Abstract:
In order to improve a device for the manufacture of a shaft assembly for a hydrodynamic bearing by pressing a shaft into a fit bore in a bearing disk, comprising a first pressing tool and a further pressing tool, in such a way that enables high accuracy to be achieved when the shaft is pressed into the bearing disk, with the lowest possible cost and effort in setting up the press, it is proposed that a shaft receiving portion which receives and guides the shaft aligned exactly to a central axis is associated with the first pressing tool, that a bearing disk receiving portion which receives and guides the bearing disk with a flat surface aligned exactly perpendicular to an axis is associated with the first pressing tool, and that for the pressfitting process, the first pressing tool acts on the shaft or the bearing disk by means of a first pressing element and a second pressing tool acts on the bearing disk or the shaft by means of a second pressing element.

Description:
The present disclosure relates to the subject matter disclosed in German application No. 103 43 319.8 of Sep. 10, 2003, which is incorporated herein by reference in its entirety and for all purposes. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a device for the manufacture of a shaft assembly for a hydrodynamic bearing by pressing a shaft into a fit bore in a bearing disk, the device comprising a first pressing tool and a second pressing tool that can be moved towards each other in a feed direction. 
   In the know manufacturing processes for such shaft assemblies, the shaft is pressed into a fit bore disposed in the center of the bearing disk by means of a first pressing tool accommodating the shaft and a second pressing tool accommodating the bearing disk, the diameter of the fit bore being less than the diameter of the shaft. 
   Since the strictest requirements are placed on the completed shaft assembly for use in a hydrodynamic bearing regarding the right angularity between a central axis of the shaft and flat surfaces of the bearing disk, the shaft and the bearing disk have to be precisely aligned to each other during the pressfitting process. 
   To ensure such exact alignment, not only is a highly accurate press required but the pressing tools have also to be aligned to each other with high precision, which means great costs and effort particularly when the pressing tools are exchanged. 
   The object of the invention is thus to improve a device of this kind in such a way that enables high accuracy to be achieved when the shaft is pressed into the bearing disk with the lowest possible cost and effort in setting up the press. 
   SUMMARY OF THE INVENTION 
   This object has been achieved for a device of the type described in the opening paragraphs in accordance with the invention in that a shaft receiving portion which receives and guides the shaft aligned exactly to a central axis is associated with the first pressing tool, that a bearing disk receiving portion which receives and guides the bearing disk with a flat surface aligned exactly perpendicular to an axis is associated with the first pressing tool, that the shaft receiving portion and the bearing disk receiving portion position the shaft and the bearing disk with respect to each other without contact in a starting position and can be movably guided with respect to each other parallel to the axis and can thus be moved from the starting position into a pressfit position, and that for the pressfitting process, the first pressing tool acts on the shaft or the bearing disk by means of a first pressing element and a second pressing tool acts on the bearing disk or the shaft by means of a second pressing element. 
   The advantage of the solution according to the invention can be seen in that the allocation of the shaft receiving portion and the bearing disk receiving portion to one of the pressing tools and the movement of these two elements with respect to each other parallel to the axis make it possible for the alignment of the shaft and the bearing disk, before pressfitting and also during the pressfitting process, to be made independent of the alignment of the two pressing tools with respect to each other, and further, the allocation of the shaft receiving portion and bearing disk receiving portion to one pressing tool, makes it possible, through the guidance of the shaft receiving portion and the bearing disk receiving portion with respect to each other, to achieve the required precision, which is thus essentially independent of the alignment of the pressing tools with respect to each other. 
   It is particularly favorable if, during the pressfitting process when the movement from the starting position in the direction of the pressing position begins, only the bearing disk receiving portion and the shaft receiving portion maintain the exact alignment of the shaft and the bearing disk with respect to each other, so that the precision of alignment of the shaft and bearing disk with respect to each other is determined by the guiding precision of the shaft receiving portion and the bearing disk receiving portion with respect to each other. 
   It is particularly favorable if the bearing disk receiving portion comprises a bearing disk carrier having a support surface against which the bearing disk engages with a first flat surface so that the bearing disk can thus be aligned via the first flat surface. 
   It is preferably if the bearing disk held in the bearing disk receiving portion is arranged in such a way that a force can be applied to its second flat surface located opposite the first flat surface by the second pressing element of the second pressing tool. 
   To establish particularly transparent conditions when the bearing disk is aligned, it is preferable if, at least from the start of the process of pressing the shaft into the bearing disk, the first flat surface of the bearing disk is held in close contact with the support surface. 
   In order to ensure that the first flat surface is fitted securely against the support surface, it is particularly expedient if the support surface is held tightly to the first flat surface by a holding force. 
   This holding force can be generated in a variety of different ways. It is conceivable, for example, to insert pressure elements acting with the holding force between the bearing disk carrier and the bearing disk. 
   A holding force acting between the support surface and the flat surface of the bearing disk can be particularly advantageously generated if a holding force acting in the direction of the starting position is exerted on the bearing disk receiving portion and the shaft receiving portion in respect of a relative movement in the direction of the axis and that the holding force works against a direction of conveyance of the pressing elements, so that when the pressing elements are conveyed, a holding force acting between the support surface and the flat surface is always present. 
   The holding force could be generated by a hydraulic or pneumatic cylinder or by another device. 
   A particularly simple solution provides for the holding force to be generated by at least one elastic energy or force storage unit. 
   So far, no precise details have been given concerning the guidance of the shaft receiving portion and the bearing disk receiving portion with respect to each other. 
   In order to achieve the required high precision, it is favorable if the shaft receiving portion and the bearing disk receiving portion are guided with respect to each other via a linear guide. 
   It is expedient if the linear guide is supported by rolling element bearings. 
   A particularly simple solution provides that a guide member carrying the shaft receiving portion forms a guide surface for the linear guide, so that the bearing disk receiving portion can be directly guided via this guide member with respect to the shaft receiving portion. 
   It is further preferable if an annular member carrying the bearing disk receiving portion encloses the guide member and has a second guide surface facing the first guide surface. 
   So far, no precise details have been given concerning the centering of the bearing disk with respect to the central axis of the shaft. In principle, it is conceivable to construct the bearing disk receiving portion in such a way that allows the bearing disk to center itself when the pressfit end is pressed into the fit bore. 
   A particularly simple construction is provided, however, if the bearing disk receiving portion centers the bearing disk precisely to the axis. 
   For this purpose, the bearing disk receiving portion is preferably provided with an aligning element that holds the bearing disk centered with respect to the axis. 
   Such an aligning element could, for example, accommodate the bearing disk as a whole. A particularly favorable solution provides for the aligning element to engage an outer surface of the bearing disk in order to center it with respect to the central axis. Engaging the outer surface of the bearing disk in this way makes it possible to arrange the bearing disk in such a way that its second flat surface facing the second pressing tool is freely exposed for the second pressing tool to act on it. 
   Concerning the securing of the aligning element, it is particularly favorable if it is secured to the bearing disk carrier and thus establishes the guiding precision of the bearing disk carrier with respect to the shaft receiving portion and at the same time the precision for centering the bearing disk with respect to the central axis of the shaft. 
   The aligning element is preferably formed in such a way that it is secured to the bearing disk carrier in a positive fit. 
   Since the device according to the invention is extremely sensitive to any kind of soiling, including soiling caused by the smallest particles, it is preferable if the aligning element can be removed from the bearing disk carrier so that both the bearing disk carrier and the aligning element can be easily cleaned. 
   Since in the solution according to the invention, the overall guiding precision of the shaft and the bearing disk during the pressfitting process is realized by the guidance of the shaft receiving portion and the bearing disk receiving portion with respect to each other, an additional precise alignment of the second pressing element to the bearing disk or the shaft would result in a redundant alignment of the two elements to each other and would thus only impair the guiding precision of the two elements with respect to each other in a negative way. 
   For this reason, it is preferable if the second pressing element is held on a base of the second pressing tool in a self-adjusting manner to the bearing disk or to the shaft. By arranging the second pressing element on the base of the second pressing tool in this way, any redundancy in the system is avoided, so that the second pressing element can adjust itself to the alignment of the shaft and bearing disk predetermined by the shaft receiving portion and the bearing disk receiving portion. 
   This means of self-adjustment of the second pressing element to the base of the second pressing tool can be realized in a variety of different ways, for example, by a cushion of a compressible or non-compressible medium. 
   A particularly simple solution provides that the second pressing element is supported on the base of the second pressing tool by an elastic spring and is in this way provided with the means of self adjustment. 
   Further characteristics and advantages of the invention form the subject matter of the description below as well as the illustration in drawings of an embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  a view of a shaft assembly for a hydrodynamic bearing which is to be manufactured using the device according to the invention; 
       FIG. 2  a view of a first pressing tool and a second pressing tool of the device according to the invention and 
       FIG. 3  an enlarged view of the first pressing tool. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A shaft assembly  10  for a hydrodynamic bearing of an electric spindle motor to be manufactured according to the invention comprises a shaft  12  which is ground on its peripheral face  14  and which is pressed at a pressfit end  16  into the fit bore  18  of a bearing disk  20  starting from an edge  22  of the fit bore  18 , the fit bore  18  being formed, for example, as a through hole. 
   An essential feature of such a shaft assembly  10  is that the central axis  24  of the shaft assembly  10  runs exactly perpendicular to a first flat surface  28  of the bearing disk  20  extending in a plane  26  and also exactly perpendicular to a second flat surface  30  of the bearing disk  20  located opposite the first surface and also running parallel to the plane  26 , since the first flat surface  28  and the second flat surface  30  of the bearing disk  20  are responsible for the axial journalling of the shaft assembly  10  in the hydrodynamic bearing. 
   In the devices known to date that are used to press a shaft  12  into the fit bore  18  of a bearing disk  20 , shaft assemblies  10  can be produced which do not meet the accuracy requirements placed on right angularity and cylindricality. 
   This is due to an unsatisfactory alignment of the bearing disk  20  with respect to the flat surface  28  perpendicular to the central axis  24  and/or an unsatisfactory centering of the fit bore  18  with respect to the pressfit end  16 . In both cases, local force peaks can occur during the pressfitting process due to one sided “touching”, which, at worst, can result in the “seizing” of the parts that are to be joined, so that the shaft assembly  10  can be subject to intolerable deviations where the required right angularity, evenness and cylindricality are concerned. 
   A device according to the invention as presented in  FIGS. 2 and 3  is provided to avoid such problems. 
   As in a conventional pressing device, this device comprises a plunger  32  and a counter support  34  of the pressing device which can, for example, be pneumatically moved towards each other. 
   In the device according to the invention, a first pressing tool  40  is mounted on the counter support  34  and a second pressing tool  42  is mounted on the plunger  32 , which are centered according to a common axis  44  which runs parallel to a direction of conveyance  46  along which the first pressing tool  40  and the second pressing tool  42  can be conveyed to each other. 
   The first pressing tool  40  includes a base  50 , mounted on the counter support  34 , carrying a column-shaped guide member  52  which is provided with a shaft receiving portion  60  in the region of an end  54  facing the second pressing tool  42  which, taking the form of a blind hole  62  extending into the guide member  52  from an opening  64  facing the second pressing tool  42 , runs as far as a first pressing surface  66  formed by the end face of a first pressing element  70  which is supported on the counter support  34  by a lower side  72  located opposite the first pressing surface  66  and extends through the base  50  and the guide member  52  in a recess  74  reaching through the base  50  and the guide member  52  so that the first pressing surface  66  closes the shaft receiving portion  60  at a face of the shaft receiving portion  60  facing the counter support  34  and forms a supporting surface for an end face  78  of the shaft  12  located opposite the pressfit end  16  when the shaft  12  is inserted into the shaft receiving portion  60  ( FIG. 2 ,  3 ). 
   The shaft receiving portion  60  is preferably designed in such a way that it centers the shaft  12  with its central axis  24  precisely coaxial to the axis  44  and thus also parallel to the direction of conveyance  46 . 
   The guide member  52  preferably has a tapered outer surface  76  extending to the opening  64 . 
   A bearing disk receiving portion, indicated in its entirety by  80 , is provided to align the bearing disk  20 , comprising, as shown in an enlarged view in  FIG. 3 , a bearing disk carrier  82  which is provided with a support surface  84  onto which the bearing disk  20  can be set with its lower flat surface  28 . 
   The support surface  84  extends around a central recess  86  in the bearing disk carrier  82  by means of which the shaft  12  with its pressfit end  16  can be led through the bearing disk carrier  82  to be pressed into the fit bore  18 . 
   For its part, the bearing disk carrier  82  is firmly connected to an annular member  88  which encloses the guide member  52  radially towards the outside and is guided along this guide member  52  by a linear guide, indicated in its entirety by  90 , parallel to the axis  44 . 
   The linear guide  90  is formed on the one hand by a guide surface  92  provided on the sleeve of the guide member  52  and a guide surface  94  of the annular member  88  facing this guide surface  92  as well as by a rolling element carrier  96 , comprising rolling elements supported on both guide surfaces  92  and  94 . The guide surfaces  92  and  94  are preferably cylindrical surfaces running coaxial to each other, and the rolling element carrier  96  includes rolling elements distributed over the two cylindrical guide surfaces  92  and  94  so that the linear guide  90  ensures high guiding precision for the movement of the annular member  88  in the direction of the axis  44  with respect to the guide member  52  and thus a high guiding precision for the movement of the bearing disk carrier  82  with the support surface  84  with respect to the shaft receiving portion  60 . 
   The high guiding precision of the linear guide  90  thus enables the support surface  84  to be guided aligned exactly perpendicular with respect to the axis  44  and thus also the first flat surface  28  of the bearing disk  20  located on the support surface  84  exactly aligned to the central axis  24  of the shaft  12 , when the bearing disk  20  is disposed in the bearing disk receiving portion  80  and the shaft  12  is disposed in the shaft receiving portion  60 . 
   In order to further ensure that the bearing disk  20  is precisely centered with respect to the axis  44  and thus also with respect to the central axis  24  of the shaft  12 , an aligning element, indicated in its entirety by  100  is provided on the bearing disk carrier  82 , the aligning element  100  fitting snugly with its aligning surface  102  on an outer sleeve surface  104  of the bearing disk  20 . 
   Moreover, the aligning element  100  extends away from the sleeve surface  104  only in a radial direction to the axis  44 , so that the second flat surface  30  of the bearing disk  20  facing the second pressing tool  42  is freely exposed enabling a force to be exerted on it by the second pressing tool  42 —as described in more detail below. 
   The aligning element  100  is preferably located on the bearing disk carrier  82  and overlaps an outer edge face  106  of the bearing disk carrier  82  with a collar  108 , an inner surface  110  of the collar  108  being exactly positioned by the edge face  106  of the bearing disk carrier  82  in order to position the aligning element  100  for its part precisely to the bearing disk carrier  82 . It is preferable if the aligning element  100  can be removed from the bearing disk carrier  82 . 
   The movement of the bearing disk carrier  82  in the direction of the axis  44  by means of the linear guide  90  is restricted by stop elements  112  which comprise, for example, stay bolts  114  fixed into the base  50  that reach through the annular member  88  and have heads  116  which form annular surfaces  118  facing the base  50 , against which the annular member  88  can rest with stop surfaces  120 . 
   Pressure surfaces  122  located opposite the stop surfaces  120  are provided in the annular member  88  against which the pressure springs  124  enclosing the stay bolts  114  act with their ends  126 , while the pressure springs  124  are supported on the base  50  by the ends  128  located opposite the ends  126 . 
   The annular member  88  is preferably formed in such a way that it includes recesses  130  in which the heads  116  of the stay bolts  114  can be sunk and the annular member  88  is further preferably provided with recesses  132  extending from a side of the annular member  88  facing the base  50  by means of which the pressure springs  124  can extend into the annular member  88  as far as a collar  134  carrying the stop surfaces  120  and the pressure surfaces  122  and enclosing the stay bolts  114 . Thus the pressure springs  124  act with holding force H in such a way that they have the tendency of always moving the bearing disk carrier  82  into the starting position and that a movement out of the starting position makes it necessary to overcome holding force H. 
   When the annular member  88  fits snugly with its stop surfaces  120  on the annular surfaces  118  of the heads  116  of the stay bolts  114 , the bearing disk carrier  82  is in a starting position, as illustrated in  FIGS. 2 and 3 , in which the bearing disk  20  accommodated in the bearing disk receiving portion  18  is located close to the pressfit end  16  of the shaft  12  without, however, being in contact with the pressfit end  16 . 
   The pressfit end  16  is now pressed into the fit bore  18  in that the first pressing tool  40  and the second pressing tool  42  are moved towards each other in the direction of conveyance  46 . In order to act on the bearing disk  20 , on the second flat surface  30  of the bearing disk  20  to be precise, the second pressing tool  42  is provided with a base  140  against which a second pressing element  142  is supported, by means of elastic spring elements  144  for example, in such a way that the second pressing element  142  can adjust itself with its second pressing surface  146 , despite the exertion of a pressing force, with respect to the axis  44  corresponding to the alignment of the second flat surface  30 , so that the alignment of the bearing disk  20  is in no way determined by the second pressing surface  146  when the pressfit end  16  is pressed into the fit bore  18 , but rather that, with regard to its alignment to the axis  44 , the second pressing surface  146  adjusts itself to the alignment of the bearing disk  20 , determined by the bearing disk carrier  82 . 
   By means of the second pressing surface  146  acting on the second flat surface  30  of the bearing disk  20 , the bearing disk  20 , together with the bearing disk carrier  82 , is moved, overcoming holding force H, in the direction of the base  50  with respect to the guide member  52  into a pressing position, so that the pressfit end  16  of the shaft  12  penetrates beyond the edge  22  into the fit bore  18  and is fully pressed into the fit bore  18 , until, for example, the pressfit end  16  of the shaft  12  is fully seated in the fit bore  18 . 
   While the shaft end  16  is being pressed into the fit bore  18  on the one hand, the shaft  12 , and thus the pressfit end  16  as well, is held by the shaft receiving portion  60  aligned exactly coaxial to the axis  44 . Moreover, the bearing disk  20  is also held aligned by the bearing disk receiving portion  80 , particularly the bearing disk carrier  82  with the support surface  84  pressing against the first flat surface  28  of the bearing disk  20  with holding force H, in such a way that the first flat surface  28  of the bearing disk  20  extends exactly perpendicular to the central axis  24  of the shaft  12 . Furthermore, the bearing disk  20  with its fit bore  18  is also held by the aligning element  100 , both before as well as during the pressfitting process, exactly centered to the central axis  24  of the pressfit end  16  and the shaft  12 , the precision of the alignment of the fit bore  18  to the central axis  24  of the pressfit end  16  and the shaft  12  being realized through the guiding precision of the shaft receiving portion  60  with respect to the bearing disk receiving portion  80  via the linear guide  90 , the linear guide  90  only needing to ensure the required guiding precision between the shaft receiving portion  60  and the bearing disk receiving portion  80  over a relatively short distance which is slightly larger than the thickness of the bearing disk  20 . 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               IDENTIFICATION REFERENCE LIST 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               10 
               Shaft assembly 
             
             
               12 
               Shaft 
             
             
               14 
               Peripheral face 
             
             
               16 
               Pressfit end 
             
             
               18 
               Fit bore 
             
             
               20 
               Bearing disk 
             
             
               22 
               Edge 
             
             
               24 
               Central axis 
             
             
               26 
               Plane 
             
             
               28 
               First flat surface 
             
             
               30 
               Second flat surface 
             
             
               32 
               Plunger 
             
             
               34 
               Counter support 
             
             
               40 
               First pressing tool 
             
             
               42 
               Second pressing tool 
             
             
               44 
               Axis 
             
             
               46 
               Direction of conveyance 
             
             
               50 
               Base 
             
             
               52 
               Guide member 
             
             
               54 
               End 
             
             
               60 
               Shaft receiving portion 
             
             
               62 
               Blind hole 
             
             
               64 
               Opening 
             
             
               66 
               First pressing surface 
             
             
               70 
               First pressing element 
             
             
               72 
               Lower side 
             
             
               74 
               Recess 
             
             
               76 
               Outer surface 
             
             
               78 
               End face 
             
             
               80 
               Bearing disk receiving portion 
             
             
               82 
               Bearing disk carrier 
             
             
               84 
               Support surface 
             
             
               86 
               Recess 
             
             
               88 
               Annular member 
             
             
               90 
               Linear guide 
             
             
               92 
               Guide surface 
             
             
               94 
               Guides 
             
             
               96 
               Rolling element carrier 
             
             
               100 
               Aligning element 
             
             
               102 
               Aligning surface 
             
             
               104 
               Sleeve surface 
             
             
               106 
               Edge face 
             
             
               108 
               Collar 
             
             
               110 
               Inner surface 
             
             
               112 
               Stop element 
             
             
               114 
               Stay bolts 
             
             
               116 
               Heads 
             
             
               118 
               Annular surface 
             
             
               120 
               Stop surfaces 
             
             
               122 
               Pressure surfaces 
             
             
               124 
               Pressure springs 
             
             
               126 
               End 
             
             
               128 
               End 
             
             
               130 
               Recess 
             
             
               132 
               Recess 
             
             
               134 
               Collar 
             
             
               140 
               Base 
             
             
               142 
               Second pressing element 
             
             
               144 
               Elastic spring element 
             
             
               146 
               Second pressing surface 
             
             
               H 
               Holding force