REFRIGERATION CYCLE DEVICE

Abstract

 A refrigeration cycle apparatus includes: a refrigerant circuit; a liquid injection pipe branching off from a pipe between a condenser and a pressure reducing device of the refrigerant circuit to be connected to a liquid injection port of a screw compressor; an adjustment device provided to the liquid injection pipe and configured to adjust a liquid injection amount; and a controller configured to control the adjustment device. The controller is configured to: perform control for controlling the adjustment device so that a discharge temperature of refrigerant discharged from the screw compressor becomes a target discharge temperature during an operation of the screw compressor; and control, when the operation of the screw compressor is to be stopped, the adjustment device to increase the liquid injection amount, and then stop the screw compressor.

Description

Technical Field

[0001] The present invention relates to a refrigeration cycle apparatus including a screw compressor configured to perform, for example, refrigerant compression.

Background Art

[0002] In related-art refrigeration cycle apparatus, when a temperature abnormally rises in a high-pressure section extending from a compressor outlet to a condenser inlet, there occur problems that refrigerant and oil deteriorate, and that a screw rotor in a screw compressor thermally expands so excessively as to be brought into contact with a casing. In general, there is known a technology for injecting refrigerant liquid from an injection pipe into a compression chamber of the screw compressor in order to prevent the above-mentioned problems (see, for example, Patent Literatures 1 and 2).

[0003] In Patent Literature 1, there is disclosed a technology for achieving a constant discharge temperature of refrigerant gas discharged from a compressor by providing a capacity control valve to be driven by a pulse motor to an injection pipe and controlling the capacity control valve to adjust the injection amount of the refrigerant liquid.

[0004] Further, in Patent Literature 2, there is disclosed a technology for achieving a constant degree of superheat of discharge gas by providing a temperature-type expansion valve with a temperature sensitive cylinder to an injection pipe and adjusting an opening degree of the temperature-type expansion valve based on a discharge temperature of a compressor detected by a temperature sensitive cylinder.

[0005] Incidentally, the refrigeration cycle apparatus configured to inject liquid into the compression chamber as described above causes the following problems when a liquid injection amount is larger than required. That is, there arise problems that extra operating power (electrical input) is required, and that the screw rotor is cooled and thermally contracted, to thereby increase a gap between the screw rotor and the casing and degrade the performance due to an increased leak of refrigerant gas. Therefore, in the related art, it is investigated to suppress the injection amount to a small level, and it is also known to minimize the injection amount of the refrigerant liquid by setting the discharge temperature or the degree of discharge superheat to a high level.

Citation List

Patent Literature

[0006] 

Patent Literature 1: Japanese Patent No. 2574864

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 05-10613

Summary of Invention

Technical Problem

[0007] A screw compressor performs an operation for sucking low-temperature and low-pressure refrigerant gas from a low-pressure (suction) chamber and discharging high-temperature and high-pressure gas to a high-pressure (discharge) chamber. When the screw compressor performing such an operation stops the operation, namely, the driving of an electric motor, the refrigerant gas flows backward from the high-pressure (discharge) chamber to the low-pressure (suction) chamber through a screw groove of a screw rotor. When the refrigerant flows backward in this manner, the high-temperature discharge gas passes through the screw groove of the screw rotor, to thereby increase the temperature of the screw rotor to thermally expand the screw rotor.

[0008] In particular, as described above, when the discharge temperature or the degree of discharge superheat is set high, the discharge temperature becomes higher than the temperature of the screw rotor or the casing. Moreover, the screw rotor has a heat capacity lower than that of the casing due to a material forming the screw rotor, and hence the thermal expansion due to the backflow of the refrigerant at the time of an operation stop is large. Therefore, there has been a problem that the casing and the screw rotor fail to maintain a gap therebetween and are brought into contact with each other, which causes seizure.

[0009] However, neither Patent Literature 1 nor Patent Literature 2 described above includes an investigation about the thermal expansion due to the backflow of the refrigerant at the time of the operation stop.

[0010] In order to solve the above-mentioned problems, the present invention has an object to provide a refrigeration cycle apparatus capable of suppressing the thermal expansion of a screw rotor due to the backflow of discharge gas at the time of an operation stop of a screw compressor.

Solution to Problem

[0011] According to one embodiment of the present invention, there is provided a refrigeration cycle apparatus including: a refrigerant circuit configured to circulate refrigerant therethrough, the refrigerant circuit including a screw compressor, a condenser, a pressure reducing device, and an evaporator; a liquid injection pipe branching off from a pipe between the condenser and the pressure reducing device and being connected to a liquid injection port of the screw compressor; an adjustment device provided to the liquid injection pipe and configured to adjust a liquid injection amount; and a controller configured to control the adjustment device, the controller being configured to control the adjustment device so that a discharge temperature of refrigerant discharged from the screw compressor becomes a target discharge temperature during an operation of the screw compressor, and control, when the operation of the screw compressor is to be stopped, the adjustment device to increase the liquid injection amount, and then stop the screw compressor.

Advantageous Effects of Invention

[0012] According to one embodiment of the present invention, the operation of the screw compressor is stopped after the discharge temperature is lowered by controlling the adjustment device to increase the liquid injection amount, and hence it is possible to suppress the thermal expansion of the screw rotor due to the backflow of the refrigerant gas at the time of the operation stop.

Brief Description of Drawings

[0013] 

Fig. 1 is a diagram for illustrating a configuration of a refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention.

Fig. 2 is a schematic sectional view of a screw compressor 102 included in the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention.

Fig. 3 is a schematic sectional view taken along the line A-A of Fig. 2.

Figs. 4 are diagrams for illustrating a basic idea of compression to be performed by the screw compressor 102 included in the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention.

Fig. 5 is a conceptual diagram of the backflow of discharge gas and the thermal expansion of a screw rotor 3 caused when the screw compressor 102 is stopped.

Fig. 6 is an explanatory diagram of the expansion of a screw rotor caused when the discharge gas flows backward.

Fig. 7 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention.

Fig. 8 is a conceptual diagram of the backflow of the discharge gas and the thermal expansion of the screw rotor 3 caused when the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention is stopped.

Fig. 9 is a diagram for illustrating a configuration of a refrigeration cycle apparatus 100 according to Embodiment 2 of the present invention.

Fig. 10 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 2 of the present invention.

Fig. 11 is a diagram for illustrating a configuration of a refrigeration cycle apparatus 100 according to Embodiment 3 of the present invention.

Fig. 12 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 3 of the present invention.

Fig. 13 is a diagram for illustrating a configuration of the refrigeration cycle apparatus 100 including a refrigeration cycle apparatus 100 according to Embodiment 4 of the present invention.

Fig. 14 is a diagram for illustrating a configuration of the refrigeration cycle apparatus 100 including the refrigeration cycle apparatus 100 according to a modification example of Embodiment 4 of the present invention.

Description of Embodiments

[0014] Now, embodiments of the present invention are described with reference to the accompanying drawings. In the drawings referred to in the following description, components denoted by the same reference symbols are assumed to be the same as or equivalent to one another and common across the entirety of the following description of the embodiments. In addition, the forms of the components described herein are merely examples, and the present invention is not limited to descriptions of those components. In particular, the combination of the components is not limited only to the combination described in each embodiment, and the component described in another embodiment may be appropriately applied to a different embodiment. The level of pressure is not particularly determined based on a relationship with an absolute value, and is assumed to be relatively determined based on the state, operation, and other factors of a system, a device, and other entities.

Embodiment 1

[0015] Fig. 1 is a diagram for illustrating a configuration of a refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention. In the following, a screw compressor 102 is a device included in a refrigerant circuit. Therefore, the description is given on the assumption that a fluid to be sucked, compressed, and discharged by the screw compressor 102 in each of Embodiment 1 and other embodiments is refrigerant.

[0016] The refrigeration cycle apparatus 100 according to Embodiment 1 includes a main refrigerant circuit configured to circulate refrigerant therethrough, the refrigerant circuit including the screw compressor 102, a condenser 103, an expansion valve 104 for main flow liquid, which serves as a pressure reducing device, and an evaporator 105, which are connected through refrigerant pipes in the stated order.

[0017] The screw compressor 102 sucks the refrigerant, and compresses the refrigerant to bring the refrigerant to a high-temperature and high-pressure state. The condenser 103 cools and condenses discharge gas, which is gaseous refrigerant discharged from the screw compressor 102. The expansion valve 104 for main flow liquid decompresses and expands main flow refrigerant flowing out of the condenser 103. Then, the evaporator 105 evaporates the refrigerant flowing out of the expansion valve 104 for main flow liquid.

[0018] The refrigeration cycle apparatus 100 further includes a liquid injection pipe 108. The liquid injection pipe 108 branches off from a pipe through which the main flow refrigerant flows between the condenser 103 and the expansion valve 104 for main flow liquid, and is connected to a liquid injection port of the screw compressor 102. In addition, the liquid injection pipe 108 is provided with an adjustment device 106 configured to adjust the liquid injection amount.

[0019] The adjustment device 106 includes an expansion valve 107 for liquid injection and a solenoid valve 109 for liquid injection, which serves as a valve configured to allow or inhibit the passage of the refrigerant. The expansion valve 107 for liquid injection is formed of an electronic expansion valve. The solenoid valve 109 for liquid injection is provided in order to achieve complete closure of the flow channel when a flow channel is closed, but the solenoid valve 109 for liquid injection can be omitted as long as the complete closure of the flow channel is not required or can be achieved by the solenoid valve 109 for liquid injection formed of an expansion valve.

[0020] A discharge temperature sensor 102a configured to detect the temperature of the discharge gas discharged from the screw compressor 102 is provided on the discharge side of the screw compressor 102. The discharge temperature sensor 102a is provided to, for example, a compressor discharge portion or a discharge pipe. A discharge temperature detected by the discharge temperature sensor 102a is output to a controller 101 described later.

[0021] The refrigeration cycle apparatus 100 further includes the controller 101. The controller 101 controls the expansion valve 104 for main flow liquid, the expansion valve 107 for liquid injection, the solenoid valve 109 for liquid injection, and other components. The controller 101 can be formed of hardware including a circuit device configured to achieve functions thereof, and can also be formed of a combination of an arithmetic unit, for example, a microcomputer or a CPU, and software to be executed thereon.

(Screw Compressor)

[0022] Fig. 2 is a schematic sectional view of the screw compressor 102 included in the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention. Fig. 3 is a schematic sectional view taken along the line A-A of Fig. 2. With reference to Fig. 2 and Fig. 3, the screw compressor 102 is described below.

[0023] As illustrated in Fig. 2, the screw compressor 102 includes a casing 1, a screw rotor 3, a gate rotor 6, an electric motor 2 configured to rotationally drive the screw rotor 3, and a slide valve 8. The casing 1 having a cylindrical shape accommodates the screw rotor 3, the gate rotor 6, the electric motor 2, the slide valve 8, and other components inside a cylinder.

[0024] The electric motor 2 includes a stator 2a fixed to be brought into contact with an inner surface of the casing 1 and a motor rotor 2b arranged inside the stator 2a. The electric motor 2 may be a constant speed device having a constant driving frequency, or may be of an inverter type that is driven to have the capacity adjustable by the change of the driving frequency.

[0025] The screw rotor 3 and the motor rotor 2b are each arranged around a screw shaft 4 serving as a rotary shaft to be fixed to the screw shaft 4. The screw rotor 3 has a plurality of helical screw grooves 5a formed on its outer peripheral surface. The screw rotor 3 is rotated in accordance with the rotation of the motor rotor 2b fixed to the screw shaft 4.

[0026] Further, the screw compressor 102 in Embodiment 1 includes two gate rotors 6. The two gate rotors 6 are respectively arranged on two sides of the screw rotor 3 at positions that are point-symmetrical with respect to the screw shaft 4. The gate rotor 6 has a disc-like shape, and has a plurality of teeth 6a provided on its outer peripheral surface along its circumferential direction. The teeth 6a of the gate rotor 6 are engaged with the screw grooves 5a. A space enclosed by the teeth 6a of the gate rotor 6, the screw grooves 5a, and the inner surface side of the cylinder of the casing 1 defines a compression chamber 5. A plurality of compression chambers 5 are formed at positions that are point-symmetrical with respect to the center in the radial direction of the screw rotor 3.

[0027] In this case, the inside of the screw compressor 102 is divided into a low-pressure side for sucking refrigerant and a high-pressure side for discharging refrigerant by a partition wall (not shown). A space on the low-pressure side is defined as a low-pressure chamber A1 under a suction pressure atmosphere. Meanwhile, a space on the high-pressure side is defined as a high-pressure chamber A2 under a discharge pressure atmosphere. In the casing 1, a discharge port 7 (see Figs. 4 referred to in the later description) for communication between the high-pressure chamber A2 and the compression chamber 5 is provided at a position on the high-pressure side of the compression chamber 5.

[0028] In addition, a slide groove 1a extending in the axial direction of the screw shaft 4 of the screw rotor 3 is formed inside the casing 1. Then, the slide valve 8 is received inside the slide groove 1a to be free to move slidably along the slide groove 1a. The slide valve 8, as well as the casing 1, forms the compression chamber 5 integrally with the casing 1.

[0029] The slide valve 8 is a mechanical capacity control mechanism configured to adjust the size of a bypass port between the compression chamber 5 and the low-pressure chamber A1 by the movement in the axial direction of the screw shaft. The adjustment of the size of the bypass port causes a change in flow rate of the refrigerant flowing from the compression chamber 5 to the low-pressure chamber A1 through the bypass port. As a result, the flow rate of the refrigerant compressed and discharged from the compression chamber 5 changes, and the flow rate of the refrigerant discharged from the screw compressor 102, namely, the operation capacity of the screw compressor 102, changes.

[0030] The slide valve 8 is described above as being a mechanical capacity control mechanism, but may be an internal volume ratio variable mechanism configured to adjust the timing of discharge from the compression chamber 5 to make the internal volume ratio variable. In this case, the internal volume ratio represents a ratio between the volume of the compression chamber 5 exhibited at the time of the completion of suction (start of compression) and the volume of the compression chamber 5 exhibited immediately before discharge.

[0031] The slide valve 8 is connected to a bypass drive device 10, for example, a piston, via a connecting rod 9. The driving of the bypass drive device 10 causes the slide valve 8 to move inside the slide groove 1a in the axial direction of the screw shaft of the screw rotor 3.

[0032] The screw compressor 102 performs a capacity control operation for controlling the position of the slide valve 8 to adjust the discharge amount of the refrigerant to be discharged from the discharge port 7 included in the compression chamber 5. The capacity control operation is performed when the controller 101 sends an instruction to position the slide valve 8 to adjust the discharge amount of the refrigerant to the bypass drive device 10. In this case, there is no limitation imposed on the bypass drive device 10 configured to drive the slide valve 8 in terms of a motive power source for the driving, and the motive power source may include one that drives the slide valve 8 by gas pressure, one that drives the slide valve 8 by hydraulic pressure, and one that drives the slide valve 8 by a motor or another mechanism instead of the piston.

[0033] As illustrated in Fig. 3, the casing 1 further includes a liquid injection flow channel 1b formed of a through hole. A liquid injection port 1c, which is an opening of the liquid injection flow channel 1b on the screw rotor 3 side, communicates to the compression chamber 5. The liquid injection pipe 108 is connected to a connection port 1d, which is an opening of the liquid injection flow channel 1b on the other side of the screw rotor 3. With such a configuration, the refrigerant flowing out of the condenser 103 and branching off from the refrigerant circuit passes through the liquid injection pipe 108, the solenoid valve 109 for liquid injection, and the expansion valve 107 for liquid injection, and then flows into the liquid injection flow channel 1b to be injected into the compression chamber 5 through the liquid injection port 1c.

(Description of Operation of Refrigerant Circuit)

[0034] Next, an operation of the refrigeration cycle apparatus 100 according to Embodiment 1 is described with reference to Fig. 1 to Fig. 3.

[0035] The screw compressor 102 sucks and compresses refrigerant gas, which is gaseous refrigerant, and then discharges the refrigerant gas. The discharge gas discharged from the screw compressor 102 is cooled by the condenser 103. The refrigerant cooled by the condenser 103 is branched off into two flows of refrigerant after the passage through the condenser 103, and of the two flows of refrigerant, the main flow refrigerant is decompressed to be expanded by the expansion valve 104 for main flow liquid. Then, the refrigerant flowing out of the expansion valve 104 for main flow liquid is heated by the evaporator 105 to become the refrigerant gas. The refrigerant gas flowing out of the evaporator 105 is sucked by the screw compressor 102.

[0036] Meanwhile, refrigerant liquid in the other one of two flows of refrigerant obtained by the branching after the passage through the condenser 103 is decompressed by the expansion valve 107 for liquid injection provided to the liquid injection pipe 108 when the solenoid valve 109 for liquid injection is open, and then flows into the liquid injection flow channel 1b provided to the casing 1. Then, a differential pressure between the pressure of the refrigerant liquid flowing into the liquid injection flow channel 1b and the pressure inside the compression chamber 5 is used to inject the refrigerant liquid from the liquid injection port 1c into the compression chamber 5. The injected refrigerant liquid is mixed with the refrigerant gas being compressed, and is discharged from the screw compressor 102.

(Description of Operation of Screw Compressor 102)

[0037] Figs. 4 are diagrams for illustrating a basic idea of compression to be performed by the screw compressor 102 included in the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention. Next, the operation of the refrigeration cycle apparatus 100 according to Embodiment 1 is described. For example, when the screw rotor 3 is rotated by the electric motor 2 illustrated in Fig. 2 via the screw shaft 4 illustrated in Fig. 2, the teeth 6a of the gate rotor 6 relatively move inside the screw grooves 5a forming the compression chamber 5 as illustrated in Figs. 4. At this time, a suction process, a compression process, and a discharge process are successively performed inside the compression chamber 5. The suction process, the compression process, and the discharge process are set as one cycle, and the cycle is repeated. In this case, each process is described by focusing on the compression chamber 5 hatched by dots in Figs. 4.

[0038] Fig. 4(a) is an illustration of a state of the compression chamber 5 during the suction process. The screw rotor 3 is driven by the electric motor 2 to be rotated in a direction indicated by the solid arrow. When the screw rotor 3 is rotated, as illustrated in Fig. 4(b), the volume of the compression chamber 5 is reduced.

[0039] Subsequently, when the screw rotor 3 is further rotated, as illustrated in Fig. 4(c), the compression chamber 5 communicates to the outside via the discharge port 7. This causes the high-pressure refrigerant gas compressed inside the compression chamber 5 to be discharged from the discharge port 7 to the outside. Then, similar compression is performed again on the back side of the screw rotor 3.

[0040] In Figs. 4, illustrations of the liquid injection port 1c, the slide valve 8, and the slide groove 1a are omitted. In the compression process, the refrigerant liquid flows into the compression chamber 5 via the liquid injection port 1c. Then, the refrigerant liquid flowing into the compression chamber 5 is compressed together with the refrigerant gas, and discharged to the outside in the discharge process.

[0041] Next, a description is given of discharge-temperature control of the screw compressor 102 to be performed at the time of a normal operation by the refrigeration cycle apparatus 100.

(Normal Operation)

[0042] In the screw compressor 102, in order to prevent deterioration of refrigerant and oil and seizure due to reduction in gap between the screw rotor 3 and the casing 1, the solenoid valve 109 for liquid injection is set open, to thereby inject the refrigerant liquid into the compression chamber 5. However, when the injection amount of the refrigerant liquid is large, the screw rotor 3 is cooled so much as to be thermally reduced, and the gap between the screw rotor 3 and the casing 1 is increased more than required. In this case, a leak of the refrigerant gas increases to degrade the performance. In addition, extra operating power (electrical input) is required.

[0043] In view of this, in the normal operation, a target value of the discharge temperature is set high, to thereby suppress the injection amount of the refrigerant liquid to the necessary minimum. Specifically, high-discharge-temperature control for controlling the expansion valve 107 for liquid injection so that the discharge temperature of the refrigerant discharged from the screw compressor 102 becomes a first target discharge temperature set as high as, for example, about 90 degrees Celsius is performed.

[0044] Then, the high-discharge-temperature control is performed at the time of the normal operation, to thereby prevent an abnormal rise in temperature and an abnormal drop in temperature. It is also possible to control the injection amount based on a condensing temperature (discharge pressure) by using an electronic expansion valve as the expansion valve 107 for liquid injection. Therefore, the expansion valve 107 for liquid injection is controlled to increase the injection amount as the condensing temperature (discharge pressure) increases, to thereby be able to control the discharge temperature at the first target discharge temperature irrespective of the condensing temperature (discharge pressure). With this, when the discharge temperature is controlled at the first target discharge temperature, the expansion valve 107 for liquid injection can be controlled to adjust the injection amount of the refrigerant liquid to the necessary minimum, and hence it is possible to improve the performance while ensuring the reliability.

[0045] Fig. 5 is a conceptual diagram of the backflow of the discharge gas and the thermal expansion of the screw rotor 3 caused when the screw compressor 102 is stopped. Fig. 6 is an explanatory diagram of the expansion of the screw rotor caused when the discharge gas flows backward.

[0046] When the screw compressor 102 is stopped, as indicated by the dotted arrow in Fig. 5, the refrigerant gas flows backward from the high-pressure chamber A2 toward the low-pressure chamber A1 through the screw groove 5a of the screw rotor 3. In this case, as described above, in the normal operation, the first target discharge temperature is set high in order to avoid degradation in performance due to a leak of the refrigerant gas increased when the gap between the screw rotor 3 and the casing 1 is increased more than required. Therefore, the discharge temperature is higher than the temperatures of the screw rotor 3 and the casing 1. In this manner, the high-temperature discharge gas flows backward to pass through the screw groove 5a of the screw rotor 3, and hence there is a fear that the screw rotor 3 may have the temperature increased and thermally expand as indicated by the dotted line in Fig. 6 to be brought into contact with the casing 1.

[0047] In view of this, Embodiment 1 has a feature that the operation of the screw compressor 102 is stopped after stop control for lowering the discharge temperature by performing the liquid injection into the compression chamber 5 is performed in order to suppress the contact between the screw rotor 3 and the casing 1 due to the thermal expansion of the screw rotor 3. Now, the stop control is described in detail. In Embodiment 1, a description is given of the stop control to be performed when the electronic expansion valve is used as the expansion valve 107 for liquid injection, which serves as an expansion mechanism configured to control the discharge temperature, as described above.

(Stop Control)

[0048] Next, the stop control to be performed at the time of stopping the operation is described.

[0049] Fig. 7 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention.

[0050] Before the operation is stopped, namely, during the normal operation, the high-discharge-temperature control with the first target discharge temperature being set high is performed as described above (Step S1). When a stop instruction to stop the operation of the screw compressor 102 is issued (Step S2), control for lowering the discharge temperature is first carried out. Specifically, the control for lowering the discharge temperature refers to control for increasing the expansion opening degree of the expansion valve 107 for liquid injection to increase the liquid injection amount (Step S3) and lowering the discharge temperature to a second target discharge temperature. The second target discharge temperature is set to a temperature lower than the first target discharge temperature by, for example, about 15 degrees Celsius.

[0051] After the discharge temperature detected by the discharge temperature sensor 102a reaches the second target discharge temperature, stop preparation control to be performed before the electric motor 2 is stopped is performed (Step S4). When the electric motor 2 is a constant speed device, the stop preparation control is performed in the following manner. That is, the controller 101 carries out control for moving the slide valve 8 in the axial direction and widening the opening area of the bypass port between the compression chamber 5 and the low-pressure chamber A1. The stop preparation control of this kind involving the slide valve 8 is control generally performed at the time of stopping the operation to reduce a differential pressure between the high-pressure chamber A2 and the low-pressure chamber A1. Through reduction of the differential pressure between the high-pressure chamber A2 and the low-pressure chamber A1, it is possible to reduce the backflow of the discharge gas and the reverse rotation of the screw rotor 3 at the time of the operation stop to as low a level as possible. After the above-mentioned stop preparation control is carried out, the controller 101 stops the operation of the screw compressor 102, namely, the driving of the electric motor 2 (Step S5).

[0052] Incidentally, even after the driving of the electric motor 2 is stopped, the backflow of the refrigerant gas from the high-pressure chamber A2 to the low-pressure chamber A1 at the time of the stop preparation control is continued until the high-pressure chamber A2 and the low-pressure chamber A1 are brought to a balanced state to have the same pressure. Therefore, even after the driving of the electric motor 2 is stopped, the reverse rotation of the screw rotor 3 is continued by a rotational force due to the backflow of the refrigerant gas for a fixed time period.

[0053] Assuming that the backflow of the refrigerant gas and the reverse rotation of the screw rotor 3 are continued in this manner, even after the driving of the electric motor 2 is stopped, the controller 101 maintains the expansion valve 107 for liquid injection under an open state, and continues the liquid injection of the refrigerant liquid for a fixed time period (Step S6). However, when the duration for performing the liquid injection after the electric motor 2 is stopped is made longer than required, the refrigerant liquid stays inside the compression chamber 5, to thereby cause the next activation with liquid being compressed. For this reason, the duration for the injection is set properly. After the duration of the liquid injection has ended, the controller 101 closes the expansion valve 107 for liquid injection (Step S7).

[0054] Fig. 8 is a conceptual diagram of the backflow of the discharge gas and the thermal expansion of the screw rotor 3 caused when the refrigeration cycle apparatus 100 according to Embodiment 1 of the present invention is stopped.

[0055] In the stop control in Embodiment 1, when the stop instruction to stop the operation of the screw compressor 102 is issued, the expansion opening degree of the expansion valve 107 for liquid injection is increased as described above to lower the discharge temperature to the second target discharge temperature. In short, the discharge temperature is lowered before the operation of the electric motor 2 is stopped. Therefore, the refrigerant gas flowing from the high-pressure chamber A2 to the low-pressure chamber A1 at the time of the operation stop exhibits a low discharge temperature. As a result, as indicated by the dotted line in Fig. 8, the thermal expansion of the screw rotor 3 is suppressed to a level lower than in the related art illustrated in Fig. 6. This enables suppression of the thermal expansion of the screw rotor 3 due to the discharge gas flowing backward through the screw groove 5a, and it is consequently possible to avoid the contact due to the reduction in gap between the screw rotor 3 and the casing 1.

[0056] As described above, with the refrigeration cycle apparatus 100 according to Embodiment 1, when the operation of the screw compressor 102 is to be stopped, the expansion opening degree of the expansion valve 107 for liquid injection is first increased to increase the liquid injection amount, the discharge temperature is lowered to the second target discharge temperature, and then the electric motor 2 is stopped. This enables the suppression of the thermal expansion of the screw rotor 3 due to the discharge gas flowing backward through the screw groove 5a. As a result, it is possible to avoid the contact due to the reduction in gap between the screw rotor 3 and the casing 1, to thereby ensure high reliability.

[0057] Further, at the time of the normal operation, in the same manner as in the related art, the discharge temperature is controlled at a target discharge temperature by the liquid injection, and hence it is possible to prevent the abnormal rise in discharge temperature or degree of discharge superheat, to thereby prevent the deterioration of refrigerant and oil. Further, in the normal operation, the first discharge target temperature is set high, and the liquid injection amount of the refrigerant liquid is suppressed to the necessary minimum. Therefore, it is possible to suppress compression of liquid at the time of an abnormally low temperature, an increase in extra operating power (electrical input), or degradation in performance due to an increased leak of the refrigerant gas ascribable to the thermal reduction of the screw rotor 3.

Embodiment 2

[0058] A refrigeration cycle apparatus 100 according to Embodiment 2 has the same essence of control itself as that of Embodiment 1, but a device configuration of the refrigeration cycle apparatus 100 for achieving the control is different from that of Embodiment 1. Specifically, the configuration of an adjustment device is different.

[0059] Fig. 9 is a diagram for illustrating a configuration of the refrigeration cycle apparatus 100 according to Embodiment 2 of the present invention. In this following, parts different from those of the refrigeration cycle apparatus 100 according to Embodiment 1 are described.

[0060] In the configuration of Embodiment 1 described above, the adjustment device 106 provided to the liquid injection pipe 108 and configured to adjust the liquid injection amount includes the expansion valve 107 for liquid injection formed of an electronic expansion valve. In contrast, an adjustment device 106A in Embodiment 2 is formed of a parallel circuit obtained by connecting two series circuits in parallel. In the two series circuits, expansion valves 107a and 107b for liquid injection and solenoid valves 109a and 109b for liquid injection, which serve as valves configured to open or close flow channels, are connected in series, respectively. In the following description, the expansion valve 107a for liquid injection is referred to as "first expansion valve 107a for liquid injection", and the expansion valve 107b for liquid injection is referred to as "second expansion valve 107b for liquid injection". Further, the solenoid valve 109a for liquid injection is referred to as "first solenoid valve 109a for liquid injection", and the solenoid valve 109b for liquid injection is referred to as "second solenoid valve 109b for liquid injection".

[0061] In Embodiment 1 described above, the electronic expansion valve capable of freely controlling the opening degree of a valve is used as the expansion valve 107 for liquid injection. Meanwhile, in Embodiment 2, a temperature-type expansion valve with a temperature sensitive cylinder, which is configured to mechanically adjust the opening degree of a valve by the expansion valve itself, is used as each of the first expansion valve 107a for liquid injection and the second expansion valve 107b for liquid injection. The temperature sensitive cylinder of each of the first expansion valve 107a for liquid injection and the second expansion valve 107b for liquid injection is arranged on the discharge side of the screw compressor 102 (not shown). Each of the first expansion valve 107a for liquid injection and the second expansion valve 107b for liquid injection adjusts the expansion amount based on the discharge temperature detected by the temperature sensitive cylinder and an inner pressure, and controls the degree of superheat on the discharge side of the screw compressor 102 at a constant degree, namely, a set degree of discharge superheat set for each.

[0062] The set degree of discharge superheat to be controlled by each of the first expansion valve 107a for liquid injection and the second expansion valve 107b for liquid injection is set to a degree of superheat different from each other. The set degree of discharge superheat of the first expansion valve 107a for liquid injection is set to, for example, 25 degrees Celsius. The set degree of discharge superheat of the second expansion valve 107b for liquid injection is set to, for example, 10 degrees Celsius. As described later in detail, the first expansion valve 107a for liquid injection functions at the time of the normal operation, and the second expansion valve 107b for liquid injection functions at the time of the operation stop. The set degree of discharge superheat of the second expansion valve 107b for liquid injection, which functions at the operation stop time, is set lower than the set degree of discharge superheat at the time of the normal operation, to thereby lower, at the operation stop time, the discharge temperature to a temperature lower than the target discharge temperature at the time of the normal operation.

[0063] Now, the stop control to be performed by the refrigeration cycle apparatus 100 according to Embodiment 2 is described. The stop control in Embodiment 2 has the same essence of control itself as that of Embodiment 1. In short, the high-discharge-temperature control is performed at the time of the normal operation, and the discharge temperature is first lowered when the operation of the screw compressor 102 is stopped, which is the same as in Embodiment 1. A control method to be performed by the adjustment device 106A when the above-mentioned control is performed is different from that of Embodiment 1. The following description is mainly given of the operation of the adjustment device 106A to be performed in the stop control.

(Stop Control)

[0064] Fig. 10 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 2 of the present invention. In Fig. 10, the same processing steps as those of Fig. 7 are denoted by the same step numbers.

[0065] The stop control in Embodiment 2 at the time of stopping the operation is described with reference to Fig. 10. Before the operation is stopped, namely, during the normal operation, the controller 101 opens the first solenoid valve 109a for liquid injection and closes the second solenoid valve 109b for liquid injection so that the refrigerant liquid flows through the first expansion valve 107a for liquid injection and does not flow through the second expansion valve 107b for liquid injection. This causes the first expansion valve 107a for liquid injection to function (Step S1a), and the degree of discharge superheat is controlled at, for example, 25 degrees Celsius being the set degree of discharge superheat of the first expansion valve 107a for liquid injection.

[0066] Subsequently, when the stop instruction to stop the operation of the screw compressor 102 is issued (Step S2), the controller 101 first opens the second solenoid valve 109b for liquid injection and closes the first solenoid valve 109a for liquid injection. This causes the second expansion valve 107b for liquid injection to function (Step S3a), and the degree of discharge superheat is controlled at a degree lower than at the time of the normal operation, for example, 10 degrees Celsius as described above. In this manner, at the operation stop time, the set degree of discharge superheat is set lower than at the time of the normal operation, to thereby be able to lower the discharge temperature due to an increased liquid injection amount.

[0067] After that, the degree of discharge superheat reaches 10 degrees Celsius being the set degree of discharge superheat exhibited when the stop instruction is issued, and then the stop preparation control to be performed before the electric motor 2 is stopped is performed (Step S4). The stop preparation control is the same as that of Embodiment 1. The control to be subsequently performed in Step S4 to Step S6 is the same as that of Embodiment 1.

[0068] After the duration of the liquid injection has ended, the controller 101 closes the second solenoid valve 109b for liquid injection (Step S7a).

[0069] As described above, with the refrigeration cycle apparatus 100 according to Embodiment 2, while the same effects as those of Embodiment 1 are produced, the temperature-type expansion valve with a temperature sensitive cylinder is used for the adjustment device 106A, and hence the following effect is obtained. That is, it is possible to automatically adjust the degree of discharge superheat only by providing the temperature-type expansion valve with a temperature sensitive cylinder to detect the pressure and the temperature without requiring complicated control.

Embodiment 3

[0070] In Embodiment 1 described above, the operation of the screw compressor 102 to be performed at the time of stopping the operation is described, but the operation relates to the operation to be performed at the time of so-called normal operation stop. In Embodiment 3, an operation to be performed at the time of sudden stop, which is different from the operation to be performed at the time of normal operation stop, is described.

[0071] Fig. 11 is a diagram for illustrating a configuration of a refrigeration cycle apparatus 100 according to Embodiment 3 of the present invention.

[0072] The refrigeration cycle apparatus 100 according to Embodiment 3 includes a protection circuit 110 provided in parallel with the adjustment device 106 provided to the liquid injection pipe 108 in Embodiment 1. The other components are the same as those of Embodiment 1 illustrated in Fig. 1.

[0073] The protection circuit 110 is a circuit obtained by connecting a capillary 107c for liquid injection and a solenoid valve 109c for a capillary, which serves as a valve for a capillary, in series. The capillary 107c for liquid injection is capable of adjusting the liquid injection amount by having the refrigerant liquid passing therethrough without performing electric control, and is adjusted in advance so that the liquid injection amount becomes a predetermined amount.

[0074] The operation stop described above in Embodiments 1 and 2 is normal operation stop, but when, for example, high pressure excessively rises or low pressure excessively drops in the refrigerant circuit, protective control may be actuated to subject the screw compressor 102 to abnormal stop. At the time of such abnormal stop, when the above-mentioned stop control is performed, that is, when the control for lowering the discharge temperature to the second target discharge temperature and the subsequent stop preparation control are performed, the stop of the screw compressor 102 may be delayed. This is because it takes much time to increase the opening degree of the expansion valve 107 for liquid injection even though the opening degree of the expansion valve 107 for liquid injection is increased and the liquid injection amount is increased after the issuance of the instruction to subject the compressor to sudden stop.

[0075] When the stop of the screw compressor 102 is delayed in this manner, the screw compressor 102 cannot be protected, which leads to a failure. Therefore, in order to perform abnormal stop, it is required to stop carrying out the stop preparation control and to subject the operation of the screw compressor 102 to sudden stop. However, the thermal expansion of the screw rotor 3 is inevitable when the operation of the screw compressor 102 is subjected to sudden stop without carrying out the stop preparation control.

[0076] In view of this, in Embodiment 3, at the time of sudden stop, the solenoid valve 109c for a capillary is opened to actuate the protection circuit 110 without adjusting the liquid injection amount by the adjustment device 106. In short, at the time of sudden stop, by causing the refrigerant liquid to flow not into the adjustment device 106 but into the protection circuit 110 and causing the refrigerant liquid to flow into the capillary 107c for liquid injection of the protection circuit 110, a fixed amount of liquid is instantaneously injected into the compression chamber 5 even at the time of sudden stop by the abnormal-stop control. In this case, the fixed amount refers to an amount larger than at the time of the normal operation for performing the high-discharge-temperature control, and the thermal expansion can be suppressed by the fixed amount of liquid.

[0077] Now that a basic idea of the control to be performed at the time of sudden stop by the screw compressor 102 in Embodiment 3 has been made clear, a description is given of control to be performed at the time of sudden stop by the adjustment device 106 and the protection circuit 110.

(Protective Control at Time of Sudden Stop)

[0078] Fig. 12 is a diagram for illustrating a stop control flow of the refrigeration cycle apparatus 100 according to Embodiment 3 of the present invention.

[0079] Before the operation stop control, namely, during the normal operation, the high-discharge-temperature control with the first target discharge temperature being set high is performed similarly to Embodiment 1 (Step S1). When the protective control of the screw compressor 102 is actuated with an issuance of a sudden stop instruction (Step S2b), the controller 101 performs the following control. That is, the controller 101 closes the solenoid valve 109 for liquid injection and opens the solenoid valve 109c for a capillary of the protection circuit 110, to thereby increase the liquid injection amount to a degree larger than at the time of the normal operation (Step S3b). That is, by opening the solenoid valve 109c for a capillary, it is possible to cause the refrigerant liquid to flow into the capillary 107c for liquid injection, and to instantaneously inject a fixed amount of refrigerant liquid into the compression chamber 5. As a result, it is possible to instantaneously lower the discharge temperature to a temperature lower than the first target discharge temperature. In this case, instead of closing the solenoid valve 109 for liquid injection at the time of sudden stop as described above, the refrigerant liquid may be caused to flow into both the solenoid valve 109c for a capillary of the protection circuit 110 and the solenoid valve 109 for liquid injection by leaving the solenoid valve 109 for liquid injection under an open state.

[0080] Then, the controller 101 stops the operation of the screw compressor 102, namely, the driving of the electric motor 2 (Step S5). After the liquid injection of the refrigerant liquid is continued for a fixed time period (Step S6), the solenoid valve 109c for a capillary is closed (Step S7b).

[0081] As described above, according to Embodiment 3, while the same effects as those of Embodiment 1 are produced, the protection circuit 110 is provided to the adjustment device 106, and hence it is possible to instantaneously lower the discharge temperature to a temperature lower than the first target discharge temperature by causing the refrigerant liquid to flow toward the protection circuit 110 side at the time of sudden stop. As a result, even when the operation of the screw compressor 102 is subjected to the sudden stop, it is possible to suppress the thermal expansion of the screw rotor 3.

[0082] The operation to be performed at the time of sudden stop has been described above, but it is to be understood that the refrigeration cycle apparatus 100 according to Embodiment 3 performs the same operation for the time of stopping the operation as that of Embodiment 1 described above.

[0083] The following modification may be made to the refrigeration cycle apparatus 100 according to Embodiment 3.

(Modification Example of Embodiment 3)

[0084] The configuration of Embodiment 3 described with reference to Fig. 11 is obtained by providing the protection circuit 110 in parallel with the adjustment device 106 in Embodiment 1 illustrated in Fig. 1. A modification example of Embodiment 3 has a configuration obtained by providing the protection circuit 110 to the adjustment device 106A in Embodiment 2 illustrated in Fig. 9. This configuration can also produce the same effects as those of Embodiment 2 and Embodiment 3 described above.

Embodiment 4

[0085] Fig. 13 is a diagram for illustrating a configuration of the refrigeration cycle apparatus 100 including a refrigeration cycle apparatus 100 according to Embodiment 4 of the present invention.

[0086] The refrigeration cycle apparatus 100 according to Embodiment 4 further includes an intermediate cooler 111 in the refrigeration cycle apparatus 100 according to Embodiment 1.

[0087] The intermediate cooler 111 performs heat exchange between the refrigerant flowing out of the condenser 103 and flowing into a high-pressure-side flow channel of the intermediate cooler 111 and the refrigerant flowing into a low-pressure-side flow channel of the intermediate cooler 111. The refrigerant flowing into the low-pressure-side flow channel of the intermediate cooler 111 is refrigerant obtained by causing a part of the refrigerant that has passed through the intermediate cooler 111 to pass through the solenoid valve 109 for liquid injection to be decompressed by the expansion valve 107 for liquid injection. The refrigerant flowing into the high-pressure-side flow channel of the intermediate cooler 111 is subjected to subcooling by the heat exchange with the refrigerant flowing into the low-pressure-side flow channel. Meanwhile, the refrigerant flowing into the low-pressure-side flow channel of the intermediate cooler 111 exchanges heat with the refrigerant flowing into the high-pressure-side flow channel, and is then injected into the screw compressor 102. Other structures, other configurations, and the control of the expansion valve 107 for liquid injection and the solenoid valve 109 for liquid injection are the same as those of Embodiment 1.

[0088] In Embodiment 4, the expansion valve 107 for liquid injection and the solenoid valve 109 for liquid injection may be controlled in the same manner as in Embodiment 1 described above. That is, the following control may be performed: when the stop instruction to stop the operation of the screw compressor 102 is issued, the discharge temperature is lowered to the second target discharge temperature set in advance, which is lower than the first target discharge temperature, by increasing the expansion opening degree of the expansion valve 107 for liquid injection to increase the injection amount of the refrigerant liquid.

[0089] According to Embodiment 4, while the same effects as those of Embodiment 1 are produced, the refrigerant flowing from the condenser 103 toward the expansion valve 104 for main flow liquid is subjected to subcooling by the intermediate cooler 111, and hence it is possible to achieve an improvement in refrigeration efficiency.

[0090] The following modification may be made to the refrigeration cycle apparatus 100 according to Embodiment 4. Also in this case, the same operations and effects can be produced.

(Modification Example of Embodiment 4)

[0091] Fig. 14 is a diagram for illustrating a configuration of the refrigeration cycle apparatus 100 including a refrigeration cycle apparatus 100 according to a modification example of Embodiment 4 of the present invention.

[0092] In Fig. 13, the configuration obtained by providing the intermediate cooler 111 to Embodiment 1 illustrated in Fig. 1 is illustrated. As illustrated in Fig. 14, the modification example of Embodiment 4 has a configuration obtained by providing the intermediate cooler 111 to the refrigeration cycle apparatus 100 according to Embodiment 3 illustrated in Fig. 11. This configuration can produce the effects of both of Embodiment 3 and Embodiment 4.

[0093] Embodiment 1 to Embodiment 4 described above are described by taking an example of applying the present invention to a screw compressor configured to perform capacity control by the slide valve 8 through use of the constant-speed electric motor 2, but a screw compressor to which the present invention is applied is not limited thereto. In addition, the present invention may be applied to, for example, a screw compressor configured to perform the capacity control not by the slide valve 8 but by controlling the rotation speed through use of the electric motor 2 of an inverter type with the rotation speed of the screw rotor 3 being set variable.

[0094] As described above, at the time of stopping the operation by the screw compressor configured to perform the capacity control by the slide valve 8, the stop preparation control for moving the slide valve 8 to widen the opening area of the bypass port in order to reduce the differential pressure between the high-pressure chamber A2 and the low-pressure chamber A1 is performed. In contrast, in a case of a screw compressor of an inverter type, the rotation speed in operation may be lowered, to thereby reduce the differential pressure between the high-pressure chamber A2 and the low-pressure chamber A1 or perform, for example, control for opening the valve provided to a bypass passage through which the high-pressure chamber A2 or the compression chamber 5 communicates to the low-pressure chamber A1 instead of performing the stop preparation control involving the movement of the slide valve 8.

Reference Signs List

[0095] 1 casing 1a slide groove 1b liquid injection flow channel 1 c liquid injection port 1d connection port 2 electric motor 2a stator 2b motor rotor 3 screw rotor 4 screw shaft 5 compression chamber 5a screw groove 6 gate rotor 6a tooth 7 discharge port 8 slide valve 9 connecting rod 10 bypass drive device 100 refrigeration cycle apparatus 101 controller 102 screw compressor 102a discharge temperature sensor 103 condenser 104 expansion valve for main flow liquid 105 evaporator 106 adjustment device 106A adjustment device 107 expansion valve for liquid injection 107a first expansion valve for liquid injection 107b second expansion valve for liquid injection 107c capillary for liquid injection 108 liquid injection pipe 109 solenoid valve for liquid injection 109a first solenoid valve for liquid injection 109b second solenoid valve for liquid injection 109c solenoid valve for capillary 110 protection circuit 111 intermediate cooler A1 low-pressure chamber A2 high-pressure chamber

Claims

1. A refrigeration cycle apparatus, comprising:

a refrigerant circuit configured to circulate refrigerant therethrough, the refrigerant circuit including
a screw compressor,
a condenser,
a pressure reducing device, and
an evaporator;

a liquid injection pipe branching off from a pipe between the condenser and the pressure reducing device and being connected to a liquid injection port of the screw compressor;

an adjustment device provided to the liquid injection pipe and configured to adjust a liquid injection amount; and

a controller configured to control the adjustment device,

the controller being configured to
control the adjustment device so that a discharge temperature of refrigerant discharged from the screw compressor becomes a target discharge temperature during an operation of the screw compressor, and
control, when the operation of the screw compressor is to be stopped, the adjustment device to increase the liquid injection amount, and then stop the screw compressor.

2. The refrigeration cycle apparatus of claim 1, wherein the adjustment device comprises an electronic expansion valve.

3. The refrigeration cycle apparatus of claim 1,
wherein the adjustment device includes a parallel circuit including two series circuits connected in parallel, in each of which an expansion valve for liquid injection and a valve configured to open or close a flow channel are connected in series,
wherein each of the expansion valves for liquid injection is a temperature-type expansion valve configured to adjust a degree of discharge superheat on a discharge side of the screw compressor to a set degree of discharge superheat, which is set for the each of the expansion valves for liquid injection,
wherein the set degree of discharge superheat of the expansion valve for liquid injection of one of the two series circuits is set higher than the set degree of discharge superheat of the expansion valve for liquid injection of an other one of the two series circuits, and
wherein the controller is configured to
open the valve of the one of the two series circuits and close the valve of the other one of the two series circuits during the operation of the screw compressor, and
close the valve of the one of the two series circuits and open the valve of the other one of the two series circuits when the operation of the screw compressor is to be stopped.

4. The refrigeration cycle apparatus of any one of claims 1 to 3, further comprising a protection circuit, which includes a capillary and a valve for a capillary connected in series, wherein the protection circuit is provided in parallel with the adjustment device provided to the liquid injection pipe.

5. The refrigeration cycle apparatus of claim 4, wherein the controller is configured to actuate the protection circuit by opening the valve for a capillary, while avoiding adjusting the liquid injection amount by the adjustment device, at a time of sudden stop of the compressor different from the stopping of the operation of the screw compressor.

6. The refrigeration cycle apparatus of any one of claims 1 to 5, further comprising an intermediate cooler provided between the condenser and the pressure reducing device and configured to cool refrigerant flowing from the condenser toward the pressure reducing device by causing the refrigerant to exchange heat with refrigerant passing through the liquid injection pipe to be injected into the screw compressor.

Drawing