HK1130868B - Slide valve with hot gas bypass port - Google Patents

Description

Slide valve with hot gas bypass port

Background

The present invention relates to a compressor comprising a slide valve with a hot gas bypass incorporated in the slide valve.

The compressors and the vapor compression systems in which they are installed must be capable of operating at their full capacity and at some reduced capacity depending on the application and the environment (i.e., outdoor temperature, temperature of the medium being cooled, and volume/flow rate of the medium being cooled). It may be desirable to have a compressor/system that can continuously operate at the smallest possible percentage of full load capacity to avoid on/off cycling of the compressor/system and to avoid temperature fluctuations of the cooled medium caused by the on/off cycling.

Since it is desirable to operate at less than full load capacity at certain times, compressors must have a way to vary the amount of refrigerant they compress. In many instances, screw compressors use slide valves as their unloading mechanism. As the slide valve moves toward the discharge end of the compressor, the displacement or swept volume of the compressor is reduced, which in turn reduces the amount of refrigerant drawn into, compressed by, and discharged from the compressor. It may be desirable to have the lowest possible percentage of the screw compressor achieving full load while minimizing the amount of slide valve movement necessary toward the discharge end of the compressor.

Screw compressors may also use "lift" or "poppet" valves, suction throttle valves, or hot gas bypasses (internal or external) to achieve partial unloading or unloading work. In particular, the hot gas bypass discharges refrigerant (that has been compressed) from the discharge plenum or discharge line back to the suction plenum thus displacing some of the refrigerant that would otherwise enter the compressor via the suction flange. The bypass line requires a solenoid valve to control the unloading through the bypass line. All of these methods reduce the amount of refrigerant circulating through the vapor compression system with varying efficiency levels. If either of these methods is used in conjunction with a slide valve to further reduce the amount of compressor unloading through it, they will require additional compressor/system controls. Accordingly, there is a need in the art for a slide valve that allows for greater loading of the compressor without requiring an increase in the length or size of the compressor or additional unloading control.

Summary of The Invention

The present invention provides a compressor including a slide valve and a passage in the slide valve that is fluidly connectable to a discharge plenum and a suction plenum of the compressor.

A compressor for use in an evaporative compression system includes a housing having a male rotor and a female rotor located in a cavity of the housing. The compressor includes a suction port communicating the suction plenum to the cavity volume, and a discharge port communicating the discharge plenum to the cavity volume. Refrigerant enters the chamber at a suction pressure from the suction plenum and is compressed between the male and female rotors. The refrigerant exits the chamber and flows into the discharge plenum at a discharge pressure.

The slide valve is positioned adjacent the male rotor and the female rotor. The position of the slide valve can be adjusted axially to control the amount of refrigerant drawn in and compressed in the compressor. When the slide valve is in the fully unloaded position or near the fully unloaded position, a passage in the slide valve is in fluid communication with the suction plenum and the discharge plenum. The passage has an axial portion that extends through the spool valve parallel to the axis along which the spool valve moves. The passage also includes a radial portion extending from the axial portion to the sidewall of the spool valve forming an opening. The housing blocks the opening when the slide valve is in the fully loaded or partially loaded position and becomes open in the fully unloaded position.

As the environment in which the compressor/vapor compression system operates changes, the required capacity of the compressor also changes. For example, when the condensing temperature decreases, the system, and therefore the compressor, need not be operated at full capacity to remove heat from the medium to be cooled. When the condensing temperature decreases, the controller moves the slide valve from the fully loaded position to the fully unloaded position based on the desired temperature in the medium to be cooled. At a predetermined position of the axial movement of the slide valve, the opening to the passage is no longer blocked by the compressor housing. At this time, the compressed refrigerant moves through the passage from a high pressure region near the discharge plenum to a low pressure region of the chamber near the suction plenum. The position of the opening in the spool valve determines at which point in the axial movement of the spool valve the fluid bypass begins.

The displacement volume of the compressor (or the volume of the chamber in its initial state) will be its minimum when the slide valve is in the fully unloaded position. The passage is in fluid communication with both the suction plenum and the discharge plenum. The housing no longer blocks the opening, allowing refrigerant to flow from the discharge plenum to the suction plenum through the passage. By reducing the displacement volume to the smallest possible volume and bypassing a portion of the refrigerant that has been compressed back to the suction plenum, the amount of compressed refrigerant exiting the compressor is reduced; the reduction in capacity prevents the compressor from having to cycle between operating and non-operating modes when ambient conditions exist such that the evaporator requires a reduced amount of refrigerant to achieve the desired heat transfer from the cooled medium.

When the slide valve is in a position where the passage opening is partially blocked by the housing and partially open to the discharge plenum, the shape of the opening controls the amount of refrigerant entering the passage. No additional mechanism is required to control unloading.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Brief Description of Drawings

FIG. 1 is a schematic view of an evaporative compression system of the present invention;

FIG. 2 is a side view of the compressor of the present invention;

FIG. 3 is a schematic view of the slide valve in the compressor of the present invention;

FIG. 4 is a schematic view of the spool valve of the present invention in a fully loaded position;

FIG. 5 is a schematic view of the slide valve of the present invention in a fully unloaded position;

FIG. 6 is a schematic view of the spool valve of the present invention in a partially loaded position;

FIG. 7a is an illustration of one embodiment of an opening in a spool valve of the present invention;

FIG. 7b is an illustration of a second embodiment of an opening in a spool valve of the present invention;

FIG. 7c is an illustration of a third embodiment of an opening in a spool valve of the present invention;

fig. 7d is an illustration of a fourth embodiment of an opening in a spool valve of the present invention.

Detailed description of the preferred embodiments

Fig. 1 shows an evaporative compression system 100, such as an air conditioning system, including a compressor 10 that compresses a fluid, such as a refrigerant, and delivers the refrigerant downstream to a condenser 102. In the condenser 102, the refrigerant rejects heat to an external fluid medium, such as air or water. The refrigerant moves to the expansion device 106 and is expanded to a low pressure. The refrigerant receives heat from another fluid medium in the evaporator 108. The refrigerant then flows to the compressor 10, completing the cycle.

A capacity control mechanism 112 is connected to the compressor 10. The capacity control mechanism controls the position of a slide valve 24 within the compressor 10. The capacity control mechanism 112 adjusts the piston connected to the spool valve 24 to control the position of the spool valve.

Fig. 2 shows a compressor 10. In one embodiment, the compressor 10 is a twin screw compressor. However, other versions of screw compressors (single screw or triple screw) may be advantageous according to the present invention. The male rotor 14 and the female rotor 16 in mesh are disposed in a cavity 18 of the housing 12. The compressor 10 includes a suction plenum 20 and a discharge plenum 22. Refrigerant enters the chamber 18 at a suction pressure from the suction plenum 20. The refrigerant passes between the male rotor 14 and the female rotor 16 where it is compressed within the compression chambers (chamber volumes) 26. The refrigerant exits the chamber 18 and flows into the discharge plenum 22 at a discharge pressure.

Fig. 3 shows the slide valve 24 positioned adjacent the female rotor 16 and the male rotor 14 (positioned behind the female rotor 16 in fig. 3). The position of the slide valve 24 may be adjusted axially along axis a by the capacity control mechanism 112 to adjust the volume of the compression pockets 26 and control the amount of refrigerant compressed between the male rotor 14 and the female rotor 16. That is, the slide valve 24 may reduce the displacement volume of the compression chamber 26 between the male rotor 14 and the female rotor 16 to reduce the amount of refrigerant that is compressed. Additionally, the slide valve 24 may increase the volume of the compression chamber 26 (shown in FIG. 2) to increase the amount of refrigerant that is compressed. In this way, the slide valve 24 can vary the amount of refrigerant that is compressed.

A piston 27 mounted to the spool valve 24 controls the position of the spool valve 24. The volume control mechanism 112 adjusts the position of the piston 27 by increasing or decreasing the pressure within the piston chamber 29. The piston 27 is moved axially along axis a when the pressure in the piston chamber 29 is adjusted. The piston 27 is connected to the slide valve 24. When the position of the piston 27 is adjusted, the position of the slide valve 24 is thus also adjusted.

The possible volume of the compression pockets 26 begins at the suction end 31 of the male and female rotors 14, 16 and continues to the discharge end 33 of the male and female rotors 14, 16. Thus, the position of one end 35 of the slide valve 24 determines where along the length of the male rotor 14 and female rotor 16 compression begins. For example, when the slide valve 24 is positioned as close as possible to the suction plenum 20, the compression pockets 26 begin at the suction end 31 to provide the maximum displacement volume of the compression pockets 26. This is referred to as the full load position and provides the maximum amount of compressed refrigerant leaving the compressor 10. Accordingly, as the slide valve 24 moves axially toward the discharge plenum 22, the end 35 of the slide valve 24 moves away from the suction end 31 of the male and female rotors 14 and 16, and the cavity volume begins to decrease in size, providing a partial load position. When the slide valve 24 reaches the end of its travel and is positioned as close as possible to the discharge plenum, the displacement volume of the compression chamber 26 is at a minimum volume. This is referred to as the fully unloaded position and provides the lowest amount of compressed refrigerant leaving the compressor 10.

In addition to controlling the amount of displacement volume of the compression chamber 26, the slide valve 24 unloads refrigerant from the discharge plenum 24 to the suction plenum through the passage 28, or hot gas bypass port, when in certain positions. The passage 28 allows the slide valve 24 to further vary the amount of refrigerant that is compressed, which exits the compressor 10 by returning a portion of the refrigerant to the suction plenum 20. Due to the position of the passage 28 within the slide valve 24, no further control is required to accomplish additional unloading. By reducing the displacement volume of compressor 10 to its minimum possible and practical amount while bypassing some of the compressed refrigerant from the discharge plenum back to the suction plenum, the amount of compression provided by compressor 10 is reduced and allows compressor 10 to operate continuously even when the system's demand for refrigerant flow is low. This provides a more efficient vapor compression system 100 than a compressor 10 that cycles through running and stationary modes.

Figure 4 schematically illustrates the spool valve 24 of the present invention in a fully loaded position as described above. The fully loaded position corresponds to the position of the slide valve 24 closest to the suction plenum 20 and providing the maximum displacement volume of the compressor 10. The maximum displacement volume of the compressor 10 corresponds to the maximum amount of compressed refrigerant leaving the compressor 10. This position is desirable when the compressor/system must deliver maximum capacity. A passage 28 is located within the spool valve 24. In the illustrated embodiment, the passage 28 has an axial portion 30 that extends through the spool 24 parallel to the axis A along which the spool 24 moves. The radial portion 32 extends from the axial portion 30 to at least one sidewall 34 of the spool 24 to form an opening 36. In the fully loaded position of the slide valve 24, the housing 12 blocks the opening 36 preventing refrigerant communication between the suction plenum 20 and the discharge plenum 22.

When the slide valve 24 is in the fully loaded position described above, the passage 28 is blocked to avoid the inefficiencies associated with venting already compressed vapor back to the suction plenum. Smaller compressor displacement volumes are required due to the need for reduced system capacity. The capacity control mechanism 112 thus adjusts the position of the spool 24. The slide valve 24 is adjusted toward the fully unloaded position. By reducing the displacement volume of the compression chamber 26 and allowing fluid communication between the discharge plenum 22 and the suction plenum 20 through the passage 28, the capacity of the compressor 10, and therefore the system, is reduced.

Figure 5 shows the slide valve 24 in the fully unloaded position described above. The fully unloaded position corresponds to the position of the slide valve 24 as close as possible to the discharge plenum and provides the lowest volume of refrigerant that is compressed. The initial state of compression chamber 26 when slide valve 24 is in the fully unloaded position is at its minimum volume. Such a location is desirable when minimum compressor/system capacity is required. Because it is desirable to have the compressor 10 operate at only a portion of full capacity, rather than at full capacity, the amount of compressed refrigerant exiting the compressor 10 is minimized.

In the fully unloaded position, the passage 28 is in fluid communication with both the suction plenum 20 and the discharge plenum 22. The housing 12 no longer blocks the opening 36 in the sidewall 34, allowing the compressed refrigerant to flow from the discharge plenum 22 to the suction plenum 20 due to the lower pressure in the suction plenum 20. By reducing the displacement volume of the compression chamber 26 to the smallest possible volume and bypassing a portion of the refrigerant that has been compressed back to the suction plenum 20, the amount of compressed refrigerant exiting the compressor 10 is reduced. Thus, reducing the capacity of the compressor 10 allows the compressor 10 to operate continuously to prevent cycling between the run mode and the rest mode.

Fig. 6 shows the slide valve 24 in a partially loaded position, i.e., between a fully loaded position and a fully unloaded position. The required capacity of the compressor 10 varies due to the change in the cooled environment. For example, as the outdoor ambient temperature decreases, the temperature and pressure of the refrigerant within the condenser 102 decreases. The compressor 10 need not operate at the same capacity level to achieve the desired temperature in the evaporator 108 within the system 100. As the ambient temperature decreases, the slide valve 24 begins to move from the fully loaded position to the fully unloaded position to reduce the amount of compressed refrigerant exiting the compressor 10. At a predetermined position in the axial movement of the slide valve 24, the opening 36 reaches a point at which it is no longer blocked by the housing 12. At this point, the compressed refrigerant moves from the high pressure discharge plenum 22, connected through the passage 28, to the low pressure suction plenum 20. The axial position of the opening 36 in the spool valve 24 determines at which point in the axial movement of the spool valve 24 the fluid bypass begins. The skilled person will know the required axial position for additional refrigerant unloading based on the parameters of the compressor application. As the environment being cooled in the vapor compression system 100 changes, the amount of capacity required will likewise change. The capacity control mechanism 112 thus adjusts the position of the slide valve between the fully loaded position and the fully unloaded position. Thus, the position of the spool valve 24 is continuously changed.

Fig. 7a, 7b, 7c and 7d show several embodiments of the spool 24 and the opening 36. When the spool valve 24 is in the part-load position, in which the opening 36 is partially blocked by the housing 12 and partially open to the discharge plenum 22, as shown in FIG. 6, the shape of the opening 36 controls the amount of refrigerant entering the passage 28. In fig. 7a, the openings are actually two holes 38a and 38 b. When the slide valve 24 is in the position shown in fig. 6, one of the orifices 38b can be blocked by the housing 12 while the other orifice 38a is exposed to the discharge plenum 22. In fig. 7b, the opening 40 is shown at an angle to the axial portion 30 of the channel 28. The shape of the opening 40 enables the amount of refrigerant entering the passage 28 to increase throughout the movement of the slide valve 24. Similarly, FIG. 7c shows an oblong opening 42 parallel to the axial portion 30 of the channel 28. The oblong opening 42 will require more displacement than the amount of displacement required to expose the opening 40. Fig. 7d shows the opening 36 described in the first embodiment above. The opening 36 provides a single bore that connects to the axial portion 30 of the channel 28.

Although several embodiments are shown, other shapes and locations of the openings 36 may be used. The skilled person will know the required shape and location of the opening 36 for each compressor application.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (14)

1. A compressor, comprising:

a housing including a chamber in fluid communication with a suction plenum and a discharge plenum;

a pair of rotors positioned in the cavity in meshing engagement with one another to compress fluid from a suction pressure at the suction plenum to a discharge pressure at the discharge plenum;

a slide valve adjacent said pair of rotors including a passage having an axial portion extending partially along an axial length of said slide valve and a radial portion extending between said axial portion and a sidewall of said slide valve, said axial portion extending from a suction end of said slide valve and said radial portion defining an opening in said sidewall,

wherein the passage is in fluid communication with the discharge plenum to allow the fluid to flow from the discharge plenum to the suction plenum when the slide valve is in a fully unloaded position within the housing; and

wherein the passage is blocked by the housing when the slide valve is in a fully loaded position within the housing to prevent fluid communication between the discharge plenum and the suction plenum to prevent the fluid from flowing from the discharge plenum to the suction plenum.

2. The compressor of claim 1, wherein said passage is in fluid communication with said discharge plenum when said slide valve is in a partially unloaded position within said housing, and said opening in said side wall is partially exposed to said discharge plenum to enable said fluid to flow from said discharge plenum to said suction plenum.

3. The compressor of claim 1, wherein said opening has a substantially uniform cross-section.

4. The compressor of claim 1, wherein said passage includes a second radial portion extending between said axial portion of said slide valve and said side wall to create a second opening in said side wall, and said second opening is fully exposed to said discharge plenum when said slide valve is in said fully unloaded position, and said second opening is blocked by said housing when said slide valve is in a fully loaded position.

5. The compressor of claim 1, further comprising a control mechanism connected to said slide valve, wherein the position of said slide valve within said housing is controlled by said control mechanism.

6. A compressor, comprising:

a housing including a cavity in fluid communication with a suction plenum and a discharge plenum;

a pair of rotors positioned in meshing engagement with each other within said chamber to compress fluid from a suction pressure at said suction plenum to a discharge pressure at said discharge plenum; and

a slide valve adjacent said pair of rotors including a passage including a sidewall, an axial portion extending partially along an axial length of said slide valve, and a radial portion extending between said axial portion of said slide valve and said sidewall to define an opening in said sidewall,

wherein the passage allows the fluid to flow along the passage from the discharge plenum to the suction plenum when the slide valve is in one of a fully unloaded position and a partially unloaded position, and the passage is blocked by the housing to prevent the fluid from flowing from the discharge plenum to the suction plenum when the slide valve is in a fully loaded position.

7. The compressor of claim 6, wherein the fully unloaded position corresponds to the opening in the sidewall being fully exposed to the discharge plenum to allow the fluid to flow along the passage from the discharge plenum to the suction plenum.

8. The compressor of claim 6, wherein the fully loaded position corresponds to the opening in the sidewall being blocked by a housing of the compressor to prevent the fluid from flowing along the passage from the discharge plenum to the suction plenum.

9. The compressor of claim 6, wherein said opening has a substantially uniform cross-section.

10. The compressor of claim 6, wherein said passage includes a second radial portion extending between said axial portion of said slide valve and said side wall to create a second opening in said side wall, and said second opening is fully exposed to said discharge plenum when said slide valve is in said fully unloaded position, and said second opening is blocked by said housing when said slide valve is in a fully loaded position.

11. The compressor of claim 6, wherein a control mechanism is connected to said slide valve, wherein the position of said slide valve within said housing is controlled by said control mechanism.

12. A method of controlling the capacity of a compressor as claimed in any one of claims 1 to 11, comprising the steps of:

compressing a fluid from a suction pressure at a suction plenum to a discharge pressure at a discharge plenum using a pair of rotors of a compressor; and

selectively delivering a portion of fluid from a discharge plenum to a suction plenum through a passage in a slide valve adjacent a pair of rotors to control a capacity of the compressor, wherein the passage includes an axial portion extending partially along an axial length of the slide valve and a radial portion extending between the axial portion and a sidewall of the slide valve.

13. The method of claim 12, wherein the selectively delivering step includes adjusting a position of the slide valve to place an opening defined by the passage in fluid communication with the discharge plenum to allow fluid to flow from the discharge plenum to the suction plenum.

14. The method of claim 12, wherein the selectively delivering step includes adjusting a position of the slide valve to block a passage in the slide valve with the housing to prevent fluid communication between the discharge plenum and the suction plenum via the passage.