EP4151858A1

EP4151858A1 - Screw compressor

Info

Publication number: EP4151858A1
Application number: EP20935127.9A
Authority: EP
Inventors: Naoya MITSUNARI
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2020-05-14
Filing date: 2020-05-14
Publication date: 2023-03-22
Anticipated expiration: 2040-05-14
Also published as: WO2021229743A1; EP4151858A4; EP4151858B1

Abstract

A screw compressor includes a casing including a discharge port, a screw rotor accommodated in the casing, the screw rotor having one end side serving as a suction side in an axial direction, and an other end side serving as a discharge side in an axial direction, and a slide valve accommodated in a slide-valve accommodating groove formed in the casing, the slide valve being slidable in a rotational axis direction of the screw rotor. The slide valve includes a valve body portion. The slide valve moves to a position where the valve body portion faces the screw rotor and to a position where the valve body portion does not face the screw rotor. The valve body portion forms a portion of the discharge port when in a position facing the screw rotor.

Description

Technical Field

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

Background Art

There is a screw compressor including one screw rotor and two gate rotors.
The screw compressor has the screw rotor and the gate rotors accommodated in a casing. The screw rotor is formed with a plurality of spiral grooves. A pair of gate rotors is located in the radial direction of the screw rotor, and is in meshing engagement with the spiral grooves, thereby forming a compression chamber. On the outer circumferential side of the screw rotor, a slide valve is located. The slide valve is movable in the rotational axis direction of the screw rotor, and can vary the internal volume ratio.
The slide valve includes a valve body portion and a guide portion that guides sliding operation of the valve body portion. The valve body portion is located facing the screw rotor. The guide portion is located facing a bearing housing. The bearing housing rotatably supports the rotational shaft of the screw rotor.
In a screw compressor including this type of slide valve, the slide valve is affected by the pressure inside the compression chamber, and thus rotates in the circumferential direction along the outer circumferential surface of the screw rotor. This may bring the valve body portion into contact with the screw rotor while it is rotating, and can possibly cause problems such as seizure.
In Patent Literature 1, in view of the above, a slide valve has a shape as described below to avoid contact between a valve body portion and a screw rotor. That is, a guide portion of the slide valve includes a protruding portion on the surface of the guide portion facing the bearing housing. The protruding portion protrudes circumferentially inward relative to the valve body portion. Due to this structure, even when the slide valve rotates in the circumferential direction during operation of the compressor, the protruding portion of the guide portion touches the bearing housing before the valve body portion comes into contact with the screw rotor. This avoids contact between the valve body portion and the screw rotor, and minimizes the occurrence of problems such as seizure.

Citation List

Patent Literature

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

Summary of Invention

Technical Problem

In Patent Literature 1, before the valve body portion of the slide valve comes into contact with the screw rotor, the protruding portion of the guide portion touches the bearing housing to thereby avoid contact between the valve body portion and the screw rotor. However, in Patent Literature 1, the valve body portion of the slide valve is always in a position facing the screw rotor. Thus, in view of the fact that various gas pressures are applied to the slide valve during operation, it is uncertain about whether the slide valve can avoid contact with the screw rotor. There is thus room for improvement.
The present disclosure has been made in view of the above problems, and it is an object of the present disclosure to provide a screw compressor that can minimize contact between a slide valve and a screw rotor.

Solution to Problem

A screw compressor according to an embodiment of the present disclosure includes: a casing including a discharge port; a screw rotor accommodated in the casing, the screw rotor having one end side serving as a suction side in an axial direction, and an other end side serving as a discharge side in the axial direction; and a slide valve accommodated in a slide-valve accommodating groove formed in the casing, the slide valve being slidable in a rotational axis direction of the screw rotor, wherein the slide valve includes a valve body portion, and moves to a position where the valve body portion faces the screw rotor and to a position where the valve body portion does not face the screw rotor, and the valve body portion forms a portion of the discharge port when in a position facing the screw rotor.

Advantageous Effects of Invention

According to an embodiment of the present disclosure, the screw compressor can move the slide valve to the position where the slide valve does not face the screw rotor. This can minimize contact between the slide valve and the screw rotor.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a schematic configuration diagram of a screw compressor according to Embodiment 1 when the screw compressor is in operation at a high compression ratio.
[Fig. 2] Fig. 2 is a schematic configuration diagram of the screw compressor according to Embodiment 1 when the screw compressor is in operation at a low compression ratio.
[Figs. 3] Figs. 3 are explanatory diagrams describing the principles of compression during operation of the screw compressor according to Embodiment 1.
[Figs. 4] Figs. 4 are developed views of the outer circumferential surface of a screw rotor of the screw compressor according to Embodiment 1 to explain operation of the screw compressor at the high compression ratio.
[Figs. 5] Figs. 5 are developed views of the outer circumferential surface of the screw rotor of the screw compressor according to Embodiment 1 to explain operation of the screw compressor at the low compression ratio.
[Fig. 6] Fig. 6 is a developed view of the outer circumferential surface of the screw rotor when the screw compressor according to Embodiment 2 is in operation at the high compression ratio.
[Fig. 7] Fig. 7 is a developed view of the outer circumferential surface of the screw rotor when the screw compressor according to Embodiment 2 is in operation at the low compression ratio.

Description of Embodiments

Embodiment 1

(Description of screw compressor configuration)

Fig. 1 is a schematic configuration diagram of a screw compressor according to Embodiment 1 when the screw compressor is in operation at a high compression ratio. Fig. 2 is a schematic configuration diagram of the screw compressor according to Embodiment 1 when the screw compressor is in operation at a low compression ratio. Note that the form of the constituent elements described throughout the entire specification is merely an example, and it is not intended to limit the constituent elements to the form described in the specification.
A screw compressor 1, as its schematic configuration is illustrated in Figs. 1 and 2, includes a cylindrical casing 2, a screw rotor 3 accommodated in the casing 2, and a motor 4 configured to rotationally drive the screw rotor 3. The motor 4 includes a stator 4a in contact with the inner surface of the casing 2 and fixed thereto, and a motor rotor 4b located on the inner side of the stator 4a. The rotation speed of the motor 4 is controlled by using an inverter. The screw rotor 3 and the motor rotor 4b are located coaxially with each other, and are both fixed to a rotational shaft 5.
The screw rotor 3 has a circular columnar shape, and is formed with a plurality of spiral screw grooves 3a on the outer circumferential surface of the screw rotor 3. The screw rotor 3 is connected with the motor rotor 4b fixed to the rotational shaft 5, and is rotationally driven by the motor 4. The rotational shaft 5 has an end portion on its discharge side (on the left side in Fig. 1). The end portion is supported rotatably by a bearing housing 13. The bearing housing 13 supports the rotational shaft 5 through a main bearing 12. The rotational shaft 5 has another end portion on its suction side (on the right side in Fig. 1). The end portion is supported rotatably by a sub-bearing (not illustrated).
The screw grooves 3a are formed on the screw rotor 3. A space in the screw grooves 3a is surrounded by an inner cylindrical surface of the casing 2 and a pair of gate rotors 6 to form a compression chamber 14 that compresses refrigerant gas. The pair of gate rotors 6 includes gate-rotor tooth portions 6a that are in meshing engagement with the screw grooves 3a. The interior of the casing 2 is partitioned by a partition (not illustrated) into two sides, the suction pressure side and the discharge pressure side. On the discharge pressure side of the casing 2, a discharge port 8 is formed and opened to a discharge flow passage 7. Hereinafter, the suction pressure side that is one end side of the screw rotor 3 in the rotational axis direction is sometimes referred to as "suction side in the axial direction," while the discharge pressure side that is the other end side of the screw rotor 3 is sometimes referred to as "discharge side in the axial direction."
The casing 2 includes a cylindrical wall 2a (hereinafter, referred to as "casing cylindrical wall 2a") within which a slide-valve accommodating groove 9 is formed. The slide-valve accommodating groove 9 has a semi-cylindrical shape and extends in the rotational axis direction of the screw rotor 3. The slide-valve accommodating groove 9 has a slide valve 10 accommodated therein. The slide valve 10 has a semi-circular columnar shape and is movable in the rotational axis direction of the screw rotor 3. Two sets of the slide-valve accommodating groove 9 and the slide valve 10 are provided in the circumferential direction of the screw rotor 3.
The slide valve 10 forms a portion of the discharge port 8. Depending on the position of the slide valve 10, the timing at which the discharge port 8 opens, that is, the timing at which the compression chamber 14 communicates with the discharge flow passage 7 varies. The discharge port 8 is opened at a variable timing in this manner, so that the internal volume ratio of the screw rotor 3 is adjusted. The internal volume ratio refers to the value obtained by dividing the volume of the compression chamber 14 at the completion of suction by the volume of the compression chamber 14 at the start of discharge.
Specifically, as illustrated in Fig. 1, the slide valve 10 is positioned on the suction side in the axial direction (on the right side in Fig. 2) to delay the timing at which the discharge port 8 is opened. This increases the internal volume ratio. In contrast, as illustrated in Fig. 2, the slide valve 10 is positioned on the discharge side in the axial direction (on the left side in Fig. 2) to advance the timing at which the discharge port 8 is opened. This decreases the internal volume ratio. In this manner, the slide valve 10 can adjust the internal volume ratio to two different levels, a low internal volume ratio and a high internal volume ratio.
The slide valve 10 includes a valve body portion 10a, a guide portion 10b, and a connection portion 10c. The valve body portion 10a has a shape of a portion of a cylinder that is obtained by removing a part of the cylinder along the arc shape of the screw rotor 3 in the rotational axis direction of the screw rotor 3. The valve body portion 10a forms a portion of the discharge port 8. The guide portion 10b has a circular columnar shape, and guides movement of the valve body portion 10a. The connection portion 10c connects the valve body portion 10a and the guide portion 10b. A space between the valve body portion 10a and the guide portion 10b serves as a discharge passage communicating with the discharge flow passage 7.
The slide valve 10 has such a structure as to slide to the position where the valve body portion 10a faces the screw rotor 3 as illustrated in Fig. 1, and to the position where the valve body portion 10a does not face the screw groove 3a of the screw rotor 3 as illustrated in Fig. 2, specifically, to the position where the valve body portion 10a faces the bearing housing 13. That is, when the valve body portion 10a is in a position facing the screw groove 3a of the screw rotor 3, the internal volume ratio is increased. When the valve body portion 10a is in a position facing the bearing housing 13, the internal volume ratio is decreased.
At an end portion of the screw rotor 3 on the opposite side to the motor 4, a slide-valve drive mechanism 11 is located to slide the slide valve 10 in the rotational axis direction of the screw rotor 3. This slide-valve drive mechanism 11 enables the slide valve 10 to slide in the rotational axis direction of the screw rotor 3.
When the screw compressor is in operation at a high compression ratio at which the difference between high pressure and low pressure in a refrigeration cycle provided with the screw compressor is larger than a set pressure, the slide-valve drive mechanism 11 slides the slide valve 10 toward the high internal volume ratio side illustrated in Fig. 1. When the screw compressor is in operation at a low compression ratio at which the difference between high pressure and low pressure in the refrigeration cycle is equal to or smaller than the set pressure, the slide-valve drive mechanism 11 slides the slide valve 10 toward the low internal volume ratio side illustrated in Fig. 2. The slide-valve drive mechanism 11 is controlled by a controller (not illustrated).

(Operation)

Next, operation of the screw compressor in the present Embodiment 1 is described.
Figs. 3 are explanatory diagrams describing the principles of compression during operation of the screw compressor according to Embodiment 1. Fig. 3(a) illustrates a suction stroke. Fig. 3(b) illustrates a compression stroke. Fig. 3(c) illustrates a discharge stroke. As illustrated in Figs. 3, the screw rotor 3 is rotated by the motor 4 (see Fig. 1) through the rotational shaft 5 (see Fig. 1), so that the gate-rotor tooth portions 6a move within, and relative to, the compression chamber 14. With this movement, in the compression chamber 14 in which a suction stroke, a compression stroke, and a discharge stroke are regarded as one cycle, this cycle is repeated. Each of the strokes is described with a focus on the compression chamber 14 shown by dots in Figs. 3.
Fig. 3(a) illustrates the state of the compression chamber 14 in the suction stroke. The screw rotor 3 is driven by the motor 4 and rotates in a direction shown by the solid arrow. Due to this rotation, the volume of the compression chamber 14 is decreased as illustrated in Fig. 3(b).
Subsequently, when the screw rotor 3 further rotates, the compression chamber 14 communicates with the discharge port 8 formed by the casing cylindrical wall 2a and the valve body portion 10a of the slide valve 10 as illustrated in Fig. 3(c). This allows refrigerant gas, compressed to a high pressure in the compression chamber 14, to be discharged from the discharge port 8 to the outside of the compressor via the discharge flow passage 7. The refrigerant gas is compressed again on the back side of the screw rotor 3 in the same manner as described above.
As illustrated in Fig. 1, when the screw compressor is in operation at the high compression ratio, the valve body portion 10a of the slide valve 10 is positioned at a position where the valve body portion 10a faces the screw rotor 3. The discharge port 8 is formed by the valve body portion 10a and the cylindrical wall 2a of the casing 2.
In contrast, as illustrated in Fig. 2, when the screw compressor is in operation at the low compression ratio, the valve body portion 10a of the slide valve 10 is positioned at a position where the valve body portion 10a faces the bearing housing 13. The discharge port 8 is formed by only the casing cylindrical wall 2a.
Figs. 4 and Figs. 5 illustrate the developed views of the outer circumferential surface of the screw rotor 3, respectively, when the screw compressor is in operation at the high compression ratio and at the low compression ratio, separately in a suction stroke, a compression stroke, and a discharge stroke.
Figs. 4 are developed views of the outer circumferential surface of the screw rotor of the screw compressor according to Embodiment 1 to explain operation of the screw compressor at the high compression ratio. Fig. 4(a) illustrates a suction stroke. Fig. 4(b) illustrates a compression stroke. Fig. 4(c) illustrates a discharge stroke. The oblique hatching extending downward toward the left side in Figs. 4 illustrates the cylindrical wall 2a of the casing 2.
As illustrated in Figs. 4(a) to 4(c), when in operation at the high compression ratio, the screw compressor moves the slide valve 10 toward the suction side in the axial direction to bring a suction-side end face 10e of the valve body portion 10a (hereinafter, referred to as "valve-body suction-side end face 10e") into contact with an end face 2b of the slide-valve accommodating groove 9 on the suction side in the axial direction. At this time, the discharge port 8 is formed by the casing cylindrical wall 2a and a valve-body discharge-side end face 10d. An end face of the discharge port 8 on the suction side in the axial direction serves as the valve-body discharge-side end face 10d. Note that since the slide-valve accommodating groove 9 is formed in the casing 2, the end face 2b of the slide-valve accommodating groove 9 on the suction side in the axial direction is hereinafter referred to as "casing end face 2b."
As illustrated in Fig. 4(b), the valve-body discharge-side end face 10d is formed to have its inclination angle equivalent to the inclination angle of a side face 3b of the screw groove 3a on the discharge side in the axial direction at the moment at which the compression chamber 14 communicates with the discharge port 8 (hereinafter, "groove inclination angle at the time of communication"). As described above, the valve-body discharge-side end face 10d forms a portion of the discharge port 8 when the screw compressor is in operation at the high compression ratio, and this valve-body discharge-side end face 10d has an inclination angle equivalent to the groove inclination angle at the time of communication. This can increase the discharge area of the discharge port 8 compared to when the inclination angle of the valve-body discharge-side end face 10d is not equivalent to the groove inclination angle at the time of communication. This can reduce the pressure loss of refrigerant gas when it is discharged. Note that the inclination angle refers to an angle of the valve-body discharge-side end face 10d relative to the rotational axis direction.
Figs. 5 are developed views of the outer circumferential surface of the screw rotor of the screw compressor according to Embodiment 1 to explain operation of the screw compressor at the low compression ratio. Fig. 5(a) illustrates a suction stroke. Fig. 5(b) illustrates a compression stroke. Fig. 5(c) illustrates a discharge stroke. The oblique hatching extending downward toward the left side in Figs. 5 illustrates the cylindrical wall 2a of the casing 2.
As illustrated in Figs. 5(a) to 5(c), when in operation at the low compression ratio, the screw compressor slides the slide valve 10 toward the discharge side in the axial direction to the position where the valve body portion 10a does not face the screw groove 3a, specifically, to the position where the valve body portion 10a faces the bearing housing 13. At this time, the discharge port 8 is formed by only the casing cylindrical wall 2a. An end face of the discharge port 8 on the suction side in the axial direction serves as the casing end face 2b. That is, when the screw compressor is in operation at the low compression ratio, the discharge port 8 is formed by only the casing 2 without using the slide valve 10. This enables the valve body portion 10a of the slide valve 10 to move to the position away from the position where the valve body portion 10a faces the screw rotor 3.
When the slide valve 10 is in a position illustrated in Figs. 5, the area of the discharge port 8 on the developed view is increased by the area of the valve body portion 10a, compared to the area of the discharge port 8 in Figs. 4 described above. That is, the volume of the compression chamber 14 at the completion of discharge is increased compared to that illustrated in Figs. 4. Thus, when the slide valve 10 is in a position illustrated in Figs. 5, the internal volume ratio is decreased compared to when the slide valve 10 is in a position illustrated in Figs. 4.
As illustrated in Fig. 5(b), the casing end face 2b of the casing cylindrical wall 2a is formed to have its inclination angle equivalent to the groove inclination angle at the time of communication. As described above, when the screw compressor is in operation at the low compression ratio, the casing end face 2b forms a portion of the discharge port 8, and has an inclination angle equivalent to the groove inclination angle at the time of communication. This can reduce the pressure loss of refrigerant gas when it is discharged.
When the valve body portion 10a of the slide valve 10 is in a position not facing the screw rotor 3, the slide valve 10 in its entirety including the valve body portion 10a is in a position not facing the screw rotor 3 as illustrated in Figs. 5. When the slide valve 10 and the screw rotor 3 have this positional relationship between them during operation of the compressor, the slide valve 10 and the screw rotor 3 do not come into contact with each other. This can avoid seizure of both the slide valve 10 and the screw rotor 3.
During operation at the low compression ratio, the connection portion 10c of the slide valve 10 is not positioned in the discharge flow passage 7 (see Fig. 2). This prevents a flow of discharged gas passing through the discharge flow passage 7 from being interfered with by the connection portion 10c, and thus can reduce the pressure loss of refrigerant gas after it is discharged. The slide valve 10 moves to the position away from the compression chamber 14, and this consequently prevents the occurrence of a phenomenon in which the slide valve 10 deflects outward in the radial direction due to the difference in pressure between the compression chamber 14 and the suction pressure side. This prevents the gap between the screw rotor 3 and the valve body portion 10a of the slide valve 10 from being increased due to this deflection. Thus, the compressor can minimize leakage of refrigerant from the gap, can operate with high efficiency, and can achieve improvement in performance.
As described above, the suction-side end face of the discharge port 8 is made up of the valve-body discharge-side end face 10d when the screw compressor is in operation at the high compression ratio, while being made up of the casing end face 2b when the screw compressor is in operation at the low compression ratio. That is, when the screw compressor is in operation at the high compression ratio, the suction-side end face of the discharge port 8 is made up of a different part from that when the screw compressor is in operation at the low compression ratio. Thus, the individual inclined surfaces can be set independently from each other, and have an optimal shape for each compression ratio. Therefore, the flow passage area for refrigerant gas to be discharged from the discharge port 8 can be set separately for the high compression ratio and the low compression ratio. The pressure loss of refrigerant gas when it is discharged can be reduced. Accordingly, the screw compressor that exhibits enhanced performance can be provided.
When the compressor stops operation, reverse rotation of the screw rotor 3 causes gas in the compression chamber 14 to expand. Consequently, the pressure in the compression chamber 14 is decreased to the level below the suction pressure. At this time, the pressure difference between the pressure in the compression chamber 14 and the suction pressure causes the slide valve 10 to be drawn inward in the radial direction, that is, toward the screw rotor 3. For this reason, when the valve body portion 10a is in a position facing the screw rotor 3, there is a possibility that the valve body portion 10a may come into contact with the screw rotor 3.
In view of this, in the present Embodiment 1, immediately before the stop of operation, the compressor moves the slide valve 10 to the position where the slide valve 10 faces the bearing housing 13. This prevents the slide valve 10 from coming into contact with the screw rotor 3 during the stop of the compressor, and thus can avoid seizure of both the slide valve 10 and the screw rotor 3. As a result of this, the highly-reliable screw compressor can be provided.
As described above, the screw compressor of the present Embodiment 1 includes the casing 2 including the discharge port 8, the screw rotor 3 accommodated in the casing 2, the screw rotor 3 having one end side serving as a suction side in the axial direction, and the other end side serving as a discharge side in the axial direction, and the slide valve 10 accommodated in the slide-valve accommodating groove 9 formed in the casing 2, the slide valve 10 being slidable in the rotational axis direction of the screw rotor 3. The slide valve 10 includes the valve body portion 10a, and moves to the position where the valve body portion 10a faces the screw rotor 3 and to the position where the valve body portion 10a does not face the screw rotor 3, and the valve body portion 10a forms a portion of the discharge port 8 when in a position facing the screw rotor 3.
As described above, the screw compressor can move the slide valve 10 to the position where the slide valve 10 does not face the screw rotor 3. This can minimize contact between the slide valve 10 and the screw rotor 3 compared to the configuration in which the slide valve 10 is always in a position facing the screw rotor 3.
The screw compressor of the present Embodiment 1 includes the bearing housing 13 located on the discharge side in the axial direction of the screw rotor 3, the bearing housing 13 being configured to support the rotational shaft 5 of the screw rotor 3. The position where the valve body portion 10a of the slide valve 10 does not face the screw rotor 3 refers to the position where the valve body portion 10a of the slide valve 10 faces the bearing housing 13.
As described above, in order that the valve body portion 10a of the slide valve 10 is positioned at a position where the valve body portion 10a does not face the screw rotor 3, it suffices that the screw compressor moves the valve body portion 10a of the slide valve 10 to the position where the valve body portion 10a faces the bearing housing 13.
When the screw compressor is in operation at a low compression ratio at which the difference between high pressure and low pressure in the refrigeration cycle provided with the screw compressor is equal to or smaller than the set pressure, the valve body portion 10a of the slide valve 10 is positioned at a position where the valve body portion 10a does not face the screw rotor 3.
This can avoid contact between the slide valve 10 and the screw rotor 3 when the screw compressor is in operation at the low compression ratio.
When the screw compressor is in operation at the low compression ratio, the casing end face 2b, that is, an end face of the slide-valve accommodating groove 9 on the suction side in the axial direction also serves as an end face of the discharge port 8 on the suction side in the axial direction.
As described above, the discharge port 8 is formed by using the casing end face 2b that makes up the slide-valve accommodating groove 9, not by using the slide valve 10. Due to this structure, the screw compressor can move the slide valve 10 to the position where the valve body portion 10a does not face the screw rotor 3.
In the developed view of the outer circumferential surface of the screw rotor 3, the end face 2b of the discharge port 8 on the suction side in the axial direction has an inclination angle that is set equal to the inclination angle of the side face 3b of the screw groove 3a on the discharge side in the axial direction. The screw groove 3a is formed on the screw rotor 3 to make up the compression chamber 14.
This can reduce the pressure loss to be generated in the discharge port 8.
Immediately before the stop of operation, the valve body portion 10a of the slide valve 10 is positioned at a position where the valve body portion 10a does not face the screw rotor 3.
Due to this structure, even when the screw rotor 3 rotates reversely during the stop of operation, and thus gas in the compression chamber 14 expands, which causes the slide valve 10 to be drawn inward in the radial direction, the valve body portion 10a of the slide valve 10 can still be prevented from coming into contact with the screw rotor 3.

Embodiment 2

In the present Embodiment 2, the differences in configuration from Embodiment 1 are mainly described, and the configuration identical to that in Embodiment 1 is not described in the present Embodiment 2.
It has been described in Embodiment 1 that the casing end face 2b (see Figs. 4 and 5) of the casing 2 is formed to have its inclination angle equivalent to the groove inclination angle at the time of communication. The present Embodiment 2 relates to a suitable structure for the case where it is difficult to machine the casing 2 to form the casing end face 2b with an angle equivalent to the groove inclination angle at the time of communication.
Fig. 6 is a developed view of the outer circumferential surface of the screw rotor when a screw compressor according to Embodiment 2 is in operation at the high compression ratio. Fig. 7 is a developed view of the outer circumferential surface of the screw rotor when the screw compressor according to Embodiment 2 is in operation at the low compression ratio.
The screw compressor of Embodiment 2 further includes a compression-chamber forming component 15 having a semi-circular columnar shape in addition to the configuration in Embodiment 1. The compression-chamber forming component 15 is located on the suction side in the axial direction of the valve body portion 10a of the slide valve 10. The compression-chamber forming component 15 includes an end face 15a on the discharge side in the axial direction. The end face 15a has an inclination angle that is set equal to the inclination angle of the casing end face 2b explained above in Embodiment 1.
The compression-chamber forming component 15 is accommodated in a component accommodating groove 9a extended from the slide-valve accommodating groove 9, formed inside the casing cylindrical wall 2a, toward the suction side in the axial direction. The compression-chamber forming component 15 has a wall surface that faces the outer circumferential surface of the screw rotor 3. The wall surface has the same shape as the casing cylindrical wall 2a. The compression-chamber forming component 15 is fixed to the casing 2 by using pins 17, such that the compression-chamber forming component 15 does not move in the rotational axis direction of the screw rotor 3 or in the circumferential direction of the screw rotor 3.
The slide valve 10 operates in the same manner as in Embodiment 1 when the screw compressor operates at either the high compression ratio or the low compression ratio. That is, when in operation at the high compression ratio, the screw compressor moves the slide valve 10 toward the suction side in the axial direction as illustrated in Fig. 6 to bring the valve-body suction-side end face 10e into contact with the discharge-side end face 15a of the compression-chamber forming component 15. When in operation at the low compression ratio, the screw compressor moves the slide valve 10 toward the discharge side in the axial direction to the position where the valve body portion 10a does not face the screw groove 3a of the screw rotor 3, specifically, to the position where the valve body portion 10a faces the bearing housing 13 as illustrated in Fig. 7.
In the present Embodiment 2, the screw compressor includes the compression-chamber forming component 15 separately from the casing 2. The compression-chamber forming component 15 is provided with the end face 15a having the groove inclination angle at the time of communication. Since the compression-chamber forming component 15 has a simpler shape than the casing 2, it is easier to machine the compression-chamber forming component 15 than machining the casing 2 to form the casing end face 2b with the groove inclination angle at the time of communication.
As explained above, in the present Embodiment 2, the screw compressor includes the compression-chamber forming component 15 located in and fixed to the casing 2 on the suction side in the axial direction of the slide valve 10. When the screw compressor is in operation at the low compression ratio, the end face of the compression-chamber forming component 15 on the discharge side in the axial direction also serves as an end face of the discharge port 8 on the suction side in the axial direction.
As described above, the compression-chamber forming component 15 separate from the casing 2 can make up the end face of the discharge port 8 on the suction side in the axial direction. It is thus unnecessary for the casing 2 to be machined to form the end face of the discharge port 8 on the suction side in the axial direction. Instead, it is only necessary to machine the compression-chamber forming component 15. This facilitates the machining.
When the screw compressor is in operation at a high compression ratio at which the difference between high pressure and low pressure in the refrigeration cycle provided with the screw compressor is larger than the set pressure, the slide valve 10 is positioned at a position where the end face 10e of the valve body portion 10a of the slide valve 10 on the suction side in the axial direction comes into contact with the end face 15a of the compression-chamber forming component 15 on the discharge side in the axial direction.
As described above, when the screw compressor is in operation at the high compression ratio, the slide valve 10 is positioned at a position where the end face 10e of the valve body portion 10a on the suction side in the axial direction comes into contact with the end face 15a of the compression-chamber forming component 15 on the discharge side in the axial direction, so that the end face 10d of the valve body portion 10a on the discharge side in the axial direction can make up the end face of the discharge port 8 on the discharge side in the axial direction.
It has been described above in Embodiments 1 and 2 that the compressor is provided with two gate rotors 6. However, a compressor provided with only one gate rotor 6 is also applicable.

Reference Signs List

1: screw compressor, 2: casing, 2a: casing cylindrical wall, 2b: casing end face, 3: screw rotor, 3a: screw groove, 3b: side face, 4: motor, 4a: stator, 4b: motor rotor, 5: rotational shaft, 6: gate rotor, 6a: gate-rotor tooth portion, 7: discharge flow passage, 8: discharge port, 9: slide-valve accommodating groove, 9a: component accommodating groove, 10: slide valve, 10a: valve body portion, 10b: guide portion, 10c: connection portion, 10d: valve-body discharge-side end face, 10e: valve-body suction-side end face, 11: slide-valve drive mechanism, 12: main bearing, 13: bearing housing, 14: compression chamber, 15: compression-chamber forming component, 15a: discharge-side end face, 17: pin

Claims

A screw compressor comprising:
a casing including a discharge port;

a screw rotor accommodated in the casing, the screw rotor having one end side serving as a suction side in an axial direction, and an other end side serving as a discharge side in the axial direction; and

a slide valve accommodated in a slide-valve accommodating groove formed in the casing, the slide valve being slidable in a rotational axis direction of the screw rotor, wherein

the slide valve includes a valve body portion, and moves to a position where the valve body portion faces the screw rotor and to a position where the valve body portion does not face the screw rotor, and the valve body portion forms a portion of the discharge port when in a position facing the screw rotor.
The screw compressor of claim 1, comprising a bearing housing located on the discharge side in the axial direction of the screw rotor, the bearing housing being configured to support a rotational shaft of the screw rotor, wherein
the position where the valve body portion of the slide valve does not face the screw rotor refers to a position where the valve body portion of the slide valve faces the bearing housing.
The screw compressor of claim 1 or 2, wherein when the screw compressor is in operation at a low compression ratio at which a difference between high pressure and low pressure in a refrigeration cycle provided with the screw compressor is equal to or smaller than a set pressure, the valve body portion of the slide valve is positioned at a position where the valve body portion does not face the screw rotor.
The screw compressor of claim 3, wherein when the screw compressor is in operation at the low compression ratio, an end face of the slide-valve accommodating groove on the suction side in the axial direction also serves as an end face of the discharge port on the suction side in the axial direction.
The screw compressor of claim 3 or 4, comprising a compression-chamber forming component located in and fixed to the casing on the suction side in the axial direction of the slide valve, wherein
when the screw compressor is in operation at the low compression ratio, an end face of the compression-chamber forming component on the discharge side in the axial direction also serves as an end face of the discharge port on the suction side in the axial direction.
The screw compressor of claim 5, wherein when the screw compressor is in operation at a high compression ratio at which a difference between high pressure and low pressure in a refrigeration cycle provided with the screw compressor is larger than a set pressure, the slide valve is positioned at a position where an end face of the valve body portion of the slide valve on the suction side in the axial direction comes into contact with an end face of the compression-chamber forming component on the discharge side in the axial direction.
The screw compressor of any one of claims 4 to 6, wherein in a developed view of an outer circumferential surface of the screw rotor, the end face of the discharge port on the suction side in the axial direction has an inclination angle that is set equivalent to an inclination angle of a side face of a screw groove on the discharge side in the axial direction, the screw groove being formed on the screw rotor to make up a compression chamber.
The screw compressor of any one of claims 1 to 7, wherein immediately before a stop of operation, the valve body portion of the slide valve is positioned at a position where the valve body portion does not face the screw rotor.