Patent Application
20230129960
Synchronous reluctance machines require the use of magnetic flux barriers to create magnetic anisotropy in the rotor construction to guarantee proper motor operation. Rotors may include a plurality of laminations that are stacked in the axial direction of the rotor. Because of the design of the rotor, the lamination may contain bridges, which may not contribute to the operational performance of the machine. Instead, a bridge may act as loss point and, because of the diminutive dimension of a bridge, may constitute a mechanical failure point. However, bridges may be needed for mechanical strength of the rotor to withstand centripetal loads.
One or more embodiments of the present invention may provide a rotor of a synchronous reluctance motor. The rotor may include: a plurality of laminations forming a stack, each lamination including: two parallel surfaces and a perimeter that define the lamination and a direction of stacking the plurality of laminations that is perpendicular to the two parallel surfaces, the lamination being at least partially filled with a first material comprising a magnetically soft electrical conductor and at least one cavity encircled by the first material and extending from a first surface of the two parallel surfaces to a second surface of the two parallel surfaces, the first material forming at least one bridge at the perimeter of the lamination from one side of the at least one cavity to another side of the at least one cavity, wherein: a value of a magnetic property of the at least one bridge differs from a value of the magnetic property of a remainder of the first material, and a value of a mechanical property of the at least one bridge differs from a value of the mechanical property of the remainder of the first material.
Further, one or more embodiments of the present invention may provide a method of increasing the saliency ratio of a rotor of a synchronous reluctance motor by modifying at least one mechanical property and at least one magnetic property of at least one region of the rotor, the rotor comprising a stack of a plurality of laminations, the laminations stacked in an axial direction of the rotor, each lamination comprising: two parallel surfaces and a perimeter that define the lamination, the parallel surfaces being perpendicular to an axial direction of the rotor, and at least the perimeter of each lamination is identical to the perimeter of every other lamination; the lamination being at least partially filled with a first material comprising a magnetically soft electrical conductor and at least one cavity encircled by the first material and extending from a first surface of the two parallel surfaces to a second surface of the two parallel surfaces, the first material forming at least one bridge at the perimeter of the lamination from one side of the at least one cavity to another side of the at least one cavity. The method may comprising: forming the laminations of the plurality of laminations from at least one sheet of the first material; stacking the laminations in the axial direction of the rotor; and plastically deforming the at least one bridge in each lamination of at least two laminations of the plurality of laminations by applying compressive stress simultaneously to the at least one bridge in each lamination of the at least two laminations, wherein the applied compressive stress is greater than or equal to a yield strength of the first material and less than or equal to an ultimate tensile strength of the first material.
One or more embodiments of the present disclosure may address modification of mechanical and magnetic properties of synchronous reluctance rotors to enhance the saliency ratio of the rotors. The saliency ratio (Iq/Id) may be defined as the inductance ratio between the two magnetic directions of the rotor, that is, between the direct (d) axis induction (Id) and the quadrature (q) axis induction (Iq). Enhancing the saliency ratio may result in superior speed and torque capabilities. In one or more embodiments, the modification may be local, applying to one or more parts of a rotor, but not all of the rotor.
Referring to
The cavities 130, 132, 134, 136 may be empty or partially or completed filled with a ferrimagnetic or ferromagnetic material. One example of a ferrimagnetic material is ferrite. An example of ferromagnetic material is Nd—Fe—B. The cavities may be filled with a mixture of ferrimagnetic or ferromagnetic material and a polymer.
It may be of technical interest to decouple electromagnetic and mechanical responses in the bridges. On one hand, it may be desirable to enhance the mechanical performance of the bridges. On the other hand, it may be of relevance to mitigate the magnetic response of bridges, i.e. to reduce the local magnetic permeability of the material at the bridges.
The present disclosure will describe at least two methods that decouple the magnetic performance and the mechanical performance of the bridges of rotor laminations. The result may include an improved saliency ratio of the rotor with consequent higher speed and torque capabilities of the rotor.
One method may involve mechanical deformation of outer regions of a rotor by means of compression (indentation), peening, or burnishing. A second method may involve strain hardening via injection molding. Both methods may generate compressive and tensile as well as shear stresses in the electrical steel of a rotor. No method presented here requires the use of a special atmosphere or elevated temperatures. For example, an atmosphere comprising 90% or more nitrogen is not required. In fact, no nitrogen-rich atmosphere of any type is required. Further, the methods described herein may be carried out between 0 degrees and 50 degrees Celsius. More particularly, the methods described herein may be carried out at room temperature. Applying plastic deformation to the electrical steel of the rotor may be a key aspect to locally reduce magnetic permeability and enhance mechanical performance in bridge regions.
A. Plastic Deformation Via Compression/Peening/Burnishing
Plastic deformation of bridges may be achieved using compression (indentation), peening, or burnishing.
Some areas of the rotor had “deep” plastic deformation (approximately 0.6 millimeters (mm) depth), whereas in others, a shallow deformation have been achieved. This difference is a consequence of distinct areas (and pressures) applied to the surface of the rotor via a pressing (indentation) die. This test allowed visualization of the dimensional change of the rotor outer region as a function of force/pressure.
Referring to
Table 1 lists the direct axis induction (Id), the quadrature axis induction (Iq), and saliency ratio. The order of deformation is shown in
In addition to the process described in the above experiment, alternative processes may be used to deform the rotor at the bridges. For example, deformation may be achieved by mechanical means such as shot peening or low plasticity burnishing. Deformation may also be achieved with laser peening.
B. Strain Hardening Via Injection Molding
Currently rotor laminations may be designed so that the laminations are punched to their desired final shape. That is, there may be no subsequent cold or hot forming process applied to the rotor lamination (with the possible exception of turning the outer diameter of the lamination). This approach may result in isotropic material characteristics. However, it may be preferable to have anisotropic material characteristics and to decouple magnetic and mechanical properties in the bridges.
In order to validate the claims on mechanical performance, simulations were performed with two separate rotor geometries: (1) a round lamination with 1 mm webs and (2) a similar lamination where the webs are shortened by 5% of their length. For this study, it has been assumed that the internal cavities are subjected to a pressure of 4,000 pounds per square inch (psi), which is uniformly distributed in the cavities (for example, due to injection molding, which, can achieve pressures of the order of 10,000 psi) and is contained by a cylindrical steel cavity of the desired final diameter. Both the plain rotor and the formed rotor are then subjected to a simulated speed ramp of 0 to 5,000 back to 0 to 6,000 and back to 0 revolutions per minute (rpm). Results are shown for the second ramp (0 to 6,000 rpm). In both cases, the material under consideration is annealed electrical steel and the model is a multilinear kinematic hardening model based on tensile test data. Another feasible model that can be fitted to the tensile test data in the plastic regime is of parabolic form with a strain hardening coefficient and a strength coefficient.
The mechanical anisotropy produced by the methods described herein may add significant mechanical safety factor as indicated in
Moreover,
If this lamination is used for rotors with polymer bonded magnets (or neat resin) then no additional processing step maybe required for strain hardening the rotor. Strain hardening may be accomplished by utilizing the injection pressure to deform the rotor laminations. If the rotor is produced via mechanical forming, the laminations may be stamped and then formed by adding an additional mechanical processing step.
One or more methods may include forming the laminations of the plurality of laminations from at least one sheet of the first material (S610). For example, the first material may be electrical steel in sheet form. The laminations may be formed by punching the initial shape of the lamination into the sheet. The methods may, perhaps subsequently, stack the laminations in the axial direction of the rotor (S620). The stacking may involve placing a bottom parallel surface of one lamination on top of a top parallel surface of an adjacent lamination. The methods may further include, perhaps subsequent to stacking, plastically deforming the at least one bridge in each lamination of at least two laminations of the plurality of laminations by applying compressive force simultaneously to the at least one bridge in each lamination of the at least two laminations (S630). The applied compressive force may generate a stress that is greater than or equal to a yield strength of the first material and may be less than or equal to an ultimate tensile strength of the first material.
In one or more embodiments, plastically deforming may include pressing externally on the perimeter of each lamination of the at least two laminations in a location of the at least one bridge. Pressing externally may include applying an external tool that simultaneously plastically deforms a plurality of the bridges of each lamination of the at least two laminations.
In one or more embodiments, plastically deforming may include strain hardening. The strain hardening may be by injection molding a second material comprising ferrimagnetic or ferromagnetic material or neat (or compounded) polymers into the at least one cavity in each lamination of the at least two laminations. Each lamination of the at least two laminations may include at least one pair of cavities with a web of the first material traversing between the at least one pair of cavities, and plastically deforming the at least one bridge may also plastically deform the web.
In one or more of the methods, forming the laminations may include forming the laminations with a non-circular cross-section in a plane parallel to either the first or the second surface the perimeter of each lamination and plastically deforming may include converting the non-circular cross-section to a circular cross-section.
Further, one or more methods may further include providing, throughout the method, an environment comprising an ambient temperature less than 50 degrees Celsius and a non-nitrogen-rich atmosphere.
In one or more methods, plastically deforming may further include applying compressive stress simultaneously to the at least one bridge in every lamination.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
