Patent Application
20180287439
The present disclosure relates to permanent magnet electric machines, and more specifically to electric machines having improved magnetic flux delivery to the stator by removing one or more bridges from the laminations of the rotor.
Many automobile manufacturers are producing electric and hybrid-electric vehicles to improve fuel economy and reduce pollution. These vehicles include a traction battery and one or more electric machines powered by the battery. Each electric machine includes a stator and a rotor that is supported for rotation within the stator. The rotor is mounted on a shaft that is driveably connected to the driven wheels by one or more powertrain components. Torque produced by the electric machine is sent to the driven wheels by the powertrain components to propel the vehicle.
According to one embodiment, an electric machine includes a stator and a rotor supported for rotation within the stator. The rotor includes a core of stacked laminations each having a hub portion and pole portions cooperating to define pockets. Magnets are disposed in the pockets. Bonding material is also disposed in the pockets. Each of the pole portions has a projection embedded in the bonding material to create a mechanical connection between the pole portions and the bonding material.
According to another embodiment, a rotor includes a rotor core defining axially extending pockets circumferentially arranged within the core. Magnets are disposed in the pockets. Bonding material is also disposed in the pockets and has raised portions that extend out of each pocket beyond an end of the core. A ring is disposed on the end and engages with the raised portions to bias the magnets towards a center of the core.
According to yet another embodiment, a rotor includes a cylindrical rotor core having a hub portion with radially projecting spokes that define slots therebetween. The rotor core further has pole portions each disposed in one of the slots such that the pole portions are not directly connected to the hub portion. A magnet is disposed in each of the slots between the hub portion and a corresponding pole portion. A non-magnetic connection attaches each of the pole portions to the hub portion.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Referring to
The electric machine 50 may include a stator 52 having a plurality of laminations (not shown). Each of the laminations includes a front side and a back side. When stacked, the front and back sides are disposed against adjacent back and front sides to form a stator core 58. Each of the laminations may be doughnut shaped and define a hollow center. Each lamination also includes an outer diameter (or outer wall) and an inner diameter (or inner wall). The outer diameters cooperate to define an outer surface of the stator core 58, and the inner diameters cooperate to define a cavity 60.
Each lamination may include a plurality of teeth extending radially inward toward the inner diameter. Adjacent teeth cooperate to define slots. The teeth and the slots of the laminations are aligned with each other to define stator slots extending through the stator core 58 between the opposing end faces 62. The end faces 62 define the opposing ends of the core 58 and are formed by the first and last laminations of the stator core 58. A plurality of windings (also known as coils, wires, or conductors) 64 are wrapped around the stator core 58 and are disposed within the stator slots. The windings 64 may be disposed in an insulating material (not shown). Portions of the windings 64 generally extend in an axial direction along the stator slots. At the end faces 62 of the stator core, the windings may bend to extend circumferentially around the end faces 62 of the stator core 58 forming end windings 66. While shown as having distributed windings, the windings could also be of the concentrated type.
A rotor 54 is disposed within the cavity 60 and supported for rotation relative to the stator 52, which is typically a stationary component. The rotor 54 has a rotor core 56 that may be formed of a plurality of stacked laminations 68. The laminations are typically steel plates but may be formed of any material having a high magnetic permeability. Each of the lamination 68 may define one or more magnet pockets 70 that divide each lamination 68 into a central hub portion 72 and a plurality of pole portions 74 circumferentially arranged around the hub portion 72 near the periphery 80 of the rotor core 56. A plurality of magnets 78 are embedded in the rotor core 56 with each magnet 78 being disposed in one of the pockets 70 and extending axially through the rotor core 56. The magnets 78 are located at the poles of the rotor 54.
The rotor 54 may be supported on a shaft 82 and positioned inside the stator 52 so that an air gap 84 is formed between the rotor 54 and the stator 52. When current is supplied to the stator 52, a rotating magnetic field is created in stator causing the rotor 54 to spin within the stator 52 generating a torque. The shaft 82 is configured to output the torque to another component such as a gearbox.
Referring to
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In the illustrated embodiment, the rotor core 102 includes eight poles 112. Each pole 112 has a pair of adjacent magnet pockets 114 defined by the cooperation of the hub portion 106, the pole portion 108, and the center bridge 110. Each pocket 114 is configured to receive one of the magnets 116. The magnets 116 extend axially through their respective pockets 114 between the opposing ends 105.
To reduce flux leakage from the pole portions 108 to the hub portion 106, the laminations 104 do not include side bridges. An air gap 118 is provided between the edges 120 of the pole portions 108 and the edges 122 of the hub portion 106. This creates slots 124 in the outer sidewall 103 that extend between the ends 105. Each slot 124 may be continuous with associated pockets 114.
To offset a loss of strength due to removal of the side bridges, a bonding material 128 is applied in the pockets 114 to attach the pole portions 108 to the hub portion 106. The bonding material forms a non-magnetic mechanical connection between the outer sides 130 of the hub portions and the inner sides 132 of the pole portions to supplement the center-bridge connection. The bonding material 128 also secures the magnets 116 within their respective pockets 114. The bonding material 128 may be applied to the pockets 114 so that bonding material flows into the slots 124. This provides a non-metallic connection between adjacent edges 120, 122 of the pole and hub portions to further secure the pole portions 108 to the hub portion 106. The bonding material may be epoxy, plastics, or composite materials.
Referring to
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The first raised portions 166 each extends above the outer surface 168 of the end 164, and the second raised portions each extends above the outer surface of the end 165. The raised portions serve as engagement points for the first ring 170 and the second ring 172. The bonding material 162 may adhere the rings to the rotor core 152. The first ring 170 is disposed on the first end 164 and may include an inner surface 174 that engages with the first raised portions 166. The second ring 172 is disposed on the second end 165 and may include an inner surface that engages with the second raised portions. The rings 170, 172 bias the magnets and the pole portions 156 towards the center of the rotor core 152 to resist centrifugal forces that urge the pole portions 108 and the magnets outwardly when the rotor 150 is rotating. The rings 170 and 172 may be formed of any non-magnetic material such as non-magnetic metal, e.g., stainless steel, plastic, composite, or bonding material. The pole portions 156 may include projections 176 that are embedded in the bonding material 162 as described above to further increase the connection between the pole portions 156 and the hub portion 158.
Referring to
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The hub portion 256 may include a plurality of spokes 260 projecting radially outward from a central region 257 of the hub portion 256. Each of the spokes 260 includes a tip 262 that forms a portion of the sidewall 255. The pole portions 258 include outer sides 259 that form the other portion of the sidewall 255. Adjacent spokes 260 cooperate to define slots 264 for receiving the magnets 276 and the pole portions 258. In the illustrated embodiment, the slots 264 are V-shaped having a narrower base and a wider mouth located at the sidewall 255. The pole portions 258 have a generally triangular shape to nest in the slots 264.
One or more magnets 276 are disposed in each of the slots 264. For example, each pole may include a pair of magnets 276 generally arranged in a V-shape. Each magnet 276 may be disposed in the air gap defined between an outer side 265 of one of the spokes 260 and an inner side 261 of one of the pole portions 258.
The rotor 250 does not include any bridges to further reduce flux leakage from the pole portions 258 to the hub portion 256. Thus, the pole portions 258 are not directly connected to the hub portion 256, and an intermediate connecting means is needed to secure the pole portions 258 in place. A bonding material 278, such as epoxy, may be applied in the air gaps to indirectly connect the pole portions 258 to the hub portion 256. The bonding material 278 also secures the magnets 276 in place. This creates a non-magnetic connection that does not contribute to flux leakage.
Each of the pole portions 258 may include a plurality of projections embedded in the bonding material 278 to increase the strength of the connection between the pole portions 258 and the bonding material 278. For example, each pole portion 258 may include a center projection 266, a pair of edge projections 268, and a pair of intermediate projections 270. Each of these projections are embedded in the bonding material 278 and are shaped to form a mechanical connection with the bonding material. The spokes 260 may also include edge projections 272 embedded in the bonding material 278. The sidewall 255 may define a plurality of axially extending slots 274 that are located between the spokes 260 and the pole portions 258. The slots 274 may be continuous with the slots 264 and have bonding material 278 disposed therein.
Referring to
In other embodiments, the rotor 250 may include rings (similar to rings 170 and 172) located on the ends 254 of the rotor core 252 made of metal, plastic, or composite. The rings may engage with raised portions of the bonding material 278 as described above.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
