Patent Application
20140009013
Various embodiments of the present invention pertain to methods and apparatus for retaining the stator of an electric machine within another member, and yet other embodiments pertain to methods and apparatus for improved transfer of heat from an electric machine.
Some embodiments of the present invention include aspects related to the fabrication of a subassembly for an electric machine that includes non-cast components that are located in the casting of another component that is in contact with the non-cast component. Yet other embodiments of the present invention include aspects pertaining to the casting of features surrounding a stator for an electric machine.
Still other embodiments include aspects pertaining to the fabrication of a stator with conductive windings in which portions of the windings are mechanically held together in a matrix of a cast metal.
One aspect of some embodiments pertains to an apparatus for an internal permanent magnet electrical machine, including a cylindrical stator assembly fabricated from a first material. Another embodiment includes a cylindrical member surrounding a portion of the stator, the member being cast from a molten second material in substantial contact with the outer surface of the stator, wherein the melting point of the second material is lower than the melting point of the first material.
Another aspect of some embodiments pertain to a method of making an electric machine, including fabricating a stator having a stator body and at least one electrically conductive winding. The winding includes a plurality of body portions that each pass through the stator body and a plurality of turn portions joining the body portions outside the stator body. Still other embodiments include casting a material to fill at least part of the volume that contains the turn portions.
It will be appreciated that the various apparatus and methods described in this summary section, as well as elsewhere in this application, can be expressed as a large number of different combinations and subcombinations. All such useful, novel, and inventive combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these combinations is unnecessary.
Some of the figures shown herein have been created from scaled objects of a computer model. It is understood that such dimensions, or the relative scaling within a figure, are by way of example, and not to be construed as limiting.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. At least one embodiment of the present invention will be described and shown, and this application may show and/or describe other embodiments of the present invention. It is understood that any reference to “the invention” is a reference to an embodiment of a family of inventions, with no single embodiment including an apparatus, process, or composition that should be included in all embodiments, unless otherwise stated. Further, although there may be discussion with regards to “advantages” provided by some embodiments of the present invention, it is understood that yet other embodiments may not include those same advantages, or may include yet different advantages. Any advantages described herein are not to be construed as limiting to any of the claims.
The use of an N-series prefix for an element number (NXX.XX) refers to an element that is the same as the non-prefixed element (XX.XX), except as shown and described thereafter. The usage of words indicating preference, such as “preferably,” refers to features and aspects that are present in at least one embodiment, but which are optional for some embodiments. As an example, an element 1020.1 would be the same as element 20.1, except for those different features of element 1020.1 shown and described. Further, common elements and common features of related elements are drawn in the same manner in different figures, and/or use the same symbology in different figures. As such, it is not necessary to describe the features of 1020.1 and 20.1 that are the same, since these common features are apparent to a person of ordinary skill in the related field of technology. This description convention also applies to the use of prime (′), double prime (″), and triple prime (′″) suffixed element numbers. Therefore, it is not necessary to describe the features of 20.1, 20.1′, 20.1″, and 20.1′″ that are the same, since these common features are apparent to persons of ordinary skill in the related field of technology.
Although various specific quantities (spatial dimensions, temperatures, pressures, times, force, resistance, current, voltage, concentrations, wavelengths, frequencies, heat transfer coefficients, dimensionless parameters, etc.) may be stated herein, such specific quantities are presented as examples only, and further, unless otherwise noted, are approximate values, and should be considered as if the word “about” prefaced each quantity. Further, with discussion pertaining to a specific composition of matter, that description is by example only, and does not limit the applicability of other species of that composition, nor does it limit the applicability of other compositions unrelated to the cited composition.
Various embodiments of the present invention pertain to the fabrication of an assembly for an electrical machine that includes a first component that is cast in substantial contact with a second component. In some embodiments, the second component is a stator, and in yet other embodiments the stator includes a plurality of conductive windings electrically insulated and arranged in a plurality of parallel electrically conductive paths. In yet other embodiments, the windings are insulated with a ceramic material. Preferably, the materials of the stator assembly are chosen to have melting points that are higher than the melting point of the cast material. Although reference will be made to embodiments pertaining to electrical motors having permanent magnets, including motors with surface permanent magnets and internal permanent magnet mounted on a rotor, it is understood that some embodiments of the present invention pertain to electrical machines in general.
This transmittal of power from stator to rotor imposes environments upon the stator in terms of both torque and heat. With regards to the former, the interaction of the stator and rotor imposes a torque on the rotor that is used to drive the vehicle (such as a rotational power input to a transmission that subsequently results in power being transmitted to one or more wheels of the vehicle). The torque imposed on the rotor by the stator is likewise reacted by an equal and opposite torque of the stator on its surroundings. With reference to motor 10, this reactive torque is passed from the stator to housing 11, and from the mounting features of the housing to the vehicle frame.
In some motors, the stator assembly 20 is received within a pocket of a housing, and this fit is accomplished after heating or cooling of the housing and/or the stator. For example, the stator assembly 22 can be reduced in temperature with a resultant reduction in its outer diameter as a result of a thermal contraction. Likewise, the housing can be heated so that the inner diameter of the pocket increases. By using one or both of these thermal effects, a cold stator can be placed within a warm housing (with the possibility of the fit between the two being an interference fit even with the temperature differential), such that when the stator and housing return to the same temperature, the stator is effectively locked in place by friction with its outer diameter being in a state of residual compression, whereas the inner diameter of the housing is in a state of residual tension.
However, the stator and housing should be designed to support these residual stresses, along with other stresses imposed by operation of the motor. Such an accounting for these residual stresses can result in a stator and a housing that both contain additional material and/or stronger material, as compared to a stator and housing that do not encounter such residual assembly stresses.
In these known motors, the reactive torque of the stator is transferred by the friction of the interference fit (potentially a combination of both thermally-created interference and mechanically designed interference) to the walls of the housing. As previously discussed, the walls of the housing and the material of the stator must be adapted and configured to withstand these residual stresses superimposed upon other operational stresses. Further, the manufacturing processes involved in such manufacturing and assembly methods can be expensive. As examples, to achieve the interference fit the outer diameter of the stator and the inner diameter of the housing must be machined to close tolerances. Further, the use of temperature differences during the assembly process can bring with it the expense of temperature controlled chambers for processing of the stator and housing.
Yet another aspect of the environment of the stator and housing is the heat that needs to be dissipated during operation. Because of various inefficiencies in motor 10 (including for example ohmic heating of the conductors within the stator slots) a portion of the power provided to the motor generates heat. The heat of the stator is typically conducted into the housing, and thereafter removed by coolant flowing within cavities or passages 11.4. However, the conductance of heat from stator to housing is negatively impacted by a less than ideal heat transfer interface from stator OD to housing ID. For example, the outer diameter of some stator assemblies are machined, and any machining grooves (even if small) limit the amount of surface area in contact between the stator and housing. Such limitations on the surface area are also provided by any machining marks on the ID of the housing.
Some embodiments of the present invention include the casting of a component surrounding some or all of the outer surface of the stator. In such embodiments a stator having a rough outer surface can provide improved heat transfer into the cast material, including those embodiments in which the outer stator surface includes features that have a size, shape, or surface roughness such that the molten cast material comes into intimate contact with the features. In such embodiments, the roughness of the outer surface provides a larger surface for conductive heat transfer than what would have been provided by the interface of a stator with a machined outer diameter and a housing with a machined inner diameter.
Various embodiments of the present invention pertain to stators that are outer components surrounding a permanent magnet rotor, and further includes embodiments in which a permanent magnet rotor surrounds an internally located status. Some embodiments of the present invention pertain to stators in which the laminates 22 and conductors 24 are placed circumferentially around an inner diameter of a rotor that includes magnets. However, yet other embodiments of the present invention pertain to motors in which the laminate assembly 22 and the conductors 24 are surrounded by a rotor such that the magnets are located proximate to the inner diameter of a rotating housing of the rotor assembly.
Generally, another embodiment of the present system pertains to an electric machine having a rotor and a stator. The windings of the stator comprise “turn” portions that connect the portions of the wire that go through the stator body. The turn portions are cast inside a heat-conductive material so that the material substantially—if not completely—envelops the turn portions. The casting in some embodiments includes a channel through which fluid flows, carrying ohmic heat away from the windings.
Referring also to
These casting fixtures are adapted and configured to fabricate a cast housing 11 that is cast around the machined stator assembly 22. In some embodiments these casting fixtures are adapted and configured to generally locate the inner diameter 22.4 of laminate assembly 22 relative to one or more mounting features of housing 11, such as mounting flange 11.1. In providing such general alignment, the cast/machined subassembly 21 requires less subsequent machining to provide accurate alignment between the centerline of laminate assembly 22 and various locating features of flange 11.1, such as holes for fasteners and dowel pins.
In some embodiments, the outer surface 22.1 of laminate assembly 22 does not need to be machined prior to having the housing cast around it. Such machining may not be required in those embodiments where the casting process is adapted and configured such that the molten material is able to flow into close contact with the outer surface of that laminated stator.
Further, in some embodiments the laminated stator comprises a plurality of individually stamped plates fabricated from a material such as a ferrous material. In some embodiments the as-stamped outer surfaces of the plates are sufficient in terms of surface finish and diameter variation to be in contact with the molten material during the casting procedure. In such embodiments, the casting material flows sufficiently freely so as to generally conform to the rougher, as-stamped outer surface. As one example, a housing 11 or a sleeve 14 can be cast from a material with a lower melting point than the melting point of the plate material. In some embodiments, the housing or sleeve are cast from a material including aluminum.
In yet other embodiments, the individual plates of the stator assembly have an outer diameter that is either non-circular, or circular about an axis different than the axis of the inner diameter. In such embodiments, the laminate plates are substantially identical to one another. However, as they are stacked together to form the stator assembly, the individual plates are angularly displaced relatively to one another (i.e., clocked relative to one another), such that the composite outer diameter of the stator is non cylindrical, whereas the inner diameter of the stator remains cylindrical (to later receive within it the outer diameter of the rotor). In such embodiments the outer surface of the stator has an outer diameter that varies both circumferentially and axially. Such an irregular outer surface of the stator assembly provides its own locking within the housing as the molten cast material solidifies. It is appreciated that the housing shown in
In some embodiments, a stator assembly 122 is located relative to a plurality of casting fixtures. These fixtures establish an axial location of stator 122 relative to various features of sleeve 114. Further, these casting fixtures prevent the flow of molten cast material into any of the slots or pockets 122.2 of stator 122. It is appreciated that the sleeve shown in
The retention features 222.3 shown in
Referring to
Referring to
A separate key 223′ such as a steel key can be inserted into the central, compound slot 222.2′ The housing 211′ is then cast around the stator and key. The molten casting material comes into contact with the keys, such that the solidified material, key, and stator assembly are substantially locked together.
Laminate assembly 322 includes a plurality of pockets 322.3 spaced apart circumferentially around the outer surface of assembly 322. In some embodiments, these pockets 322.3 are generally symmetrical about a centerline, and that centerline intersects the longitudinally-extending axis of the stator inner diameter. In comparison to retention features 222.3, retention features 222.3 are substantially symmetrical about their respective centerlines.
Cast subassembly 321 further includes a plurality of cast projections 314.2 that extend into and intimately contact the inner surfaces of the laminate stator retention features 322.3. In some embodiments, cast retention features 314.2 and 314.1 are generally opposite one another, although in yet other embodiments they are circumferentially spaced apart to minimize peak stresses within the cast sleeve 314. Preferably, the outermost retention features 314.1 are subsequently received within complementary-shaped retention features within a housing. In such embodiments, the retention features 314.1 transmit torque from the sleeve to the housing, whereas retention features 314.2 transmit torque from the stator assembly to the sleeve. As best seen in
In yet other embodiments, the retention features of the laminate plate assemblies include an outer diameter that is not concentric with the inner diameter of the stator. In some of these embodiments the stator plates are fabricated substantially identically, but during the assembly process, the plates are angularly registered relative to one another with an offset, such that the outer diameter of the assembled stator includes one or more recessed circumferentially-extending sectors. Within the angular extent of the sectors the outer diameters of the two adjacent stator plates are realized as steps or grooves in some embodiments.
As a hybrid machined and cast subassembly 421 (not shown) is produced, the molten material of the sleeve or housing flows in and around the individual retention features 422.3. By spacing apart the torque retention features in both axial and circumferentially directions, it is possible in some embodiments to both minimize stress concentrations in the housing or sleeve, and further to increase the surface area of the stator assembly that is in intimate contact with the solidified cast material.
Turning to
Those skilled in the art also understand that the turn portion 524.3 of the windings (preferably fabricated from a material containing copper) generates ohmic losses in the system. In some embodiments, however, at least the turn portions of conductor 524 are covered by an insulator 524.3, such as one of the ceramic insulators disclosed in U.S. patent application Ser. No. 13/236,685, which is hereby incorporated by reference. Application of ceramic or other insulation in various embodiments occurs preferably before conductors 524 are placed in passages 522.2 and positioned through turn regions 525 adjacent stator faces 522.5 and 522.6. In this illustrated embodiment, turn regions 525 are cast from a heat-conductive material, such as aluminum, during the process in which the housing 511 or the sleeve or similar part is cast. It is appreciated that the casting material may have a melting point lower than the melting point of the conductors, the insulation, the stator plates. Further, yet other embodiments contemplate the casting of a material that preferably has thermal conductivity greater than about five watts per degree Kelvin-meter. In yet other embodiments, more preferably the thermal conductivity is greater than about one hundred watts per degree Kelvin-meter.
Various embodiments allow heat from the turn portions of wires 524 to be disposed of through the heat-conductive casting material. Heat transferred through the casting material in some embodiments is transferred to a cooling passage or cavity 511.4 that is cast into the housing. Preferably passage 511.4 is integrally cast as the cast material solidifies around turn regions 525. However, the present invention also contemplates those embodiments in which a portion of the cooling passage is cast integrally with the cast material surrounding turn portions 525, in which case other components or processes are used to complete the cooling passage.
Various embodiments of the present invention contemplate any type of cooling medium C flowing within cavity 511.4, including air, gas, and solutions including oil, ethylene, or propylene. In some embodiments, the cooling passages include a plurality of fins that extend within the passage and serve to increase the surface area of the passage without substantial detriment to the flow characteristics of the passage. For example, cooling air can be passed over surfaces of the passage, or cooling fluid (such as water) can be moved along those surfaces to further remove heat from the system.
One example of this kind of heat removal is the embodiment illustrated as electric machine 610, shown in
Housing 611 is preferably cast in a single piece, this casting including the various features used for aligning and mounting motor 610 on a support frame. It is appreciated that housing 611 as shown in
In this embodiment, stator assembly 620 of motor 610 is positioned in proximity to rotor portion 650, separated by an air gap, and relative rotational movement between rotor and stator is enabled while they are kept in alignment by bearings 654. Stator assembly 620 houses conductor windings 624 in cast assembly 621, which in some embodiments is a hybrid fabrication including a fabricated stator 620 substantially surrounded by a cast housing 611. Coolant passage or cavity 611.4 is defined within housing 611. Coolant passage 511.4 includes heat exchange surfaces in proximity to turn region 625. In this way, heat from windings 624—especially heat from the turn portion 624.2 of windings 624 in turn region 625—is conducted efficiently through that part of the cast aluminum housing 611 to coolant within channel 611.4
One process of manufacture 700 is illustrated as a flowchart in
A plurality of plates are then assembled 720 into a stator body, such that the slots are in substantial alignment across the stack of plates. In some embodiments, the outer diameter of this stacked body is machined to a predetermined diameter and surface finish. In yet other embodiments various retention features are machined into the outer diameters. Yet other embodiments of the present invention contemplate the machining of various patterns of retention features that are adapted and configured for the viscosity and surface tension of a molten cast material, such that the molten material freely flows into the machined retention feature. In yet other embodiments the retention features are created on the outer diameter during stamping of the laminate plates. Further, it is understood that in some embodiments the stacked assembly of plates are assembled to create substantial alignment among the internal slots or pockets of adjacent plates, but which plates are angularly registered to one another such that one or more retention features on the outer surface of adjacent plates are not in substantial alignment.
Process 700 further includes insulating a plurality of conductor wires, preferably with an insulation material having a melting point that is higher than the melting point of the cast material to be later used. Preferably, this insulating material extends substantially along the entire length of the conductors, both inside the slots or pockets of the laminate plates and also into the end turn regions extending axially outward from the fore and aft faces of the stacked assembly. The insulated conductors are inserted 740 into the stator slots, preferably for three different phases of electrical power.
Following this partial assembly of the stator and conductive windings, this assembly is then placed within one or more casting fixtures. These fixtures preferably define one or more annular volumes adjacent the stator and faces, these annular volumes substantially encapsulating the conductor end turns in molten casting material. In some embodiments, the casting fixtures include provisions for cooling some portions of the stator.
A housing or sleeve is cast 750 around some or all of the stator subassembly. In yet other embodiments, the casting fixtures further establish a sleeve or housing having a wall that is in intimate contact with the outer surface of the stator subassembly. In such embodiments the casting fixtures facilitate the flow of molten material into any retention features fabricated into the outer surface of the stator subassembly. In still other embodiments, the casting fixtures further define an annular volume extending substantially around the stator subassembly that will later serve as a passageway for the flow of coolant.
Process 700 further includes machining 760 of the hybrid subassembly of the subassembled stator within the raw casting. Various features of the cast material are machined, including mounting features, features for locating one or more bearings, and the like.
The machined cast and fabricated subassembly is then assembled 770 into a functional electric machine, including the placement of bearings, a rotor, various connectors, and various connections and covers for the machine cooling system. During operation 780 of electric machine, heat is transferred 790 from the windings directly into the cast material, and thereafter into coolant C within the flow passage of the cast housing.
In some embodiments, no insulation is used on the winding wires, and the heat-conductive material is not substantially electrically conducting. In other embodiments, insulation is applied to the wires, and the heat-conductive material may or may not be electrically conductive.
In some embodiments, the heat-conductive casting material is made to contact the turn portions of the windings over substantially all of their surface area. In other embodiments, such care is not taken, and contact between the casting material and the turn portion of the windings is achieved over portions of the surface area of the windings.
In some embodiments, motor 810 is mechanically coupled to a vehicle to provide motive power to the vehicle.
Rotor assembly 820 includes a support ring 827 that has located within it a plurality of laminate subassemblies 822 spaced about the periphery of support ring 827. These laminate subassemblies 822 are provided a transient magnetic field by a plurality of conductors 824 (not shown), as generally described herein. Further as discussed previously herein, in some embodiments support ring 827 is cast integrally with laminate assemblies 822 and/or conductor assemblies 824.
Rotor assembly 850 includes a plurality of magnets 870, such as permanent magnets, located within an inner diameter of the housing of the rotor assembly, and passing close to the laminate assemblies 822, separated by an air gap.
Stator assembly 820 further includes a backing plate 828 that mechanically couples support ring 827 to the vehicle suspension (by way of inner studs 893). In some embodiments, backing plate 828 is mechanically connected to support ring 827 by a plurality of fasteners (not shown). As shown in
An invention according to one embodiment of the present invention includes an apparatus for an electrical motor including a cylindrical rotor with magnets. The apparatus comprises a ring-shaped stator assembly adapted and configured for placement within the magnets and having an outer circumference with a plurality of slots. The assembly includes a retention feature on a surface of the assembly. The assembly includes a member in fixed relationship with the retention feature and the surface of said stator. The member is cast with the molten material being in substantial contact with the outer surface of said stator.
Although what has been shown and described herein is a hybrid subassembly including both cast and fabricated portions, in which the two portions are fabricated from materials of different melting points, yet other embodiments of the present invention are not so limited. In yet other embodiments the stator and the sleeve or housing can be fabricated from the same material (i.e., such as a steel stator surrounded by a cast steel or cast iron housing). Further, various embodiments herein are described such that the stator material has a higher melting point than the housing or sleeve material, but it is to be noted that various other embodiments are not so limited. In some embodiments the stator material and the housing or sleeve material have melting temperatures that are substantially similar. In such embodiments portions of the casting fixtures may be actively cooled. In yet other embodiments there may be sufficient time lag such that portions of the stator or conductors do not become too hot because of the temperature lag introduced by their own thermal mass.
While the inventions have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.
The present application is related to U.S. application Ser. No. 13/236,685, Attorney Docket 23475-95254 which was filed Sep. 20, 2011, under the title “Electrical Machine with Winding Conductor Having Ceramic Insulation, incorporated herein by reference in its entirety.”
