| WO/2012/020349 | SEALING ARRANGEMENT FOR AN ELECTRIC MOTOR OR GENERATOR |
| JP2001112203 | ROTARY ELECTRIC MACHINE |
| JP02231931 | SYNCHRONOUS MOTOR AND ROTOR THEREOF |
KITAHARA, Makoto (of 1 Toyota-cho, Toyota-shi, Aichi-ken, 471-8571, JP)
KOGURE, Tomonari (of 1 Toyota-cho, Toyota-shi, Aichi-ken, 471-8571, JP)
KITAHARA, Makoto (of 1 Toyota-cho, Toyota-shi, Aichi-ken, 471-8571, JP)
| CLAIMS: 1. A motor that includes a stator and a rotor disposed inside the stator and a cleft magnet disposed within the rotor, the motor characterized in that a notch is formed in an outer lateral face of the cleft magnet that faces the stator, wherein the notch serves as a cleavage origin, and the cleft magnet is cleaved into a plurality of strips along a cleavage face that extends from the notch as a cleavage origin to an inner lateral face of the cleft magnet, which faces away from the stator. 2. The motor according to claim 1, wherein the cleavage face of the cleft magnet is cleaved along a grain boundary phase that is lower in strength than a main phase of the cleft magnet. 3. The motor according to claim 1 or 2, wherein the cleft magnet includes a plurality of parallel notches that are zonation. 4. A method of manufacturing a motor that includes a stator and a rotor disposed inside the stator and a cleft magnet disposed within the rotor, the method characterized by comprising: preparing a magnet equipped, in one lateral face thereof, with a notch serving as a cleavage origin; cleaving the magnet using the notch as a cleavage origin to form two or more cleft strips and fitting cleavage faces of adjacent cleft strips to one another to reintegrate the magnet; and disposing the reintegrated magnet in a slot formed through the rotor such that the notch corresponds to an outer lateral face of the magnet that faces the stator. 5. The method of manufacturing according to claim 4, wherein the magnet, which has formed in the one lateral face thereof a plurality of parallel zonate notches spaced apart from one another by a clearance, is prepared, and the magnet is cleft by applying thereto a diagonal tensile force as a resultant force of a tensile component in a direction perpendicular to the notches and a tensile component in a direction from the one lateral face toward the other lateral face. 6. The method according to claim 5, wherein the magnet is gripped, at one end that extends parallel to the plurality of the notches, by a fixed gripper, the magnet is gripped, at the other end thereof extending parallel to the plurality of the notches, by a tension gripper, and the magnet is cleft by pulling the magnet diagonally from the one lateral face in which the notches are provided toward the other lateral face via the tension gripper. |
THE MOTOR
B CKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The invention relates to a motor having a cleft magnet in, for example, a slot formed in a rotor (an interior permanent magnet motor, which will be referred to hereinafter as an ΓΡΜ motor), and to a method of manufacturing the motor.
2. Description of the Related Art
[0002] Among various types of motors, including a brushless DC motor, a motor that includes a permanent magnet-embedded rotor, in which a plurality of permanent magnets are embedded within the rotor core (hereinafter referred to as an IPM motor) is well known. For example, IPM motors may be employed as motors for hybrid vehicles.
[0003] Generally, a coil is formed by winding a winding wire around stator teeth in a concentrated manner or in a distributed manner. A current is applied to the coil to generate a magnetic flux and create magnetic torque and a reluctance torque between the generated magnetic flux and the magnetic flux resulting of the permanent magnet. In a distributed-winding coil, the number of magnetic poles is greater than that of a concentrated-winding coil, and accordingly, the magnetic flux (or a change in magnetic flux) entering the permanent magnet of a rotor from the teeth side during rotation of the rotor is relatively continuous. Therefore, the change in magnetic flux during rotation of the rotor is relatively small. In contrast, in the case of the concentrated-winding coil, because the change in magnetic flux is relatively large, an eddy current is likely to be created in the permanent magnet. The permanent magnet generates heat due to the creation of the eddy current, and the magnetic characteristic of the permanent magnet itself deteriorates due to the induction of irreversible thermal demagnetization.
[0004] As for a drive motor employed in a hybrid vehicle or an electric vehicle in recent years, while an enhancement of the output performance of the motor has been pursued, an attempt to increase, for example, the rotational speed of the motor or the number of poles in the motor has been made. The fluctuation rate of a magnetic field acting on a magnet increases with increases in the rotational speed or the like. As a result, eddy currents are more likely to be induced. In some cases, the performance of the motor deteriorates contrary to expectations due to thermal demagnetization, which thereby reduces the durability of the motor.
[0005] In order to prevent the induction of eddy Currents and the accrual of thermal demagnetization resulting therefrom the permanent magnet may be formed out of a plurality of split pieces that are bundled together before being installed in a rotor slot, as described in, for example, Japanese Patent Application Publication No. 2005-198365 (JP-A-2005- 198365), Japanese Patent Application Publication No. 2004-96868
(JP-A-2004-96868), and Japanese Patent Application Publication No. 2006-238565 (JP-A-2006-238565).
[0006] The permanent magnet may be effectively manufactured from the plurality of the split pieces to suppress the possible induction of eddy currents in the permanent magnet, as described in JP-A-2005-198365, JP-A-2004-96868, and
JP-A-2006-238565. The split pieces constituting the permanent magnet described in JP-A-2005-198365, JP-A-2004-96868, and JP-A-2006-238565 are manufactured separately from one another, or according to a method in which a permanent magnet molded into an inner void shape and inner void dimension of a rotor slot into which the permanent magnet should be inserted is machined (cut) into a plurality of split strips. From the standpoint of manufacturing efficiency and manufacturing cost, it is prevalent to adopt the latter processing method.
[0007] However, in machining the permanent magnet, an expensive cutting tool with a diamond chip attached to, for example, the outer periphery of a super steel disc is required. However, because the cutting tool is a consumable article, maintenance and a sharp rise in manufacturing cost are considered to be caused by the necessity to periodically replace the cutting tool, an increase in the frequency of replacement resulting from an increase in the number of split pieces, and the like.
[0008] Furthermore, in the method of cutting the permanent magnet through the machining, a ferrite magnet or a rare earth magnet such as a neodymium magnet or the like as a permanent magnet has a metal structure composed of a main phase S contributing to magnetization and a grain boundary phase R contributing to a coercive force, as shown in FIG 6 as an enlarged view of the structure of the magnet. When this permanent magnet is split through machining, split strips are formed along a cutting line indicated by an LI line of FIG. 6. As is apparent from FIG. 6 as well, this LI line is formed while cutting and splitting the main phase S. Therefore, the main phase S is smaller in size after it is cut than before it is cut. This constitutes a factor in a fall in residual magnetic flux density Br in comparison with a state prior to the cutting of the main phase S.
[0009] Furthermore, the grain boundary phase R applies a coercive force to the main phase S covered therewith. However, the main phase S that is in contact with a cutting face is uncovered with the grain boundary phase R and is therefore likely to undergo magnetization inversion with respect to an external magnetic field. This magnetization inversion phase serves as an origin to reduce the coercive force of the entire magnet.
[0010] A method of manufacturing split magnets by cleaving a permanent magnet instead of machining it is described in Japanese Patent Application Publication No. 2009-33958 (JP-A-2009-33958).
[0011] However, when the cleft magnet obtained by cleaving and then reintegrating the permanent magnet is simply used as disclosed in JP-A-2009-33958, the dimensions of the respective cleft strips of the cleft magnet tend to disperse. In particular, that one of the cleft strips which is larger in width or area than the other cleft strips has a relatively large area for the passage of magnetic flux and hence a large eddy-current loss, thereby counterbalancing the advantage of the cleft magnet.
SUMMARY OF INVENTION [0012] The invention provides a motor that includes cleft magnets that do not cause an inconvenience in the case of the aforementioned machining in manufacturing a split magnet and prevents especially a stator-side dimension (width) of some of respective cleft strips of the cleft magnet from becoming larger than that of the other cleft strips to cause an increase in eddy-current loss as a result of dimensional dispersion of the cleft strips, and a method of manufacturing the motor.
[0013] A motor that includes a stator and a rotor disposed inside the stator and a cleft magnet is disposed within the rotor, wherein, a notch is formed in an outer lateral face of the cleft magnet that faces the stator, wherein the notch serves as a cleavage origin, and the cleft magnet is cleaved into a plurality of strips along a cleavage face that extends from the notch as a cleavage origin to an inner lateral face of the cleft magnet, which faces away from the stator.
[0014] Further, in a motor that includes the cleft magnet according to the first aspect of the invention, the cleavage face of the cleft magnet may be cleaved along a grain boundary phase that is lower in strength than a main phase of the cleft magnet.
[0015] Further, in the motor that includes the cleft magnet according to the first aspect of the invention, the cleft magnet may include a plurality of parallel notches that are zonation.
[0016] It should be noted herein that the magnet (permanent magnet) applied to the motor equipped with the cleft magnet according to the first aspect of the invention includes a rare earth magnet, a ferrite magnet, an alnico magnet or the like. The magnet is not limited in particular as long as it has a metal structure composed of a main phase contributing to magnetization and a grain boundary phase contributing to a coercive force. Further, the "permanent magnet" mentioned herein is meant to include an unmagnetized sintered body and a simple green compact as well as the aforementioned magnetized rare earth magnet and the like. A three-component neodymium magnet obtained by adding iron and boron to neodymium, a samarium-cobalt magnet made of a two-component alloy of samarium and cobalt, a samarium-iron-nitrogen magnet, a praseodymium magnet or the like can be mentioned as the rare earth magnet. Above all, the rare earth magnet is larger in maximum energy product (BH) max than the ferrite magnet and the alnico magnet, and hence is suited to be applied to a motor for driving a hybrid vehicle or the like, that is, a motor requiring high output.
[0017] For example, a plurality of zonate notches serving as cleavage origins are formed at intervals of a predetermined distance in one lateral face of a hexahedron
(rectangular parallelepiped) permanent magnet, more specifically, that lateral face of the permanent magnet which faces a stator when this permanent magnet is inserted into a magnet slot of a rotor core. Cleft strips cleft with these notches serving as the cleaving notches are reintegrated into the permanent magnet of an original shape and an original dimension by fitting respective cleavage faces of the cleft strips to one another after cleaving. The permanent magnet thus reintegrated is inserted into the magnet slot to be installed therein.
[0018] In this case, it is desirable that the aforementioned plurality of the notches be formed in, for example, only one lateral face of the hexahedron permanent magnet. For example, it also seems reasonable to consider that when notches are formed respectively in two opposed lateral faces of the hexahedron at corresponding positions, a cleavage path is more likely to be formed from the notch in one of the faces toward the notch in the other face. However, according to the empirical rule of the inventors and the like, it is apparent that the permanent magnet tends to develop chips, cracks and the like and deteriorates in magnetic characteristic due to the provision of the notches in the two opposed lateral faces, namely, an increase in chipped cross-sectional area.
[0019] The notches prescribed by a constant dimensional clearance in advance face the stator side, and the stator-side dimension of the respective cleft strips constituting the permanent magnet is hence prescribed by the dimension of the notches. Therefore, there is no difference in width dimension, which could be created in the course of cleaving, among the respective cleft strips. That is, since the width of the respective cleft strips on the stator side is uniformly prescribed, there is no cleft strip that has, for example, an excessively large area for the passage of a magnetic flux entering the permanent magnet side from the stator side. In consequence, the above-mentioned problem in the case of the cleft magnet, namely, the problem of a possible creation of a large eddy-current loss in a cleft strip with a large width due to a difference in width among the respective cleft strips at the time of cleaving and a resultant increase in the eddy-current loss of the entire permanent magnet is effectively solved.
[0020] Further, through the application of the cleft magnet obtained by cleaving the permanent magnet whose metal structure is composed of the main phase and the grain boundary phase, the magnet is split along the grain boundary phase exhibiting relatively low strength (so-called grain boundary separation). Therefore, the problems in manufacturing the split magnet through machining, namely, a fall in residual magnetic flux density, a decrease in coercive force resulting from magnetization inversion, also the troublesomeness of maintenance in replacing the cutting tool, and a rise in manufacturing cost can all be solved. Owing to the foregoing, in addition to an effect of obtaining a magnet exhibiting a high residual magnetic flux density and a large coercive force as an inherent effect achieved in applying a cleft magnet, an additional effect of obtaining a magnet with a minimized eddy-current loss in spite of the application of a cleft magnet is achieved.
[0021] A method of manufacturing a motor that includes a stator and a rotor disposed inside the stator and a cleft magnet disposed within the rotor, the method including: preparing a magnet equipped, in one lateral face thereof, with a notch serving as a cleavage origin; cleaving the magnet using the notch as a cleavage origin to form two or more cleft strips and fitting cleavage faces of adjacent cleft strips to one another to reintegrate the magnet; and disposing the reintegrated magnet in a slot formed through the rotor such that the notch corresponds to an outer lateral face of the magnet that faces the stator.
[0022] Further, in the method of manufacturing the motor that includes the cleft magnet according to the second aspect of the invention, the magnet, which has formed in the one lateral face thereof a plurality of parallel zonate notches spaced apart from one another by a clearance, is prepared, and the magnet may be cleft by applying thereto a diagonal tensile force as a resultant force of a tensile component in a direction
perpendicular to the notches and a tensile component in a direction from the one lateral face toward the other lateral face.
[0023] Further, in the method of manufacturing the motor that includes the cleft magnet according to the second aspect of the invention, the magnet may be gripped, at one end that extends parallel to the plurality of the notches, by a fixed gripper, the magnet may be gripped, at the other end thereof extending parallel to the plurality of the notches, by a tension gripper, and the magnet may be cleft by pulling the magnet diagonally from the one lateral face in which the notches are provided toward the other lateral face via the tension gripper..
[0024] According to the method of manufacturing the motor that includes the cleft magnet according to the second aspect of the invention, the magnet is cleft by being subjected to a diagonal tensile force transmitted from the lateral face side where the notches are formed toward the other lateral face or tensile bending. Therefore, in addition to the promotion of the cleaving of the magnet, cleft strips whose error in width dimension has been minimized can be obtained on the lateral face located opposite the lateral face in which the notches are provided.
[0025] Motors equipped with cleft magnets according to the first aspect of the invention and motors (IPM motors) obtained through the manufacturing method according to the second aspect of the invention have been actively mass-produced in recent years, and are also suitable as motors for driving hybrid vehicles and electric vehicles of which high-output performance is expected.
[0026] According to the motor that includes the cleft magnet and the method of manufacturing the same according to the aspects of the invention, owing to a simple improvement in structure in which the lateral face of the magnet in which the notch serving as the cleavage origin is formed faces the stator side and the magnet is disposed in the slot of the rotor and an improvement in manufacturing method, an effect of obtaining a magnet having an eddy-current loss much less than the cleft magnet according to the related art is achieved in addition to an effect intrinsically exerted by a cleft magnet, namely, an effect of obtaining a magnet with a high magnet flux density and a large coercive force. As a result, an IPM motor excellent in output performance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of an example embodiment of the invention with reference to the accompanying drawings, in which like numerals are used to represent like elements and wherein:
FIG. 1 is a perspective view of a motor according to the embodiment of the invention;
FIG. 2 is a schematic view illustrating how cleft magnets constituting the motor of FIG. 1 according to the embodiment of the invention are disposed in a rotor core;
FIG. 3 is a view illustrating a cleavage path formed in cleaving a permanent magnet according to the embodiment of the invention;
FIG 4 is a view illustrating the method of cleaving a permanent magnet (a first step) in a method of manufacturing a motor according to the embodiment of the invention;
FIG. 5A is a graph showing the result of an analysis of the width and magnet loss of cleft or split magnets;
FIG. 5B is a graph showing a result of an analysis of a comparison in magnet eddy-current loss among a motor equipped with cleft magnets cut through machining (Comparative Example 1), a motor equipped with cleft magnets each having a magnet lateral face with a notch directed toward a stator side (Example), and a motor equipped with cleft magnets each having a magnet lateral face with a notch directed toward the opposite of a stator side (Comparative Example 2); and
FIG. 6 is a view illustrating a splitting line in a structure of a permanent magnet split by a machine according to the related art.
DETAILED DESCRIPTION OF EMBODIMENT 2878
9
[0028] The embodiment of the invention will be described hereinafter with reference to the drawings. FIG 1 is a perspective view showing a motor that includes cleft magnets according to the embodiment of the invention. FIG 2 is a schematic view showing a relationship between the cleft magnets disposed in a rotor core constituting the motor of FIG 1 and a stator, with the cleft magnets in the rotor core seen through.
[0029] An IPM motor 100 shown in FIG. 1 is generally composed of a stator 20 and a rotor 10. The stator 20 is formed by laminating a plurality of electromagnetic steel plates 2 composed of yokes 22 generally annular in a plan view and teeth 21 that protrude radially inward from the yokes 22. The rotor 10 is rotatably disposed inside the stator 20, and formed by laminating a plurality of electromagnetic steel plates 1 in the shape of a circular disc. A rotor shaft 11 (a drive shaft slot) is opened through this rotor 10 at the center of the rotor, and a plurality of magnet slots, extending along the rotor shaft 11, are formed through the rotor 10 near the periphery of the rotor. Cleft magnets 30, formed by cleaving a permanent magnet, are inserted into each magnet slot. Gaps between the slots and the cleft magnets 30 may be filled with, for example, a fixing resin to ensure that the cleft magnets 30 remain fixed in the slots. It should be noted that although the example shown in FIGS. 1 and 2 is configured so that one of the cleft magnets 30 is disposed per pole in such a posture that a longitudinal direction thereof is arranged face to face with the teeth 21 in a plan view , a configuration in which one pole is formed by two permanent magnets and the permanent magnets are disposed in the shape of V in a plan view.
[0030] The stator 20 is integrally formed of, for example, the plurality of the laminated electromagnetic steel plates 2 caulked at the yokes 22. The rotor 10 is also integrally formed of the plurality of the electromagnetic steel plates 1 caulked in regions between the cleft magnets 30 and the rotor shaft 11 respectively.
[0031] It should be noted the formation of both the stator 20 and the rotor 10 is not restricted to lamination of electromagnetic steel plates. Suitable alternative include a dust core made of a soft magnetic metallic powder of iron, an iron-silicon alloy, an iron-nitrogen alloy, an iron-nickel alloy, an iron-carbon alloy, an iron-boron alloy, an iron-cobalt alloy, an iron-phosphorus alloy, an iron-nickel-cobalt alloy, an
iron-aluminum-silicon alloy or the like or a magnetic powder having a soft magnetic metallic oxide powder covered with a resin binder such as a silicon resin or the like.
[0032] Each cleft magnet 30 is formed by cleaving a rectangular parallelepiped permanent magnet in which a plurality of zonate notches 31, as shown in FIG. 2, formed in one lateral face of the cleft magnet 30 and are used as cleavage origins. After cleaving the cleft magnet 30, cleft strips 30A to 30E are fitted together along the cleavage faces of the notches 31, and reintegrated into a permanent of an original shape and an original dimension.
[0033] Each cleft magnet 30 is then inserted into the rotor slot and fixed therein so that the outer lateral face 30a of the cleft magnet 30, in which the plurality of the notches 31 are formed, faces toward the stator (radially outward of the rotor 10).
[0034] That is, the clearance between adjacent ones of the notches 31 and 31 is uniformly prescribed in advance as a predetermined clearance t as shown in FIG. 2. Accordingly, in each of the cleft magnets 30 obtained by cleaving the permanent magnet, the respective cleft strips on the lateral face 30a in which the plurality of the notches 31 are formed are still ensured of a constant width and hence a constant area. On the other hand, the respective cleft strips are inhomogeneous in width on a lateral face 30b of each of the cleft magnets 30 (radially inward of the rotor 10) located on the other side, depending on the proceeding of cleaving. As is apparent from the example shown in the drawings, while some of the cleft strips may be relatively narrow, others may be relatively wide.
[0035] However, because the area through which magnetic flux flowing from the teeth 21 of the stator passes into the lateral face of the cleft magnet 30 facing the stator (the lateral face 30a in which the notches are formed) mainly determines the possible eddy-current loss in the cleft magnet 30, it is appropriate that each cleft strip constituting the lateral face 30a facing the stator be all ensured of a desired width or area that is uniformly assumed at first (determined at the stage of designing). The variation in width or area of each cleft strip constituting the lateral face 30b located on the other side does not greatly affect the eddy-current loss in the cleft magnet.
[0036] The motor 100 according to the invention has a new technical concept in that a mode of disposing the cleft magnets as described above is applied, and also is obtained through an extremely simple structural improvement, namely, a construction in which the plurality of the notches are provided in the permanent magnet and the magnet is inserted into the slot and fixed therein in such a posture that the lateral face of the magnet in which these notches are provided is arranged face to face with the stator side.
[0037] It should be noted that the clearance between the respective notches 31 and 31 is uniformly set as a width t in the example shown in the drawings, but that the clearance between the notches may not necessarily be uniform in view of the fact that the possible eddy-current loss also decreases as the width t decreases, and that it is appropriate to adopt a configuration in which the eddy-current loss in the cleft strip having the widest clearance between the notches is so adjusted as to be equal to or smaller than a desired value. For example, in four cleft strips whose widths establish a relationship of t4 > t3 > t2 > tl, as long as the possible eddy-current loss in the cleft strip having the largest width t4 is equal to or smaller than a permissible value at the stage of designing, it is not required that all the cleft strips be uniform in width.
[0038] FIG. 3 is a view illustrating a cleavage path formed in cleaving the permanent magnet according to the embodiment of the invention, and also shows the internal composition of the permanent magnet. The cleft strips are formed by cleaving the permanent magnet along the cleavage path L2, as shown in FIG. 3. The metallic composition of the permanent magnet is formed through the interposition of a grain boundary phase R, which contributes to a coercive force between main phases S, which contribute to magnetization. Mechanically cutting the permanent magnet, as in the method according to the related art, a cutting line LI segmenting the main phase S, as shown in FIG. 6 is formed. In contrast, in the embodiment of the invention, by cleaving the permanent magnet, the cleavage path L2 is formed along the grain boundary phase R, which has a lower strength than the main phases S. Therefore, the cleft strips are formed in which each main phase S maintains its original size and is protected by the grain boundary phase R along the outer periphery thereof. Thus, residual magnetic flux density and coercive force are greater in the cleft magnet than the split magnet that has been mechanically cut.
[0039] Next, the outline of a method of manufacturing a motor according to the embodiment of the invention will be described. As shown in FIG. 2, the method of manufacturing the motor according to the embodiment of the invention, namely, the method of manufacturing the motor 100 shown in FIGS. 1 and 2 is made up of a first step of preparing a permanent magnet equipped in one lateral face thereof with a plurality of notches 31 serving as cleaving origins, a second step of cleaving the permanent magnet using the plurality of the notches 31 as the cleaving origins to form two or more cleft strips 30A to 30E and fitting cleavage faces of adjacent ones of the cleft strips to each other respectively to reintegrate the permanent magnet and hence obtain the cleft magnet 30, and a third step of disposing this cleft magnet 30 in the slot of the rotor 10 such that the notches 31 correspond to the stator side.
[0040] FIG. 4 shows one embodiment of a step of cleaving the permanent magnet in the first step of the aforementioned manufacturing method.
[0041] One end of a permanent magnet 30' so machined as to fit the shape and dimension of the slot, more specifically, one end of the permanent magnet 30' that extends parallel to the plurality of the notches 31 formed in one lateral face of the permanent magnet 30' is gripped by a fixing gripper K, and the other end of the permanent magnet 30' is gripped by a tension gripper H.
[0042] The permanent magnet 30' is then subjected to a tensile (bending) process diagonally on the lateral face side thereof located opposite the lateral face in which the notches 31 are provided, via the tension gripper H. The cleft strips can thereby be efficiently manufactured using the respective notches 31 as the cleaving origins.
[0043] This diagonal tensile force P may be regarded as a resultant tensile force composed of a tensile component PI applied horizontally to the permanent magnet 30' and a tensile component P2 applied vertically downward to the permanent magnet 30', and can also be regarded as diagonally downward tensile bending.
[0044] In any case, as shown in FIG 4, the knowledge that the cleaving of the permanent magnet can be efficiently carried out by diagonally pulling the permanent magnet 30' from the lateral face in which the notches are provided toward the other lateral face and the error in width (area) between the lateral face in which the notches are formed and the other lateral face can be minimized in the obtained respective cleft strips has been obtained from the empirical rule of the inventors and the like.
[0045] Next, an analysis of a comparison in magnet eddy-current loss among a motor equipped with a mechanically cut split magnet (Comparative Example 1), a motor equipped with a cleft magnet whose magnet lateral face having notches is directed toward a stator side (Example), and a motor equipped with a cleft magnet whose magnet lateral face having notches is directed toward the other side of a stator (Comparative Example 2) and a result of the analysis will be described. First of all, the inventors and the like found out through an analysis a general relationship between magnet dimensions (a width and an area) and a loss (an eddy-current loss). It should be noted herein that a current condition as a condition of this analysis was set as an amplitude of 4.8 (A), a frequency of 1700 (Hz), and a phase of 0 (deg). It should be noted that this amplitude condition is a condition for ensuring the magnets of a magnet flux density of 0.1 (T). The magnets used are neodymium sintered magnets with an Hcb of 985000 A/m, a recoil ratio magnetic permeability of 1.05, a specific resistance of 1.35xl0 ~6 (Qm), and a density of 7600 (kg/m 3 ). Furthermore, electromagnetic steel plates forming rotor cores and stator cores are isotropic electromagnetic steel plates, and the magnetization characteristic thereof is so set as to prevent the electromagnetic steel plates from being saturated.
Under these conditions thus set, a magnetic field analysis was carried out using
JMAG-Studio 9.0 as an analysis tool.
[0046] FIG. 5A shows an analysis result of a magnet width and a magnet loss. As is apparent from FIG. 5A, while the magnet loss increases like a quadratic curve with increases in width and there is almost no loss when the width is about 2 mm, the increase in magnet loss is remarkable from an inflexion point corresponding to a width of about 3 mm.
[0047] This demonstrates that the loss of an entire cleft magnet is extremely large in the case where the cleft magnet has a cleft strip with a relatively large width (area) when a lateral face of an original permanent magnet in which no notch is formed is directed toward a lateral face located on a stator side of the cleft magnet.
[0048] In view of this result, the inventors and the like further analyzed the eddy-current losses of the magnets in the rotors in the motor equipped with the mechanically cut split magnet (Comparative Example 1), the motor equipped with the cleft magnet whose magnet lateral face having notches is directed toward the stator side (Example), and the motor equipped with the cleft magnet whose magnet lateral face having notches is directed toward the other side of the stator (Comparative Example 2) and attempted to compare the eddy-current losses with one another. It should be noted that the condition of the analysis is the same as described above, and that a difference between machining and cleaving and a difference between lateral faces of even a cleft magnet subjected to cleaving during insertion into a rotor slot thereof (whether or not that lateral face which has notches is directed toward a stator side) are added as the conditions to be set.
[0049] FIG 5B shows respective analysis conditions of Comparative Examples 1 and 2 and Example. It has been substantiated from FIG. 5B that the eddy-current loss of Comparative Example 1 in which the respective split magnets are uniformly processed into the same width (the same dimension) is the smallest, and that Example in which the lateral face in which the notches are formed is arranged face to face with the stator side achieves an eddy-current loss reduction effect of no less than 1 kW in comparison with Comparative Example 2.
[0050] It should be added again that although the split magnet subjected to machining can be made smaller in eddy-current loss than the cleft magnet as described already, the coercive force performance and magnetization performance (residual magnetic flux density) of the split magnet deteriorates and leads to a decrease in maximum energy product as a matter of course. [0051] This analysis has substantiated that an eddy-current loss in a permanent magnet can be reduced by equipping a motor with a cleft magnet whose lateral face in which notches are formed is arranged face to face with a stator side, and that an IPM motor can be made excellent in torque performance and rotation performance in view of the fact that a magnet high in coercive force performance and magnetization performance (residual magnetic flux density) is obtained as an effect intrinsically exerted through the application of a cleft magnet.
[0052] The invention has been described with reference to the example embodiment thereof for illustrative purposes only. It should be understood that the description is not intended to be exhaustive or to limit the form of the invention and that the invention may be adapted for use in other systems and applications. The scope of the invention embraces various modifications and equivalent arrangements that may be conceived by one skilled in the art.
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