Patent Publication Number: US-2022239183-A1

Title: Hermetic motor cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/838,147, entitled “HERMETIC MOTOR COOLING SYSTEM,” filed Apr. 24, 2019, which is herein incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     A compressor of a refrigeration cycle is driven by a shaft which may be rotated by an electric motor. Heat (e.g., thermal energy) may be generated as electrical current passes through a series of windings forming a stator, which drive rotation of a rotor coupled to the shaft. The rotor and stator are contained within a motor housing that may experience an increase in temperature as heat is generated during operation of the motor. In some compressors, the rotor may be supported by electromagnetic bearings, which may also generate heat and further increase the temperature within the motor housing. Accordingly, cooling fluid may be provided to the motor via a cooling system to remove heat and avoid a decrease in performance or shut-down of the motor caused by overheating. Unfortunately, some cooling systems for motors of a refrigeration cycle may experience reduced cooling fluid flow to portions of the stator when a low pressure refrigerant is utilized in the refrigeration cycle. As such, the operational limits of existing motor cooling systems may generate large temperature gradients (e.g., hot spots) along the stator, thereby affecting the total operating range of the compressor and/or the refrigeration system. 
     BRIEF SUMMARY 
     In one embodiment, a system for cooling a hermetic motor includes a housing of the hermetic motor that is configured to be disposed along a motor cooling refrigerant flow path. The housing is configured to surround at least a portion of a stator of the hermetic motor and includes an annular cavity configured to receive refrigerant from a refrigerant loop. The system also includes a sleeve configured to be positioned between the annular cavity and the stator, where the sleeve includes a plurality of discharge ports oriented generally parallel to a central axis of the stator. The plurality of discharge ports is configured to discharge the refrigerant from the annular cavity toward the stator. 
     In one embodiment, a method includes directing, via a compressor, a refrigerant flow along a refrigerant loop, where the compressor is driven by a hermetic motor. The method includes diverting a portion of the refrigerant flow from the refrigerant loop into an annular cavity formed within a housing of the hermetic motor, where the housing surrounds at least a portion of a stator of the hermetic motor, and where a sleeve is positioned radially between the annular cavity and the stator. The method further includes directing, via a plurality of discharge ports formed in the sleeve, an amount of the portion of the refrigerant flow from the annular cavity toward the stator, where the plurality of discharge ports is oriented generally parallel to a central axis of the stator. 
     In one embodiment, a hermetic motor includes a housing disposed about a stator of the hermitic motor. The housing includes an annular cavity formed therein, where the annular cavity is configured to receive a refrigerant from a refrigerant loop. The hermetic motor also includes a sleeve positioned between the annular cavity and the stator, where the sleeve includes a plurality of discharge ports oriented generally parallel to a central axis of the stator. The plurality of discharge ports is configured to receive the refrigerant from the annular cavity and to discharge the refrigerant toward the stator. 
    
    
     
       DRAWINGS 
         FIG. 1  is a schematic of an embodiment of a heating, ventilation, air conditioning, and/or refrigeration (HVAC&amp;R) system having a hermetic motor that may utilize an improved cooling system, in accordance with an aspect of the present disclosure; 
         FIG. 2  is a cross-sectional side view of an embodiment of a hermetic motor that includes an improved cooling system, in accordance with an aspect of the present disclosure; 
         FIG. 3  is a partial cross-sectional side view, taken within line  3 - 3  of  FIG. 2 , of an embodiment of a hermetic motor that includes an improved cooling system, in accordance with an aspect of the present disclosure; 
         FIG. 4  is a partial cross-sectional side view, taken within line  4 - 4  of  FIG. 2 , of an embodiment of a hermetic motor that includes an improved cooling system, in accordance with an aspect of the present disclosure; 
         FIG. 5  is a front view of an embodiment of a stator for a hermetic motor, in accordance with an aspect of the present disclosure; and 
         FIG. 6  is a cross-sectional side view of an embodiment of a hermetic motor that includes an improved cooling system, in accordance with an aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     Motors (e.g., hermetic motors) may be utilized to drive a compressor of a heating, ventilating, air conditioning, and/or refrigeration (HVAC&amp;R) system. Motors produce heat during operation as a result of winding resistance and eddy current losses from the electrical current that is supplied to the motor. The heat produced by the motor transfers thermal energy to a motor housing, thereby increasing a temperature of the motor. Accordingly, at least a portion of a cooling system may be included in the motor housing to absorb the thermal energy and reduce the temperature of the motor (e.g., cool the motor). In some embodiments, the cooling system circulates refrigerant from a refrigerant loop of the HVAC&amp;R system into the motor housing to absorb the thermal energy in the motor housing. For example, refrigerant (e.g., the cooling fluid of the cooling system) is directed from a condenser of the HVAC&amp;R system and into the motor housing to absorb thermal energy generated during operation of the motor. The refrigerant may then be directed back to the refrigerant loop of the HVAC&amp;R system from the motor. 
     In some cases, the refrigerant entering the motor cooling system from the condenser may have a relatively low pressure. As used herein, low pressure refrigerants may include refrigerants that have a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure. As used herein, “normal boiling point” may refer to a boiling point temperature measured at one atmosphere of pressure. As a result, the motor cooling system may inadequately direct refrigerant toward certain motor components within the motor housing, such as a stator of the motor. Indeed, utilizing low pressure refrigerant within the motor cooling system may cause inadequate refrigerant flow toward, for example, end windings of the stator, thereby generating large temperature gradients along a length of the stator. Therefore, typical motor cooling systems may not provide sufficient thermal energy transfer for refrigerant systems that use a low pressure refrigerant. 
     The present disclosure is directed to an improved motor cooling system that is configured to facilitate more even distribution of refrigerant along the stator, such that a low pressure refrigerant may effectively be utilized in an HVAC&amp;R system and particularly for motor cooling. Accordingly, the improved motor cooling system may increase an amount of thermal energy transfer between the refrigerant and the motor components within the motor housing, thereby enhancing an operational life and/or an operational efficiency of the motor. 
     For example, in some embodiments, the improved motor cooling system includes a sleeve that is positioned between the stator and the motor housing. An annular cavity may be formed within the motor housing and may be positioned between the sleeve and an interior surface of the motor housing. The annular cavity is configured to receive a refrigerant flow from the HVAC&amp;R system and is in fluid communication with a plurality of discharge ports (e.g., axial discharge ports) that are formed within the sleeve. During operation, the refrigerant is discharged from the annular cavity via the discharge ports, thereby enabling the refrigerant to directly contact at least a portion of the stator to absorb thermal energy from the stator. Indeed, the discharge ports of the motor cooling system may be configured to direct the refrigerant toward particular portions of the stator (e.g., toward end windings of the stator) to facilitate generation of a more even temperature distribution across the stator. Accordingly, the motor cooling system may mitigate or substantially eliminate temperature spikes (e.g., hot spots) at, for example, the end windings of the stator. As such, embodiments of the motor cooling system disclosed herein may improve efficiency of the motor and increase the operating range of the compressor and/or the refrigeration system. 
     To help illustrate the manner in which the present embodiments may be used in a system,  FIG. 1  is a schematic representation of a heating, ventilating, air conditioning, and/or refrigeration (HVAC&amp;R) system  10  that includes a compressor  12  driven by a motor  14  (e.g., a hermetic motor, an electric motor, a hydraulic motor, a pneumatic motor, etc.). As shown in the illustrated embodiment of  FIG. 1 , the compressor  12  is disposed along a refrigerant loop  16 , and the compressor  12  is configured to circulate refrigerant within the refrigerant loop  16 . Refrigerant exiting the compressor  12  is received by a condenser  18 . In some embodiments, the condenser  18  is an air cooled condenser, such that air is directed over coils of the condenser  18  to absorb thermal energy (e.g., heat) from the refrigerant flowing through the coils. In other embodiments, the condenser  18  may be a shell and tube heat exchanger that places the refrigerant in a heat exchange relationship with a cooling fluid (e.g., water). In any case, the refrigerant transfers thermal energy to a working fluid of the condenser  18  (e.g., air, water, or another suitable cooling fluid), thereby reducing a temperature of the refrigerant exiting the condenser  18 . 
     The refrigerant exiting the condenser  18  may continue along the refrigerant loop  16  toward an expansion device  20 . The expansion device  20  is configured to reduce a pressure of the refrigerant, which also further reduces a temperature of the refrigerant. The refrigerant then enters an evaporator  22  disposed along the refrigerant loop  16 . The refrigerant flowing through the evaporator  22  absorbs thermal energy (e.g., heat) from a working fluid (e.g., water and/or air). In some embodiments, the evaporator  22  is a shell and tube heat exchanger that places the refrigerant in a heat exchange relationship with a cooling fluid (e.g., water). In other embodiments, the evaporator  22  places the refrigerant in a heat exchange relationship with air. The working fluid of the evaporator  22  (e.g., water, air, or another suitable fluid) may be configured to cool a load, such as a building, a room, a house, or another conditioned space. The refrigerant exiting the evaporator  22  then completes the refrigerant loop  16  by re-entering the compressor  12 . 
     As shown in the illustrated embodiment of  FIG. 1 , a portion of the refrigerant exiting the condenser  18  may be diverted to a motor cooling loop  24  via a tee  26  (e.g., a first tee and/or a first three-way valve). A valve  28  (e.g., a ball valve, a butterfly valve, a gate valve, a globe valve, a diaphragm valve, and/or another suitable valve) may be disposed along the motor cooling loop  24  downstream of the tee  26  with respect to the flow of the refrigerant through the motor cooling loop  24 . The valve  28  may be configured to adjust an amount of the refrigerant that is diverted into the motor cooling loop  24  from the refrigerant loop  16 . In some embodiments, the valve  28  is coupled to a controller  30 , which is configured to adjust a position of the valve  28  to control a flow of the refrigerant through the motor cooling loop  24  based on a temperature of the motor  14  monitored by a sensor  29  (e.g., a temperature sensor, such as an infrared camera, resistance temperature detector, and/or thermocouple), for example. The refrigerant flowing through the motor cooling loop  24  is directed into a housing (see, e.g.,  FIG. 2 ) of the motor  14  to place the refrigerant in a heat exchange relationship with a component (e.g., a stator, a rotor, and/or bearings) of the motor  14 . Accordingly, the refrigerant absorbs thermal energy (e.g., heat) from the motor  14  to reduce a temperature of the motor  14 . The refrigerant is then directed from the motor  14  back toward the refrigerant loop  16 , where the refrigerant flows into the evaporator  22 . It should be appreciated that, in some embodiments, the motor cooling loop  24  may include a flow generating device, such as a pump, an eductor, a compressor, or another suitable device that facilitates forcing the refrigerant through the motor cooling loop  24 . 
       FIG. 2  is a cross-sectional side view of an embodiment of the motor  14  that illustrates a flow path of the refrigerant in the motor cooling loop  24  through the motor  14 .  FIG. 3  is a partial cross-sectional side view, taken within line  3 - 3  of  FIG. 2 , of an embodiment of the motor  14 , and  FIG. 4  is a partial cross-sectional side view, taken within line  4 - 4  of  FIG. 2 , of an embodiment of the motor  14 .  FIGS. 2-4  are discussed concurrently below. As shown in the illustrated embodiment of  FIG. 2 , the motor  14  includes a housing  60 , as well as a stator  62 , a rotor  64  coupled to a shaft  66 , and bearings  68  (e.g., ball bearings, sleeve bearings, magnetic bearings, or other suitable bearings) disposed within the housing  60 . A central portion  70  of the stator  62  may be surrounded by a sleeve  72  that is positioned between the stator  62  and the housing  60 . Particularly, the sleeve  72  may extend along a length of the central portion  70  from a first end face  74  of the central portion  70  to a second end face  76  of the central portion  70 . The motor  14  may include an annular cavity  78  that is formed within the housing  60  and extends radially between an inner surface of the housing  60  and the sleeve  72 . In some embodiments, one or more seals  80  (e.g., O-rings, gaskets) may be positioned within respective grooves formed within the sleeve  72  and are configured to form a fluid seal between the annular cavity  78  and an interior region  81  of the housing  60 . However, it should be noted that, in other embodiments, the seals  80  may be omitted from the sleeve  72 . Indeed, in such embodiments, the sleeve  72  itself may be configured to abut (e.g., via a compression fit) the interior surface of the housing  60  to substantially block fluid flow from the annular cavity  78  to the interior region  81  via an interface between the sleeve  72  and the housing  60 . 
     In any case, as shown in the illustrated embodiment, the housing  60  includes an inlet port  82  that enables the motor cooling loop  24  to direct a flow of refrigerant into the annular cavity  78 . That is, the annular cavity  78  may be in fluid communication with the motor cooling loop  24  via an inlet line  84  of the motor cooling loop  24  that is coupled to the inlet port  82 . As discussed above, in some embodiments, the refrigerant entering the motor cooling loop  24  may include a portion of the refrigerant discharged from the condenser  18 . Indeed, the inlet line  84  may be fluidly coupled to a portion of the condenser  18  or a portion of the refrigerant loop  16  downstream of the condenser  18 , such that the inlet line  84  may receive refrigerant in a substantially liquid state (e.g., in a condensed state). In some embodiments, an electronic expansion valve  86  may be coupled to the inlet line  84  and configured to expand the refrigerant from the substantially liquid state into a vapor state or a mixture of liquid and vapor before the refrigerant enters the annular cavity  78  via the inlet port  82 . The electronic expansion valve  86  may be communicatively coupled to the controller  30 , which may be configured to operate (e.g., control) the electronic expansion valve  86  to control an amount of refrigerant that is expanded into a vapor state. As such, the electronic expansion valve  86  is operable (e.g., via signals provided by the controller  30 ) to control a phase composition (e.g., a ratio of vaporous refrigerant to liquid refrigerant) of the refrigerant entering the annular cavity  78 . Additionally or alternatively, the controller  30  may operate the electronic expansion valve  86  to control, for example, a flow rate of refrigerant entering the annular cavity  78  and/or a pressure of refrigerant within the annular cavity  78 . 
     As shown in  FIGS. 3 and 4 , the sleeve  72  may include a plurality of ports  90  (e.g., axial discharge ports) or passages that are in fluid communication with the annular cavity  78  and are configured to discharge refrigerant (e.g., represented by arrows  91 ) from the annular cavity  78  into the interior region  81  of the housing  60 . Specifically, the sleeve  72  may include a first group of ports  92  ( FIG. 3 ) that are formed within a first end portion  93  of the sleeve  72 , proximate the first end face  74 , and a second group of ports  94  ( FIG. 4 ) that are formed within a second end portion  95  of the sleeve  72 , proximate the second end face  76 . In this manner, the first group of ports  92  may discharge a flow of the refrigerant in a first direction  96 , toward and across a first end winding  98  of the stator  62 , while the second group of ports  94  may discharge a flow of the refrigerant in a second direction  100 , generally opposite to the first direction  96 , toward and across a second end winding  102  of the stator  62 . Accordingly, the refrigerant may directly contact the first and second end windings  98 ,  102  and particularly portions of the end windings  98 ,  102  (e.g., roots and/or distal ends of the end windings  98 ,  102 ) that may generate a relatively large amount of thermal energy (e.g., heat) during operation of the motor  14 . Accordingly, the refrigerant may absorb thermal energy from the first and second end windings  98 ,  102  to ensure that a temperature gradient along the first end winding  98 , the central portion  70  of the stator  62 , and the second end winding  98  is reduced or substantially negligible. It should be appreciated that each of the ports  90  extends through the sleeve  72  such that a respective flow path along each port  90  is enclosed by the sleeve  72 . 
     In some embodiments, the ports  90  may extend generally parallel (e.g., within five degrees) to a central axis  120  of the stator  62 . As used herein, the term “parallel” or “generally parallel” refers to a spatial relationship between features or elements that extend in a common direction but are also not necessarily constrained by a mathematical or Euclidean parallel relationship. In other embodiments, the ports  90  may extend at an angle relative to the central axis  120 . For example, the first and second groups of ports  92 ,  94  may extend radially inward from the annular cavity  78  toward the first end winding  98  or the second end winding  102 , respectively. In some embodiments, the first and second groups of ports  92 ,  94  may be configured to discharge respective refrigerant flows at different flow rates. For example, as discussed in detail below, a quantity of the ports  90  and/or a size of the ports  90  may be adjusted to enable the first group of ports  92  to discharge refrigerant from the annular cavity  78  at a first flow rate (e.g., a relatively large flow rate), while the second group of ports  94  may discharge refrigerant from the annular cavity  78  at a second flow rate (e.g., a relatively low flow rate). In this manner, the motor cooling loop  24  may be configured to mitigate or substantially reduce temperature fluctuations (e.g., hot spots) along a length of the stator  62  and/or throughout other motor components (e.g., the rotor  64 , the shaft  66 ) within the housing  60 . That is, the size, number, and/or other configuration of the ports  90  may be selected or biased to discharge a greater flow rate of refrigerant toward portions of the stator  62  and/or other motor components within the housing  60  that are expected to undergo greater thermal loading during operation of the motor  14 . 
     In some embodiments, the ports  90  may be configured to discharge substantially all refrigerant entering the annular cavity  78  from the inlet line  84 . In certain embodiments, the annular cavity  78  may be in fluid communication with an outlet line  128  that is formed within the housing  60  and is configured to receive at least a portion of the refrigerant from the annular cavity  78 . For example, in some embodiments, the outlet line  128  may be fluidly coupled to the evaporator  22 , or to another suitable section of the refrigerant loop  16 , and may be configured to discharge a portion of the refrigerant back to the evaporator  22 . For example, a valve may be used to control a flow rate of refrigerant discharging from the annular cavity  78  to the evaporator  22 . 
     In other embodiments, the outlet line  128  may be configured to direct a refrigerant flow from the annular cavity  78  and toward the bearings  68 , thereby enabling the refrigerant to contact the bearings  68  and absorb thermal energy from the bearings  68 . As an example, in the illustrated embodiment, the outlet line  128  extends toward and is configured to direct a flow of refrigerant onto an impeller-side bearing  130  of the bearings  68 . Indeed, the outlet line  128  may direct an auxiliary refrigerant flow (e.g., represented by arrow  131 ) onto the impeller-side bearing  130 . In certain embodiments, a flow control device  132  (e.g., an additional electronic expansion valve, a step-less control valve) may be coupled to the outlet line  128  and is operable to regulate a flow rate of refrigerant that discharges from the annular cavity  78  via the outlet line  128 . 
     In certain embodiments, the valve  28  (see, e.g.,  FIG. 1 ), the electronic expansion valve  86 , the flow control device  132 , or a combination thereof, may be operable (e.g., via the controller  30 ) to control a flow rate of refrigerant discharging through the ports  90 . In other words, the motor cooling loop  24  may include an active control system that is configured to regulate refrigerant flow through the ports  90  of the motor cooling loop  24 . As an example, transitioning the electronic expansion valve  86  toward an open position (e.g., based on inputs from the controller  30 ) may increase a flow rate of refrigerant entering the annular cavity  78 , and thus, may increase a flow rate and/or a discharge pressure of refrigerant that is discharged through the ports  90 . Conversely, transitioning the electronic expansion valve  86  toward a closed position (e.g., based on inputs from the controller  30 ) may decrease a flow rate of refrigerant entering the annular cavity  78 , and thus, may decrease a flow rate and/or a discharge pressure of refrigerant that is discharged through the ports  90 . It should be noted that, in some embodiments, the valve  28 , the electronic expansion valve  86 , and/or the flow control device  132  may be omitted from the motor cooling loop  24 . In such embodiments, a flow rate of refrigerant discharging via the ports  90  may correspond to a refrigerant pressure within, for example, the condenser  18 . That is, in such embodiments, the motor cooling loop  24  includes a passive control system, where refrigerant flow through the motor cooling loop  24  is determined based on refrigerant parameters (e.g., refrigerant pressure) within the condenser  18  or another portion of the refrigerant loop  16 . 
     In any case, the refrigerant discharging from the ports  90  may absorb a significant quantity of thermal energy (e.g., heat) from motor components within the housing  60 , such as from the first and second end windings  98 ,  102  of the stator  62 , which may cause the refrigerant to evaporate into a refrigerant vapor or a mixture of refrigerant vapor and liquid refrigerant. Accordingly, the housing  60  may include a drain  140  that enables refrigerant vapor to discharge from the interior region  81  of the housing  60  and flow back toward the refrigerant loop  16  (e.g., via a conduit). Additionally, the housing  60  may also include a vent  142  that enables liquid refrigerant to flow from the interior region  81  back toward the refrigerant loop  16  (e.g., via a conduit). It should be appreciated that, as the refrigerant flows from the sleeve  72  toward the drain  140  and/or the vent  142 , the refrigerant may further contact and absorb heat (e.g., thermal energy) from motor components within the housing  60 , such as the rotor  64  and/or the bearings  68 . 
       FIG. 5  is a front view of an embodiment of the stator  62  illustrating the first group of ports  92  formed within the sleeve  72 . For clarity, it should be noted that the second group of ports  94  may be formed and arranged within the sleeve  72  in a substantially similar manner as the first group of ports  92 . However, for conciseness, the first group of ports  92  will be discussed below with reference to  FIG. 5 . The first group of ports  92  may be arrayed about the central axis  120  of the stator  62  in a symmetrical or uniform arrangement, or an asymmetrical arrangement. In some embodiments, certain of the ports  90  may include plugs  144  that are configured to block refrigerant flow through these ports  90 . Accordingly, the sleeve  72  may be biased to discharge refrigerant toward particular portions of the stator  62  that may experience higher thermal loading than other portions of the stator  62  during operation of the motor  14 . For example, in some embodiments, empirical trials (e.g., thermal data collection via the sensor  29 ) or thermal analysis using computational modeling software may be used to determine if or whether a first side portion  146  of the stator  62  experiences less thermal loading than a second side portion  148  of the stator  62 , opposite the first side portion  146 , during operation of the motor  14 . Accordingly, in such embodiments, a greater quantity of plugs  144  may be coupled to ports  90  positioned near the first side portion  146  than a quantity of plugs  144  coupled to ports  90  positioned near the second side portion  148 , thereby biasing refrigerant flow toward the second side portion  148  of the stator  62 . Indeed, testing or analysis may be conducted to determine any portion of the stator  62  that experiences more or less thermal loading than another portion, and the plugs  144  may be utilized with one or more of the ports  90 , as desired. In this manner, the arrangement of ports  90  with the sleeve  72  may be adjusted to achieve a substantially or more even uniform temperature distribution across the stator  62  during operation of the motor  14 . 
     It should be noted that, in other embodiments, instead of using the plugs  144  to bias refrigerant flow discharging from the sleeve  72 , a quantity of ports  90  near certain portions of the stator  62  may be increased or decreased. That is, to bias refrigerant flow toward, for example, the second side portion  148  of the stator  62 , a quantity of ports  90  positioned or formed near the second side portion  148  may be increased as compared to a quantity of ports  90  positioned or formed near the first side portion  146  of the stator  62 . Accordingly, refrigerant may discharge from the sleeve  72  near the second side portion  148  of the stator  62  at a flow rate that is greater than a flow rate of refrigerant discharging near the first side portion  146  of the sleeve  72 . Moreover, in certain embodiments, refrigerant flow may be biased toward certain portions of the stator  62  by increasing or decreasing a cross-sectional area of various ports  90  arrayed within the sleeve  72 . As an example, to bias refrigerant flow to the second side portion  148  of the stator  62 , a cross-sectional area of ports  90  positioned near the second side portion  148  may be increased as compared to a cross-sectional area of ports  90  positioned near the first side portion  146  of the stator  62 . 
     It should be appreciated that, in accordance with these techniques, refrigerant flow may also be biased toward the first end windings  98  or the second end windings  102  of the stator  62 , in particular, via adjustments to the aforementioned parameters of the first group of ports  92  and/or the second group of ports  94 . For example, to bias refrigerant flow toward the first end windings  98 , as compared to a flow rate of refrigerant that may be directed toward the second end windings  102 , the sleeve  72  may be manufactured to include a greater quantity of ports  90  in the first group of ports  92  than a quantity of ports  90  included in the second group of ports  94 . Additionally or alternatively, the first group of ports  92  may be configured to have a greater cumulative cross-sectional area (e.g., a combined cross-sectional area of the ports  90  in the first group of ports  92 ) than a cumulative cross-sectional area of the second group of ports  94  (e.g., a combined cross-sectional area of the ports  90  in the second group of ports  94 ). 
       FIG. 6  is a cross-sectional side view of another embodiment of the motor  14  that illustrates a flow path of the refrigerant in the motor cooling loop  24  through the motor  14 . In some embodiments, as shown, the electronic expansion valve  86  may be omitted from the inlet line  84  of the motor cooling loop  24 , such that the annular cavity  78  may receive a flow of liquid refrigerant or substantially liquid refrigerant from the condenser  18 . As such, a pressure of the refrigerant within the annular cavity  78 , and thus, a flow rate of refrigerant discharging from the annular cavity  78  via the ports  90 , may correspond to the refrigerant pressure within the condenser  18 . Accordingly, a relatively high condenser pressure may enable the ports  90  to discharge a relatively large flow rate of refrigerant (e.g., the refrigerant  91 ), while a relatively low condenser pressure may enable the ports  90  to discharge a relatively low flow rate of refrigerant (e.g., the refrigerant  91 ). In other words, the motor cooling loop  24  may be passively controlled via control of the condenser  18  pressure. In certain embodiments, the ports  90  may discharge the refrigerant from the annular cavity  78  in a liquid state, such that the refrigerant may flow substantially as a liquid along the first and second end windings  98 ,  102  of the stator  62 . In other embodiments, directing the refrigerant through the ports  90  may cause the refrigerant to vaporize, and thus, enable the ports  90  to discharge refrigerant vapor toward the first and second end windings  98 ,  102 . In further embodiments, the ports  90  may discharge a mixture of liquid refrigerant and refrigerant vapor. 
     In some embodiments, as shown, the electronic expansion valve  86  may be fluidly coupled to the outlet line  128  instead of the inlet line  84 . The electronic expansion valve  86  may be operable (e.g., via the controller  30 ) to control a flow rate of refrigerant discharging from the annular cavity  78  and flowing into a first axial outlet line  150  and/or a second axial outlet line  152  that are formed within the housing  60 . In certain embodiments, the electronic expansion valve  86  may be configured to expand (e.g., vaporize) the refrigerant from the substantially liquid state within the annular cavity  78  into a vapor state, or a mixture of liquid and vapor, before the refrigerant enters the first and second axial outlet lines  150 ,  152 . However, it should be noted that, in other embodiments, the electronic expansion valve  86  may be omitted from the outlet line  128 , such that the first and/or second axial outlet lines  150 ,  152  may receive a refrigerant flow (e.g., a substantially liquid refrigerant flow) directly from the outlet line  128 . 
     In some embodiments, the first axial outlet line  150  and the second axial outlet line  152  may be in fluid communication with a first radial discharge port  154  and a second radial discharge port  156 , respectively, which are configured to discharge refrigerant from the first and second axial outlet lines  150 ,  152  toward the stator  62  or toward another suitable motor component within the housing  60 . For example, the first radial discharge port  154  may be configured to direct a first flow of refrigerant (e.g. represented by arrow  158 ) toward and across the first end winding  98  of the stator  62 , and the second radial discharge port  156  may be configured to direct a second flow of refrigerant (e.g., represented by arrow  160 ) toward and across the second end winding  102  of the stator  62 . In certain embodiments, the first axial outlet line  150  may be in fluid communication with a third radial discharge port  162  (e.g., an inlet port angled toward the central axis  120 ), which may be configured to direct refrigerant (e.g., the auxiliary refrigerant flow  131 ) toward the impeller-side bearing  130 . 
     Although the motor  14  includes three radial discharge ports (e.g., the radial discharge ports  154 ,  156 ,  162 ) in the illustrated embodiment, in other embodiments, any suitable quantity of radial discharge ports may be formed within the housing  60  and positioned about the central axis  120 . As an example, in some embodiments, the motor  14  may include 1, 2, 3, 4, 5, 6, or more than six radial discharge ports formed within the housing  60  that are configured to direct a flow of refrigerant onto or toward various components disposed within the housing  60 . Further, it should be noted that, in other embodiments, the first axial outlet line  150 , the second axial outlet line  152 , or both, may be omitted from the motor cooling loop  24 . In such embodiments, refrigerant entering the outlet line  128  may be directed toward back toward the refrigerant loop  16 , such as via a conduit coupled to the housing  60 , where the refrigerant flows into the evaporator  22 . In further embodiments, the outlet line  128  may be omitted from the housing  60 , such that all refrigerant entering the annular cavity  78  through the inlet line  84  discharges into the interior region  81  via the ports  90 . Additionally or alternatively, the motor  14  may include any one or combination of the motor cooling features discussed above. 
     As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for mitigating or substantially eliminating temperature gradients along the stator  62  of the motor  14 . More specifically, the disclosed motor cooling system is configured to direct refrigerant flow toward particular portions of the stator  62  (e.g., the end windings  98 ,  102 ) that typically receive inadequate refrigerant flow when using a low pressure refrigerant within a conventional motor cooling system. Indeed, the improved hermetic motor cooling system discussed herein facilitates a more even distribution of refrigerant across the stator  62 , such that a low pressure refrigerant may effectively be utilized in the motor cooling loop  24  of the HVAC&amp;R system  10  to cool the motor  14 . In this manner, the improved motor cooling system may increase amount of thermal energy transfer between the refrigerant and motor components (e.g., the stator  62 ) within the housing  60 , thereby enhancing an operational life and/or an operational efficiency of the motor  14 . 
     While only certain features and embodiments of the present disclosure have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the present disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode of carrying out the present disclosure, or those unrelated to enabling the claimed embodiments. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.