers (50a, 50b) are each provided with the reduction portions (71, 76).

[0022] In the seventh aspect, since the reduction portions (71, 76) are provided on both of the pair of impellers (50a, 50b), the pressure in the back spaces (61b, 66b) of the impellers (50a, 50b) can be adjusted under various operating conditions.

[0023] An eighth aspect is any one of the first to seventh aspects, wherein the pair of impellers (50a, 50b) includes a first impeller (50a) that compresses a fluid at a suction pressure introduced into the casing (20) to an intermediate pressure that is higher than the suction pressure, and a second impeller (50b) that compresses the fluid at the intermediate pressure to a discharge pressure that is higher than the intermediate pressure, and the outer diameter of the second impeller (50b) is smaller than the outer diameter of the first impeller (50a).

[0024] In the eighth aspect, since the outer diameter of the second impeller (50b) is smaller than the outer diameter of the first impeller (50a), the load acting from the back surface (52) of the second impeller (50b) can be reduced.

[0025] A ninth aspect is any one of the first to ninth aspects, further comprising a bearing (41, 45, 45) disposed in the casing (20) and rotatably supporting the rotating shaft (40), the bearing (41, 45, 45) being a foil bearing or a magnetic bearing.

[0026] In the ninth embodiment, the bearings (41, 45, 45) are foil bearings or magnetic bearings, and therefore do not use oil.

[0027] A tenth aspect is any one of the first to ninth aspects, wherein the maximum rotation speed of the rotating shaft (40) is 30000 rpm or more.

[0028] In the tenth aspect, the maximum rotation speed of the rotating shaft (40) is 30,000 rpm or more, and therefore the present invention can be applied to a turbo fluid machine (10) that rotates at high speed.

[0029] An eleventh aspect is any one of the first to tenth aspects, wherein the turbo fluid machine is a turbo compressor (10), and the fluid is a refrigerant.

[0030] In the eleventh aspect, the fluid is a refrigerant. When the fluid is a refrigerant, the pressure acting on the back surface (52) of the impeller (50a, 50b) is greater than when the fluid is air. As a result, the thrust load acting on the rotating shaft (40) is greater.

[0031] A twelfth aspect is directed to a refrigeration system including a refrigerant circuit (2) that performs a refrigeration cycle. The refrigerant circuit (2) includes the turbo fluid machine of the eleventh aspect.

[0032] In a thirteenth aspect, in the twelfth aspect, the refrigeration capacity of the refrigeration unit is 100 US refrigeration tons or less.

[0033] In the thirteenth aspect, the refrigeration capacity of the refrigeration unit is 100 American refrigeration tons or less, and therefore the present invention can be applied to refrigeration units with relatively small refrigeration capacity. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic configuration diagram of a refrigeration device according to an embodiment. [Diagram 2] FIG. 2 is a schematic vertical cross-sectional view showing the overall configuration of the turbo compressor. [Diagram 3] FIG. 3 is an enlarged view of the area enclosed by the box III in FIG. [Figure 4] FIG. 4 is a block diagram of a turbo compressor. [Diagram 5] FIG. 5 is a diagram showing an operating area map of the turbo compressor. [Figure 6] FIG. 6 is a diagram corresponding to FIG. 3 of the first modified example. [Figure 7] FIG. 7 is a diagram of the second modified example corresponding to FIG. [Figure 8] FIG. 8 is a diagram of the third modified example corresponding to FIG. [Figure 9] FIG. 9 is a diagram of the fourth modified example corresponding to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible within the scope of the technical idea of ​​the present disclosure. Since each drawing is intended to conceptually explain the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for easy understanding.

[0036] <<Embodiment>> A turbo fluid machine according to an embodiment will be described below. The turbo fluid machine according to the present embodiment is a turbo compressor (10). The turbo compressor (10) (hereinafter, referred to as a compressor) is provided in a refrigeration system (1).

[0037] (1) Refrigeration equipment As shown in Fig. 1, a refrigeration system (1) includes a refrigerant circuit (2). The refrigerant circuit (2) is filled with a refrigerant. The fluid compressed by the compressor (10) of this example is a refrigerant. For example, the refrigerant is an HFC (hydrofluorocarbon) refrigerant such as R32, an HFO (hydrofluoroolefin) refrigerant such as R1234yf, a natural refrigerant containing HC such as propane, or a mixed refrigerant thereof such as R454C (a mixed refrigerant of R32 and R1234yf).

[0038] The refrigerant circuit (2) includes a compressor (10), a radiator (condenser) (3), a pressure reduction mechanism (4), and an evaporator (5). The compressor (10), the radiator (3), the pressure reduction mechanism (4), and the evaporator (5) are connected in series by piping. The pressure reduction mechanism (4) is, for example, an expansion valve. The refrigerant circuit (2) circulates the refrigerant to perform a vapor compression refrigeration cycle.

[0039] In the refrigeration cycle, the refrigerant compressed by the compressor (10) dissipates heat to the air in the radiator (3). At this time, the refrigerant is liquefied. The refrigerant that has dissipated heat is depressurized by the depressurization mechanism (4). The depressurized refrigerant evaporates in the evaporator (5). The evaporated refrigerant is drawn into the compressor (10). The compressor (10) compresses the drawn refrigerant.

[0040] The refrigeration system (1) is, for example, an air conditioner. The air conditioner may be a dual-purpose cooling and heating machine that switches between cooling and heating. In this case, the air conditioner has a switching mechanism that switches the refrigerant circulation direction. The switching mechanism is, for example, a four-way switching valve. The air conditioner may be a dedicated cooling machine or a dedicated heating machine.

[0041] The refrigeration device (1) may be a water heater, a chiller unit, a cooling device for cooling the air inside a storage unit, etc. The cooling device is a device for cooling the air inside a refrigerator, a freezer, a container, etc.

[0042] The refrigeration capacity of the refrigeration unit (1) of this embodiment is 100 American refrigeration tons or less. In other words, the refrigeration unit (1) of this embodiment is a refrigeration unit with a relatively small refrigeration capacity.

[0043] (2) Compressor The compressor (10) draws in low-pressure gas refrigerant and compresses the drawn gas refrigerant. The compressor (10) discharges the compressed high-pressure gas refrigerant. The compressor (10) of the present embodiment is a two-stage compressor that compresses the refrigerant in two stages.

[0044] In the following description, the direction along the axis of the rotating shaft (40) of the compressor (10) is referred to as the “axial direction,” the direction perpendicular to the axial direction is referred to as the “radial direction,” and the direction along the periphery of the rotating shaft (40) is referred to as the “circumferential direction.”

[0045] In this embodiment, the maximum rotation speed of the rotating shaft (40) is 30,000 rpm or more. The maximum rotation speed defines the maximum value of the rotation speed of the electric motor (30). In the compressor (10), increasing the maximum rotation speed of the rotating shaft (40) increases the amount of refrigerant circulating in the refrigerant circuit (2) and is preferable for ensuring the maximum amount of refrigerant circulating. This is advantageous for increasing the cooling capacity in cooling operation and increasing the heating capacity in heating operation.

[0046] As shown in Fig. 2, the compressor (10) includes a casing (20), an electric motor (30), a rotating shaft (40), bearings (41, 45, 45), and a pair of impellers (50a, 50b). The electric motor (30), the rotating shaft (40), the bearings (41, 45, 45), and the pair of impellers (50a, 50b) are housed in the casing (20). The compressor (10) further includes a connecting pipe (11). The connecting pipe (11) is provided outside the casing (20). The compressor (10) further includes a reducing portion (71, 76).

[0047] (2-1) Casing As shown in Fig. 2, the casing (20) is a generally cylindrical sealed container with both ends sealed. The casing (20) is disposed in an orientation in which its center line is substantially horizontal. The casing (20) has a body portion (21), a first closing portion (22), and a second closing portion (24). The body portion (21) is formed in a generally cylindrical shape with both axial ends open. The body portion (21) extends in the axial direction.

[0048] The first closing part (22) closes the open part at one axial end side (left side in FIG. 2) of the body part (21). The first closing part (22) is formed in a thick-walled cylindrical shape. The first closing part (22) includes a first housing (23). The first housing (23) is fitted into a hole (22a) at one axial end (left end in FIG. 2) of the first closing part (22). The first housing (23) is formed in a thick-walled cylindrical shape. The first housing (23) is positioned such that its axis coincides with the axis of the first closing part (22).

[0049] The second closing part (24) closes the open part at the other axial end side (the right end in FIG. 2) of the body part (21). The second closing part (24) is formed in a thick-walled cylindrical shape. The second closing part (24) includes a second housing (25). The second housing (25) is fitted into a hole (24a) at the other axial end (the right end in FIG. 2) of the first closing part (22). The second housing (25) is formed in a thick-walled cylindrical shape. The second housing (25) is positioned such that its axis coincides with the axis of the second closing part (24).

[0050] The casing (20) has a partition wall (26). The partition wall (26) is disposed inside the body portion (21). The partition wall (26) is disposed at the other axial end of the body portion (21). In other words, the partition wall (26) is disposed on the side of the body portion (21) facing the second closing portion (24). An insertion hole (26a) is formed in the center of the partition wall (26). The rotating shaft (40) is inserted through the insertion hole (26a). The partition wall (26) divides the internal space (27) of the body portion (21) into a motor chamber (28) and an intermediate pressure flow path (29).

[0051] The motor chamber (28) is located on one axial side (left side in FIG. 2 ) of the partition wall (26) in the internal space (27). The motor chamber (28) is formed in the internal space (27) between the first closing portion (22) and the partition wall (26). The intermediate pressure flow path (29) is located on the other axial side (right side in FIG. 2 ) of the partition wall (26) in the internal space (27). The intermediate pressure flow path (29) is formed in the internal space (27) between the second closing portion (24) and the partition wall (26).

[0052] A first impeller chamber (61), a diffuser (62), and a scroll passage (63) are formed inside the first closing portion (22). The first impeller chamber (61) is a space formed in a generally conical shape. The first impeller chamber (61) communicates with the motor chamber (28). The diffuser (62) is formed on the outer periphery of the first impeller chamber (61) in the first closing portion (22). The diffuser (62) is formed in an annular shape between the first impeller chamber (61) and the scroll passage (63). The diffuser (62) communicates between the first impeller chamber (61) and the scroll passage (63). The scroll passage (63) is formed in a spiral shape around the diffuser (62).

[0053] A second impeller chamber (66), a diffuser (67), and a scroll passage (68) are formed inside the second blocking portion (24). The second impeller chamber (66) is a space formed in a generally conical shape. The second impeller chamber (66) is in communication with the intermediate pressure passage (29). The diffuser (67) is formed on the outer periphery of the second impeller chamber (66) in the second blocking portion (24). The diffuser (67) is formed in an annular shape between the second impeller chamber (66) and the scroll passage (68). The diffuser (67) connects the second impeller chamber (66) and the scroll passage (68). The scroll passage (68) is formed in a spiral shape around the diffuser (67).

[0054] The casing (20) is provided with a first suction port (20a), a first discharge port (20b), a second suction port (20c), and a second discharge port (20d). The first suction port (20a) is formed in the body portion (21) at a position axially closer to the first closing portion (22). The first suction port (20a) communicates with the motor chamber (28). The first suction port (20a) is connected to a suction pipe (12). A suction passage (12a) is formed inside the suction pipe (12). The first discharge port (20b) is formed at an outer end of the scroll flow passage (63) of the first closing portion (22). The first discharge port (20b) communicates with the scroll flow passage (63). The first discharge port (20b) is connected to a connecting pipe (11).

[0055] The second suction port (20c) is formed in an end portion of the body portion (21) on the axial side of the second closing portion (24). The second suction port (20c) communicates with the intermediate pressure flow path (29). The communication pipe (11) is connected to the second suction port (20c). The second discharge port (20d) is formed in an outer end of the scroll flow path (68) of the second closing portion (24). The second discharge port (20d) communicates with the scroll flow path (68). The second discharge port (20d) is connected to a discharge pipe (13). A discharge passage (13a) is formed inside the discharge pipe (13).

[0056] (2-2) Connecting pipe The communication pipe (11) connects the first discharge port (20b) and the second suction port (20c) of the casing (20). The communication pipe (11) connects the first discharge port (20b) and the second suction port (20c). A communication passage (11a) is formed inside the communication pipe (11). An inflow end of the communication passage (11a) is connected to the first discharge port (20b). An outflow end of the communication passage (11a) is connected to the second suction port (20c). The communication passage (11a) connects the first impeller chamber (61) and the second impeller chamber (66) to each other.

[0057] (2-3) Electric motor The electric motor (30) drives and rotates the rotating shaft (40). As shown in FIG. 2, the electric motor (30) is accommodated inside the body (21). The electric motor (30) is disposed approximately in the center of the body (21) in the axial direction. The electric motor (30) has a stator (31) and a rotor (32). The stator (31) is formed in a cylindrical shape. The stator (31) is fixed to the inner peripheral surface of the body (21). The rotor (32) is formed in a cylindrical shape. The rotor (32) is disposed radially inward of the stator (31). The rotor (32) is fixed to the outer peripheral surface of the rotating shaft (40).

[0058] The operation frequency (rotation speed) of the electric motor (30) is adjusted by an inverter device. The compressor (10) is an inverter type compressor with a variable rotation speed. Therefore, the rotation speed of the electric motor (30) can be varied between low speed and high speed.

[0059] (2-4) Rotation axis 2, the rotating shaft (40) extends from one end to the other end of the body portion (21) of the casing (20) along the center line of the casing (20). The rotating shaft (40) extends horizontally.

[0060] In this embodiment, the rotating shaft (40) is provided with a thrust plate (40a). The thrust plate (40a) is fixed to the rotating shaft (40) closer to the second blocking portion (24) than the electric motor (30). The thrust plate (40a) is formed in a disk shape. The thrust plate (40a) extends radially outward from the rotating shaft (40). In this embodiment, the thrust plate (40a) is configured as a separate part from the rotating shaft (40). The thrust plate (40a) may be configured integrally with the rotating shaft (40).

[0061] (2-5) Bearings The compressor (10) has, as the bearings (41, 45, 45), a thrust bearing (41) and a pair of radial bearings (45, 45).

[0062] The thrust bearing (41) is disposed on the other axial side of the electric motor (30) in the electric motor chamber (28). The thrust bearing (41) is configured as a bearing that does not use oil. The thrust bearing (41) of this embodiment is a magnetic bearing. The thrust bearing (41) floats the thrust plate (40a) of the rotating shaft (40) by electromagnetic force and supports it rotatably without contact. The thrust bearing (41) receives a thrust load acting in the axial direction of the rotating shaft (40). The thrust bearing (41) is attached to the partition wall (26) of the casing (20).

[0063] The thrust bearing (41) has a pair of electromagnets (42). Each of the pair of electromagnets (42) is formed in an annular shape. The pair of electromagnets (42) are disposed opposite each other across the thrust plate (40a) of the rotating shaft (40). Each electromagnet (42) is disposed with a gap between it and the thrust plate (40a).

[0064] The radial bearings (45) are arranged on both sides of the electric motor (30) in the motor chamber (28). The radial bearings (45) are held in the body portion (21) of the casing (20) by holding members (not shown). The holding members are fixed to the inner wall of the body portion (21).

[0065] The radial bearing (45) rotatably supports the rotating shaft (40). The radial bearing (45) is disposed on the outer periphery of the rotating shaft (40). The radial bearing (45) is configured as a bearing that does not use oil. The radial bearing (45) of this embodiment is a foil bearing. The radial bearing (45) forms a gas film between the radial bearing (45) and the rotating shaft (40), and the gas film floats the rotating shaft (40) to rotatably support it without contact. The radial bearing (45) receives a radial load acting on the outside in the radial direction of the rotating shaft (40). The radial bearing (45) has a bearing housing, a top foil, and a back foil.

[0066] The thrust bearing 41 may be a foil bearing, and the radial bearing 45 may be a magnetic bearing.

[0067] (2-6) Impeller As shown in Fig. 2, the compressor (10) includes a pair of impellers (50a, 50b). The pair of impellers (50a, 50b) includes a first impeller (50a) and a second impeller (50b). Note that, in Fig. 2, the outer circumferential surface of each impeller (50a, 50b) is shown for ease of understanding. In other words, the cross section of each impeller (50a, 50b) in Fig. 2 is not shown.

[0068] The first impeller (50a) is housed in the first impeller chamber (61). One end (the left end in FIG. 2) of the rotating shaft (40) is coupled to the first impeller (50a). The second impeller (50b) is housed in the second impeller chamber (66). The other end (the right end in FIG. 2) of the rotating shaft (40) is coupled to the second impeller (50b). Each impeller (50a, 50b) rotates integrally with the rotating shaft (40) and pumps the refrigerant.

[0069] Each impeller (50a, 50b) is formed in a generally conical shape. Each impeller (50a, 50b) has a front surface (51) and a rear surface (52). The rear surface (52) is the surface opposite to the front surface (51) in the axial direction. A plurality of blades (53) are provided on the front surface (51) of each impeller (50a, 50b). The pair of impellers (50a, 50b) are arranged such that their respective front surfaces (51) face each other with the electric motor (30) therebetween. In this embodiment, the outer diameter D2 of the second impeller (50b) is smaller than the outer diameter D1 of the first impeller (50a) (D1>D2).

[0070] The first impeller chamber (61) has a first compression chamber (61a) and a first rear space (61b). In the first compression chamber (61a), the refrigerant that has flowed into the first compression chamber (61a) is compressed by the blades (53) of the first impeller (50a). The first compression chamber (61a) is formed on the front surface (51) side of the first impeller (50a) in the first impeller chamber (61). Specifically, the first compression chamber (61a) is formed between the front surface (51) of the first impeller (50a) and the inner surface of the first blocking portion (22).

[0071] The first rear space (61b) is formed in the first impeller chamber (61) on the rear surface (52) side of the first impeller (50a). Specifically, the first rear space (61b) is formed between the rear surface (52) of the first impeller (50a) and the inner surface of the first housing (23). The suction side of the first compression chamber (61a) communicates with the motor chamber (28). The discharge side of the first compression chamber (61a) communicates with the first rear space (61b). The discharge side of the first compression chamber (61a) communicates with the diffuser (62).

[0072] The second impeller chamber (66) has a second compression chamber (66a) and a second rear space (66b). In the second compression chamber (66a), the refrigerant that has flowed into the second compression chamber (66a) is compressed by the blades (53) of the second impeller (50b). The second compression chamber (66a) is formed on the front surface (51) side of the second impeller (50b) in the second impeller chamber (66). Specifically, the second compression chamber (66a) is formed between the front surface (51) of the second impeller (50b) and the inner surface of the second blocking portion (24).

[0073] The second back space (66b) is formed in the second impeller chamber (66) on the side of the back surface (52) of the second impeller (50b). Specifically, the second back space (66b) is formed between the back surface (52) of the second impeller (50b) and the inner surface of the second housing (25). The suction side of the second compression chamber (66a) communicates with the intermediate pressure flow path (29). The discharge side of the second compression chamber (66a) communicates with the second back space (66b). The discharge side of the second compression chamber (66a) communicates with the diffuser (67).

[0074] In the first compression chamber (61a), the first impeller (50a) compresses the refrigerant at suction pressure (low pressure) introduced into the casing (20) to an intermediate pressure higher than the suction pressure. The intermediate-pressure refrigerant discharged from the first compression chamber (61a) flows into the second compression chamber (66a) through the diffuser (62), the scroll passage (63), the communication passage (11a), and the intermediate-pressure passage (29). At the same time, the intermediate-pressure refrigerant discharged from the first compression chamber (61a) flows into the first back space (61b).

[0075] In the second compression chamber (66a), the intermediate-pressure refrigerant is compressed by the second impeller (50b) to a discharge pressure (high pressure) that is higher than the intermediate pressure. The refrigerant at the discharge pressure discharged from the second compression chamber (66a) passes through the diffuser (67) and the scroll passage (68) and flows into the discharge passage (13a). At the same time, the refrigerant at the discharge pressure discharged from the second compression chamber (66a) flows into the second back space (66b).

[0076] Here, since the front surfaces (51) of the pair of impellers (50a, 50b) of the present embodiment are arranged to face each other with the electric motor (30) interposed therebetween, the refrigerant discharged from each compression chamber (61a, 66a) flows into the rear space (61b, 66b) corresponding to each compression chamber (61a, 66a), and the pressure in each rear space (61b, 66b) acts on the entire rear surface (52) of the impeller (50a, 50b) corresponding to each rear space (61b, 66b).

[0077] Specifically, since the discharge side of the first compression chamber (61a) communicates with the first rear space (61b), the pressure in the first rear space (61b) becomes the intermediate pressure. On the other hand, since the discharge side of the second compression chamber (66a) communicates with the second rear space (66b), the pressure in the second rear space (66b) becomes the high pressure. Therefore, the pressure P2 acting on the rear surface (52) of the second impeller (50b) is greater than the pressure P1 acting on the rear surface (52) of the first impeller (50a) (P1 < P2).

[0078] The thrust load L acting on one side of the rotating shaft (40) is calculated by multiplying the rear surface area Z of the impeller on one side by the pressure P acting on the rear surface of the impeller (L = Z × P). Therefore, when the rear surface area Z1 of the first impeller (50a) and the rear surface area Z2 of the second impeller (50b) are the same, the thrust load L2 acting from the second impeller (50b) side is greater than the thrust load L1 acting from the first impeller (50a) side (L1 < L2), and the thrust loads acting from both sides of the rotating shaft (40) are unbalanced. When the balance of the thrust loads on both sides is poor, the load on the thrust bearing (41) increases.

[0079] In contrast, as described above, in this embodiment, the outer diameter D2 of the second impeller (50b) is smaller than the outer diameter D1 of the first impeller (50a) (D1>D2). By making the outer diameter D2 of the second impeller (50b) smaller than the outer diameter D1 of the first impeller (50a), the back surface area Z2 of the second impeller (50b) is smaller than the back surface area Z1 of the first impeller (50a) (Z1>Z2). This makes it easier to balance the thrust load L1 from the first impeller (50a) side and the thrust load L2 from the second impeller (50b) side.

[0080] The height of the impeller blades is determined by the diameter of the impeller. Specifically, when the impeller diameter is large, the height of the blades is small, and when the impeller diameter is small, the height of the blades is large. In this embodiment, since the outer diameter D2 of the second impeller (50b) is smaller than the outer diameter D1 of the first impeller (50a) (D1>D2), the height of the blades (53) of the second impeller (50b) can be made higher than the height of the blades (53) of the first impeller (50a). By relatively increasing the height of the blades (53) of the second impeller (50b), the gap between the second blocking portion (24) and the blades (53) of the second impeller (50b) in the second compression chamber (66a) can be made relatively small. This makes it possible to prevent the refrigerant compressed in the second compression chamber (66a) from leaking out from the gap, thereby improving the compression efficiency.

[0081] (2-7) Reduction section The pressure reducing portion (71, 76) reduces the pressure in a rear space (61b, 66b) of one of the pair of impellers (50a, 50b). In this embodiment, the pair of impellers (50a, 50b) is provided with the pressure reducing portion (71, 76). Specifically, the compressor (10) includes a first pressure reducing portion (71) provided in the first impeller (50a) and a second pressure reducing portion (76) provided in the second impeller (50b).

[0082] 2, the first reduction section (71) has a first seal section (72), a first bypass passage (73a), and a first flow rate adjustment valve (74). The second reduction section (76) has a second seal section (77), a second bypass passage (78a), and a second flow rate adjustment valve (79). The flow rate adjustment valves (74, 79) correspond to the valves of the present disclosure.

[0083] In this embodiment, the first reduction portion (71) and the second reduction portion (76) have the same structure. In the following, the second reduction portion (76) will be described as an example with reference to Fig. 3. Note that in Fig. 2, the same components are denoted by the same reference numerals in the first reduction portion (71) and the second reduction portion (76).

[0084] (2-7-1) Second reduction section As shown in Fig. 3, the second seal portion (77) divides the second rear space (66b) into a first space (S1) and a second space (S2). In other words, the second seal portion (77) seals between the first space (S1) and the second space (S2). The second seal portion (77) is defined by a gap (A) formed between the partition member (80) and the second housing (25). The partition member (80) corresponds to the first member of the present disclosure.

[0085] The partition member (80) is provided on the back surface (52) of the second impeller (50b). The partition member (80) is disposed in the second back surface space (66b). The partition member (80) of this embodiment has a tubular portion (81). The tubular portion (81) is formed in a cylindrical shape. The tubular portion (81) extends from the back surface (52) of the second impeller (50b) toward the other side in the axial direction (the right side in FIG. 3). In other words, the tubular portion (81) extends away from the back surface (52) of the second impeller (50b) in the axial direction. The tubular portion (81) is disposed in the center of the back surface (52) of the second impeller (50b). The axis of the tubular portion (81) roughly coincides with the axis of the rotating shaft (40).

[0086] A first hole (91) and a second hole (92) are formed in the center of the second housing (25). The first hole (91) and the second hole (92) extend in the axial direction. The axis of the second housing (25), the center of the first hole (91), and the center of the second hole (92) generally coincide with each other. The first hole (91) and the second hole (92) are formed continuously.

[0087] The first hole (91) is formed in one axial end (the left end in FIG. 3) of the second housing (25). The second hole (92) is formed in the other axial end (the right end in FIG. 3) of the second housing (25). The diameter of the first hole (91) is larger than the diameter of the second hole (92). The axial length of the first hole (91) is shorter than the axial length of the second hole (92).

[0088] The tip of the tubular portion (81) of the partition member (80) is inserted into the second hole (92). A small cylindrical gap is formed between the second hole (92) and the outer circumferential surface of the tip of the tubular portion (81). In this example, the second hole (92) corresponds to the first surface of the present disclosure.

[0089] This minute gap forms a refrigerant flow path (R) through which the refrigerant flows. The refrigerant flow path (R) extends straight along the axial direction. In other words, the second seal portion (77) of this embodiment is configured with a refrigerant flow path (R) that extends straight along the axial direction. Because the refrigerant flow path (R) of this embodiment is very narrow, when the refrigerant flows from the first space (S1) into the refrigerant flow path (R), the narrow flow path creates resistance and functions as a seal.

[0090] In the second rear space (66b), a space radially outside the cylindrical portion (81) is a first space (S1). In the second rear space (66b), a space radially inside the cylindrical portion (81) is a second space (S2).

[0091] The second bypass passage (78a) is a passage for bypassing the refrigerant in the second space (S2) to the suction passage (12a). The second bypass passage (78a) connects the second space (S2) and the suction passage (12a). An inflow end of the second bypass passage (78a) is connected to the second space (S2). An outflow end of the second bypass passage (78a) is connected to the suction passage (12a). In this embodiment, the second bypass passage (78a) is formed inside the second bypass pipe (78).

[0092] The second flow rate control valve (79) is disposed in the second bypass passage (78a). The second flow rate control valve (79) is configured so that its opening degree is adjustable. The second flow rate control valve (79) is configured so that it can be opened and closed. The second flow rate control valve (79) adjusts the flow rate of the refrigerant flowing through the second bypass passage (78a).

[0093] The first space (S1) of the second rear space (66b) communicates with the second compression chamber (66a). Therefore, the pressure in the first space (S1) is a pressure equivalent to the high pressure, which is the discharge pressure of the second compression chamber (66a). The second space (S2) of the second rear space (66b) communicates with the second bypass passage (78a). Therefore, when the second flow rate control valve (79) is open, the second space (S2) communicates with the suction passage (12a), and the pressure in the second space (S2) is a pressure equivalent to the low pressure (suction pressure). In other words, at this time, the pressure in the second space (S2) is lower than the pressure in the first space (S1).

[0094] When the second flow rate control valve (79) is closed, the pressure in the second space (S2) corresponds to the pressure in the first space (S1). In other words, at this time, the pressure in the second space (S2) and the pressure in the first space (S1) are the same. This is because the second space (S2) is cut off from the suction passage (12a) and a small amount of refrigerant in the first space (S1) flows into the second space (S2) through the gap (A).

[0095] In this manner, by opening the second flow rate control valve (79), the pressure in the second space (S2) can be reduced. This makes it possible to reduce the pressure acting on the entire back surface (52) of the second impeller (50b) as compared with an impeller not provided with a pressure reducing portion. As a result, the thrust load acting on the rotating shaft (40) from the second impeller (50b) can be relatively reduced.

[0096] (2-7-2) First reduction section The first seal portion (72) of the first reduction portion (71) divides the first rear space (61b) into a first space (S1) and a second space (S2). The cylindrical portion (81) of the partition member (80) in the first reduction portion (71) extends from the rear surface (52) of the first impeller (50a) toward one side in the axial direction (the left side in FIG. 2).

[0097] A first hole (91) and a second hole (92) are formed in the center of the first housing (23). The axis of the first housing (23), the axis of the first hole (91), and the axis of the second hole (92) generally coincide with each other. The first hole (91) is formed in the other end (the right end in FIG. 2) of the first housing (23) in the axial direction. The second hole (92) is formed in the other end (the left end in FIG. 2) of the first housing (23) in the axial direction.

[0098] A minute gap is formed between the second hole (92) and the outer circumferential surface of the tip of the cylindrical portion (81). This minute gap constitutes a first seal portion (72). In the first rear space (61b), a space on the radially outer side of the cylindrical portion (81) is a first space (S1). In the first rear space (61b), a space on the radially inner side of the cylindrical portion (81) is a second space (S2). The first bypass passage (73a) has the same configuration as the second bypass passage (78a). The first bypass passage (73a) of the present embodiment is formed inside the first bypass pipe (73). The first flow rate adjustment valve (74) has the same configuration as the second flow rate adjustment valve (79).

[0099] The first space (S1) of the first rear space (61b) communicates with the first compression chamber (61a). Therefore, the pressure in the first space (S1) is a pressure equivalent to the intermediate pressure, which is the discharge pressure of the first compression chamber (61a). The second space (S2) of the first rear space (61b) communicates with the first bypass passage (73a). Therefore, when the first flow rate adjustment valve (74) is opened, the second space (S2) communicates with the suction passage (12a). As a result, the pressure in the second space (S2) is a pressure equivalent to the low pressure (suction pressure). In other words, at this time, the pressure in the second space (S2) is lower than the pressure in the first space (S1). On the other hand, when the first flow rate adjustment valve (74) is closed, the pressure in the second space (S2) is equivalent to the pressure in the first space (S1). In other words, at this time, the pressure in the second space (S2) and the pressure in the first space (S1) are the same.

[0100] In this manner, by opening the first flow rate control valve (74), the pressure in the second space (S2) can be reduced. This reduces the pressure acting on the entire back surface (52) of the first impeller (50a) compared to an impeller not having a pressure reducing portion. As a result, the thrust load acting on the rotating shaft (40) from the first impeller (50a) can be relatively reduced.

[0101] As described above, the compressor (10) is provided with the reduction portions (71, 76), so that the difference in pressure acting on the respective back surfaces (52) of the pair of impellers (50a, 50b), which occurs depending on the operating conditions, can be reduced.

[0102] (2-7) Sensor As shown in FIG. 4, the compressor (10) includes five pressure sensors (101, 102, 103, 104, 105).

[0103] The first pressure sensor (101) is disposed in the suction pipe (12). The first pressure sensor (101) detects the pressure of the suction passage (12a). In other words, the first pressure sensor (101) detects the pressure of the refrigerant introduced into the first compression chamber (61a). The first pressure sensor (101) may be disposed near the first suction port (20a) in the casing (20) or in the motor chamber (28).

[0104] The second pressure sensor (102) is disposed in the communication pipe (11). The second pressure sensor (102) detects the pressure in the communication passage (11a). In other words, the second pressure sensor (102) detects the pressure of the refrigerant introduced into the second compression chamber (66a). The second pressure sensor (102) may be disposed in the casing (20) near the first discharge port (20b) or at the second suction port (20c).

[0105] The third pressure sensor (103) is disposed in the discharge pipe (13). The third pressure sensor (103) detects the pressure in the discharge passage (13a). In other words, the third pressure sensor (103) detects the pressure of the refrigerant discharged from the casing (20). The third pressure sensor (103) is disposed in the casing (20) near the second discharge port (20d).

[0106] The fourth pressure sensor (104) is disposed in the second hole (92) of the first housing (23). The fourth pressure sensor (104) detects the pressure in the second space (S2) of the first rear space (61b). In other words, the fourth pressure sensor (104) detects the rear pressure of the first impeller (50a). The fourth pressure sensor (104) may be disposed in the first bypass pipe (73). In this case, the fourth pressure sensor (104) is disposed in the first bypass pipe (73) near the inlet end of the first bypass passage (73a).

[0107] The fifth pressure sensor (105) is disposed in the second hole (92) of the second housing (25). The fifth pressure sensor (105) detects the pressure in the second space (S2) of the second rear space (66b). In other words, the fifth pressure sensor (105) detects the rear pressure of the second impeller (50b). The fifth pressure sensor (105) may be disposed in the second bypass pipe (78). In this case, the fifth pressure sensor (105) is disposed in the second bypass pipe (78) near the inlet end of the second bypass passage (78a).

[0108] (2-8) Control section The control unit (110) controls the operation of the compressor (10). The control unit (110) includes a microcomputer and a memory device. The memory device stores various programs and data. The microcomputer executes the programs read from the memory device.

[0109] The control unit (110) controls the operation of the first flow rate control valve (74) and the second flow rate control valve (79). The control unit (110) adjusts the opening / closing or the opening degree of the first flow rate control valve (74) and the second flow rate control valve (79) based on detection values ​​of the first pressure sensor (101), the second pressure sensor (102), the third pressure sensor (103), the fourth pressure sensor (104), and the fifth pressure sensor (105).

[0110] Specifically, the control unit (110) acquires detection values ​​of the first to fifth pressure sensors (101, 102, 103, 104, 105). The control unit (110) calculates thrust loads acting from both sides of the rotating shaft (40) based on the detection values ​​of the pressure sensors (101, 102, 103, 104, 105). The control unit (110) adjusts the opening / closing or the opening degree of the first flow rate control valve (74) and the second flow rate control valve (79) based on the calculated thrust loads.

[0111] Since the opening / closing or the opening degree of each flow control valve (74, 79) is adjusted based on the pressure, which is a direct index of the thrust load acting on the rotating shaft (40), each flow control valve (74, 79) can be controlled in accordance with the thrust load actually acting thereon, thereby improving the reliability of the compressor (10).

[0112] (3) Driving behavior The operation of the compressor (10) will now be described.

[0113] When the compressor (10) is in operation, the electric motor (30) is energized. This rotates the rotary shaft (40). When the rotary shaft (40) rotates, the impellers (50a, 50b) connected to the rotary shaft (40) rotate. When the first impeller (50a) rotates, low-pressure (suction pressure) refrigerant flows from the suction pipe (12) through the first suction port (20a) into the motor chamber (28). The refrigerant that has flowed into the motor chamber (28) flows into the first compression chamber (61a). In the first compression chamber (61a), the blades (53) of the first impeller (50a) send the refrigerant radially outward, increasing the flow rate of the refrigerant. This increased speed of the refrigerant increases the pressure of the refrigerant.

[0114] The low-pressure refrigerant that has flowed into the first compression chamber (61a) is compressed to an intermediate pressure that is higher than the suction pressure. The refrigerant compressed to the intermediate pressure passes through the diffuser (62) and flows into the scroll passage (63). The refrigerant that has flowed through the scroll passage (63) passes through the first discharge port (20b) and flows into the communication passage (11a).

[0115] The intermediate-pressure refrigerant that has flowed into the communication passage (11a) flows into the intermediate-pressure flow path (29) through the second suction port (20c). The refrigerant that has flowed into the intermediate-pressure flow path (29) flows into the second compression chamber (66a). In the second compression chamber (66a), the speed of the refrigerant is accelerated by the blades (53) of the second impeller (50b), as in the first compression chamber (61a), and the pressure of the second compression chamber (66a) increases. The refrigerant that has flowed into the second compression chamber (66a) is compressed to a high pressure (discharge pressure) that is higher than the intermediate pressure.

[0116] The refrigerant compressed to the discharge pressure passes through the diffuser (67) and flows through the scroll passage (68). The refrigerant that has flowed through the scroll passage (68) passes through the second discharge port (20d) and flows into the discharge pipe (13). The high-pressure refrigerant that has flowed into the discharge pipe (13) is sent to the outside of the casing (20). The refrigerant discharged from the compressor (10) is used in the refrigeration cycle of the refrigeration system (1).

[0117] (4) Operation of flow control valve Next, the operation of the first flow rate control valve (74) and the second flow rate control valve (79) will be described.

[0118] In the compressor (10), the balance of the thrust loads acting from both sides of the rotating shaft (40) may be lost depending on the operating conditions. Specifically, depending on the operating conditions, the thrust load L2 acting from the second impeller (50b) side may be greater than the thrust load L1 acting from the first impeller (50a) side, or the thrust load L2 may be smaller. In the following description, it is assumed that the first flow control valve (74) and the second flow control valve (79) are closed when the compressor (10) starts operating.

[0119] 5 shows an operation area map with the horizontal axis representing the evaporation temperature Te and the vertical axis representing the condensation temperature Tc. In the operation area map of FIG. 5, the gray area represents the operation possible area, and the black area represents the operation impossible area.

[0120] In Fig. 5, (a) shows a case where the first flow rate control valve (74) and the second flow rate control valve (79) are both closed, (b) shows a case where only the first flow rate control valve (74) is open, (c) shows a case where only the second flow rate control valve (79) is open, and (d) shows a case where both the first flow rate control valve (74) and the second flow rate control valve (79) are open. Fig. 5(e) is a combined view of Figs. 5(a) to (d) and shows the operable area of ​​the compressor (10) as a whole. Note that detailed numerical values ​​are omitted in Fig. 5.

[0121] (4-1) When only the first flow control valve is opened When the thrust load L1 is greater than the thrust load L2 (L1 < L2), the control unit (110) opens the first flow control valve (74). When the first flow control valve (74) is opened, the second space (S2) of the first back space (61b) communicates with the suction passage (12a), and the pressure in the second space (S2) decreases. Accordingly, the pressure acting on the entire back surface (52) of the first impeller (50a) becomes relatively small. Thereby, the balance between the thrust load L1 on the first impeller (50a) side and the thrust load L2 on the second impeller (50b) side can be achieved.

[0122] Here, when the first flow control valve (74) is opened, a part of the refrigerant discharged from the first compression chamber (61a) flows into the suction passage (12a), so the flow rate of the refrigerant flowing from the first compression chamber (61a) into the communication passage (11a) decreases. As the flow rate of the refrigerant flowing into the communication passage (11a) decreases, the amount of the refrigerant compressed in the second compression chamber (66a) decreases. Thereby, the flow rate of the refrigerant discharged from the casing (20) to the outside also decreases. At this time, as shown in FIGS. 5(a) and 5(b), the operable area of the compressor (10) transitions from the central region in FIG. 5 to the lower right region.

[0123] When the first flow control valve (74) is opened, the flow rate of the refrigerant discharged from the casing (20) to the outside may be adjusted by adjusting the opening degrees of the flow control valves (74, 79).

[0124] (4-2) When only the second flow control valve is opened When the thrust load L2 is greater than the thrust load L1 (L1 < L2), the control unit (110) opens the second flow control valve (79). When the second flow control valve (79) is opened, the second space (S2) of the second back space (66b) communicates with the suction passage (12a), and the pressure in the second space (S2) decreases. Accordingly, the pressure acting on the entire back surface (52) of the second impeller (50b) becomes relatively small. Thereby, the balance between the thrust load L1 on the first impeller (50a) side and the thrust load L2 on the second impeller (50b) side can be achieved.

[0125] Here, by opening the second flow rate control valve (79), a portion of the refrigerant discharged from the second compression chamber (66a) flows into the suction passage (12a), and the flow rate of the refrigerant flowing from the second compression chamber (66a) into the discharge passage (13a) decreases. As a result, the flow rate of the refrigerant discharged from the casing (20) to the outside also decreases. At this time, as shown in (a) and (c) of FIG. 5, the operable area of ​​the compressor (10) changes from the central area to the upper left area in FIG. 5.

[0126] When the second flow rate control valve (79) is opened, the flow rate of the refrigerant discharged to the outside from the casing (20) may be adjusted by adjusting the opening degree of each of the flow rate control valves (74, 79).

[0127] (4-3) When the first flow control valve and the second flow control valve are opened When the control unit (110) needs to significantly reduce the amount of refrigerant discharged from the casing (20) to the outside, it opens the first flow rate control valve (74) and the second flow rate control valve (79). At this time, the pressure in both the second space (S2) of the first rear space (61b) and the second space (S2) of the second rear space (66b) is reduced, so that the balance between the thrust load L1 on the first impeller (50a) side and the thrust load L2 on the second impeller (50b) side is maintained.

[0128] When the first flow rate control valve (74) is opened, a part of the refrigerant discharged from the first compression chamber (61a) flows into the suction passage (12a), and the flow rate of the refrigerant flowing from the first compression chamber (61a) through the communication passage (11a) into the second compression chamber (66a) is reduced. Then, the second flow rate control valve (79) is also opened, and a part of the refrigerant discharged from the second compression chamber (66a) flows into the suction passage (12a). This further reduces the flow rate of the refrigerant flowing from the second compression chamber (66a) into the discharge passage (13a). This makes it possible to significantly reduce the flow rate of the refrigerant discharged from the casing (20) to the outside. At this time, the operable area of ​​the compressor (10) is expanded, as shown in (a) and (d) of FIG. 5.

[0129] In addition, when the first flow rate control valve (74) and the second flow rate control valve (79) are opened, the flow rate of the refrigerant discharged to the outside from the casing (20) may be adjusted by adjusting the opening degree of each flow rate control valve (74, 79).

[0130] As described above, the operable area of ​​the compressor (10) can be changed and expanded by changing the opening / closing and the opening degree of the first flow rate control valve (74) and the second flow rate control valve (79). As a result, as shown in FIG 5(e), the operable area of ​​the compressor (10) as a whole can be expanded.

[0131] Here, the compressor (10) of the present embodiment is designed to be most efficient with the first flow control valve (74) and the second flow control valve (79) closed under operating conditions (rated conditions) for evaluating the compressor efficiency. The operating conditions (rated conditions) for evaluating the compressor efficiency are the most frequently occurring operating conditions of the compressor. Therefore, during operation of the compressor (10), the first flow control valve (74) or the second flow control valve (79) is opened relatively infrequently.

[0132] When the first flow rate control valve (74) or the second flow rate control valve (79) is opened, a part of the refrigerant compressed in the first compression chamber (61a) and the second compression chamber (66a) flows into the suction passage (12a), which may reduce the efficiency of the compressor. However, since the frequency with which the first flow rate control valve (74) or the second flow rate control valve (79) is opened is relatively low, the efficiency of the compressor (10) does not decrease significantly even if the compressor (10) includes the first reduction section (71) and the second reduction section (76).

[0133] On the other hand, when the compressor (10) is operated under operating conditions other than the rated conditions, as described above, the balance of the thrust loads acting on both sides of the rotating shaft (40) may be lost depending on the operating conditions. In such a case, the balance of the thrust loads on both sides in the axial direction can be maintained by opening the first flow rate control valve (74) or the second flow rate control valve (79). This reduces the load on the thrust bearing (41) under a given operating condition, and prevents the thrust bearing (41) from becoming large. In addition, the flow rate of the refrigerant can be adjusted by opening the first flow rate control valve (74) or the second flow rate control valve (79) or adjusting the opening degree of the first flow rate control valve (74) or the second flow rate control valve (79). This makes it possible to expand the operable area of ​​the compressor (10) without increasing the size of the thrust bearing (41).

[0134] (5) Features (5-1) The compressor (10) of this embodiment includes a pair of impellers (50a, 50b) arranged so that their front faces (51) on which the blades (53) are provided face each other across the electric motor (30), and a reduction section (71, 76) that reduces the pressure in the rear space (61b, 66b) of one of the pair of impellers (50a, 50b).

[0135] Therefore, the pressure in the rear space (61b, 66b) of one of the impellers (50a, 50b) can be reduced by the reduction portion (71, 76), thereby reducing the difference in pressure acting on the respective rear surfaces (52) of the pair of impellers (50a, 50b). This reduces the load on the thrust bearing (41), thereby preventing the thrust bearing (41) from becoming large. As a result, windage loss occurring when the rotating shaft (40) rotates at high speed can be reduced. In addition, since the thrust bearing (41) can be prevented from becoming large, a decrease in the rigidity of the entire rotating shaft (40) can be prevented. In this way, a decrease in the mechanical efficiency of the turbo fluid machine (10) can be prevented.

[0136] (5-2) The compressor (10) of this embodiment further includes a suction passage (12a) for introducing a fluid into the casing (20). The pressure reducing section (71, 76) includes a seal portion (72, 77) for dividing the rear space (61b, 66b) into a first space (S1) and a second space (S2), and a bypass passage (73a, 78a) for bypassing the fluid in the second space (S2) to the suction passage (12a). The pressure in the first space (S1) corresponds to the discharge pressure of the compression chamber (61a, 66a) corresponding to one of the impellers (50a, 50b). The pressure in the second space (S2) is lower than the pressure in the first space (S1).

[0137] As a result, the pressure acting on the entire back surface (52) of one of the impellers (50a, 50b) is smaller than in a case where the second space (S2) is not formed, thereby making it possible to reduce the difference in pressure acting on each of the back surfaces (52) of the pair of impellers (50a, 50b).

[0138] (5-3) In the compressor (10) of this embodiment, one of the impellers (50a, 50b) has a cylindrical first member (80) extending away from the back surface (52) of the one of the impellers (50a, 50b) in the axial direction. The casing (20) has a first surface (92) facing the outer circumferential surface of the first member (80). The seal portion (72, 77) is defined by a gap (A) formed between the outer circumferential surface of the first member (80) and the first surface (92). Therefore, the seal portion (72, 77) can be formed with a small number of additional parts.

[0139] (5-4) In the compressor (10) of this embodiment, the pressure reducing section (71, 76) further includes a valve (74, 79) arranged in the bypass passage (73a, 78a). Therefore, the pressure in the second space (S2) can be adjusted by opening / closing or changing the opening degree of the valve (74, 79).

[0140] (5-5) The compressor (10) of the present embodiment further includes a control unit (110) that controls the valves (74, 79). The control unit (110) adjusts the opening / closing or the opening degree of the valves (74, 79) based on the suction pressure of the fluid introduced into each of the pair of compression chambers (61a, 66a), the discharge pressure of the fluid discharged from the casing (20), and the back pressure of one of the impellers (50a, 50b).

[0141] (5-6) In the compressor (10) of the present embodiment, the pair of impellers (50a, 50b) are each provided with a pressure reducing portion (71, 76), so that the pressure in the back space (61b, 66b) of the impeller (50a, 50b) can be adjusted under various operating conditions.

[0142] (5-7) In the compressor (10) of this embodiment, the pair of impellers (50a, 50b) includes a first impeller (50a) that compresses the fluid at the suction pressure introduced into the casing (20) to an intermediate pressure higher than the suction pressure, and a second impeller (50b) that compresses the fluid at the intermediate pressure to a discharge pressure higher than the intermediate pressure. The outer diameter of the second impeller (50b) is smaller than the outer diameter of the first impeller (50a). This makes it possible to reduce the load acting from the back surface (52) of the second impeller (50b).

[0143] (5-8) The compressor (10) of the present embodiment further includes bearings (41, 45, 45) that are disposed in the casing (20) and rotatably support the rotating shaft (40). The bearings (41, 45, 45) are foil bearings or magnetic bearings. Since the bearings (41, 45, 45) are foil bearings or magnetic bearings, they do not use oil.

[0144] (5-9) In the compressor (10) of the present embodiment, the maximum rotation speed of the rotating shaft (40) is equal to or greater than 30,000 rpm. Since the maximum rotation speed of the rotating shaft (40) is equal to or greater than 30,000 rpm, the compressor (10) can be used as a turbo fluid machine (10) that rotates at high speed.

[0145] (5-10) The turbo fluid machine (10) of this embodiment is a turbo compressor. The fluid is a refrigerant. When the fluid is a refrigerant, the pressure acting on the back surface (52) of the impeller (50a, 50b) is greater than when the fluid is air. As a result, the thrust load acting on the rotating shaft (40) is greater.

[0146] (5-11) The refrigeration system (1) of this embodiment includes a refrigerant circuit (2) that performs a refrigeration cycle. The refrigerant circuit (2) includes a turbo compressor (10).

[0147] (5-12) The refrigeration capacity of the refrigeration system (1) of this embodiment is 100 US refrigeration tons or less. Since the refrigeration capacity of the refrigeration system (1) is 100 US refrigeration tons or less, the turbo compressor (10) can be applied to the refrigeration system (1) having a relatively small refrigeration capacity.

[0148] (6) Variations The above embodiment may be modified as follows. In the following description, differences from the above embodiment will be mainly described.

[0149] (6-1) Variation 1 The first seal portion (72) or the second seal portion (77) in the above embodiment may be a labyrinth seal having a labyrinth structure. As shown in Fig. 6, the seal portions (72, 77) in this modification are expansion-type labyrinth seals having an expansion chamber. Note that Fig. 6 shows an enlarged view of the second reduction portion (76). The first seal portion (72) of the first reduction portion (71) may have the same structure as the second seal portion (77) in this modification.

[0150] The second seal portion (77) is defined by a gap (A) formed between the partition member (80) and the second housing (25). In this modification, the second seal portion (77) is defined by a refrigerant flow path (R) and a plurality of expansion chambers (E).

[0151] The second housing (25) of this modified example has the same configuration as that of the above embodiment. The partition member (80) of this modified example has a cylindrical portion (81) and multiple protrusions (82). The cylindrical portion (81) has the same configuration as that of the above embodiment. Each protrusion (82) protrudes radially outward from the outer circumferential surface of the cylindrical portion (81). Each protrusion (82) is formed in an annular shape surrounding the cylindrical portion (81). Expansion chambers (E) are formed between each of the protrusions (82). The multiple expansion chambers (E) are arranged at regular intervals in the axial direction.

[0152] An end of each of the projections (82) faces a second hole (92) in the second housing (25). A minute gap is formed between the end of each of the projections (82) and the second hole (92) in the second housing (25). The minute gap forms a refrigerant flow path (R). The refrigerant flow path (R) extends straight along the axial direction. The refrigerant flow path (R) communicates with the multiple expansion chambers (E).

[0153] In this modification, the refrigerant flowing from the first space (S1) to the second space (S2) flows along the refrigerant flow path (R). When the refrigerant flows into the expansion chamber (E) formed in the middle of the refrigerant flow path (R), the refrigerant expands and is decompressed. The refrigerant that flows out of the expansion chamber (E) flows into the refrigerant flow path (R) and then flows into the adjacent expansion chamber (E). In this manner, the refrigerant flows from the refrigerant flow path (R) to the expansion chamber (E) multiple times. When the refrigerant flows from the expansion chamber (E) into the refrigerant flow path (R), the refrigerant is suddenly prevented from flowing. This causes flow resistance and generates a pressure loss. This pressure loss makes it possible to suppress the flow of the refrigerant from the first space (S1) to the second space.

[0154] (6-2) Variation 2 The first seal portion (72) or the second seal portion (77) in the above embodiment may be a labyrinth seal having another labyrinth structure. As shown in Fig. 7, the seal portions (72, 77) in this modification are labyrinth seals having a maze-type structure. Note that Fig. 7 shows an enlarged view of the second reduction portion (76). The first seal portion (72) of the first reduction portion (71) may have the same structure as the second seal portion (77) in this modification.

[0155] The second seal portion (77) is defined by a gap (A) formed between the partition member (80) and the second housing (25). In this modification, the second seal portion (77) is defined by a refrigerant flow path (R).

[0156] The partition member (80) of this modified example has a tubular portion (81) and a plurality of protrusions (82). The tubular portion (81) has the same configuration as in the above embodiment. Each of the protrusions (82) protrudes radially outward from the outer circumferential surface of the tubular portion (81). Each of the protrusions (82) is formed in an annular shape surrounding the tubular portion (81). The multiple protrusions (82) are arranged at regular intervals in the axial direction.

[0157] The second housing (25) of this modified example has a plurality of recesses (94) formed in the second hole (92). The recesses (94) are recessed radially outward. The plurality of recesses (94) are arranged at regular intervals in the axial direction. The recesses (94) face the protrusions (82) of the partition member (80).

[0158] Each of the protrusions (82) of the partition member (80) is disposed so as to mesh with a corresponding one of the recesses (94) of the second housing (25). A minute gap is formed between each of the protrusions (82) and the recesses (94) of the second housing (25). This minute gap forms a refrigerant flow path (R). The refrigerant flow path (R) is curved in a zigzag pattern.

[0159] In this modification, a part of the refrigerant in the first space (S1) flows into the refrigerant flow path (R) through a gap between the second hole (92) of the second housing (25) and the tip of the left-end protrusion (82) of the partition member (80). The refrigerant that has entered this gap flows radially inward along the right side surface of the left-end protrusion (82) and then flows to the other axial direction along the outer circumferential surface of the cylindrical portion (81). Then, the refrigerant flows radially outward along the left side surface of the other adjacent protrusion (82). In this way, the refrigerant flows through the gap (A) to the other axial direction while alternately changing direction between radially inward and radially outward, thereby flowing through a very narrow flow path over a relatively long distance. This makes it possible to suppress the inflow of the refrigerant from the first space (S1) to the second space.

[0160] (6-3) Variation 3 The first seal portion (72) or the second seal portion (77) in the above embodiment may be a labyrinth seal having another labyrinth structure. As shown in Fig. 8, the seal portions (72, 77) in this modification are labyrinth seals having a maze-type structure. Note that Fig. 8 shows an enlarged view of the second reduction portion (76). The first seal portion (72) of the first reduction portion (71) may have the same structure as the second seal portion (77) in this modification.

[0161] The second seal portion (77) is defined by a gap (A) formed between the partition member (80) and the second housing (25). In this modification, the second seal portion (77) is defined by a refrigerant flow path (R).

[0162] The partition member (80) of this modified example has a tubular portion (81). The tubular portion (81) extends in the axial direction from the back surface (52) of the second impeller (50b). A first step portion (83) is provided on the outer circumferential surface of the tubular portion (81). The outer diameter of each step of the first step portion (83) decreases toward the other axial side (the right side in FIG. 8 ).

[0163] A second step portion (95) is provided on the inner circumferential surface of the second housing (25). The second step portion (95) is formed between the first hole (91) and the second hole (92) in the second housing (25). The inner diameter of each step of the second step portion (95) decreases toward the other axial side (the right side in FIG. 8 ).

[0164] The first step portion (83) and the second step portion (95) correspond to each other. A minute gap is formed between the outer circumferential surface of the first step portion (83) and the inner circumferential surface (96) of the second step portion (95). This minute gap forms a refrigerant flow path (R). The refrigerant flow path (R) is formed in a stepped shape. The inner circumferential surface (96) of the second step portion (95) corresponds to a first aspect of the present disclosure.

[0165] In this modification, a part of the refrigerant in the first space (S1) flows into the refrigerant flow path (R) formed in a stepped shape, and flows through a very narrow flow path over a relatively long distance, thereby suppressing the inflow of the refrigerant from the first space (S1) to the second space.

[0166] (6-4) Variation 4 The first seal portion (72) or the second seal portion (77) in the above embodiment may be a seal having a different structure. As shown in Fig. 9, the seal portion (72, 77) in this modification is formed by a gap (B) between the rear surface (52) of the second impeller (50b) and the second housing (25). In other words, the second impeller (50b) in this modification is not provided with a partition member. Note that Fig. 9 shows an enlarged view of the second reduction portion (76). The first seal portion (72) of the first reduction portion (71) may have the same structure as the second seal portion (77) in this modification.

[0167] Specifically, as shown in Fig. 9, the second housing (25) is disposed to face the back surface (52) of the second impeller (50b). The second housing (25) corresponds to the wall portion of the present disclosure. The second housing (25) has a protrusion (97). The protrusion (97) protrudes toward the back surface (52) of the second impeller (50b). The protrusion (97) is formed in an annular shape so as to surround the periphery of a through hole formed in the center of the second housing (25).

[0168] A gap (B) is formed between the back surface (52) of the second impeller (50b) and the tip surface (97a) of the protruding portion (97) of the second housing (25). The seal portion (72, 77) of this modified example is defined by the gap (B). The seal portion (72, 77) is defined by a refrigerant flow path (R) extending straight in the radial direction. In this modified example, in the second back surface space (66b), the space radially outward of the protruding portion (97) is the first space (S1). In the second back surface space (66b), the space radially inward of the protruding portion (97) is the second space (S2).

[0169] Since the refrigerant flow path (R) in this embodiment is very narrow, when the refrigerant flows from the first space (S1) into the refrigerant flow path (R), the narrow flow path creates resistance and functions as a seal.

[0170] (6-5) Variation 5 The pressure reducing section (71, 76) in the above embodiment may have an on-off valve instead of the flow rate adjustment valve (74, 79). In other words, the valve does not have to be capable of adjusting the flow rate. In this modification, the pressure in the second space (S2) can be changed by changing the opening and closing of the on-off valve.

[0171] (6-6) Variation 6 The reduction portion (71, 76) in the above-described embodiment may be constituted by the seal portion (72, 77) and the bypass passage (73a, 78a). In other words, the reduction portion (71, 76) does not have to include a valve.

[0172] (6-7) Variation 7 The compressor (10) in the above embodiment may include either the first reduction section (71) or the second reduction section (76). In other words, the compressor (10) does not have to include both the first reduction section (71) and the second reduction section (76).

[0173] When the compressor (10) includes only the first reduction section (71), the compressor (10) does not include the fifth pressure sensor (105). In this case, the control section (110) adjusts the opening / closing or the degree of opening of the first flow rate control valve (74) based on the detection values ​​of the first pressure sensor (101), the second pressure sensor (102), the third pressure sensor (103), and the fourth pressure sensor (104).

[0174] When the compressor (10) includes only the second reducing section (76), the compressor (10) does not include the fourth pressure sensor (104). In this case, the control section (110) adjusts the opening / closing or the degree of opening of the second flow rate control valve (79) based on the detection values ​​of the first pressure sensor (101), the second pressure sensor (102), the third pressure sensor (103), and the fifth pressure sensor (105).

[0175] (6-8) Variation 8 The control unit (110) in the above embodiment may adjust the opening / closing or the opening degree of the first flow rate control valve (74) and the second flow rate control valve (79) based on the temperature of the refrigerant.

[0176] Other Embodiments The above embodiment may be configured as follows.

[0177] The pressure reducing portion (71, 76) in the above embodiment may be a screw provided on the back surface of the impeller (50a, 50b). In this case, the screw is fixed to the center of the back surface of the impeller (50a, 50b) and rotates integrally with the rotary shaft (40). The blades of the screw are provided to release the pressure in the back space (61b, 66b) of the impeller (50a, 50b) to the outside as the screw rotates. As a result, the pressure in the portion where the screw is provided decreases as the screw rotates, and the pressure acting on the entire back surface (52) of the impeller (50a, 50b) can be reduced.

[0178] The communication passage (11a) in the above embodiment may be a passage formed in the casing (20) instead of the connecting pipe (11).

[0179] The turbo fluid machine of the above embodiment may be a pump (for example, a centrifugal pump) instead of the turbo compressor 10. In this case, a liquid is used as the fluid.

[0180] Although the embodiment and the modified examples have been described above, it will be understood that various modifications of the form and details are possible without departing from the spirit and scope of the claims. In addition, the elements of the above embodiment, modified examples, and other embodiments may be appropriately combined or substituted.

[0181] The descriptions "first," "second," "third," etc. mentioned above are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words. [Industrial Applicability]

[0182] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful for turbo fluid machines and refrigeration devices. [Explanation of symbols]

[0183] 1 Refrigeration equipment 2 Refrigerant circuit 11a Communication path 12a Suction passage 20 Casing 25 Second housing (wall) 30 Electric motor 40 Rotational Axis 41,45,45 Bearings 50a 1st impeller (impeller) 50b Second impeller (impeller) 51 Front 52 Back 53 Blade 61a, 66a Compression chamber 61b,66b Back space 71,76 Reducer 72,77 Seal part 73a, 78a Bypass passage 74,79 Flow control valve (valve) 80 Partition member (first member) 97 Protrusion 97a Tip surface 110 Control section S1 1st space S2 2nd space

Claims

1. 1. A turbo fluid machine that compresses an introduced fluid having a suction pressure to an intermediate pressure higher than the suction pressure, and then compresses the fluid having the intermediate pressure to a discharge pressure higher than the intermediate pressure, A rotating shaft (40); an electric motor (30) that drives the rotating shaft (40); a pair of impellers (50a, 50b) which rotate integrally with the rotating shaft (40) to compress a fluid sucked into a compression chamber (61a, 66a) and are arranged such that their front faces (51) on which blades (53) are provided face each other across the electric motor (30); a casing (20) having the compression chambers (61a, 66a) corresponding to the pair of impellers (50a, 50b), respectively; a communication passage (11a) connecting the pair of compression chambers (61a, 66a) to each other; a pressure reducing portion (71, 76) that reduces the pressure in a rear space (61b, 66b) of one of the pair of impellers (50a, 50b), a suction passage (12a) for introducing a fluid into the casing (20), The reduction portion (71, 76) a seal portion (72, 77) that divides the rear space (61b, 66b) into a first space (S1) and a second space (S2); a bypass passage (73a, 78a) for bypassing the fluid in the second space (S2) to the suction passage (12a), the pressure in the first space (S1) corresponds to the discharge pressure of the compression chamber (61a, 66a) corresponding to the one of the impellers (50a, 50b), The pressure in the second space (S2) is lower than the pressure in the first space (S1). Turbo fluid machinery.

2. the one of the impellers (50a, 50b) has a cylindrical first member (80) extending away from a back surface (52) of the one of the impellers (50a, 50b) in the axial direction, the casing (20) has a first surface (92, 96) facing an outer circumferential surface of the first member (80), The seal portion (72, 77) is constituted by a gap (A) formed between the outer circumferential surface of the first member (80) and the first surface (92, 96). The turbofluid machine according to claim 1 .

3. The casing (20) has a wall portion (25) facing a back surface (52) of the one of the impellers (50a, 50b), the wall portion (25) has an annular protrusion (97) protruding toward a back surface (52) of the one of the impellers (50a, 50b), The seal portion (72, 77) is constituted by a gap (B) formed between the back surface (52) of the one impeller (50a, 50b) and the tip surface (97a) of the protrusion (97). The turbofluid machine according to claim 1 .

4. The reduction section (71, 76) further includes a valve (74, 79) disposed in the bypass passage (73a, 78a). The turbo fluid machine according to any one of claims 1 to 3.

5. a control unit (110) that controls the valves (74, 79), The control unit (110) adjusts the opening / closing or the opening degree of the valves (74, 79) based on the suction pressure of the fluid introduced into each of the pair of compression chambers (61a, 66a), the discharge pressure of the fluid discharged from the casing (20), and the back pressure of one of the impellers (50a, 50b). The turbo fluid machine according to claim 4.

6. The pair of impellers (50a, 50b) are each provided with the reduction portion (71, 76). The turbofluid machine according to claim 1 .

7. The pair of impellers (50a, 50b) a first impeller (50a) that compresses a fluid at a suction pressure introduced into the casing (20) to an intermediate pressure that is higher than the suction pressure; a second impeller (50b) that compresses the fluid at the intermediate pressure to a discharge pressure that is higher than the intermediate pressure, The outer diameter of the second impeller (50b) is smaller than the outer diameter of the first impeller (50a). The turbofluid machine according to claim 1 .

8. the rotating shaft (40) is rotatably supported by a bearing (41, 45, 45) disposed in the casing (20), The bearings (41, 45, 45) are foil bearings or magnetic bearings. The turbofluid machine according to claim 1 .

9. The maximum rotation speed of the rotating shaft (40) is 30,000 rpm or more. The turbofluid machine according to claim 1 .

10. The turbo fluid machine is a turbo compressor (10), The fluid is a refrigerant. The turbofluid machine according to claim 1 .

11. A refrigeration apparatus including a refrigerant circuit (2) that performs a refrigeration cycle, The refrigerant circuit (2) includes a turbo fluid machine according to claim 10. Refrigeration equipment.

12. The refrigeration capacity of the refrigeration unit is less than 100 US refrigeration tons.

12. The refrigeration system of claim 11.

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