Electric machine with rotor magnet overhang

Abstract

An electric motor is provided that includes a stator having a length and a rotor inserted into the stator and having a length. The rotor length being longer than the stator length such that a rotor overhang portion extends beyond the stator. The rotor includes an axis and wherein the rotor overhang portion increases the BEMF between the stator and the rotor and provides increased efficiency and torque.

Description

ELECTRIC MACHINE WITH ROTOR MAGNET OVERHANGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 626,448, filed January 29, 2024, titled Electric Machine with Rotor Magnet Overhang, and naming Subhash Brahmavar et al. as inventors, the contents of which are hereby incorporated herein by reference.TECHNICAL FIELD

[0002] The field of the disclosure relates generally to electrical machine assemblies and, more specifically, to rotor overhangs for motor assemblies.BACKGROUND

[0003] Electric machines such as electrically commutated motors or permanent magnet motors generally include a stator and a rotor. The stator includes a plurality of windings and magnets that deliver a magnetic flux to magnets on the rotor when the windings are energized. The magnetic flux traverses a flux path over an air gap defined between the stator and the rotor. More specifically, the air gap is defined between the surface of the stator adjacent the rotor and the surface of the rotor adjacent the stator. The flux causes the rotor to turn.

[0004] Conventional stator and rotor assemblies are of equal axial length, i.e. , the rotor axial length is roughly the same as the stator axial length. Some stator and rotor combinations include a rotor of greater length, i.e., having a slight rotor magnet overhang, of up to 0.3 inches, which generally improves motor performance and efficiency. Prior modifications to the stator and rotor, implemented to yield greater motor performance and efficiency have comprised modifications to the structure of the stator and rotor including changes to the shape and number of rotor magnets, the configuration of the rotor pole pieces that separate adjacent rotor magnets, or modifications to the stator windings. The improvements from such prior art modifications are insubstantial, and such modifications can be complicated and pose achal lenge to implement . There is a need to develop modi fications to conventional stators and rotors that improve motor performance and ef ficiency and that are easy to implement .

[0005] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure described or claimed below . This description is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present di sclosure . Accordingly, it should be understood that these statements are to be read in this light and not as admi ssions of prior art .BRIEF DESCRI PTION

[0006] In one aspect , an electric motor includes a stator having a length and a rotor inserted into the stator and having a length . The rotor length being longer than the stator length such that a rotor overhang portion extends beyond the stator . The rotor includes an axis and wherein the rotor overhang portion increases the BEMF between the stator and the rotor and provides increased ef ficiency and torque .

[0007] In another aspect, a method of assembling an electric motor i s provided . The motor includes an axis , a stator having a length and a rotor having a length that is longer than the stator length . The method comprises inserting the rotor into the stator and positioning the rotor such that the rotor extends at least 0 . 5 inches beyond the length of the stator core such that the position of the rotor within the stator increases the BEMF generated between the rotor and the stator .

[0008] Various refinements exist of the features noted in relation to the above-mentioned aspects . Further features may al so be incorporated in the above-mentioned aspects as well . These refinements and additional features may exist individually or in any combination . For instance , various features discussed below in relation to any of the illustrated examples may be incorporated into any of the above-described aspects , alone or in any combination .BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure. The disclosure may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein .

[0010] FIG. 1 is a perspective view of a stator and rotor assembly including a rotor overhang portion;

[0011] FIG. 2 is perspective view of the stator and rotor assembly shown in FIG. 1 without stator windings;

[0012] FIG. 3 is a side view of the stator and rotor assembly shown in FIG. 2 illustrating rotor overhang portions;

[0013] FIG. 4 is a graph plotting back electromotive force versus the length of the rotor overhang portion;

[0014] FIG. 5 is a graph plotting back electromotive ratio versus the ratio of the length of the rotor overhang portion;

[0015] FIG. 6 is a graph plotting torque versus the length of the rotor overhang portion; and

[0016] FIG. 7 is a graph plotting torque ratio versus the ratio of the length of the rotor overhang portion.

[0017] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings . Although specific features of various examples may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced or claimed in combination with any feature of any other drawing.DETAILED DESCRIPTION

[0018] The following detailed description and examples set forth preferred materials, components, and procedures used in accordance with the present disclosure. This description and these examples, however, are provided by way of illustration only, andnothing therein shall be deemed to be a limitation upon the overall scope of the present disclosure.

[0019] The motor assembly disclosed in the present application comprise a stator and rotor having an overhang portion. In one embodiment, the rotor overhang is at least 0.5 inches long. This rotor overhang yields increased air gap flux density, increased back electromotive force (BEMF) , increased torque, and increased overall motor efficiency. The motor assembly may be more efficient relative to conventional rotor overhang lengths and traditional stator and rotor combinations having equal axial length. Moreover, alternative designs to achieve similar improvements in performance, such as, for example, increased lamination stack dimensions, may require increased manufacturing costs. Accordingly, the motor assembly disclosed herein reduces costs and increases efficiency over conventional electric motors.

[0020] FIGs . 1 and 2 are perspective views of a motor assembly 100. Motor assembly 100 includes a stator 110 and a rotor 120 disposed inside stator 110 such that stator 110 and rotor 120 are arranged coaxially with respect to a longitudinal axis Z, about which rotor 120 turns. Axis Z is defined through the center of stator 110 and rotor 120. In various embodiments, motor assembly 100 may be a single-phase motor or a three-phase motor.

[0021] Stator 110 includes a stator core 113, windings 114 and slots 119. Stator core 113 is generally composed of a ferrous material, such as, for example, iron or steel. Stator core 113 defines a structure of teeth 112 about which windings 114 are formed. Windings 114 are electrical conductors and are typically formed by conductive wire, or strands, wound around stator core teeth 112. The windings are wound around teeth 112 within the slots 119 of the stator core. Windings 114, for example, may be aluminum or copper wire. Windings 114 are configured to be electrically energized by a power source (e.g., utility power) to generate an electromagnetic field. The windings 114 may be energized by an alternating electric current. When windings 114 are energized, the generated electromagnetic field interacts with magnets 121 to cause rotation of rotor 120. It should be understood that stator 110 isillustrated for purposes of describing an embodiment of the disclosure. However it is contemplated that other stationary assemblies 110 of various other constructions having different shapes and with different number of teeth 112 may be utilized. Motor assembly 100, in some embodiments, may include any even number of rotor poles and any number of stator poles. Stator 110 has a stator core length 320.

[0022] Rotor 120 includes a spoke structure in which a rotor core 123 is populated with a plurality of magnets 121. In one embodiment, rotor core 123 includes oppositely polarized magnets 121. Rotor core 123 may be ferromagnetic and is constructed by stacking a plurality of laminations to a desired rotor length 310. Magnets 121 are embedded within rotor core 123. Magnets 121 may be permanent magnets or ferrite magnets. Magnets 121 may alternate polarity such that adjacent magnets 121 have different polarities. While magnets 121 are illustrated on rotor 120, for purposes of disclosure, it is contemplated that other rotors having different constructions and other magnets different in both number and construction, and flux fields may be utilized with such other rotors within the scope of the disclosure. Rotor 120 has a rotor length 310.

[0023] Referring to FIG 2, windings 114 are not shown to better illustrate stator slots 119. In various embodiments of the present disclosure, rotor length 310 exceeds stator core length 320. Rotor 120 includes a rotor overhang portion 330 that is rotor length 310 minus stator core length 320. Overhang portion 330 is provided adjacent each of the lateral faces of the stator 110.

[0024] The rotor overhang portion is illustrated by rotor 120 extending axially from stator 110. As illustrated in FIG. 2, each rotor overhang portion 330 extends at least 0.5 inches beyond the length of stator core 113. Rotor overhang portion 330 alters the magnetic field generated by magnets 121 in rotor 120 with regards to conventional rotor constructions. Accordingly, rotor overhang portion 330 provides an altered interaction between the magnetic field of rotor 120 and stator 110 and increase the BEMF generated during operation of motor assembly 100. The improvementof BEMF caused by rotor overhang portion 330 corresponds to an increase in the overall performance of motor assembly 100.

[0025] In various embodiments, rotor overhang portion 330 may correspond to a cost-effective process for increasing BEMF in a motor assembly such as motor assembly 100. In one embodiment, rotor overhang portion 330 corresponds to the most cost-effective process for increasing BEMF in a motor assembly such as motor assembly 100.

[0026] FIG. 3 is a side view of motor assembly 100 shown in FIG. 2 further illustrating rotor overhang portion 330. As illustrated in FIG. 3, rotor length 310 extends beyond stator core length 320. In one embodiment, rotor length 310 extends at least 0.5 inches beyond stator core length 320. Rotor overhang portion 330 of at least 0.5 inches provides a more efficient interaction between the magnetic fields of stator 110 and rotor 120. Motor assembly 100 generates more BEMF during operation resulting from rotor overhang portion 330 extending at least 0.5 inches beyond stator core length 320.

[0027] That is, rotor overhang portion 330 may be used to increase the output of motor assembly 100 by increasing the amount of magnetic flux generation in a limited space by raising the permanent magnet to the end turn height.

[0028] FIG. 4 is a graph 400 plotting back electromotive force versus the length of rotor overhang portion 330 of motor assembly 100. Graph 400 includes a left vertical axis representing phase BEMF. Graph 400 also includes a horizontal axis representing a length of rotor overhang portion 330. Graph 400 includes a phase BEMF curve measured in Vrms against the length of rotor overhang portion 330 in inches. As illustrated through graph 400, as rotor overhang portion 330 increases in length, the phase BEMF also increases .

[0029] FIG. 5 is a graph 500 plotting back electromotive ratio versus the rotor overhang ratio. Graph 500 includes a left vertical axis representing the phase BEMF ratio. Graph 500 also includes a horizontal axis representing the rotor overhang ratio,where the rotor overhang ratio is the ratio of rotor length 310 to stator core length 320. Graph 500 includes a phase BEMF ratio curve measured against the rotor overhang ratio. As shown in graph 500, as the rotor overhang ratio increases, the phase BEMF ratio also increases .

[0030] FIG. 6 is a graph 600 plotting torque versus the length of rotor overhang portion 330. Graph 600 includes a left vertical axis representing the torque, measured in ounce-feet. Graph 600 also includes a horizontal axis representing the rotor overhang, measured in inches, corresponding to the length of rotor overhang portion 330. Graph 600 includes a torque curve measured against the length of rotor overhang portion 330. As shown in graph 600, as the length of rotor overhang portion 330 increases, the torque of motor assembly 100 also increases.

[0031] FIG. 7 is a graph 700 plotting torque ratio versus the rotor overhang ratio. Graph 700 includes a left vertical axis comprising the torque ratio. Graph 700 also includes a horizontal axis representing the rotor overhang ratio, where the rotor overhang ratio is the ratio of rotor length 310 to stator core length 320. Graph 700 includes a torque ratio curve measured against the rotor overhang ratio. As shown in graph 700, as the rotor overhang ratio increases, the torque ratio also increases.

[0032] Before conducting the overhang study outlined in the disclosure provided herein, the impact of rotor overhang on motor performance or how increasing rotor overhand could improve efficiency was not recognized. The study provided accurate mathematical models and predictions of rotor overhang effects, demonstrating a clear improvement in motor performance with longer overhang. Additionally, considering the cost fluctuations of stator and rotor laminations, increasing rotor overhang offers a more cost-effective design than increasing the stator core, while achieving the same performance. Overall, this study has provided valuable insights into optimizing motor design for both performance and cost efficiency.

[0033] As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural elements or steps unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the disclosure or an "exemplary" or "example" embodiment are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Likewise, limitations associated with "one embodiment" or "an embodiment" should not be interpreted as limiting to all embodiments unless explicitly recited.

[0034] Disjunctive language such as the phrase "at least one of X, Y, or Z, " unless specifically stated otherwise, is generally intended, within the context presented, to disclose that an item, term, etc. may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z) . Likewise, conjunctive language such as the phrase "at least one of X, Y, and Z," unless specifically stated otherwise, is generally intended, within the context presented, to disclose at least one of X, at least one of Y, and at least one of Z.

[0035] The disclosed systems and methods are not limited to the specific embodiments described herein. Rather, components of the systems or steps of the methods may be utilized independently and separately from other described components or steps.

[0036] This written description uses examples to disclose the embodiment of the disclosure, including the best mode, and to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

WE CLAIM:

1. An electric motor comprising: a stator having a length; and a rotor inserted into the stator and having a length, the rotor length being longer than the stator length such that a rotor overhang portion extends beyond the stator, wherein the rotor includes an axis; wherein the rotor overhang portion increases the BEMF between the stator and the rotor and provides increased efficiency and torque.

2. The electric motor of claim 1, wherein the rotor overhang portion includes two overhang portions extending along the axis, one overhang portion on each side of the rotor adjacent each side of the stator, each of the overhang portions extending at least 0.25 inches beyond the stator.

3. The electric motor of claim 2, wherein the overhang portions extend at least 0.50 inches beyond the stator.

4. The electric motor of claim 1, wherein the rotor comprises at least one of a plurality of permanent magnets or a plurality of ferrite magnets.

5. The electric motor of claim 1, wherein the stator includes a plurality of slots and a plurality of windings arranged in the plurality of slots.

6. The electric motor of claim 1, wherein the motor is a single-phase motor.

7. The electric motor of claim 1, wherein the motor is a three-phase motor.

8. The electric motor of claim 1, wherein the motor has a rotor overhang ratio that is the ratio of the rotor length to the stator core length, wherein the rotor overhang ratio is 1.4 or greater .

9. The electric motor of claim 9, wherein the rotor overhang ratio is 1.8 or greater.

10. A method of assembling an electric motor, the motor including an axis, a stator having a length and a rotor having a length that is longer than the stator length, the method comprising : inserting the rotor into the stator; and positioning the rotor such that the rotor extends at least 0.5 inches beyond the length of the stator core, wherein the position of the rotor within the stator increases the BEMF generated between the rotor and the stator.

11. The method of claim 10, wherein the motor further comprises a plurality of permanent magnets, the method further includes inserting the permanent magnets into the rotor.

12. The method of claim 10, wherein the motor further comprises a plurality of ferrite magnets, the method further includes inserting the ferrite magnets into the rotor.

13. The method of claim 10, wherein the rotor includes a plurality of windings and the stator includes a plurality of slots, the method further includes inserting the plurality of windings into the plurality of slots.

14. The method of claim 10, wherein the method further includes positioning the rotor within the stator such that two overhang portions are formed and each extend at least 0.25 inches beyond the stator.

15. The method of claim 10, wherein the method further includes positioning the rotor within the stator such that two overhang portions are formed and each extend at least 0.5 inches beyond the stator.

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