Abstract:
A disk memory drive includes a brushless drive outer rotor motor having an internal space and a stator with windings. The outer rotor coaxially encircles the stator and a substantially cylindrical air gap is defined between the stator and the rotor. The rotor includes permanent magnets and a hub fixedly connected with the magnet. A disk mounting section is provided on the hub for accommodating at least one storage disk positioned in a clear space, the mounting section being adapted to extend through a central aperture of the storage disk. The windings and the magnets interacting with the windings are disposed for at least half of the axial longitudinal dimension thereof within a space surrounded by the disk mounting section of the hub. Bearings rotatably mount the rotor and the hub.

Description:
BACKGROUND OF THE INVENTION 
     This is a continuation of Ser. No.  08 / 360 , 226 , filed Dec.  20 ,  1994 , now abandoned, which is a broadening reissue application of U.S. Pat. No.  5 , 173 , 814 , issued Dec.  22 ,  1992  from Ser. No.  653 , 100 , filed Feb.  8 ,  1991 , which is a continuation of application Ser. No. 07/402,917, filed Sep. 5, 1989, now U.S. Pat. No. 5,001,581, issued Mar. 19, 1991, which is a continuation of application Ser. No. 201,736, filed Jun. 2, 1988, now U.S. Pat. No. 4,894,738, issued Jan.  16, 1990, now U.S. Pat. No. Re. 35,792,  which is a continuation-in-part of application Ser. No. 038,049, filed Apr. 14, 1987, now U.S. Pat. No. 4,843,500, issued Jun. 27, 1989, which is a continuation-in-part of application Ser. No. 767,671, filed Aug. 21, 1985, now U.S. Pat. No. 4,658,312, issued Apr. 14, 1987, which is a continuation of application Ser. No. 412,093, filed Aug. 27, 1982, now abandoned, which is a continuation- in - part of application Ser. No.  326 , 559 , Dec.  2 ,  1981 , U.S. Pat. No.  4 , 519 , 010 . The  412 , 093  application also is a continuation - in - part of Ser. No.  244 , 971 , Mar.  18 ,  1981 , abandoned. The  201 , 736  application also is a continuation - in - part of application Ser. No.  32 , 954 , filed Mar.  31 ,  1987 , U.S. Pat. No.  4 , 779 , 165 , now U.S. Pat. No. Re.  34 , 412 , which is a continuation of application Ser. No.  733 , 231 , filed May  10 ,  1985 , now abandoned, which is a continuation - in - part of application Ser. No.  412 , 093 , filed Aug.  27 ,  1982 , now abandoned.   
    
    
     On Jun.  9 ,  1999 , five continuation applications from this application ( Ser. No.  08 / 819 , 099   )  were filed. On Nov.  17 ,  1999 , a sixth continuation application from the  08 / 819 , 099  application was filed. These applications, as currently pending, are described below:    
       a )  “Disk Storage Device Having A Sealed Bearing Tube,” attorney docket no.  2634 / 75790 , inventors Elsässer and von der Heide, filed Jun.  9 ,  1999 , Ser. No.  09 / 333 , 399 ;    
       b )  “Disk Storage Device Having A Radial Magnetic Yoke Feature,” attorney docket no.  2634 / 75791 , inventors Elsässer, von der Heide, and Müller, filed Jun.  9 ,  1999 , Ser. No.  09 / 333 , 398 ;    
       c )  “Disk Storage Device Having A Hub Sealing Member Feature,” attorney docket no.  2634 / 75792 , inventors Elsässer and von der Heide, filed Jun.  9 ,  1999 , Ser. No.  09 / 333 , 397 ;    
       d )  “Disk Storage Device Having An Underhub Spindle Motor,” attorney docket no.  2634 / 75793 , inventors Elsässer, von der Heide, and Müller, filed Jun.  9 ,  1999 , Ser. No.  09 / 333 , 396 ;    
       e )  “Disk Storage Device Having A Particular Magnetic Yoke Feature,” attorney docket no.  2634 / 75794 , inventors Elsässer and von der Heide, filed Jun.  9 ,  1999 , Ser. No.  09 / 333 , 400 ; and    
       f )  “Disk Storage Device Having An Undercut Hub Member,” attorney docket no.  2634 / 77523 , inventors Elsässer and von der Heide, filed Nov.  17 ,  1999 , Ser. No.  09 / 441 , 504 .   
     The invention relates to a disk storage drive for receiving at least one storage disk having a central opening, with an outer rotor type driving motor having a rotor casing mounted by means of a shaft in a bearing system so as to rotate relative to a stator and on which can be placed the storage disk for driving by the rotor casing, as described in U.S. patent application Ser. No. 353,584, now U.S. Pat. No. 4,438,542, issued Mar. 27, 1984. 
     The content of this patent is incorporated herein by reference to avoid unnecessary repetition. It relates to a storage drive for receiving at least one storage disk having a central opening. The driving motor extends coaxially at least partly through the central opening of the storage disk, and means are provided for connecting the storage disk and the driving motor rotor. 
     BRIEF SUMMARY OF THE INVENTION 
     One problem of the present invention is to further simplify the construction of a disk storage described in the aforementioned U.S. Pat. No. 4,438,542, while improving its operation. For example, the storage disk is to be reliably protected against undesired influencing by the magnetically active parts of the driving motor. In addition, a particularly space-saving and robust construction of the driving motor are to be achieved. 
     According to the invention, this first problem is solved in that at least the part of the rotor casing receiving the storage disk is made from a non-ferromagnetic material and carries the shaft directly or by means of a hub and in that a magnetic shield made from a ferromagnetic material in the form of a drawn can projects onto the storage disk receiving part of the rotor casing and is connected thereto. The shielding surrounds the periphery of the magnetically active parts of the driving motor and also envelops the parts at one end. The shield has a central opening whose edge is directly radially adjacent the shaft or parts of the driving motor carrying or supporting the shaft. A rotor casing constructed in this way can be easily manufactured, and it effectively protects the magnetically sensitive storage disks, particularly magnetic hard storage disks, against magnetic stray flux emanating from the magnetically active parts of the driving motor. The shield is preferably in the form of a deep-drawn can, and the part of the rotor casing receiving the storage disk can be made from a lightweight metal by die casting. 
     If, in the manner described in the aforementioned U.S. Pat. No. 4,438,542, the driving motor is constructed as a brushless direct current motor with a permanent magnet rotor, then in accordance with a further development of the invention a printed circuit board with at least one rotary position detector and perhaps other electronic components for the control and regulation of the driving motor are mounted on the side of the stator remote from the closed end of the shielding can. This ensures that the rotary position detector and any further circuit components of the magnetic shielding arrangement do not interfere with the rotating parts. 
     Further advantageous developments of the invention also are disclosed, including features that contribute to a compact construction of the disk storage drive. In connection with disk storage drives of the present type, high demands are made on the concentricity of the storage disks. It is therefore generally necessary to machine the storage disk receiving part or to work it in some other way so that it is dimensionally true. As a result of other features of the invention, the necessary machining is reduced to a relatively small part of the circumferential surface of the storage disk receiving part and a trouble-free engagement of a storage disk on the shoulder of the storage disk receiving part is permitted. 
     Other features of the invention provide a robust precision mounting support for utilizing the available axial overall length for maximizing the distance between the bearings; and permit particularly large distances between the bearings where the axial installation area between a mounting or assembly flange and the end of the storage disk receiving part is limited. Installation space is available on the other side of this flange. Still other features provide for alternative solutions leading to particularly small radial runouts of the rotor; ensure a space-saving housing of the circuit board; and for solutions where importance is attached to a particularly shallow construction. 
     In a further development of the invention, a disk storage drive of the type disclosed in U.S. Pat. No. 4,779,165, issued Oct. 18, 1988, is considered. Some such disk storage drives have stationary shafts and a sealed off internal space within the motor. 
     In the construction of such data storage disk drives with stationary shafts, problems also have arisen in the following areas: 
     a) Achieving extremely high level of precision required for repeatable shaft runout; 
     b) Improving the sealing of the clean chamber; and 
     c) Achieving a and b within acceptable costs. 
     Yet another purpose of the present invention, therefore, is to provide a further development of the data storage disk drive of the above type having a stationary shaft by providing viable solutions for various combinations of the above problems, such as a and c; b and c; and a, b and c. 
     If the rotational position sensor device has several rotational position sensors, preferably of the type sensitive to magnetic fields, it is advantageous for these sensors to be supported on a common molded piece, especially if it is made by injection molding. The construction of the molded piece for the accommodation of several rotational position sensors in accordance with the invention simply ensures the precise mutual alignment of these sensors. 
     If required, the rotary position sensing arrangement can be mounted on a printed circuit board, together with any known type of commutation electronics. This printed circuit board can be supported on a fixed flange or bracket which is, in turn, connected to the shaft through which the connecting leads to the rotary position sensors may be brought out. 
     The control arrangement, which preferably takes the form of a control magnet device, can be mounted on the outside of a cover which seals off the space inside the motor. This cover may preferably serve as a bearing bracket as well. The control arrangement, however, also can be mounted on a part of the hub at a distance from the disk carrier stage outside the sealed internal space of the motor. A flange which serves to support the data storage disk or disks, may be connected to the remaining hub parts as one piece, or alternatively, this flange may form part of the cover which seals off the internal space of the motor. 
     In accordance with one variant of the present invention, at least the electric supply leads to the stator windings are brought out of the sealed internal space of the motor over a bearing support ring. This arrangement obviates the need to provide passages in the shaft to accommodate the winding connections. In yet another alternative arrangement, the rotary position sensing arrangement, together with the commutation electronics, if necessary, can both be housed in the sealed internal space of the motor with their leads and connections being brought out over the bearing support ring. In any event, none of the above arrangements requires the provision of passages formed through the stationary shaft, thus avoiding the need to weaken the shaft or to perform additional machining operations in the manufacturing thereof. 
     The bearing support ring can be a prefabricated component provided with recesses for the passage of the electric leads and connections. Alternatively, the aforesaid connections can be potted in situ inside the bearing support ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein: 
     FIG. 1 is a vertical partial sectional view through an embodiment of the invention along the line I—I of FIG. 2; 
     FIG. 2 is a plan view of the arrangement of FIG. 1; 
     FIG. 3 is a sectional view through another embodiment of the invention with an extended bearing tube; 
     FIG. 4 is a sectional view through a further embodiment of the invention; 
     FIG. 5 is a section through a disk storage drive motor, less the hub, according to the invention along line V—V of FIG. 6; 
     FIG. 6 is a section along line VI—VI of FIG.  5  and illustrating a rotational position sensor device located outside the sealed internal space of the motor; 
     FIG. 7 is a section similar to FIG. 6 of a modified embodiment of the invention; 
     FIG. 8 is a section similar to FIG. 6 of another modified embodiment of the invention; 
     FIG. 9 is a section similar to FIG. 6 of yet another modified embodiment of the invention; 
     FIG. 10 is a section similar to FIG. 6 of yet another embodiment of the invention; 
     FIG. 11 is a section through a disk storage drive according to the invention illustrating a rotational position sensor device located inside the sealed internal space of the motor with leads brought out through bearing support ring; 
     FIG. 11A is an axial partial section through a further modified embodiment of a disk storage drive with a fixed shaft;  
     FIG. 11B is a partial section corresponding to FIG. 11A for a modified embodiment of a disk storage drive with a fixed shaft; 
     FIG. 12 is a partial section similar to but yet a variant of FIG. 7 of yet another embodiment of the invention having the rotational position sensor device located outside the sealed internal space of the motor; 
     FIG. 13 is a section illustrating a further variant of the embodiment shown in FIG. 6; and 
     FIG. 14 is a section illustrating yet another variant of the embodiment shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The disk storage drive illustrated in FIG. 1, having an extremely shallow construction, has a brushless direct current motor  45  having a rotor casing  47  fixed to and coaxial with a rotor shaft  46 . A stator lamination  48 , carrying a stator winding  49 , is mounted on a bearing tube  50 . The rotor shaft  46  is rotatably mounted within the bearing tube  50  by means of two bearings  52  and  53 . These are kept axially spaced by a pair of retaining rings  54 . A cup spring  55  is supported on the underside of the bearing  53  by a retaining ring  56  resting on the rotary shaft  46 , so that the bearings  52 ,  53  are axially braced relative to one another. The bearings  52 ,  53  are pressed into the bearing tube  50  at the time of assembly. Together with an assembly flange  24 , the bearing tube  50  forms a one-piece die casting. 
     The rotor casing  47  comprises a storage disk receiving part  25  and a shielding can  26 , which are joined together, for example, by riveting. The storage disk receiving part  25  is made from a non-ferromagnetic material, preferably lightweight metal. The rotor shaft  46  is pressed into a central opening of the storage disk receiving part  25 . As an alternative, the shaft can be cast into the receiving part. 
     The shielding can  26  is made from a ferromagnetic material and can in particular be constructed as a soft iron deep-drawn part. A plurality of permanent magnetic segments or a one-part permanent magnet  69  are fixed to the inner face of shielding can  26  radially facing the stator lamination  48 . The permanent magnet  69  preferably comprises a mixture of hard ferrite, for example, barium ferrite, and an elastic material. Thus, it is a so-called rubber magnet. The latter is trapezoidally or approximately trapezoidally radially magnetized via the pole pitch in a motor construction having a relatively small pole clearance. At the same time, the shielding can  26  forms the magnetic return path for magnet  69 . The shielding can  26  surrounds the magnetically active parts  48 ,  49 ,  69  of the driving motor  45  on the periphery thereof, as well as on one end thereof. The bottom  28  of shielding can  26  is adapted to the shape of the coil winding heads  27  of the stator winding  49  and contains a central opening  29 , whose edge is in the immediate radial vicinity of the circumferential surface of the bearing tube  50 . In this way, the shielding can effectively prevents the magnetic flux from straying towards the outside of the storage disk receiving part  25 . 
     The storage disk receiving part  25  has two stepped stages  74  and  75 , each of whose circumferential surfaces in the present embodiment carry a plurality of radially distributed and projecting bearing webs  79  or  80 . The outsides of bearing webs  79 ,  80  are ground in a dimensionally true manner to accommodate the internal diameter of the hard storage disks to be placed on the receiving part  25 . The stepped stages  74 ,  75  form shoulders  81 ,  82  and are provided respectively with an annular recess  83  and  84  at the foot axially of bearing webs  79 ,  80 . This structure ensures that storage disks mounted on the bearing webs  79 ,  80 , and having either one of two opening diameters, will cleanly engage against either the shoulder  81  or  82 . 
     The assembly flange  24  is provided with a recess  85  in which is housed a printed circuit board  86 . This printed circuit board carries a rotary position detector, for example, a Hall IC, as well as other circuit components for the control and regulation of the driving motor  45 . The Hall IC  63  extends up axially from the circuit board  86  to the immediate vicinity of the stator lamination  48 . The permanent magnet  69  projects axially over the stator lamination  48  in the direction of circuit board  86  until it partly overlaps the Hall IC  63 . In this way, the Hall IC  63  or, if desired, some other magnetic field-dependent semi-conductor component, determines the rotary position of the rotor of the driving motor  45 . 
     In the illustrated embodiment, the two bearings  52 ,  53  are spaced approximately the same axial distance from the axial center of the permanent magnet  69  and the stator lamination  48 . 
     Disk storages are most usually operated in “clean chamber” environments to protect them against contaminants. By means of the assembly flange  24 , the storage drive is arranged on a partition (not shown) which separates the ultra-clean area for receiving the storage disks from the remainder of the interior of the equipment. Dirt particles, grease vapors and the like from bearing  52  and parts of the driving motor  45  are prevented from passing into the storage disk receiving area by labyrinth seals  90  and  91 . The labyrinth seal  90  is formed in the end of the bearing tube  50  away from the assembly flange  24  that projects into an annular slot  87  on the inside of the storage disk receiving part  25 , accompanied by the formation of sealing gaps. Similarly, for forming the labyrinth seal  91 , the end of the shield can  26  projects into the annular slot  88  of the assembly flange  24 . The labyrinth seals  90 ,  91  are preferably dimensioned in the manner described in the aforementioned U.S. Pat. No. 4,438,542. 
     The embodiment of FIG. 3 differs from the arrangement according to FIGS. 1 and 2 in that storage disks having the same opening diameters are placed on bearing webs  79  of a storage disk receiving part  89 , which surrounds the majority of the axial dimension of the magnetic shielding can  26 . In other words, the magnetically active parts  48 ,  49 ,  69  of the driving motor  45  are partially located within the central opening of the storage disk. A bush-like hub  98  is pressed or cast into the storage disk receiving part  89 . The rotor shaft  46  is then pressed into the hub  98 . The edge of the central opening  29  in the bottom  28  of the shielding can  26  extends up to the portion  99  of the receiving part  89  which received the hub  98 . 
     The bearing tube  50  projects in the axial direction on the side of the assembly flange  100  remote from the stator lamination  48 . As a result, a particularly large axial spacing between the two bearings  52 ,  53  can be achieved. Axially, bearing  52  is in the vicinity of the axial center of the permanent magnet  69  and of the stator lamination  48 . The axial spacing between bearings  52  and  53  is equal to or larger than double the bearing external diameter. To prevent electrical charging of the rotor which in operation rotates at high speed and which would disturb at the operational reliability of the disk storage device, the rotor shaft  46  is electrically conductively connected to the equipment chassis by means of a bearing ball  78  and a spring contact (not shown). The printed circuit board  101 , carrying the rotary position detector  63  and the other electronic components, is supported on the end of a spacer ring  102  facing an assembly flange  100  and is located between the flange and the stator lamination  48 . An annular slot  103  is formed in assembly flange  100  and is aligned with the annular circuit board  101 . The annular slot  103  provides space for receiving the wire ends and soldered connections projecting from the underside of the circuit board  101 . 
     FIG. 4 shows an embodiment in which a storage disk receiving part  105  is axially extended in order to be able to house a larger number of storage disks than in the arrangement of FIG.  3 . The bearing tube  50  is correspondingly axially extended in order to be able to use the existing installation space with a view to a maximum axial spacing between the bearings  52  and  53 . The end of the bearing tube  50 , remote from an assembly flange  106 , embraces the hub  98  connecting the receiving part  105  and the shaft  46 , accompanied by the formation of a labyrinth seal  107 . The edge of the central opening  29  of shielding can  26  extends up close to the outside of the bearing tube  50 . The free end of the shielding can  26  engages a recess  108  in the assembly flange  106 . As a result, a further labyrinth seal  109  is formed. This embodiment otherwise corresponds to the structures already described herein. 
     In FIGS. 5 and 6, a brushless drive motor, designated as  110  has a stator  111  with a stator lamination stack  112 . The stator lamination stack  112  is arranged radially and symmetrically with respect to a central axis of rotation  113  and forms six stator poles  114 A to  114 F in an essentially T-shaped configuration as seen from above in accordance with FIG. 5, which poles are positioned at regular angular intervals of 60°. Instead of one lamination stack, for example, a sintered iron core can also be provided. Pole shoes  115 A to  115 F, together with a permanent magnetic rotor magnet  116  define an essentially cylindrical air gap  117 . The rotor magnet  116  is radially magnetized in four poles around its periphery as indicated in FIG. 5; that is to say, it has four sections  118 A to  118 D, and, on the internal side of the annular rotor magnet  116  toward the air gap  117  there are positioned, in alternating sequence, two magnetic north poles  119  and two magnetic south poles  120 . The poles  119 ,  120  have, in the example depicted, a width of substantially 180°-el (corresponding to 90° mechanical). Thus, in the circumferential direction of the air gap  117 , an approximately rectangular or trapezoidal magnetization is obtained. The rotor magnet  116  is mounted, typically by bonding, in an outer rotor casing or bell  121  of soft magnetic material, preferably steel, which serves both as a magnetic return path and as a magnetic shield. The casing  121  and the magnet  116  together form an external rotor  122 . The rotor magnet  116  can include in particular a rubberized magnetic unit, or a plastic-bound magnet. Instead of a single-piece magnetic ring, curved magnetic segments can also be bonded or otherwise attached in the casing  121 . Magnetic materials made from synthetic bonding compounds, a mixture of hard ferrite and elastomers, ceramic magnetic materials or samarium cobalt are all particularly suitable as materials for the magnetic ring or segments. 
     The stator poles  114 A to  114 F abut a total of six stator slots  123 A to  123 F. A three-phase stator winding is inserted into these slots. Each of the three phases comprises two 1200°-el fractional pitch windings or coils  124 ,  125 ;  126 ,  127 ; and  128 ,  129 , each of which is wound around one of the stator poles  114 A to  114 F. Both of the coils of each phase, which are connected in series, lie, as depicted in FIG. 5, in a diametrically opposed manner and are preferably bifilar wound. As can be seen from the schematic depiction in FIG. 5, any overlapping between the coils  124  to  129  is avoided. This arrangement allows the end turns of the windings  130  (FIG. 6) to be kept as short as possible. In this embodiment of the present invention, optimal filling of the stator slots  123 A- 123 F by the windings is achieved. Fasteners are generally not required to close the slot openings. 
     A hub  132 , not depicted in FIG. 5, is provided with a cylindrical disk mounting section  131  and preferably is made of a light metal, especially aluminum or an aluminum alloy. It is mounted on the outer rotor casing  121 . One or more storage disks  134 , preferably magnetic or optical fixed storage disks, are provided on the disk mounting section  131 , whereby the disk mounting section  131  extends through the conventional central aperture  135  of the storage disks. The lowest storage disk in FIG. 6 is located on a flange  133  of the hub  132  projecting radially outwardly. The data storage disks  134  can be maintained at an axial distance from each other by suitable spacers  136  and are secured to the hub  133  by means of a tightening device, not depicted, of a known type. In the embodiment shown in FIG. 6, the stator  111 , the stator stack  112  and the stator winding (coils  124  through  129 ) as well as the rotor magnet  116  and the outer rotor casing  121  forming the iron shield, are all completely encompassed within the space occupied by the storage disk stage  131  on the hub  132 . 
     In a central aperture  137  of a frontal wall  138  of the hub  132 , which is relatively heavy for reasons of stability, are a ball bearing  139  and a magnetic fluid seal  140  on the side of the support which is axially oriented away from the drive motor  110 . The seal  140  consists of two annular pole pieces  141 ,  142 , a permanent magnet ring  143  located between both these pole pieces, and a magnetic fluid (not shown), which is inserted into an annular gap  144  between the magnetic ring  143  and a stationary shaft  145 . Seals of this type are known under the designation of “Ferrofluidic Seal”. An internal space  146  is located within the motor and is sealed on the side of the space oriented away from the frontal wall  138  by means of a motor cover  147 , which is inserted into the outer rotor casing  121  and the hub  132 , by means, for example, of adhesion. The internal space  146  includes the internal parts such as the stator  111  and permanent magnet  116  as well as bearings  139  and  149 . The motor cover  147  abuts with its cylindrical outer edge  247  the lower edge of the rotor casing  121 . This allows a particularly easy assembling of the cover  147  within the hub  132 . For sealing purposes, adhesive material  190  is placed in a circumferential groove  191  between the cover  147  and the hub  132 . 
     The motor cover  147  is supported on the shaft  145  by means of an additional ball bearing  149 . On the side of the ball bearing  149  away from the drive motor  110 , there is a magnetic fluid seal  150 , which has a construction corresponding to the seal  140 . The seals  140 ,  150  ensure an effective sealing of the motor internal space  146 , including the bearings  139 ,  149 , relative to a clean chamber  148  which accommodates the storage disks  134 . 
     The motor cover  147  is provided on the frontal side facing away from the drive motor  110  with an annular groove  151  receiving a control magnet ring  152 . The control magnet ring  152  has four sections of alternating circumferential magnetization corresponding to the rotor magnets  116 , which run in sequence in the circumferential direction and extend over 90°, so that alternating north and south poles, aligned with poles  119 ,  120  in the circumferential direction, are provided on the bottom side of the control magnetic ring  152 . 
     A stationary flange  154  is disposed on the lower end of the shaft  145  in FIG.  6 . The flange  154  is provided with threaded bores  192  for receiving fastening screws by which the disk storage drive may be connected to the disk drive frame, for example, over a wall delimiting the clean chamber  148 , or the like. The flange  154  supports a printed circuit board  155  on its frontal side relative to the motor cover  147 . Three rotational position sensors  156 ,  157 ,  158  are mounted on the printed circuit board  155 . In the embodiment shown, these magnetic field sensors may be Hall generators, Hall-IC&#39;s, magnetically controlled photocells, magnetic diodes, or the like, which interact with the control magnet ring  152 . The rotational position sensors  156 ,  157 ,  158  are suitably positioned in the circumferential direction with regard to the coils  124  to  129  so that the changes of the sensor switching conditions essentially coincide with the zero passages of current in the correspondingly positioned coils. This is attained, in accordance with the embodiment shown in FIG. 5, through the fact that the rotational position sensors are displaced by 15-mech with respect to the center of the apertures of the stator slots  123 A to  123 F. The rotational position sensors  156 ,  157 ,  158  may be supported by a common molded part  159  (see, for example, FIG.  14 ), preferably a plastic injection molded part. By using a common molded part  159  as the support for the rotational position sensors, their relative positioning with respect to one another can be maintained and reproduced in a particularly precise manner. The printed circuit board  155  is fixed to a ring  193  and is tightly pulled against the flange  154  by screws  194  screwed into a ring  193 . An upwardly projecting outer rim  195  of flange  154  defines a hollow cylinder extending into an annular groove  196  provided in the bottom side of the flange  154 . Thereby a labyrinth gap  197  is formed which provides for additional sealing between the stationary flange  154  and the rotary motor cover  147 . 
     The connections of the rotational position sensors  156 ,  157 ,  158  and/or commutational electronics likewise positioned on the printed circuit board are conducted through one or more apertures  161  of the flange  154  which open into peripheral cutouts of the ring  193 . The connections of the stator winding coils  124  to  129  of the drive motor  110  are, on the other hand, conducted outwardly through bores  162 ,  163  of the stationary shaft  145  out of the internal space of the disk storage drive, which is sealed off by means of the magnetic fluid seals  140 ,  150 . The bores  162 ,  163  can be dimensioned relatively narrowly, because they only have to accommodate the connections of the stator winding but not the connections of the rotational position sensors and/or the commutation electronics (not shown). Furthermore, the rotational position sensors  156  to  158  located outside of the sealed space  146  can be closely adjusted. An excessive weakening of the shaft  145  is thereby avoided. 
     In a further modified embodiment shown in FIG. 7, the rotor magnet  116  is located directly within the hub  132 ′, which itself forms the magnetic shield, and is made of magnetically conductive material, preferably soft iron. The control magnet ring  152 ′ is located on the frontal side of the flange  133  facing away from the disk mounting section  131  of the hub  132 ′, and alternately magnetized in the axial direction. In this embodiment, the rotational position sensors  156 ,  157 ,  158  are axially opposed to the control magnet ring  152 ′. The magnetic fluid seal  150  ensures, together with a labyrinth seal  165  which replaces the magnetic fluid seal  140  of the embodiment in FIG. 6, the sealing of the internal space  146 , including the bearings  139 ,  149  relative to the clean chamber  148 . The connections of the stator winding  166  are conducted through the bores  162 ,  163  of the stationary shaft  145 . It should be understood that, even in this embodiment, the rotational position sensors  156 ,  157 ,  158 , can, if desired, be accommodated by a common support corresponding to the molded part  159  (FIG.  14 ), which support is attached to the printed circuit board  155 . 
     If it is desirable to manufacture the hub  132 ′ from magnetically non-conducting, or poorly conducting, materials, such as light metal or alloy, a separate iron shield can be provided. This can be seen in the embodiment in FIG.  8 . There, the rotor magnet  116  is accommodated in an iron shielding ring  167 . The flange  169  supporting the storage disk  134  forms a part, separated from the hub  132 ″, of the cover  170  which accommodates the ball bearing  149 . The hub  132 ″ and the cover  170  are closely connected with one another, so that the axial end section of the hub  132 ″, which extends towards the cover  170 , engages in an annular groove  171  of the cover  170 . 
     In both embodiments of FIGS. 9 and 10, the control magnet ring  152 ′ is located in a groove  173  of a bearing support ring  174  on the end of the hub  132 . The hub  132  itself forms the magnetic shield, and is accordingly made from conductive material, particularly steel. The control magnet ring  152 ′ interacts, as shown in FIG. 7, with the rotational position sensors  156 ,  157 ,  158 , which are not shown in FIGS. 9 and 10. In the embodiment in FIG. 9, the internal space  146  is sealed off by means of the magnetic fluid seals  140 ,  150 , but in the embodiment in FIG. 10, labyrinth seals  175  are provided in their place. The embodiment of FIG. 10 further differs from that of FIG. 9 by the stationary shaft  145 ′ in the area where it supports the stator lamination stack  112 , and the area directly adjoining the same axially, being axially thickened so that the shaft  145  forms shoulders  176 , on which the ball bearings  139 ,  149  are supported. 
     In the embodiments shown in FIGS. 8,  9 , and  10 , the connections of the stator winding are, in a manner preferably corresponding to the embodiments shown in FIGS. 6 and 7, brought out externally through recesses of the shafts  145  and  145 ′. 
     FIG. 11 depicts an embodiment similar to that of FIG. 11 of copending U.S. Ser. No. 733,231, in which a soft magnetic yoke ring  167  is inserted in the hub  132 , the latter forming a disk mounting section  132  and preferably being made of light metal. Both the rotor magnet  116  and the control magnet  152 ′ are accommodated in the inner circumference of the yoke ring  167 . In this embodiment, the printed circuit board  155  together with the rotational position sensors  156 ,  157 ,  158  are located within the space  146  sealed by the magnetic fluid seals  140 ,  150 . The circuit board  155  may be suspended from the stator lamination stack  112  by supports  178 . A bearing support ring  180  is provided for bringing outwardly the connections  180 ′ of the stator winding as well as the connections  180 ″ of the rotational position sensors  156 ,  157 ,  158  and/or of the electronic commutating means which likewise may be mounted on the printed circuit board  155 . The support ring  180  is made of the soft magnetic material, preferably ferromagnetic metal, and surrounds and is firmly fixed to shaft  145 ″. The ball bearing  149  and the magnetic fluid seal  150  are disposed between the cover  147 ′ and the support ring  180 . At least one and preferably a plurality of axially extending apertures  181  are provided in the support ring  180  for receiving the aforementioned connections. After introduction of the connections therein, which together are indicated at  182 , the apertures  181  are sealed, e.g. by a potting compound or a mastic. This embodiment completely avoids bores in the stationary shaft  145 ″ and therefore the solid shaft retains its full strength. The provision of a bearing support ring  180  provides for a particularly small eccentricity or run-out of the rotating members. A soft magnetic shield ring  184  is provided on the inside of the frontal wall  183  of the hub  132 . 
     The embodiment of FIG. 12 corresponds to that of FIG. 7 with the exception that a connection  166  of the stator winding extends through a bearing support ring  185  rather than the bores in the stationary shaft  145 . The ring  185  surrounds the lower portion of the shaft  145 . The ball bearing  149  and magnetic fluid seal  150  are disposed in the annular space between the support ring  185  and the ferromagnetic ring  153 , which is inserted into hub  132 ′. 
     In an embodiment where the rotary position sensors are located externally, the winding leads can also be brought out through an inner bearing support ring encompassing the bearing  149 , corresponding to the support ring  180  in FIG.  11 . Furthermore, in an embodiment provided with an inboard rotary position sensing arrangment similar to that shown in FIG. 11, a bearing support ring  185  according to FIG. 12 mounted on the stationary shaft  145  and supporting the ball bearing  149  on the inside can be used to bring the connections out to the exterior. 
     The metal support ring  185  according to FIG. 12 ensures that the rotating parts will display particularly limited runout. The magnetic field of the magnetic liquid seal  150  can be contained in either the ferromagnetic support ring  185  or the ferromagnetic ring  153 . 
     Instead of providing the bearing support rings  180  or  185  with apertures through which the connections can be brought out, the connections can also be potted in the bearing support ring directly. 
     FIG. 13 shows an embodiment similar to that shown in FIG. 6, of which it is only a further development in many respects. 
     A particular feature of this further embodiment is the provision of a flat air gap between rotational position indicator or magnetic control ring  152  and the rotational position sensor  156 . The printed circuit board  155  is firmly fastened to a stationary flange part  154  with the screw  194 . The outside edge of this flange  154  engages in a disk-shaped ring member  147 ″, which may be the motor cover  147  (FIG. 6) in an axial direction like a hollow cylinder, so as to provide a labyrinth gap  197  acting as an additional seal between the stationary flange  154  and the disk-shaped ring member  147 ″. The lower edge of the soft iron outer rotor casing  121  bears on the rotating ring member  147 ″ whose cylindrical outer edge  244  is more easily inserted in the hub body  132  than the arrangement shown in FIG. 6. A mastic  190  is used as the sealant in a peripheral groove between the ring member  147 ″ and the hub  132 . 
     From the user&#39;s point of view, the entire motor assembly is fastened by use of appropriate fasteners in the hole  192 . The connecting leads from the printed circuit board  155  to the rotational position sensor  156  are brought out through the passage or bore  161  shown with the disked lines, which extends outwardly from an oblique channel  161 ′ until it terminates in the peripheral apertures in the ring  193  which is brought to bear on the flange  154  by a screw  194 . 
     The ring member  147 ″ corresponds to the elements described in the various embodiments and examples as the covers  170 ,  147 ,  147 ′ and the rings  53 ,  74 . Preferably, therefore, only 2 parts are needed to completely enclose the inner space  146  of the motor other than the stationary shaft  145  and the bearings  139 ,  149 ; namely, the rotor casing  132  and the disk-shaped ring member  147 ″. 
     FIG. 10 shows a ring  175 , somewhat L-shaped in section, which rotates together with the outer rotor of the hub, whereby the ring  175  encompases an inner, essentially complementary mating part  165 , so that the longer leg of the outside part  175  is only separated from the stationary shaft by a narrow gap  275 . In combination with the inside mating part  165 , this arrangement provides an effective labyrinth seal. This is referenced item  175 ′ in the lower part of FIG. 10, where the basic L-shaped section of the seal is indicated by a solid line and the complementary mating section is referenced  165 ′. The effectiveness of the labyrinth seal can be enhanced if a projection  174 ″ on the part  175  is provided to project into a recess  165 ″′, of the complementary part  165 ′. The arrangement may be seen also in the upper part of the drawing. In this way, the need to use a substantially more costly magnetic liquid seal of the type shown in FIG. 9 as items  140  and  150 , can be avoided. Of course, the incorporation of a labyrinth seal of this type provided with these two interlocking L-shaped leg profiles has an independent significance in connection with data storage disk drives and is not required by the other design features of this motor. As already mentioned, the additional recesses  165 ″′ provides further enhancement of the sealing action of the labyrinth seals. Elements of this type are manufactured as large volume extrusions or deep drawn die pressings and their cost hardly bears comparison with that of magnetic liquid seals. They provide a good low-cost means of the sealing of the clean chamber, because they can be installed at the points of access to the space inside the motor, either in an axial direction or otherwise. 
     FIG. 14 is a variant of FIG. 6 primarily in the provision of the groove  151  in the motor cover  147  which receives the magnet ring  152  and allows the rotational position sensor  156  to face the magnet ring across a cylindrical air gap vis-a-vis a planar gap in the embodiment shown in FIG.  6 . 
     This invention is not restricted to use the magnetic field-sensitive rotational position sensors. It can also be used, for example, with optical sensors. 
     Although the invention has been described in connection with a preferred embodiment and certain alternatives, other alternatives, modifications, and variations may be apparent to those skilled in the art in view of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and scope of the appended claims.