Screw compressor with asymmetric ports

A multi-rotor screw compressor includes a housing, a sun rotor, and first and second planet rotors. The first planet rotor intermeshes with the sun rotor to define a first compression pair. The second planet rotor intermeshes with the sun rotor to define a second compression pair. The first and second compression pairs are rotatably mounted in the housing. The housing includes a first port, a portion of which is in communication with the first compression pair, and a second port, a portion of which is in communication with the second compression pair. The portions of the first and second ports which communicate with the first and second compression pairs have a different geometry for offsetting pulsations in a working fluid flowing through the ports.

BACKGROUND

The present invention relates to helical screw compressors. More particularly, the present invention relates to a multi-rotor screw compressor having three or more rotors.

Multi-rotor screw type compressors are typically used to compress various working fluids for air conditioning and refrigeration applications. Multi-rotor compressors generally include a housing to enclose and protect the interior components of the compressor (such as the rotors). In a multi-rotor compressor, the rotors usually include a lobed sun rotor that intermeshes with, and typically drives, multiple adjacent lobed planet rotors. The intermeshed sun rotor and each adjacent planet rotor act as a compression pair; rotating about their axes relative to the housing to move the working fluid from suction inlet ports at a low pressure to discharge outlet ports at a higher pressure. The compression of the working fluid takes place in the spaces between and adjacent the flutes and lobes of the sun and planet rotors and the housing. These spaces are typically referred to as compression pockets. Each compression pocket receives working fluid as the pocket rotates with the rotors to open to a portion of the suction port. Each compression pair is also in communication with a portion of at least one discharge port. Working fluid within each compression pocket rotates with the rotors and is discharged as the rotors align with the discharge ports.

After flowing through the discharge ports, the working fluid enters a discharge channel, which interconnects with a piping system to transfer the working fluid to other components in the air conditioning or refrigeration system. It is desirable to achieve an internal pressure of the working fluid in each compression pocket equal to the pressure in the discharge channel at the moment just before each compression pocket opens to the discharge port. If the internal pressure at this moment differs from the pressure in the discharge channel, a rapid flow of working fluid through the discharge port occurs each time each compression pocket opens. This rapid flow of working fluid allows the internal pressure and the discharge channel pressure to become equalized. The flow velocity of the working fluid through the ports during this short moment of equalization is often much higher than the flow velocity of the working fluid when it is displaced out through the discharge ports by the rotors. This increase in fluid flow velocity, (and associated pressure pulsations) causes noise that may be disturbing to individuals located near the system, and may cause pressure pulsations and vibrations in various other system components that may damage the system components. The pressure pulsations may also decrease the efficiency of the compressor. It is often difficult to adapt the internal pressure to be equal to the discharge channel pressure. This is because the difference between the discharge channel pressure and the internal pressure at the end of compression process may vary as a result of many factors including: outside ambient conditions (including temperature and humidity), condenser size, and the cooling ability of the cooling medium used at the condenser.

Similarly, a change in suction flow rate may also cause suction pressure pulsations and fluid flow surges in the suction channel upstream of the suction ports. These pulsations may result in undesirable noise and vibration, and may also detrimentally affect system operating efficiency.

Typically, multi-screw compressor designs include multiple suction ports and discharge ports which correspond to and communicate with the multiple compression pairs. The geometry (the size, shape, and disposition) of each of the multiple suction ports is identical. Likewise, the geometry of each of the discharge ports is also usually identical. The identical geometry of the ports, coupled with the fact that the planet rotors are also usually of an identical size and helical geometry, and are rotated at the same angular velocity in a sun driven multi-rotor compressor, exposes or “opens” the working fluid from each compression pocket to a portion of the ports at the same time. Similarly, each compression pocket “opens” and “closes” to a portion of the suction ports at the same time. This identical porting is due to the symmetrical geometry of the suction ports with respect to the compression pairs, and the equivalent angular velocity of the planet rotors driven by the common sun rotor.

Thus, in a typical multi-rotor compressor the simultaneous opening and closing of multiple compression pockets has the undesirable effect of increasing the flow velocity of working fluid to and from the channels, as the internal pressure of several compression pockets open simultaneously to the channel and must be equalized with the pressure in the channel. Thus, when multiple compression pockets open simultaneously (in-phase with each other), the peak amplitude of the pressure pulsations in the channels increases.

SUMMARY

A multi-rotor screw compressor includes a housing, a sun rotor, and first and second planet rotors. The first planet rotor intermeshes with the sun rotor to define a first compression pair. The second planet rotor intermeshes with the sun rotor to define a second compression pair. The first and second compression pairs are rotatably mounted in the housing. The housing includes a first port, a portion of which is in communication with the first compression pair, and a second port, a portion of which is in communication with the second compression pair. The portions of the first and second ports which communicate with the first and second compression pairs have a different geometry for offsetting pulsations in a working fluid flowing through the ports.

DETAILED DESCRIPTION

FIG. 1is a top sectional view of a compressor10in accordance with the present invention including a rotor housing section12, a motor housing section14, a motor16, a drive shaft18, rotors20, a discharge housing section22, and a discharge housing cover24. As known in the art, instead of an electric motor driven design, the rotors20can be driven by other means, as for example by being coupled to an engine. The rotors20include a sun rotor26, a first planet rotor28, and a second planet rotor30. The motor housing section14defines a suction channel32. The rotor housing section12defines a first suction port34and a second suction port36. The discharge housing section22defines a first discharge port38and a second discharge port40. The second discharge port40is disposed on the opposite radial side of the rotors20(thus would be visible to the viewer from a bottom sectional view of the compressor10), and therefore, is shown with a dashed line. The discharge housing cover24defines a discharge channel42.

FIG. 1illustrates an embodiment of the present invention in which the compressor10housing is interconnected in several sections. The sections can be separated for ease of assembly, repair or replacement of interior components of the compressor10. In other embodiments, the compressor10is comprised of a single housing. The rotor housing section12encloses the rotors20. The motor housing section14encloses the motor16which drives the rotors20via the drive shaft18. The drive shaft18extends from the motor housing section14into the rotor housing section12to turn the rotors20about an axis defined by the drive shaft18. The rotors20are rotatably disposed in the rotor housing section12. InFIG. 1, the drive shaft18aligns with and turns the sun rotor26. The sun rotor26has helical flutes and lobes that intermesh with corresponding helical flutes and lobes on the first planet rotor28and the second planet rotor30. In this configuration, the sun rotor26drives the planet rotors28,30to rotate the planet rotors28,30in the opposite direction as the sun rotor26. Although two planet rotors are portrayed inFIG. 1, more than two planet rotors may be driven by a single or multiple sun rotor(s) intermeshed with the multiple planet rotors.

A working fluid is drawn into the rotor housing section12from the motor housing section14through the suction channel32. The working fluid passes from the suction channel32through the suction ports34and36in the rotor housing section12into the portion of the rotor housing section12containing the rotors20. More specifically, the suction ports34and36define a communication pathway through the housing12, (which otherwise radially and axially surrounds a good deal of the rotors20), which allows the working fluid to pass from the suction channel32to the rotors20. A portion of each of the suction ports34and36communicates with the rotors20adjacent an axial end portion (and in some embodiments a radial portion) of the rotors20. The rotors20compress the working fluid drawn therebetween, and communicate with the first discharge port38and the second discharge port40in the discharge housing section22to discharge the working fluid through the discharge housing section22to the discharge channel42. A portion of each of the discharge ports38and40communicates with the rotors20adjacent a radial portion and a second axial end portion of the rotors20. The working fluid is discharged through the discharge ports38and40in the discharge housing section22to the discharge channel42in the discharge housing cover24. The discharge channel42interconnects with piping (not shown) to transfer compressed working fluid to the other components in the air conditioning or refrigeration system.

FIGS. 2A and 2Bare cross sectional views of the compressor10viewed from the same perspective illustrating different embodiments of the interior of the rotor housing section12upstream (as defined by the flow path of the working fluid) and immediately adjacent to the axial end portions of the rotors26,28and30. The sun rotor26and first planet rotor28cooperate to define a first compression pair44, with a first plurality of compression pockets50being defined between the flutes and lobes of a portion of the sun rotor26and the inner wall of the housing12. The first compression pockets50are also defined by any intermeshing space between the sun rotor26and the first planet rotor28, and the space between flutes and lobes of the first planet rotor28and the inner wall of the housing12. InFIGS. 2A and 2B, the portion of the first suction port34which communicates with the first compression pair44corresponds to the shaded area used to indicate the first compression pockets50which communicate directly with the first suction port34. Likewise, the sun rotor26and the second planet rotor30cooperate to define a second compression pair46, with a second plurality of compression pockets52being defined between the flutes and lobes of the sun rotor26and the inner wall of the housing12. The compression pockets52are also defined by any intermeshing space between the sun rotor26and the second planet rotor30, and the space between the flutes and lobes of the second planet rotor and the inner wall of the housing12. InFIGS. 2A and 2B, the portion of the second suction port36which communicates with the second compression pair46corresponds to the shaded area also used to indicate the second compression pockets52which communicate directly with the second suction port36.

Still referring toFIGS. 2A and 2B, the rotor housing section12is configured to define the first suction port34and the second suction port36through a wall thereof adjacent the motor housing section14.FIGS. 2A and 2Billustrate an axial section of the ports34and36. Depending upon the implementation of the compressor10, the housing12may be configured to define suction ports34and36of various shapes, volumetric capacity and dimensions. Accordingly, the suction ports34and36are orifices defined by the housing12which allow for the working fluid to travel therethrough from the suction channel32(FIG. 1) towards the rotors26,28, and30.

A portion of the first suction port34is disposed in communication with an inlet end of the rotors26and28. BecauseFIGS. 2A and 2Bare cross sectional views of the compressor10, the first and second plurality of compression pockets50and52are shown as dashed bounded area and shaded area around the first and second compression pairs44and46. Because the compression pockets50and52are defined by the area between the flutes and lobes of the rotors26,28, and30and the housing12, the compression pockets50and52rotate angularly with the rotation of the rotors26,28, and30within the housing12. However, not all of the compression pockets50and52are in communication with the portions of the suction ports34and36(indicated as the shaded areas inFIGS. 2A and 2B) at the same moment in time. This is because the housing12which defines the suction ports34and36extends radially (and in some embodiments axially) with respect to the rotors26,28, and30, to communicate with the axial end portions (or the radial portions if the suction ports34and36extend axially along the rotors26,28, and30) of several of the compression pockets50,52. A portion of the first suction port34is in direct fluid communication with the first compression pockets50in the shaded area. In the shaded area, the first compression pockets50rotate angularly into alignment and communication with the first suction port34. The angular rotation of the first compression pockets50relative to the housing12allows the first compression pockets50to be exposed to and “open” to the first suction port34for a limited time period. Likewise, a portion of the second suction port36communicates with the second compression pair46in the shaded area which also delineates a portion of the second plurality of compression pockets52. In the shaded area, the second plurality of compression pockets52rotate angularly into alignment and communication with the second suction port36. The angular rotation of the second plurality of compression pockets52relative to the housing12allows the second compression pockets52to be exposed to and “open” to the second suction port36for a limited time period.

Thus, the affect of the geometry of the housing12is to “obstruct” the pockets50and52from direct communication with portions of the suction ports34and36for a portion of their angular rotation with respect to the housing12. As each pocket50and52rotates angularly into communication with portions of the suction ports34and36, each pocket50,52“opens” to the suction ports34and36in the shaded areas. Likewise, as each pocket50and52rotates angularly out of communication with portions of the suction ports34and36in the shaded areas, each pocket50,52“closes” to the suction ports34and36. After each pocket50and52closes to the suction ports34and36, (and at some point during the rotation of the rotors26,28, and30) the rotors26,28and30and the housing12are configured to reduce the volume of the pockets50and52, thus compressing the working fluid within the pockets50and52to a higher pressure. The working fluid flows in the compression pockets50,52from the suction ports34and36to the discharge ports38,40(FIG. 1).

FIG. 2Ashows a cross section of the rotor housing section12. InFIG. 2A, the portions of the suction ports34and36in communication with the axial end portions of the compression pairs44and46have an asymmetric geometry with respect to each other. This asymmetric geometry is due to the different size and shape of the portion of the first suction port34in communication with the compression pair44relative to the portion of the second suction port36in communication with the compression pair46. More specifically, the housing12is configured such that the portion of the first suction port34(indicated as shaded area50inFIGS. 2A and 2B) in communication with the axial end portion of the first compression pair44is larger than the portion of the second suction port36(indicated as shaded area52inFIGS. 2A and 2B) in communication with the axial end portion of the second compression pair46. Because of the discrepancy in the size and shape of the portions of the suction ports34and36in communication with the compression pairs44and46inFIG. 2A, the second plurality of compression pockets52(which angularly rotate with respect to the housing12as the sun rotor26rotates the second planet rotor30) “close” to the second suction port36under trailing edges48before the first plurality of compression pockets50(which angularly rotate with respect to the housing12as the sun rotor26and first planet rotor28) “close” to the first suction port34under trailing edges49. The difference in size and/or shape between the portions of the two suction ports34and36in communication with the compression pairs44and46may be three dimensional as well as two dimensional.

In another embodiment, the asymmetry in geometry between the portions of the suction ports34and36in communication with the compression pairs44and46may be generated by shifting the disposition or alignment of the rotors26,28, and30with respect to the housing12, while maintaining the same port34and36size and/or shape. Shifting the disposition or alignment of the rotors26,28, and30with respect to the housing12, generates the asymmetric geometry because the location (axial and/or radial) where the suction ports34and36would come into communication with the rotors26,28, and30would differ for each suction port34and36. Thus, to generate a dispositional asymmetry geometry between the suction ports34and36and rotors26,28, and30, the first and second planet rotors28,30and the sun rotor26may be aligned with respect to the housing12such that the first suction port34is disposed radially further way from an the rotational axis of the sun rotor26(the intersection of the X and Y axes) than the second suction port36. This arrangement would dispose a smaller axial portion of the first planet rotor28in communication with the first suction port34(vis-à-vis the axial portion of the second planet rotor30in communication with the second suction port36). If the suction ports34and36also extend axially with respect to the rotors26,28, and30, the asymmetric geometry may also be generated by aligning the first and second planet rotors28,30and the sun rotor26with respect to the housing12such that the first suction port34is disposed axially further away from the centroid of the sun rotor26than the second suction port36. The asymmetry in geometry may also be generated by changing the shape of the portion of the first suction port34in communication with the first compression pair44relative to the shape of the portion of the second suction port36in communication with the second compression pair44while maintaining the overall size of the suction ports36,38.

The asymmetric geometry between the portions of the suction ports34and36in communication with the compression pairs44and46affects the time when each of the compression pockets50,52(which angularly rotate with respect to the housing12as the rotors26,28, and30angularly rotate) rotates free of the axial (and/or radial) “obstruct” that is the housing12to come into communication with the shaded portions of the suction ports34and36. InFIG. 2A, for example, each compression pocket52“closes” to the second suction port36by rotating angularly with respect to the housing12such that the compression pocket52passes behind the trailing edges48(as defined by the directions of rotation of the sun rotor26and the second planet rotor30) and is “obstructed” by the housing12(and therefore, is not in direct communication with a portion of the suction port36) before each compression pocket50passes behind the trailing edges49(as defined by the directions of rotation of the sun rotor26and the first planet rotor28) and is “obstructed” by the housing12(and therefore, is not in direct communication with a portion of the suction port34). Because both planet rotors28and30rotate at an equivalent angular velocity, the compression pockets52are “open” to the portion of the second suction port36(indicated by the shaded area52) for a shorter period of time than compression pockets50are “open” to the portion of the first suction port34(indicated by the shaded area50). The smaller size of the second suction port36in communication with the second compression pair46also results in the “closing” (as the sun rotor26rotates angularly with respect to the housing12such that it is obstructed by the trailing edge48of the housing12adjacent the sun rotor26) of the first compression pocket50around the sun rotor26at a point in time prior to when the second compression pocket52(located generally diametrically across from the first compression pocket50) “closes” (by rotating angularly with respect to the housing12such that it is obstructed by the trailing edge49of the housing12adjacent the sun rotor26).

FIG. 2Bshows another embodiment of the invention viewed from the same perspective asFIG. 2A. Similar toFIG. 2A, the portions of the suction ports34and36in communication with the compression pairs44and46have an asymmetric geometry with respect to each other. This asymmetric geometry is due to the different size and shape of the portion of the first suction port34in communication with the first compression pair44relative to the portion of the second suction port36in communication with the second compression pair46. More specifically, the housing12is configured such that the portion of the second suction port36(indicated as shaded area52inFIGS. 2A and 2B) in communication with the axial end portion of the second compression pair46is larger than the portion of the first suction port34(indicated as shaded area50inFIGS. 2A and 2B) in communication with the axial end portion of the first compression pair44.

Because the portion of the first suction port34in communication with the first compression pair44has a smaller size than the portion of the second suction port36in communication with the second compression pair46, each compression pocket50“closes” to the first suction port34by rotating angularly with respect to the rotor housing12to pass behind the trailing edge53at a point in time before the corresponding compression pocket52“closes” to the second suction port36by rotating angularly with respect to the rotor housing12to pass behind the trailing edges54.

The asymmetric geometry between the portions of the suction ports34and36in communication with the compression pairs44and46offsets the timing of the pressure pulsations associated with each suction port34and36. Specifically, inFIGS. 2A and 2B, the different size and shape of the suction ports34and36allows each compression pocket50and52to “open” and/or “close” at a different period in time as the compression pairs44and46rotate. Offsetting the opening and/or closing of the compression pockets50and52, results in reduced peak amplitude of pressure pulsations, and more uniform working fluid flow rates in the suction channel32, which reduces compressor10sound and vibration.

FIGS. 3A and 3Bare cross sectional views of the compressor10viewed from the same perspective illustrating different embodiments of the interior of the discharge housing section22downstream (as defined by the flow direction of the working fluid) of the rotors26,28, and30, which are disposed in the rotor housing section12. InFIGS. 3A and 3B, The discharge housing section22defines a first axial discharge port38A section of the first discharge port38ofFIG. 1, and the discharge housing section22defines a second axial discharge port40A section of the second discharge port40ofFIG. 1.

The axial discharge ports38A and40A are orifices in the housing22which allow for communication of the working fluid therethrough from the compression pairs44and46to the discharge channel42(FIG. 1). More specifically, the first axial discharge port38A provides an outlet for high pressure working fluid exiting from the first compression pocket50. The second axial discharge port40A provides an outlet for high pressure working fluid exiting the second compression pocket52. The discharge housing section22extends to immediately adjacent the axial ends of the rotors26,28, and30and abuts the rotor housing section12. The cross sectional shape, size and disposition of the housing22with respect to the compression pairs44and46determines the geometry of the portions of the axial discharge ports38A and40A in communication with the compression pairs44and46.

BecauseFIGS. 3A and 3Bare end views of the rotors26,28, and30, the first plurality of compression pockets50and second plurality of compression pockets52are shown as dashed bounded areas and as shaded areas around the rotors26,28, and30. As previously discussed, the sun rotor26and first planet rotor28cooperate to define the first compression pair44, with the first plurality of compression pockets50being defined between the flutes and lobes of a portion the sun rotor26and the inner wall of the housing12, by any intermeshing space between the sun rotor26and the first planet rotor28, and the flutes and lobes of the first planet rotor28and the inner wall of the housing12. InFIGS. 3A and 3B, the portion of the first axial discharge port38A which communicates with the first compression pair44corresponds to the shaded area also used to indicate the portion of the first compression pockets50in direct communication with the first axial discharge port38A. In the shaded area, the first compression pockets50rotate angularly into alignment with the first axial discharge port38A. The angular rotation of the first compression pockets50relative to the housing12allows the first compression pockets50to be exposed to and “open” to the first axial discharge port38A for a limited time period.

Likewise, the sun rotor26and the second planet rotor30cooperate to define the second compression pair46, with the second plurality of compression pockets52being defined between the flutes and lobes of the sun rotor26and the inner wall of the housing12, by any intermeshing space between the sun rotor26and the second planet rotor30, and the flutes and lobes of the second planet rotor and the inner wall of the housing12. The portion of the second axial discharge port40A which communicates with the second compression pair46corresponds to the shaded area used to indicate the portion of the second compression pockets52in direct communication with the second axial discharge port40A. In the shaded area, the second plurality of compression pockets52rotate angularly into alignment with the second axial discharge port40A. The angular rotation of the second compression pockets52relative to the housing12allows the second compression pockets52to be exposed to andaopenoto the second axial discharge port40A for a limited time period.

FIG. 3Ashows a cross sectional view of the discharge housing section22. InFIG. 3A, the portions of the axial discharge ports38A and40A in communication with the compression pairs44and46have an asymmetric geometry with respect to each other. This asymmetric geometry results from the different size and shape of the axial discharge ports38A and40A in communication with the compression pairs44and46. InFIG. 3A, the portion of the first axial discharge port38A in communication with the axial portion of the first compression pair44is smaller than the portion of the second axial discharge port40A in communication with the axial portion of the second compression pair46.

Similar to the suction ports34and36, (FIGS. 2A and 2B) the asymmetry in geometry between the axial discharge ports38A and40A may be generated by shifting the disposition or alignment of the rotors26,28, and30with respect to the housing22, while maintaining the same axial discharge port38A and40A size and shape. The shifting the disposition or alignment of the rotors26,28, and30with respect to the housing22generates an asymmetric geometry because the axial location where the axial discharge ports38A and40A would come into communication with the rotors26,28, and30would be different. The asymmetry in geometry may also be generated by changing the shape of the first axial discharge port38A relative to the shape of the second axial discharge port40A while maintaining the overall size of the axial discharge ports38A and40A in communication with the compression pairs44and46.

The asymmetric geometry between the portions of the axial discharge ports38A and40A in communication with the compression pairs44and46affects the timing when each of the compression pockets50and52(which rotate angularly with respect to the rotor housing12and discharge housing22as the rotors26,28, and30rotate) rotates free of the axial “obstruct” that is the discharge housing22to come into communication with portions of the axial discharge ports38A and40A. For example, because the second axial discharge port40A is larger in size than the first axial discharge port38A inFIG. 3A, each compression pocket52“opens” to the second axial discharge port40A (by angularly rotating past the leading edges61of the housing22) at a point in time before the corresponding compression pocket50“opens” to the first axial discharge port38A (by angularly rotating past the leading edges60of the housing22). Thus, each compression pocket52begins to clear the leading edges61of the housing22and comes into direct communication with a portion of the second axial discharge port40A before each corresponding compression pocket50begins to clear the leading edges60of the housing22and comes in direct communication with a portion of the first axial discharge port38A. The compression pockets52remain “open” to the second axial discharge port40A for a longer period of time than compression pockets50remain “open” to the first axial discharge port38A.

FIG. 3Bshows another embodiment of the invention viewed from the same perspective asFIG. 3A. Similar toFIG. 3A, the portions of the axial discharge ports38A and40A in communication with the compression pairs44and46have an asymmetric geometry with respect to each other. This asymmetric geometry is the result of the different size and shape of the axial discharge ports38A and40A in communication with the compression pairs44and46. More specifically, the housing22is configured such that the portion of the first axial discharge port38A in communication with the axial portion of the first compression pair44is larger than the portion of the second axial discharge port40A in communication with the second compression pair46. InFIG. 3B, asymmetry of the ports38A and40A allows each first compression pocket50to “open” to the portion of the first axial discharge port38A at a point in time prior to when each corresponding second compression pocket52“opens” to the shaded portion of the second axial discharge port40A.

The asymmetric geometry between the portions of the axial discharge ports38A and40A in communication with the compression pairs44and46offsets the timing of the pressure pulsations associated with each axial discharge port38A and40A. Specifically inFIGS. 3A and 3B, the different size and shape of the suction ports34and36allows each compression pocket50and52to “open” and/or “close” at a different period in time as the compression pairs44and46rotate. Offsetting the opening and/or closing of the compression pockets50and52, results in reduced peak amplitude of pressure pulsations, and more uniform working fluid flow rates in the discharge channel42, which reduces sound and vibration.

FIG. 4Ais a top view of the first compression pair44with the rotor housing section12shown in phantom rather than cross hatched to better illustrate the intermeshing of the sun rotor26and first planet rotor28.FIG. 4Ashows the first radial discharge port38R which extends generally axially along a downstream portion of the first compression pair44. The first radial discharge port38R also extends generally radially outward from the first compression pair44and would be visible from a top sectional view of the compressor10.

FIG. 4Bis a bottom view of the second compression pair46with the rotor housing section12shown in phantom rather than cross hatched to better illustrate the intermeshing of the sun rotor26and second planet rotor30.FIG. 4Bshows the second radial discharge port40R which extends generally axially along a downstream portion of the second compression pair46. The second radial discharge port40R extends generally radially outward from the second compression pair46.

The disposition of the radial discharge ports38R and40R with respect to the rotors26,28, and30may be varied to create an asymmetric housing12geometry, and therefore, the ports38R and40R need not necessarily be aligned between the compression pairs44and46along axes I1and I2as shown. In one embodiment, however, the first and second planet rotors28and30and the sun rotor26are aligned with respect to the housing12such that a leading or trailing edges68and69of the portion of the housing12which defines the first radial discharge port38R is disposed radially further away from (and intersect further away from) the rotational axis of the sun rotor26than a leading or trailing edges70and71of the portion of the housing12which defines the second radial discharge port40R. Similarly, the first and second planet rotors28and30and the sun rotor26may be aligned with respect to the housing12such that the leading or trailing edges68and69of the housing12which defines the first radial discharge port40R is disposed axially further away from (and intersect further away from) the centroid of the sun rotor26than the leading or trailing edges70and71of the portion of the housing12which defines the second radial discharge port40R.

InFIGS. 4A and 4B, the asymmetric geometry between the portions of the radial discharge ports38R and40R in communication with the radial portion of the compression pairs44and46is the result of the different size and shape of the radial discharge ports38R and40R. InFIG. 4A, the rotor housing12is configured such that the portion of the first radial discharge port38R in communication with the first compression pair44is smaller than the portion of the second radial discharge port40R in communication with the second compression pair46. The difference in size and shape between the portions of the radial discharge ports38R and40R in communication with the compression pairs44and46allows the second compression pocket52(FIGS. 3A and 3B) to “open” to the second radial discharge port40R prior to when the corresponding first compression pocket50(FIGS. 3A and 3B) “opens” to the first radial discharge port38R.

Similar to the suction ports34and36(FIGS. 2A and 2B) and the axial discharge ports38A and40A (FIGS. 3A and 3B), the asymmetry in the geometry between the portions of the radial discharge ports38R and40R in communication with the compression pairs44and46may be generated by shifting the disposition or alignment of the rotors26,28, and30with respect to the housing12, while maintaining the same radial discharge port38R and40R size and shape. Shifting the disposition or alignment of the rotors26,28, and30with respect to the housing12generates the asymmetric geometry because the axial and/or radial location along each compression pair44and46where the radial discharge ports38R and40R would come into communication with the rotors26,28, and30would be different. The asymmetry in geometry may also be generated by changing the shape of the first radial discharge port38R relative to the shape of the second radial discharge port40R while maintaining the overall size of the ports38R and40R in communication with the compression pairs44and46.

By generating the asymmetric geometry between the portions of the radial discharge ports38R and40R in communication with the compression pairs44and46, the amplitude of pressure pulsations associated with each port38R and40R may be offset from each other. The different size and shape of the radial discharge ports38R and40R allows each compression pocket50and52to open and/or close to the discharge ports38R and40R at a different period in time as the rotors26,28, and30rotate relative to the housing12. By offsetting the opening and closing of the compression pockets50and52, the peak amplitude of the pressure pulsations downstream of the rotors26,28, and30is reduced. A more uniform discharge flow rate in the discharge channel42(FIG. 1) and piping also results from the modifications to the discharge ports. The asymmetry of the radial discharge ports38R and40R reduces the noise and vibration levels in the attached piping and other system components.

The embodiments shown inFIGS. 2-4are exemplary embodiments only. In other embodiments, different geometric housing configurations may result in different asymmetries between the portions of the ports in communication with the compression pairs44and46. If more than three rotors are used in a compressor, the housing may be configured with more than two suction ports and more than two discharge ports. The housing may be configured to produce any number of asymmetries between the portions of the suction and/or discharge ports in communication with the rotors.

The housing may be simultaneously configured such that the suction ports and the discharge ports both have asymmetric geometries with respect to the compression pairs44and46. This simultaneous asymmetric suction and discharge port arrangement may maintain the built-in volume ratio (Vi) on the both the planet rotors28and30without changing the helical shape, diameter, rotational velocity, or lobe/flute size of either planet rotor28and30. As is known in the art, Vi is defined as a ratio of suction volume trapped in the compression pockets right after the compression pocket is closed off and discharge volume of the compression pocket just before the discharge port is open. A configuration that maintains Vi can be achieved, for example, by configuring the housing to create an asymmetric geometry between the portions of the first discharge port38and the second discharge port40(FIG. 1) in communication with a discharge portion of the compression pairs44and46, while simultaneously configuring the housing to create an asymmetric geometry between the portions of the first suction port34and the second suction port36(FIG. 1) in communication with a suction portion of the compression pairs44and46. Additional geometric arrangements of the housing which would result in an asymmetry between the axial and/or radial discharge ports and the axial and/or radial suction ports with respect to the compression pairs44and46, while maintaining the Vi would be recognized by those skilled in the art.