EP3505765A1

EP3505765A1 - Screw compressor and refrigeration cycle device

Info

Publication number: EP3505765A1
Application number: EP16914144.7A
Authority: EP
Inventors: Katsuya Maeda
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-08-23
Filing date: 2016-08-23
Publication date: 2019-07-03
Anticipated expiration: 2036-08-23
Also published as: CN109642579B; EP3505765B1; CN109642579A; EP3505765A4; WO2018037469A1

Abstract

A screw compressor includes: a casing having a refrigerant liquid flow passage through which refrigerant liquid from an outside passes; a screw rotor having an outer peripheral surface with a plurality of screw grooves that form compression chambers and is arranged so as to be rotated inside the casing; and a slide valve provided between the casing and the screw rotor and configured to move slidably in a direction of a rotary shaft of the screw rotor. Further, the casing, the slide valve, or each of the casing and the slide valve has an oil injection port configured to supply oil to the plurality of screw grooves, and the slide valve has a refrigerant liquid injection flow passage configured to communicate the refrigerant liquid flow passage with any one of the plurality of screw grooves and is configured to move between a first position of allowing the refrigerant liquid injection flow passage to be communicated with one of the plurality of screw grooves from a time immediately before start of compression to a time immediately after the start of compression and a second position of allowing the refrigerant liquid injection flow passage to be brought into communication with an other one of the plurality of screw grooves which is in a suction stroke before the start of compression and being closer to the oil injection port in the direction of the rotary shaft than the first position.

Description

Technical Field

The present invention relates to a screw compressor and a refrigeration cycle apparatus, which are to be used for, for example, compression of refrigerant for a refrigerating machine.

Background Art

A single-screw compressor includes a screw rotor and two disc-shaped gate rotors, which are accommodated in a casing. The screw rotor has a plurality of helical screw grooves formed in an outer peripheral surface. The two disc-shaped gate rotors each have a plurality of teeth. Spaces surrounded by the casing, the screw grooves of the screw rotor, and the teeth of the gate rotors form compression chambers. Along with rotation of the screw rotor, the teeth of the gate rotors move in the screw grooves of the screw rotor to repeat an operation of increasing and decreasing a capacity of each of the compression chambers. During a period of time in which the capacity of the compression chamber is increased, refrigerant is sucked into the compression chamber. After the capacity of the compression chamber starts decreasing, the sucked refrigerant is compressed. Then, when the screw groove being the compression chamber is communicated with a discharge port, compressed high-pressure refrigerant is discharged from the compression chamber.
In this type of single-screw compressor, a discharge temperature of discharge refrigerant gas discharged from the compressor increases under operating conditions at a large pressure difference between a high pressure and a low pressure or while a motor rotation speed is being increased by an inverter. When the discharge temperature is increased, there is a possibility that a trouble that the screw rotor may thermally expand to come into contact with the casing and is seized occurs.
Therefore, hitherto, when the discharge temperature is higher than a set temperature, oil contained in the discharge refrigerant gas discharged from the compressor is separated by an oil separator so that the separated oil is cooled by an oil cooler to be injected into the screw groove being the compressor chamber, thereby suppressing a rise in discharge temperature (see, for example, Patent Literature 1).

Citation List

Patent Literature

Patent Literature 1: Japanese Unexamined Utility Model Application Publication No. Sho 63-130686

Summary of Invention

Technical Problem

A temperature of suction gas sucked into the compressor is lower than the temperature of the discharge gas. Therefore, during a steady operation, the screw rotor can be cooled by the suction of the suction gas into the screw grooves of the screw rotor. However, during a non-steady operation, the temperature of the suction gas itself sucked into the compressor is high, and hence a cooling effect for the screw rotor, which is provided by the suction gas, is reduced. The non-steady operation is an operation in which a degree of superheat of the suction gas (hereinafter referred to as "suction SH") rapidly rises or becomes higher than the suction SH given during the steady operation, for example, at start of the operation. When the cooling effect for the screw rotor is reduced as described above, there is a fear of causing seizing due to the thermal expansion of the screw rotor. Therefore, prevention of the seizing of the screw rotor during the non-steady operation is demanded.
Patent Literature 1 describes that the oil separated by the oil separator is cooled and is injected into the compression chamber to decrease the discharge temperature. However, a temperature rise of the oil during the non-steady operation has not been examined. During the non-steady operation, the discharge temperature rises, and therefore a temperature of the oil separated by the oil separator also inevitably increases. Thus, even when the oil is cooled by the oil cooler, the oil cannot be sufficiently cooled. Hence, the oil is supplied to the compression chamber while the temperature is kept high. Further, as described above, the temperature of the suction gas also increases during the non-steady operation. Therefore, the problem of seizing of the screw rotor still remains. Further, even in a case of a configuration including no oil cooler, the oil at a high temperature is directly injected into the compression chamber during the non-steady operation. Thus, there is a possibility that the seizing of the screw rotor may occur.
The present invention has been attained to solve the problems described above, and an object thereof is to provide a screw compressor and a refrigeration cycle apparatus, which are capable of suppressing a rise in discharge temperature and suppressing seizing of a screw rotor during a non-steady operation.

Solution to Problem

According to one embodiment of the present invention, there is provided a screw compressor, including: a casing having a refrigerant liquid flow passage through which refrigerant liquid from an outside passes; a screw rotor having an outer peripheral surface with a plurality of screw grooves that form compression chambers and being arranged so as to be rotated inside the casing; and a slide valve provided between the casing and the screw rotor and configured to move slidably in a direction of a rotary shaft of the screw rotor, wherein the casing, the slide valve, or each of the casing and the slide valve has an oil injection port configured to supply oil to the plurality of screw grooves, and wherein the slide valve has a refrigerant liquid injection flow passage configured to bring the refrigerant liquid flow passage to communicate with any one of the plurality of screw grooves and configured to move between a first position of allowing the refrigerant liquid injection flow passage to communicate with one of the plurality of screw grooves from a time immediately before start of compression to a time immediately after the start of compression and a second position of allowing the refrigerant liquid injection flow passage to be communicated with an other one of the plurality of screw grooves which is in a suction stroke before the start of compression and being closer to the oil injection port in the direction of the rotary shaft than the first position.
The refrigeration cycle apparatus according to one embodiment of the present invention includes a refrigerant circuit formed by sequentially connecting the screw compressor described above, a condenser, a main pressure-reducing device, and an evaporator.

Advantageous Effects of Invention

According to one embodiment of the present invention, the slide valve is located at the first position so that the liquid injection is started from the time immediately before the start of compression to the time immediately after the start of the compression. In this manner, the rise in discharge temperature can be suppressed. Further, the slide valve is located at the second position so that the liquid injection is performed at a position closer to the oil injection port than the first position in the direction of the rotary shaft. In this manner, the seizing of the screw rotor during the non-steady operation can be suppressed.

Brief Description of Drawings

Fig. 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus including a screw compressor according to Embodiment 1 of the present invention.
Fig. 2 is a schematic configuration view of the screw compressor according to Embodiment 1 of the present invention.
Fig. 3 is a developed view of an outer peripheral surface of a screw rotor of the screw compressor according to Embodiment 1 of the present invention and is an illustration of a positional relationship between screw grooves and an injection port when a slide valve is arranged at a first position on a discharge side.
Fig. 4 is a developed view of the outer peripheral surface of the screw rotor of the screw compressor according to Embodiment 1 of the present invention and is an illustration of the positional relationship between the screw grooves and the injection port when the slide valve is arranged at a second position on a suction side.
Figs. 5 are illustrations of a mechanism of compression by the screw compressor according to Embodiment 1 of the present invention.
Fig. 6 is a flowchart of liquid injection control in the refrigeration cycle apparatus including the screw compressor according to Embodiment 1 of the present invention.
Fig. 7 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 2 of the present invention.

Description of Embodiments

Embodiment

1

Fig. 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus including a screw compressor according to Embodiment 1 of the present invention. In Fig. 1 and other drawings referred to below, components denoted by the same reference symbols are the same or corresponding components, and this similarly applies to the entirety of the description. Further, forms of components given in the entirety of the description are merely examples, and are not limited to those given in the description.
A refrigeration cycle apparatus 100 includes a refrigerant circuit formed by sequentially connecting a screw compressor 102, a condenser 104, a main expansion valve 105, and an evaporator 106 by refrigerant pipes. The refrigeration cycle apparatus 100 further includes a refrigerant liquid pipe 108. The refrigerant liquid pipe 108 branches from a pipe between the condenser 104 and the main expansion valve 105, and is connected to the screw compressor 102. A flow control valve 111 configured to control a flow rate through the refrigerant liquid pipe 108 is provided to the refrigerant liquid pipe 108. The flow control valve 111 is formed of, for example, an electronic expansion valve. The refrigeration cycle apparatus 100 further includes an oil separator 112 and an oil supply pipe 113. The oil separator 112 is configured to separate oil from refrigerant discharged from the screw compressor 102. The oil supply pipe 113 is configured to supply the oil separated by the oil separator 112 to the screw compressor 102. Description is given on the configuration in which the oil separator 112 is installed independently of the compressor. However, a configuration in which an oil separator is integrated with a compressor to thereby allowing the compressor to have functions of the oil separator may also be used.
The screw compressor 102 is configured to suck the refrigerant and compress the refrigerant into a high-temperature and high-pressure state. The screw compressor 102 is driven by supply of power from a power supply source (not shown) to a motor 103 through an inverter 101.
The condenser 104 is configured to cool and condense discharge refrigerant gas from the screw compressor 102. The main expansion valve 105 is configured to expand refrigerant liquid passing through a refrigerant liquid pipe 109, and includes an electronic expansion valve. The main expansion valve 105 corresponds to a main pressure-reducing device according to the present invention. Besides the electronic expansion valve, devices in other forms such as a mechanical expansion valve, a thermal expansion valve, or a capillary tube may be used as the main pressure-reducing device as long as a similar role is fulfilled. The evaporator 106 is configured to evaporate the refrigerant having flowed out from the main expansion valve 105.
A suction gas temperature sensor 120 configured to detect a temperature of suction gas sucked into the screw compressor 102 is provided on a suction side of the screw compressor 102. An inlet temperature detected by the suction gas temperature sensor is output to a controller 110 described later.
The refrigeration cycle apparatus 100 further includes the controller 110. The controller 110 is configured to perform overall control of the refrigeration cycle apparatus 100 such as opening-degree control of the main expansion valve 105, position control of a slide valve described later, and opening-degree control of the flow control valve 111. As the opening-degree control of the main expansion valve 105, the controller 110 controls the main expansion valve 105 so that a suction SH takes a target value during a steady operation. In this case, the steady operation means an operation other than a non-steady operation, and the non-steady operation means an operation in which a degree of superheat of the suction gas (hereinafter referred to as "suction SH") rapidly rises or becomes higher than the suction SH given during the steady operation, for example, at start of the operation.
Further, as the opening-degree control of the flow control valve 111, the controller 110 controls the flow control valve 111 in accordance with a discharge temperature. Specifically, the controller 110 controls the flow control valve 111 so that the discharge temperature falls within a preset set range. The controller 110 may include hardware such as a circuit device configured to achieve functions thereof, or may include a combination of a computing device such as a microcomputer or a CPU and software executed thereon.

(Description of Operation of Refrigerant Circuit)

Next, an operation of the refrigeration cycle apparatus 100 according to Embodiment 1 is described with reference to Fig. 1.
The screw compressor 102 sucks and compresses the refrigerant gas being gaseous refrigerant, and thereafter discharges the refrigerant gas. The discharge gas discharged from the screw compressor 102 flows into the oil separator 112. In the oil separator 112, the refrigerant and the oil mixed with the refrigerant are separated from each other. The refrigerant is cooled in the condenser 104. The refrigerant having been cooled in the condenser 104 is split after passing through the condenser 104. Main-flow refrigerant thereof is reduced in pressure and expanded by the main expansion valve 105. Then, the refrigerant having flowed out from the main expansion valve 105 is heated in the evaporator 106 to turn into refrigerant gas. The refrigerant gas having flowed out from the evaporator 106 is sucked into the screw compressor 102.
Meanwhile, refrigerant as part of refrigerant liquid having passed through the condenser 104 and is split from the main-flow refrigerant flows into the refrigerant liquid pipe 108. Then, the refrigerant liquid is injected into compression chambers 5 due to a differential pressure between a pressure of the refrigerant liquid in the refrigerant liquid pipe 108 and a pressure in the compression chamber of the screw compressor 102. The injected refrigerant liquid is mixed with the refrigerant gas being currently compressed, is compressed, and is discharged from the screw compressor 102.
Further, the oil discharged together with the refrigerant from the screw compressor 102 is separated from the refrigerant in the oil separator 112, and is returned to the screw compressor 102 through the oil supply pipe 113. As described above, the action of returning the oil to the screw compressor 102 prevents the screw compressor 102 from running out of the oil.

(Screw Compressor)

Now, the screw compressor 102 according to Embodiment 1 of the present invention is described with reference to Fig. 2 to Fig. 4. Fig. 2 is a schematic configurational view of the screw compressor according to Embodiment 1 of the present invention. Fig. 3 is a developed view of an outer peripheral surface of a screw rotor of the screw compressor according to Embodiment 1 of the present invention and is an illustration of a positional relationship between screw grooves and an injection port when the slide valve is arranged at a first position on a discharge side. Fig. 4 is a developed view of the outer peripheral surface of the screw rotor of the screw compressor according to Embodiment 1 of the present invention and is an illustration of a positional relationship between the screw grooves and the injection port when the slide valve is arranged at a second position on the suction side.
As illustrated in Fig. 2, the screw compressor 102 includes a casing 1, a screw rotor 3, gate rotors 6, the motor 103 configured to drive the screw rotor 3 to rotate, a slide valve 7, and other components. The casing 1 is configured to accommodate the screw rotor 3, the gate rotors 6, the motor 103, the slide valve 7, and other components.
The casing 1 has an accommodation wall 1a having a cylindrical shape, which internally defines an approximately cylindrical space. Inside the accommodation wall 1a, the screw rotor 3 having an approximately columnar shape is arranged. The screw rotor 3 has one end being a suction side (right side of Fig. 2) for the refrigerant and the other end being a discharge side (left side of Fig. 2). A plurality of helical screw grooves 3a are formed on an outer peripheral surface of the screw rotor 3. Further, a rotary shaft 4 is provided in a center of the screw rotor 3 so as to rotate integrally therewith. The rotary shaft 4 is borne by a bearing 2, which is provided to the casing 1, so as to be freely rotatable.
The motor 3 having a frequency controlled by, for example, the invertor 101 is coupled to an end of the rotary shaft 4, which is on a side opposite to the bearing 2. The motor 103 includes a stator 103a and a motor rotor 103b. The stator 103a internally contact and fixed to the casing 1. The motor rotor 103b is arranged inside the stator 103a. The rotary shaft 4 is coupled to the motor rotor 103 so as to drive the screw rotor 3 to rotate.
Each of the gate rotors 6 has a disc-like shape and has an outer peripheral portion having a plurality of teeth 6a to be meshed with the screw grooves 3a. Spaces surrounded by the teeth 6a of the gate rotors 6, the screw grooves 3a, and the accommodation wall 1a of the casing 1 define the compression chambers 5.
The space inside the casing 1 is partitioned by a partition wall (not shown) into a low-pressure side into which low-pressure gas refrigerant is introduced from the evaporator 106 of the refrigerant circuit and a high-pressure side into which high-pressure gas refrigerant discharged from the compression chamber 5 flows. A discharge port (see Figs. 5 referred to later) 10, which is open to a discharge chamber (not shown), is formed on the high-pressure side of the casing 1.
Further, the casing 1 has an oil injection port 114 configured to supply the oil separated by the oil separator 112 to the screw grooves 3a. The oil injection port 114 is formed at a position facing the screw groove 3a from a time immediately before start of the compression to a time immediately after the start of the compression, as illustrated in Fig. 3 and Fig. 4. The oil injection port 114 is formed in the casing 1. However, the oil injection port 114 may be formed in a capacity-control slide valve or an internal capacity ratio variable slide valve described later. Further, the oil injection ports may be formed in both the casing and the capacity-control or internal capacity ratio variable slide valve described above.
As illustrated in Fig. 2, on an inner peripheral surface 1aa side of the accommodation wall 1a of the casing 1, a slide groove 1b extending in a direction of the rotary shaft 4 of the screw rotor 3 is formed. In the slide groove 1b, the slide valve 7 for changing a liquid injection position is accommodated so as to be freely movable slidably in the direction of the rotary shaft 4. The slide valve 7 closes openings of the screw grooves 3a to define the compression chambers 5, and therefore forms part of the inner peripheral surface 1aa together with the casing 1. Fig. 2 illustrates a configuration in which the single slide valve 7 for changing a liquid injection position is provided in the casing 1. However, the capacity control slide valve or the internal capacity ratio variable slide valve may be additionally provided. In Fig. 3 and Fig. 4, illustration is given on an example in which an internal capacity variable slide valve 11 is provided.
The slide valve 7 is configured to change an injection position for injection of the refrigerant liquid to the screw grooves 3a that define the compression chambers 5 and has a refrigerant liquid injection flow passage 7a, which is configured to inject the refrigerant liquid from an outside into the screw grooves 3a and is formed to pass therethrough. The refrigerant liquid injection flow passage 7a has a liquid reservoir groove 7aa having an elongated groove shape and an injection port 7ab having a cylindrical shape. The liquid reservoir groove 7aa is formed on a surface side of the slide valve 7 facing the accommodation wall 1a of the casing 1, and extends in a sliding direction. The injection port 7ab is formed so as to communicate with the liquid reservoir groove 7aa, and is open to the screw rotor 3 side.
The slide valve 7 is configured to be movable between the first position (see Fig. 3) on the discharge side and the second position (see Fig. 4) on the suction side. When the slide valve 7 moves to the first position on the discharge side, injection timing can be delayed. When the slide valve 7 moves to the second position on the suction side, the injection timing can be advanced.
The position of the injection port 7ab in a state in which the slide valve 7 is located at the first position is a position on the discharge side (left side of Fig. 3) along a suction side end surface 1d of the casing 1 on a plan view of the slide valve 7 and the casing 1 as viewed from an outer side, as illustrated in Fig. 3. Therefore, from another point of view, the position of the injection port 7ab in the state in which the slide valve 7 is located at the first position can be described as a position facing the screw groove 3a from the time immediately before the start of compression to the time immediately after the start of compression. Therefore, under the state in which the slide valve 7 is located at the first position, the liquid injection of the refrigerant liquid to the screw grooves 3a is started between the time immediately before the start of compression and the time immediately after the start of compression.
The position of the injection port 7ab in a state in which the slide valve 7 is located at the second position on the suction side is a position facing a screw groove 3ab before the start of compression, specifically, in a suction stroke, as illustrated in Fig. 4. Therefore, under the state in which the slide valve 7 is located at the second position, the refrigerant liquid is injected into the screw groove 3a before the start of compression. For injection of the refrigerant liquid to the screw groove 3a in the suction stroke, when the refrigerant liquid is injected at an early stage of the suction stroke, the suction of the suction gas into the compression chambers 5 is inhibited. Therefore, it is preferred that the injection of the refrigerant liquid to the screw groove 3a in the suction stroke be carried out in a later stage of the suction stroke.
The position of the injection port 7ab and the position of the oil injection port 114 in the state in which the slide valve 7 is located at the first position are each "the position facing the screw groove 3a from the time immediately before the start of compression to the time immediately after the start of compression", but are different in position in a circumferential direction. Specifically, as illustrated in Fig. 3, the slide valve 7 is provided in a direction opposite to a rotating direction of the screw rotor 3 with respect to the oil injection port 114. Therefore, the injection port 7ab and the oil injection port 114 in the state in which the slide valve 7 is located at the first position are different in position in the direction of the rotary shaft 4 (position in a horizontal direction of Fig. 3), and the oil injection port 114 is located closer to the suction side (right side of Fig. 3). Therefore, when the slide valve 7 is located at the second position on the suction side, the position of the injection port 7ab in the direction of the rotary shaft 4 is closer to the oil injection port 114 in comparison to the case in which the slide valve 7 is located at the first position on the discharge side.
The slide valve 7 is connected to a drive device 9 such as a piston via a coupling rod 8 and is movable between the first position and the second position inside the slide groove 1b by drive of the driving device 9. In this case, the drive device 9 may be driven by a gas pressure or a hydraulic pressure, and, besides the piston, may be a motor or other devices without limiting a driving method.
The casing 1 has a refrigerant liquid flow passage 1c, which brings the outside of the casing 1 to communicate with slide groove 1b, as illustrated in Fig. 2. A positional relationship between the refrigerant liquid flow passage 1c and the slide valve 7 is set so that an opening of the refrigerant liquid flow passage 1c on the slide groove 1b side communicates with the liquid reservoir groove 7aa formed on the side valve 7 regardless of whether the slide valve 7 is located at the first position or the second position. The refrigerant liquid pipe 108 (see Fig. 1) is connected to an opening of the refrigerant liquid flow passage 1c on an outer side of the casing.
Due to the configuration described above, regardless of whether the slide valve 7 is located at the first position or the second position, the refrigerant liquid split from the refrigerant liquid flowing between the condenser 104 and the main expansion valve 15 flows into the screw grooves 3a that define the compression chambers 5 through the refrigerant liquid pipe 108, the refrigerant liquid flow passage 1c, and the refrigerant liquid injection flow passage 7a.
The refrigerant used for the refrigerant circuit is not particularly limited. For example, as the refrigerant, an HFC-based refrigerant such as R134a, an HFO-based refrigerant being a low GWP refrigerant, or other refrigerants is used.

(Description of Operation)

Now, an operation of the screw compressor according to Embodiment 1 is described.
Figs. 5 are illustrations of a mechanism of compression by the screw compressor according to Embodiment 1 of the present invention.
As illustrated in Figs. 5, the screw rotor 3 is rotated by the motor 103 (see Fig. 2) via of the rotary shaft 4 (see Fig. 1). As a result, the teeth 6a of the gate rotors 6 move relatively in the screw grooves 3a. In this manner, a cycle including the suction stroke, a compression stroke, and a discharge stroke is repeated in the compression chambers 5. A portion surrounded by the dotted line in Figs. 5 represents the accommodation wall 1a of the casing 1. The compression chambers 5 formed by the screw grooves 3a located in a region surrounded by the accommodation wall 1a are in the compression stroke. In this case, focusing on the compression chamber 5 which is indicated by the dot hatching in Figs. 5, each of the strokes is described.
In Fig. 5(a), screw grooves 3ac and 3ad are in the compression stroke, screw grooves 3aa and 3ab are in the suction stroke, and a screw groove 3ae is in the discharge stroke. When the screw rotor 3 in the state illustrated in Fig. 5(a) is driven by the motor 103 to rotate in the direction indicated by the solid arrow, the lower gate rotor 6 illustrated in Figs. 5 is rotated in a direction indicated by the outlined arrow along with the rotation of the screw rotor 3. The upper gate rotor 6 illustrated in Figs. 5 is rotated in a direction opposite to the direction of rotation of the lower gate rotor 6, as indicated by the outlined arrow. In the suction stroke, the compression chamber 5 has a maximized capacity, communicates with a low-pressure space in the casing 1, and is filled with the low-pressure refrigerant gas.
When the screw motor 3 is further rotated, the teeth 6a of the two gate rotors 6 rotationally move in a sequential manner toward the discharge port 10 in conjunction with the rotation. As a result, the capacity (volume) of the compression chamber 5 is decreased, as illustrated in Fig. 5(b).
When the screw rotor 3 is further continuously rotated, the compression chamber 5 is communicated with the discharge port 10, as illustrated in Fig. 5(c). As a result, the high-pressure refrigerant gas compressed in the compression chamber 5 is discharged to the outside from the discharge port 10. Then, a similar compression is performed again with a back surface of the screw rotor 3.
In Figs. 5, illustration of the slide groove 1b and the refrigerant liquid injection flow passage 7a of the slide valve 7 is omitted. However, the refrigerant liquid flows into the screw groove 3a through the refrigerant liquid injection flow passage 7a to cool the refrigerant gas in the compression chamber 5, is compressed together with the suction gas in the compression stroke, and is discharged to the outside in the discharge stroke. Further, in Figs. 5, illustration of the oil injection port 114 is omitted. However, the oil separated by the oil separator 112 is supplied from the oil injection port 114 to the screw groove 3a.
In the screw compressor configured as described above, during the steady operation, the injection of the refrigerant liquid (hereinafter often referred to as "liquid injection") for the purpose of suppressing increase in discharge temperature is performed. The liquid injection during the steady operation is started in the compression chamber 5 from a time immediately before completion of the suction of the suction gas and a time immediately after the completion of the suction of the suction gas. As a result, a defect that the refrigerant liquid leaks and flows to the suction side to inhibit the suction of the suction gas into the compression chamber 5 can be prevented.
Embodiment 1 is characterized in that seizing of the screw rotor 3 during the non-steady operation is suppressed while the liquid injection is performed during the steady operation to suppress the increase in discharge temperature as described above.
In order to suppress the seizing of the screw rotor 3 during the non-steady operation, the position of the liquid injection port and the position of the oil injection port 114 (positions in the horizontal direction in Fig. 3 and Fig. 4), which are close to each other in the direction of the rotary shaft 4, are effective. A high-temperature oil separated by the oil separator 112 during the non-steady operation is supplied from the oil injection port 114 to the screw groove 3a. At this time, the screw rotor 3 is rotating. Therefore, the oil is supplied to a circumferential region of the screw rotor 3, which includes a portion of the screw rotor 3 in the direction of the rotary shaft 4, in which the oil injection port 114 is located. Therefore, in particular, the circumferential region of the outer peripheral surface of the screw rotor 3 is liable to have an increased temperature and expand.
Thus, when the liquid injection is performed for the circumferential region, the portion having a high temperature can be cooled intensively to suppress thermal expansion of the screw rotor 3 so as to suppress the seizing of the screw rotor 3. In order to perform the liquid injection to the circumferential region, the position of the injection port 7ab in the direction of the rotary shaft 4 is only required to be set closer to the oil injection port 114.
As described above, the injection position during the steady operation and the injection position during the non-steady operation are required to be different from each other. The different injection positions are achieved by movement of the slide valve 7. Specifically, the slide valve 7 moves to the first position on the discharge side during the steady operation, whereas the slide valve 7 moves to the second position on the suction side during the non-steady operation. Whether a current operating state is a steady operation state or a non-steady operation state is determined based on the suction SH. Specifically, it is determined that the steady operation is being performed when the suction SH is low and that the non-steady operation is being performed when the suction SH is high.
Now, liquid injection control for moving the slide valve 7 is described with reference to a flowchart of Fig. 6.
Fig. 6 is a flowchart of the liquid injection control in the refrigeration cycle apparatus including the screw compressor according to Embodiment 1 of the present invention. The flow control valve 111 is opened at an initial opening degree at the start of the operation.
The controller 110 (see Fig. 1) calculates an actually measured suction SH based on the suction gas temperature detected by the suction gas temperature sensor 120. Then, when the actually measured suction SH is equal to or larger than a set suction SH_A and equal to or smaller than a set suction SH_B (Step S1; Yes), specifically, the current operating state is the steady operation state, the controller 110 moves the slide valve 7 to the first position on the discharge side as illustrated in Fig. 3 (Step S2). The set suction SH_A and the set suction SH_B are preset in the controller 110. The set suction SH_A and the set suction SH_B are threshold values for determining whether the operation is the steady operation or the non-steady operation. Specifically, when the actually measured suction SH is smaller than the set suction SH_A, a liquid return operation (non-steady operation) is being performed. When the actually measured suction SH is larger than the set suction SH_B, a suction SH rise operation (non-steady operation) is being performed. Gasified refrigerant is generally sucked into the compressor. However, the refrigerant is sucked into the compressor under a state in which liquid and gas are mixed in the liquid return operation. Then, when the slide valve 7 moves to the first position, the injection port 7ab moves to the position facing the screw groove 3ac from the time immediately before the start of compression to the time immediately after the start of compression.
Subsequently, the controller 110 controls the flow control valve 111 in accordance with an actually measured discharge temperature detected by a discharge temperature sensor (not shown). Specifically, when the actually measured discharge temperature is higher than a preset first temperature (Step S3; No), the opening degree of the flow control valve 111 is increased (Step S4). When the actually measured discharge temperature is lower than a second set temperature that is lower than the first set temperature (Step S5; No), the opening degree of the flow control valve 111 is decreased (Step S6). Meanwhile, when the actually measured discharge temperature is equal to or higher than the second set temperature and equal to or lower than the first set temperature (Step S3;Yes, Step S5; Yes), the current opening degree is maintained.
Meanwhile, when the determination in Step S1 is No and the actually measured suction SH is larger than the set suction SH_B (Step S7; Yes), specifically, the current operating state is the non-steady operation state, the controller 110 moves the slide valve 7 to the second position on the suction side as illustrated in Fig. 4 (Step S8). In this manner, as described above, the position of the injection port 7ab in the direction of the rotary shaft 4 can move closer to the oil injection port 114. Thus, the screw rotor 3 can be effectively cooled. Further, the liquid injection is performed for the screw groove 3ab before the start of the compression, specifically, the screw groove 3ab in the suction stroke and therefore contributes to a decrease in actually measured suction SH. As described above, when the liquid injection is performed for the screw groove 3ab in the suction stroke, the actually measured suction SH is gradually decreased.
Then, in order to decrease the suction SH, the opening degree of the main expansion valve 105 is increased (Step S9). Then, when the actually measured discharge temperature is higher than the first set temperature (Step S10; No), the opening degree of the flow control valve 111 is increased (Step S11). Then, the processing returns to Step S9 to repeat the operation of increasing the opening degree of the main expansion valve 105. Meanwhile, when the actually measured discharge temperature is equal to or lower than the first set temperature (Step S10; Yes), the opening degree of the flow control valve 111 is decreased (Step S12). Then, the processing returns to Step S1 to check a condition of decrease of the actually measured suction SH.
When the actually measured suction SH is not equal to or higher than the set suction SH_A or equal to or smaller than the set suction SH_B and the actually measured suction SH is not larger than the set suction SH_B (Step S1; No, Step S7; No), specifically, when the actually measured SH is smaller than the set suction SH_A, it is determined that the liquid return operation (non-steady operation) is being performed. When it is determined that the liquid return operation (non-steady operation) is being performed, the controller 110 moves the slide valve 7 to the first position on the discharge side (step S13) and subsequently decreases the opening degree of the main expansion valve 105 so as to increase the suction SH (Step S14). As a result, a state is switched to a state in which the liquid injection is started from the time immediately before the start of compression and the time immediately after the start of compression. A subsequent operation is as described above.
As described above, according to Embodiment 1, the slide valve 7 having the injection port 7ab that moves in accordance with the suction SH is provided. Therefore, the injection position for the liquid injection can be changed for each of the steady operation and the non-steady operation. Thus, during the steady operation, when the liquid injection is started from the time immediately before the start of compression and the time immediately after the start of compression, the rise in discharge temperature can be suppressed without bringing about a defect that the liquid refrigerant leaks to the suction side to inhibit the suction of the suction gas refrigerant to the compression chamber 5.
During the non-steady operation, the liquid injection can be performed for the circumferential region in which the thermal expansion is liable to occur due to the supply of oil from the oil injection port 114. Thus, a quality defect such as seizing between the screw rotor 3 and the casing 1 can be suppressed. Further, during the non-steady operation, the rise in suction SH can be suppressed by performing the liquid injection to the screw groove 3a in the suction stroke.
Further, the flow rate of the liquid injection can be adjusted by the flow control valve 111 in accordance with the discharge temperature. Thus, the rise in discharge temperature can be suppressed with an optimal liquid injection amount. Thus, the inhibition of suction of the refrigerant into the compression chambers 5 can be minimized. Thus, an influence on performance degradation can be reduced.

Embodiment 2

In Embodiment 2, the configuration according to Embodiment 1 further includes an on-off valve 107 configured to open and close a flow passage of the refrigerant liquid pipe 108, which is provided to the refrigerant liquid pipe 108. The on-off valve 107 includes, for example, a solenoid valve. Differences from Embodiment 1 are described in Embodiment 2, and a configuration that is not described in Embodiment 1 is similar to the configuration of Embodiment 1.
Fig. 7 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 2 of the present invention.
The refrigeration cycle apparatus 100 according to Embodiment 2 has a configuration in which the on-off valve 107 is additionally provided to the refrigerant liquid pipe 108 of Embodiment 1, which is illustrated in Fig. 1. The expansion valve serving as the flow control valve 111 is not generally guaranteed to completely close the flow passage. Therefore, when only the flow control valve 111 is provided to the refrigerant liquid pipe 108, the flow passage of the refrigerant liquid pipe 108 cannot be completely closed. Thus, even when the flow control valve 111 is closed in a case in which the liquid injection is not required to be performed, the liquid injection is slightly performed. Thus, when the on-off valve 107 is provided, the flow passage of the refrigerant liquid pipe 108 can be completely closed to stop the liquid injection.
In Embodiment 2, the same effects as those obtained in Embodiment 1 are obtained. In addition, the on-off valve 107 is provided to the refrigerant liquid pipe 108, and therefore Embodiment 2 additionally has the following effect. Specifically, in an operating region in which the discharge temperature is unlikely to increase, the liquid injection can be stopped by closing the on-off valve 107. Thus, performance deterioration due to a rise in intermediate pressure caused by the liquid injection performed at timing that is originally unnecessary can be prevented.
The screw compressor 102 is the single-screw compressor in Embodiment 1 and Embodiment 2. However, the present invention is applicable to other screw compressors, for example, a twin-screw compressor. Further, the present invention is applicable to specifications with an economizer as the configuration of the refrigeration cycle.

Reference Signs List

1 casing 1a accommodation wall 1aa inner peripheral surface 1b slide groove 1c refrigerant liquid flow passage 1d end surface 2 bearing 3 screw rotor 3a screw groove 3aa screw groove 3ab screw groove
3ac screw groove 3ad screw groove 3ae screw groove 4 rotary shaft 5 compression chamber 6 gate rotor 6a teeth 7 slide valve 7a refrigerant liquid injection flow passage 7aa liquid reservoir groove
7ab injection port 8 coupling rod 9 drive device 10 discharge port11 slide valve 100 refrigeration cycle apparatus 101 inverter 102 screw compressor 103 motor 103a stator 103b motor rotor 104 condenser
105 main expansion valve 106 evaporator 107 on-off valve 108 refrigerant liquid pipe 109 refrigerant liquid pipe 110 controller 111 flow control valve 112 oil separator 113 oil supply pipe 114 oil injection port
120 suction gas temperature sensor

Claims

A screw compressor, comprising:
a casing having a refrigerant liquid flow passage through which refrigerant liquid from an outside passes;

a screw rotor having an outer peripheral surface with a plurality of screw grooves that form compression chambers and being arranged so as to be rotated inside the casing; and

a slide valve provided between the casing and the screw rotor and configured to move slidably in a direction of a rotary shaft of the screw rotor,

wherein the casing, the slide valve, or each of the casing and the slide valve has an oil injection port configured to supply oil to the plurality of screw grooves, and

wherein the slide valve has a refrigerant liquid injection flow passage configured to bring the refrigerant liquid flow passage to communicate with any one of the plurality of screw grooves and is configured to move between a first position of allowing the refrigerant liquid injection flow passage to communicate with one of the plurality of screw grooves from a time immediately before start of compression to a time immediately after the start of compression and a second position of allowing the refrigerant liquid injection flow passage to communicate with an other one of the plurality of screw grooves which is in a suction stroke before the start of compression and being closer to the oil injection port in the direction of the rotary shaft than the first position.
The screw compressor of claim 1, wherein a position of the slide valve is switched to the first position or the second position in accordance with a degree of suction superheat of suction gas.
The screw compressor of claim 1 or 2, wherein the refrigerant liquid injection flow passage has a liquid reservoir groove communicating with the refrigerant liquid flow passage regardless of whether the slide valve is located at the first position or the second position, and an injection port intercommunicating with the liquid reservoir groove.
A refrigeration cycle apparatus, comprising a refrigerant circuit formed by sequentially connecting the screw compressor of any one of claims 1 to 3, a condenser, a main pressure-reducing device, and an evaporator.
The refrigeration cycle apparatus of claim 4, further comprising:
a refrigerant liquid pipe branching from a pipe between the condenser and the main pressure-reducing device and being connected to the refrigerant liquid flow passage of the screw compressor;

a flow control valve provided to the refrigerant liquid pipe and configured to control a flow rate of refrigerant flowing through the refrigerant liquid pipe;

an oil separator configured to separate oil from the refrigerant discharged from the screw compressor;

an oil supply pipe configured to supply the oil separated by the oil separator to the oil injection port of the screw compressor; and

a controller configured to move the slide valve to the first position or the second position in accordance with a degree of suction superheat of the refrigerant sucked into the screw compressor.
The refrigeration cycle apparatus of claim 5, wherein the controller moves the slide valve to the first position when the degree of suction superheat is equal to or lower than a preset degree of suction superheat, and moves the slide valve to the second position when the degree of suction superheat is larger than the set degree of suction superheat.
The refrigeration cycle apparatus of claim 5 or 6, wherein the controller is configured to control the flow control valve so that a discharge temperature of the refrigerant discharged from the screw compressor falls within a preset range.
The refrigeration cycle apparatus of any one of claims 5 to 7, further comprising an on-off valve configured to open and close a flow passage of the refrigerant liquid pipe.