Patent Application
20220278568
The technical field generally relates to synchronous reluctance machines, and more particularly to methods for manufacturing components thereof.
Permanent Magnet Synchronous Machines (PMSMs) with rare-earth magnets are utilized in various applications ranging from house appliances to electric vehicles and wind generators, as they can provide high efficiency and torque density. Due to an increase in rare-earth prices, the electric motor industry is looking for alternative designs and technologies that reduce the dependency on rare-earth elements without sacrificing motor performance. The Synchronous Reluctance Motor (SynRM) is considered a promising alternative to PMSMs, due to its robust rotor design and its comparable performance to conventional induction motors. While SynRMs can achieve power density and efficiency comparable to induction motors, their performance is still inferior to PMSMs with rare-earth magnets. There is therefore room for improvement.
According to an aspect, a rotor for a Synchronous Reluctance Motor (SynRM) is provided. The rotor includes: a shaft; and a core fixed relative to the shaft. The core includes alternating layers of radially fabricated flux carrier and flux barrier material, defining flux barriers extending through the core without bridges and/or center-posts. In an embodiment, the alternating layers include layers of permanent magnet (PM) and soft magnetic composite (SMC) material fabricated on, and adhered directly to, the rotor shaft.
According to an aspect, a method for manufacturing a rotor for a SynRM is provided. The method includes the steps of: a) providing a support structure; b) fabricating a first layer of flux carrier material on the support structure; c) fabricating a layer of flux barrier material over the first layer of flux carrier material, to define a flux barrier; d) fabricating a subsequent layer of flux carrier material over the layer of flux barrier material; and e) repeating steps c) and d) to form the rotor with a desired number of flux barriers. In an embodiment, the layers are formed by fabricating PM and SMC material using cold spray additive manufacturing.
With reference to
The rotor portion 151 comprises a rotor core 153 made of a high magnetic permeability material and comprises a plurality of flux barriers 155 made of non-magnetic material for defining magnetic flux paths through the rotor core 153. In the present illustration, the flux barriers 155 are arc-shaped air gaps defined in the rotor core 153, extending between opposite radial extremities of the rotor core 153. The rotor core 153 is transversally laminated in that it is formed by stacking a plurality of laminations along the longitudinal axis of rotor shaft 161, with each lamination extending in a plane transverse relative to the longitudinal axis of rotor shaft 161. Each of the laminations are substantially identical, and the flux barriers 155 are carved out into each lamination. In such a configuration, to facilitate assembly and maintain structural integrity of the rotor core 153, center-posts 157 and bridges 159 are provided. The center-posts 157 comprise a portion of the rotor core material intersecting the air gaps of the flux barriers 155, and the bridges 159 comprise a portion of the rotor core material spacing the air gaps of the flux barriers 155 apart from the radial extremities of the rotor core 153. As can be appreciated, the posts/bridges 157, 159 can allow for the components of each lamination to be held together as a single piece, thereby facilitating assembly. Moreover, the assembled laminations will have increased structural integrity, which is especially required when the rotor core 153 is operating at high speeds.
Although the center-posts 157 and bridges 159 facilitate assembly and provide additional structural integrity, they can have a significant impact on the performance of the SynRM motor 100. As can be appreciated, the center-posts 157 and bridges 159 increase leakage flux through the flux barriers 155 and lead to a reduction in the motor's torque capability. As show in
One way to counteract this effect is to provide a rotor core without bridges and/or center-posts, for example as shown in the segmented rotor core 151a of
With reference now to
Referring back to
The rotor core 253 is axially layered in that it comprises a plurality of layers which each extend along axes substantially parallel to the longitudinal axis of shaft 261. In particular, the rotor core 253 is formed via alternating layers of flux carrier material 265 (i.e. core material) and flux barrier material 263. The layers 263, 265 alternate along a radial direction relative to the shaft 261. The flux carrier material 265 can comprise a substantially high magnetic permeability material, for example having a relative permeability much greater than 1, and preferably greater than 100. In the present embodiment, the flux carrier material 265 comprises a soft magnetic composite (SMC), but it is appreciated that other similar materials are possible in other embodiments, such as soft magnetic materials. The flux barrier material 263, on the other hand, can comprise a substantially low magnetic permeability material, for example having a relative permeability lower than 100, and preferably close to 1. In the present embodiment, the flux barrier material 263 comprises a permanent magnet material, but it is appreciated that in other embodiments, the flux barrier material 263 can comprise a non-magnetic material and/or a combination of magnetic and non-magnetic materials.
The layers of rotor core 253 are arranged to prevent leakage flux between the magnetic flux paths defined by the flux barriers 255. More specifically, in the present embodiment, the layers of flux carrier material 265 are completely separated from one another via a corresponding layer of flux barrier material 263. In other words, each layer of flux barrier material 263 extends continuously and uninterrupted along a thickness 273, between an outer radial boundary 271a of a first flux carrier layer, and an inner radial boundary 271b of a second flux carrier layer. In such a configuration, substantially no flux carrier material 265 extends within or through the layers of flux barrier material 263.
In the present embodiment, the layers of rotor core 253 are also configured such that the rotor core 253 is a substantially solid mass. In other words, there are no air gaps or pockets between inner 266 and outer 267 surfaces of the rotor core 253, and adjacent layers of flux carrier material 265 and flux barrier material 263 are contiguous and fully adhered to one another along their boundaries. In this fashion, the rotor core 253 essentially consists of a solid mass comprising complex shaped magnets embedded in a soft magnetic material.
As can be appreciated, various geometric properties of the layers can be adjusted depending on the requirements of the rotor portion 251. For example, the flux barrier layer thickness 273 and flux carrier layers thickness 275 can vary from one embodiment to another. In some embodiments, for example as shown in
It is further appreciated that the geometric properties can be adjusted to optimize performance parameters of the rotor 251. In the embodiment shown in
Although in the above-described embodiments the flux barriers 255 extend up to the rotor surface 267 (specifically between the first 267a and second 267b radial extremities of the rotor core 253), it is appreciated that other configurations are possible. For example, with reference to
As can be appreciated, the above-described axially layered rotor core 253 can have good magnetic, and mechanical properties. However, it can also be suitable for mass manufacturing, as it can be fabricated using different additive manufacturing techniques which involve fabricating layers of flux carrier material and flux barrier material in an alternating fashion to obtain a final structure. For example, and with reference to
In the present embodiment, the flux barrier material 263 is a magnetic material. When the layers of flux barrier material 263 are fabricated in step c), the material 263 is not in a magnetized state. Accordingly, an additional step can comprise magnetizing the flux barrier material 263. In the present embodiment, the step of magnetizing the barrier material 263 is carried our after step e) (i.e. after rotor assembly). However, it is appreciated that in other embodiments, magnetization can be done at any time after fabricating one or more layers of the barrier material 263. Magnetizing the flux barrier material 263 can comprise applying a magnetic field to the one or more layers of flux barrier material 263. As can be appreciated, the required magnetization of the flux barriers 255 can vary based on the rotor configuration and materials used, and different magnetic field strengths can be required to fully magnetize all flux barrier layers. In the present embodiment, the flux barriers 255 are magnetized by the armature coils 207 of stator 201. More specifically, motor 200 is a 3-phase motor, and magnetization is carried out by applying a current through two phases of the armature coils 207 (phase A and phase B), with the direct axis (d-axis) of the rotor aligned with the armature magnetic field. A current of at least 2,000 A is applied to the armature coils 207 to generate a magnetic field of at least 1,000 kA/m and 1,300 kA/m in each of the flux barriers 255, thereby fully magnetizing the flux barrier material 263. It is appreciated, however, that different currents can be used in different rotor and/or stator winding configurations. Moreover, in some embodiments, the flux barrier material 263 can be magnetized by other sources of magnetic fields.
Different additive manufacturing techniques can be used in order to build the rotor core 253, for example by radially fabricating layers of flux barrier 263 and flux carrier 265 materials relative to the central axis 250 and/or rotor shaft 261. In other words, each layer can be deposited, formed, or fabricated such that it is built up in a radial direction relative to central axis 250 and/or rotor shaft 261. Once a desired thickness of a given layer is achieved, a subsequent layer of different material can be deposited, formed or fabricated thereon. In this fashion, the layers 263, 265 of the rotor core 253 will alternate along a radial direction relative to central axis 250 and/or rotor shaft 261. As can be appreciated, when building the layers radially, each layer 263, 265 can be deposited, formed, or fabricated along a length of the central axis 250 and/or rotor shaft 261, and about a circumference thereof. In this fashion, the radially formed layers can be described as axial layers, in that they extend along an axis substantially parallel to the central axis 250 and/or longitudinal axis of rotor shaft 261.
As can be appreciated, additive manufacturing allows for complex structures to be formed within the core 253, whereas traditional manufacturing technologies would limit rotor structures to simple shapes. Moreover, forming the core in this manner allows the flux carrier 265 layers (for example fabricated using SMC) to accept 3D magnetic flux, and thus accept flux in any direction. This is as opposed to traditional laminations which accept flux only in the plane of the laminations. In the present embodiment, cold spray manufacturing is used to deposit alternating layers of flux barrier material 263 and flux carrier material 265, respectively comprising permanent magnet (PM) and soft magnetic composite (SMC) material. It is appreciated, however, that any type of additive manufacturing technique which allows for building layers of metallic structures can be used. For example, techniques such as big area additive manufacturing, fused filament fabrication, laser sintering, binder jetting and powder bed manufacturing can be used, among others, in additional to techniques such as molding or pressing. It is further appreciated that different spray-based manufacturing techniques (i.e. any technique which involves the controlled depositing of layers or coats using atomized and/or particulate matter) can be used, such as aerosol spray, High-Velocity Air-Fuel (HVAF), High-Velocity Oxygen-Fuel (HVOF), or other thermal spraying techniques. Moreover, it is appreciated that a combination of different techniques can be used. For example, the first layer of SMC can be pressed directly on the rotor shaft, with subsequent layers built thereon using spray-based manufacturing techniques. Finally, it is appreciated that different combinations of materials can be used, such as compounds of the following families, including any alloys and/or mixtures thereof: a) Permanent magnets: ferrites, Neodymium Iron Boron, Samarium Cobalt, and Aluminum Nickel Cobalt, and b) SMCs: pure Iron, Cobalt Iron, Silicon iron, or any of such materials obtained from a powder coated with a surrounding organic or inorganic insulating layer. A person having ordinary skill in the art would acknowledge that the various properties of these materials can be tailored to the application by the inclusion of other elements.
In the description provided above, exemplary embodiments of a rotor structure and method of manufacturing the same have been provided. It is appreciated that these embodiments are provided for illustrative purposes only and should not be taken so as to limit the scope of the invention. For example, it should be appreciated that minor modifications and substitutions can be made to the above-described configurations without departing from the scope of the invention. It should be further appreciated that the layered structure of the described rotor can be applied to other structures having similar requirements, such as a stator or a differently shaped rotor. Finally, it should be appreciated that although the invention was described in relation to a motor, similar principles and structures can be used in connection with other types of electrical machines.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2020/051074 | 8/6/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62890110 | Aug 2019 | US |
