Screw compressor and refrigeration cycle device

Abstract

The purpose of the present invention is to acquire a screw compressor and a refrigeration cycle device that make it possible to suppress a reduction in intake / circulation amount caused by leakage of a refrigerant gas into a low-pressure space via a piston chamber. In the present invention, a slide valve movement mechanism of a screw compressor comprises: a hollow cylinder (17); a piston (19) that partitions a piston chamber (26) in the cylinder into a first chamber (26a) and a second chamber (26b) and that is connected to a slide valve; a first oil introduction pipe (31a) that introduces a high-pressure refrigerator oil into one chamber (26b) among the first chamber and the second chamber; and a pressure adjustment device (22) that adjusts the amount of refrigerator oil in the one chamber to adjust the pressure in the one chamber. The slide valve movement mechanism changes the internal volume ratio by using the pressure adjustment device to change the pressure in the one chamber, moving the piston, and controlling the position of the slide valve.

Description

Screw compressor and refrigeration cycle device

[0001] The present disclosure relates to a screw compressor and a refrigeration cycle device used for compressing refrigerant in, for example, a refrigerator or an air conditioner.

[0002] In a screw compressor, if the internal volume ratio, which is the ratio of the suction volume to the discharge volume, is fixed, compression loss increases due to over- or under-compression depending on the operating conditions. For this reason, screw compressors equipped with a slide valve that adjusts the internal volume ratio are known (see, for example, Patent Document 1). In this type of screw compressor, the slide valve is moved in the direction of the rotation axis of the screw rotor to change the discharge start position of high-pressure refrigerant gas from the compression chambers formed in the spiral grooves of the screw rotor, thereby changing the discharge volume and adjusting the internal volume ratio.

[0003] Patent Document 1 discloses a structure for moving a slide valve in which a piston connected to the slide valve is disposed in a piston chamber within a cylinder (see FIG. 4 of Patent Document 1). In this structure, the piston chamber is divided into a first chamber and a second chamber by the piston. The piston is moved by the pressure difference between the first chamber and the second chamber, thereby moving the slide valve. The first chamber and the second chamber each have a small-diameter inlet hole (not shown), through which high-pressure refrigerant gas flows into the first chamber and the second chamber. A communication passage is connected to the second chamber, allowing the refrigerant gas in the second chamber to flow out to a low-pressure space. By opening and closing a valve provided in the communication passage, the pressure in the second chamber is controlled to high or low, thereby moving the piston and, therefore, the slide valve.

[0004] JP 2013-036403 A

[0005] In Patent Document 1, when the slide valve is moved to one side in the rotational axis direction of the screw rotor, a valve provided in the communication flow path must be opened to connect the second chamber to the low-pressure space and reduce the pressure. In this way, in Patent Document 1, while the second chamber is connected to the low-pressure space, high-pressure refrigerant gas is constantly flowing into the second chamber. The high-pressure refrigerant gas that has flowed into the second chamber constantly leaks into the low-pressure space while the valve is open. Patent Document 1 had a problem in that when the high-pressure refrigerant gas leaks into the low-pressure space through the piston chamber, it expands and increases in volume, hindering the compressor from suctioning refrigerant and reducing the suction circulation rate.

[0006] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a screw compressor and a refrigeration cycle device that can suppress a decrease in the suction circulation rate caused by refrigerant gas leaking into a low-pressure space through a piston chamber.

[0007] a slide valve moving mechanism that moves the slide valve in the direction of the rotation axis; a hollow cylinder; a piston that divides a piston chamber in the cylinder into a first chamber and a second chamber and is connected to the slide valve; a first oil inlet pipe that introduces high-pressure refrigeration oil into one of the first and second chambers; and a pressure adjusting device that adjusts the pressure of the one chamber by adjusting the amount of refrigeration oil in the one chamber. The pressure adjusting device changes the pressure in the one chamber to move the piston and control the position of the slide valve, thereby changing the internal volume ratio.

[0008] A refrigeration cycle device according to the present disclosure includes the screw compressor described above, a condenser, a pressure reducing device, and an evaporator.

[0009] The screw compressor and refrigeration cycle device according to the present disclosure introduce refrigeration oil, which is an incompressible fluid, into the piston chamber of the screw compressor, thereby suppressing the decrease in the amount of refrigerant suctioned and circulated, which occurs in a configuration in which refrigerant gas is introduced into the piston chamber.

[0010] FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle device according to embodiment 1. FIG. 2 is a schematic cross-sectional view of the slide valve moving mechanism of the screw compressor according to embodiment 1 when the piston is moved toward the second chamber. FIG. 3 is a schematic cross-sectional view of the slide valve moving mechanism of the screw compressor according to embodiment 1 when the piston is moved toward the first chamber. FIG. 4 is an explanatory diagram showing the operation of a compression section of the screw compressor according to embodiment 1, illustrating the suction stroke. FIG. 5 is an explanatory diagram showing the operation of the compression section of the screw compressor according to embodiment 1, illustrating the compression stroke. FIG. 6 is an explanatory diagram showing the operation of the compression section of the screw compressor according to embodiment 1, illustrating the discharge stroke. FIG. 7 is an explanatory diagram showing the operation of the slide valve moving mechanism of the screw compressor according to embodiment 1. FIG. 8 is a diagram summarizing the operation of a pressure regulating device of the screw compressor according to embodiment 1. FIG. 9 is an explanatory diagram of the operation of the slide valve moving mechanism of a screw compressor of a comparative example. FIG. 10 is an explanatory diagram of the operation of the slide valve moving mechanism of the screw compressor according to embodiment 2. FIG. 11 is an explanatory diagram of the operation of the slide valve moving mechanism of the screw compressor according to embodiment 3. FIG. 12 is a diagram summarizing the operation of a pressure regulating device of the screw compressor according to embodiment 3. FIG. 13 is an explanatory diagram of the operation of the slide valve moving mechanism of the screw compressor according to embodiment 4. 1 is a diagram showing a first modified example of the pressure adjustment device for the screw compressor according to the first to fourth embodiments; FIG. 2 is a diagram showing a second modified example of the pressure adjustment device for the screw compressor according to the first to fourth embodiments; and FIG. 3 is a diagram showing modified examples of the screw compressor according to the first to fourth embodiments.

[0011] A refrigeration cycle apparatus according to an embodiment of the present disclosure will be described below with reference to the drawings. In the following drawings, including FIG. 1, identical reference numerals denote identical or equivalent components, and these are common throughout the embodiments described below. The configurations of components shown throughout the specification are merely examples and are not intended to be limiting. Furthermore, the level of pressure is not determined in relation to an absolute value, but is determined relatively based on the state and operation of the refrigeration cycle apparatus.

[0012] 1 is a refrigerant circuit diagram of a refrigeration cycle apparatus 50 according to embodiment 1. The refrigeration cycle apparatus 50 includes a screw compressor 51, an oil separator 52, a condenser 53, a pressure reducing device 54, and an evaporator 55.

[0013] The screw compressor 51 draws in a refrigerant and compresses it to a high-temperature, high-pressure state. The screw compressor 51 is a positive displacement compressor capable of varying its operating frequency. The screw compressor 51 includes a compression section 2 that compresses the refrigerant and a motor 4 that drives the compression section 2. The screw compressor 51 also includes a low-pressure communication passage 21 that connects one of a first chamber 26a and a second chamber 26b of a piston chamber 26 (described later), i.e., the second chamber 26b in the illustrated example, to a low-pressure space 28 (described later, see FIG. 2 ) within the screw compressor 51, and a pressure regulator 22 provided in the low-pressure communication passage 21. The pressure regulator 22 includes an expansion valve 22a and an on-off valve 22b, and regulates the pressure in the second chamber 26b of the piston chamber 26. Details of the screw compressor 51 will be described later.

[0014] The oil separator 52 is provided on the discharge side of the screw compressor 51 and separates refrigeration oil discharged together with the refrigerant from the screw compressor 51. The oil separator 52 is in communication with the interior of the screw compressor 51 via an oil return circuit 31. The oil return circuit 31 is composed of piping. The oil return circuit 31 includes a first oil inlet pipe 31a, an oil return pipe 31b, and a second oil inlet pipe 31c.

[0015] The oil return circuit 31 introduces the refrigeration oil separated in the oil separator 52 into the second chamber 26b of the piston chamber 26 via the first oil introduction pipe 31a. The oil return circuit 31 returns the refrigeration oil separated in the oil separator 52 to the compression chamber 29 via the oil return pipe 31b. By returning the refrigeration oil to the screw compressor 51, the refrigeration cycle device 50 prevents the screw compressor 51 from seizing due to a shortage of refrigeration oil in the screw compressor 51. The second oil introduction pipe 31c will be described later in embodiment 2.

[0016] The condenser 53 is a fin-tube heat exchanger including a pipe through which a refrigerant flows and fins into which the pipe is inserted. The condenser 53 is not limited to a fin-tube heat exchanger, and may be configured as a heat exchanger of other configurations, such as a plate-type heat exchanger. The pressure reducing device 54 expands the refrigerant. The pressure reducing device 54 is formed, for example, by an electronic expansion valve or a thermostatic expansion valve whose opening is adjustable, but may also be formed by a capillary tube whose opening is not adjustable. The evaporator 55 is a fin-tube heat exchanger including a pipe through which a refrigerant flows and fins into which the pipe is inserted. The evaporator 55 is not limited to a fin-tube heat exchanger, and may be configured as a heat exchanger of other configurations, such as a plate-type heat exchanger.

[0017] The configuration of the refrigerant circuit of the refrigeration cycle device 50 is not limited to the configuration shown in the figure, and may be configured to include a four-way valve, an internal heat exchanger, etc.

[0018] Fig. 2 is a schematic cross-sectional view of the slide valve moving mechanism 13 of the screw compressor 51 according to embodiment 1 when the piston 19 is moved toward the second chamber 26b. Fig. 3 is a schematic cross-sectional view of the slide valve moving mechanism 13 of the screw compressor 51 according to embodiment 1 when the piston 19 is moved toward the first chamber 26a.

[0019] The screw compressor 51 according to the first embodiment is a single-screw compressor that is provided in a refrigerant circuit that performs a refrigeration cycle and compresses a refrigerant. As shown in FIGS. 2 and 3 , the screw compressor 51 includes a casing 1a including a cylindrical casing body 1, a compression section 2 disposed within the casing body 1 and compressing the refrigerant, and a motor 4 that drives the compression section 2. The motor 4 includes a stator 4a fixed to the casing body 1 and inscribed within it, and a motor rotor 4b disposed inside the stator 4a. The rotation speed of the motor 4 is controlled by an inverter system. The screw rotor 3 and the motor rotor 4b are disposed coaxially and are both fixed to a screw shaft 5.

[0020] The compression section 2 includes a screw rotor 3 and a pair of gate rotors 6. The screw rotor 3 is cylindrical and has multiple spiral grooves 3a formed on its outer periphery. The screw rotor 3 is coupled to a motor rotor 4b fixed to a screw shaft 5 and is driven to rotate. One end of the screw rotor 3 is the refrigerant suction side in the rotational axis direction, which is the direction in which the screw shaft 5 extends, and the other end is the refrigerant discharge side. In Figures 2, 3, and the figures described below, X1 indicates the suction side and X2 indicates the discharge side. The screw shaft 5 is rotatably supported by a main bearing 11 and an auxiliary bearing (not shown). The main bearing 11 is disposed in a main bearing housing 12 provided at the end of the screw rotor 3 on the discharge side X2. The auxiliary bearing is provided at the end of the screw shaft 5 on the suction side X1 of the screw rotor 3.

[0021] The gate rotor 6 is configured in a disk shape with a plurality of gate rotor teeth 6a arranged radially. The gate rotor 6 has a plurality of gate rotor teeth 6a that mesh with and engage with grooves 3a formed in the cylindrical surface of the screw rotor 3, thereby forming a compression chamber 29 in a space surrounded by the gate rotor teeth 6a, the space within the grooves 3a, the inner cylindrical surface of the casing main body 1, and the slide valve 10.

[0022] A high-pressure space 27 and a low-pressure space 28 are formed within the casing body 1. The interior of the casing body 1 is separated into the high-pressure space 27 and the low-pressure space 28 by a partition wall (not shown). A discharge port 8 that opens to the discharge chamber 7 is formed on the high-pressure space 27 side. The high-pressure space 27 is filled with refrigerant gas at a high pressure, which is the discharge pressure, and is therefore high-pressure, while the low-pressure space 28 is filled with refrigerant gas at a low pressure, which is the suction pressure, and is therefore low-pressure. An outer casing member (not shown) is installed at the end of the casing body 1 opposite the motor 4. The outer casing member, together with the casing body 1, constitutes the casing 1a of the screw compressor 51. The high-pressure space 27 is formed within the outer casing member, and a slide valve movement mechanism 13 (described later) is housed within this outer casing member.

[0023] A slide groove 9 is formed on the inner wall surface of the casing body 1, and a slide valve 10 that is movable in the direction of the rotation axis of the screw rotor 3 is housed in the slide groove 9. The slide valve 10 forms part of the discharge port 8, and the timing at which the discharge port 8 opens, i.e., the timing at which the compression chamber 29 communicates with the discharge chamber 7, changes depending on the position of the slide valve 10. By changing the timing at which the discharge port 8 opens in this way, the internal volume ratio of the screw rotor 3 is adjusted. The internal volume ratio is the ratio between the volume of the compression chamber 29 at the end of suction and the volume of the compression chamber 29 at the start of discharge.

[0024] The slide valve 10 moves between the suction side X1 and the discharge side X2, and changes its stopping position to change the internal volume ratio. Specifically, as shown in FIG. 2 , the slide valve 10 is positioned on the discharge side X2, delaying the timing at which the discharge port 8 opens, thereby increasing the internal volume ratio. In FIG. 2 , the slide valve 10 is stopped in a position where the second chamber side end surface 19c of the piston 19 is seated on the cylinder lid 17b. Also, as shown in FIG. 3 , the slide valve 10 is positioned on the suction side X1, advancing the timing at which the discharge port 8 opens, thereby decreasing the internal volume ratio. In FIG. 3 , the slide valve 10 is stopped in a position where the suction side end 10g of the slide valve 10 is seated on the casing main body 1.

[0025] The slide valve 10 has a valve body 10a, a guide portion 10b, and a connecting portion 10c. A discharge port side end 10d on the opposite side of the suction side end 10g of the valve body 10a is connected to a discharge port side end 10e of the guide portion 10b by the connecting portion 10c, and forms a discharge flow path 10f communicating with the discharge port 8.

[0026] In the slide valve 10, suction pressure acts on the suction-side end 10g of the valve body 10a, and discharge pressure immediately after discharge acts on the discharge-side end 10d. Furthermore, a pressure equal to the pressure acting on the discharge-side end 10d acts on the discharge-side end 10e of the guide portion 10b in the opposite direction to the pressure acting on the discharge-side end 10d. Furthermore, discharge pressure acts on the discharge-side end 10h of the guide portion 10b. Therefore, the loads acting on the discharge-side end 10d and the discharge-side end 10e inside the slide valve 10 are canceled out. Therefore, focusing only on the pressure acting on the slide valve 10, a rightward load (load Fs, described below) acts on the slide valve 10 during operation, tending to move the slide valve 10 toward the suction side X1 due to the pressure difference between the pressures acting on the discharge-side end 10h and the suction-side end 10g.

[0027] A slide valve moving mechanism 13 that slides and moves the slide valve 10 in the direction of the rotation axis of the screw rotor 3 is disposed at the end of the screw rotor 3 opposite to the motor 4. The slide valve moving mechanism 13 includes a hollow cylinder 17 provided in the casing body 1, a piston 19, a connecting arm 15 connected to a piston rod 19d of the piston 19, a rod 14, and a spring 14a.

[0028] The cylinder 17 is a hollow member extending in the direction of the rotational axis of the screw rotor 3. The cylinder 17 includes a cylinder body 17a within which a piston 19 moves and a cylinder lid 17b that closes an opening on the discharge side X2 of the cylinder body 17a. The piston 19 is disposed within the cylinder 17 and divides the interior of the cylinder 17 into a first chamber 26a on the low-pressure space 28 side and a second chamber 26b on the high-pressure space 27 side. The first chamber 26a and the second chamber 26b are aligned in the direction of the rotational axis of the screw rotor 3, with the first chamber 26a located on the suction side X1 and the second chamber 26b located on the discharge side X2. The piston 19 moves in the direction of the rotational axis of the screw rotor 3 due to the pressure difference between the first chamber 26a and the second chamber 26b, and the slide valve 10 moves in conjunction with the movement of the piston 19.

[0029] A first inlet hole 24 is formed through the cylinder body 17a and communicates with the first chamber 26a. The first inlet hole 24 communicates with the high-pressure space 27. Therefore, high-pressure refrigerant gas always flows into the first chamber 26a, and the first chamber 26a is kept at a high pressure.

[0030] Further, a second inlet hole 20 and a third inlet hole 25 are formed through the cylinder body 17a and communicate with the second chamber 26b. The second inlet hole 20 is configured to communicate with the low-pressure space 28 via a low-pressure communication passage 21 (described later). The other inlet hole communicating with the second chamber 26b, the third inlet hole 25, communicates with the oil separator 52 (see FIG. 1) via a first oil introduction pipe 31a of the oil return circuit 31. Because the third inlet hole 25 communicates with the oil separator 52, high-pressure refrigeration oil constantly flows into the second chamber 26b.

[0031] A small gap is provided between the inner circumferential surface 18 of the cylinder body 17a and the outer circumferential surface 19a of the piston 19, allowing the piston 19 to move within the cylinder body 17a. A small gap is also provided between the inner circumferential surface 19b of a piston rod passage hole provided in the center of the cylinder lid 17b and the outer circumferential surface of the piston rod 19d, allowing the piston rod 19d to move through the piston rod passage hole. A seal may be provided to close these small gaps in order to prevent high-pressure refrigerant gas from flowing into the second chamber 26b from outside the second chamber 26b.

[0032] An outwardly extending flange portion 17a1 is formed on the outer peripheral surface of the suction side X1 of the cylinder body 17a. A through hole is formed in the flange portion 17a1 in the axial direction, and the rod 14 is movably passed through the through hole.

[0033] The rod 14 is a member that connects the slide valve 10 and the connecting arm 15, and the end of the rod 14 on the suction side X1 is fixed to the slide valve 10, and the end of the rod 14 on the discharge side X2 is fixed to the connecting arm 15 with a bolt and nut 16.

[0034] The spring 14a is a cylindrical coil spring and is arranged to surround the rod 14. The spring 14a is arranged to surround the portion of the rod 14 between the flange portion 17a1 and the connecting arm 15. The spring 14a is arranged between the flange portion 17a1 and the connecting arm 15 in a state where it is compressed from its natural length, and urges the connecting arm 15 in a direction away from the flange portion 17a1. In other words, the spring 14a urges the slide valve 10 toward the discharge side X2. The spring 14a is used to move the piston 19 toward the second chamber 26b as shown in FIG. 2 when the pressure inside the screw compressor 51 is atmospheric before operation starts.

[0035] The slide valve movement mechanism 13 further includes a low-pressure communication passage 21 and a pressure adjustment device 22. The low-pressure communication passage 21 is a passage that connects the second chamber 26b to the low-pressure space 28 and allows the refrigeration oil in the second chamber 26b to flow into the low-pressure space 28. As a specific configuration, the low-pressure communication passage 21 may be configured, for example, by drilling holes in the casing body 1 and the cylinder 17, or may be configured by piping arranged outside the casing body 1.

[0036] The pressure regulating device 22 regulates the pressure of the second chamber 26b by adjusting the amount of refrigeration oil in the second chamber 26b. Specifically, the pressure regulating device 22 regulates the pressure of the second chamber 26b of the piston chamber 26 by adjusting the flow rate of refrigeration oil flowing from the second chamber 26b to the low-pressure space 28 via the low-pressure communicating flow path 21. The pressure regulating device 22 has an expansion valve 22a whose opening degree can be adjusted, and an on-off valve 22b that opens and closes the flow path. Because the expansion valve 22a cannot fully close the flow path due to its structure, the pressure regulating device 22 regulates the flow rate of the low-pressure communicating flow path 21 using the expansion valve 22a and the on-off valve 22b. The on-off valve 22b is configured as a solenoid valve or an electric valve.

[0037] The slide valve moving mechanism 13 also includes a pressure sensor 40a that measures the pressure in the first chamber 26a and a pressure sensor 40b that measures the pressure in the second chamber 26b. The pressures measured by the pressure sensors 40a and 40b are input to a control device 100, which will be described later.

[0038] The slide valve moving mechanism 13 controls the pressure adjusting device 22 to change the pressure in the second chamber 26b and move the slide valve 10 together with the piston 19. The slide valve moving mechanism 13 can change the internal volume ratio (hereinafter referred to as Vi) between two levels: high Vi and low Vi, by changing the stop position of the slide valve 10. The slide valve moving mechanism 13 can continuously adjust the Vi in multiple levels to a value corresponding to operating conditions such as the compression ratio within the intermediate Vi between high Vi and low Vi. The operation of the slide valve moving mechanism 13 will be described later.

[0039] The control device 100 controls the expansion valve 22a and the on-off valve 22b that constitute the pressure adjusting device 22, the pressure reducing device 54, the rotation speed of the motor 4, and the like.

[0040] The control device 100 is configured by dedicated hardware or a CPU (Central Processing Unit, also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or processor) that executes programs stored in memory.

[0041] When the control device 100 is dedicated hardware, the control device 100 may be, for example, a single circuit, a composite circuit, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. Each functional unit realized by the control device 100 may be realized by a separate piece of hardware, or each functional unit may be realized by a single piece of hardware.

[0042] When the control device 100 is a CPU, each function executed by the control device 100 is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in memory. The CPU realizes each function of the control device 100 by reading and executing the program stored in memory. Here, the memory is, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, or EEPROM.

[0043] Note that some of the functions of the control device 100 may be realized by dedicated hardware, and other functions may be realized by software or firmware.

[0044] Next, the operation of the screw compressor 51 according to the first embodiment will be described with reference to Figures 4 to 6. Figure 4 is an explanatory diagram showing the operation of the compression section 2 of the screw compressor 51 according to the first embodiment, illustrating the suction stroke. Figure 5 is an explanatory diagram showing the operation of the compression section 2 of the screw compressor 51 according to the first embodiment, illustrating the compression stroke. Figure 6 is an explanatory diagram showing the operation of the compression section 2 of the screw compressor 51 according to the first embodiment, illustrating the discharge stroke. Note that in Figures 4 to 6, each step will be described with a focus on the compression chamber 29 indicated by dotted hatching.

[0045] 4 to 6, in the screw compressor 51, the screw rotor 3 is rotated by the motor 4 via the screw shaft 5, causing the gate rotor teeth 6a of the gate rotor 6 to move relatively within the compression chamber 29. As a result, within the compression chamber 29, one cycle is repeated, consisting of a suction stroke (FIG. 4), a compression stroke (FIG. 5), and a discharge stroke (FIG. 6).

[0046] Figure 4 shows the state of the compression chamber 29 during the suction stroke. When the screw rotor 3 is driven by the motor 4 to rotate in the direction of the solid arrow from the state shown in Figure 4, the volume of the compression chamber 29 decreases as shown in Figure 5. As the screw rotor 3 continues to rotate, the compression chamber 29 communicates with the discharge port 8 as shown in Figure 6. The high-pressure refrigerant gas compressed in the compression chamber 29 is discharged from the discharge port 8 to the discharge chamber 7 as the compression chamber 29 communicates with the discharge port 8. Then, the same compression occurs again on the back surface of the screw rotor 3.

[0047] Next, the operation of the slide valve moving mechanism 13 will be described with reference to FIGS.

[0048] Fig. 7 is an explanatory diagram of the operation of the slide valve moving mechanism 13 of the screw compressor 51 according to embodiment 1. Fig. 8 is a diagram summarizing the operation of the pressure adjusting device 22 of the screw compressor 51 according to embodiment 1. As shown in Fig. 7, when the slide valve 10 moves to the high Vi side (discharge side X2), the internal volume ratio increases, and when the slide valve 10 moves to the low Vi side (suction side X1), the internal volume ratio decreases.

[0049] (i) Operation in the Case of High Vi: The slide valve moving mechanism 13 moves the piston 19 toward the second chamber 26b, thereby moving the slide valve 10 toward the high Vi. In this case, the control device 100 controls the pressure regulating device 22 to widen the opening of the expansion valve 22a and open the on-off valve 22b (as shown in FIG. 8). Here, as described above, high-pressure refrigerant oil flows into the second chamber 26b of the cylinder 17 from the oil separator 52 via the first oil inlet pipe 31a. When both the expansion valve 22a and the on-off valve 22b are closed, the second chamber 26b is under high pressure. By widening the opening of the expansion valve 22a and opening the on-off valve 22b, the refrigerant oil in the second chamber 26b flows into the low-pressure space 28 through the low-pressure communication channel 21. This causes the second chamber 26b to be under low pressure. Meanwhile, the first chamber 26a of the cylinder 17 is constantly under high pressure due to the inflow of high-pressure refrigerant gas. As a result, a load F1 acts on the piston 19 in the direction of the discharge side X2 due to the pressure difference between the first chamber 26a and the second chamber 26b.

[0050] Furthermore, a load Fk in the direction of the discharge side X2 acts on the piston 19 due to the reaction force of the spring 14a. As described above, a load Fs in the direction of the suction side X1 acts on the slide valve 10. Note that each of the loads F1, Fs, and Fk is the product of the differential pressure acting on each component and the pressure-receiving area.

[0051] Here, the pressure-receiving area of ​​the piston 19 is set so as to roughly satisfy the following load relationship: The sign of the load toward the discharge side X2 is positive, and the sign of the load toward the suction side X1 is negative. F1-Fs+Fk>0

[0052] Since "F1-Fs+Fk" is greater than 0, i.e., positive, the piston 19 and the slide valve 10 move toward the high Vi side, and the piston 19 stops at a position where the second chamber side end face 19c is seated on the cylinder lid 17b, as shown in FIG. 2.

[0053] As described above, when the piston 19 moves toward the second chamber 26b, the slide valve 10 also moves toward the second chamber 26b, in other words, toward the discharge side X2, in conjunction with the piston 19. This delays the timing at which the discharge port 8 opens, as described above, resulting in an increase in the internal volume ratio. Therefore, when the operating condition is such that the ratio between high and low pressures (compression ratio) of the refrigerant circuit to which the screw compressor 51 is applied is relatively large, the control device 100 controls the pressure adjustment device 22 as described above to increase the internal volume ratio. This allows the screw compressor 51 to prevent insufficient compression.

[0054] (ii) Operation in the case of low Vi The slide valve moving mechanism 13 moves the piston 19 toward the first chamber 26a, thereby moving the slide valve 10 toward the low Vi side. In this case, the control device 100 controls the pressure regulating device 22 to reduce the opening of the expansion valve 22a and turn off (close) the on-off valve 22b as shown in Fig. 8. Closing the on-off valve 22b blocks the flow of refrigerating machine oil through the low-pressure communication flow path 21. As a result, the second chamber 26b of the cylinder 17 becomes high pressure.

[0055] In the screw compressor 51, when the on-off valve 22b is closed and the second chamber 26b becomes high pressure, refrigerant oil may flow from the second chamber 26b to the first oil inlet pipe 31a and the oil return pipe 31b and backflow into the compression chamber 29. In the screw compressor 51, when the on-off valve 22b is closed and the second chamber 26b becomes high pressure, high-pressure refrigerant in the first chamber 26a may leak into the second chamber 26b through a gap between the piston 19 and the cylinder 17, and the leaked refrigerant may backflow into the compression chamber 29. For this reason, the screw compressor 51 may be provided with an additional check valve on the first oil inlet pipe 31a to prevent the flow of refrigerant oil and refrigerant from the first oil inlet pipe 31a to the oil return pipe 31b. In the screw compressor 51, an additional on-off valve that opens and closes in accordance with the opening and closing of the on-off valve 22b may be provided on the first oil inlet pipe 31a.

[0056] Since both the first chamber 26a and the second chamber 26b are at high pressure, the pressure difference between the first chamber 26a and the second chamber 26b becomes 0. Therefore, the load F1 acting on the piston 19 becomes 0.

[0057] Here, the pressure-receiving area of ​​the piston 19 is set to satisfy the following load relationship: The sign of the load toward the discharge side X2 is positive, and the sign of the load toward the suction side X1 is negative. F1-Fs+Fk<0

[0058] Since "F1-Fs+Fk" is smaller than 0, i.e., negative, the piston 19 and slide valve 10 move toward the low Vi side, and the piston 19 stops at a position where the suction side end 10g of the piston 19 is seated on the casing body 1, as shown in Figure 3.

[0059] As described above, when the piston 19 moves toward the first chamber 26a, the slide valve 10 also moves toward the first chamber 26a, in other words, toward the suction side X1, in conjunction with the piston 19. This advances the timing at which the discharge port 8 opens, as described above, resulting in a smaller internal volume ratio. Therefore, when the operating condition is such that the difference between the high and low pressure ratios (compression ratios) of the refrigerant circuit to which the screw compressor 51 is applied is relatively small, the control device 100 controls the pressure regulating device 22 as described above to reduce the internal volume ratio. This allows the screw compressor 51 to prevent over-compression.

[0060] (iii) Operation in the case of medium Vi Medium Vi is between low Vi and high Vi. The slide valve moving mechanism 13 adjusts the position of the slide valve 10 by adjusting the pressure in the second chamber 26b with the pressure adjusting device 22, thereby adjusting the internal volume ratio. The slide valve moving mechanism 13 adjusts the pressure in the second chamber 26b with the pressure adjusting device 22, thereby stopping the position of the slide valve 10 at any position between a position where the internal volume ratio is high Vi and a position where the internal volume ratio is low Vi.

[0061] The control device 100 calculates the differential pressure between the pressure in the first chamber 26a and the pressure in the second chamber 26b based on the measured values ​​from the pressure sensors 40a and 40b, and controls the pressure regulating device 22 so that the differential pressure becomes a target value preset according to the internal volume ratio. By controlling the pressure regulating device 22 so that the differential pressure between the pressure in the first chamber 26a and the pressure in the second chamber 26b becomes a target value preset according to the internal volume ratio, the slide valve 10 stops at a position corresponding to the internal volume ratio. The target value of the differential pressure corresponding to the internal volume ratio is stored in the control device 100. Here, as shown in FIG. 8 , the control device 100 sets the opening of the expansion valve 22a to medium and the on-off valve 22b to ON (Open). Although the opening of the expansion valve 22a is expressed as medium in FIG. 8 , in more detail, the opening of the expansion valve 22a is controlled to a predetermined opening corresponding to the target value of the differential pressure.

[0062] The screw compressor 51 can continuously control the internal volume ratio between a high Vi and a low Vi in multiple stages by controlling the opening of the expansion valve 22a with the pressure regulator 22 and adjusting the position of the slide valve 10. Therefore, the screw compressor 51 can adjust the internal volume ratio to achieve optimal compressor efficiency according to the operating state, and can operate with high efficiency. Furthermore, the screw compressor 51 can perform the above-mentioned multi-stage control of the internal volume ratio without requiring any components dedicated to multi-stage control, and can adjust the internal volume ratio in multiple stages while keeping costs down.

[0063] The slide valve movement mechanism of the screw compressor of the comparative example will now be described with reference to FIG. 9 . FIG. 9 is an explanatory diagram of the operation of the slide valve movement mechanism 130 of the screw compressor of the comparative example. In the comparative example, high-pressure refrigerant gas is introduced into the second chamber 26b. In the comparative example, the pressure in the second chamber 26b is controlled to a high or low pressure by opening and closing the valve 220a provided in the low-pressure communication passage 210, thereby moving the piston 19 and the slide valve 10. In the comparative example, because high-pressure refrigerant gas, which is a compressible fluid, is introduced into the second chamber 26b, if the high-pressure refrigerant gas leaks into the low-pressure space 28, the volume increases, which may hinder the suction of refrigerant into the compressor, reducing the suction circulation rate of the compressor and potentially resulting in a decrease in performance.

[0064] In contrast, the slide valve movement mechanism 13 of the screw compressor 51 of embodiment 1 introduces high-pressure refrigerating machine oil, which is an incompressible fluid, into the second chamber 26b. Therefore, in the screw compressor 51 of embodiment 1, the volume of the refrigerating machine oil does not increase when the high-pressure refrigerating machine oil leaks into the low-pressure space 28, so that it is possible to suppress the obstruction of suction of the refrigerant. As a result, the screw compressor 51 can suppress a decrease in capacity and an increase in input power, thereby improving performance.

[0065] As described above, the screw compressor 51 of the first embodiment includes the casing body 1 having the high-pressure space 27 and the low-pressure space 28 formed therein, and the screw rotor 3 that compresses a refrigerant from low pressure to high pressure in the compression chamber 29 inside the casing body 1. The screw compressor 51 also includes the slide valve 10 that moves between the suction side and the discharge side in the direction of the rotation axis of the screw rotor 3 and changes its stop position to change the internal volume ratio, which is the ratio between the volume of the compression chamber 29 at the end of suction and the volume of the compression chamber 29 at the start of discharge, and the slide valve moving mechanism 13 that moves the slide valve 10 in the direction of the rotation axis. The slide valve moving mechanism 13 includes a hollow cylinder 17 and a piston 19 that divides the piston chamber 26 in the cylinder 17 into a first chamber 26a and a second chamber 26b and is connected to the slide valve 10. The slide valve moving mechanism 13 includes a first oil inlet pipe 31a that introduces high-pressure refrigeration oil into the second chamber 26b, and a pressure adjusting device 22 that adjusts the pressure of the second chamber 26b by adjusting the amount of refrigeration oil in the second chamber 26b. The slide valve moving mechanism 13 changes the internal volume ratio by changing the pressure in the second chamber 26b using the pressure adjusting device 22 to move the piston 19 and control the position of the slide valve 10.

[0066] With the above configuration, the screw compressor 51 is configured to introduce refrigerant oil into the second chamber 26b, thereby suppressing a decrease in the suction circulation rate caused by leakage of refrigerant gas into the low-pressure space 28 when refrigerant gas is introduced into the second chamber 26b.

[0067] A first inlet 24 communicating with the high-pressure space 27 is formed in the cylinder 17, and the first chamber 26a communicates with the high-pressure space 27 via the first inlet 24, through which high-pressure refrigerant gas is introduced.

[0068] With the above configuration, the screw compressor 51 can maintain a constant high pressure in the first chamber 26 a. Therefore, compared to a configuration in which the first chamber 26 a is always maintained at a low pressure, the screw compressor 51 can prevent refrigeration oil introduced into the second chamber 26 b from leaking into the first chamber 26 a from the gap between the inner circumferential surface 18 of the cylinder body 17 a and the outer circumferential surface 19 a of the piston 19.

[0069] The pressure adjusting device 22 has an expansion valve 22a and an on-off valve 22b whose opening degree can be adjusted.

[0070] With the above-described configuration, the screw compressor 51 can adjust the pressure in the second chamber 26b by the expansion valve 22a and the on-off valve 22b.

[0071] Embodiment 2. In the screw compressor 51 of the above-described embodiment 1, high-pressure refrigerant gas is introduced into the first chamber 26a, but in the screw compressor 51 of embodiment 2, high-pressure refrigeration oil is introduced into the first chamber 26a. The following description will focus on the configuration of embodiment 2 that differs from embodiment 1, and the configuration not described in embodiment 2 is the same as embodiment 1.

[0072] 10 is a diagram illustrating the operation of the slide valve moving mechanism 13 of the screw compressor 51 according to the second embodiment. The screw compressor 51 of the second embodiment introduces high-pressure refrigeration oil into the first chamber 26a. Specifically, the refrigeration oil in the oil separator 52 (see FIG. 1) is introduced into the first chamber 26a through the second oil introduction pipe 31c of the oil return circuit 31.

[0073] The screw compressor 51 of the second embodiment can obtain the same effects as those of the first embodiment.

[0074] Embodiment 3. In the screw compressors 51 of the first and second embodiments, the first chamber 26a is constantly at high pressure, the oil return circuit 31 and the low-pressure communicating passage 21 are connected to the second chamber 26b, and high-pressure refrigerating machine oil is introduced therein to change the pressure. In the screw compressor 51 of the third embodiment, the oil return circuit 31 and the low-pressure communicating passage 21 are connected to the first chamber 26a, high-pressure refrigerating machine oil is introduced therein to change the pressure, and the second chamber 26b is constantly at high pressure. In other words, the screw compressor 51 may be configured such that the oil return circuit 31 and the low-pressure communicating passage 21 are connected to one of the first and second chambers 26a and 26b, high-pressure refrigerating machine oil is introduced therein to change the pressure, and the other chamber is constantly at high pressure. The following description of the third embodiment will focus on the differences from the first and second embodiments. The configuration not described in the third embodiment is the same as that of the first and second embodiments.

[0075] Fig. 11 is a diagram illustrating the operation of the slide valve moving mechanism 13 of the screw compressor 51 according to embodiment 3. Fig. 12 is a diagram summarizing the operation of the pressure adjusting device 22 of the screw compressor 51 according to embodiment 3.

[0076] (i) Operation in the Case of High Vi The slide valve moving mechanism 13 moves the piston 19 toward the second chamber 26b, thereby moving the slide valve 10 toward the high Vi side. In this case, the control device 100 controls the pressure regulating device 22 to reduce the opening of the expansion valve 22a and turn off (close) the on-off valve 22b, as shown in FIG. 12 . Closing the on-off valve 22b blocks the flow of refrigerant oil through the low-pressure communication flow path 21. This causes the first chamber 26a of the cylinder 17 to become high pressure. Meanwhile, high-pressure refrigerant gas constantly flows into the second chamber 26b of the cylinder 17, keeping it at high pressure.

[0077] Both the first chamber 26a and the second chamber 26b become high pressure, and the piston rod 19d of the piston 19 is not subjected to the pressure in the first chamber 26a but is subjected to the pressure of the high-pressure space 27, so that the differential pressure acting before and after the piston 19 becomes zero. Therefore, the load F1 acting on the piston 19 becomes zero.

[0078] Here, the pressure-receiving area of ​​the piston 19 is set to satisfy the following load relationship: The sign of the load toward the discharge side X2 is positive, and the sign of the load toward the suction side X1 is negative: F1-Fs+Fk>0 (F1=0).

[0079] Since "F1-Fs+Fk" is greater than 0, i.e., positive, the piston 19 and the slide valve 10 move toward the high Vi side, and the piston 19 stops at a position where the second chamber side end face 19c is seated on the cylinder lid 17b, as shown in FIG. 2.

[0080] (ii) Operation in the Case of Low Vi The slide valve moving mechanism 13 moves the piston 19 toward the first chamber 26a, thereby moving the slide valve 10 toward the low Vi side. In this case, the control device 100 controls the pressure regulating device 22 to widen the opening of the expansion valve 22a and turn the on-off valve 22b ON (Open) as shown in FIG. 12 . As a result, refrigerating machine oil flowing from the first oil inlet pipe 31a into the first chamber 26a of the cylinder 17 flows out into the low-pressure space 28 via the low-pressure communication flow path 21, thereby lowering the pressure in the first chamber 26a. Meanwhile, high-pressure refrigerant gas constantly flows into the second chamber 26b of the cylinder 17, maintaining the second chamber 26b at high pressure. As a result, a load F1 toward the suction side X1 acts on the piston 19 due to the pressure difference between the first chamber 26a and the second chamber 26b.

[0081] Furthermore, a load Fk in the direction of the discharge side X2 acts on the piston 19 due to the reaction force of the spring 14a. As described above, a load Fs in the direction of the suction side X1 acts on the slide valve 10.

[0082] Here, the pressure-receiving area of ​​the piston 19 is set to satisfy the following load relationship: the sign of the load toward the discharge side X2 is positive, and the sign of the load toward the suction side X1 is negative. −F1−Fs+Fk<0

[0083] Since "-F1-Fs+Fk" is less than 0, i.e., negative, the piston 19 and slide valve 10 move toward the low Vi side, and the piston 19 stops at a position where the suction side end 10g of the piston 19 is seated on the casing body 1, as shown in Figure 3.

[0084] (iii) Operation in the Case of Medium Vi The operation of the slide valve moving mechanism 13 in this case is the same as in the first embodiment.

[0085] As shown in Figures 2 and 3, a small gap is provided between the inner circumferential surface 19b of the piston rod hole provided in the center of the cylinder lid 17b and the outer circumferential surface 19a of the piston rod 19d, allowing the piston rod 19d to move through the piston rod hole. Therefore, if the second chamber 26b in Figure 11 is under low pressure, high-pressure refrigerant may flow into the second chamber 26b from outside the cylinder body 17a through this gap. Such a flow of refrigerant from a high-pressure space to a low-pressure space is considered a refrigerant leak and results in a leakage loss in the compressor. However, in the screw compressor 51, the second chamber 26b is under high pressure, which prevents leakage due to a pressure difference between the space in the second chamber 26b and the space outside the cylinder body 17a.

[0086] The screw compressor 51 of the third embodiment can obtain the same effects as the screw compressors 51 of the first and second embodiments.

[0087] Embodiment 4. While the screw compressor 51 of the above-described embodiment 3 is configured to constantly introduce high-pressure refrigerant gas into the second chamber 26 b, the screw compressor 51 of embodiment 4 is configured to constantly introduce intermediate-pressure refrigerant gas into the second chamber 26 b. The following description will focus on the configuration of embodiment 4 that differs from embodiment 3, and the configuration not described in embodiment 4 is the same as embodiment 3.

[0088] Fig. 13 is a diagram illustrating the operation of the slide valve moving mechanism 13 of the screw compressor 51 according to embodiment 4. Fig. 14 is a diagram summarizing the operation of the pressure adjusting device 22 of the screw compressor 51 according to embodiment 4.

[0089] The screw compressor 51 constantly introduces intermediate-pressure refrigerant gas, which is higher than the suction pressure and lower than the discharge pressure, into the second chamber 26b. The screw compressor 51 introduces intermediate-pressure refrigerant gas into the second chamber 26b by configuring the second chamber 26b to be connected to the intermediate-pressure space 30 via the intermediate-pressure communicating passage 23. The intermediate-pressure space 30 is a pressure space between the high-pressure space 27 and the low-pressure space 28. The intermediate-pressure space 30 is, for example, a space in the casing main body 1 in which the gate rotor 6 is installed. As a specific configuration, the intermediate-pressure communicating passage 23 may be, for example, configured by drilling holes in the casing main body 1 and the cylinder 17, or may be configured by piping arranged outside the casing main body 1.

[0090] The screw compressor 51 of embodiment 4 is similar to embodiment 3 in the operation when the slide valve 10 is moved to the high Vi side or the low Vi side and in the operation of the pressure adjusting device 22, but differs from the screw compressor 51 of embodiment 3 in the following points.

[0091] In the screw compressor 51 of the fourth embodiment, when the slide valve 10 is moved toward the high Vi side, a load F1 acts on the piston 19 toward the discharge side X2 due to the pressure difference between the first chamber 26a and the second chamber 26b. Here, in the screw compressor 51 of the fourth embodiment, intermediate-pressure refrigerant gas is introduced into the second chamber 26b, so the load F1 toward the discharge side X2 is larger than in the screw compressor 51 of the third embodiment, in which high-pressure refrigerant gas is introduced into the second chamber 26b. Therefore, the load Fk, which has the same force direction as the load F1, i.e., the load Fk related to the spring force of the spring 14a, can be reduced. Therefore, the screw compressor 51 of the fourth embodiment can use a spring 14a with a weaker spring force than that of the third embodiment.

[0092] The screw compressor 51 of the fourth embodiment has the same effects as those of the third embodiment, and by introducing intermediate-pressure refrigerant gas into the second chamber 26b, it becomes possible to use a spring 14a with weaker spring force than that of the third embodiment.

[0093] As described above, the screw compressors 51 of the first to fourth embodiments can all suppress a decrease in the amount of refrigerant gas suctioned and circulated by introducing refrigeration oil into the first chamber 26a or the second chamber 26b of the piston chamber 26. Leakage of high-pressure refrigerant gas into the low-pressure space 28 via the piston chamber 26 is likely to result in a decrease in compressor performance during operation when the amount of refrigerant gas suctioned and circulated is small. For this reason, the screw compressors 51 of the first to fourth embodiments are particularly effective during operation when the compressor load is small and the amount of refrigerant gas suctioned and circulated is small.

[0094] Furthermore, in the screw compressor 51 of the above-described first to fourth embodiments, both the expansion valve 22a and the on-off valve 22b are arranged in the low-pressure communication flow path 21 in the pressure adjustment device 22, but the following configuration may also be used.

[0095] Fig. 15 is a diagram showing a first modification of the pressure regulating device 22 of the screw compressor 51 according to any one of the first to fourth embodiments. As shown in Fig. 15, the pressure regulating device 22 may be configured such that the expansion valve 22a is disposed in the low-pressure communication flow path 21 and the on-off valve 22b is disposed in the first oil introduction pipe 31a. Note that Fig. 15 shows an example in which the first modification is applied to the screw compressor 51 according to the first embodiment shown in Fig. 7, but the modification can also be applied to the screw compressors 51 according to any one of the second to fourth embodiments.

[0096] Furthermore, in the screw compressor 51 of the first to fourth embodiments, the pressure regulating device 22 has the expansion valve 22a and the on-off valve 22b, but is not limited to this configuration and may have the following configuration.

[0097] Fig. 16 is a diagram showing a second modification of the pressure regulating device 22 of the screw compressor 51 according to any one of the first to fourth embodiments. As shown in Fig. 16, the pressure regulating device 22 may be configured to have two on-off valves 22b1 and 22b2, with one on-off valve 22b1 being disposed in the first oil supply pipe 31a and the other on-off valve 22b2 being disposed in the low-pressure communication flow path 21. In other words, the screw compressor 51 may be configured such that the pressure regulating device 22 does not use an expansion valve and still perform the same function.

[0098] In a configuration in which the pressure regulating device 22 has two on-off valves 22b1 and 22b2, the pressure of one of the first chamber 26a and the second chamber 26b (in the illustrated example, the second chamber 26b) can be adjusted by adjusting the opening and closing timing of the two on-off valves 22b1 and 22b2. For example, the pressure regulating device 22 can adjust the pressure of one of the chambers by opening the on-off valve 22b1 disposed in the first oil inlet pipe 31a to fill the one of the chambers with high-pressure refrigerating machine oil, and then adjusting the duration for which the on-off valve 22b2 disposed in the low-pressure communicating flow path 21 is opened to adjust the amount of refrigerating machine oil flowing out of the one of the chambers. Note that while FIG. 16 illustrates an example in which Modification 2 is applied to the screw compressor 51 of the first embodiment shown in FIG. 7, the same can be applied to the screw compressors 51 of the second to fourth embodiments.

[0099] The screw compressor 51 and the refrigeration cycle device 50 of the present disclosure are not limited to the above configurations, and can be modified, for example, as follows, without departing from the gist of the present disclosure.

[0100] FIG. 17 is a diagram showing a modified example of the screw compressors according to the first to fourth embodiments. In the above example, the oil separator 52 is provided separately from the screw compressor 51, and the refrigeration oil separated by the oil separator 52 is introduced into the second chamber 26b or the first chamber 26a using the first oil inlet pipe 31a or the second oil inlet pipe 31c provided outside the screw compressor 51. However, the present invention is not limited to this example. As shown in FIG. 17, the oil separator 52 may be provided integrally within the screw compressor 51. In this case, the screw compressor 51 is configured to include the oil separator 52 inside the casing 1a, and to introduce the refrigeration oil separated from the refrigerant by the oil separator 52 into the second chamber 26b or the first chamber 26a using the first oil inlet pipe 31a or the second oil inlet pipe 31c provided inside the casing 1a. 17 has a flow path 60 that connects the compression chambers 29 and the oil separator 52, and refrigeration oil discharged from the compression chambers 29 flows into the oil separator 52 via the flow path 60. The flow path 60 may be configured as a pipe, or may be a hole that penetrates a wall portion 61 that partitions the inside of the casing 1a and forms the oil separator 52.

[0101] Furthermore, when the screw compressor 51 is configured to include the oil separator 52 inside the casing 1a, the screw compressor 51 may be configured as follows: The screw compressor 51 may be configured such that the oil separated in the oil separator 52 is first introduced to the outside of the casing 1a using the first oil introduction pipe 31a or the second oil introduction pipe 31c disposed externally to the outside of the casing 1a, and then introduced back into the casing 1a and into the second chamber 26b or the first chamber 26a.

[0102] In this way, the present disclosure is applicable to configurations in which the oil separator 52 is provided either outside or inside the screw compressor 51.

[0103] DESCRIPTION OF SYMBOLS 1 Casing body, 1a Casing, 2 Compression section, 3 Screw rotor, 3a Groove, 4 Motor, 4a Stator, 4b Motor rotor, 5 Screw shaft, 6 Gate rotor, 6a Gate rotor tooth portion, 7 Discharge chamber, 8 Discharge port, 9 Slide groove, 10 Slide valve, 10a Valve body, 10b Guide portion, 10c Connecting portion, 10d Discharge port side end, 10e Discharge port side end, 10f Discharge flow path, 10g Suction side end, 10h Discharge side end, 11 Main bearing, 12 Main bearing housing, 13 Slide valve moving mechanism, 14 Rod, 14a Spring, 15 Connecting arm, 16 Nut, 17 Cylinder, 17a Cylinder body, 17a1 Flange portion, 17a2 Flange portion, 17b Cylinder cover, 18 Inner surface, 19 Piston, 19a Outer surface, 19b Inner peripheral surface, 19c second chamber side end face, 19d piston rod, 20 second inlet hole, 21 low pressure communication flow path, 22 pressure regulating device, 22a expansion valve, 22b on-off valve, 22b1 on-off valve, 22b2 on-off valve, 23 intermediate pressure communication flow path, 24 first inlet hole, 25 third inlet hole, 26 piston chamber, 26a first chamber, 26b second chamber, 27 high pressure space, 28 low pressure space, 29 compression chamber, 30 intermediate pressure space, 31 oil return circuit, 31a first oil introduction pipe, 31b oil return pipe, 31c second oil introduction pipe, 40a pressure sensor, 40b pressure sensor, 50 refrigeration cycle device, 51 screw compressor, 52 oil separator, 53 condenser, 54 pressure reducing device, 55 evaporator, 60 flow path, 61 wall portion, 100 Control device, 130 slide valve moving mechanism, 210 low pressure communication flow path, 220a valve.

Claims

a slide valve that moves in the direction of the rotation axis of the screw rotor between the suction side and the discharge side and changes its stop position to change an internal volume ratio, which is the ratio of the volume of the compression chamber at the completion of suction to the volume of the compression chamber at the start of discharge, and a slide valve moving mechanism that moves the slide valve in the direction of the rotation axis, wherein the slide valve moving mechanism comprises: a hollow cylinder; a piston that divides a piston chamber in the cylinder into a first chamber and a second chamber and is connected to the slide valve; a first oil introduction pipe that introduces high-pressure refrigeration oil into one of the first and second chambers; and a pressure regulating device that adjusts the amount of the refrigeration oil in the one chamber to adjust the pressure of the one chamber, 2. A screw compressor as claimed in claim 1, wherein said cylinder is formed with a first inlet hole communicating with said high pressure space, and the other of said first chamber and said second chamber communicates with said high pressure space via said first inlet hole, through which high pressure refrigerant gas is introduced.

3. A screw compressor according to claim 1, wherein said slide valve moving mechanism has a second oil introduction pipe for introducing high pressure refrigeration oil into the other of said first chamber and said second chamber.

4. A screw compressor as claimed in claim 3, wherein the first chamber and the second chamber are aligned in the direction of the rotation axis, the first chamber being located on the suction side and the second chamber being located on the discharge side, the slide valve moving mechanism is provided with a spring which urges the slide valve towards the discharge side, an intermediate pressure space which is a pressure space between the high pressure space and the low pressure space is formed inside the casing body, the second chamber is connected to the intermediate pressure space and intermediate pressure refrigerant gas is introduced into the screw compressor.

5. A screw compressor according to any one of claims 1 to 4, wherein the pressure regulating device has an expansion valve and an on-off valve whose opening degree is adjustable.

6. A screw compressor as claimed in claim 5, wherein the slide valve moving mechanism is provided with a low pressure communication passage which connects the one of the chambers to the low pressure space, and the pressure regulating device is provided in the low pressure communication passage.

7. A screw compressor as described in claim 5, wherein the slide valve moving mechanism is provided with a low pressure communication passage which connects the one of the chambers to the low pressure space, and the pressure regulating device is such that the expansion valve is disposed in the low pressure communication passage and the on-off valve is disposed in the first oil introduction pipe.

8. A screw compressor as claimed in any one of claims 1 to 4, wherein the slide valve moving mechanism comprises a low pressure communicating flow path which connects the one of the chambers with the low pressure space, and the pressure regulating device has two on-off valves, one on-off valve being disposed in the first oil introduction pipe and the other on-off valve being provided in the low pressure communicating flow path.

9. A screw compressor as described in any one of claims 1 to 8, wherein the first oil introduction pipe is provided inside a casing including the casing body or is provided externally to the casing.

10. A screw compressor as described in claim 3 or any one of claims 4 to 9 dependent on claim 3, wherein the second oil supply pipe is provided inside a casing including the casing body or is provided externally to the casing.

11. A screw compressor according to claim 9 or claim 10, further comprising an oil separator disposed inside said casing for separating refrigerating machine oil from the refrigerant, said refrigerating machine oil separated by said oil separator being introduced into said first chamber or said second chamber.

12. A refrigeration cycle system comprising the screw compressor according to any one of claims 1 to 8, a condenser, a pressure reducing device, and an evaporator.

13. A refrigeration cycle device as claimed in claim 12, further comprising: an oil separator which separates refrigeration oil from the refrigerant discharged from the screw compressor; and an oil return circuit which introduces the refrigeration oil separated by the oil separator into the one of the chambers via the first oil introduction pipe.

14. A refrigeration cycle system comprising the screw compressor according to any one of claims 9 to 11, a condenser, a pressure reducing device, and an evaporator.

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