The present technique relates generally to the field of electric motors and generators, and to methods and apparatus for cooling such. For example, the present invention relates to a novel technique for dissipating heat in motors and generators by routing fluid along surfaces of a stator core. Although the present discussion focuses on electric motors and generators, the present invention affords benefits to a number of applications related to lamination stacks and to the cooling of such stacks.
Electric motors and generators of various types are commonly found in industrial, commercial and consumer settings. In industry, motors are employed to drive various kinds of machinery, such as pumps, conveyors, compressors, fans and so forth, to mention only a few. Conversely, generators translate kinetic energy into electrical energy. Conventional alternating current electric (ac) motors and generators may be constructed for single or multiple phase power, and are typically designed to operate at predetermined speeds or revolutions per minute (rpm), such as 3600 rpm, 1800 rpm, 1200 rpm, and so on. Such motors and generators generally include a stator, comprising a multiplicity of windings, surrounding a rotor, which is supported by bearings for rotation in the frame. In the case of ac motors, ac power applied to the motor causes the rotor to rotate within the stator. The speed of this rotation is typically a function of the frequency of ac input power (i.e., frequency) and of the motor design (i.e., the number of poles defined by the stator windings). A rotor shaft extending through the motor housing takes advantage of this produced rotation and translates the rotor's movement into a driving force for a given piece of machinery. That is, rotation of the shaft drives the machine to which it is coupled. By contrast, in generators, rotation of the magnetized rotor induces current in the stator windings, generating power.
During operation, conventional motors and generators generate heat. Indeed, the physical interaction of the devices various moving components produces heat by way of friction. Additionally, the electromagnetic relationships between the stator and the rotor produce currents that, in turn, generate heat due to resistive heating, for example. As yet another source of heat, ac magnetic fields lead to losses in the magnetic steel supporting the windings and conductors in the stator and rotor, respectively. If left unabated, excess heat may degrade the performance of the device. Worse yet, excess heat may contribute to any number of malfunctions, which may lead to system downtime and require maintenance. Undeniably, reduced efficiency and malfunctions are undesirable events that may lead to increased costs.
To dissipate heat, conventional motors and generators route a coolant, such as forced air or liquid coolant, through the stator or rotor and through the air gap between the stator and rotor. However, the tight fit between the stator and the frame supporting the stator prevents coolant from directly affecting the outer regions of the stator. Indeed, in traditional motors and generators, losses generated in the stator-whether in the conductors or in the magnetic steel-create heat in the stator that is typically dissipated by routing air or coolant over the outer surfaces of the frame.
In some cases, the motor or generator frame is surrounded by a coolant jacket through which cooling liquid (i.e., fluid) is routed. Unfortunately, such coolant jackets are an extra component that is assembled to the active parts of the motor or generator, leading to increased manufacturing costs. Furthermore, such cooling jackets are radially outward of the frame assembly, increasing the distance of cooling jacket from the heat generating components and, as such, limiting the overall efficacy of the cooling jacket. Generally, effective cooling of motors and generators is desired because excess heat in the stator windings, bearings, and rotor conductors, for example, can negatively influence the overall machine efficiency and component life, for instance.
The main magnetic path in an electric motor or generator is generally through the magnetic material that supports the stator or rotor conductors. This magnetic material makes up the stator and rotor core. To reduce magnetic flux produced losses, which generate heat, the magnetic core is laminated, with the lamination plane being in the same plane as the direction of the main magnetic flux path. In conventional radial air gap motors and generators, the stator and rotor core are, therefore, constructed from laminations that are assembled into an axial stack (i.e., a lamination stack). Traditionally, the lamination stack's outer surface is a smooth surface that is designed to be placed on and shrink fitted to the inner surface of a frame. Thus, the frame inner surface is in direct contact with the outer surface of the lamination stack in all locations circumferentially and axially along the lamination stack. In some cases, the frame is separated from the stator core in several locations to allow coolant flow or the passage of electrical wiring axially along the periphery of the stator core and between the core and the frame. In these types of core-to-frame constructions, the inner surface of the frame is generally machined or cast with well defined coolant paths that allow coolant flow over the outer smooth surfaces of the stator core. This special frame geometry adds complexity and cost to construction of the motor or generator stator.
There is a need, therefore, for improved methods and apparatus for cooling electric motors and generators. Moreover, there is a particular need for methods and apparatus that reduce temperature variations in the motor and provide a mechanism for cooling the outer regions of the stator.
According to one embodiment, the present invention provides a lamination for an electric machine. The exemplary laminations are supported in a frame and cooperate with one another to form a lamination stack. Each exemplary lamination comprises a central aperture sized to receive a rotor, and a plurality of slots disposed circumferentially about the central aperture. These slots are configured to receive a plurality of windings. Additionally, the lamination comprises an outer periphery that defines a lamination cross-section such that the lamination is disposable in the frame. The outer periphery has at least one recessed section extending longitudinally between the ends of the lamination that is configured to cooperate with the frame to form a closed passageway for routing fluid. Accordingly, by routing fluid through the recessed sections of a plurality of laminations disposed within the frame, a mechanism for cooling the radially outward regions of the lamination stack that forms the stator is provided. Advantageously, cooling these outer regions of the stator improves the distribution of cooling resources. Additionally, to increase the efficacy of the cooling effect of the fluid, the recessed section of each lamination may be configured to cooperate with the frame and with adjacent laminations to form a labyrinthine passageway for routing the fluid along perimetric or peripheral surfaces of the assembled stator. Advantageously, the labyrinthine passageway provides a larger surface area of contact for the fluid while minimizing effects on structural integrity.
According to another exemplary embodiment, a lamination for a lamination stack is provided. The lamination includes a central aperture sized to receive a rotor and a plurality of slots disposed circumferentially about the central aperture at equiangular positions with respect to one another. Additionally, the lamination has an outer periphery that defines a generally circular lamination cross-section. The outer periphery also has at least one recessed section extending longitudinally between the ends of the lamination. The at least one recessed section is configured to cooperate with adjacent laminations of the stack to form a labyrinthine passageway extending along a circumferential surface of the lamination stack. Advantageously, a fluid may be routed through the labyrinthine passageway to dissipate heat developed in the lamination stack during operation of a motor, for example. As discussed above, the labyrinthine nature of the passageway creates a larger contact surface area for a cooling fluid routed through the passageway. Thus, the labyrinthine passageway facilitates more uniform cooling of the lamination stack and better dissipation of heat generated in the lamination slack or other loss producing elements of the machine.
According to another embodiment of the present invention, an electric motor is provided. The electric motor includes an enclosure that comprises first and second endcaps and a frame disposed between the endcaps. The exemplary motor also includes a stator core formed of a plurality of substantially identical stator laminations disposed in the frame. The plurality of substantially identical stator laminations each includes a recessed section that cooperates with the frame and one another to form a closed passageway for routing fluid along perimetric surfaces of the stator core. Advantageously, the closed passageway facilitates cooling of the outer portions of the stator core during operation of the motor. Moreover, the closed passageway forms a labyrinthine path for cooling fluid routed therethrough and, as such, provides a greater contact surface area for the cooling fluid in comparison to a direct axial passageway. By increasing the contact surface area of the cooling fluid, the efficacy of the convective cooling of the fluid is increased.
According to another embodiment of the present invention, an electric device having a frameless stator construction is provided. In this embodiment, the labyrinthine passageway extending through the stator core is formed by cooperation between appropriately configured apertures located within the stator lamination. That is to say, the labyrinthine passageways extend longitudinally through the stator lamination stack and radially inboard of the outer peripheral surface of the stack. Accordingly, improved cooling may be effectuated without use of a framed construction.
According to yet another exemplary embodiment of the present invention, a method for manufacturing a motor is provided. The method includes the act of providing a plurality of substantially identical laminations, wherein each lamination has at least one recessed section along an outer periphery of the lamination and longitudinally between the ends of the lamination. The exemplary method also includes the act of arranging the plurality of laminations with respect to one another to form a lamination stack, such that the at least one recessed section of the respective laminations cooperate to form a passageway extending along perimetric surfaces of the lamination stack. The lamination stack may be disposed within a motor frame such that the motor frame and the channel cooperate to form a closed passageway for routing fluid. Again, by routing fluid through the passageway, which extends axially and circumferentially along perimetric surfaces of the stack, the outer regions of the lamination stack can be more effectively cooled.
The foregoing and other advantages and features of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
a and 15b are respective front views of stator laminations that are each disposed in a frame, which is illustrated in dashed line, in accordance with an embodiment of the present invention;
As discussed in detail below, embodiments of the present invention provide apparatus and methods for cooling electric machines having lamination stacks. Although the discussion regarding the present invention focuses on electric motors and generators, the present invention also affords benefits to a number of applications in which the cooling of a lamination stack is a concern. Accordingly, the following discussion relates to exemplary embodiments of the present invention and, as such, should not be viewed as limiting the appended claims to the embodiments described.
Turning to the drawings,
To induce rotation of the rotor, current is routed through stator windings disposed in the stator. (See
During operation, the motor 10 generates heat. By way of example, the physical interaction between various components of the motor 10 generates heat via friction. Additionally, current in the stator windings as well as in the rotor generates heat via resistive heating. Moreover, in the case of ac motors, eddy currents developed in the stator laminations and as well as hysteresis losses in the stator also produce heat. If left unabated, excess heat leads to a degradation in performance of the motor 10 and, in certain instances, may lead to malfunction of the motor. To improve heat dissipation, the illustrated motor 10 carries a cooling assembly 28 mounted to the motor housing and configured to convectively cool the motor 10. As discussed further below, the cooling assembly 28 circulates a fluid (e.g., liquid coolant or air) through the motor, thereby convectively cooling the motor. Simply put, the cooling assembly 28 convectively cools the motor 10 by dissipating heat into the environment surrounding the motor 10, as represented by arrows 29. It is worth noting that the motor may carry a plurality of cooling units 28, if desired.
In cooperation with the frame 12, the recessed section of each lamination 30 defines an incremental segment of a closed and contiguous passageway 40 that extends axially along an outer or perimetric surface 38 of the stator core 32. In
In the exemplary motor 10, a rotor assembly 50 resides within the rotor chamber 34. Similar to the stator core 32, the rotor assembly 50 comprises a plurality of rotor laminations 52 aligned and adjacently placed with respect to one another. Thus, the rotor laminations 52 cooperate to form a contiguous rotor core 54. The exemplary rotor assembly 50 also includes rotor end rings 56, disposed on each end of the rotor core 54, that cooperate to secure the rotor laminations 52 with respect to one another. It is worth noting, however, that the rotor may be a cast rotor or a fabricated rotor, for instance. When assembled, the rotor laminations 52 cooperate to form shaft chamber that extends through the center of the rotor core 54 and that is configured to receive the rotor shaft 26 therethrough. Once inserted, the rotor shaft 26 is secured with respect to the rotor core 54. Accordingly, the rotor core 54 and the rotor shaft 26 rotate as a single entity, the rotor assembly 50. The exemplary rotor assembly 50 also includes rotor conductor bars 58 disposed in the rotor core 54. As discussed further below, inducing current in the rotor assembly 50, specifically in the conductor bars 58, causes the rotor assembly 50 to rotate. By harnessing the rotation of the rotor assembly 50 via the rotor shaft 26, a machine coupled to the rotor shaft 26, such as a pump or conveyor, may operate.
To support the rotor assembly 50, the exemplary motor 10 includes drive-end and opposite drive-end bearing sets 60 and 62, respectively, that are secured to the rotor shaft 26 and that facilitate rotation of the rotor assembly 50 within the stationary stator core 32. During operation of the motor 10, the bearing sets 60 and 62 transfer the radial and thrust loads produced by the rotor assembly 50 to the motor housing. In summary, the bearing sets 60 and 62 facilitate rotation of the rotor assembly 50 while supporting the rotor assembly 50 within the motor housing, i.e., the frame 12 and the endcaps 14 and 16. To reduce the coefficient of friction between various components of the bearing sets 60 and 62, these components are coated with a lubricant. During operation, however, the physical interaction of and within the bearing sets 60 and 62 generate heat.
As discussed above, the exemplary motor 10 includes a cooling assembly 28 that dissipates heat generated in the motor 10 during operation. The cooling assembly 28 can comprise an assembly of parts or, alternatively, a self-contained unit housed in a single assembly as illustrated in
As coolant 78 enters the closed passageway 40, the impermeable surfaces of the respective stator laminations 30 and the frame 12 cooperate to route the coolant 78 through the passageway 40 and along the perimetric surfaces 38 of the stator core. In the exemplary embodiment, the stator laminations 30 and the frame 12 cooperate to change the direction of the flow of the coolant 78 (i.e., route the coolant) down the perimetric surfaces 38 of the stator core 32, as represented by directional arrow 94. Subsequently, the closed passageway 40 routes the coolant 78 axially along surface 38 of the stator core 32, as represented by directional arrow 96. The closed passageway then routes the coolant 78 back up the perimetric surfaces 38 of the stator core 32, as represented by directional arrow 98. By repeating this route axially along the length of the stator core 32, the closed passageway 40 routes the coolant 78 in a labyrinthine path along the perimetric surfaces of the stator core. As the coolant 78 reaches the exit end of the closed passageway 40, an egress artery 42 located in the drive-end endcap 14 meets the closed passageway 40 and receives the coolant 78. This artery 42 routes the fluid to the output reservoir 82, as represented by arrows 100.
To maintain sufficient pressure differential for circulating the coolant 78, the exemplary cooling assembly 28 includes a pumping mechanism 104. Alternatively, in the case of a gaseous cooling fluid, the pumping mechanism 104 includes a fan. As illustrated, the pumping mechanism 104 draws fluid from the output reservoir 82 and to the input reservoir 80, as represented by directional arrows 106. Advantageously, the pumping mechanism 104, the reservoirs 80 and 82, the arteries 42, and the passageway 40 cooperate to form a closed system. Thus, circulating coolant 78 is, for the most part, conserved.
By circulating coolant 78 through the closed passageway 40, the coolant 78 draws in heat from the stator core 32. More particularly, the coolant 78 comes into contact with the perimetric surfaces 38 of the stator core 32 and absorbs some of the heat generated by operation of the motor 10. The proximity of the closed passageway 40 to the radially outward regions of the stator core 32 provides a mechanism for focusing cooling on such regions. Thus, the likelihood of uneven cooling or hotspots in the motor can be mitigated. In the exemplary embodiment, the passageway 40 provides an indirect or labyrinthine path for the coolant along the surfaces of the stator core 32. Accordingly, the coolant 78 comes into contact with a larger portion of the perimetric surface 38 of the stator core 32 in comparison to a direct axial path and, as such, absorbs more heat into the circulating coolant 78.
Once the coolant 78 has circulated through the closed passageway 40, a heat exchanger 110, located in the housing of the cooling assembly 28, facilities dissipation of the absorbed heat from the coolant 78 into the environment, as represented by arrows 29. By way of example, the heat exchanger 110 may include a series of flat plates across which the coolant 78 is directed. The flat plates increase the circulating surface area of the coolant 78 and, as such, facilitate improved dissipation of the absorbed heat in the coolant 78 to the environment. In any event, after the absorbed heat in the coolant 78 has been dissipated, the coolant 78 is directed back into the input reservoir 80 and the circulation cycle is repeated.
Advantageously, the recessed sections 126 may be configured to form a labyrinthine path for the coolant 78 (see
In the illustrated lamination 30, the larger recessed portion 126 begins at an angular position midway between “Slot 11” and “Slot 12” and extends along the outer periphery 122 to a radial position midway between “Slot 4” and “Slot 5.” The smaller recessed portion 126 begins at an angular position midway between “Slot 5” and “Slot 6” and extends to an angular position midway between “Slot 6” and “Slot 7.” For the purposes of this discussion, the larger recessed section is said to correspond with Slots 12 through 4 and the smaller recessed section is said to correspond with Slot 6. This nomenclature scheme extends to the laminations 30 illustrated in
When arranged in a lamination stack or stator core 32, the lamination 30 of
The stator core 32 is capped on each end by drive-end and opposite drive-end endcaps 14 and 16, respectively. As discussed above, each endcap 14 and 16 includes at least one artery 42 that facilitates coolant flow into or out of the passageways 40 of the stator core 32. The first row in the chart represents a group of laminations 30 (Group 1) disposed in the frame 12 in the orientation illustrated in
This orientation pattern is repeated for the remaining groups, i.e., the orientation of Group 5 matches the orientation of Group 1, the orientation of Group 6 matches the orientation of Group 2, and so on. Thus, when coolant 78 reaches the last group in the stator core 32, Group 8, the two passageways 40 both feed into the artery 42 in the drive-end endcap 14, and coolant 78 is circulated through the cooling assembly 28 as described above. By routing coolant 78 in a labyrinthine path, coolant 78 comes into contact with a larger portion of the perimetric surfaces 38 of the stator core 32 in comparison to a direct axial path, and, as such, increases the efficacy of the circulating coolant 78. Additionally, it should be noted that although the recessed section 126 pattern is presented for a twelve-slot stator core 32, the pattern is applicable to stator cores 32 that have an integer multiple of the twelve-slot pattern, e.g., twenty-four-slot, thirty-six-slot, etc. Advantageously, radially recessed portions of each stator lamination facilitates the circulation of coolant 78 between the smooth, unmachined inner surface of the frame 12 and the outer peripheral surface of each respective lamination. Thus, a coolant path can be provided without machining of the frame, which is an often difficult and expensive process.
Beginning with the first passageway, the first group of laminations (i.e., Group 1) routes coolant from Slot 6 of the first Group to Slot 2 of the second group of laminations (i.e., Group 2). Group 2 is oriented at 180 degrees clockwise with respect to Group 1. The coolant 78 is then routed from Slot 2 of Group 2 to Slot 6 of Group 3. Group 3 is oriented at 330 degrees clockwise with respect to Group 1. Coolant 78 is then routed from Slot 6 of Group 3 to Slot 6 of Group 4. Group 4 is orientated at 150 degrees clockwise with respect to Group 1. This orientation pattern is repeated axially with respect to the stator core 32, as the orientation of Group 5 corresponds to the orientation of Group 1, the orientation of Group 6 corresponds to Group 2, the orientation of Group 7 corresponds to Group 3, and the orientation of Group 8 corresponds to Group 4. The first passageway concludes at Slot 6 of Group 8, as coolant is routed into the egress artery 42 located in the drive-end endcap 14.
The second passageway 40 presents a labyrinthine flow path that is the mirror image of the first passageway. In this passageway 40, coolant 78 is provided to the recessed section corresponding with Slot 8 of Group 1 via the ingress artery 42 in the opposite drive-end endcap 16. Coolant 78 is then routed in the passageway from Slot 8 of Group 1 to Slot 8 of Group 2. Subsequently, coolant 78 is routed from Slot 8 of Group 2 to Slot 12 of Group 3. From this position in the second passageway, coolant 78 is routed from Slot 12 of Group 3 to Slot 6 of Group 4. This pattern is repeated, as the orientation of Group 5 matches the orientation of Group 1, the orientation of Group 6 matches that of Group 2, and so on. Upon its conclusion, the second passageway routes coolant 78 into the egress artery 42 in the drive-end endcap 14, and the processes is repeated as coolant 78 is circulated.
Additionally, the recessed sections 126 may present more complex cross-sections configured to increase the contact surface area between the circulating coolant and the perimetric surfaces 38 of the respective stator core 32. By way of example,
Turning to
Coolant ingresses at the recessed section corresponding to Slot 6 of the first stator lamination group (i.e. Group I). Because the recessed section of the second lamination 30b extends part way into the region angularly corresponding to Slot 6, fluid from the Group I laminations is routed into the recessed portion corresponding to half of Slot 6 of Group II. In Group II, fluid is routed from half way into Slot 6 to Slot 11. From this location, coolant is routed into Slot 11 of Group III and to halfway into Slot 6 of Group IV. From Slot 6 of Group IV, coolant is routed to Slot 6 of Group V and into the egress artery 42 for recirculation.
Keeping
Turning to
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims. For example, although the foregoing discussion focuses on electric motors and generators, the present invention affords benefits to a number of applications involving lamination stack and the cooling of such.