Screw compressor and refrigeration cycle device

Abstract

This screw compressor comprises: a casing that constitutes an outer shell; a screw rotor that has a plurality of screw grooves on the outer peripheral surface thereof; a PM motor that has a PM motor stator internally fixed to the casing and a PM motor rotor that is disposed inside the PM motor stator and that has a permanent magnet, the PM motor rotor being disposed coaxially with the screw rotor; a screw shaft that transmits driving force from the PM motor to the screw rotor to rotate the screw rotor; a first bearing that supports one end of the screw shaft; a second bearing that supports the other end of the screw shaft; and a third bearing that is provided between the PM motor rotor and the screw rotor and supports a portion between the one end and the other end of the screw shaft.

Description

Screw compressor and refrigeration cycle device

[0001] The present disclosure relates to a screw compressor and a refrigeration cycle device.

[0002] In refrigeration systems equipped with compressors that compress refrigerants, factors such as the seasonal coefficient of performance, which takes into account performance under partial load operation, are becoming increasingly important due to growing environmental awareness. In order to improve compressor performance under partial load operation, screw compressors are increasingly being equipped with inverter drives and PM motors.

[0003] Conventionally, an induction motor is used as a drive source to drive a screw compressor. When an induction motor is not in operation, it does not generate magnetic attraction. Therefore, a major feature of this type of motor is its ease of assembly. Typically, screw compressors are positioned sideways. In this state, a load equal to the weight of the motor rotor and the screw rotor is applied to the screw shaft during operation, causing deflection (eccentricity) of the screw shaft. A known method of aligning the screw shaft using balancing components (balance adjustment components) is one means of suppressing this deflection (see, for example, Patent Document 1).

[0004] In the screw compressor of Patent Document 1, an eccentric load is applied to at least one of the ends of the motor rotor shaft and the screw rotor shaft (hereinafter referred to as the "shaft end") by a balancing component (balance adjustment component). Therefore, when the screw compressor is in operation, centrifugal force acting on the shaft end causes deflection of the screw rotor shaft and the motor rotor shaft. By superimposing the displacement of the shaft end caused by the centrifugal force due to the eccentric load applied by the balancing component (balance adjustment component) so as to cancel out the displacement of the shaft end during rotation caused by dynamic imbalance of at least one of the screw rotor and the motor rotor, it is possible to reduce deflection of the screw rotor shaft and the motor rotor shaft in portions where deflection tolerance is low.

[0005] JP 2019-35388 A

[0006] The prior art described in Patent Document 1 allows for alignment of a screw compressor equipped with an induction motor even after assembly. However, in the case of a screw compressor equipped with a motor using a permanent magnet in the motor rotor, such as a PM motor, the motor rotor has magnetic attraction even when the compressor is not operating. This magnetic attraction is applied to the motor rotor portion of the screw shaft in addition to its own weight, causing deflection of the screw shaft. Even if balancing components (balance adjustment components) are installed to align the magnetic attraction during operation, the air gap of the PM motor becomes smaller when the compressor is not operating, generating magnetic attraction. This magnetic attraction during shutdown adds to the influence of the magnetic attraction, making alignment difficult. In particular, because PM motors are driven by inverters, the amount of deflection varies with each rotation speed. Therefore, even if balancing components (balance adjustment components) designed for a certain rotation speed are used, there is a problem in that deflection at other rotation speeds cannot be fully suppressed.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a screw compressor and a refrigeration cycle device that can suppress deflection of the screw shaft when operation is stopped even when a PM motor is provided.

[0008] The screw compressor according to the present disclosure comprises a casing forming an outer shell, a screw rotor having a plurality of screw grooves on its outer peripheral surface, a PM motor stator inscribed and fixed within the casing, and a PM motor rotor arranged inside the PM motor stator and having a permanent magnet, wherein the PM motor rotor and the screw rotor are arranged coaxially, a screw shaft that transmits driving force from the PM motor to the screw rotor to rotate the screw rotor, a first bearing that supports one end of the screw shaft, a second bearing that supports the other end of the screw shaft, and a third bearing provided between the PM motor rotor and the screw rotor and providing support between one end and the other end of the screw shaft.

[0009] The refrigeration cycle device according to the present disclosure includes the screw compressor, the condenser, the throttle device, and the evaporator, all of which are connected by piping to form a refrigerant circuit through which the refrigerant circulates.

[0010] The screw compressor and refrigeration cycle device according to the present disclosure includes a third bearing that is provided between the PM motor rotor and the screw rotor and that supports the screw shaft between one end and the other end. This makes it possible to suppress deflection of the screw shaft when operation is stopped, even when a PM motor is provided.

[0011] 7 is a diagram showing the configuration of a refrigeration cycle device having a screw compressor according to embodiment 1. FIG. 7 is a schematic cross-sectional view of the screw compressor according to embodiment 1. FIG. 8 is a diagram explaining the compression principle of the screw compressor according to embodiment 1. FIG. 9 is an enlarged view of the portion viewed from arrow A in FIG. 2. FIG. 10 is a diagram explaining the amount of deflection of the screw shaft during operation of the screw compressor according to embodiment 1. FIG. 11 is a diagram explaining a change in the position of the center of gravity due to a reduction in the amount of deflection of the screw shaft during operation of the screw compressor according to embodiment 1. FIG. 12 is a schematic cross-sectional view of a first modified example of the screw compressor according to embodiment 1. FIG. 13 is an enlarged view of the portion viewed from arrow B in FIG. 14. FIG. 15 is an enlarged view of a main part of a second modified example of the screw compressor according to embodiment 1.

[0012] Hereinafter, screw compressors and refrigeration cycle devices according to embodiments will be described with reference to the drawings. In the following drawings, components denoted by the same reference numerals are identical or equivalent, and are common throughout the following embodiments. The configurations of components shown throughout the specification are merely examples and are not limited to the configurations described in the specification. Furthermore, the level of pressure, etc., is not determined in relation to an absolute value, but is determined relatively in terms of the state, operation, etc. of a system, device, etc.

[0013] Embodiment 1. <Refrigerant Circuit> Fig. 1 is a diagram showing the configuration of a refrigeration cycle apparatus 100 having a screw compressor 101 according to embodiment 1. The refrigeration cycle apparatus 100 according to embodiment 1 has a refrigerant circuit configured by connecting the screw compressor 101, a condenser 102, a throttling device 103, and an evaporator 104 in this order via piping 109. The refrigerant circuit circulates a refrigerant and transports heat.

[0014] The refrigerant circulating through the refrigerant circuit is not particularly limited here, but may be, for example, a fluorocarbon or fluoroolefin refrigerant such as HFC or HFO, a hydrocarbon refrigerant such as HC, or a natural refrigerant such as carbon dioxide or ammonia.

[0015] The screw compressor 101 compresses the refrigerant it draws in, and discharges it at a high temperature and high pressure. The screw compressor 101 according to the first embodiment is driven by power supplied from a power supply source (not shown) via an inverter device 105. The screw compressor 101 will be described later.

[0016] The condenser 102 cools and condenses the gaseous refrigerant (refrigerant gas) discharged from the screw compressor 101. The throttling device 103 throttles the liquid refrigerant (refrigerant liquid) flowing from the condenser 102, reducing its pressure and expanding it. The throttling device 103 is a capillary tube, or an electronic expansion valve or a thermostatic expansion valve that can variably adjust the throttle opening. The evaporator 104 evaporates the refrigerant flowing out of the throttling device 103.

[0017] The refrigeration cycle apparatus 100 includes an inverter device 105 and a control device 106. Here, the inverter device 105 and the control device 106 function as a braking device for braking the rotation of a PM (Permanent Magnet) motor 5 in the screw compressor 101. The control device 106 controls the devices included in the refrigeration cycle apparatus 100 and controls the entire refrigeration cycle apparatus 100. For example, the control device 106 controls the expansion device 103 and the drive frequency of the inverter device 105 that drives the screw compressor 101. The control device 106 can be configured with hardware such as a circuit device that realizes its functions. Alternatively, the control device 106 can be configured with software and an arithmetic device including a microcomputer and a CPU. The arithmetic device executes and processes the software to realize control of the devices in the refrigeration cycle apparatus 100.

[0018] The inverter device 105 supplies power to the PM motor 5 of the screw compressor 101 at a drive frequency based on instructions from the control device 106 to drive the PM motor 5. The inverter device 105 changes the drive frequency and changes the rotation speed of the PM motor 5, for example, when changing the capacity of the screw compressor 101, starting (starting), stopping operation, or performing protective control. The inverter device 105 according to the first embodiment applies a DC voltage to the PM motor stator 5a to generate torque in the PM motor 5 during rotation braking control of the compression mechanism in the screw compressor 101. The inverter device 105 also has a function of performing rotation braking control of the compression mechanism so that the PM motor rotor 5b does not rotate reversely even when a force attempting to rotate the PM motor rotor 5b reverse is applied, or so that the reverse rotation of the PM motor rotor 5b is suppressed. In the first embodiment, the control device 106 and the inverter device 105 are described as being separate from the screw compressor 101, but this is not limited thereto. The control device 106 for the screw compressor 101 and the inverter device 105 may be integrated into the screw compressor 101 by being built in the screw compressor 101, for example.

[0019] <Screw compressor 101> Fig. 2 is a schematic cross-sectional view of the screw compressor 101 according to embodiment 1. The screw compressor 101 according to embodiment 1 is, for example, a single screw type in which one gate rotor 11 is fitted to one screw rotor 6. However, the screw compressor 101 is not limited to the single screw type and may be a twin screw type or the like.

[0020] 2, the screw compressor 101 includes a cylindrical casing 2 that forms an outer shell. The casing 2 accommodates a motor cover 3, a screw shaft 4, a PM motor 5, a screw rotor 6, a first bearing 8, and a second bearing 9. The casing 2 also includes a suction strainer 10 that draws refrigerant therein.

[0021] The screw rotor 6 has a cylindrical shape and is formed with a plurality of spirally extending screw grooves 6a (see FIG. 3 described later) on its outer circumferential surface. The screw rotor 6 is fixed to the screw shaft 4. A gate rotor 11 and a slide valve 12 are provided on the side of the screw rotor 6 so as to be axially symmetrical with respect to the screw shaft 4.

[0022] The gate rotor 11 has a disk shape, and its axial direction is perpendicular to the axial direction of the screw rotor 6. A plurality of teeth 11a are formed on the outer peripheral surface of the gate rotor 11, and the plurality of teeth 11a are arranged so as to mesh with the screw grooves 6a of the screw rotor 6. The slide valve 12 is slidable in the axial direction of the screw shaft 4 along the slide grooves 2a formed in the casing 2, and an opening 12a is provided in the center of the slide valve 12.

[0023] The space surrounded by the screw grooves 6a of the screw rotor 6, the teeth 11a of the gate rotor 11, the inner circumferential surface of the casing 2, and the slide valve 12 forms a compression chamber 19 filled with compressed refrigerant gas. Refrigerating machine oil is injected into the compression chamber 19 to lubricate the first bearing 8 and the second bearing 9 and to seal the compression chamber 19.

[0024] The slide valve 12 changes the internal volume ratio by adjusting the timing at which the refrigerant is discharged from the compression chamber 19. Here, the internal volume ratio is the ratio of the volume of the tooth groove space that becomes the compression chamber 19 when the refrigerant is sucked to the volume of the tooth groove space just before the refrigerant is discharged.

[0025] The PM motor 5 rotates to compress the refrigerant in the compression mechanism, and its rotation speed is controlled by the inverter device 105. This allows the capacity of the screw compressor 101 to be adjusted. The PM motor 5 is disposed in the motor chamber 20 formed within the casing 2. The PM motor 5 is composed of a PM motor stator 5a fixed within the casing 2 and a PM motor rotor 5b disposed inside the PM motor stator 5a. The PM motor rotor 5b is fixed to the screw shaft 4 and disposed coaxially with the screw rotor 6. The PM motor 5 is an electric motor having a permanent magnet in its rotor, which becomes the PM motor rotor 5b. Furthermore, the PM motor 5 has low torque during operation. Furthermore, since no secondary current flows through the rotor, the PM motor 5 is an energy-saving, highly efficient motor. However, magnetic materials such as permanent magnets tend to demagnetize with increasing temperature. For this reason, it is necessary to suppress demagnetization of the PM motor 5 by suppressing the rise in motor temperature and driving and braking the motor so that the temperature is below a set temperature.

[0026] Here, the PM motor 5 has a magnetic attraction force. When working with the screw compressor 101 open, if a magnetic object such as iron is held, the magnetic attraction force may excite the magnetic object and cause it to adhere to the PM motor rotor 5b. Therefore, it is difficult to perform alignment work after assembling the PM motor rotor 5b into the screw compressor 101, as in the prior art. However, in the first embodiment, balance adjustment is possible without opening the cover and performing alignment work.

[0027] One end of the screw shaft 4, which is the end (left side in FIG. 2) on the side where the PM motor rotor 5b is not fixed, is rotatably supported by the bearing housing 7 via a first bearing 8, and the other end (right side in FIG. 2) on the side where the PM motor rotor 5b is fixed, is rotatably supported by the motor cover 3 via a second bearing 9. The screw shaft 4 transmits the driving force from the PM motor 5 to the screw rotor 6, causing the screw rotor 6 to rotate.

[0028] FIG. 3 is a diagram illustrating the compression principle of the screw compressor 101 according to the first embodiment. Next, the operation of the screw compressor 101 will be described. When the PM motor 5 in the screw compressor 101 is started by the inverter device 105, the screw shaft 4 rotates, causing the screw rotor 6 to rotate in the direction indicated by the solid arrow in FIG. 3 . Because the teeth 11a of the gate rotor 11 mesh with the screw grooves 6a of the screw rotor 6, when the screw rotor 6 rotates, the teeth 11a of the gate rotor 11 move relatively within the screw grooves 6a. As a result, the gate rotor 11 rotates in the direction indicated by the thin white arrow in FIG. 3 . At this time, a cycle consisting of a suction stroke, a compression stroke, and a discharge stroke is repeated within the compression chamber 19. Here, each stroke will be described, focusing on the compression chamber 19 indicated by the dotted hatching in FIG. 3 .

[0029] Figure 3(a) shows the state of the compression chamber 19 during the suction stroke. The screw rotor 6 is driven by the PM motor 5 to rotate in the direction of the solid arrow. In conjunction with the rotation of the screw rotor 6, the teeth 11a of the gate rotor 11 rotate sequentially toward the discharge port 18. As a result, the volume of the compression chamber 19 decreases, and the refrigerant gas in the compression chamber 19 is compressed, as shown in Figure 3(b).

[0030] As the screw rotor 6 continues to rotate, as shown in Figure 3(c), the compression chamber 19 communicates with the space of the high-pressure section (the high-pressure space on the refrigerant discharge side inside the casing 1) through the discharge port 18. As a result, the high-pressure refrigerant gas compressed in the compression chamber 19 is discharged from the discharge port 18 to the high-pressure section. Then, the same compression occurs again on the back surface of the screw rotor 6.

[0031] Here, a minute gap (not shown) is provided in the compression chamber 19, which is constituted by the gate rotor 11, the screw rotor 6, etc., to allow the gate rotor 11 and the screw rotor 6 to rotate. The minute gap in the compression chamber 19 serves as a flow path through which the refrigerant gas compressed and high-pressure in the compression chamber 19 and the refrigeration oil supplied to the compression chamber 19 leak into the low-pressure section (the low-pressure space on the refrigerant suction side inside the casing 1).

[0032] Fig. 4 is an enlarged view of the portion indicated by the arrow A in Fig. 2. Next, the main parts of the screw compressor 101 will be described with reference to Fig. 4. As shown in Fig. 4, a third bearing 15 that generates a variable load on the screw shaft 4 is provided between the screw rotor 6 of the screw shaft 4 and the PM motor rotor 5b. This third bearing 15 is composed of an iron core 15a and a coil 15b. Note that, although a radial bearing (perpendicular to the axial direction of the screw shaft 4) is used as the third bearing 15, the third bearing 15 is not limited thereto, and may be an electromagnet that can generate a variable load (magnetic attractive force) in the radial direction, or may be used in combination with a cylindrical roller bearing.

[0033] The third bearing 15 is supported by the magnetic bearing holder 14. The third bearing 15 supports the screw shaft 4 between one end and the other end. It is desirable to position the third bearing 15 as close as possible to the PM motor rotor 5b, which is subjected to the greatest load, in order to suppress the amount of deflection of the screw shaft 4 when the motor is not in operation. For this reason, it is desirable to provide the third bearing 15 closer to the PM motor rotor 5b than the coil end 5a1 of the PM motor stator 5a.

[0034] The problem caused by the deflection of the screw shaft 4 when the compressor is not operating is as follows. If the deflection of the screw shaft 4 causes an imbalance in the amount of clearance between the screw rotor 6 and the inner circumferential surface of the casing 2, the screw rotor 6 will come into contact with the inner circumferential surface of the casing 2 during startup, making it more likely to seize. Furthermore, the deflection of the screw shaft 4 causes the screw rotor 6 to tilt slightly. Normally, the screw rotor 6 and the gate rotor 11 mesh horizontally to form the compression chamber 19, but the tilt of the screw rotor 6 increases the contact surface between the gate rotor 11 and the screw grooves 6a, making the gate rotor 11 more susceptible to wear. Therefore, the above problem can be solved by suppressing the deflection of the screw shaft 4 when the compressor is not operating.

[0035] The screw shaft 4 is also provided with a position sensor 16 for measuring the amount of deflection (eccentricity) of the screw shaft 4. During operation of the screw compressor 101, the amount of deflection of the screw shaft 4 is measured using the position sensor 16, and feedback control is performed using the control device 106. This generates a load (magnetic attractive force) from the third bearing 15 in a direction that suppresses the deflection of the screw shaft 4, thereby supporting the screw shaft 4 and suppressing the deflection. Note that by arranging the position sensor 16 at a position where the screw shaft 4 is most deflected, feedback control can be performed according to the amount of deflection at that position, thereby achieving a greater deflection suppression effect. In other words, arranging the position sensor 16 as close as possible to the PM motor rotor 5b achieves a greater deflection suppression effect.

[0036] FIG. 5 is a diagram illustrating the amount of deflection of the screw shaft 4 during operation of the screw compressor 101 according to the first embodiment. FIG. 6 is a diagram illustrating a change in the center of gravity position due to a reduction in the amount of deflection of the screw shaft 4 during operation of the screw compressor 101 according to the first embodiment. In the first embodiment, a load is generated from the third bearing 15 in a direction directly opposite to the direction of the eccentric force (F1, F2 in FIG. 5 ). When the amount of deflection of the screw shaft 4 changes due to the generation of the load, as shown in FIG. 5 , the balance of the screw shaft 4 is adjusted by the counterbalance generated by the force (F3 in FIG. 5 ) generated by the third bearing 15, thereby suppressing the amount of deflection of the screw shaft 4. Note that in FIG. 5 , F1 is the weight of the screw rotor 6, F2 is the weight of the PM motor rotor 5b plus the magnetic attractive force of the PM motor 5, and F3 is the magnetic attractive force of the third bearing 15. When the rotation speed of the screw compressor 101 changes, eccentricity occurs in the PM motor rotor 5b due to centrifugal force, increasing the amount of eccentricity near the PM motor rotor 5b. Since the magnetic attractive force also increases accordingly, a variable load can be applied from the third bearing 15 in a direction to suppress the eccentricity. The amount of deflection is measured using a position sensor 16, and a variable load is generated on the third bearing 15 using a control device 106. As shown in FIG. 5 , the deflection of the screw shaft 4 is greatest at the PM motor rotor 5b, so it is advisable to position the position sensor 16 near the PM motor rotor 5b.

[0037] As shown in Figure 6, by generating a variable load on the screw shaft 4 from the third bearing 15, a force acts in the opposite direction to the eccentricity (the direction of the arrow in Figure 6), thereby adjusting the balance. The position of the center of gravity of the screw shaft 4 then moves from position Gb before the variable load was generated to position Ga (the screw shaft 4 moves from the broken line to the solid line position), approaching the center of rotation O, thereby reducing the amount of deflection of the screw shaft 4. The reduced amount of deflection of the screw shaft 4 also reduces the centrifugal force generated by the deflection. This reduces the vibration of the entire screw shaft 4 due to the centrifugal force, thereby suppressing the humming noise. Here, the amount of deflection is the distance between the position of the center of gravity of the screw shaft 4 and the center of rotation O, and the smaller the amount of deflection, the greater the reduction in centrifugal force.

[0038] When generating a variable load on the third bearing 15 using the control device 106, the air gap of the PM motor 5 (the gap between the PM motor stator 5a and the PM motor rotor 5b) or the gap of the third bearing 15 may be measured using the position sensor 16.

[0039] FIG. 7 is a schematic cross-sectional view of a first modified example of the screw compressor 101 according to the first embodiment. FIG. 8 is an enlarged view of the portion indicated by the arrow B in FIG. 7 . FIG. 9 is an enlarged view of a main portion of a second modified example of the screw compressor 101 according to the first embodiment. Note that FIG. 9 is an enlarged view of the same portion as FIG. 8 . In the first embodiment, the third bearing 15 is supported by the magnetic bearing holder 14, but this is not limited thereto. As shown in FIGS. 7 and 8 , a structure for supporting the third bearing 15 may be provided within the casing 2, and the third bearing 15 may be supported by a partition wall 2 b of the casing 2 that separates the motor chamber 20 and the compression chamber 19. Furthermore, as shown in FIG. 9 , the third bearing 15 may be fitted between the partition wall 2 b. This configuration reduces the influence of magnetic attraction of the PM motor 5. Furthermore, because the third bearing 15 does not suppress the amount of deflection during shutdown, a bearing 17 for supporting the screw shaft 4 during shutdown may be disposed near the third bearing 15. During operation, the deflection of the screw shaft 4 is reduced by the third bearing 15, so the bearing 17 also functions as a bearing that supports the screw shaft 4 in the radial direction.

[0040] As described above, the screw compressor 101 according to the first embodiment includes a casing 2 forming an outer shell, a screw rotor 6 having a plurality of screw grooves 6a on its outer peripheral surface, a PM motor 5 having a PM motor stator 5a inscribed and fixed within the casing 2 and a PM motor rotor 5b having a permanent magnet and arranged inside the PM motor stator 5a, with the PM motor rotor 5b and the screw rotor 6 being arranged coaxially, a screw shaft 4 that transmits driving force from the PM motor 5 to the screw rotor 6 to rotate the screw rotor 6, a first bearing 8 that supports one end of the screw shaft 4, a second bearing 9 that supports the other end of the screw shaft 4, and a third bearing 15 that is provided between the PM motor rotor 5b and the screw rotor 6 and provides support between one end and the other end of the screw shaft 4.

[0041] The screw compressor 101 according to the first embodiment is provided with a third bearing 15 that is disposed between the PM motor rotor 5b and the screw rotor 6 and that supports one end of the screw shaft 4 from the other end, and therefore it is possible to suppress deflection of the screw shaft 4 when operation is stopped even when the PM motor 5 is provided. Furthermore, the provision of the third bearing 15 suppresses the amount of deflection of the screw shaft 4 during operation, so that seizure caused by the screw rotor 6 coming into contact with the inner peripheral surface of the casing 2 does not occur, and operation of the screw compressor 101 can be continued.

[0042] Furthermore, in the screw compressor 101 according to the first embodiment, the third bearing 15 is a magnetic bearing that generates a variable load on the screw shaft 4, and is equipped with a position sensor 16 that measures the amount of deflection of the screw shaft 4, and a control device 106 that measures the amount of deflection of the screw shaft 4 using the position sensor 16 during operation, and generates a load according to the measured amount of deflection from the magnetic bearing in a direction that suppresses the deflection of the screw shaft 4.

[0043] According to the screw compressor 101 of the first embodiment, during operation, the position sensor 16 is used to measure the amount of deflection of the screw shaft 4, and a load corresponding to the measured amount of deflection is generated from the magnetic bearing in a direction that suppresses deflection of the screw shaft 4. Therefore, during operation, the balance of the screw shaft 4 is adjusted by the variable load applied by the magnetic bearing, and deflection of the screw shaft 4 can be suppressed when operation is stopped, even when the screw compressor is equipped with a PM motor 5.

[0044] By measuring the amount of deflection, which varies depending on the rotation speed, using the position sensor 16, load adjustment can be performed according to the amount of deflection. This allows the amount of deflection to be suppressed when operating at any rotation speed, thereby suppressing vibration and humming noise of the screw compressor 101. The use of a magnetic bearing eliminates the need to supply oil to the magnetic bearing disposed between the screw rotor 6 and the PM motor rotor 5b. Furthermore, since deflection measurement using the control device 106 can also include differences due to individual differences, vibration and humming noise of the screw compressor 101, including changes in deflection due to individual differences between the screw compressors 101, can be suppressed. Furthermore, suppressing the amount of deflection allows the gap between the screw rotor 6 and the casing 2 to be further reduced, enabling further improvement in operating performance.

[0045] In the screw compressor 101 according to the first embodiment, the third bearing 15 is provided closer to the PM motor rotor 5b than the coil end 5a1 of the PM motor stator 5a.

[0046] According to the screw compressor 101 of the first embodiment, the third bearing 15 is disposed as close as possible to the PM motor rotor 5b on which the greatest load acts, thereby making it possible to further suppress the amount of deflection.

[0047] In the screw compressor 101 according to the first embodiment, a compression chamber 19 filled with compressed refrigerant gas and a motor chamber 20 in which the PM motor 5 is disposed are formed within the casing 2, the casing 2 has a partition wall 2b separating the motor chamber 20 from the compression chamber 19, and the third bearing 15 is supported by the partition wall 2b.

[0048] According to the screw compressor 101 of the first embodiment, the third bearing 15 is configured to be supported by the partition wall 2 b of the casing 2 , so that the influence of the magnetic attraction of the PM motor 5 can be reduced.

[0049] In addition, the refrigeration cycle device 100 according to embodiment 1 has a refrigerant circuit in which the screw compressor 101, the condenser 102, the throttling device 103, and the evaporator 104 are connected by piping 109, and in which the refrigerant circulates.

[0050] According to the refrigeration cycle apparatus 100 of the first embodiment, the same effects as those of the screw compressor 101 described above can be obtained.

[0051] 2 Casing, 2a Slide groove, 2b Partition wall, 3 Motor cover, 4 Screw shaft, 5 PM motor, 5a PM motor stator, 5b PM motor rotor, 5a1 Coil end, 6 Screw rotor, 6a Screw groove, 7 Bearing housing, 8 First bearing, 9 Second bearing, 10 Suction strainer, 11 Gate rotor, 11a Tooth portion, 12 Slide valve, 12a Opening, 14 Magnetic bearing holder, 15 Third bearing, 15a Iron core, 15b Coil, 16 Position sensor, 17 Bearing, 18 Discharge port, 19 Compression chamber, 20 Motor chamber, 100 Refrigeration cycle device, 101 Screw compressor, 102 Condenser, 103 Throttle device, 104 Evaporator, 105 Inverter device, 106 Control device, 109 Piping.

Claims

1. A screw compressor comprising: a casing forming an outer shell; a screw rotor having a plurality of screw grooves on its outer peripheral surface; a PM motor stator fixed inscribed in the casing; and a PM motor rotor arranged inside the PM motor stator and having a permanent magnet, the PM motor rotor and the screw rotor being arranged coaxially; a screw shaft that transmits driving force from the PM motor to the screw rotor to rotate the screw rotor; a first bearing that supports one end of the screw shaft; a second bearing that supports the other end of the screw shaft; and a third bearing that is provided between the PM motor rotor and the screw rotor and supports the space between one end and the other end of the screw shaft.

2. The screw compressor according to claim 1, wherein the third bearing is provided closer to the PM motor rotor than a coil end of the PM motor stator.

3. A screw compressor as claimed in claim 1 or 2, comprising: a position sensor that measures the amount of deflection of the screw shaft, wherein the third bearing is a magnetic bearing that generates a variable load on the screw shaft; and a control device that measures the amount of deflection of the screw shaft using the position sensor during operation and generates a load according to the measured amount of deflection from the magnetic bearing in a direction that suppresses the deflection of the screw shaft.

4. A screw compressor as claimed in any one of claims 1 to 3, wherein a compression chamber filled with compressed refrigerant gas and an electric motor chamber in which the PM motor is disposed are formed within the casing, the casing has a partition wall separating the electric motor chamber and the compression chamber, and the third bearing is supported by the partition wall.

5. A refrigeration cycle device comprising the screw compressor according to any one of claims 1 to 4, a condenser, a throttling device, and an evaporator connected by piping to form a refrigerant circuit through which a refrigerant circulates.

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