Patent Application
20230052600
The field of the disclosure relates generally to electric motors, and more particularly, to radially embedded permanent magnet rotors and methods of increasing flux density and specific torque.
Radial flux electric machines generally include permanent magnets positioned within a rotor core, commonly referred to as an interior permanent magnet rotor. The rotor is formed from multiple laminations and circumferentially spaced poles. Slots are formed between adjacent poles, and magnets are inserted into the slots. However, in some known radial flux electric machines, Flux may leak across laminations pole and radiate out from the rotor, which may induce eddy currents in nearby conductive structure. The leakage flux, while relatively small, can cause significant eddy current losses which has a detrimental effect on both torque and efficiency of the electric machine during operation.
At least some radial flux electric machines increase the axial length of the rotor, that is, use additional laminations, to overcome the loss of torque resulting from the flux leakage. However, additional laminations undesirably increase the cost and overall size of the electric machine and also increases manufacturing complexity.
Similarly, at least some radial flux electric machines use an over-molding technique to increase the robustness of the rotor structure. However, over-molding requires additional tooling and manufacturing steps that increase the cost of the electric machine.
In one embodiment, a rotor assembly for use in a radial flux electric motor assembly is provided. The rotor assembly includes a rotor core having a plurality of rotor poles circumferentially spaced about a central axis, wherein the rotor core includes a first end and an opposing second end. The rotor assembly further includes a plurality of core magnets alternately spaced with the plurality of rotor poles. The plurality of rotor poles define a radial aperture between each pair of circumferentially adjacent rotor poles, and each radial aperture is configured to receive at least one core magnet of the plurality of core magnets therein. A plurality of end magnets are coupled to at least one of the first end and the second end, and at least one end plate coupled to the plurality of end magnets.
In another embodiment, an electric motor assembly is provided. The electric motor assembly includes a stator assembly having a stator core and a plurality of windings. The motor assembly also includes a rotor assembly having a rotor core with a plurality of rotor poles circumferentially spaced about a central axis, wherein the rotor core includes a first end and an opposing second end. The rotor assembly further includes a plurality of core magnets alternately spaced with the plurality of rotor poles. The plurality of rotor poles define a radial aperture between each pair of circumferentially adjacent rotor poles, and each radial aperture is configured to receive at least one core magnet of the plurality of core magnets therein. A plurality of end magnets of the rotor assembly are coupled to at least one of the first end and the second end, and at least one steel end plate of the rotor assembly is coupled to the plurality of end magnets.
In yet another embodiment, a rotor assembly for use in a radial flux electric motor assembly is provided. The rotor assembly includes a rotor core having a plurality of rotor poles circumferentially spaced about a central axis, wherein the rotor core includes a first end and an opposing second end. The rotor assembly further includes a plurality of core magnets alternately spaced with the plurality of rotor poles. The plurality of rotor poles define a radial aperture between each pair of circumferentially adjacent rotor poles, and each radial aperture is configured to receive at least one core magnet of the plurality of core magnets therein. The rotor assembly also includes at least one steel end plate coupled to the rotor core and the core magnets.
Rotor assembly 20 includes a permanent magnet rotor core 36 and a shaft 38. In the exemplary embodiment, rotor core 36 is formed from a stack of laminations made of magnetically permeable material. Rotor core 36 is substantially received in a central bore of stator core 28 for rotation along an axis of rotation X.
In the exemplary embodiment, electric motor 10 is coupled to a fan or centrifugal blower (not shown) for moving air through an air handling system, for blowing air over cooling or heating coils, and/or for driving a compressor within an air conditioning/refrigeration system. More specifically, motor 10 may be used in air moving applications used in the heating, ventilation, and air conditioning (HVAC) industry, for example, in residential applications using ⅕ horsepower (hp) to 1 hp motors. Alternatively, motor 10 may be used in fluid pumping applications. Motor 10 may also be used in commercial and industrial applications and/or hermetic compressor motors used in air conditioning applications, where motor 10 may have a rating of greater than 1 hp. Although described herein in the context of an air handling system, electric motor 10 may engage any suitable work component and be configured to drive such a work component.
Stator base 110 includes an inner surface 116 and an outer surface 118. Inner surface 116 and outer surface 118 extend about central axis 102 and are spaced radially apart. Inner surface 116 and outer surface 118 define a thickness 120 of base 110 therebetween. In alternative embodiments, stator assembly 104 includes any base 110 that enables motor assembly 100 to operate as described herein.
Also, in the exemplary embodiment, stator assembly 104 has an outer diameter D1 defined by base 110. In some embodiments, the outer diameter D1 is in a range of about 100 mm (4 inches (in.)) to about 350 mm (14 in.). For example, in some embodiments, bas 110 has an outer diameter of approximately 240 mm (9.5 in.) or approximately 310 mm (12.2 in.). In alternative embodiments, stator assembly 104 has any diameter that enables motor assembly 100 to operate as described herein.
In addition, in the exemplary embodiment, stator teeth 112 extend radially from base 110. In some embodiments, stator teeth 112 are integral with base 110. In further embodiments, stator teeth 112 are coupled to base 110. In the exemplary embodiment, each stator tooth 112 includes a distal tip 122 that is positioned proximate rotor assembly 106.
In addition, in the exemplary embodiment, stator teeth 112 are spaced circumferentially about base 110 and define slots 124 therebetween. Stator teeth 112 are configured to receive conduction coils or windings 114 such that windings 114 extend around teeth 112 and through slots 124. In some embodiments, stator teeth 112 define no more than 24 slots. In the exemplary embodiment, stator assembly 104 includes eighteen stator teeth 112 defining eighteen slots 124. In alternative embodiments, motor assembly 100 includes any number of stator teeth 112, such as twelve, that enable motor assembly 100 to operate as described herein.
In some embodiments, stator assembly 104 is assembled from a plurality of laminations. Each of the plurality of laminations is formed in a desired shape and thickness. The laminations are coupled together to form stator assembly 104 having the desired cumulative thickness. In further embodiments, stator assembly 104 includes a first configuration, e.g., a flat or strip configuration, and a second configuration, e.g., a round configuration. Stator assembly 104 is moved or “rolled” from the first configuration to the second configuration to form a roll-up stator assembly 104 having a substantially cylindrical shape. In alternative embodiments, stator assembly 104 is assembled in any manner that enables stator assembly 104 to function as described herein.
Also, in the exemplary embodiment, outer surface 118 includes curved portions 126 and straight portions 128. Curved portions 126 extend circumferentially about base 110. Straight portions 128 extend along chords between curved portions 126. In addition, curved portions 126 and straight portions 128 extend longitudinally relative to central axis 102 from a first end to a second end of base 110. Curved portions 126 provide increased strength to base 110 to increase hoop stress capacity and resist deformation of base 110. In alternative embodiments, outer surface 118 includes any portion that enables motor assembly 100 to operate as described herein. For example, in some embodiments, outer surface 118 is curved about the entire periphery of base 110.
With continued reference to
Accordingly, in the exemplary embodiment, rotor assembly 106 is a spoked rotor and is configured to provide increased magnetic flux in comparison to at least some known rotor assemblies. Stator assembly 104 is configured to provide capacities for the increased magnetic flux and the increased hoop stress due to the increased magnetic flux. In alternative embodiments, motor assembly 100 includes any rotor assembly 106 that enables motor assembly 100 to operate as described herein.
Rotor core 130 is substantially cylindrical and includes an outer periphery 142 and a shaft central opening 144 having a diameter suitable for the diameter of shaft 136. Rotor core 130 and shaft 136 are concentric and are configured to rotate about axis of rotation 102. In the exemplary embodiment, rotor core 130 includes the plurality of circumferentially spaced rotor poles 134 each having an outer wall 146 along rotor outer periphery 142. Further, rotor core 130 includes a rotor diameter D2 defined between midpoints of outer walls 146 of opposing rotor poles 134. As used herein, the term “substantially cylindrical” is meant to describe that the rotor core 130 includes a generally circular or oval cross-section but is not required to be perfectly circular. For example, rotor core 130 may include one or more flattened or planar portions distributed about outer periphery 142, or outer walls 146 of rotor poles 134 may include a different radius than the overall rotor core 130 or even different radii between circumferential ends of each pole 134. Although described in relation to rotor core 130, the term “substantially cylindrical” applies to each rotor core of the disclosure.
As shown in
Furthermore, in the exemplary embodiment, rotor core 130 includes the plurality of radial apertures 140 alternately spaced with rotor poles 134. Each radial aperture 140 is configured to receive one or more permanent magnets 138 such that each magnet 138 is radially embedded in rotor core 130 and extends at least partially from a rotor first end 152 to a rotor second end 154. In the exemplary embodiment, radial apertures 140 are generally rectangular. Alternatively, radial apertures 140 may have any suitable shape corresponding to the shape of the permanent magnets that enables electric motor to function as described herein. In the exemplary embodiment, permanent magnets 138 are ceramic magnets magnetized in a direction tangent to axis of rotation X. However, magnet 116 may be fabricated from any suitable material that enables motor 10 to function as described herein, for example, bonded neodymium, AlNiCo, sintered neodymium, bonded and ceramic ferrite, and/or samarium cobalt.
In the exemplary embodiment, the number of radial apertures 140 is equal to the number of rotor poles 134, and one magnet 138 is positioned within each radial aperture 140 between a pair of rotor poles 134. Although illustrated as including ten rotor poles 134, rotor core 130 may have any number of poles that allows motor 100 to function as described herein, for example, six, eight or twelve poles.
In the exemplary embodiment, each rotor pole 134 includes one or more permanent magnet retention member or protrusions 156. For example, a first pair of protrusions 158 is located proximate pole outer wall 146 along rotor outer edge 142 and extends into adjacent radial apertures 140 from circumferential end walls 160 and 162. Each protrusion 156 of the first pair of protrusions 158 is configured to facilitate retention of magnet 138 within radial aperture 140 by substantially preventing movement of magnet 138 in a radial direction towards outer edge 142. Further, a second pair of protrusions 164 is located proximate web 148 and extend adjacent radial apertures 140 from circumferential end walls 160 and 162. Each protrusion 156 of the second pair of protrusions 164 is configured to facilitate retention of magnet 138 within radial aperture 140 by substantially preventing movement of magnet 138 in a radial direction towards shaft 136. Alternatively, rotor core 130 may have any number and location of protrusions 156 that enable rotor core 130 to function as described herein.
Additionally, in the exemplary embodiment, rotor assembly 106 includes at least one end plate 172 coupled to plurality of end magnets 166. More specifically, rotor assembly 106 includes a first end plate 174 coupled to first plurality 168 of end magnets 166 and a second end plate 176 coupled to second plurality 170 of end magnets 166. Eddy current losses into surrounding conductive structures can be eliminated or reduced by preventing flux leakage from the axial face of radial spoke rotors. End plates 174 and 176 provide a barrier to the flux radiating from rotor core 130 into the surrounding structure of motor assembly 100 and therefore eliminates eddy current losses. In the exemplary embodiment, end plates 174 and 176 are formed from a magnetic material, such as but not limited to ferritic steel and magnetic stainless steel. Alternatively, end plates 174 and 176 are formed from any material that facilitates operation of rotor assembly 106 as described herein. In some embodiments, end plates 174 and 176 may cause flux shorting, which may reduce the overall torque of motor assembly 100. In the exemplary embodiment, end magnets 166 are added to rotor assembly 106 to restore flux, resulting in substantial increases in both torque and efficiency. More specifically, first plurality 168 of end magnets 166 is positioned between first end 152 of rotor core 130 and first end plate 174. Similarly, second plurality 170 of end magnets 166 is positioned between second end 154 of rotor core 130 and second end plate 176.
In the exemplary embodiment, first plurality 168 of end magnets 166 comprises a first subset 178 having a first polarity and a second subset 180 having a second polarity different from the first polarity. Similarly, second plurality 170 of end magnets 166 comprises a first subset 182 having a first polarity and a second subset 184 having a second polarity different from the first polarity. As shown in
Regarding the positioning of end magnets 166, in the exemplary embodiment, each end magnet 166 at least partially covers an interface 186 between a rotor pole 134 and an adjacent core magnet 138. More specifically, each end magnet 166 will at least partially overlap with a corresponding rotor pole 134 and core magnet 138 such that end magnets 166 provide a path for flux to flow between rotor pole 134 and core magnet 138. Alternatively, in cases where end magnets 166 may not cover interface 186, a circumferential edge of end magnets 166 is flush with a circumferential edge of the corresponding rotor pole 134. In one embodiment, end magnets 166 are secured to rotor core 130 using an adhesive. Alternatively, end magnets 166 are secured to rotor core 130 in any manner that facilitates operation of rotor assembly as described herein.
In the exemplary embodiment, as shown in
As shown in
Referring specifically to
Described herein are exemplary systems and apparatus that reduce eddy current loses and to increase the torque and efficiency of an electric motor. The systems and apparatus described herein may be used in any suitable application. However, they are particularly suited for HVAC and pump applications.
Specifically, eddy current losses into surrounding conductive structures can be eliminated or reduced by preventing flux leakage from the axial face of radial spoke rotors. The end plates described herein provide a barrier to the flux radiating from the rotor core into the surrounding structure of the motor assembly and therefore eliminates eddy current losses. Eddy current losses are reduced, for example, from 146 W to 10 W (93% reduction). Adding axial magnets and rotor steel end caps to radial spoked rotors increases efficiency and torque by preventing flux leaking axially which induce eddy currents in surrounding conductive structure. Additionally, the rotor assembly described herein is more simply manufactured compared to other known rotor assemblies due to the use of mechanical fasteners to secure the components of the rotor assembly together. In such an embodiment, tooling and processes used to over-mold the rotor are no longer required, thus leading to reduced manufacturing time and costs.
Exemplary embodiments of rotor cores for electric machines are described above in detail. The electric motor and its components are not limited to the specific embodiments described herein, but rather, components of the systems may be utilized independently and separately from other components described herein. For example, the components may also be used in combination with other motor systems, methods, and apparatuses, and are not limited to practice with only the systems and apparatus as described herein. Rather, the exemplary embodiments can be implemented and utilized in connection with many other applications.
Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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.
