EP3832138A1

EP3832138A1 - Screw compressor

Info

Publication number: EP3832138A1
Application number: EP18927914.4A
Authority: EP
Inventors: Yu KOBA
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-07-27
Filing date: 2018-07-27
Publication date: 2021-06-09
Anticipated expiration: 2038-07-27
Also published as: EP3832138A4; EP3832138B1; WO2020021707A1

Abstract

A screw compressor includes a casing forming an outer shell, a screw shaft located in the casing, the screw shaft being configured to be rotationally driven, a screw rotor fixed to the screw shaft, the screw rotor including a tooth groove with a spiral shape on an outer circumferential surface of the screw rotor, a gate rotor including a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor, the gate rotor forming a compression chamber together with the casing and the screw rotor, and a slide valve provided in a slide groove formed on an inner cylindrical surface of the casing, the slide valve being configured to be slidably movable in a rotational-axis direction of the screw rotor. Key grooves are formed facing each other on an outer surface of the slide valve and on an inner surface of the casing, and a key common to the key grooves is inserted in the key grooves.

Description

Technical Field

The present invention relates to a screw compressor to be used to compress refrigerant in, for example, a refrigerating machine.

Background Art

As disclosed in Patent Literature 1, a screw compressor has been commonly known as one of the types of positive-displacement compressors. For example, the screw compressor is used as a constituent part of a refrigerant circuit incorporated in a refrigerating machine. As a type of the screw compressor, a single screw compressor has been commonly known in which, for example, one screw rotor and two gate rotors are accommodated in a casing. The screw rotor includes a tooth groove with a spiral shape. Each of the gate rotors includes a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor. In the single screw compressor, the tooth groove of the screw rotor, and the gate-rotor tooth portions of the gate rotors mesh and engage with each other, which forms a plurality of compression chambers. The screw rotor has one end in a rotational-axis direction thereof on the suction side for refrigerant, and has the other end on the discharge side for refrigerant. The interior of the casing is partitioned into a lower-pressure space provided on the suction side of the compression chamber, and a higher-pressure space provided on the discharge side of the compression chamber.
The screw rotor is fixed to a screw shaft that is rotated by a drive portion provided in the casing. The screw shaft is supported at one axial end portion rotatably by a bearing housing having a bearing therein, while being connected with the drive portion at the other axial end of the screw shaft. In the configuration of the screw compressor, when the screw rotor is rotationally driven through the screw shaft that is rotated by the drive portion, refrigerant in the lower-pressure space is suctioned into the compression chamber and compressed, and then the refrigerant compressed in the compression chamber is discharged to the higher-pressure space.
There is a screw compressor including a pair of slide valves located in a slide groove formed on the inner cylindrical surface of the casing, the pair of slide valves being provided in a slidably movable manner in the rotational-axis direction of the screw rotor. The slide valves are provided to slide in the rotational-axis direction of the screw rotor to change the position at which high-pressure gas refrigerant compressed in the compression chamber starts being discharged, to thereby change the timing of opening the discharge port to change the internal volume ratio. Each of the slide valves includes a valve body portion facing the screw rotor, and a guide portion formed with a sliding surface facing the outer circumferential surface of the bearing housing.
Between the outer circumferential surface of the screw rotor and the inner cylindrical surface of the casing, and between the outer circumferential surface of the screw rotor and the slide valve, it is necessary to provide a clearance to allow the screw rotor to be rotationally driven. However, the screw compressor has a problem in that fluid being compressed leaks from this clearance to the adjacent compression chamber, and this leads to a decrease in operational efficiency.
To minimize the decrease in operational efficiency in the screw compressor, it is effective to reduce the leakage of fluid being compressed by setting a small clearance between the outer circumferential surface of the screw rotor and the inner cylindrical surface of the casing, and between the outer circumferential surface of the screw rotor and the slide valve. However, in the screw compressor, there is a possibility that the screw rotor and the slide valve may thermally expand due to an increase in temperature of the refrigerant gas compressed in the compression chamber, and this may result in a reduction in the clearance between the outer circumferential surface of the screw rotor and the inner cylindrical surface of the casing, and between the outer circumferential surface of the screw rotor and the slide valve. In addition, after operation of the screw compressor is stopped, the screw rotor may rotate reversely due to a difference between higher pressure and lower pressure in the casing. When the screw rotor rotates reversely, there is a possibility that the valve body portion of the slide valve may fall toward the screw rotor or may rotate in the circumferential direction due to a change in internal pressure in the compression chamber and other influences. Further, even during normal operation of the screw compressor, the valve body portion of the slide valve may fall toward the screw rotor or may rotate in the circumferential direction due to a change in pressure applied from the compression chamber. That is, when the clearance between the slide valve and the screw rotor is excessively small, there is a possibility that the slide valve may contact the screw rotor, and this may cause burning or other problems.
For example, Patent Literature 1 discloses a structure in which a step portion is provided on the arc-shaped surface of a slide valve facing a screw rotor, and dynamic pressure of the refrigerant gas sprayed onto the step portion prevents the slide valve from rotating to secure a clearance between the slide valve and the screw rotor.
Patent Literature 2 discloses a structure in which a guide portion of a slide valve is provided with a protruding portion protruding in a circumferential direction relative to a valve body portion, and when the slide valve rotates in the circumferential direction, the protruding portion is brought into contact with a bearing holder to avoid the slide valve from contacting the screw rotor.

Citation List

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-168011
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2013-60877

Summary of Invention

Technical Problem

In the invention disclosed in Patent Literature 1, the key factor to secure a clearance between the slide valve and the screw rotor is the dynamic pressure to be applied by fluid. Since the dynamic pressure can vary depending on the operational conditions, it may be difficult to regard the configuration of this invention as reliably securing the clearance. In a case where, for example, the screw rotor rotates reversely when the compressor is stopped, there is a possibility that the dynamic pressure may not be applied to the step portion as intended, and accordingly the clearance between the slide valve and the screw rotor may be reduced more than necessary. As a result of this, the slide valve may contact the screw rotor.
In the invention disclosed in Patent Literature 2, in a case where deformation such as twisting occurs between the valve body portion and the guide portion of the slide valve, even when the protruding portion provided on the guide portion contacts the bearing holder, there is still a possibility that the clearance between the valve body portion and the screw rotor may be reduced more than necessary and the slide valve may contact the screw rotor.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a screw compressor that is reliable and can prevent a slide valve from contacting a screw rotor, while minimizing a decrease in efficiency in the compressor by reducing a clearance between the slide valve and the screw rotor as small as possible.

Solution to Problem

A screw compressor according to one embodiment of the present invention includes: a casing forming an outer shell; a screw shaft located in the casing, the screw shaft being configured to be rotationally driven; a screw rotor fixed to the screw shaft, the screw rotor including a tooth groove with a spiral shape on an outer circumferential surface of the screw rotor; a gate rotor including a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor, the gate rotor forming a compression chamber together with the casing and the screw rotor; and a slide valve provided in a slide groove formed on an inner cylindrical surface of the casing, the slide valve being configured to be slidably movable in a rotational-axis direction of the screw rotor, wherein key grooves are formed facing each other on an outer surface of the slide valve and on an inner surface of the casing, respectively, and a key common to the key grooves is inserted in the key grooves.
A screw compressor according to another embodiment of the present invention includes: a casing forming an outer shell; a screw shaft located in the casing, the screw shaft being configured to be rotationally driven; a screw rotor fixed to the screw shaft, the screw rotor including a tooth groove with a spiral shape on an outer circumferential surface of the screw rotor; a gate rotor including a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor, the gate rotor forming a compression chamber together with the casing and the screw rotor; and a slide valve provided in a slide groove formed on an inner cylindrical surface of the casing, the slide valve being configured to be slidably movable in a rotational-axis direction of the screw rotor, wherein a key groove is formed on one of an outer surface of the slide valve and an inner surface of the casing, and a projecting portion to be fitted in the key groove is formed on an other one.

Advantageous Effects of Invention

In the screw compressor according to one embodiment of the present invention, rotation of the slide valve in the circumferential direction is restricted by the key grooves and the key, or by the key groove and the projecting portion. Thus, the screw compressor can prevent the slide valve from contacting the screw rotor since the slide valve does not rotate in the circumferential direction even when there may be variations in the pressure applied to the inner cylindrical surface of the slide valve, the inner cylindrical surface facing the outer circumferential surface of the screw rotor. Consequently, the screw compressor can be achieved as a reliable screw compressor that can secure a clearance between the slide valve and the screw rotor, while minimizing a decrease in efficiency in the compressor by reducing the clearance between the slide valve and the screw rotor as small as possible. Brief Description of Drawings

[Fig. 1] Fig. 1 is a cross-sectional view illustrating an internal structure of a screw compressor according to Embodiment 1 of the present invention.
[Fig. 2] Fig. 2 is a cross-sectional view taken along the line A-A illustrated in Fig. 1.
[Fig. 3] Fig. 3 is an explanatory view illustrating a suctioning process that is operation of a compression portion of the screw compressor according to Embodiment 1 of the present invention.
[Fig. 4] Fig. 4 is an explanatory view illustrating a compressing process that is operation of the compression portion of the screw compressor according to Embodiment 1 of the present invention.
[Fig. 5] Fig. 5 is an explanatory view illustrating a discharging process that is operation of the compression portion of the screw compressor according to Embodiment 1 of the present invention.
[Fig. 6] Fig. 6 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 1 of the present invention.
[Fig. 7] Fig. 7 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 2 of the present invention.
[Fig. 8] Fig. 8 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 3 of the present invention.
[Fig. 9] Fig. 9 is an enlarged cross-sectional view illustrating principal parts of a modification of the screw compressor according to Embodiment 3 of the present invention.
[Fig. 10] Fig. 10 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 4 of the present invention.
[Fig. 11] Fig. 11 is an enlarged cross-sectional view illustrating principal parts of a modification of the screw compressor according to Embodiment 4 of the present invention.

Description of Embodiments

Embodiments of the present invention will be described hereinafter with reference to the drawings. Note that in each of the drawings, the same or equivalent components are denoted by the same reference signs, and their descriptions are appropriately omitted or simplified. The shape, size, location, and other factors of the constituent components described in each of the drawings may be appropriately changed within the scope of the present invention.

Embodiment 1.

Fig. 1 is a cross-sectional view illustrating an internal structure of a screw compressor according to Embodiment 1 of the present invention. Fig. 2 is a cross-sectional view taken along the line A-A illustrated in Fig. 1. As a screw compressor 100 according to Embodiment 1, a single-stage single screw compressor will be described as an example. As illustrated in Fig. 1, the screw compressor 100 is constituted by a casing 1 having a cylindrical shape and forming an outer shell, a compression portion 2, and a drive portion 3. The compression portion 2 and the drive portion 3 are provided in the casing 1. The interior of the casing 1 is partitioned into a lower-pressure space 10 and a higher-pressure space 11.
As illustrated in Fig. 1, the compression portion 2 includes a screw shaft 4, a screw rotor 5 fixed to the screw shaft 4, a pair of gate rotors 6, a gate rotor support 7, a pair of slide valves 8, and a bearing housing 9 having a bearing 90 therein, the bearing 90 rotatably supporting an end portion of the screw shaft 4.
The screw shaft 4 extends in the pipe axis direction of the casing 1. The screw shaft 4 is supported at one axial end portion rotatably by the bearing 90 located facing the discharge side of the screw rotor 5, while being connected with the drive portion 3 at the other axial end portion of the screw shaft 4. The screw shaft 4 is rotated by the drive portion 3.
As illustrated in Fig. 2, the screw rotor 5 includes a plurality of tooth grooves 5a with a spiral shape on the outer circumferential surface of the columnar body of the screw rotor 5. The screw rotor 5 is fixed to the screw shaft 4 and rotates with the screw shaft 4 that is rotated by the drive portion 3. As illustrated in Fig. 1, one side of the screw rotor 5 in the rotational-axis direction, which is closer to the lower-pressure space 10, is the suction side for refrigerant, while the other side of the screw rotor 5, which is closer to the higher-pressure space 11, is the discharge side for refrigerant.
Each of the gate rotors 6 is formed with a plurality of gate-rotor tooth portions 6a on the outer circumferential portion of the gate rotor 6. The gate-rotor tooth portions 6a are fitted correspondingly in the tooth grooves 5a of the screw rotor 5. As illustrated in Fig. 1, the gate rotors 6 are located with the screw rotor 5 interposed between the gate rotors 6 in the radial direction. In the compression portion 2, the tooth grooves 5a of the screw rotor 5, and the gate-rotor tooth portions 6a of the gate rotors 6 mesh and engage with each other, which forms a compression chamber 20. In the configuration of the screw compressor 100, two gate rotors 6 are located opposite to each other with reference to one screw rotor 5 by being displaced from each other at an angle of 180 degrees relative to the screw rotor 5. Due to this configuration, two compression chambers 20 are formed, one of which is formed on the upper side of the screw shaft 4, while the other is formed on the lower side of the screw shaft 4. As illustrated in Fig. 2, the gate rotor support 7 includes a plurality of gate-rotor-support tooth portions 7a that are provided respectively facing the gate-rotor tooth portions 6a. The gate rotor support 7 supports the gate rotor 6.
As illustrated in Fig. 1, the slide valve 8 is provided in a slide groove 12 formed on the inner cylindrical surface of the casing 1. The slide valve 8 is configured to be slidably movable in the rotational-axis direction of the screw rotor 5. An example of the slide valve 8 is an internal volume-ratio regulating valve. The slide valve 8 includes a valve body portion 80 facing the screw rotor 5, and a guide portion 81 with a sliding surface facing the outer circumferential surface of the bearing housing 9. The valve body portion 80 and the guide portion 81 are connected by a connection portion 82. Between the valve body portion 80 and the guide portion 81, a discharge port 8a is provided for refrigerant compressed in the compression chamber 20. The refrigerant discharged from the discharge port 8a is then discharged into the higher-pressure space 11 through a discharge gas passage formed on the back side of the guide portion 81.
The slide valve 8 is connected to a slide-valve drive device 84 through a rod 83 fixed to an end surface of the guide portion 81. That is, the slide valve 8 moves in a direction parallel to the screw shaft 4 through the rod 83 that operates in the axial direction by driving of the slide-valve drive device 84. For example, the slide-valve drive device 84 is configured to be driven by gas pressure, is configured to be driven by hydraulic pressure, or is configured to be driven by a motor.
In the screw compressor 100, the valve body portion 80 of the slide valve 8 moves in a direction parallel to the screw shaft 4, so that the timing of discharging refrigerant suctioned into the compression chamber 20 is adjusted. Specifically, the slide valve 8 is positioned on the suction side to open the discharge port 8a earlier, so that the timing of discharging the refrigerant can be advanced. The slide valve 8 is moved toward the discharge side to delay opening the discharge port 8a, so that the timing of discharging the refrigerant can be delayed. That is, the screw compressor 100 operates at a lower internal volume ratio when the timing of discharging the refrigerant is advanced, and the screw compressor 100 operates at a higher internal volume ratio when the timing of discharging the refrigerant is delayed.
The drive portion 3 is constituted by an electric motor 30. The electric motor 30 is in internal contact with the inner portion of the casing 1 and fixed thereto. The electric motor 30 is constituted by a stator 31 and a motor rotor 32. The stator 31 has a clearance in the radial direction. The motor rotor 32 is located on the inner side of the stator 31 in a rotatable manner. The motor rotor 32 is connected to the axial end portion of the screw shaft 4, and is located on the same axial line as the screw rotor 5. In the screw compressor 100, the electric motor 30 drives and rotates the screw shaft 4 to rotate the screw rotor 5. Note that the electric motor 30 is driven by an inverter at a variable rotational speed although illustrations of the inverter are omitted. The electric motor 30 is operated while increasing or decreasing the rotational speed of the screw shaft 4.
Next, with reference to Figs. 3 to 5, operation of the screw compressor 100 according to Embodiment 1 will be described. Fig. 3 is an explanatory view illustrating a suctioning process that is operation of a compression portion of the screw compressor according to Embodiment 1 of the present invention. Fig. 4 is an explanatory view illustrating a compressing process that is operation of the compression portion of the screw compressor according to Embodiment 1 of the present invention. Fig. 5 is an explanatory view illustrating a discharging process that is operation of the compression portion of the screw compressor according to Embodiment 1 of the present invention. Note that the respective processes are described with a focus on the compression chamber 20 illustrated by dotted hatching in Figs. 3 to 5.
As illustrated in Figs. 3 to 5, in the screw compressor 100, the screw rotor 5 is rotated through the screw shaft 4 by the electric motor 30, so that the gate-rotor tooth portions 6a of the gate rotors 6 move within, and relative to, the tooth grooves 5a forming the compression chamber 20. With this movement, in the compression chamber 20, the suctioning process (Fig. 3), the compressing process (Fig. 4), and the discharging process (Fig. 5) are considered as one cycle, and this cycle is repeated.
Fig. 3 illustrates the state of the compression chamber 20 in the suctioning process. The screw rotor 5 is driven by the electric motor 30 and is rotated in a direction shown by the solid arrow. Due to this rotation, the volume of the compression chamber 20 is decreased as illustrated in Fig. 4.
Subsequently, when the screw rotor 5 is rotated, the compression chamber 20 communicates with the discharge port 8a as illustrated in Fig. 5. This allows refrigerant gas at high pressure, compressed in the compression chamber 20, to be discharged from the discharge port 8a to the outside. Refrigerant gas is compressed again on the back side of the screw rotor 5 in the same manner as described above.
To minimize the decrease in operational efficiency in the screw compressor 100, it is effective to reduce the leakage of fluid being compressed by setting a small clearance between the outer circumferential surface of the screw rotor 5 and the inner cylindrical surface of the casing 1, and between the outer circumferential surface of the screw rotor 5 and the slide valve 8. However, in the screw compressor 100, there is a possibility that the screw rotor 5 and the slide valve 8 may thermally expand due to an increase in temperature of the refrigerant gas compressed in the compression chamber 20, and this may result in a reduction in the clearance between the outer circumferential surface of the screw rotor 5 and the inner cylindrical surface of the casing 1, and between the outer circumferential surface of the screw rotor 5 and the slide valve 8. In addition, after operation of the screw compressor 100 is stopped, the screw rotor 5 may rotate reversely due to a difference between higher pressure and lower pressure in the casing 1. When the screw rotor 5 rotates reversely, there is a possibility that the valve body portion 80 of the slide valve 8 may fall toward the screw rotor 5 or may rotate in the circumferential direction due to a change in internal pressure in the compression chamber 20 and other influences. Further, even during normal operation of the screw compressor 100, the valve body portion 80 of the slide valve 8 may fall toward the screw rotor 5 or may rotate in the circumferential direction due to a change in pressure to be applied from the compression chamber 20. That is, when the clearance between the slide valve 8 and the screw rotor 5 is excessively small, the slide valve 8 may contact the screw rotor 5, and this may cause burning or other problems.
Fig. 6 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 1 of the present invention. As illustrated in Fig. 6, in the screw compressor 100 according to Embodiment 1, key grooves 13 and 14 with a rectangular shape are formed facing each other on the outer surface of the slide valve 8 and on the inner surface of the casing 1, respectively. A key 15 common to the key grooves 13 and 14 is inserted in the key grooves 13 and 14. The key 15 is formed into a rectangular shape to be fitted in the key grooves 13 and 14 with a rectangular shape. That is, rotation of the slide valve 8 in the circumferential direction is restricted by the key grooves 13 and 14 and the key 15.
Note that the rectangular shape of the key grooves 13 and 14 means that the key grooves 13 and 14 have the rectangular shape when the slide valve 8 is viewed in vertical cross-section. Between the key 15 and the key grooves 13 and 14, a slight clearance is formed which is necessary for the slide valve 8 to be slidably moved in the rotational-axis direction. The key groove 13 formed on the slide valve 8, and the key groove 14 formed on the casing 1 are configured to have an identical shape with an identical size. However, the key grooves 13 and 14 may be configured to have different shapes with different sizes. The key groove 13 formed on the slide valve 8 may be formed in the guide portion 81 or may be formed in the valve body portion 80.
It is desirable that the key 15 is made of material with a smaller linear expansion coefficient than linear expansion coefficients of the materials of the slide valve 8 and the casing 1. In the screw compressor 100, components in the vicinity of the screw rotor 5 may reach high temperature depending on the operational conditions, and thus the casing 1, the slide valve 8, and the key 15 may thermally expand. Even in this case, a slight clearance can be secured between the key 15 and the key grooves 13 and 14, so that the slide valve 8 can still be slidably moved in the rotational-axis direction of the screw rotor 5.
As described above, the screw compressor 100 according to Embodiment 1 includes the casing 1 forming an outer shell, the screw shaft 4 with one end thereof connected with the drive portion 3 to be rotationally driven, the screw rotor 5 including the tooth grooves 5a with a spiral shape on the outer circumferential surface of the screw rotor 5, the screw rotor 5 being fixed to the screw shaft 4, the gate rotor 6 including a plurality of the gate-rotor tooth portions 6a to be fitted in the tooth grooves 5a of the screw rotor 5, the gate rotor 6 forming the compression chamber 20 together with the casing 1 and the screw rotor 5, and the slide valve 8 provided in the slide groove 12 formed on the inner cylindrical surface of the casing 1 in a slidably movable manner in the rotational-axis direction of the screw rotor 5. The key grooves 13 and 14 are formed facing each other on the outer surface of the slide valve 8 and on the inner surface of the casing 1, respectively. The key 15 common to the key grooves 13 and 14 is inserted in the key grooves 13 and 14.
Therefore, the screw compressor 100 according to Embodiment 1 can prevent the slide valve 8 from contacting the screw rotor 5 since the slide valve 8 does not rotate in the circumferential direction even when there may be variations in the pressure applied to the inner cylindrical surface of the slide valve 8, the inner cylindrical surface facing the outer circumferential surface of the screw rotor 5. Consequently, the screw compressor 100 can be achieved as a reliable screw compressor that can secure a clearance between the slide valve 8 and the screw rotor 5, while minimizing a decrease in efficiency in the compressor by reducing the clearance between the slide valve 8 and the screw rotor 5 as small as possible.

Embodiment 2.

Next, with reference to Fig. 7, a screw compressor 101 according to Embodiment 2 of the present invention will be described. Fig. 7 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 2 of the present invention. Note that the constituent components that are the same as those of the screw compressor 100 described in Embodiment 1 are denoted by the same reference signs, and descriptions thereof are appropriately omitted.
In the screw compressor 101 according to Embodiment 2, key grooves 16 and 17 with a dovetail groove-like shape are formed facing each other on the outer surface of the slide valve 8 and on the inner surface of the casing 1, respectively. A key 18 common to the key grooves 16 and 17 is inserted in the key grooves 16 and 17. The key 18 is formed with its upper and lower portions relative to the midsection being formed into a dovetail shape corresponding to the dovetail groove-like shape of the key grooves 16 and 17. That is, rotation of the slide valve 8 in the circumferential direction, and movement of the slide valve 8 in the radial direction are restricted by the key grooves 16 and 17 and the key 18.
Note that the dovetail groove-like shape of the key grooves 16 and 17 means that the key grooves 16 and 17 have a trapezoidal shape when the slide valve 8 is viewed in vertical cross-section. Between the key 18 and the key grooves 16 and 17, a slight clearance is formed which is necessary for the slide valve 8 to be slidably moved in the rotational-axis direction. The key groove 16 formed on the slide valve 8, and the key groove 17 formed on the casing 1 are configured to have an identical shape with an identical size. However, the key grooves 16 and 17 may be configured to have different shapes with different sizes. The key groove 16 formed on the slide valve 8 may be formed in the guide portion 81 or may be formed in the valve body portion 80.
Note that as described in Embodiment 1, it is desirable that the key 18 is made of material with a smaller linear expansion coefficient than linear expansion coefficients of the materials of the slide valve 8 and the casing 1.
Thus, the screw compressor 101 according to Embodiment 2 can prevent the slide valve 8 from contacting the screw rotor 5 since the slide valve 8 does not rotate in the circumferential direction or move in the radial direction even when there may be variations in the pressure applied to the inner cylindrical surface of the slide valve 8, the inner cylindrical surface facing the outer circumferential surface of the screw rotor 5. Consequently, the screw compressor 100 can be achieved as a reliable screw compressor that can secure a clearance between the slide valve 8 and the screw rotor 5, while minimizing a decrease in efficiency in the compressor by reducing the clearance between the slide valve 8 and the screw rotor 5 as small as possible.

Embodiment 3.

Next, with reference to Figs. 8 and 9, a screw compressor 102 according to Embodiment 3 of the present invention will be described. Fig. 8 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 3 of the present invention. Note that the constituent components that are the same as those of the screw compressor 100 described in Embodiment 1 are denoted by the same reference signs, and descriptions thereof are appropriately omitted.
As illustrated in Fig. 8, in the configuration of the screw compressor 102 according to Embodiment 3, the key groove 14 with a rectangular shape is formed on the inner surface of the casing 1, which is one of the outer surface of the slide valve 8 and the inner surface of the casing 1, and a projecting portion 15a having a rectangular shape to be fitted in the key groove 14 is formed on the outer surface of the slide valve 8. That is, the screw compressor 102 according to Embodiment 3 is characterized in that the key 15 explained in Embodiment 1 described above is provided integrally with the slide valve 8. Thus, the screw compressor 102 according to Embodiment 3 can omit the key 15 and accordingly reduce the number of parts, and consequently can contribute to a cost reduction and improve product management.
Note that in the screw compressor 102 according to Embodiment 3, rotation of the slide valve 8 in the circumferential direction is restricted by the key groove 14 and the projecting portion 15a, and thus the screw compressor 102 can prevent the slide valve 8 from contacting the screw rotor 5 since the slide valve 8 does not rotate in the circumferential direction even when there may be variations in the pressure applied to the inner cylindrical surface of the slide valve 8, the inner cylindrical surface facing the outer circumferential surface of the screw rotor 5. Consequently, the screw compressor 102 can be achieved as a reliable screw compressor that can secure a clearance between the slide valve 8 and the screw rotor 5, while minimizing a decrease in efficiency in the compressor by reducing the clearance between the slide valve 8 and the screw rotor 5 as small as possible.
Fig. 9 is an enlarged cross-sectional view illustrating principal parts of a modification of the screw compressor according to Embodiment 3 of the present invention. In the screw compressor 102 according to Embodiment 3 illustrated in Fig. 9, the key groove 13 with a rectangular shape is formed on the outer surface of the slide valve 8, which is one of the outer surface of the slide valve 8 and the inner surface of the casing 1, and a projecting portion 15b having a rectangular shape to be fitted in the key groove 13 is formed on the inner surface of the casing 1. The screw compressor 102 according to Embodiment 3 illustrated in Fig. 9 also achieves the same effects as those obtained from the configuration illustrated in Fig. 8.

Embodiment 4.

Next, with reference to Figs. 10 and 11, a screw compressor 103 according to Embodiment 4 of the present invention will be described. Fig. 10 is an enlarged cross-sectional view illustrating principal parts of the screw compressor according to Embodiment 4 of the present invention. Note that the constituent components that are the same as those of the screw compressors 100 and 101 described in Embodiment 1 and Embodiment 2 are denoted by the same reference signs, and descriptions thereof are appropriately omitted.
As illustrated in Fig. 10, in the configuration of the screw compressor 103 according to Embodiment 4, the key groove 17 with a dovetail groove-like shape is formed on the inner surface of the casing 1, which is one of the outer surface of the slide valve 8 and the inner surface of the casing 1, and a projecting portion 18a having a dovetail shape to be fitted in the key groove 17 is formed on the outer surface of the slide valve 8. That is, the screw compressor 103 according to Embodiment 4 is characterized in that the key 18 explained in Embodiment 2 described above is provided integrally with the slide valve 8. Thus, the screw compressor 103 according to Embodiment 4 can omit the key 18 and accordingly reduce the number of parts, and consequently can contribute to a cost reduction and improve product management.
Note that in the screw compressor 103 according to Embodiment 4, rotation of the slide valve 8 in the circumferential direction, and movement of the slide valve 8 in the radial direction are restricted by the key groove 17 and the projecting portion 18a, and thus the screw compressor 103 can prevent the slide valve 8 from contacting the screw rotor 5 since the slide valve 8 does not rotate in the circumferential direction or move in the radial direction even when there may be variations in the pressure applied to the inner cylindrical surface of the slide valve 8, the inner cylindrical surface facing the outer circumferential surface of the screw rotor 5. Consequently, the screw compressor 103 can be achieved as a reliable screw compressor that can secure a clearance between the slide valve 8 and the screw rotor 5, while minimizing a decrease in efficiency in the compressor by reducing the clearance between the slide valve 8 and the screw rotor 5 as small as possible.
Fig. 11 is an enlarged cross-sectional view illustrating principal parts of a modification of the screw compressor according to Embodiment 4 of the present invention. In the configuration of the screw compressor 103 according to Embodiment 4 illustrated in Fig. 11, the key groove 16 with a dovetail groove-like shape is formed on the outer surface of the slide valve 8, which is one of the outer surface of the slide valve 8 and the inner surface of the casing 1, and a projecting portion 18b having a dovetail shape to be fitted in the key groove 16 is formed on the inner surface of the casing 1. The screw compressor 103 according to Embodiment 4 illustrated in Fig. 11 also achieves the same effects as those obtained from the configuration illustrated in Fig. 10.
While the present invention has been described above based on the embodiments, the present invention is not limited to the configuration according to the above embodiments. For example, the internal configuration of the screw compressor 100 is not limited to the particulars described above, but may include other constituent elements. The screw compressor 100 has been described by using a single-stage single screw compressor as an example, but may be, for example, a two-stage single screw compressor. The slide valve 8 is not limited to the internal volume-ratio regulating valve, but may be configured to regulate the compression capacity, for example. The number of the gate rotors 6 is not limited to two as illustrated in the drawings, but may be one. The shape of the key groove is not limited to the rectangular shape or the dovetail groove-like shape, but may be another shape. In this case, the key or the projecting portion has a shape corresponding to the key groove. To sum up, the present invention includes a range of design changes and application variations usually made by those skilled in the art without departing from the technical scope of the present invention.

Reference Signs List

1 casing 2 compression portion 3 drive portion 4 screw shaft 5 screw rotor 5a tooth groove 6 gate rotor 6a gate-rotor tooth portion 7 gate rotor support 7a gate-rotor-support tooth portion 8 slide valve 8a discharge port 9 bearing housing 10 lower-pressure space 11 higher-pressure space 12 slide groove 13, 14 key groove 15 key 15a, 15b projecting portion 16, 17 key groove 18 key 18a, 18b projecting portion 20 compression chamber 30 electric motor 31 stator 32 motor rotor 80 valve body portion 81 guide portion 82 connection portion 83 rod 84 slide-valve drive device 90 bearing 100-103 screw compressor

Claims

A screw compressor comprising:
a casing forming an outer shell;

a screw shaft located in the casing, the screw shaft being configured to be rotationally driven;

a screw rotor fixed to the screw shaft, the screw rotor including a tooth groove with a spiral shape on an outer circumferential surface of the screw rotor;

a gate rotor including a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor, the gate rotor forming a compression chamber together with the casing and the screw rotor; and

a slide valve provided in a slide groove formed on an inner cylindrical surface of the casing, the slide valve being configured to be slidably movable in a rotational-axis direction of the screw rotor, wherein

key grooves are formed facing each other on an outer surface of the slide valve and on an inner surface of the casing, and a key common to the key grooves is inserted in the key grooves.
A screw compressor comprising:
a casing forming an outer shell;

a screw shaft located in the casing, the screw shaft being configured to be rotationally driven;

a screw rotor fixed to the screw shaft, the screw rotor including a tooth groove with a spiral shape on an outer circumferential surface of the screw rotor;

a gate rotor including a plurality of gate-rotor tooth portions to be fitted in the tooth groove of the screw rotor, the gate rotor forming a compression chamber together with the casing and the screw rotor; and

a slide valve provided in a slide groove formed on an inner cylindrical surface of the casing, the slide valve being configured to be slidably movable in a rotational-axis direction of the screw rotor, wherein

a key groove is formed on one of an outer surface of the slide valve and an inner surface of the casing, and a projecting portion to be fitted in the key groove is formed on an other one.
The screw compressor of claim 1, wherein the key is made of material with a smaller linear expansion coefficient than linear expansion coefficients of materials of the slide valve and the casing.
The screw compressor of any one of claims 1 to 3, wherein the key groove has a dovetail groove-like shape.