This invention relates in general to stator windings for switched reluctance machines. More particularly, this invention relates to shaped windings that are highly conforming to the stator shape and stator pole shape of a switched reluctance machine.
A switched reluctance machine (SRM) is a doubly salient machine, that is, it comprises multiple poles on both stator and rotor. The SRM may have a plurality of stator poles, each with multiple loops of electrically conductive wires or in total a coil or winding positioned thereabout. The stator poles of the SRM are integral parts of the stator. The stator windings comprising each machine phase winding are connected in series or in parallel, so that when a phase winding is excited, magnetic flux produced in the corresponding pair(s) of stator poles combines additively. The phases of the stator are energized sequentially in a cyclical fashion so that a magnetic force of attraction occurs between the energized stator pole and the rotating rotor, thereby causing the rotor to rotate. As is well known in the art, this current must be switched on and off at proper times at proper rotor position to provide the attraction between rotor poles and the energized stator pole without producing a negative or braking attraction once the rotor reaches its aligned position with the stator.
Normally, in a conventional SRM, each of the stators and the rotors has a salient structure. The stator has a winding wound on salient parts thereof to generate a reluctance torque according to variations in magnetic reluctance, while the rotor has no magnetization mechanism such as a coil or a permanent magnet. The rotor is connected at a central part thereof, to and rotated together with, a rotational axis that transmits a driving force of the machine. The SRM is an electric machine that converts the reluctance torque into mechanical power. The torque is produced by the alignment tendency of poles. The rotor will shift to a position where reluctance of the magnetic circuit is minimized and the inductance of the energized winding of the stator is maximized. The SRM rotates the rotor by using the reluctance torque generated according to variations in magnetic reluctance.
One conventional SRM disclosed in U.S. Pat. No. 8,541,920 comprises a conventional SRM with a stator having plurality of poles, each of which has its concentric windings connected in a manner that achieves a required number of machine phases. The conventional SRM further comprises a rotor having a plurality of poles with neither windings nor magnets on the rotor poles. The windings in this disclosure are of either an L shape or a triangular shape, with each one representing the part of the coil on one side of the pole winding. Because they each constitute a coil side of the pole winding, the pole windings will have two of them side by side for placement on the stator poles, with interconnection for each of the individual conductors and that populate the coil sides. The space volume between the stator poles is filled with a maximum number of winding turns so as to have maximum number of turns per phase winding in the SRM. The shapes and forms are simple to realize in practice and manufacture through automation. However, this conventional approach fails to produce curved stator windings conforming to the stator curved shape. Also, this approach fails to fully utilize the potential copper fill factor.
Another conventional approach describes a rotary electric machine, the rotary electric machine includes a stator having an open slot configuration and a plurality of stator poles with a coil positioned about each stator pole. As described in U.S. Pat. No. 9,118,225 to Caterpillar Inc., the coil has a plurality of electrically conductive wires defining a group of wires and the group of wires is wrapped generally around a stator pole to define a plurality of turns. The coil may be formed with a generally symmetrical cross-section and the lateral movement of at least some of the electrically conductive wires of each turn while mounting the coil on the stator pole may modify the shape of the coil to form a generally asymmetrical cross-section across a portion thereof. The asymmetrical cross-section may extend across a portion of a pair of adjacent stator slots that are separated by a stator pole. This assembly of the machine is complicated. Further, this conventional approach does not teach shaping of the windings and does not facilitate formation of stator shape-conforming windings for SRMs.
Another approach is disclosed in US Patent Publication 2005/0258702, wherein disclosed is a stator comprising a plurality of stator teeth, a first set of windings and a second set of windings. The first set of windings are wound around some of the stator teeth that define a first cross section, the first cross section including an approximately equal number of turns along the stator tooth and is generally rectangular-shaped. The second set of windings is formed around others of the stator teeth that each defines a second cross section, the second cross section includes an increasing number of turns along the stator tooth and is generally trapezoidal-shaped. The first and second sets of windings are interleaved around the teeth of the stator. This multiple shape windings method improves the torque density of the electric machine. However, this approach does not follow a two-step process to achieve the shaping of the windings. Furthermore, this approach fails to produce curved stator windings conforming to the stator curved shape.
Therefore, there is a need for shaping of stator windings to increase the copper fill factor for SRMs. The associated method of shaping the stator windings would produce curved stator windings, the curved stator windings being highly conforming to the stator shape. This needed method of shaping of windings would include two main embodiments—symmetrical shaping and asymmetrical shaping. Further, such curved stator windings conforming to the stator curved shape would allow more copper in the SRM. A design using this method of shaping stator windings would allow the motor to provide more torque, more speed, higher power density, lower noise, and/or many other smart tradeoffs for overall better performance. Such a system would be highly efficient and reliable. The present embodiment overcomes shortcomings in this area by accomplishing these critical objectives.
To minimize the limitations found in the prior art, and to minimize other limitations that will be apparent upon the reading of the specification, the present invention is a process for shaping a plurality of stator windings for a switched reluctance machine (SRM). The present invention proposes an apparatus and method for making an apparatus utilizing a plurality of curved stator windings, the invention comprising two main embodiments: a symmetrical winding and an asymmetrical winding. In either case, the plurality of stator poles is highly conforming to a stator shape. The plurality of curved stator windings further provides an additional degree of freedom, such that a motor using this method allows more torque, more speed, higher power density, lower noise, and/or many others smart tradeoffs for overall better performance, such as, higher efficiency, lower noise, higher torque and lower temperature rise to the machine. The plurality of curved stator windings conforms to the stator curved shape, increasing the copper fill factor, which in turn allows maximum copper in the machine, ultimately resulting in increased efficiency and reduced noise in the machine. The increase in the copper fill factor can be utilized in different ways, including but not limited to increasing the number of turns, using thicker magnetic wire and a combination of a greater number of turns with thicker magnetic wire.
The method for producing the plurality of curved stator windings by shaping the plurality of stator windings for the SRM is initiated by winding a first stator coil with a magnetic wire on a tooling implement such as but not limited to a mandrel, mold or fixture. Heating the first stator coil in a straight form is a next step, followed by removing the first stator coil from the tooling, resulting in a simple winding coil. In the preferred embodiment, the next step is assembling the simple winding coil into a cylindrical form tooling. Then, heating the simple winding coil and pressing the simple winding coil into the curved stator winding shape. Finally, optionally providing insulation to the curved stator windings by utilizing a plurality of insulation means. Thus, the plurality of curved stator windings is produced by shaping the plurality of stator coils in the SRM. Of note, the herein described heating steps are flexible in terms of their ordering. The heating steps may also be removed from the method completely.
It is a first objective of the present invention to provide a method for producing a plurality of curved stator windings by shaping a plurality of stator windings for an SRM.
A second objective of the present invention is to provide a method for shaping of windings to increase the copper fill factor for an SRM.
A third objective of the present invention is to produce curved stator windings which are conformed to a stator shape.
A fourth objective of the present invention is to produce curved stator windings which enable higher efficiency and lower noise in an SRM.
These and other advantages and features of the present invention are described with specificity so as to make the present invention understandable to one of ordinary skill in the art.
Elements in the figures have not necessarily been drawn to scale in order to enhance their clarity and improve understanding of the various elements and embodiments of the invention. Furthermore, elements that are known to be common and well understood to those in the industry are not depicted in order to provide a clear view of the various embodiments of the invention, thus the drawings are generalized in form in the interest of clarity and conciseness.
The foregoing aspects and many of the attendant advantages of the invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the attached figures.
In the following discussion that addresses a number of embodiments and applications of the present invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustrating specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and changes may be made without departing from the scope of the present invention.
Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. In the following discussion that addresses a number of embodiments and applications of the present invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustrating specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and changes may be made without departing from the scope of the present invention.
The shaping process contemplated by the present invention produces curved stator windings 104, the curved stator windings 104 being highly conformed to the stator shape in all embodiments. This method of shaping comprises two main embodiments including symmetrical shaping and asymmetrical shaping. The primary difference between these two embodiments is the shape of the final product.
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As described above, in the preferred embodiment every symmetrical winding may be substantially identical in shape. In another embodiment, symmetrical windings are substantially identical in volume and surface area as well. As a result, every stator winding in a symmetrical system may be interchangeable with any of the other windings in that SRM. In the preferred embodiment of the asymmetric model on the other hand, the windings are non-identical in shape, although they may continue to maintain substantially the same surface area and volume as the other asymmetric windings in a given SRM. Notably, in the preferred embodiment of the asymmetric model, no winding is greater than 1 mm in distance from an adjacent winding. In a less preferred embodiment, no winding is greater than 2 mm in distance from an adjacent winding.
As described above, the present invention is a process for shaping a plurality of stator coils for an SRM. Notably, the present invention also proposes an apparatus, utilizing a plurality of curved stator windings 104 and has two main embodiments: a symmetrical winding and an asymmetrical winding. The plurality of curved stator windings 104 are highly conformed to a stator shape. The plurality of curved stator windings 104 provide serval performance enhancements including higher efficiencies and lower noise output to the SRM. The plurality of curved stator windings 104 also provide one more degree of freedom, such that a motor using this method allows more torque, more speed, higher power density, lower noise, and/or many others beneficial tradeoffs resulting in an overall enhanced performance. Such enhanced performance further comprises a greater output efficiency, increased torque and lower temperature rise to the machine. As described above, the plurality of curved windings 104 also closely conform to the stator curved shape, increases the copper fill factor, which in turn allows maximum copper utilization in the machine. Maximum copper utilization translates to reduced noise, a greater number of winding turns, and/or an electrically conductive material with a thickness greater than the industry standard along the length of the electrically conductive material. The plurality of curved stator windings 104 may also be insulated to a higher degree relative to the industry standard in some embodiments.
As described herein, the method permits use of an electrically conductive material such as a magnetic wire, or any highly conductive metal, with a thickness greater than the industry standard along the length of the electrically conductive material. The magnet wire may be simple or a bondable magnetic wire. Further, the magnetic wire may be made of aluminum or any comparable metallic wire. In the case of bondable magnetic wire, the bondable magnetic wire may be activated by any means, such as alcohol, suitable chemicals, heat, or resistive heating by applying the voltage/current to the magnet wire. The wire may be at room temperature or heated during any step of the process. Furthermore, the molds used for winding or shaping may be at room temperature or heated and this could be done at any step in the process.
The claimed subject matter has been provided here with reference to one or more features or embodiments. Those skilled in the art will recognize and appreciate that, despite the detailed nature of the exemplary embodiments provided here; changes and modifications may be applied to said embodiments without limiting or departing from the generally intended scope. These and various other adaptations and combinations of the embodiments provided here are within the scope of the disclosed subject matter as defined by the claims and their full set of equivalents.
The foregoing description of the preferred embodiment of the present invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in the shaping of the stator coils of the SRM of the above teachings. It is intended that the scope of the present invention not be limited by this detailed description, but by the claims and the equivalents to the claims appended hereto.
This application claims priority from the United States provisional application with Ser. No. 62/744,707 and filed Oct. 12, 2018. The disclosure of that provisional application is incorporated herein as if set out in full.
Number | Date | Country | |
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62744707 | Oct 2018 | US |