Abstract:
In a DC motor, a permanent magnet rotor comprising a shaft, a rotor sheet packet supported by the shaft, which rotor sheet packet comprises close to the periphery thereof completely closed and tangentially extending rectangular recesses for receiving planar permanent magnet plates. At least one permanent magnet plate is accommodated in each recess, the permanent magnet plates are held by spring elements free of play by force locking, the recesses have free spaces connected to the permanent magnet plates in the tangential direction, which free spaces extend across the major part of the side surfaces of the permanent magnet plates and the rotor sheet packet consists essentially of a radial outer annular region and a radial inner core region, wherein the annular region in a large part is delimited by the recesses and the free spaces and is integral with the core region via thin radial webs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present patent application is a continuation of International Application No. PCT/DE2014/200031, filed Jan. 28, 2014, which is based on, and claims priority from. German Application No. 10 2013 206 438.1, filed Apr. 11, 2013, both of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The invention relates to permanent magnet rotors for electronically commutated direct current motors with a shaft and a laminated rotor core carried by the shaft. 
         [0004]    (2) Description of Related Art Including Information Disclosed Under 37 CFR §1.97 and §1.98 
         [0005]    From US 2007/004009 A2, a generic rotor is known, in which, in an inner region of the laminated rotor core, which is radial to the permanent magnet plates, there are additional recesses, which are open to the recesses for the permanent magnet plates. Spring elements, which exert an outward radial force on the permanent magnet plates, are inserted into each of these additional recesses. This known solution has the disadvantage that the permanent magnet plates are not clearly fixed in the tangential direction by the spring force; as a result, the magnets may move under external load within the recess at right angles to the spring force. The springs furthermore have no effect on imbalances, which may possibly arise. An additional disadvantage exists therein that, due to the additional recess, the magnetic resistance of the magnetic circuit is increased because the recess is arranged in the main flux region. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a permanent magnet rotor for an electronically commutated direct current motor with a shaft and a laminated rotor core carried by the shaft. The laminated rotor core has rectangular recesses extending tangentially, that are closed over the entire circumference of the laminated rotor core, near its periphery, for the accommodation of planar permanent magnet plates. At least one permanent magnet plate is accommodated in each recess, and the permanent magnet plates are held non-positively without play by spring elements. The recesses have in the tangential direction clearances adjoining the permanent magnet plates, which clearances extend over the majority of the side surfaces of the permanent magnet plates. The laminated rotor core is essentially comprised of a radial outer ring region and a radial inner core region, wherein the ring region is in large part limited by the recesses and the clearances and is integral with the core region over thin radial webs. 
         [0007]    No additional recesses in the laminated rotor core are necessary for the spring elements, because they are housed in the already present clearances adjoining the permanent magnet plates. Therefore, there is no danger of weakening the magnetic circuit and, with this, limited power of the electric motor. In order to prevent a magnetic short circuit, the spring elements are produced from a non-magnetic material. This is important because the magnets are disposed in a region, which is recessed to form a magnetic resistance and prevent a magnetic short circuit. Due to the spring forces acting predominantly tangentially on planar side surfaces of the permanent magnet plates, all magnets are pushed in the same direction or at least aligned so that the magnets are arranged symmetrically around a rotation axis of the permanent magnet rotor, whereby imbalances are avoided. By definition, the radii of the permanent magnet plates, which adjoin the side surfaces, are also counted among the side surfaces. The webs, which border the clearances, or the side surfaces of other permanent magnet plates, may serve as a support surface for the spring elements. The spring elements produce a reliable, secure mounting of the permanent magnet plates in that they hold these at ends that are situated opposite the spring elements in a radial position free of play. Contrary to methods employing adhesives, the rotor weight may be kept calculably and reproducibly within narrow limits. 
         [0008]    Provisions are made so that the spring elements are sheet metal strips, which are curved in a V-shape and/or U-shape. These are particularly simple to manufacture and may also be supplied simply during the installation, for example in that they are supplied taped together as strip stock. The springs may also transition over their length from a V-shaped form into a U-shaped form, wherein they have a triangular yoke, which connects the spring legs to one another. This embodiment facilitates the installation significantly. Such sheet metal springs may simply be adapted to different requirements by changing the sheet thickness, the spring material, and the spring geometry to meet the different requirements. Moreover, curved sheet springs allow the design of the magnetically optimized sheet section to be retained without modification. In principle, the sheet section may also be used as needed for other attachment methods without modifications. Examples of such attachment methods are adhesion, joining by forming or by forming. If necessary, sheet springs may also be provided with positive fit, by means of which the magnets may additionally be axially secured. Identical springs may also conditionally be used for different rotor diameters and rotor lengths. 
         [0009]    As an alternative to the V-shape or the U-shape, C-shaped oval or circular metal strips or metal strips transitioning from an oval shape into a circular shape may be used. An advantage of this embodiment is an edge-free contact with the permanent magnet plates so that scraping or chipping can largely be avoidable. 
         [0010]    In an advantageous development of the invention, the spring elements are curved so that the burs formed during manufacture, usually when cutting with shears, are shifted to the side of the sheet metal that does not come into contact with the permanent magnet plates. Scraping and chipping during the installation are thereby avoided. 
         [0011]    The installation is particularly simple, if the spring elements exclusively are held non-positively in the clearances; the same also applies to permanent magnet plates that are exclusively held non-positively in the recesses. An uninstallation of the permanent magnet plates, which may be required for environmental protection reasons and for the purpose of recycling the valuable magnetic material, is likewise facilitated by the exclusively non-positive connection. The economics are also improved hereby over the entire life cycle of the product, up to the reuse of materials. 
         [0012]    In a first embodiment, the number of spring elements corresponds to the number of permanent magnet plates. In this case, each spring element is supported on one side at a side surface of a permanent magnet plate and on the other side at a web. Preferably, all permanent magnet plates are pushed by the respective spring elements in the same direction, and thus imbalances are equalized and the symmetry of the magnetic field is maintained. 
         [0013]    In a second particularly preferred embodiment, only half the number of spring elements are provided relative to the number of permanent magnet plates. In this embodiment, only every second one of the webs present in the first embodiment is provided. In the installed state, two permanent magnet plates are thereby separated from one another alternately by a web or by a spring element. The spring elements thus act on the side surfaces of two permanent magnet plates. The number of permanent magnet plates typically is an even number, whereby also in the second embodiment a symmetrical distribution of the permanent magnet plates results over the circumference of the permanent magnet rotor. 
         [0014]    An alternative arrangement of the spring elements is also possible, wherein a main elastic line of the spring elements is directed radially outward and the sheet metal legs are directed radially inward. It can furthermore be provided that, within the clearance, the spring elements adjoin the laminated core radially on the outside. 
         [0015]    Independently of the embodiment, provisions may be made in a particularly preferred variation that angular cross-section regions of the spring elements do not adjoin the planar side surfaces of the permanent magnet plates. 
         [0016]    The spring elements preferably comprise a paramagnetic or diamagnetic material, such as stainless steel, bronze, copper beryllium or paramagnetic spring steel. These substances possess a high magnetic resistance, and therefore do not lead to magnetic short circuits. 
         [0017]    The inventive permanent magnet rotor is intended primarily for brushless direct current motors, however, it is likewise also usable for synchronous motors and other types of motors. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]    The invention is explained in greater detail in the following using exemplary embodiments. 
           [0019]      FIG. 1   a  shows a front view of a first embodiment of a permanent magnet rotor according to the invention; 
           [0020]      FIG. 1   b  shows a plan view of the permanent magnet rotor of  FIG. 1   a;    
           [0021]      FIG. 1   c  shows a representation of a spring element; 
           [0022]      FIG. 2   a  shows an end view of a first variation of the first embodiment. 
           [0023]      FIG. 2   b  is a detailed view of a portion of  FIG. 2   a;    
           [0024]      FIG. 3   a  shows an end view of a second variation of the first embodiment; 
           [0025]      FIG. 3   b  is a detailed view of a portion of  FIG. 3   a;    
           [0026]      FIG. 3   c  shows a section through a permanent magnet rotor according to  FIG. 3   a;    
           [0027]      FIG. 3   d  is a detailed view of a portion of  FIG. 3   c;    
           [0028]      FIG. 4   a  shows an end view of a second embodiment of a permanent magnet rotor according to the invention; 
           [0029]      FIG. 4   b  is a detailed view of a portion of  FIG. 5   a;    
           [0030]      FIG. 5   a  shows a spatially depicted arrangement of a variant of the second embodiment; 
           [0031]      FIG. 5   b  shows a first variation of the spring element; 
           [0032]      FIG. 6   a  shows an end view of a second variation of the second embodiment; 
           [0033]      FIG. 6   b  shows a spatial representation of the variation from  FIG. 6   a;    
           [0034]      FIG. 7  shows a spatial presentation of an installation process of a permanent magnet plate; 
           [0035]      FIG. 8  shows a spatial representation of an installation process of a spring element; 
           [0036]      FIG. 9  shows a variant of the installation position of the spring element; and 
           [0037]      FIG. 10  shows a third variation of the spring element in a similar, installed position. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    It is therefore an object of the present invention to produce a permanent magnet rotor of the aforementioned kind, which enables the permanent magnet plates to be installed securely, free of play, and thereby allows a magnetic circuit that is optimum for this construction, retains flexibility in the production of a large palette of permanent magnet rotors for different requirements and uses, in which imbalances are minimized by design, for which both the installation and also dismantling are possible in a simple manner, for which energy use in production is low and high environmental standards are satisfied both in production and in disposal, for which noise development in operation is minimized, tolerances as well as length changes due to thermal expansion may be compensated, which has good chemical and fatigue resistance, can be produced quickly and can be connected with a high mechanical strength between permanent magnet plates and laminated core can be achieved. 
         [0039]      FIG. 1   a  shows a front view of a first embodiment of a permanent magnet rotor  1  according to the invention, comprising a shaft  2 , and a laminated rotor core  3 , that comprises thin magnetic steel sheets that are insulated from one another in order to suppress eddy currents. The laminated rotor core  3  is pressed onto the shaft  2  and with this forms a compact structural group. 
         [0040]      FIG. 1   b  shows a plan view of the permanent magnet rotor of  FIG. 1   a  with the shaft  2 , the laminated rotor core  3 , recesses  4 , permanent magnet plates  5 , clearances  7  and spring elements  6 . The recesses  4  are matched to the permanent magnet plates  5  so that a correct installation of the magnet plates is possible with a minimal air gap. A spring element is arranged in every second clearance  7  and pushes a permanent magnet plate  5  into a tapering region between the recess  4  and the clearance  7 . Since the permanent magnet plates  5  are arranged near the periphery of the permanent magnet rotor  3 , the outer contour of the clearance  7  follows the rotor periphery and is therefore angled relative to the recess. This commonly used geometry is employed in the present invention to keep the magnet free of play. The edges of the permanent magnet plates are slightly rounded, and are therefore jammed easily in the constriction. The laminated rotor core  3  is comprised of a care region  10 , which extends between the shaft  2  and the permanent magnet plates  5 , and an outer ring region  9 , which is arranged radially outside of the permanent magnet plates  5  and is integral with the core region  10  via webs  11 . 
         [0041]      FIG. 1   c  shows a spring element  6 , which consists of an elongated metal strip that is curved or folded in a V-shape. One end of the spring element has advantageous insertion aids  15  which, in the present example, are curved inward on a crease line  16  running at an angle to the main bent line  17 . The length of the spring element  6  corresponds approximately here to the length of the laminated rotor core  3  and the length of the permanent magnet plates  5 ; however, it can also be shorter. Burs  12 , which are created when the metal strips are cut with shears, are located on the inside  13  of sheet metal legs  15  so that they cannot scrape away any sheet metal material during the installation. 
         [0042]      FIG. 2   a  shows a front view of a first variation of the first embodiment of the permanent magnet rotor  1 , with the shaft  2 , the laminated rotor core  3 , the core region  10 , the ring region  9 , the recesses  4 , the permanent magnet plates  5 , the webs  11  and the spring elements  6 . 
         [0043]    A section from  FIG. 2   a  is shown enlarged in  FIG. 2   b . The permanent magnet plates  5  are accommodated in the recesses  4 . A bulge  18  is provided at a transition region of the recesses  4  to a clearance  7 , at the ring region  9  of the laminated rotor core  3 , which bulge  18  interacts with a rounding  19  and, when acted upon with the force of the spring element  6  in the tangential direction, results in the permanent magnet plate  5  being free of play in the radial direction. In principle, absence of play would also be possible by placing the rounding  19  in a corner  12  of the clearance  7 , but with smaller force components in the radial direction. The bulge  18  can be disposed both on the outside and on the inside of the recess  4 , or on both sides of it. The flatter the angle at the placement point with the permanent magnet plate  5 , the greater is the clamping effect. A greater distance of the permanent magnet plate  5  from the web  11 , and therefore a greater magnetic resistance is also achievable due to the bulge  18 . The webs  11  are dimensioned so that, on the one hand, they are as thin as possible in order to enter into magnetic saturation as quickly as possible and, on the other hand, sufficiently wide in order to ensure a sufficient stability of the laminated rotor core. Due to the symmetrical design, the centrifugal forces largely balance out, so that the webs  11  can be constructed relatively thin. The spring elements  6  are designed as V-shaped, curved sheet metal strips. The sheet metal legs  14  of each spring element  6  are located, on the one hand, on a web  11  and on the other, on a side surface  8  of a permanent magnet plate  5 . The cut edge  20  of the respective spring element  16  in the region of a rounding  19  is thereby arranged, so that the permanent magnet plate  5  cannot be damaged during installation. 
         [0044]      FIG. 3   a  shows a front view of a second variation of the first embodiment of the permanent magnet rotor  1 , with the shaft  2 , the laminated rotor core  3 , the core region  10 , the ring region  9 , the recesses  4 , the webs  11 , the spring elements  6  and the permanent magnet plates  5 . 
         [0045]      FIG. 3   b  shows an enlarged section from  FIG. 3   a , with the core region  10 , the ring region  9 , the recesses  4 , the permanent magnet plates  5 , and the spring elements  6 . Instead of a bulge, a rounded transition region  22  is provided here between the recess  4 , the clearance  7  and the web  11 . This transition region  22  has an effect similar to that of the bulge  18  of  FIGS. 2   a  and  2   b —it forms a flat angle in the contact point with the permanent magnet plates  5 , and therefore produces a radial freedom from play and jamming of the permanent magnet plates  5  when being acted upon by the force of a spring element  6 . Precisely one spring element  6 , which is disposed in every second clearance, is assigned to each permanent magnet plate  5 . The spring elements  6  preferably all act in the same direction about the axis of rotation  23  (clockwise or counterclockwise). 
         [0046]      FIG. 3   c  shows a section through a permanent magnet rotor  1  according to  FIG. 3   a , with the laminated rotor core  3 , the shaft  2 , the recesses  4 , the permanent magnet plates  5 , the core region  10 , the ring region  9 , the webs  11  and the spring elements  6  ( FIG. 3   c  is rotated by 30° relative to  FIG. 3   a ). 
         [0047]      FIG. 3   d  shows a section from  FIG. 3   c , with the force directions depending on an angle α, which represents the angle of the tangents at the rounding  19  of the permanent magnet plates  5  at the contact point with the transition region  22 , relative to the spring force direction in the permanent magnet plate  5 . The spring force  24  produces a radial force  25  and a resulting force  26 . 
         [0048]      FIG. 4   a  and, in an enlarged section,  4   b  show an end view of a second embodiment of the permanent magnet rotor  1 ′ according to the invention, wherein the essential difference from the first embodiment is that every second web  11  and every second spring element  6 ′ have been omitted. A portion of the original clearances  7  were merged into a common spring clearance  7 ′. The springs  6 ′ are no longer supported here on a web, but rather on an additional permanent magnet plate  5 . In the present example, the ring region  9  is integral with the core region  10  over three webs. 
         [0049]    The permanent magnet plates  5  may also be composed of multiple individual plates, without leaving the protective scope of the invention. Such an arrangement of a variation of the second embodiment is spatially depicted in  FIG. 5   a , in which the laminated rotor core is not depicted. Shown are the shaft  2 , the permanent magnet plates  5 ′ divided in the axial direction, and variants of the spring element  6 ′ which, through a slit  27 , can compensate for slight geometric differences between the permanent magnet plates  5 ′ that adjoin one another. 
         [0050]      FIG. 5   b  shows the variant of the spring element  6 ′ as a single part with the slit  27 , which extends across approximately ⅔ of the leg height in both sheet metal legs  14 ′. The slits  27  are arranged on either side of the main bending line  17 ′. 
         [0051]    The permanent magnet plates may also be divided in the tangential direction, without leaving the protective scope of the invention.  FIGS. 6   a  and  6   b  show such a variant of the permanent magnet rotor  1  as a second variant of the second embodiment, with the shaft  2 , the laminated rotor core  3 ′, with the core region  10 , the ring region  9 , the webs  11 , the recesses  4 , the clearances  7  and  7 ′, permanent magnet plates  5 ″ divided in the circumferential direction, and the spring elements  6 ′. 
         [0052]    In principle, it is also possible to combine permanent magnet plates divided axially and in the circumferential direction. 
         [0053]      FIG. 7  shows a representation of an installation process of a permanent magnet plate  5  into one of the recesses  4  of the laminated rotor core  3  with the aid of a magnetic press-fit die  28 , wherein the magnetic press-fit die exerts a force F 1  on the permanent magnet plate  5 . 
         [0054]      FIG. 8  shows a representation of an installation process of a spring element  6  into one of the clearances  7  of the laminated rotor core  3  with the aid of a magnetic press-fit die  29 , wherein the magnetic press-fit die exerts a force F 2  on the spring elements  6 . Both press-fit processes may be implemented horizontally as well as vertically. 
         [0055]      FIG. 9  shows a variation of the installation position of the spring element  6 , wherein the sheet metal legs  14  point inward while the main elastic bended portion  17  points radially outward. Moreover, the spring element  6  lies within the clearance  7 ′ at the ring region  9 . Here the spring element  6  acts on the permanent magnet plates  5  with their cut edges  20  and forces them tangentially in the end of the recess  4  that is situated in the direction opposite the clearance  7 ′. 
         [0056]    A third variation of the spring element  6 ″ is shown in the installed state in  FIG. 10 . As in  FIG. 9 , the sheet metal legs  14 ″ are also directed radially inwards here. The spring element  6 ″ is largely designed in a U-shape, a yoke  30 , which connects the sheet metal legs  14 ″ with one another within the clearance T, lying radially outward at the ring region  9  of the laminated core  3 ′. The spring element  6 ″ does in fact also act upon the permanent magnet plates  5  with their cut edges  20  here, but at a flatter angle of the sheet metal legs  14 ″relative to the side surfaces  8  of the permanent magnet plates  5 . The U-shaped spring element  6 ″ has two main bending lines  17 ″ that are arranged near to the ring region  9  of the laminated core  3 ′. 
         [0057]    In the description of the Figure, the two embodiments of the invention—in particular of the laminated rotor core—have been labeled  3  or  3 ′. The additional variants pertaining to bulge  18  and transition region  22  were not identified separately. 
         [0058]    It is to be understood that the present invention is not limited to the illustrated embodiments described herein. Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  permanent magnet rotor 
           2  shaft 
           3 ,  3 ′ laminated rotor core 
           4  recess 
           5 ,  5 ′,  5 ″ permanent magnet plate 
           6 ,  6 ′,  6 ″ spring element 
           7 , T clearance 
           8  side surface 
           9  ring region 
           10  core region 
           11  web 
           12  fin 
           13  inner side 
           14 ,  14 ′,  14 ″ metal sheet leg 
           15  insertion aids 
           16  bend line 
           17 ,  17 ′,  17 ″ main bending line 
           18  bulge 
           19  rounding 
           20  edge cut 
           21  corner 
           22  transition region 
           23  rotation axis 
           24  spring force 
           25  radial force 
           26  resulting force 
           27  slit 
           28  magnetic press-fit die 
           29  elastic press-fit die 
           30  yoke