CN210127943U9

CN210127943U9 - Screw compressor

Info

Publication number: CN210127943U9
Application number: CN201690001836.6U
Authority: CN
Inventors: 伊藤健
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-12-16
Filing date: 2016-12-16
Publication date: 2020-04-17
Anticipated expiration: 2026-12-16
Also published as: WO2018109939A1; EP3557063A1; EP3557063A4; EP3557063B1; CN210127943U; JPWO2018109939A1

Abstract

The utility model discloses a screw compressor, when the screw rotor counter-rotation, the front end of the tooth portion of gate rotor becomes the non-contact structure with at least some of the region of discharge lateral wall portion opposition, discharge lateral wall portion is the wall that forms the discharge side that supplies the engaged helicla flute of the front end of tooth portion.

Description

Screw compressor

Technical Field

The present invention relates to a screw compressor, and more particularly, to a countermeasure for preventing damage to a gate rotor.

Background

A single screw compressor used as a compressor for cooling, air conditioning, and the like has been known. For example, a single screw compressor of patent document 1 includes: a screw rotor having a plurality of spiral grooves on an outer circumferential portion thereof; and two disk-shaped gate rotors, the teeth of which are arranged radially. The screw rotor is rotatably disposed in a cylindrical wall provided in a casing of the compressor. The gate rotor is configured such that the tooth portions penetrate the cylindrical wall and mesh with the spiral grooves. The axial cores of the two gate rotors are orthogonal to the axial core of the screw rotor and are symmetrically arranged with the screw rotor therebetween. Two compression chambers are formed in the cylindrical wall by the inner circumferential surface of the cylindrical wall, the spiral groove, and the tooth portion of the gate rotor.

In this single screw compressor, the following operations are repeated with the rotation of the screw rotor: that is, the tooth portion of the gate rotor moves in the spiral groove, and the volume of the compression chamber is enlarged and then reduced. While the volume of the compression chamber is expanding, the refrigerant is sucked into the compression chamber, and when the volume of the compression chamber starts to decrease, the sucked refrigerant is compressed. When the spiral groove constituting the compression chamber communicates with the discharge port, the compressed high-pressure refrigerant is discharged from the compression chamber through the discharge port.

In a single screw compressor in operation, a screw rotor is rotated while a suction-side surface of a pair of circumferentially opposed side surfaces of a tooth portion of a gate rotor, which side surface is located on a suction side in a state where the tooth portion is meshed with a spiral groove, is in contact with a wall portion constituting the spiral groove. On the other hand, the screw rotor rotates reversely due to the difference in high and low pressures of the refrigerant during the stop. When the screw rotor rotates in reverse, the discharge-side surface of the pair of side surfaces of the tooth portion rotates while contacting the wall portion constituting the spiral groove. The gate rotor may be damaged or worn due to the reverse rotation.

Therefore, in the single screw compressor of patent document 1, the refrigerant gas is injected from the economizer port into the spiral groove at the time of stop to reduce the difference in high and low pressures, thereby suppressing the reverse rotation time and suppressing damage or wear of the gate rotor.

Patent document 1: japanese laid-open patent publication No. 2013-136957

However, the structure of patent document 1 is premised on the provision of an economizer port for introducing refrigerant gas into a compression chamber, and therefore cannot be applied to a compressor without an economizer port.

SUMMERY OF THE UTILITY MODEL

The present invention has been made in view of the above problems, and an object of the present invention is to suppress damage or wear of a gate rotor when a screw rotor rotates reversely.

The utility model discloses a screw compressor possesses: a screw rotor having a plurality of spiral grooves formed on an outer circumferential surface thereof, one end of the screw rotor serving as a fluid suction side and the other end serving as a discharge side; and a gate rotor having a plurality of teeth formed on an outer peripheral portion thereof to mesh with the spiral groove, the gate rotor rotating with rotation of the screw rotor to compress the fluid, wherein at least a portion of a region where tip portions of the teeth face a discharge side wall portion which is a wall forming a discharge side of the spiral groove with which the tip portions of the teeth mesh is in a non-contact structure when the screw rotor rotates in reverse.

Preferably, the non-contact structure is configured to have a gap between a tip end portion of the tooth portion and the discharge side wall portion.

Preferably, a tip end portion of a discharge-side surface, which becomes a discharge side in a state where the tooth portion is meshed with the spiral groove, of a pair of circumferentially opposed side surfaces of the tooth portion is located closer to a suction side than a portion other than the tip end portion, and a tooth width of the tip end portion of the tooth portion is shorter than other portions.

Preferably, the tooth portion has a shape in which a corner portion of the discharge side of the tip portion is cut off.

Preferably, the gap is 20 to 70 μm.

Preferably, a region of the discharge side wall portion facing the tip end portion of the tooth portion is located closer to the discharge side than other regions during the reverse rotation, a groove width of the spiral groove is increased on the discharge side, and the gap is formed between the tip end portion of the tooth portion and the discharge side wall portion.

Preferably, the fluid discharge device further includes a casing having a discharge port for discharging the compressed fluid, wherein a region communicating with the discharge port on a front end side in a rotation direction of the screw rotor during reverse rotation among regions opposed to the front end portions of the tooth portions in the discharge side wall portions during reverse rotation is located on a discharge side with respect to other regions, a groove width of the spiral groove is widened on the discharge side, and the gap is formed between the front end portions of the tooth portions and the discharge side wall portions.

According to the screw compressor of the present invention, at the time of reverse rotation, at least a part of the region where the tip portion of the tooth portion of the gate rotor is opposed to the discharge side wall portion is formed in the non-contact structure, and the discharge side wall portion is formed in the spiral groove in which the tip portion of the tooth portion is engaged, so that damage or wear of the gate rotor can be suppressed.

Drawings

Fig. 1 is a schematic sectional view of a screw compressor according to embodiment 1 of the present invention.

Fig. 2 is a perspective view showing a meshing portion between a helical groove of a screw rotor and a tooth portion of a gate rotor in a screw compressor according to embodiment 1 of the present invention.

Fig. 3(a) to 3(c) are explanatory views of the operation of the screw compressor according to embodiment 1 of the present invention.

Fig. 4 is an explanatory diagram of the position of the tooth portion of the gate rotor with respect to the spiral groove when the spiral rotor is rotating.

Fig. 5 is an explanatory diagram of the positions of the teeth of the gate rotor with respect to the spiral grooves when the spiral rotor is rotated reversely.

Fig. 6 is an enlarged schematic view showing a part of a screw compressor according to embodiment 1 of the present invention.

Fig. 7 is a schematic sectional view of a main part of a screw compressor according to embodiment 2 of the present invention.

Fig. 8 is a view of the groove bottom of the spiral groove of the screw compressor according to embodiment 2 of the present invention.

Fig. 9 is a schematic sectional view of a main part of a screw compressor according to embodiment 3 of the present invention.

Fig. 10 is a view of the groove bottom of the spiral groove of the screw compressor according to embodiment 3 of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Note that, in the drawings, the same or corresponding structures are denoted by the same reference numerals, and this is common throughout the specification. Note that the form of the constituent elements shown throughout the specification is merely an example, and is not limited to the above description.

Embodiment 1.

A screw compressor according to embodiment 1 will be described with reference to fig. 1 to 6. The screw compressor is connected to a refrigeration circuit that circulates a refrigerant to perform a vapor compression refrigeration cycle.

Fig. 1 is a schematic sectional view of a screw compressor according to embodiment 1 of the present invention. In fig. 1, the right side is a suction side, and the left side is a discharge side. Fig. 2 is a perspective view showing a meshing portion between a helical groove of a screw rotor and a tooth portion of a gate rotor in a screw compressor according to embodiment 1 of the present invention. In fig. 2, the right-rear side is a suction side, and the left-lower side is a discharge side. In fig. 2, solid arrows indicate the rotation direction of the screw shaft, and hollow arrows indicate the state in which suction gas is sucked.

The screw compressor 1 according to embodiment 1 is a single screw compressor, and here, embodiment 1 will be described by taking an example of a single screw compressor of a type in which two gate rotors 7 mesh with one screw rotor 5.

As shown in fig. 1, the screw compressor 1 includes a cylindrical casing 2, a motor 3 housed in the casing 2, a screw shaft 4 fixed to the motor 3 and rotationally driven by the motor 3, a screw rotor 5 fixed to the screw shaft 4, and the like. The end of the screw shaft 4 not fixed to the motor 3 is rotatably supported by a bearing 6.

The motor 3 includes a stator 3a fixed to the housing 2 in an inscribed manner and a motor rotor 3b disposed inside the stator 3 a. The motor rotor 3b is fixed to the screw shaft 4 in the same manner as the screw rotor 5 and is disposed on the same axis as the screw rotor 5.

The screw rotor 5 is cylindrical, and a plurality of helical grooves 5a extending spirally from one end of the screw rotor 5 to the other end are formed in the outer circumferential portion. One end side (right side in fig. 1) of the screw rotor 5 serves as a refrigerant gas suction side, and the other end side (left side in fig. 1) serves as a refrigerant gas discharge side. The inside of the casing 2 is partitioned by a partition wall (not shown) into a suction pressure space filled with a low-pressure refrigerant gas and a discharge pressure space filled with a high-pressure refrigerant gas, and one end side of the screw rotor 5 communicates with the suction pressure space and the other end side communicates with the discharge pressure space.

Two gate rotors 7 are disposed on the side surfaces of the screw rotor 5 so as to be axisymmetrical with respect to the screw shaft 4.

The gate rotor 7 is disc-shaped, has a plurality of teeth 7a radially arranged in the circumferential direction on the outer circumferential surface, and is supported by the gate rotor support 8. The gate rotor 7 is arranged such that the tooth portion 7a meshes with the helical groove 5a of the screw rotor 5, and a compression chamber 10 is formed by a space surrounded by the helical groove 5a, the tooth portion 7a of the gate rotor 7, the inner circumferential surface of the housing 2, and the slide valve 9. The compression chamber 10 is filled with refrigerant gas sucked from the suction pressure space, and oil for lubricating the bearing 6 and sealing the compression chamber 10 is injected.

Further, a slide valve 9 is disposed between the inner peripheral surface of the housing 2 and the screw rotor 5. The spool valve 9 is provided slidably in the direction of the screw axis 4 of the screw rotor 5 along the outer peripheral surface of the screw rotor 5, and has an opening 9 a.

The casing 2 is formed with a discharge port 2a (see fig. 3a to 3 c described later) connected to a discharge chamber 11 formed as a partition in the casing 2. The high-pressure refrigerant gas and oil filled in the compression chamber 10 pass through the opening 9a of the spool valve 9 and are then discharged to the discharge chamber 11 through the discharge port 2 a.

Next, an operation of the screw compressor 1 according to embodiment 1 will be described.

In the screw compressor 1, when the motor 3 is started, the screw rotor 5 rotates along with the rotation of the screw shaft 4. The rotation here is a positive rotation. As the screw rotor 5 rotates, the gate rotor 7 also rotates, and the intake stroke, the compression stroke, and the discharge stroke are repeated in the compression chamber 10. Here, the compression operation will be described with attention paid to the compression chamber 10 indicated with dots in fig. 3(a) to 3 (c).

Fig. 3(a) shows a state of the compression chamber 10 in the intake stroke. The spiral groove 5a formed with the compression chamber 10 is engaged with the tooth portion 7a of the gate rotor 7. Then, the screw rotor 5 is driven by the motor 3 to rotate in the direction of the solid arrow, the teeth 7a move relatively toward the end of the spiral groove 5a, and the gate rotor 7 rotates in the direction of the thin hollow arrow. The compression chamber 10 in the intake stroke has the largest volume, communicates with the space on the intake side of the casing 2, and is filled with low-pressure refrigerant gas.

When the screw rotor 5 rotates, the teeth 7a of the gate rotor 7 sequentially rotate toward the discharge port 2a in conjunction with the rotation, whereby the volume of the compression chamber 10 is reduced and the refrigerant gas in the compression chamber 10 is compressed as shown in fig. 3 (b).

When the screw rotor 5 continues to rotate, the compression chamber 10 communicates with the discharge port 2a as shown in fig. 3 (c). As a result, the high-pressure refrigerant gas compressed in the compression chamber is discharged from the discharge port 2a to the discharge chamber 11 through the opening 9a of the slide valve 9, which is not shown in fig. 3(a) to 3 (c). The refrigerant discharged to the discharge chamber 11 is discharged to the outside of the screw compressor 1.

During operation of the screw compressor 1, the pressure in the compression chamber 10 gradually increases in the order of (a) > (b) > (c), and becomes high in the order of (c). When the operation of the screw compressor 1 is stopped, the screw rotor 5 is reversely rotated by the pressure difference between the low pressure side and the high pressure side of the screw rotor 5 as described above. If the screw rotor 5 is rotated reversely, the pressure in the compression chamber 10 is lower than the pressure on the suction side, and the gate rotor 7 is damaged in the improved existing structure. This phenomenon will be described again with reference to fig. 4 and 5.

Fig. 4 is an explanatory diagram of the position of the tooth portion of the gate rotor with respect to the spiral groove when the spiral rotor is rotating. Fig. 5 is an explanatory diagram of the positions of the teeth of the gate rotor with respect to the spiral grooves when the spiral rotor is rotated reversely. Fig. 4 and 5 each show one spiral groove along with the tooth portion of the gate rotor engaged with the spiral groove. The arrow in fig. 4 indicates the moving direction when the screw rotor 5 is rotating forward, and the arrow in fig. 5 indicates the moving direction when the screw rotor 5 is rotating backward. In fig. 4 and 5, the right side is a suction side, and the left side is a discharge side.

During operation of the screw compressor 1, that is, while the screw rotor 5 is rotating, as shown in fig. 2 and 4, the teeth 7a of the gate rotor 7 are in contact with the suction-side wall portion 5bb, which is the wall portion on the suction side of the two wall portions 5b constituting the spiral groove 5a into which the teeth 7a bite. More specifically, the suction-side surface 7c of the tooth portion 7a is in contact with the suction-side wall portion 5 bb. The suction-side surface 7c is a side surface on the suction side in a state where the tooth portion 7a is engaged with the spiral groove 5a, out of a pair of circumferentially opposing side surfaces of the tooth portion 7 a. Hereinafter, the discharge side of the pair of circumferentially opposed side surfaces of the tooth portion 7a is referred to as a discharge side surface 7 b. Of the two wall portions 5b, the wall portion on the discharge side is referred to as a discharge side wall portion 5 ba.

On the other hand, when the screw rotor 5 rotates reversely and the pressure in the compression chamber 10 becomes lower than the pressure in the suction chamber, a pressing force in the direction opposite to the operation acts on the gate rotor 7, and the discharge side surface 7b of the tooth portion 7a comes into contact with the discharge side wall portion 5ba as shown in fig. 5. The portions shown by the broken lines in fig. 5 represent the tooth shapes of the conventional tooth portions having the same tooth width of the tooth portion 7a from the root to the tip, and the solid lines represent the tooth portions 7a of embodiment 1.

In the reverse rotation, when the teeth 7a of the gate rotor 7 bite into the screw rotor 5, the discharge-side surfaces 7b of the teeth 7a come into contact with the discharge side wall portion 5 ba. Here, the tip portions 70 of the discharge side surfaces 7b of the tooth portions 7a are always in contact with the discharge side wall portion 5ba in the reverse rotation.

Here, attention is paid to the tooth portion 7a which meshes with the spiral groove 5a communicating with the discharge port 2a when switching from the forward rotation to the reverse rotation. In the state of fig. 2, the tooth portion 7a communicating with the discharge port 2a does not contact the discharge side wall portion 5ba from the central portion to the root portion of the discharge side surface 7b of the tooth portion 7a, and only the tip portion 70 contacts. Before the tooth portion 7a is disengaged from the spiral groove 5a by the reverse rotation from this state, the tip portion 70 of the discharge side surface 7b of the tooth portion 7a is always in contact with the discharge side wall portion 5 ba.

In this way, during the reverse rotation, the tip end portions 70 of the discharge side surfaces 7b of the tooth portions 7a are in contact with the discharge side wall portion 5ba for a longer time than the central portion and the root portion of the discharge side surfaces 7b, and therefore, damage or abrasion is likely to occur.

As shown in fig. 4 and 5, in the tooth portion 7a of the gate rotor 7, the angle formed by the surface 7d of the tooth portion 7a and the suction-side surface 7c is an obtuse angle, whereas the angle formed by the surface 7d and the discharge-side surface 7b is an acute angle, that is, the thickness of the tooth portion 7a on the discharge side is reduced. In the tooth portion 7a of the gate rotor 7, the acute angle between the surface 7d and the discharge-side surface 7b is not the entire discharge-side end of the tooth portion 7a but the tip end of the discharge side, and the other part is an obtuse angle. Thus, the thickness reduction of the discharge-side tip portions of the tooth portions 7a does not become a factor that the tooth portions 7a are easily damaged. The reason why the angle of the tooth portion 7a is formed to be an acute angle and an obtuse angle depending on the position is: the tangential angle of the discharge side wall portion 5b with respect to the spiral groove 5a becomes closer to perpendicular as it approaches the discharge side.

Therefore, in embodiment 1, the following structure is adopted in order to prevent damage to the gate rotor 7.

In embodiment 1, as shown in fig. 6, a gap 12 is provided between the tip end portion of the tooth portion 7a and the discharge side wall portion 5 ba. That is, the tip end portion 7ba of the discharge side surface 7b of the tooth portion 7a is positioned closer to the suction side than the other portions, and the tooth width of the tip end portion of the tooth portion 7a is smaller than the tooth width of the other portions. More specifically, the tooth portion 7a is formed by cutting off a corner portion indicated by a broken line in fig. 5, which is formed by the discharge-side surface 7b and the leading end surface 7e of the conventional tooth portion 7 a. In this way, the tip end portion 7ba of the discharge side surface 7b of the tooth portion 7a is formed in a non-contact structure not contacting the discharge side wall portion 5ba in a state where the tooth portion 7a meshes with the spiral groove 5 a.

The gaps 12 are uniform in each tooth portion 7a of the gate rotor 7, and a preferable gap size is set to 20 μm to 70 μm, for example. The gap 12 is always formed while the tooth portion 7a bites into the spiral groove 5 a.

With this configuration, during the reverse rotation, the tooth portions 7a come close to the discharge side wall portion 5ba side of the screw rotor 5 and come into contact with the discharge side wall portion 5ba as shown in fig. 5, but the center portions to the root portions of the tooth portions 7a are brought into contact, and the tip end portions are not brought into contact. Therefore, damage to the tip end of the tooth portion 7a can be suppressed.

Effect of embodiment 1

According to embodiment 1, since the gap 12 is provided between the tip end portion of the tooth portion 7a of the gate rotor 7 and the discharge side wall portion 5ba, damage and wear of the tip end portion of the tooth portion 7a of the gate rotor 7 during reverse rotation can be suppressed. By providing the gap 12 in this way, the portion of the tooth portion 7a that contacts the discharge side wall portion 5ba during reverse rotation is from the center portion to the root portion of the tooth portion 7 a. The portion from the center to the root of the tooth portion 7a is a portion where the angle between the suction-side surface 7c of the tooth portion 7a and the surface 7d is not acute but obtuse as in the tip portion and has high strength. Therefore, in this respect, it is possible to suppress damage to the gate rotor 7 and to suppress degradation of performance.

In addition, when the damage of the gate rotor 7 is suppressed in this way, it is only necessary to provide the gap 12 without providing a complicated control mechanism or member, and therefore, the damage of the gate rotor 7 can be easily suppressed without increasing the number of constituent members. In addition, when the gap 12 is provided, the shape of the tip of the tooth portion 7a can be easily applied to existing products because the shape of the tip of the tooth portion of the existing conventional structure in which the tooth width is the same from the root to the tip is only required to be changed.

Embodiment 2.

In embodiment 1, as a structure for forming a gap between the tip end portion of the tooth portion 7a and the discharge side wall portion 5ba, the tip end portion 7ba of the discharge side surface 7b of the tooth portion 7a is positioned closer to the suction side, and the tooth width on the tip side of the tooth portion 7a is shorter than the tooth width on the root side of the tooth portion 7 a. In contrast, embodiment 2 is different from embodiment 1 in the configuration for forming the gap between the tip end portion of the tooth portion 7a and the discharge side wall portion 5 ba. Hereinafter, differences from embodiment 1 will be mainly described, and configurations not described in embodiment 2 are the same as those in embodiment 1.

Fig. 7 is a schematic sectional view of a main part of a screw compressor according to embodiment 2 of the present invention. Fig. 8 is a view of the groove bottom of the spiral groove of the screw compressor according to embodiment 2 of the present invention.

In embodiment 2, the region 5c of the discharge side wall portion 5ba that faces the tip end portion of the tooth portion 7a during reverse rotation is located on the discharge side of the other regions, and a gap 13 is formed between the tip end portion of the tooth portion 7a and the discharge side wall portion 5 ba. In fig. 8, the two-dot chain line indicates the position of the discharge side wall portion 5ba in the other area of the discharge side wall portion 5ba where the gap 13 is not formed.

The region 5c is a region equivalent to the thickness from the groove bottom to the tooth portion 7a in the discharge side wall portion 5ba and extending in the groove direction (arrow direction in fig. 8) of the spiral groove 5 a. The length of the gap 13 in the groove direction is at least the length over which the tooth portion 7a moves in the spiral groove 5a during the period from the state in which the tooth portion 7a is engaged with the spiral groove 5a to the state in which the tooth portion is disengaged during reverse rotation. The gap 13 is always formed while the tooth portion 7a bites into the spiral groove 5 a.

Effect of embodiment 2

According to embodiment 2, the same effects as those of embodiment 1 can be obtained.

Embodiment 3.

In embodiment 2 described above, the gap 13 is formed to extend in the groove direction of the spiral groove 5 a. In embodiment 3, the length of the gap 13 in the groove direction is shorter than that in embodiment 2, and the position thereof is limited. Hereinafter, differences from embodiment 2 will be mainly described, and configurations not described in embodiment 3 are the same as those in embodiment 2.

Fig. 9 is a schematic sectional view of a main part of a screw compressor according to embodiment 3 of the present invention. Fig. 10 is a view of the groove bottom of the spiral groove of the screw compressor according to embodiment 3 of the present invention.

In embodiment 3, a part of the region of the discharge side wall portion 5ba facing the tip end portions of the tooth portions 7a in the reverse rotation, that is, the region extending in the groove direction (arrow direction in fig. 10) is located on the discharge side of the other region, and the groove width is enlarged and increased on the discharge side. Specifically, a part of the region extending in the groove direction (arrow direction in fig. 10) is an end region on the tip side in the rotation direction of the screw rotor 5 at the time of reverse rotation, that is, a region communicating with the discharge port 2a (see fig. 2).

In this area, a gap 13 is provided so that the contact between the screw rotor 5 and the gate rotor 7 in the area communicating with the discharge port 2a at the time of reverse rotation, that is, the contact between the discharge side wall portion 5ba of the screw rotor 5 and the discharge side surface 7b of the gate rotor 7 disappears. Therefore, the time for which the tip end portion of the gate rotor 7 contacts the discharge side wall portion 5ba of the screw rotor 5 is shortened, and therefore the effect of suppressing the breakage of the gate rotor 7 can be sufficiently obtained.

In addition, the region where the gap 13 is provided is narrowed to the region communicating with the discharge port 2a in the spiral groove 5a, and the length of the gap 13 in the groove direction becomes shorter than that of embodiment 2. As a result, the length of the gap 13 in the groove direction is shortened, and leakage of the refrigerant from the gap 13 during normal rotation, i.e., during normal operation, can be suppressed. Therefore, the performance during the normal operation of embodiment 3 is improved as compared with embodiments 1 and 2.

Effect of embodiment 3

According to embodiment 3, the same effects as those of embodiment 2 can be obtained, and the position of the gap 13 can be reduced to a position where the breakage suppression of the tooth portion 7a is more effective than that of embodiment 2, that is, a region communicating with the discharge port 2a, so that the following effects can be obtained. That is, as compared with embodiment 1 and embodiment 2, leakage of the refrigerant from the gap 13 during normal operation can be suppressed. Therefore, the performance during the normal operation of embodiment 3 is improved as compared with embodiments 1 and 2.

Description of reference numerals: 1 … screw compressor; 2 … shell; 2a … discharge port; 3 … motor; 3a … stator; 3b … motor rotor; 4 … helix axis; 5 … helical rotor; 5a … spiral groove; 5b … wall portion; 5ba … discharge side wall portion; 5bb … suction side wall part; region 5c …; 6 … bearing; 7 … gate rotor; 7a … teeth; 7b … discharge side; 7ba … front end portion; 7c … suction side; 7d … surface; 7e … front face; 8 … gate rotor support; 9 … a slide valve; 9a … opening; 10 … compression chamber; 11 … discharge chamber; 12 … gap; 13 … gap; 70 … front end.

Claims

1. A screw compressor is provided with:

a screw rotor having a plurality of spiral grooves formed on an outer circumferential surface thereof, one end of the screw rotor serving as a fluid suction side and the other end serving as a discharge side; and

a gate rotor having a plurality of teeth formed on an outer peripheral portion thereof to be engaged with the spiral groove,

the gate rotor rotates with the rotation of the screw rotor to compress the fluid,

the screw compressor is characterized in that it is provided with,

when the screw rotor rotates reversely, at least a part of a region where a tip of the tooth portion faces a discharge side wall portion, which is a wall forming a discharge side of the spiral groove in which the tip of the tooth portion meshes, is in a non-contact structure.

2. The screw compressor according to claim 1,

the non-contact structure is configured to have a gap between a tip end portion of the tooth portion and the discharge side wall portion.

3. The screw compressor according to claim 1 or 2,

the tip end portion of the discharge-side surface, which becomes the discharge side in a state where the tooth portion is meshed with the spiral groove, of the pair of circumferentially opposed side surfaces of the tooth portion is located closer to the suction side than a portion other than the tip end portion, and the tooth width of the tip end portion of the tooth portion is shorter than other portions.

4. The screw compressor according to claim 1 or 2,

the tooth portion has a shape obtained by cutting off a corner portion on the discharge side of the tip portion.

5. The screw compressor according to claim 4,

the gap is 20-70 μm.

6. The screw compressor according to claim 1 or 2,

in the reverse rotation, a region of the discharge side wall portion facing the tip end portion of the tooth portion is located on the discharge side of the other region, the groove width of the spiral groove is increased on the discharge side, and the gap is formed between the tip end portion of the tooth portion and the discharge side wall portion.

7. The screw compressor according to claim 1 or 2,

a casing having a discharge port for discharging the compressed fluid,

in the discharge side wall portion, a region that is located on a front end side in a rotation direction of the screw rotor during reverse rotation and communicates with the discharge port, among regions facing the front end portions of the tooth portions at the discharge side wall portion during reverse rotation, is located on a discharge side with respect to other regions.