Abstract:
Disclosed herein is an apparatus relating to a magnet member for a dynamoelectric machine comprising, a first portion of the magnet member made of a first magnetic material and a second portion of the magnet member made of a second magnetic material. Further disclosed is a method that relates to increasing performance of an electric machine comprising, determining locations of high demagnetization fields at the dynamoelectric machine, and positioning a magnetic member having a first portion having a higher level of coercivity and a second portion having a lower level of coercivity in the machine such that the portion having a higher level of coercivity is more proximate the location of high demagnetization fields than the portion having the lower level of coercivity.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/813,115, filed Jun. 12, 2006, the entire contents of which are specifically incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    Dyanmoelectric machines often use permanent magnets in conversion of mechanical energy to electrical energy and vice versa. Several parameters regarding the permanent magnets are specified to optimize the performance of the machine such as: shape, size, material and positional locations within the dynamoelectric machine. 
         [0003]    The material from which a permanent magnet is fabricated is a primary factor in determining flux density. The performance of a permanent magnet is evaluated in engineering applications by using its maximum energy product, which is the product of flux density (B) and magnetic field strength (H), that is, (BH) max . Generally, a permanent magnet with a higher (BH) max  improves the performance of a dynamoelectric machine. For a given (BH) max , however, magnet materials with high remanence (Br) typically are more susceptible to unrecoverable demagnetization than magnet materials with a low remanence. This is because higher remanence causes a lower coercive force (Hc). Unrecoverable demagnetization occurs when an operation point defined by a flux density (B) and a magnetic field strength (H) in the magnetized direction is below the knee point on the demagnetization curve of the permanent magnet. 
         [0004]    Demagnetization occurs when a permanent magnet experiences a magnetic field in a direction that is opposite to that in which the magnet is initially magnetized. Because in a dynamoelectric machine there are electromagnetic fields generated during operation of the machine, and which in some instances subject permanent magnets to reverse polarity fields, unrecoverable demagnetization can be problematic for machine longevity. Coercivity, also known by the symbol H c , is a measure of the reverse field needed to drive the magnetization of the magnet to zero. The coercivity of a magnet is primarily a function of the material from which the magnet is produced. In general, the properties of coercivity and remanence are inversely proportional to one another such that an increase in remanence is accompanied by a drop in coercivity for a permanent magnet with a given (BH) max . While it is possible to obtain both high remanence and coercivity, the materials required to do so are more expensive than materials that have a moderate to low value of either coercivity or remanence. Designers of dynamoelectric machines must therefore balance coercivity, remanence and cost when specifying permanent magnets for a machine. 
         [0005]    Improvements in the art that reduce the effects of the compromise are ubiquitously well received. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    Disclosed herein is an apparatus that relates to a magnet member for a dynamoelectric machine comprising, a first portion of the magnet member made of a first magnetic material and a second portion of the magnet member made of a second magnetic material. Further disclosed herein is an apparatus that relates to a dynamoelectric machine member with at least one magnet member wherein, the at least one magnet member comprises a plurality of magnetic materials having different values of coercivity from one another. 
         [0007]    Further disclosed is a method that relates to increasing performance of an electric machine comprising, determining locations of high demagnetization fields at the dynamoelectric machine, and positioning a magnetic member having a first portion having a higher level of coercivity and a second portion having a lower level of coercivity in the machine such that the portion having a higher level of coercivity is more proximate the location of high demagnetization fields than the portion having the lower level of coercivity. 
         [0008]    Further disclosed herein is a method that relates to tailoring flux distribution in a dynamoelectric machine comprising, creating a magnet member having a first portion having a first level of coercivity and a second portion having a second level of coercivity, and positioning the magnetic member to achieve a desired flux distribution. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
           [0010]      FIG. 1  depicts a partial cross sectional view of a rotor disclosed herein; 
           [0011]      FIG. 2  depicts a partial cross sectional view of another rotor disclosed herein; 
           [0012]      FIG. 3  depicts a partial cross sectional view of another rotor disclosed herein; 
           [0013]      FIG. 4  depicts a cross sectional view of a direct current motor disclosed herein; 
           [0014]      FIG. 5  depicts a cross sectional view of another rotor disclosed herein; and 
           [0015]      FIG. 6  depicts a partial cross sectional view of another rotor disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIG. 1  a dynamoelectric machine member  10 , of an internal permanent magnet machine, depicted in this exemplary embodiment as a rotor, has a cavity  14  formed therein for locating and positioning magnet members  18 . The cavity  14 , in one embodiment, is sized to provide a press-fit with the magnet members  18  thereby preventing relative movement between the rotor  10  and the magnet members  18 . It is to be appreciated that while machine member  10  and other similar members are illustrated herein as rotors, they may equally exist as stators, motor casings, etc. without departing from the scope of the invention. 
         [0017]    As described above, the magnetic properties of remanence and coercivity are important to the overall performance of the machine. Other factors affecting performance are the shape of magnet members  18  and the position of the magnet members  18  within the machine. In addition to performance, the shape and position of the magnet members  18  also affects their susceptibility to magnetic fields that may be in an opposite direction to the permanent magnetic field of the magnetic members  18 . Such an oppositely directed field, sometimes referred to as a reverse magnetic field, and as noted above, will have an effect of demagnetizing the magnetic members  18  if the reverse magnetic field is of adequate strength. The demagnetizing effect, however, is stronger on certain areas of the members  18  than on other areas. The corners  22 , ends  26  and surfaces  30  of the magnet members  18  are often more susceptible to demagnetization fields than other portions of the magnet members  18 . Consequently, some demagnetization sometimes occurs in these areas resulting in a lower overall remanence of the magnet members  18 . Such a drop in the remanence of the magnet member  18 , as discussed above, results in a drop in the overall performance of the dynamoelectric machine. 
         [0018]    An embodiment of the present invention depicted in  FIG. 1  shows the magnet members  18  divided into two portions. A first portion  34  extends from the surface  30  of the magnet member  18  through a partial thickness of the magnet member  18  to a depth delineated herein by borderline  36 . A second portion  38  comprises the balance of the magnet member  18  that is not part of the first portion  34 . The first portion  34  may be fabricated from a first magnetic material that has a higher coercivity than a material used to fabricate the second portion  38 . Similarly, the second portion  38  may be constructed from a magnetic material that has a higher remanence than the material used to fabricate the first portion  34 . Such a construction of a magnet member  18  permits the magnet member  18  to have a higher resistance to demagnetization at the first portion  34  than at the second portion  38 . Similarly, the construction permits the second portion  38  to have a higher magnetic flux density resulting from the higher remanence level thereof. Tailoring portions of magnet members for a variety of dynamoelectric machines may be performed, in a manner similar to the foregoing description, to optimize the coercivity of magnet members while maintaining high levels of remanence at economical cost levels. 
         [0019]    Referring to  FIG. 2  and alternate embodiment of magnet members within a rotor are shown. Magnet members  118  are positioned within a cavity  114  of the dynamoelectric machine member  110  shown herein as a rotor. The magnet members  118  are divided into first portions  134  and second portions  138  separated by borderlines  136 . The first portions  134  may be constructed of magnetic material with a higher coercivity than the material of the second portions  138 , while the second portions  138  may be constructed of magnetic material with a higher remanence than the material of the first portions  134 . Consequently, magnet members  118  have a higher resistance to demagnetization of the first portions  134  than of the second portions  138 . Though the magnet members  18 ,  118  shown thus far have been rectangular in shape the concept of multiple portions of magnet members made from various magnet materials is applicable to other shapes as well. 
         [0020]    Referring to  FIG. 3  a magnet member  218 , of a surface-mounted permanent magnet machine, with an arcuate shape is depicted. The magnet member  218  forms a circumferential portion of a dynamoelectric machine member  210  shown here as a rotor, which is surrounded by a stator  240  with an air-gap  244  therebetween. The magnet members  218  are divided into first portions  234  and second portions  238  separated by borderlines  236 . The first portions  234  may be constructed of magnetic material with a higher coercivity than the material of the second portions  238 , while the second portions  238  may be constructed of magnetic material with a higher remanence than the material of the first portions  234 . Consequently, the magnet members  218  have a higher resistance to demagnetization of the first portions  234  than of the second portions  238 . 
         [0021]    Referring to  FIG. 4  another embodiment of the invention depicts a dynamoelectric machine  310  that is a direct current (DC) motor. A dynamoelectric machine member  324 , shown here as a motor casing, surrounds four arc shaped magnet members  318 . An armature  340  is located concentrically within the magnet members  318  with a radial air-gap  344  formed therebetween. The magnet members  318  are divided into first portions  334  and second portions  338  separated by borderlines  336 . The first portions  334  may be constructed of magnetic material with a higher coercivity than the material of the second portions  338 , while the second portions  338  may be constructed of magnetic material with a higher remanence than the material of the first portions  334 . Consequently, the magnet members  318  have a higher resistance to demagnetization of the first portions  334  than of the second portions  338 . 
         [0022]    The magnet members  18 ,  118 ,  218 ,  318  of  FIGS. 1-4  have the first portions  34 ,  134 ,  234 ,  334  separated from the second portions  38 ,  138 ,  238 ,  338  by borderlines  36 ,  136 ,  236 ,  336 . The construction of the first portions  34 ,  134 ,  234 ,  334  and the second portions  38 ,  138 ,  238 ,  338  determines the form that the borderlines  36 ,  136 ,  236 ,  336  take. For example, if the first portions  34 ,  134 ,  234 ,  334  and the second portions  38 ,  138 ,  238 ,  338  are formed as independent permanent magnet segments, then the borderlines  36 ,  136 ,  236 ,  336  may simply be the butting together of surfaces of the two contacting portions held in contact by forces normal to the surfaces. Such normal forces may be created by, for example, the dynamoelectric machine member  10 ,  110 ,  210 ,  324  to which the magnet members  18 ,  118 ,  218 ,  318  are attached. Alternately, the portions may be held together by adhesive at the borderlines  36 ,  136 ,  236 ,  336 . 
         [0023]    Alternately, the first portions  34 ,  134 ,  234 ,  334  and the second portions  38 ,  138 ,  238 ,  338  maybe integrally formed as the magnet members  18 ,  118 ,  218 ,  318  are fabricated. For example, if the magnet members  18 ,  118 ,  218 ,  318  are fabricated from powdered materials compressed to shape and sintered, the different magnetic materials used for the first portions  34 ,  134 ,  234 ,  334  and the second portions  38 ,  138 ,  238 ,  338  may be placed into the press prior to pressing to shape. Such a fabrication method will create borderlines  36 ,  136 ,  236 ,  336  that are less distinct than those where the two portions are fabricated as separate segments. This technique can be used to fabricate magnet members  18  with two or more grades of magnetic material within a single magnet member  18 . In so doing, the designer of the dynamoelectric machine can custom design magnet members  18  by positioning magnetic materials with specific magnetic properties in different areas of a magnet member  18 . For example, the corners  22  may have a higher percentage of material with a high coercivity level than the balance of the magnet member  18 , which may use a material with a higher percentage of material with a high remanence level. Both of the magnetic materials used may have lower per volume costs than a single magnet material that had both a high coercivity level and high remanence level, thereby lowering the overall material cost of the magnet member  18 . 
         [0024]    Referring to  FIG. 5  in yet another embodiment magnet members  418  comprise a plurality of portions, such as first portions  434  and second portions  438  that are proximate each other while not actually being in contact with each other. Such portions  434 ,  438  are located in cavities  444 ,  448  respectively, of a dynamoelectric machine member  410  shown here as a rotor. The first portions  434  may be constructed of magnetic material with a higher coercivity than the material of the second portions  438 , while the second portions  438  may be constructed of magnetic material with a higher remanence than the material of the first portions  434 . Consequently, the magnet members  418  have a higher resistance to demagnetization of the first portions  434  than of the second portions  438 . 
         [0025]    Referring to  FIG. 6  an alternate embodiment with magnet members  518  comprise a plurality of portions, such as first portions  534  and second portions  538  that are proximate each other while not actually being in contact with one another. Such portions  534 ,  538  are located in cavities  544 ,  548  respectively, of a dynamoelectric machine member  510  shown here as a rotor. The first portions  534  further comprises first sub-portions  535  and second sub-portions  536 , and the second portions  538  further comprises third sub-portion  539  and fourth sub-portion  540 . The first sub-portions  535  are constructed of magnetic material with a higher coercivity than the material of second sub-portions  536 , which are constructed of magnetic material with a higher coercivity than the material of third sub-portions  539 , which are constructed of magnetic material with a higher coercivity than the material of fourth sub-portions  540 . Consequently, the magnet members  518  have a higher resistance to demagnetization of the first sub-portions  535  than of the second sub-portions  536  than of the third sub-portions  539  than of the fourth sub-portions  540 . It should be noted that the number of sub-portions is not limited to four as depicted in this embodiment but may be any practical number of sub-portions. Additionally, the relationship of coercivity value between any two of the sub-portions may be set as appropriate to the particular application. 
         [0026]    Constructing magnet members  18  with multiple materials provides greater design flexibility in other ways as well. For example, the waveform of the flux density in the air-gap of a dynamoelectric machine may be shaped to reduce torque ripple and core losses. For two layer sinusoidal internal permanent magnet machines the resulting high residual flux density at a bottom layer can make the air-gap flux density more sinusoidal and thereby reduce the harmonic components of the air-gap flux density. Further, portioning the magnet members into different grades of magnetic material may help reduce the eddy current losses inside the magnet members, thereby improving low temperature performance of the dynamoelectric machine. Further still, portioning the magnet members allows a dynamoelectric machine with one set of components, with fixed sizes, to have differing levels of performance, thereby avoiding costs that would be expended to fabricate tools for components of various sizes to build dynamoelectric machines with different performance levels. The grades of permanent magnets may be more than two grades, such as three or more. 
         [0027]    While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.