Abstract:
A rotor for a permanent magnet synchronous machine. A first layer of cavities formed circumferentially within the rotor core structure. Pairs of the cavities in the first layer form V-shaped configurations and are spaced circumferentially about the rotor core structure in the first layer. A second layer of cavities is formed circumferentially within the rotor core structure. Pairs of the cavities in the second layer form V-shaped configurations and are spaced circumferentially about the rotor core structure in the second layer. A first set of permanent magnets is inserted within each cavity in the first layer and a second set of permanent magnets inserted within each cavity in the second layer. Each respective V-shaped configuration of the second layer having permanent magnets disposed therein extend greater than half a radial distance from the outer cylindrical wall to the inner cylindrical wall.

Description:
BACKGROUND OF INVENTION 
     An embodiment relates generally to permanent magnet motors. 
     A permanent magnet synchronous motor is an AC motor in which rotation rate of the shaft is synchronized with the frequency of the AC supply current. A rotating electric field is generated in the stator and the rotor follows the rotating electrical field of the stator. The rotor rotates in step with the field of the stator at a same rate. The rotor and the stator are said to be in synchronization. 
     The permanent magnets used in conventional rotors are configured to provide a uniform field strength. Neodymium magnets, also known as rare earth magnets, are often desired due to their strong magnetic field strength which provides enhanced torque in motors. However, using rare earth magnets in a motor is costly and increases the overall price of the motor. 
     SUMMARY OF INVENTION 
     An advantage of an embodiment is the reduction overall cost of the motor by utilizing bi-permanent magnets having different field strengths. The interior permanent synchronous machine utilizes bi-permanent magnets (i.e., the combination of two or more different types of magnet materials) for reducing the number and mass of rare earth magnets utilized in the rotor. A combination of rare earth magnets and ferrite magnets, or magnets of a same material composition having different magnetic field strengths, is utilized in the rotor in a multilayer structure. Moreover, the magnets of the lesser magnetic strength (e.g., ferrite magnets) extend at least half the radial distance between outer cylinder wall of the rotor in the inner cylinder wall of the rotor thereby generating a magnetic field over a substantial portion of the rotor for increasing torque and rotational speed. 
     An embodiment contemplates a rotor for a permanent magnet synchronous machine. A rotor core structure having a cylindrical body. The cylindrical body includes an inner cylindrical wall and an outer cylindrical wall. A first layer of cavities formed circumferentially within the rotor core structure. Pairs of the cavities in the first layer form V-shaped configurations and are spaced circumferentially about the rotor core structure in the first layer. Each V-shaped configuration includes a first leg cavity and a second leg cavity. An apex of each V-shaped configuration formed by the first leg cavity and the second leg cavity extends toward the inner cylindrical wall. An open end of each V-shape configuration extends toward the outer cylindrical wall. A second layer of cavities is formed circumferentially within the rotor core structure. Pairs of the cavities in the second layer form V-shaped configurations and are spaced circumferentially about the rotor core structure in the second layer. Each V-shaped configuration of the second layer includes a first leg cavity and a second leg cavity. An apex of each V-shaped configuration in the second layer formed by the first leg cavity and the second leg cavity extends toward the inner cylindrical wall. An open end of each V-shape configuration in the second layer extends toward the outer cylindrical wall. A first set of permanent magnets is inserted within each cavity in the first layer. A second set of permanent magnets inserted within each cavity in the second layer. The magnetic field strength of the first set of permanent magnets is greater than the magnetic field strength of the second set of permanent magnets. Each respective V-shaped cavity and associated magnets of the first layer is paired with a respective V-shaped cavity and associated magnets of the second layer to form rotor poles. Each respective first leg in the second layer of each respective pole is outwardly offset and parallel to an associated first leg in the first layer of each respective pole. Each respective second leg in the second layer of each respective pole is outwardly offset and parallel to an associated second leg in the second layer of each respective pole. Each respective V-shaped configuration of the second layer having permanent magnets disposed therein extend greater than half a radial distance from the outer cylindrical wall to the inner cylindrical wall. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a section view of a permanent magnet motor. 
         FIG. 2  is an enhanced view of the flux flow of the permanent magnet motor utilizing a magnet configuration. 
         FIG. 3  is an enhanced view of the flux flow of the permanent magnet motor utilizing the magnet configuration. 
     
    
    
     DETAILED DESCRIPTION 
     There is shown in  FIG. 1  a section view of a permanent magnet motor  10 . The permanent magnet motor  10  includes a rotor  12  coupled to a shaft  14  or vehicle integration gearing. The rotor  12  can include any number of poles (e.g. 2, 4, 6, etc). The sectional view as shown illustrates respective poles of the rotor  12 . A stator  16  is radially offset from the rotor  12  and is separated therefrom by a primary air gap  18 . 
     The function of the rotor  12  is to drive a component coupled to the shaft  14  or gearing. The stator  16  when excited by an excitation voltage (e.g., 3-phase supply) generates a rotating magnetic field within the motor  10 . The rotor, which functions as a permanent magnet locks in with the rotating magnetic field generated by the stator  16 . The rotor  12  rotates along with the rotating magnetic field. When the rotor locks in with the rotating magnetic field, the motor  10  is in synchronization. 
     The rotor  12  as shown in  FIG. 1  utilizes interior permanent magnets  20 . It should be understood that the motor can be any type of permanent magnet motor and does not require interior permanent magnets. The interior permanent magnets  20  are inserted within a plurality of cavities that include first cavity legs  24  and second cavity legs  26  forming a first layer  27 , and third cavity legs  28  and fourth cavity legs  30  forming a second layer  31  within the rotor  12 . A pair of legs within a respective layer cooperatively forms a V-shaped configuration. For example, the first cavity leg  24  and the second cavity leg  26  form a respective V-shaped configuration in the first layer  27 . Similarly, the third cavity leg  28  and the fourth cavity leg  30  cooperatively form a respective V-shaped configuration in the second layer  31 . For each of the cavities in both layers, the open end of each V-shaped configuration is directed toward an outer cylinder wall  32  of the rotor  12 . The apex of the V-shaped configuration is directed at the inner cylinder wall  33  of the rotor  12 . The V-shaped configurations of the second layer  31  are deep V-shaped configurations in that the respective cavity legs extends at least half of the radial distance of the rotor. 
     The V-shaped configurations between the first layer and the second layer are structured in an overlapping multilayer structure where a respective V-shaped configuration of the second layer overlaps a respective V-shaped configuration of the first layer such that when permanent magnets are disposed in the these respective cavities, the overlapping V-shaped configurations of the first and second layers form a respective rotor pole during motor operation. The term overlapping as used herein refers to a respective leg of a respective V-shaped configuration of the first layer that is offset and parallel to a respective leg of the V-shaped configuration of the second layer in the same pole, and the other respective leg forming the V-shaped configuration of the first layer is offset and parallel to the other respective leg forming the V-shaped configuration of the second layer of the same pole. 
     Each respective cavity leg includes a first end section  34  and second end section  36 . The first end section  34  extends toward the outer cylindrical surface wall  32  of the rotor  12 . The second end section  36  extends toward the inner cylindrical surface wall  33 . 
     The permanent magnets  20  disposed in the cavity legs of the first layer  27  include a first set of magnets  40 , and the permanent magnets  20  disposed in the cavity legs of the second layer  31  includes a second set of magnets  42 . The first set of magnets  40  are smaller in comparison to the second set of magnets  42 , however, the magnetic properties of the first set of magnets  40  disposed in the first layer  27  are stronger than the second set of magnets  42  disposed in the second layer  31 . The first set of magnets  40  are preferably of a different material composition than the second set of magnets  42 . For example, the first set of magnets  40  may be a rare earth magnet (e.g., neodymium magnet) and the second set of magnets  42  may be a ferrite magnet. Alternatively, the first and second set of magnets  40  and  42  may be of a same material composition, but have different magnetic field strengths. For example, the first set of magnets  40  and the second set of magnets  42  may all be ferrite magnets or all rare earth magnets where the first set of magnets generates a stronger magnetic field than the second set of magnets. The overall cost of the magnets is reduced by requiring less of the higher magnetic field strength materials; however, the torque of the motor is increased due to the permanent magnets disposed in the deep V-shaped configuration cavities. 
     Each of the plurality of cavities includes a first air gap  46  and a second air gap  48 . The first air gap  46  is disposed at a distal end of each cavity closest to the inner circumference wall  32 . The second air gap  48  is disposed at a distal end of each cavity closest to the outer circumference wall  31 . The respective air gaps formed at the distal ends of each cavity around the first set of magnets  40  and the second set of magnets  42  reduce demagnetization. As a result, each of the air gaps  46  and  48  minimize demagnetization. 
     The rotor  12  includes a top bridge  50  disposed between each of the first air gaps  46  and the outer circumference wall  32 . The rotor  12  further includes a bottom bridge  52  disposed between each of the air gaps  48  and the inner circumference wall  33 . The top bridge  50  and the bottom bridge  52  assist in achieving high-speed operation and reduced torque ripple. The rotor  12  further includes an interim bridge  54  located between an adjacent set of air gaps  48  within a same pole. The interim bridge  54  between the adjacent sets the air gaps  48  maintains rotor integrity, limits the short-circuited flux, and allows the rotor structure to be formed as a single-piece lamination. 
     Typical conventional rotors have cavities that extend less than half the distance between the outer circumference wall of the rotor and the inner circumference wall of the rotor. As described herein, the deep V-shaped configuration of the cavities of the second layer extends well beyond half the distance from substantially the outer cylinder wall to the substantially inner cylinder wall of the rotor. The deep V-shaped configuration of the cavities of the second layer  31  extends as far as possible toward the inner circumference wall  33  for extending the magnetic field generated by the permanent magnets (e.g., at least half the radial distance or at least three-quarters of the radial distance). Alternatively, the deep V-shaped configuration may extend to the depth where the bottom bridge is substantially four millimeters width. However, the depth is limited by the mechanical stress exerted on both the top bridge  50  and the bottom bridge  52  as well as the saturation level. This configuration is preferred for use in applications where an increased number of poles are required for enhanced flux concentration. 
       FIG. 2  illustrates an enlarged section view of the rotor illustrating the deep V-shaped configuration and flux flow between permanent magnets of adjacent poles. As shown in  FIG. 2 , the second layer of cavities have air gaps  46  formed by the spacing between the permanent magnet  42  and the cavity wall. A locator  54  is formed on a wall of each cavity layer for positioning each permanent magnet therein. A respective magnet  60  of a pole forming a first deep V-shaped configuration is adjacent to a respective magnet  62  of an adjacent pole for the second set of magnets forming the adjacent deep V-shaped configuration. The flux flow generated by the permanent magnet  60  of the first deep V-shaped configuration is in a same direction to the flux flow of the permanent magnet  62  of the second deep V-shaped configuration. 
       FIG. 3  illustrates an enlarged section view of the rotor illustrating the deep V-shaped configuration and flux flow. The permanent magnets as shown are from the same deep V-shaped configuration for a respective pole that represent the apex of the V-shape configuration. As shown in  FIG. 3 , each of the cavities have air gaps  48  formed by the spacing between the permanent magnet and the cavity wall. The flux flow for a set of adjacent magnets within a pole is in opposite directions of one another. That is, the flux flow generated by the permanent magnet  62  in a respective leg of the deep V-shaped configuration is opposite to the flux flow of a permanent magnet  64  of the other respective leg of the same deep V-shaped configuration in the same pole. As a result, flux flow generated from permanent magnets within a deep V-shaped configuration flow in opposite directions with respect to one another, whereas flux flow from permanent magnets of adjacent deep V-shaped configurations from different poles flow in a same direction relative to one another. 
     Since the second set of magnets extend deep toward the inner circumference of the rotor, a magnetic field is generated throughout a substantial portion of the rotor, which enhances both the torque of the rotor and the rotational speed of the rotor. 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.