Patent Publication Number: US-2013241340-A1

Title: Rotor and rotating electrical machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2012-061829, filed on Mar. 19, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are directed to a rotor and a rotating electrical machine. 
     BACKGROUND 
     As one of the rotors used in rotating electrical machines, there is a so-called permanent magnet embedded rotor in which permanent magnets are disposed in a rotor core so that pole faces are formed on the outer circumference of the rotor core. 
     In such a permanent magnet embedded rotor, to obtain desired magnetic properties, sintered rare-earth magnets of strong magnetic force are typically used as the permanent magnets. Moreover, to further improve magnetic properties, a rotor in which such sintered rare-earth magnets and rare-earth bonded magnets are disposed in combination is known. 
     The documents concerning the above-described art include, for example, Japanese Patent Application Laid-open No. 2009-112121. 
     SUMMARY 
     A rotor according to an aspect of an embodiment includes: a cylindrical rotor core in which a plurality of magnet embedding grooves are radially arranged; and ferrite magnets and samarium-based magnets arranged in juxtaposition in a radial direction in the magnet embedding grooves. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is an explanatory diagram schematically illustrating a configuration of a motor (rotating electrical machine) according to a first embodiment; 
         FIG. 2  is an explanatory diagram of a rotor in the first embodiment; 
         FIG. 3  is an explanatory diagram of magnet embedding grooves provided on a rotor core; 
         FIG. 4  is an explanatory diagram of a motor (rotating electrical machine) according to a first modification example of the first embodiment; 
         FIG. 5  is an explanatory diagram of a motor (rotating electrical machine) according to a second modification example of the first embodiment; 
         FIG. 6  is an explanatory diagram of a motor (rotating electrical machine) according to a second embodiment; 
         FIG. 7  is an explanatory diagram of a motor (rotating electrical machine) according to a first modification example of the second embodiment; and 
         FIG. 8  is an explanatory diagram of a motor (rotating electrical machine) according to a second modification example of the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A rotor according to embodiments includes a cylindrical rotor core in which a plurality of magnet embedding grooves are radially arranged, and ferrite magnets and samarium-based magnets arranged in juxtaposition in a radial direction in a stacked manner in the magnet embedding grooves. 
     With reference to the accompanying drawings, embodiments of a rotor and a motor as a rotating electrical machine provided with the rotor disclosed in the present application will be described in detail hereinafter. However, the present invention is not intended to be restricted by exemplification in the following embodiments. 
     First Embodiment 
       FIG. 1  is an explanatory diagram schematically illustrating a configuration of a motor  1  as a rotating electrical machine according to a first embodiment.  FIG. 2  is an explanatory diagram of a rotor  10  of the motor  1 .  FIG. 3  is an explanatory diagram of magnet embedding grooves  2  provided on a rotor core  11 . In  FIGS. 1 and 3 , one half of the whole is schematically illustrated in a planar sectional view. 
     The motor  1  in the first embodiment includes, as illustrated in  FIG. 1 , the cylindrical rotor  10  and a tubular stator  20  disposed opposite to the outer circumferential surface of the rotor  10  with a given gap. 
     In the stator  20 , a stator core  210  composed of a laminated core in which a plurality of magnetic steel sheets are laminated is shrink-fitted on a frame (not depicted) formed in a roughly tubular form. On the stator core  210 , coils  220  are wound and coil ends thereof are molded by resin. On an inner circumferential side of the stator core  210 , a plurality of teeth  230  projecting towards a radial center are formed along a circumferential direction, and in slots  240  formed between the teeth  230 , the coils  220  are housed. 
     The rotor  10  includes, as illustrated in  FIG. 2 , the cylindrical rotor core  11  in which the magnet embedding grooves  2  are radially arranged, a rotation spindle  30  (see  FIG. 1 ) fitted to the rotor core  11  by insertion, and permanent magnets disposed in the magnet embedding grooves  2 . The rotor core  11  is formed of a laminated core in which a plurality of annularly formed magnetic steel sheets  110  are laminated, and is formed with the magnet embedding grooves  2  in a uniformly spaced manner in a circumferential direction. 
     Typically, as the rotor  10  of the motor  1 , neodymium (Nd) magnets of high magnetic performance yet extremely expensive are used, while ferrite magnets  3  which are inferior in performance are almost never used even though they are inexpensive. However, in the first embodiment, the motor  1  (rotating electrical machine) that exercises desired magnetic performance and is advantageous in terms of cost is realized by daringly using the ferrite magnets  3 . 
     More specifically, the ferrite magnets  3  are not used single-handedly, but the ferrite magnets  3  and samarium-based magnets that are one type of rare-earth magnets are combined and disposed in the rotor  10  in a predetermined form. 
     In the first embodiment, as the samarium-based magnets, samarium-iron-nitrogen magnets (Sm—Fe—N magnets)  4  that have roughly equivalent magnetic performance to that of neodymium magnets but are less expensive than the neodymium magnets are used. The ferrite magnets  3  and the samarium-iron-nitrogen magnets  4  are then configured to be arranged in juxtaposition in a radial direction and in a manner firmly attached to each other in the magnet embedding grooves  2 . 
     The ferrite magnets  3  and the samarium-iron-nitrogen magnets  4  are, as illustrated in  FIG. 2 , formed in the shape of a bar extending in an axial direction of the rotor core  11 . The samarium-iron-nitrogen magnets  4  are bonded magnets having flexibility with rubber and resin such as plastic as binder. Meanwhile, the ferrite magnets  3  are sintered magnets formed by powder sintering. However, the ferrite magnets  3  may be bonded magnets as the same as the samarium-iron-nitrogen magnets  4 . 
     The magnet embedding grooves  2  include, as illustrated in  FIG. 3 , first areas  21  and second areas  22  divided in the radial direction of the rotor core  11 . The first area  21  and the second area  22  are both in a rectangular shape the width of which along the circumferential direction is nearly equal and the entire shape of the magnet embedding groove  2  is in a roughly rectangular shape with long sides in the radial direction. 
     In the first embodiment, the ferrite magnets  3  are disposed in the first areas  21  positioned on the outer circumferential side of the rotor core  11 , and the samarium-iron-nitrogen magnets  4  of relatively high performance are disposed in the second areas  22  positioned on the inner circumferential side of the rotor core  11 . 
     In comparison with the ferrite magnets  3  and the samarium-iron-nitrogen magnets  4 , in terms of cost, the ferrite magnets  3  are quite inexpensive, while the samarium-iron-nitrogen magnets  4  are relatively expensive. Meanwhile, in terms of performance, when expressed in maximum energy product that is one of the indices to represent performance, the ferrite magnets  3  have maximum energy products of 4 to 5 MegaGauss Oersted (MGOe), while the samarium-iron-nitrogen magnets  4  have those of 12 to 14 MegaGauss Oersted. 
     In the relationship of dimensional factors of permanent magnets and motor characteristics when providing the permanent magnets to the rotor  10 , it is known that the lengths of permanent magnets in the radial direction in the rotor core  11  are strongly related to the motor characteristics. 
     Therefore, the respective lengths of the ferrite magnet  3  and the samarium-iron-nitrogen magnet  4  in the radial direction in the rotor core  11  are determined in consideration of respective performance and cost-effectiveness of the ferrite magnet  3  and the samarium-iron-nitrogen magnet  4  so that the desired motor characteristics within an acceptable range can be obtained. 
     In the rotor  10  in the first embodiment, as illustrated in  FIGS. 1 to 3 , the dimension (length in the radial direction in the rotor core  11 ) of the samarium-iron-nitrogen magnet  4  of relatively high performance is made to be roughly one half of that of the ferrite magnet  3 . Even with such a dimensional ratio, the desired motor characteristics can be obtained. 
     In this case, naturally, the collective size of magnets, in other words, the total amount of magnets used is significantly smaller for the samarium-iron-nitrogen magnets  4 , which is expensive, than that for the ferrite magnets  3 . Accordingly, an increase in cost can be suppressed as much as possible. 
     Furthermore, in the rotor  10  in the first embodiment, the samarium-iron-nitrogen magnets  4  are disposed in the second areas  22  formed on the inner circumferential side of the rotor core  11 . 
     More specifically, because the samarium-iron-nitrogen magnet  4  has strong magnetic characteristics and an extremely strong magnetic force, care needs to be taken in handling near the magnetic material. In that respect, because the samarium-iron-nitrogen magnet  4  is a bonded magnet, it is possible, for example, to use the magnet embedding groove  2  formed in the rotor core  11  as a mold. In other words, the samarium-iron-nitrogen magnet  4  can be injection molded by casting the material of magnetic powder primarily consisting of samarium-iron-nitrogen mixed with binding resin into the second area  22 . 
     FIRST MODIFICATION EXAMPLE 
       FIG. 4  is an explanatory diagram of the motor (rotating electrical machine)  1  according to a first modification example. As illustrated in  FIG. 4 , the samarium-iron-nitrogen magnets  4  are disposed in the first areas  21  positioned on the outer circumferential side of the rotor core  11  and the ferrite magnets  3  are disposed in the second areas  22  positioned on the inner circumferential side of the rotor core  11 . Even when the rotor  10  according to the first modification example is used, the desired motor characteristics can be obtained. 
     In regard to the length in the radial direction in the rotor core  11 , the ferrite magnets  3  of low magnetic characteristics are made long. More specifically, in the second areas  22  positioned on the inner circumferential side of the rotor core  11 , the ferrite magnets  3  the long sides of which are relatively long are disposed. 
     Consequently, as can be appreciated from  FIGS. 1 and 4 , either the ferrite magnet  3  or the samarium-iron-nitrogen magnet  4  may be disposed on the inner circumferential side or on the outer circumferential side in the magnet embedding groove  2  in the radial direction. 
     In the first modification example, the samarium-iron-nitrogen magnets  4  that are difficult to handle are disposed in the first areas  21  formed on the outer circumferential side of the rotor core  11 . Therefore, even after the samarium-iron-nitrogen magnets  4  are formed in the shape of a bar, there is no great difficulty in attaching them to the rotor core  11 . 
     In the above-described embodiment, the samarium-iron-nitrogen magnet  4  is used as the samarium-based magnet to be combined with the ferrite magnet  3 . Accordingly, as illustrated in  FIGS. 1 to 4 , both the first areas  21  and the second areas  22  of the magnet embedding grooves  2  can be made in rectangular shapes the widths of which along the circumferential direction are roughly equal, whereby the magnet embedding grooves  2  can be easily formed. 
     SECOND MODIFICATION EXAMPLE 
       FIG. 5  is an explanatory diagram of the motor (rotating electrical machine)  1  according to a second modification example. As illustrated in  FIG. 5 , the magnet embedding grooves  2  are formed in a roughly sector form, the ferrite magnets  3  are disposed in the relatively wide first areas  21  positioned on the outer circumferential side of the rotor core  11 , and the samarium-based magnets are disposed in the relatively narrow second areas  22  positioned on the inner circumferential side of the rotor core  11 . 
     More specifically, the magnet embedding groove  2  includes the first area  21  and the second area  22  that are divided in the radial direction of the rotor core  11  and the widths thereof along the circumferential direction are different from each other. The ferrite magnet  3  is disposed in the relatively wide first area  21  and the samarium-based magnet is disposed in the relatively narrow second area  22 . Even when the rotor  10  according to the second modification example is used, the desired motor characteristics can be obtained. 
     While the relatively wide first areas  21  are formed on the outer circumferential side of the rotor core  11  and the relatively narrow second areas  22  are formed on the inner circumferential side of the rotor core  11 , the arrangement of the first areas  21  and the second areas  22  can be reversed. 
     As for the samarium-based magnet, as illustrated in  FIG. 5 , the above-described samarium-iron-nitrogen magnet  4  can be used, or as described later, a samarium-cobalt magnet (Sm—Co magnet) that is said to have a magnetic force next to a neodymium magnet can be used. 
     In the second modification example, the width along the circumferential direction is narrower for the samarium-based magnets than that for the ferrite magnets  3 , whereby a significant increase in cost can be prevented. 
     Second Embodiment 
     Next, with reference to  FIG. 6 , the motor  1  and the rotor  10  according to a second embodiment will be explained.  FIG. 6  is an explanatory diagram of the motor  1  in the second embodiment. In the following, the same constituent elements as those in the foregoing embodiment are given with the same reference symbols and their detailed explanations are omitted. 
     With the motor  1  in the second embodiment and the motor  1  in the first embodiment, the configuration of the stator  20  is the same for the both, but the configuration of the rotor  10  is different from each other. 
     More specifically, as the samarium-based magnets, samarium-cobalt magnets (Sm—Co magnets)  5  are used in place of the samarium-iron-nitrogen magnets  4 . 
     As illustrated in  FIG. 6 , the relatively wide first areas  21  are formed on the inner circumferential side of the rotor core  11 , and the relatively narrow second areas  22  are formed on the outer circumferential side of the rotor core  11 . The ferrite magnets  3  are disposed in the wide first areas  21  formed on the inner circumferential side of the rotor core  11 , while the samarium-cobalt magnets (Sm—Co magnets)  5  are disposed in the relatively narrow second areas  22  formed on the outer circumferential side of the rotor core  11 . More specifically, in the magnet embedding groove  2 , the ferrite magnet  3  is disposed on the inner circumferential side and the samarium-cobalt magnet  5  is disposed on the outer circumferential side in juxtaposition in a manner firmly attached to each other. 
     The samarium-cobalt magnet  5 , as in the foregoing, is said to have a magnetic force next to a neodymium magnet, and when expressed in maximum energy product, has a maximum energy product of about 32 MegaGauss Oersted. Consequently, the magnetic loading as the rotor  10  is increased, and thus the motor  1  of small and lightweight can be realized. 
     Moreover, the samarium-cobalt magnet  5  excels a neodymium magnet in temperature characteristics. Accordingly, the rotor  10  in the second embodiment and the motor  1  using the rotor  10  can sufficiently withstand the use in a high-temperature environment. 
     Furthermore, as illustrated in  FIG. 6 , in the rotor  10  in the second embodiment, the dimension (length in the radial direction of the rotor core  11 ) of the samarium-cobalt magnet  5  of relatively high performance is made to be roughly one half of that of the ferrite magnet  3 . However, the desired motor characteristics can be obtained. 
     Moreover, in this case, because the width along the circumferential direction is narrower for the samarium-cobalt magnet  5  than that for the ferrite magnet  3 , the collective size of the magnets, i.e., the total amount of magnets used is significantly smaller for the expensive samarium-cobalt magnets  5  than that for the ferrite magnets  3 . Consequently, an increase in cost can be suppressed as much as possible. 
     FIRST MODIFICATION EXAMPLE 
       FIG. 7  is an explanatory diagram of the motor  1  (rotating electrical machine) according to a first modification example of the second embodiment. As illustrated in  FIG. 7 , the ferrite magnets  3  are disposed in the first areas  21  positioned on the outer circumferential side of the rotor core  11  and the samarium-cobalt magnets  5  are disposed in the second areas  22  positioned on the inner circumferential side of the rotor core  11 . Even when the rotor  10  according to the first modification example is used, the desired motor characteristics can be obtained. 
     Consequently, as can be appreciated from  FIGS. 6  and  7 , even in the combination of the ferrite magnet  3  and the samarium-cobalt magnet  5 , either the ferrite magnet  3  or the samarium-cobalt magnet  5  may be disposed on the inner circumferential side or on the outer circumferential side in the magnet embedding groove  2  in the radial direction. 
     The samarium-cobalt magnets  5  in the form of either sintered magnets or bonded magnets can be used. 
     SECOND MODIFICATION EXAMPLE 
       FIG. 8  is an explanatory diagram illustrating a motor (rotating electrical machine) according to a second modification example of the second embodiment. The motor  1  in the second modification example is characterized by the configuration of the magnet embedding grooves  2  of the rotor  10 . 
     In other words, as illustrated in  FIG. 8 , the second areas  22  of the magnet embedding grooves  2  are formed with a pair of a first narrow groove  22 C and a second narrow groove  22 C opposite to and spaced from each other by a given interval. More specifically, the relatively wide first areas  21  are formed on the outer circumferential side of the rotor core  11 , and the relatively narrow second areas  22  are formed on the inner circumferential side of the rotor core  11 . The second area  22  is then formed with the first narrow groove  22 C and the second narrow groove  22 C both being arranged within the width of the first area  21 . 
     By such a configuration, the relatively wide ferrite magnets  3  are positioned on the outer circumferential side of the rotor core  11 , and thus the width of the magnetic steel sheets between the ferrite magnets  3  is narrowed. Accordingly, an inductance that increases in response to the width of the magnetic steel sheets can be suppressed. Moreover, as compared with the configuration illustrated in  FIG. 6 , the distance between the adjacent ferrite magnets  3  can be made long, thereby making the ferrite magnets  3  harder to be subjected to demagnetizing fields, whereby the reduction in ability to withstand demagnetization can be prevented. 
     Furthermore, in the rotor  10  according to the second modification example, a void portion  61  is formed on the inner circumferential side of the rotor core  11  in each of the first narrow groove  22 C and the second narrow groove  22 C. 
     By forming such void portions  61 , the leakage of magnetic flux between the first narrow groove  22 C and the second narrow groove  22 C that are adjacent but not opposite to within the width of the first area  21  can be prevented. 
     In terms of preventing the leakage of magnetic flux, in the second modification example, in the relatively wide first areas  21  formed on the outer circumferential side of the rotor core  11 , second void portions  62  that prevent the leakage of magnetic flux between the ferrite magnets  3  are formed on the inner circumferential side of the rotor core  11 . While the shapes of the void portions  61  and the second void portions  62  here are made to be rectangular, their shapes are not restricted. 
     As in the foregoing, in the second modification example, the ferrite magnets  3  are disposed on the outer circumferential side of the rotor core  11 , and the halved and strip formed samarium-cobalt magnets  5  are disposed on the inner circumferential side of the rotor core  11 . As a consequence, the amount of the samarium-cobalt magnets  5  used can be reduced while an increase in inductance is suppressed and a given ability to withstand demagnetization is maintained. 
     In each of the above-described embodiments, when the rotation spindle  30  and a connecting portion of the magnetic steel sheets constituting the rotor core  11  are made of non-magnetic material, the leakage of magnetic flux can be further prevented, whereby further improvement in motor characteristics can be expected. 
     As explained in the foregoing, with the rotor  10  and the motor  1  according to the above-described embodiments, the desired magnetic properties and motor characteristics can be obtained while the inexpensive ferrite magnets  3  are used. 
     In the above-described embodiments, the rotating electrical machine is explained as the motor  1 . However, the present invention can naturally be applied to a generator. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.