Abstract:
An electric motor has a housing with at least two housing parts ( 24, 86 ), within which a stator ( 82 ) is arranged. The motor further includes an internal rotor ( 38 ) mounted on a shaft ( 34 ), the rotor interacting with the stator ( 82 ) and being separated from it by an air gap ( 88 ). The shaft ( 34 ) is rotatably supported in the housing by roller bearings ( 30, 72 ). A first one ( 30 ) of the roller bearings has an inner ring ( 32 ) secured at a first predetermined position on the shaft ( 34 ), and an outer ring ( 28 ) secured in a recess ( 26 ) of a first housing part ( 24 ). A second one ( 72 ) of the roller bearings has an inner ring ( 70 ) secured at a second predetermined position on the shaft ( 34 ) and an outer ring ( 74 ) arranged in an associated recess ( 96 ) of a second housing part ( 86 ). The second roller bearing ( 76 ) is urged, by an ondular washer ( 98 ) in said recess ( 96 ), axially in the direction of the first roller bearing ( 30 ) when the first housing part ( 24 ) and the second housing part ( 86 ) are assembled together.

Description:
CROSS-REFERENCES 
       [0001]    This application claims priority from our German application DE 20 2006 012 901.4, filed 15 Aug. 2006, and from our European application 07 010 942.6, filed 4 Jun. 2007, the entire contents of which are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an electric motor having a stator mounted in a housing thereof, and an internal rotor mounted on a shaft, magnetically interacting with the stator across an air gap and, more particularly, to an improved arrangement for supporting the shaft in the housing by means of roller bearings. 
       BACKGROUND 
       [0003]    Motors of this kind often need to satisfy special requirements, which result from the kind of device they are to drive, and these requirements tend to make the assembly of the bearings more difficult. 
       SUMMARY OF THE INVENTION 
       [0004]    Therefore, it is an object of the invention to provide an improved motor structure, which reduces the difficulty of assembling the motor and its bearings. 
         [0005]    According to a first aspect of the invention, the rotor shaft is supported in the housing by a plurality of roller bearings. A first roller bearing and a second roller bearing each have a respective inner ring mounted in a predetermined position along the rotor shaft, and a respective outer ring which fits within a recess in a respective part of a two-part housing. This facilitates inserting the outer ring of the second roller bearing, from within, into the associated recess in the second housing part, and enables a cost-effective assembly process. 
         [0006]    According to a further aspect of the invention, an ondular washer is arranged against an axial endface of the second roller bearing, to urge it toward the first roller bearing, a springy part of the washer being compressed or tensioned by a movement during assembly which axially displaces the second roller bearing with respect to its associated recess, defined in the second housing part. 
     
     
       BRIEF FIGURE DESCRIPTION 
         [0007]    Further details and advantageous refinements of the invention will be apparent from the following description and accompanying drawings of exemplary embodiments, which are not to be understood as limiting the invention. 
           [0008]      FIG. 1  illustrates a motor module with a housing part  24  in which a hollow shaft  34  is rotatably supported, the shaft forming part of an internal rotor; 
           [0009]      FIG. 2  is a section, along lines II-II of  FIG. 1 , shown greatly enlarged; 
           [0010]      FIG. 3  is a longitudinal section through the structure of  FIG. 1 , connected to a second module  26 , in which the external stator  92  of the motor is secured, to work together with the internal rotor  38  of  FIG. 1 ; 
           [0011]      FIG. 4  is an enlarged detail (rotated 90 degrees) of the  FIG. 3  structure, according to which a so-called sinuous spring or ondular washer  98  is arranged between a bearing and one wall of its associated recess, the spring having been treated so that it has increased friction, at least on its engagement surfaces; 
           [0012]      FIG. 5  illustrates a variant of  FIG. 4 , in which an outer surface of the bearing and of an opposing abutment surface of the housing are each provided with a friction coating, in order to increase the friction between these friction coatings and both sides of an ondular washer  98  inserted there; 
           [0013]      FIG. 6  illustrates a second variant, in which two annular washers are used, both sides of which are treated for increased friction, a first annular washer located between bearing  74  and an undulating washer  98  and the other located between undulating washer  98  and the associated recess  97  defined in the motor housing; 
           [0014]      FIG. 7  illustrates a variant of the detail of  FIG. 3 ; 
           [0015]      FIG. 8  is a section, taken longitudinally along line VIII-VIII of  FIG. 7 , and 
           [0016]      FIG. 9  is a perspective view of an elastomer ring  142  of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In the following description, the same reference numerals are used for identical or functionally equivalent parts, and these parts are generally only described once. The terms “left,” “right,” “top,” and “bottom” refer to the respective Figure. 
         [0018]      FIG. 1  illustrates, at an enlarged scale, the lower part  24  of an electronically commutated motor shown in  FIG. 3 . The motor has a first housing part  24 , shaped essentially like an end shield, and formed with a recess  26 , into which the outer ring  28  of a first roller bearing  30  is press-fitted. The inner ring  32  of first roller bearing  30  is pressed onto the outside of a hollow shaft  34  at a first predetermined position, i.e. the shaft is supported for rotation relative to the first housing part  24 . 
         [0019]    Onto the upper part of the shaft  34  shown in  FIG. 1 , the lamination stack  36  of an internal rotor  38  is pressed, the rotor having eight pockets  40  therein as shown in  FIG. 2 . In these are located a total of eight permanent magnets  42  which are, in the manner shown, radially magnetized, i.e. the internal rotor  38  is, in this embodiment, eight-poled. Clearly a different number of poles is possible, depending upon the intended use of the motor. Magnets  42  have, on their radially outer surface, an essentially roof-shaped profile, which facilitates their insertion into the pockets  40 , and which can favorably influence the course of the magnetic flux density at the outside  46  of the internal rotor  38 . One strives in most cases for a sinusoidal course of this magnetic flux density in order, in conjunction with sinusoidal stator currents, to obtain an essentially constant torque in such a motor. One thus often refers to a “sinus motor.” 
         [0020]    As  FIG. 2  shows, the hollow shaft  34  has four longitudinally extending notches  50 ,  52 ,  54 ,  56  which are cross-sectionally essentially triangular in the embodiment shown. Treating the shaft as a clockface, they are preferably at approximately the following places: 
         [0000]                                                Notch 50   10 o&#39;clock            Notch 52   2 o&#39;clock           Notch 54   4 o&#39;clock           Notch 56    8 o&#39;clock.                        
The notches  50  and  56  are aligned with each other. A line  60 , drawn along their inner faces, preferably extends approximately tangent to the inner surface  62  of hollow shaft  34 . The same applies for a line  64  which connects the notches  52  and  54 . The inner faces of notches  50 ,  56  coincide with line  60  and the inner faces of notches  52 ,  54  coincide with line  64 . Lines  60 ,  64  extend essentially parallel to each other. The notches  50  through  56  each define, as shown, an acute angle α, and forming them causes a material-excess  57  to be pressed outward as shown which, during pressing-on of the lamination stack  66 , creates a particularly good and durable connection between the stack and the hollow shaft  34 . Further, the magnetic circuit for the flux of permanent magnets  42 , which runs partly through the lamination stack  36 , and partly through shaft  34 , is improved.
 
         [0021]    As  FIG. 1  shows, above internal rotor  38 , at a second predetermined position on the hollow shaft  34 , the inner ring  70  of a roller bearing  72  is pressed on. The outer diameter of roller bearing  72  is smaller than the outer diameter of internal rotor  38 . Roller bearing  72  has an outer ring  74 . 
         [0022]    As shown in  FIG. 1 , the lower portion of hollow shaft  34  is formed with a flange  76  which cooperates with a device (not shown) for detecting the rotational orientation of internal rotor  38 . For this purpose, the first housing part  24  has an annular space  78 , in which the electronic components (not shown) of motor  22  can be arranged. Alternatively, these could be arranged outside the motor. 
         [0023]    As  FIG. 3  shown, the internal rotor  38  is, together with hollow shaft  34 , inserted into an external stator  82 , secured on the inner face  84  of a second housing part  86 . In the assembled state, that stator is separated from internal rotor  38  by a cylindrical air gap  90 . The external stator has, in this embodiment, twelve salient poles  90 . On it, there is a three-phase winding, connected for example in star configuration. The magnetic return path of stator poles  90  is designated  92 . Stator  82  is, like internal rotor  38 , formed of laminations.  FIG. 3  illustrates end turns  94  of the stator windings. 
         [0024]    For receiving the outer ring  74  of second roller bearing  72 , the second housing part  86  is formed with an associated recess  96 , whose upper end is designated in  FIG. 3  with numeral  97 . 
         [0025]    Into this associated recess  96 , during the assembly process, one inserts the outer ring  74  of second roller bearing  72 . Thereby, an ondular washer  98 , located between outer ring  74  and the upper end  97  of recess  96 , becomes compressed, and the two roller bearings  30  and  72  are thereby placed under tension or biased with respect to each other, i.e. urged toward one another. 
         [0026]    The ondular washer  98  also increases the friction between the outer ring  74  and the associated recess  96 , which is desirable, in order to prevent the outer ring  74  from rotating. 
         [0027]    If the roller bearing  72 , to which the stationary outer ring  74  belongs, turns, a frictional torque is created, which tends to cause the ring  74  to turn within recess  96 . The magnitude of this frictional torque is a function of: 
         [0028]    the general manufacturing tolerance of the roller bearing used, 
         [0029]    the bearing&#39;s structure type, 
         [0030]    the bearing tolerance, 
         [0031]    the prestress effective between the inner &amp; outer rings of the bearing, 
         [0032]    the kind of lubrication in the bearing, and 
         [0033]    the eddy currents which arise in the bearing during operation and which heat it up. 
         [0034]    This frictional torque is counteracted by a clamping-friction torque whose magnitude is caused by the biasing force exerted by ondular washer  98 , which is effective between the outer ring  74  and the second housing part  86  and between the outer ring  74  and the washer  98  or—in FIG.  6 —between outer ring  74  and an annular washer  124  or—in FIG.  7 —a clamping-friction torque generated by the clamping force of an elastomer ring  142 , effective between the outer ring  74  and the second housing part  86 . 
         [0035]    If the frictional torque, arising during rotation, effective upon the outer ring  74 , ever has a magnitude greater than that caused by the clamping, the outer ring  74  will rotate within recess  96 . 
         [0036]    For this reason, within the scope of the present invention, various means can be employed, all of which are intended to increase the clamping-friction torque and/or raise the friction coefficient μ r . 
         [0037]    According to  FIG. 4 , on both sides of ondular washer  98 , the surfaces  126  (left) and  128  (right), shown black in  FIG. 4 , are treated or altered to increase their frictional torque. For this, there are various possibilities: for example, at least one of the surfaces  126 ,  128  can be coated with a layer which increases the friction, e.g. with a thin layer of elastomeric material such as tetraphenyl ethene or TPE=(C6H5)2C═C(C6H5)2 or of lacquer containing elements which increase friction, like sandpaper or emery paper. Also, at least one of the surfaces  126 ,  128  can be roughened, or it can be textured with depressions or grooves or pointy projections. It would suffice to provide these alterations of the surfaces just where the washer  98  contacts the outer ring  74  or the surface  97 , i.e. only in predetermined areas. A coating with a material having adhesive characteristics is also possible, e.g. using a pressure-sensitive adhesive. 
         [0038]    Alternatively, according to  FIG. 5 , a standard ondular washer  98  without coating can be used, and instead a corresponding alteration of the opposing surface  130  of face  97  and of the opposing surface  132  of outer ring  74  can be undertaken, i.e. coating, mechanical roughening, or the like. 
         [0039]    According to  FIG. 6 , one can use special annular washers  124 ,  134  in conjunction with a standard ondular washer  98 . The washers  124 ,  134  are identical. On the left, they have a surface alteration  136 , and on the right, a surface alteration  138  of the kind described above, e.g. coating with an elastomer having a high friction coefficient, lacquering with a substance analogous to emery paper, roughening of surfaces  136 ,  138  in the manner described, coating in a dipping tank, coating with a pressure-sensitive adhesive, etc. 
         [0040]    During assembly, the second housing part  86  and the first housing part  24  interengage with each other as shown in  FIG. 3 , center or align with each other, and are coupled together using assembly bolts (not shown). The upper end of second housing part  86  has an opening  100 , through which the hollow shaft  34  can be directly connected to an element to be driven, e.g. the drive of a blind or shutter. 
         [0041]      FIG. 7  illustrates a variant of  FIG. 3  for the axial biasing of outer ring  74  of roller bearing  72  within recess  96 . For this purpose, this variant uses a ring  142  made of a suitable elastomer. Ring  142  has, on its upper side as seen in  FIG. 7 , an annular projection  144  ( FIG. 8 ) which, in an assembled state, engages into an annular groove  146  ( FIG. 7 ) of housing part  86 , and thereby is centered within recess  96  and held there. 
         [0042]    Ring  142  has a cylindrical outer face  148 , with which it is guided in housing part  86 , and has, on its underside, a frusto-conical annular shoulder  150  whose included angle α approximates, e.g., 5 degrees, as the (imaginary) diverging lines of the cone indicate. This shoulder  150  abuts, with its radially outer rim  152  ( FIG. 8 ), against the radially outer rim  156  ( FIG. 7 ) of the upper side  154  of bearing outer ring  74 . 
         [0043]    The remaining structure is identical to that of  FIG. 3 . Due to the deformation of elastomeric ring  142  during assembly, a corresponding force on the upper side  154  of bearing ring  74  is created. 
         [0044]    In this, it is immaterial whether side  150  of ring  142  is frusto-conical, and the upper side  154  of the bearing ring is untapered, or conversely, side  150  is untapered, and the upper side  154  frusto-conical, as shown in  FIG. 7 . An important feature is that, just as in the  FIG. 3  structure, a biasing force on the bearings  30 ,  72  is created, which assures smooth running, and keeps outer ring  142  from rotating within recess  96 .  FIG. 9  shows a preferred embodiment of elastomeric ring  142 , in perspective. 
         [0045]    Naturally, within the scope of the present invention, many variations and modifications are possible, and these can also be combined with each other, depending upon the requirements of the intended use.