Patent Publication Number: US-2022216755-A1

Title: Rotor of rotary electric machine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-001393 filed on Jan. 7, 2021, which is incorporated herein by reference in its entirety including the specification, claims, drawings, and abstract. 
     TECHNICAL FIELD 
     This application discloses a rotor of a permanent magnet type rotary electric machine having permanent magnets embedded inside a rotor core. 
     BACKGROUND 
     Conventionally, a rotor having permanent magnets inserted and fixed in magnet holes formed inside a rotor core is known. As a structure for fixing permanent magnets, there is a structure in which the clearance between the magnet hole and the permanent magnet is filled with a resin or the like. Such a structure can reliably fix the permanent magnets, but manufacturing processes tend to be complicated. One of various conventional techniques proposed in view of this is a structure in which end plates arranged at both axial ends of the rotor core are used to fix the permanent magnets in the magnet holes. 
     For example, Patent Literature 1 discloses a technique in which end plates are bent and deformed toward the magnet hole side (i.e., inner side in the axial direction) at portions corresponding to magnet holes to form claw-shaped protrusions. When a direction orthogonal to the axial direction of the rotor is defined as a “lateral direction”, the protrusions are provided on both sides of the permanent magnet in the lateral direction, and the permanent magnet is sandwiched between a pair of protrusions. With this arrangement, the movement of the permanent magnet in the lateral direction can be restricted. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2016-005419 A 
       
    
     However, the structure disclosed in Patent Literature 1 requires arranging one end plate at one axial end of the rotor core, then inserting the permanent magnet into the magnet hole, and subsequently arranging another end plate at the other axial end of the rotor core. According to such an arrangement of the end plates, or at the time of inserting the permanent magnets, the protrusions move in the axial direction while keeping tight contact with peripheral surfaces of the permanent magnets, and therefore the permanent magnets may be cracked or scratched due to friction. 
     Accordingly, this application discloses a rotary electric machine rotor capable of easily fixing permanent magnets while preventing the permanent magnets from being damaged. 
     SUMMARY 
     A rotor of a rotary electric machine disclosed in this application includes a rotor core having one or more magnet holes each being formed so as to extend in an axial direction, a permanent magnet inserted in each of the one or more magnet holes, and one or more end plates each being arranged at an axial end face of the rotor core, as one or more end plates each being provided with one or more fixing holes via which the permanent magnet is exposed to the outside in the axial direction, wherein one or more fixing pieces extend from the periphery of the fixing hole, with a fixing piece having an inclined part that extends in a direction approaching the center of the permanent magnet when advancing to the outside in the axial direction and being in contact with the permanent magnet, thereby pressing the permanent magnet in both the axial direction and a lateral direction orthogonal to the axial direction. 
     With such a configuration, the contact area between the fixing piece and the permanent magnet, and thus the friction, can be reduced, and the permanent magnet can be effectively prevented from being damaged. Further, the inclined part presses the permanent magnet in both the axial direction and the lateral direction, and therefore the permanent magnet can be reliably positioned in both the axial direction and the lateral direction. As a result, it is possible to easily fix the permanent magnet while preventing the permanent magnet from being damaged. 
     In this case, the fixing pieces may be positioned on both sides of the permanent magnet intervening therebetween in the lateral direction, and the permanent magnet may be sandwiched by a pair of inclined parts positioned on both sides of the permanent magnet intervening therebetween in the lateral direction. 
     With such a configuration, the permanent magnet can be naturally positioned at a position where the urging forces of a pair of inclined parts aligned in the lateral direction are balanced. 
     Further, the end plates may be provided on both sides of the rotor core in the axial direction, and the inclined parts may be present on both sides of each permanent magnet in the axial direction. 
     With such a configuration, the permanent magnet can be naturally positioned at a position where the urging forces of a pair of inclined parts aligned in the axial direction are balanced. 
     Further, the magnet hole may have a main part, which larger than the permanent magnet, and a pocket part being a cavity continuous to the main part, and the fixing piece may be provided at a position where at least a part thereof is overlapped with the pocket part in the axial direction. 
     Depending on a relative positional relationship with the permanent magnet, it may be desired that at least a part of the fixing piece advances axially inward from the end plate. Adopting the above-described configuration enables the pocket part to partly receive the fixing piece advancing axially inward. 
     Further, the permanent magnet may protrude outward from the end plate in the axial direction, and the fixing piece may linearly extend from the periphery of the fixing hole to a terminating end, without being bent. 
     Forming the fixing piece so as to have a simple shape is desirable in that the fixing piece can be easily improved in various kinds of accuracies. This leads to improvement in positioning accuracy of the permanent magnet. 
     Further, an axial end face of the permanent magnet may be positioned axially inside an axial end face of the end plate, and the fixing piece may be bent once or more in a region from a proximal end thereof to a terminating end thereof, so that an axial inner end of the inclined part is positioned more toward the inside in the axial direction than the axial end face of the permanent magnet. 
     With such a configuration, the axial dimension of the permanent magnet can be prevented from increasing, and the cost can be further reduced. 
     Further, the rotor core may be configured by a plurality of electro-magnetic steel sheets laminated in the axial direction, and the end plate may be configured by an electro-magnetic steel sheet, which is the same type as the electro-magnetic steel sheets configuring the rotor core. 
     With such a configuration, the number of component types can be reduced, and the cost can be further reduced. 
     Further, the end plate may be configured by a non-magnetic material. 
     With such a configuration, leakage fluxes flowing through the end plate can be reduced, and the efficiency of the rotary electric machine can be further improved. 
     According to the technique disclosed in this application, it is possible to easily fix the permanent magnets while preventing the permanent magnets from being damaged. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiment(s) of the present disclosure will be described based on the following figures, wherein: 
         FIG. 1  is a lateral cross-sectional view of an exemplary rotor; 
         FIG. 2  is a partial view of an end face of the rotor seen from the axial direction; 
         FIG. 3  is a cross-sectional view taken along a line A-A of  FIG. 2 ; 
         FIG. 4  is a conceptual diagram illustrating a manufacturing flow of the rotor; 
         FIG. 5  is a vertical cross-sectional view of another exemplary rotor; 
         FIG. 6  is a vertical cross-sectional view of another exemplary rotor; 
         FIG. 7  is a partial view of an end face of another exemplary rotor seen from the axial direction; 
         FIG. 8  is a vertical cross-sectional view of another exemplary rotor; and 
         FIG. 9  is a vertical cross-sectional view of a comparative rotor. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an exemplary configuration of a rotor  10  will be described with reference to attached drawings.  FIG. 1  is a lateral cross-sectional view of the rotor  10 . Further,  FIG. 2  is a partial view of an end face of the rotor  10  seen from the axial direction, and  FIG. 3  is a cross-sectional view taken along a line A-A of  FIG. 2 . In the following description, unless otherwise mentioned, “axial direction”, “radial direction”, and “circumferential direction” indicate the axial direction, radial direction, and circumferential direction of the rotor  10 , respectively. Further, in the following description, directions orthogonal to the axial direction, such as the radial direction and the circumferential direction, are collectively referred to as “lateral directions”. 
     This rotor  10  is used for a rotary electric machine such as a three-phase synchronous rotary electric machine that serves as a power source of an electrically driven vehicle, for example. The rotor  10  includes a rotor core  12 , permanent magnets  14  embedded inside the rotor core  12 , and a pair of end plates  16  arranged on both axial ends of the rotor core  12 . 
     The rotor core  12  is substantially a toroid having an axial bore formed in the center thereof. The rotor core  12  is composed of a plurality of electro-magnetic steel sheets (e.g., silicon steel sheets) laminated in the axial direction. In the vicinity of the outer periphery of the rotor core  12 , a plurality of magnet holes  18  are arranged side by side at intervals in the circumferential direction. Each magnet hole  18  penetrates in the axial direction and has an inner space in which the permanent magnet  14  configuring a magnetic pole of the rotor  10  is arranged. In order to explain the shape of the magnet hole  18 , one magnet hole  18  in which the permanent magnet  14  is not inserted is illustrated in  FIG. 1 . 
     In the present example, neighboring permanent magnets  14  are arranged so as to form a V shape. That is, each magnetic pole  15  is configured by a pair of permanent magnets  14  in a V-shaped arrangement, which is widened outward in the radial direction. In the example of  FIG. 1 , the rotor  10  has twelve permanent magnets  14  that configure six magnetic poles  15 . Each permanent magnet  14  has a lateral cross-sectional shape that is a substantially flat rectangular shape, and is magnetized in a minor axis direction thereof. Of the permanent magnets  14 , the permanent magnets  14  configuring S magnetic poles are arranged in such a manner that S poles are directed outward in the radial direction, and the permanent magnets  14  configuring N magnetic poles are arranged in such a manner that the N poles are directed outward in the radial direction. 
     Further, in the present example, the axial dimension of the permanent magnet  14  is larger than the axial dimension of the rotor core  12 . Therefore, as illustrated in  FIG. 3 , an axial end face of the permanent magnet  14  protrudes axially outward from an axial end face of the rotor core  12 . 
     In order to receive the permanent magnets  14  having the V-shaped arrangement, neighboring magnet holes  18  are arranged so as to form a corresponding V shape. That is, the rotor core  12  is provided with the magnet holes  18  in a plurality of pairs (6 pairs in the illustrated example) that are evenly arranged in the circumferential direction, in which each pair of magnet holes  18  is arranged in the V shape that is widened outward in the radial direction. The magnet hole  18  has a substantially rectangular shape and is larger than the permanent magnet  14  in major axis dimension. More specifically, the magnet hole  18  has a main part  20 , which is larger than the permanent magnet  14 , and pocket parts  22  being cavities continuous to both ends of the main part  20  in the major axial direction. The pocket parts  22  are provided to reduce useless magnetic fluxes not contributing to torque production (so-called leakage fluxes) and increase valid magnetic fluxes. 
     The end plates  16  are fixed to both axial ends of the rotor core  12 . For example, the end plate  16  is configured by an electro-magnetic steel sheet, which is the same type as the electro-magnetic steel sheets configuring the rotor core  12 , namely, an electro-magnetic steel sheet that has the same material and dimensions. Such a configuration can reduce the number of components configuring the rotor  10  and accordingly contribute to cost reduction. However, it is needless to say that the end plate  16  may be configured by a plate member different in type from the electro-magnetic steel sheet of the rotor core  12 . For example, the end plate  16  may be configured by a non-magnetic material such as brass. 
     Fixing holes  30  via which the permanent magnets  14  are exposed in the axial direction are formed at positions of the end plates  16  where they are overlapped with the permanent magnets  14  in the axial direction. The number of the provided fixing holes  30  is the same as the number of the permanent magnets  14 . Like the permanent magnet  14 , each fixing hole  30  has a flat shape elongated in one direction. 
     Fixing pieces  32  for fixing the permanent magnet  14  extend from the periphery of the fixing hole  30 . For example, these fixing pieces  32  are provided on both sides of the permanent magnet  14  in the lateral direction. In the example of  FIG. 2 , with the permanent magnet  14  intervening therebetween, the fixing pieces  32  are provided on both sides of the permanent magnet  14  in the major axial direction, in other words, at positions where they are overlapped with the pocket parts  22  in the axial direction. 
     The fixing piece  32  is a cantilever-shaped portion having a proximal end connected to the end plate  16  and a distal end serving as a free end. A part or the whole of the fixing piece  32  functions as an inclined part  40 . The inclined part  40  is a portion extending in an inclined direction so as to approach the center of the permanent magnet  14  when advancing to the outside in the axial direction. In the example illustrated in  FIGS. 2 and 3 , the fixing piece  32  extends linearly from the periphery of the fixing hole  30  to the terminating end, without being bent, so that the fixing piece  32  serves wholly as the inclined part  40 . 
     The inclined part  40  extends in the inclined direction, as mentioned above, and functions as a leaf spring having an appropriate elasticity. This inclined part  40  is in line contact with the periphery of the axial end face of the permanent magnet  14 . Further, while being in contact with the permanent magnet  14 , the inclined part  40  presses the permanent magnet  14  in both of the axial direction and the lateral direction. As a result, the permanent magnet  14  is automatically positioned and fixed in both the lateral direction and the axial direction, as will be described below. The end plate  16  having the fixing holes  30  and the fixing pieces  32  as described above can be manufactured by press-molding an electro-magnetic steel sheet, for example. 
     Next, the reason why the fixing holes  30  and the fixing pieces  32  described above are provided will be described by giving a comparison with a comparative example. In general, the magnet hole  18  is larger than the permanent magnet  14 . Therefore, it is necessary to position and fix the permanent magnet  14  in the magnet hole  18 . For this fixing, a structure in which the clearance between the magnet hole  18  and the permanent magnet  14  is filled with a resin or the like is known. However, such a fixing structure using a resin or the like encounters a problem that processes for manufacturing the rotor  10  are complicated and time-consuming. 
     In view of the above, there is a proposed structure in which the end plates  16  are used to fix the permanent magnets  14 . For example, as will be understood from a comparative example illustrated in  FIG. 9 , there is a known structure in which protrusions  50  are formed by partly bending the end plates  16  inward in the axial direction so that the protrusions  50  are provided on both sides of the permanent magnet  14  in the lateral direction. According to this structure, attaching the end plates  16  to the rotor core  12  can fix the permanent magnets  14 . Therefore, the manufacturing processes can be simplified. 
     However, the comparative example of  FIG. 9  is such that the protrusions  50  press the permanent magnet  14  only in the lateral direction. Therefore, although the permanent magnet  14  can be sufficiently fixed in the lateral direction, it may not be sufficiently fixed in the axial direction. Further, in the comparative example, the protrusions  50  are in planar contact with the permanent magnet  14 . Therefore, in the comparative example, if the end plates  16  are configured by a magnetic material, leakage of fluxes thorough the end plates  16  will increase and the efficiency of the rotary electric machine will decrease. Therefore, in the case of the comparative example, the end plate  16  needs to be configured by a non-magnetic material. This causes an increase in the number of component types. 
     In addition, when manufacturing the rotor  10  of  FIG. 9 , one end plate  16  is attached to one axial end side (e.g., the lower side of the paper in  FIG. 9 ) of the rotor core  12  and then the permanent magnet  14  is attached in the magnet hole  18  from one axial end side. Further, subsequently, another end plate  16  is attached to the other axial end side (e.g., the upper side of the paper in  FIG. 9 ) of the rotor core  12 . According to such an arrangement of the end plates  16 , or at the time of inserting the permanent magnet  14 , the protrusions  50  move relatively in the axial direction while keeping the tight contact with peripheral surfaces of the permanent magnet  14 . As a result, the permanent magnet  14  may be cracked or scratched due to friction between the protrusions  50  and the permanent magnet  14 . 
     On the other hand, in the rotor  10  of the present example, the fixing pieces  32  (the inclined parts  40 ) extend in the inclined direction so as to approach the center of the permanent magnet  14  when advancing to the outside in the axial direction, and are in line contact with the permanent magnet  14 . Therefore, the fixing pieces  32  can press the permanent magnet  14  in both the axial direction and the lateral direction. As a result, the fixing pieces  32  can fix the permanent magnet  14  not only in the lateral direction but also in the axial direction. 
     Further, at this time, the fixing pieces  32  are in contact with only the periphery of the axial end face of the permanent magnet  14 . This means that the contact area between the end plate  16  including the fixing piece  32  and the permanent magnet  14  can be kept smaller. As a result, even if the end plate  16  is configured by a magnetic material, for example, by an electro-magnetic steel sheet of the same type as the electro-magnetic steel sheets configuring the rotor core  12 , the leakage flux can be kept smaller. 
     Further, in the case of the rotor  10  of the present example, during the manufacturing processes, there is no chance that the fixing pieces  32  will slide while keeping planar contact with the permanent magnet  14 . Accordingly, the permanent magnet  14  can be effectively prevented from being damaged. This will be described with reference to  FIG. 4 .  FIG. 4  is a conceptual diagram illustrating a manufacturing flow of the rotor  10 . 
     As illustrated in  FIG. 4 , in step S 1 , a first end plate  16   a  is fixed to one axial end side of the rotor core  12  (the lower side of the paper in the illustrated example). However, this fixing may be a final fixing or may be a temporary fixing. For example, this fixing may be chemical reaction based fixing using an adhesive or the like or may be mechanical engagement based fixing such as caulking. 
     Subsequently, in step S 2 , the permanent magnet  14  is inserted into the magnet hole  18  from the other axial end side of the rotor core  12  (the upper side of the paper in the illustrated example). When the insertion is completed, one axial end face of the permanent magnet  14  is in line contact with the fixing pieces  32  of the first end plate  16   a . On the other hand, in an insertion process, the permanent magnet  14  can advance through the magnet hole  18  without contacting the fixing pieces  32 . As a result, in the process of inserting the permanent magnet  14 , the permanent magnet  14  is not damaged by the fixing pieces  32 . 
     Next, in step S 3 , a second end plate  16   b  is fixed to the other axial end side of the rotor core  12  (the upper side of the paper in the illustrated example). With this arrangement, the other axial end face of the permanent magnet  14  is brought into contact with the fixing pieces  32  of the second end plate  16   b , but this contact is a line contact and therefore the friction is very small. Accordingly, at the time of fixing the second end plate  16   b , there is no chance that the permanent magnet  14  will be damaged by the fixing pieces  32 . Finally, an axial compression force (so-called axial force) is applied to the entire rotor  10  including the end plates  16 , thereby completing the manufacturing of the rotor  10 . Upon application of this axial force, two fixing pieces  32  axially aligned with the permanent magnet  14  intervening therebetween come close to each other. With such a configuration, an increased urging force is applied to the permanent magnet  14  from the fixing pieces  32 , and the permanent magnet  14  can be firmly fixed. 
     As will be apparent from the above description, in the present example, the end plates  16  having the fixing pieces  32  formed thereon are fixed to axial end faces of the rotor core  12 . Accordingly, the permanent magnet  14  can be fixed in both the axial direction and the lateral direction. Further, at the time of this fixing, the contact between the permanent magnet  14  and the fixing pieces  32  can be kept small, and therefore the permanent magnet  14  can be effectively prevented from being damaged. That is, according to this example, it is possible to easily fix the permanent magnet  14  while preventing the permanent magnet  14  from being damaged. 
     The above-described configuration is merely an example. As long as the end plate  16  has the fixing piece  32  extending from the periphery of the fixing hole  30  and the fixing piece  32  has the inclined part  40  extending in a direction approaching the center of the permanent magnet  14  when advancing to the outside in the axial direction and is brought into contact with the permanent magnet  14 , other configurations may be changed appropriately. For example, the number of the end plates  16  arranged at axial end faces of the rotor core  12  may be changed appropriately. Accordingly, as illustrated in  FIG. 5 , two or more end plates  16 , namely, the inclined parts  40 , may be arranged in a laminated manner on one axial end side of the rotor core  12  (the upper side of the paper in  FIG. 5 ). With such a configuration, the urging force to be generated by the inclined part  40  can be increased and the permanent magnet  14  can be further firmly fixed. 
     Further, it suffices that the end plate  16  having the fixing piece  32  is provided at least at one axial end face of the rotor core  12 , and the fixing piece  32  need not be provided on the other axial end face. That is, as illustrated in  FIG. 5 , an end plate  16   c  that does not have the fixing piece  32  may be arranged on the other axial end side of the rotor core  12  (the lower side of the paper in  FIG. 5 ). In this case, the end plate  16   c  is only required to prevent the permanent magnet  14  from coming off. Accordingly, the end plate  16   c  may have a fixing hole  30  that is a size smaller than the permanent magnet  14 , or need not have the fixing hole  30 . 
     Further, in the above description, the fixing piece  32  extends linearly from its proximal end to its terminating end without being bent. However, the fixing piece  32  may be bent once or more at an intermediate part thereof as long as it has the inclined part  40 . For example, as illustrated in  FIG. 6 , the fixing piece  32  may have a substantially V shape so that it advances inward once in the axial direction from the periphery of the fixing hole  30  and then bends outward in the axial direction. In this case, a portion extending outward in the axial direction and in a direction approaching the center of the permanent magnet  14 , after bending, functions as the inclined part  40 . With such a configuration, even in a case where the axial end face of the permanent magnet  14  is positioned axially inside the end plate  16 , the inclined part  40  can be brought into contact with the permanent magnet  14  and the permanent magnet  14  can be fixed. In other words, bending the fixing piece  32  can reduce the dimensions of the permanent magnet  14 . This leads to a reduction in the cost. 
     Forming the fixing piece  32  extending inward in the axial direction from the end plate  16  as illustrated in  FIG. 6  requires provision of a cavity for receiving the fixing piece  32  on the rotor core  12  side. However, specially providing such a cavity is not preferable for the rotor  10  in that magnetic characteristics deteriorate and the mechanical strength reduces. Therefore, in the case of forming the fixing piece  32  extending inward in the axial direction from the end plate  16 , the fixing piece  32  may be provided at an end of the fixing hole  30  in the major axis direction so that the fixing piece  32  is positioned so as to be overlapped with the pocket part  22  of the magnet hole  18  in the axial direction. The pocket part  22  is a cavity that is also formed in a conventional rotor in order to reduce the leakage flux. Providing the fixing piece  32  so as to enter the pocket part  22  does not require the formation of an extra cavity. As a result, the deterioration in magnetic characteristics and the reduction in mechanical strength can be prevented. 
     Further, in the above description, the fixing pieces  32  are provided on both sides of the permanent magnet  14  intervening therebetween in the lateral direction. In other words, in the above description, two fixing pieces  32  are provided in one fixing hole  30 . However, it suffices that one fixing hole  30  is provided with one or more fixing pieces  32  and the number of the fixing pieces  32  is not particularly limited. For example, as illustrated in  FIG. 7 , a total of four fixing pieces  32  may be provided, in which two fixing pieces  32  may be arranged in the major axis direction with the permanent magnet  14  intervening therebetween and another two fixing pieces  32  may be arranged in the minor axis direction with the permanent magnet  14  intervening therebetween. With such a configuration, the permanent magnet  14  can be reliably fixed not only in the major axis direction but also in the minor axis direction. 
     Further, as another embodiment, one fixing hole  30  may be provided with only one fixing piece  32  as illustrated in  FIG. 8 . In this case, the fixing piece  32  can position the permanent magnet  14  by pressing the permanent magnet  14  against the periphery of the fixing hole  30  on the opposite side of the fixing piece  32 . 
     Further, the rotor core  12  and the permanent magnet  14  may have other configurations appropriately modified. For example, the number and arrangement of the permanent magnets  14  may be appropriately changed. Accordingly, the permanent magnets  14  are not limited to the V shape arrangement, and straight line arrangement or arc-shaped arrangement may be adopted. Further, the rotor core  12  may be configured by a powder magnetic core formed by compressing magnetic powder, instead of a laminated steel sheet formed by laminating a plurality of electro-magnetic steel sheets. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 : Rotor 
               12 : Rotor core 
               14 : Permanent magnet 
               15 : Magnetic pole 
               16 : End plate 
               18 : Magnet hole 
               20 : Main part 
               22 : Pocket part 
               30 : Fixing hole 
               32 : Fixing piece 
               40 : Inclined part 
               50 : Protrusion