Patent Publication Number: US-2005140227-A1

Title: Spindle motor with bearing system

Description:
BACKGROUND OF THE INVENTION  
      The invention relates to a spindle motor having a bearing system according to the preamble of patent claim  1 .  
     PRIOR ART  
      Conventional types of spindle motors as used, for example, to drive the platters of a hard disk drive have a bearing system including at least one rotating part, such as a shaft, which is rotatably supported with respect to at least one stationary part, such as a bearing sleeve, by means of a roller bearing, a sliding bearing or a hydrodynamic bearing. The actual rotor of the spindle motor is fixed to the rotating part, the shaft for example. The rotor carries parts of the electromagnetic drive system of the motor and the platters of the hard disk drive. In the kind of design and construction described above, the bearing system is an independent unit whose rotating part has to be connected to the rotor. This means that separate bearing components are necessary which require additional space and go to increase costs.  
     SUMMARY OF THE INVENTION  
      The object of the present invention is to create a spindle motor having a bearing system which can be built to a small scale due to a reduction in the number of necessary components and which provides a means of manufacturing very flat, small-scale hard disk drives.  
      This object has been achieved according to the invention by the characteristics outlined in patent claim  1 .  
      Beneficial embodiments and further preferred characteristics of the invention are revealed in the subordinate patent claims.  
      According to the invention, the gap that separates the components of the electromagnetic drive system simultaneously forms the bearing gap of the bearing system. Such an integrated rotor/bearing arrangement makes it possible to manufacture very small spindle motors and consequently to manufacture small-scale hard disk drives as well. It is advantageous if the bearing system takes the form of a hydrodynamic bearing system.  
      According to a preferred embodiment of the invention, the rotating part of the bearing system is formed by a rotor which carries the magnet arrangement of the drive system. The stationary part of the bearing system is formed by a stator base on which the stator arrangement of the electromagnetic drive system is arranged. This consequently supersedes a bearing system made up of separate components, formed until now, for example, from a shaft rotatably supported in a stationary bearing sleeve.  
      For assembly purposes, the stator base is formed as a single integral piece but can include a removable cover plate, the rotor being arranged between the stator base and the cover plate. A sandwich-type construction is also conceivable in which the stator is arranged between the baseplate (stator base) and the cover plate.  
      The rotating and the stationary part of the preferred hydrodynamic bearing system are spaced apart from each other by the bearing gap, a bearing fluid being filled into the bearing gap. The bearing fluid can be a liquid, e.g. a bearing oil, a magnetic fluid or even a gas, such as air. According to the invention, provision can be made for the rotor and the stator base or the cover plate to form not only a radial bearing, in which both the stator base and the rotor have bearing surfaces located opposite each other and running concentric to the rotational axis, but also an axial bearing, in which the stator base or the cover plate and the rotor include bearing surfaces located opposite each other and running essentially perpendicular to the rotational axis. The bearing surfaces are provided in the conventional way with a surface structure, a groove pattern for example, to generate the hydrodynamic pressure within the bearing gaps. The bearing surfaces could additionally have a friction and/or wear-reducing coating.  
      The bearing fluid is preferably kept in the bearing gap through the use of capillary seals or magnetic seals. Here, the capillary seals can advantageously form an equalizing volume which continues in extension of the bearing gap between the surfaces of the rotating and of the stationary part and acts as a reservoir for the bearing fluid.  
      Depending on the intended application of the spindle motor, according to the invention the rotor can either take the form of an inner rotor motor or an outer rotor motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Two embodiments of the invention are explained in more detail below on the basis of the drawings. Further characteristics, advantages and possible applications of the invention can be derived from the drawings and the following description.  
       FIG. 1  shows a schematic sectional view through a spindle motor including the bearing system according to the invention in a first embodiment;  
       FIG. 2  shows a schematic sectional view through a spindle motor including the bearing system according to the invention in a second embodiment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION  
      The spindle motor according to  FIG. 1  comprises a stator base  10  which has an approximately T-shaped cross-section and is rotationally symmetric with respect to a rotational axis  36 . The stator arrangement  14  with the phase windings, which form the stationary part of the electromagnetic drive system of the motor, is located in the central part of the stator base  10 . The stator arrangement  14  is supplied with power via electrical connections  16 . A cover plate  12  is set on the stator base  10  and is connected to it by some means of fastening  18  such as a central screw.  
      Between the stator base  10 , the cover plate  12  connected to it and the stator arrangement located between the two, there is an annular cavity in which, according to the invention, a likewise annual rotor  20  is arranged. The rotor  20  has an annular slot on its inside diameter in which a preferably annular permanent magnet  22 , held in a yoke  24 , is arranged. The permanent magnet  22  is spaced slightly apart from and positioned opposite the stator arrangement  14  and forms the rotating part of the electromagnetic drive system of the motor. On its outside diameter, the rotor  20  has an annular recess in which a platter  26  is held and preferably secured by a mounting clamp  28 .  
      According to the invention, the surfaces of the stator base  10 , the cover plate  12  and the rotor  20  that face each other form a hydrodynamic bearing system having a bearing gap  30  that keeps those parts of the bearing system rotating with respect to each other separate from one another. The bearing gap  30  is filled in the conventional way with a bearing fluid such as a bearing oil.  
      On the one hand, the rotor  20  and the stator base  10  form a radial bearing having bearing surfaces located opposite each other and running concentric to the rotational axis  36 . On the other hand, the rotor  20  and the stator base  10  or the cover plate  12  form an axial bearing, having bearing surfaces located opposite each other and running essentially perpendicular to the rotational axis  36 . To generate hydrodynamic pressure in the bearing gap  30 , the bearing surfaces are provided in the conventional way with a surface structure, taking, for example, the form of a groove pattern. The bearing surfaces can additionally have a friction and/or wear reducing coating.  
      Sealing regions  32  are provided at the ends of the bearing gap  30  which prevent bearing fluid from escaping in the region of the platters  26 . In the illustrated embodiment, capillary seals are used. The cross-section of the bearing gap  30  widens at its ends to form an essentially conical shape so that an annular equalizing volume  34  is formed in each case which is partly filled with bearing fluid and acts as a reservoir for the bearing fluid.  
      The spindle motor in  FIG. 2  is largely identical to the spindle motor illustrated in  FIG. 1  and similarly comprises an approximately T-shaped stator base  100 . A stator arrangement  104  provided with a plurality of phase windings is provided at the central part of the stator base  100  and goes to form the stationary part of the electromagnetic drive system of the motor. The stator arrangement  104  is supplied with power via electrical connections  106 . A cover plate  102  is set on the stator base  100  and connected to it by some means of fastening  108  such as a central screw.  
      Between the stator base  100 , the cover plate  102  and the stator arrangement  104  there is an annular cavity in which, according to the invention, the rotor  110  is arranged. The rotor  110  has an annular slot on its inside diameter in which a preferably annular permanent magnet  112 , held in a yoke  114 , is arranged. On its outside diameter, the rotor  110  has an annular recess in which a plurality of platters  116  are held and preferably secured by a mounting clamp  118 .  
      According to the invention, the surfaces of the stator base  100 , the cover plate  102  and the rotor  110  that face each other form a hydrodynamic bearing system having a bearing gap  120  that keeps those parts of the bearing system rotating with respect to each other separate from one another. The bearing gap  120  is filled in the conventional way with a bearing fluid such as a bearing oil.  
      In contrast to  FIG. 1 , the cover plate  102  does not directly form one of the stationary bearing surfaces, but rather an annular counter bearing  128  is set into the cover plate  102 , the annular counter bearing  128  directly abutting the bearing gap  120  and defining a stationary bearing surface.  
      In the same manner as in  FIG. 1 , both a radial bearing and an axial bearing are formed from the rotor  110 , the cover plate  102  or the counter bearing  128  and the stator base  100  whose bearing gaps run concentric or approximately perpendicular to the rotational axis  130  respectively.  
      At the ends of the bearing gap  120 , sealing regions  122  are provided which take the form of capillary seals. End rings  126  are arranged on the stator base  100  or the cover plate  102 , the inner sleeve surfaces of the end rings  126  forming the radially inner boundary of the sealing regions  122 . The bearing gap  120  forms two equalizing volumes  124  between the inside diameter of the end rings  126  and the outside diameter of the rotor  110  as part of the sealing arrangement.  
      The rotor/bearing arrangement according to the invention can be modified in many different ways without departing from the basic idea behind the invention. Thus the rotor  20  or  110  can take the form of an outer rotor motor as illustrated in the drawings, or it can just as well take the form of an inner rotor motor.  
      Identification Reference List  
     
         
         
           
               10  Stator base  
               12  Cover plate  
               14  Stator arrangement  
               16  Electrical connections  
               18  Means of fastening  
               20  Rotor  
               22  Magnet (arrangement)  
               24  Yoke  
               26  Platter  
               28  Mounting clamp (platter)  
               30  Bearing gap  
               32  Sealing region  
               34  Equalizing volume  
               36  Rotational axis  
               100  Stator base  
               102  Cover plate  
               104  Stator arrangement  
               106  Electrical connections  
               108  Means of fastening  
               110  Rotor  
               112  Magnet  
               114  Yoke  
               116  Platters  
               118  Mounting clamp (platter)  
               120  Bearing gap  
               122  Sealing region  
               124  Equalizing volume  
               126  End ring  
               128  Counter bearing  
               130  Rotational axis